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May 31, 2013

This week's picks

Functional Extinction of Birds Drives Rapid Evolutionary Changes in Seed Size "areas deprived of large avian frugivores for several decades present smaller seeds than nondefaunated forests, with negative consequences for palm regeneration"

Molecular evolution of peptidergic signaling systems in bilaterians "phylogenetic reconstruction tools... show that a large fraction of human PSs [peptide-based signaling systems] were already present in the last common ancestor of flies, mollusks, urchins, and mammals"

Honey constituents up-regulate detoxification and immunity genes in the western honey bee Apis mellifera "apicultural use of honey substitutes, including high-fructose corn syrup, may thus compromise the ability of honey bees to cope with pesticides and pathogens and contribute to colony losses"

Palaeontological evidence for an Oligocene divergence between Old World monkeys and apes" "the oldest known fossil 'ape', represented by a partial mandible... the oldest stem member of the Old World monkey clade, represented by a lower third molar... recovered from a precisely dated 25.2-Myr-old stratum in... the East African Rift in Tanzania."

Experimental evidence that evolutionarily diverse assemblages result in higher productivity "Species produced more biomass than predicted from their monocultures when they were in plots with distantly related species and produced the amount of biomass predicted from monoculture when sown with close relatives."

February 22, 2013

Mimic defectors to keep them from winning... and more

Stabilization of cooperative virulence by the expression of an avirulent phenotype "host manipulation by S. typhimurium is a cooperative trait that is vulnerable to the rise of avirulent defectors; the expression of a phenotypically avirulent [but genetically identical] subpopulation that grows as fast as defectors slows down this process, and thereby promotes the evolutionary stability of virulence"

Evolution of a genetic polymorphism with climate change in a Mediterranean landscape "significant increase in the proportion of morphs that are sensitive to winter freezing... associated with relaxed selection (less extreme freezing events)"

Behavioural and genetic analyses of Nasonia shed light on the evolution of sex pheromones "male Nasonia vitripennis evolved an additional pheromone compound differing only in its stereochemistry from a pre-existing one... females responded neutrally to the new pheromone... new pheromone compounds can persist in a sender's population, without being selected against by the receiver and without the receiver having a pre-existing preference for the new pheromone phenotype, by initially remaining unperceived."

Differential requirements for mRNA folding partially explain why highly expressed proteins evolve slowly "Counterintuitively, selection for mRNA folding also impacts the nonsynonymous-to-synonymous nucleotide substitution rate ratio, requiring a revision of the current interpretation of this ratio as a measure of protein-level selection."

January 11, 2013

Predictability, multiple fitness peaks, fungus-growing ants, pesticide resistance...

Predictability of evolution depends nonmonotonically on population size
"evolutionary predictability based on an experimentally measured eight-locus fitness landscape for the filamentous fungus Aspergillus niger.... entropies display an initial decrease and a subsequent increase with population size N"

Multiple Fitness Peaks on the Adaptive Landscape Drive Adaptive Radiation in the Wild "We measured the adaptive landscape in a nascent adaptive radiation of Cyprinodon pupfishes endemic to San Salvador Island, Bahamas, and found multiple coexisting high-fitness regions driven by increased competition at high densities"

Laccase detoxification mediates the nutritional alliance between leaf-cutting ants and fungus-garden symbionts "laccase activity is highest where new leaf material enters the fungus garden [in ant feces], but where fungal mycelium is too sparse"

A link between host plant adaptation and pesticide resistance in the polyphagous spider mite Tetranychus urticae "selection for the ability to mount a broad response to the diverse defense chemistry of plants predisposes the evolution of pesticide resistance in generalists"

See my Darwinian Agriculture Blog for links to videos of two of my talks.

December 27, 2012

Antibiotic resistance, camouflage, exinction...

Small changes in enzyme function can lead to surprisingly large fitness effects during adaptive evolution of antibiotic resistance "Using experimental evolution and deep sequencing to monitor the allelic frequencies of the seven most biochemically efficient TetX2 mutants in 10 independently evolving populations, we showed that the model correctly predicted the success of the two most beneficial variants"

Early evolution and ecology of camouflage in insects Lacewings were carrying "trash" (parts of ferns) as camouflage 110 million years ago.

The Evolutionary Landscape of Alternative Splicing in Vertebrate Species "Within 6 million years, the splicing profiles of physiologically equivalent organs diverged such that they are more strongly related to the identity of a species than they are to organ type."

Mass extinction of lizards and snakes at the Cretaceous-Paleogene boundary "The recovery was prolonged; diversity did not approach Cretaceous levels until 10 My after the extinction"

Equatorial decline of reef corals during the last Pleistocene interglacial "poleward range expansions of reef corals occurring with intensified global warming today may soon be followed by equatorial range retractions. "

September 7, 2012

This week's picks

Stone tool production and utilization by bonobo-chimpanzees (Pan paniscus)
Just last week, we gave a kid a copy of "Monkey with a tool belt." No, this paper doesn't show that humans are descended from bonobos. DNA evidence shows that the bonobo-chimp split occurred after humans split from the common ancestor of all three.

Reproductive queue without overt conflict in the primitively eusocial wasp Ropalidia marginata "The dominance rank of an individual is not a significant predictor of its position in the succession hierarchy. "

Predatory Fish Select for Coordinated Collective Motion in Virtual Prey
"collective motion could evolve as a response to predation, without prey being able to detect and respond to predators"

Profibrogenic chemokines and viral evolution predict rapid progression of hepatitis C to cirrhosis
"disease severity is predicted by the evolutionary dynamics of hepatitis C virus"

August 10, 2012

Fossils, convergent evolution, cooperation, and "groundwater footprints"

New fossils from Koobi Fora in northern Kenya confirm taxonomic diversity in early Homo "The new fossils confirm the presence of two contemporary species of early Homo, in addition to Homo erectus, in the early Pleistocene of eastern Africa."

A transitional snake from the Late Cretaceous period of North America "...snakes evolved from burrowing lizards. The skull is intermediate..."

Community-wide convergent evolution in insect adaptation to toxic cardenolides by substitutions in the Na,K-ATPase The same molecular change to a sodium pump, previously seen in Monarch butterflies, was found in four insect species (separated by 300 million years of evolution) feeding on plants making the same natural insecticides.

Heterogeneous networks do not promote cooperation when humans play a Prisoner's Dilemma "1,229 volunteers chosen among last year's high school students"

Water balance of global aquifers revealed by groundwater footprint" "80 per cent of aquifers have a groundwater footprint that is less than their area" but "the global groundwater footprint is currently about 3.5 times the actual area of aquifers", putting water supplies for 3.5 million people at risk. My book briefly compares the ecological footprints of conventional and organic farms.

July 30, 2012

Correcting Science and PNAS, evolution of more-deadly suicide bombers, blind composers, transcending tradeoffs, light-responsive rhizobia

Absence of Detectable Arsenate in DNA from Arsenate-Grown GFAJ-1 Cells
GFAJ-1 Is an Arsenate-Resistant, Phosphate-Dependent Organism
Surprise! They don't use arsenic instead of phosphorus after all.

Unobserved time effects confound the identification of climate change impacts "PNAS reported statistical evidence of a weather-driven causal effect of crop yields on human migration from Mexico to the United States. We show that this conclusion is based on a different statistical model than the one stated in the paper."

Evolution of music by public choice ...as in natural selection, variation is random but selection isn't.

Explosive Backpacks in Old Termite Workers ...they weren't going to reproduce anyway, but I wonder how long these "suicide vests" took to evolve.

Compensatory mechanisms for ameliorating the fundamental trade-off between predator avoidance and foraging "enhanced nutritional physiology allows caterpillars to compensate when threatened. However, we report physiological costs of predation risk, including altered body composition (decreased glycogen) and reductions in assimilation efficiency later in development." Similarly, reducing investments in research may not affect economic development much between now and the next election.

Light regulates attachment, exopolysaccharide production, and nodulation in Rhizobium leguminosarum through a LOV-histidine
"illumination of bacterial cultures before inoculation of pea roots increases the number of nodules per plant and the number of intranodular bacteroids."

September 9, 2011

This week's picks

A Gene for an Extended Phenotype "The viral gene that manipulates climbing behavior of the [Gypsy moth] host was identified"

The Foot and Ankle of Australopithecus sediba [hominin fossil from 1.78 and 1.95 million years ago] "may have practiced a unique form of bipedalism and some degree of arboreality"

Assured fitness returns in a social wasp with no worker caste "experimentally orphaned brood... continue to be provisioned by surviving adults... no evidence that naturally orphaned offspring received less food than those that still had mothers in the nest."

The sudden emergence of pathogenicity in insect-fungus symbioses threatens naive forest ecosystems "symbioses between wood-boring insects and fungi... are shifting from non-pathogenic saprotrophy in native ranges to a prolific tree-killing in invaded ranges... when several factors coincide"

Ultra-fast underwater suction traps "this unique trapping mechanism conducts suction in less than a millisecond and therefore ranks among the fastest plant movements known"

The taming of an impossible child - a standardized all-in approach to the phylogeny of Hymenoptera using public database sequences "combines some well-established programs with numerous newly developed software tools"

July 8, 2011

Resistance is futile!

Pathogens and pests evolve resistance to our control measures, from antibiotics and pesticides to crop rotation and pest-resistant crop varieties. Slowing the evolution of resistance is an important practical application of evolutionary biology.

An iconic agricultural example, discussed in my forthcoming book, is the "high-dose/refuge strategy" to slow the resistance of crop-eating insects to the bacterial toxin, Bt, which has been genetically engineered into corn, cotton and other crops. The "high dose" refers to crop Bt levels high enough that only insects with two resistance genes (genotype rr) can survive. Bt-free refuges serve as a source of so many susceptible (ss) insects that any rs mutants that arise will mate with them (producing susceptible ss and rs progeny) rather than with each other (with 25% of their progeny resistant rr).

But rs mutants could arise in the Bt-free refuge, not just in the Bt crop. If, in the refuge, the fitness of rs mutants is as high as that of ss insects (i.e., if there is no cost to Bt resistance), then rs individuals could become common enough that two of them could mate, producing rr progeny that could then devastate the nearby crop. So it would be good if, in the refuge, rs insects had lower fitness than ss insects.

This week's paper shows one way that this goal might be achieved. "Fitness Cost of Resistance to Bt Cotton Linked with Increased Gossypol Content in Pink Bollworm Larvae" was published recently in PLoS One.

Continue reading "Resistance is futile!" »

April 8, 2011

This week's picks

Workers influence royal reproduction
"worker aggressive and non-aggressive behaviour towards queens predicted which queen monopolized reproduction. In contrast, among-queen interactions were rare and did not predict queen reproduction. Furthermore, parentage analysis showed workers favoured their mother when present"
[Maybe "inclusive fitness" is useful after all!]

Updated chronology for the Miocene hominoid radiation in Western Eurasia
"Eurasian pongines [orangutans and extinct relatives] and African hominines [humans, chimps, bonobos, and extinct relatives] might have independently evolved in their respective continents from similar kenyapithecin ancestors [apes living 14 million years ago], resulting from an early Middle Miocene [5-23 MYA] intercontinental range extension followed by vicariance [geographic separation, reducing or eliminating interbreeding so allowing evolutionary divergence]. "

Ribozyme-Catalyzed Transcription of an Active Ribozyme "we recombined traits evolved separately in different ribozyme [catalytic enzyme made of RNA rather than protein] lineages. This yielded a more general polymerase ribozyme that was able to synthesize a wider spectrum of RNA sequences, as we demonstrate by the accurate synthesis of an enzymatically active RNA, a hammerhead endonuclease ribozyme. "

An evolutionary process that assembles phenotypes through space rather than through time "assortative mating between fast-dispersing individuals at the invasion front results in an evolutionary increase in dispersal rates in successive generations"

Fork-tailed drongos use deceptive mimicked alarm calls to steal food
"false alarm calls when watching target species handling food, in response to which targets flee to cover abandoning their food"

Moving calls: a vocal mechanism underlying quorum decisions in cohesive groups
"a sharp increase in the probability of changing foraging patch when the number of group members joining the chorus increased from two up to three"

Differences in the temporal dynamics of phenotypic selection among fitness components in the wild "The consistency in direction and stronger long-term average strength of selection through mating success and fecundity suggests that selection through these fitness components should cause more persistent directional evolution relative to selection through survival."

Rapid Spread of a Bacterial Symbiont in an Invasive Whitefly Is Driven by Fitness Benefits and Female Bias "Rickettsia sp. nr. bellii swept into a population of an invasive agricultural pest, the sweet potato whitefly, Bemisia tabaci, in just 6 years. Compared with uninfected whiteflies, Rickettsia-infected whiteflies produced more offspring, had higher survival to adulthood, developed faster, and produced a higher proportion of daughters. The symbiont thus functions as both mutualist and reproductive manipulator. "

The evolutionary biology of child health "cancer, the primary cause of non-infectious childhood mortality, mirrors child growth rates from birth to adolescence, with paediatric cancer development impacted by imprinted genes"

Tradeoffs associated with constitutive and induced plant resistance against herbivory "Across all 58 plant species, we demonstrate a tradeoff between constitutive and induced resistance, which was robust to accounting for phylogenetic history of the species. Moreover, the tradeoff was driven by wild species and was not evident for cultivated species."

Towards a quantitative understanding of the late Neoproterozoic carbon cycle
"all of the main features of the carbonate and organic carbon isotope record can be explained by the release of methane hydrates from an anoxic dissolved organic carbon-rich ocean into an atmosphere containing oxygen levels considerably less than today"

March 31, 2011

This week's picks

Chimpanzees help conspecifics obtain food and non-food items "...given that the donor cannot get the food herself.... the key factor... is the recipients' attempts to either get the food or get the attention of the potential donor."

On the earliest evidence for habitual use of fire in Europe
"...spectacular cases of Neandertal pyrotechnological knowledge..."

Sizing up your enemy: individual predation vulnerability predicts migratory probability
"trade-off between seasonal fluctuations in predation risk and growth potential... Smaller, high-risk individuals migrate with a higher probability"

Plant-ants feed their host plant, but above all a fungal symbiont to recycle nitrogen
"In many ant-plant symbioses, a fungal patch grows within each domatium."

More closely related species are more ecologically similar in an experimental test
"Species also competed more with close relatives than with distant relatives in field soils; however, in potting soil this pattern reversed..."

Assassin bug uses aggressive mimicry to lure spider prey "vibrations from bugs had a temporal structure and amplitude... similar to vibrations generated by leg and body movements of prey and distinctly different... from courting males or leaves..."

Social and Ecological Synergy: Local Rulemaking, Forest Livelihoods, and Biodiversity Conservation "participation in forest governance institutions by local forest users is strongly associated with jointly positive outcomes"

Oxygen isotopes of East Asian dinosaurs reveal exceptionally cold Early Cretaceous climates "cold local climatic conditions linked to the paleolatitudinal position of northeastern China and global icehouse climates..."

Adaptation to local ultraviolet radiation conditions among neighbouring Daphnia
"we separated the effects of shared population ancestry and environmental variables in predicting phenotypic divergence among populations."

March 11, 2011

Aging primates, agricultural ants, efficent cooperation, etc.

Lots of interesting papers this week, but I only have time for some brief comments.

I can't believe Obama's response to the earthquake in Japan was to go ahead with a speech on gasoline prices. (BBC cut him off!) Higher prices for nonrenewable resources are an efficient way (relative to rationing, say, or complicated mandates) to encourage us to use them more slowly, so they'll last longer. And although adding more carbon dioxide to the atmosphere may increase photosynthetic efficiency and make our winters here in Minnesota a little less cold, I'm not willing to bet that those benefits will outweigh risks such as rising sea level from melting glaciers. If civilization must be at war with nature, I'm on the side of civilization, but let's not shoot ourselves in the foot. For example, we can stay warm inside insulated houses, while agricultural pests perish in the cold, reducing the need for pesticides later. Cold winters are good! Hmmm... maybe I should turn comments back on; but I'm still deleting all commercial links.

Aging in the Natural World: Comparative Data Reveal Similar Mortality Patterns Across Primates "in neither females nor males did we find evidence of a negative correlation between IMR [initiral mortality risk, at onset of adulthood] and RoA [rate of aging, increase in mortality with age],which would be indicative of a trade-off..."
[I wouldn't have expected a trade-off between those parameters, but what about a tradeoff with reproduction (mentioned only in the definition of adulthood)?]

How within-group behavioural variation and task efficiency enhance fitness in a social group "females of both phenotypes [aggressive versus docile] experience increased fitness when occupying colonies containing unlike individuals"

Experimental peripheral administration of oxytocin elevates a suite of cooperative behaviours in a wild social mammal

Co-Residence Patterns in Hunter-Gatherer Societies Show Unique Human Social Structure

The influence of maternal effects on indirect benefits associated with polyandry

Primate extinction risk and historical patterns of speciation and extinction in relation to body mass

Evolution of cold-tolerant fungal symbionts permits winter fungiculture by leafcutter ants at the northern frontier of a tropical ant-fungus symbiosis

Structural basis for nonribosomal peptide synthesis by an aminoacyl-tRNA synthetase paralog

Global CO2 rise leads to reduced maximum stomatal conductance in Florida vegetation

November 15, 2010

Lengthy comment on group selection

Someone left a comment on an old post about group selection, here. Its length and use of an apparent pseudonym make me suspect cut-and-paste, in which case I'll delete it. IT WAS SO I DID.

See also this recent post.

August 24, 2010

Another way to alarm aphids

A new paper in Current Biology shows that aphids drop off their host plant when breathed on by an animal that's about to eat the plant: Mammalian herbivore breath alerts aphids to flee host plant.

Last week I discussed a paper about transgenic plants that make aphid alarm signals, scaring them away (at least for a generation or two). This latest paper suggests a related approach. Getting crops to release hot, humid "breath" might be hard, but could we make a machine to blast crops with artificial breath, maybe in greenhouses?

August 19, 2010

Evolution-proof pest-resistant crops?

This week's paper is "Alarm pheromone habituation in Myzus persicae has fitness consequences and causes extensive gene expression changes", published in PNAS by Martin de Vos and others.

Aphids suck. This wouldn't be too big a problem for their host plants, except that they sometimes transmit viruses. Some plants repel these pests by giving off gases very similar to the chemical alarm signals aphids release when attacked by predators. Could crops be genetically engineered to do this? Probably, but would it work, or would the aphids evolve to ignore these signals and keep on sucking?

To answer this question, the authors studied aphids on plants genetically engineered to make aphid alarm signal.

Continue reading "Evolution-proof pest-resistant crops?" »

July 31, 2010

Evolutionary history of yucca moths

I've written a few posts about ancestral-state reconstruction, where we use molecular or other information from living species to infer the traits of their shared ancestors. But I really like this post in which PhD student Jeremy Yoder describes his own work.

There's a nice diagram showing the general approach, then he looks at yucca moths and their relatives to figure out what their ancestors did. Yucca moths, like fig wasps, lay their eggs in flowers. Their larvae eat seeds, but the moths pollinate the flowers, so it's not too bad a deal overall. Their ancestors, he concludes, fed inside developing flowers, but without pollinating them. Maybe the world is getting a little more cooperative, after all.

May 7, 2010

E-word in NYT -- a bigger surprise than Roundup-ready weeds?

There have been isolated reports, for years, of various weeds evolving resistance to glyphosate (sold commercially as Roundup etc.), but now glyphosate-resistance is showing up in pigweed, a major problem for farmers in the US and elsewhere. Among alternative ways to kill weeds, other herbicides are mostly more toxic and break down more slowly, whereas mechanical cultivation tends to increase erosion.

On the positive side, maybe more people will buy my book on Darwinian Agriculture, although I'll have to revise it before publication to turn what was a prediction into a fact. Maybe I can get some Neanderthal crackpot with a radio show to accuse me of deliberately spreading Roundup-resistant weeds to increase sales. You can't buy publicity like that! But I'd rather have clean rivers than a best-selling book.

I was impressed that many of the experts discussing the problem in the New York Times referred to "evolution" or "natural selection", although one referred to weeds as "opponents that can adjust" (as if individual plants were trying different ways to survive herbicides) and said that some weeds can "mutate to survive", as if mutation were somehow directed. Plants have evolved so that individuals can adjust to certain changes in their environment (drying soil, for example). But it's populations, not individuals, that evolve. And, in this case, they evolved mainly because herbicide-susceptible individuals did not survive. I assume the author knows this, but some readers could be misled.

Maybe now people will start paying more attention to management practices that slow the evolution of herbicide resistance. Resistance-management programs for insect pests, to slow the evolution of resistance to the Bt toxin, seem to be working reasonably well, but there's nothing similar in place for weeds yet.

One important difference is that the insects plaguing an individual farmer may well come from a distant neighbor, so there's little individual incentive to implement expensive resistance-management programs. An individual farmer's weed problems, on the other hand, are much more dependent on how they were managed on that same farm in the past. So farmers may be more motivated to invent and implement resistance-management strategies for weeds.

One of my favorite weed management strategies is alternating, every few years, between using a field for grazed pasture, where weeds of row crops tend to die out, in rotation with row crops, where pasture weeds tend to die out. That requires farmers with the expertise and willingness to work with both crops and livestock, however. And milk or meat from animals eating mostly grass and clover may be more expensive than the same products produced in a feedlot.

April 16, 2010

Sanctions and cheating in pollination and protection mutualisms

The most-cited paper from my lab is one by Toby Kiers, showing that soybean plants impose fitness-reducing sanctions on "cheating" rhizobia, which multiply inside root nodules but then fail to provide their hosts with nitrogen. This week I will briefly discuss two recent papers on the role of sanctions in two different kinds of mutually beneficial interactions between species.

Toby is also one of the coauthors on the first paper by Ryutaro Goto and others. The author/year citation (Goto 2010 ) reminds me of programming computers in Fortran, but the full title is "Selective flower abortion maintains moth cooperation in a newly discovered pollination mutualism." The second paper, by David Edwards and others, discusses ants that protect trees from browsing animals. This paper asks, "Can the failure to punish promote cheating in mutualism?"

Clochidion trees in Japan are pollinated by moths. Like the moths that pollinate yuccas and the wasps that pollinate figs, these moths lay eggs as they pollinate, and their larvae then consume some seeds. What keeps the moths from laying too many eggs in a given flower?

Continue reading "Sanctions and cheating in pollination and protection mutualisms" »

January 22, 2010

Evolution threatens Darwin

Dengue ("breakbone") fever was much in the news last month in Australia last month, when I was there for the Applied Evolution Summit. The mosquitoes that spread this deadly disease are currently found in Queensland, where we were, but not further west, in the city of Darwin. They were found in Darwin in the early 1900s, however. Could some combination of climate change, human activity, and evolution put Darwin at risk once again? That was one of the questions discussed by Ary Hoffmann at the summit, largely based on a paper titled "Integrating biophysical models and evolutionary theory to predict climatic impacts on species' ranges: the dengue mosquito Aedes aegypti in Australia", published in Functional Ecology last year.

Continue reading "Evolution threatens Darwin" »

January 17, 2010

Altruistic punishment by fig trees?

As I was getting ready to write about some of the talks at the Applied Evolution Summit, I received a very interesting paper: Host sanctions and pollinator cheating in the fig tree - fig wasp mutualism, which was recently published in Proceedings of the Royal Society by Charlotte Jander and Allen Herre.

Fig-tree fruits are lined with many little flowers. Female wasps crawl inside to lay their eggs, often carrying pollen from the fig where they, themselves, hatched from an egg. Different fig species host different wasp species. Some wasp species are like many other pollinators, carrying pollen only by accident; fig trees pollinated by these species have to make lots of pollen. Other figs are pollinated by wasps that actively collect pollen and actively pollinate flowers inside fig fruits; these fig species can make less pollen, which frees resources to make more seeds.

But there is presumably some cost to the wasps of transporting pollen. Why not save this cost, travel light, and lay eggs in a fig fruit without pollinating its flowers? This is essentially the same question people in my lab have asked about rhizobia, the bacteria that provide legume plants with nitrogen: once rhizobia have reproduced inside a root nodule, why stick around and invest resources in pulling nitrogen out of the atmosphere and converting it to a form the plant can use?

The questions are similar and so are the answers....
wasp.JPG
Wasp inside a fig; photo by Charlotte Jander.

Continue reading "Altruistic punishment by fig trees?" »

December 18, 2009

Tradeoff-free longevity?

I'm working on my talk for the Applied Evolution Summit, so don't have time to write a detailed post, but here are some papers that looked interesting, with brief comments on some of them:

Amino-acid imbalance explains extension of lifespan by dietary restriction in Drosophila
(published in Nature by Richard Grandison, Matthew Piper & Linda Partridge)
Dietary restriction reduces reproduction and increases longevity in many species. This study, using fruit-flies, showed that adding the amino acid, methionine, to a restricted diet restored total lifetime reproduction to that of fully-fed flies, but with the greater longevity of restricted-diet flies. Extrapolating to humans, the paper suggests that

the benefits of dietary restriction for health and lifespan may be obtained without impaired fecundity

But, if there would be no reproductive cost to doing so, why haven't flies evolved the ability to discard the "extra" food they get when fully-fed -- except for the methionine -- and live longer? I suspect that the restricted-plus-methionine diet affects the timing of reproduction, but data on timing weren't reported. (Instead, they give an "index of lifetime fecundity.") If overall population size is increasing (as fully-fed flies might expect), individuals that reproduce earlier make a disproportionate contribution to the gene pool. So the evolutionary trade-off may be between longevity and earliness of reproduction, not total reproduction. If population is decreasing, however, individuals who delay reproduction make a larger contribution to the gene pool, as laid out in our "shrinking pool" hypothesis. My guess is that flies respond to the restricted-plus-methionine diet as a cue predicting population decline and reproduce later, thereby gaining the observed increase in longevity. Extrapolating to humans again, we might be able to develop diets or other treatments that increase life-span and health, but which cost us teenage pregnancy. Hmmm... might be worth it.

Click "aging" at right for other posts relevant to this topic.

Regulating Alternative Lifestyles in Entomopathogenic Bacteria

Mozambican Grass Seed Consumption During the Middle Stone Age
If our ancestors were eating grass seeds 100,000 years ago, as this paper seems to show, what kind of selection, inadvertent or perhaps deliberate, were they imposing on those grasses?

Phylogeographic reconstruction of a bacterial species with high levels of lateral gene transfer

On the Origin of Species by Natural and Sexual Selection


Coots use hatch order to learn to recognize and reject conspecific brood parasitic chicks
"When experimentally provided with the wrong reference chicks, coots can be induced to discriminate against their own offspring"

Increasing phylogenetic resolution at low taxonomic levels using massively parallel sequencing of chloroplast genomes

Have giant lobelias evolved several times independently? Life form shifts and historical biogeography of the cosmopolitan and highly diverse subfamily Lobelioideae (Campanulaceae)
DNA analysis suggests that giant Lobelias evolved once and then spread, even to remote places like Hawaii, rather than evolving separately in different locations.

December 1, 2009

Better ant fungus farming through chemistry

Leaf-cutter ants feed the leaves to fungi and eat the fungi. Another fungus can parasitize their crop. A few years ago, it was reported that bacteria living on the ants' bodies make antifungal compounds that kill the parasite.

I wondered about this: wouldn't a bacterium that invests resources in antifungal production grow more slowly than a mutant that avoids this costly investment? In the long run, this might hurt ants and bacteria alike, but natural selection has no foresight. So why haven't bacterial "cheaters" that don't make antifungals displaced "altruists" that do? When yeasts (single-cell fungi) were found on the same ants, I suggested that antifungal production might benefit individual bacteria in their war with the yeasts, with activity against the parasitic fungus as a side effect. (Similarly, bacteria that make antibiotics that protect plant roots from fungi have their own selfish reasons.)

Consistent with this hypothesis, it turns out that the antifungal chemicals made by the bacteria aren't active only against the parasitic fungi, and may even harm the fungal crop. But the bacteria presumably benefit the ants more than they harm them, because the ants have specialized structures and secretions whose main function seems to be to support the bacteria. At least, this is true of some fungus-growing ant species. Other species have apparently abandoned use of these bacteria. Instead, they control harmful fungi with antibiotics they make themselves, in special glands. This is an example of a species abandoning one symbiosis (ant/bacteria) when it's no longer beneficial, while retaining a beneficial symbiosis (ant/fungus).
ants.jpg
Black lines shows fungus-growing ant lineages that rely on antibiotics they make themselves, rather than those made by symbiotic bacteria, to control parasitic fungi that attack their fungal crop.
Source: Hermógenes Fernández-Marín, Jess K. Zimmerman, David R. Nash, Jacobus J. Boomsma and William T. Wcislo (2009) Reduced biological control and enhanced chemical pest management in the evolution of fungus farming in ants. Proceedings of the Royal Society B 276:2263-2269.

November 23, 2009

Are ants' fungus gardens a source or sink for nitrogen?

This week's paper, Symbiotic Nitrogen Fixation in the Fungus Gardens of Leaf-Cutter Ants, has already been discussed by Ed Yong, whose blog is among my favorites, and by the always-interesting Susan Milius of Science News. When she interviewed me, I endorsed the main conclusions of the article but expressed skepticism on one point.

The paper clearly shows that the fungus "gardens" cultivated by leaf-cutter ants contain bacteria that extract nitrogen from the air. The part I wondered about was their statement that:

Continue reading "Are ants' fungus gardens a source or sink for nitrogen?" »

August 7, 2009

Ants versus fungi

Ants that grow fungi for food have to control other fungi that attack their gardens, but what about fungi that attack the ants themselves? Two papers published recently reveal surprising sophistication in both ants and fungi.

Sandra Anderson and colleagues discuss "The life of a dead ant: the expression of an adaptive extended phenotype" in American Naturalist. Richard Dawkins coined the term "extended phenotype" to refer to a consistent effect of a gene inside an individual on something outside that individual. For example, it might be possible to link differences in the shape of webs made by different spiders to genetic differences among those spiders. This week's paper shows that ants infected by certain fungi show complex behavior that benefits the fungi. Ants infected by fungi with different genes would probably not show this behavior, but the genes involved have not yet been identified.

Before the fungus-infected ants die, they attach themselves (by biting) to the underside of leaves that are ideally located for fungal reproduction: on the cooler and moister north side of trees, near (but not on) the ground. The researchers showed that these locations were favorable for fungal reproduction by moving infected ants higher in the canopy or down to the ground. Ants on the ground mostly disappeared, but fungi grew abnormally in those that remained. Fungi were unable to compete their life-cycle on ants moved higher in the canopy.

I can imagine a fungus producing an ant hormone (or perhaps destroying a particular neuron) to make its ant host bite a leaf, but getting ants to bite leaves in a particular humidity and temperature range and then hold on until dying seems pretty sophisticated. It would be easier if the ants spent most of their time in that zone anyway, but the one ant colony they found was much higher, about 15 meters.

The second paper shows greater sophistication on the part of the ants. "Adaptive social immunity in leaf-cutting ants" was published by Tom Walker and William Hughes in Biology Letters. The paper is freely available on-line.

These social ants protect each other from fungal infection by grooming each other, much like meerkats or baboons. Ants exposed to the fungus got groomed about twice as long as ants exposed to a control solution without the fungus, or about three times as long if their nest had been exposed to the same fungus two days before. (Another example of learning in insects.) Ants placed in nests that were previously exposed to the fungus were twice as likely to survive for two weeks after they were inoculated.

July 24, 2009

Microbes evolve; flies evolve and learn

"Can plants predict the future?" asked one of my Crop Ecology lectures at UC Davis. Yes, they can. Plants use decreasing daylength to predict oncoming winter, and flower early enough to finish seed development before it gets too cold. Some plants detect early signs of drying soil and reduce their own water use, saving water in the soil for later.(Davies & Zhang. 1991, Bano, et al. 1993) Others detect "distress signals" from neighbors under insect attack, turning on chemical defenses in anticipation (Karban, et al. 2004).

But these anticipatory responses do not require learning: a beneficial change in individual behavior in response to individual experience. An alfalfa plant will never learn that the farmer always irrigates before it actually runs out of water. At least, I assume it won't. An evolving alfalfa population is a different story. Over a few generations under irrigation, genotypes that reduce their water use as the soil starts to dry (thereby reducing their growth) will be out-competed by genotypes that keep using water and growing.

Like plants, microbes can predict the future. As in plants, this trait can evolve. As they pass through the gut, bacteria typically see lactose before they see maltose. So they have evolved to "anticipate" maltose availability, turning genes for maltose use on as soon as they are exposed to lactose. After 500 generations of evolution on lactose without maltose, however, the bacteria have lost lose this anticipatory response, so that they turn maltose genes on only when they actually see maltose.(Mitchell, et al. 2009) The title of the news story in Nature about this work asked whether microbes can "learn from history", but this is clearly not an example of individual cells modifying their responses to lactose based on their individual experience.

Individual insects can learn. But is learning always a good thing? Aimee Dunlap, a grad student in my department working with David Stephens, just published a paper in Proceedings of the Royal Society exploring the conditions under which natural selection will favor learning (Dunlap & Stephens. 2009).
Fly Learning Graphics.jpg

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May 8, 2009

"If evolution is true, why are there still chimps?"

I once heard PZ reply to this popular creationist question by pointing out that, although many Minnesotans are descended from Norwegians, there are still Norwegians. This isn't really a good analogy, however, because Minnesotans and Norwegians aren't separate species. We know this because they can interbreed, producing healthy children. At the end of this post I suggest a better answer, indirectly inspired by this week's paper.

Two of evolutionary biology's central questions are: how do species change over generations? and how does one species split into two? We have many detailed examples of small evolutionary changes occurring over days (in bacteria) or years (in animals and plants), so one would have to be very close-minded to deny major evolutionary change over millions of years. But major evolutionary change is not enough, by itself, to split one species into two. One subpopulation within a species must change, while the rest of the species either stays the same or changes in different ways. This divergence cannot happen if the two subpopulations continue to interbreed at high rates. In other words, speciation requires some reproductive isolation.

Often, reproductive isolation is a byproduct of geography. After a few individuals (or a pregnant female) cross a mountain range or are blown from the mainland to an island, they no longer interbreed with their ancestral population. Over many generations, random genetic drift or nonrandom natural selection can change the isolated population enough that they can no longer produce healthy offspring with the original population, even if they come back into contact.

Sometimes speciation can occur without a major geographic barrier, but reproductive isolation is still required. This week's paper shows that this has happened and is still happening in Europe.

"A continuum of genetic divergence from sympatric host races to species in the pea aphid complex", by Jean Peccoud and others, was just published online in the Proceedings of the National Academy of Science.
aphid.jpg
Photo by Jean Peccoud

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April 8, 2009

Evolution-Proof?

Which animals kill the most humans? Lions and tigers and bears? Oh no, malaria-transmitting mosquitoes! The risks of using insecticides to kill mosquitoes may be outweighed by the benefits, but those benefits only last until mosquito populations evolve resistance. Careful use (insecticide-treated bed-nets, for example, rather than spraying wetlands) can slow the evolution of resistance, but we haven't yet achieved a goal I recently saw on a bumper sticker, namely, to "Stop Evolution Now!"

Can we do better? A paper published today suggests a new approach. "How to make evolution-proof insecticides for malaria control" was written by Andrew Read and colleagues. It's in the open-access journal, PLoS Biology, so you can read the whole article for details, but here's my summary:

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March 20, 2009

No butterflies were harmed by this research

With a species using cryptic resemblance [camouflage] for its protection, the very existence of neighbours involves a danger to the individual, since the discovery of one by a predator will be a step in teaching it to recognize the crypsis. With an aposematic [bad-tasting, warning-coloration] species, on the other hand, the existence of neighbours is an asset, since they may well serve to teach an inexperienced predator the warning pattern. -- William Hamilton, 1964
This week's paper describes research that could have been a winning science fair project. "Does colour polymorphism enhance survival of prey populations?", published online by Lena Wennersten and Anders Forsman in Proceedings of the Royal Society, helps answer an interesting evolutionary question, using materials available in many kitchens.

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January 2, 2009

Ford Denison, amateur scientist

My NSF grant will run out soon, so I get to spend the year in which we celebrate the 200th anniversary of Darwin's birth and the 150th anniversary of The Origin of Species as an amateur scientist, like Darwin himself. I'm not as smart or as rich as he was, but I do have imaginative and hard-working students and much better equipment.

I'm working on two grant proposals and several papers while dreaming of getting back to writing my book, so no detailed paper analysis this week. But Nature is highlighting 15 major papers on evolution they have published in the last few years.

October 18, 2008

Cooperative fish, cheating ants

Cooperation is widespread in nature, despite theoretical predictions that "cheating" mutants could displace cooperators over just a few generations of evolution. We don't apply human moral standards to other species, of course, but define cheating as contributing less, while benefiting from activities of others. The evolutionary persistence of cooperation is usually attributed to reciprocity (trading resources or services) or to kin selection: cooperation among relatives, such as parental care, can persist even without reciprocity. Fish that clean parasites from other fish are a standard example of reciprocity -- they get to eat the parasites -- whereas nonreproductive worker ants are a standard example of kin selection. I will briefly discuss one recent paper on each of these.

Redouan Bshary and coauthors report in Nature that "Pairs of cooperating cleaner fish provide better service quality than singletons." Cleaner fish often prefer to eat client mucus (yum!) than client parasites, but clients don't like this and tend to leave. When a male and female cleaner work together, the client fish may leave if either of them takes a bite of mucus. Females, in particular, were less likely to do this when cleaning with their male partner rather than alone. The authors also did an experiment to see whether cleaner fish would eat a less-preferred food (fish flakes, perhaps analogous to client parasites) if eating their more-preferred food (prawns, perhaps analogous to client mucus) resulted in the food plate being taken away. They did, especially the females. This may have been because the male often chased her if she ate a prawn, costing them both the rest of their meal. Overall, pairs appear to provide better service to clients, because they are better-behaved together than alone, especially the female.

Shigeto Dobata and coauthors reported on "Cheater genotypes in the parthenogenetic ant Pristomyrmex punctatas" in Proceedings of the Royal Society. Social insects, such as ants and bees, usually have reproductive queens and nonreproductive workers. Worker genes are transmitted to the next generation by the queen, who is typically the workers' mother and therefore shares most of their genes. Pristomyrmex punctatas is different. An individual ant may reproduce (usually when young) and also work. Some individuals are more like queens, however. These are larger, reproduce more, and do little or no work for the colony. If these nonworking ants were close relatives of the workers, this behavior could perhaps be maintained by kin selection. It could be an example of division of labor for mutual benefit, a less-extreme version of the more-familiar worker/queen division. So Dobata and coauthors analyzed the DNA of hundreds of ants to see how they were related. They found that these nonworking ants were much less closely related to workers than queens usually are. Most of the ants (working or not) reproduced parthenogenetically, essentially cloning themselves without sex. Working hard while unrelated individuals profit from your work doesn't usually work out over the long run, but these nonworking ants have been seen in the field for over 25 years. Is this an evolutionary dead end? A similar situation with Cape honey bees, whose colonies are parasitized by unrelated "pseudoqueens" usually leads to colony extinction. I look forward to reading more about this interesting ant species.

July 17, 2008

More talks from Evolution 2008

I’m done with two grant proposals, revising a book chapter, and checking the final version of a review article. I still have a pile of interesting reading and writing to do before I can get back into the lab – actually, I did help Ryoko set up an experiment yesterday – but no more looming deadlines for awhile. So, here are two more summaries of talks from Evolution 2008.

Do I know you?

The ability to tell other individuals apart by their faces is presumably maintained by natural selection, so you can recognize and avoid bad guys. But is there also selection for looking different enough to be recognizable? Or is it better to blend in with the crowd, so you can get away with stuff?

Michael Sheehan and Elizabeth Tibbetts are studying individual recognition in wasps (Tibbetts and Dale, 2007). Their hypothesis is that distinctive-looking individuals benefit, because they get in fewer fights over dominance.
4fuscatus.jpg

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June 29, 2008

Evolution 2008: sexy plants, battling bacteria, durable cooperation

About 1500 scientists attended Evolution 2008 here last week. The four-day meeting was filled with 15-minute talks (usually ten at once, in different rooms), plus two evening poster sessions (like a science fair, for grownups, with discussions rather than judging), scenically located on a pedestrian bridge over the Mississippi. Reports that “scientists are abandoning evolution�? appear to be exaggerated.

Here are summaries of some of the talks I enjoyed.

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May 31, 2008

Traditional values in bees

The beehive was an early Mormon icon, symbolizing hard work and cooperation. To an evolutionary biologist, however, a beehive could symbolize reproductive skew, a situation where some individuals reproduce much more than others. Extreme reproductive skew is one of the defining characteristics of eusocial species, of which honey bees are a prime example. Reproductive skew can differ between the sexes. In honey bees, the queen lays most of the eggs, and most females don't reproduce at all. Polygamous species and groups show the opposite pattern: males vary much more in reproductive success than females do. Maybe an inverted beehive would have been a better symbol. Note that the cells in our bodies behave somewhat like a eusocial bee colony; any children we have are directly descended from a few sex cells, while brain cells and skin cells play the supporting role of worker bees.

This week's paper, "Ancestral monogamy shows kin selection is key to the evolution of eusociality" was published in Science by William Hughes and others. Like humans, some bees are monogamous, meaning that the queen mates with only one male, so her daughters (the workers) are all sisters. In other bee species, the queen mates with several males, so her daughters are half-sisters. Relatedness generally favors cooperation, although there are some possible complications, discussed below.

This week's paper asks how mating behavior affects the evolution of eusociality. They reasoned that, if mating system doesn't matter, then today's eusocial species could be descended from either monogamous, polygamous, polyandrous (each female has multiple mates), or promiscuous ancestors. Alternatively, eusociality may evolve more easily with one of these mating systems than with the others.

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May 25, 2008

Pest control for ants

Ant.jpeg

(Top) A small leafcutter worker atop a leaf guards her sister against attacks by parasitic flies. Ants carrying leaves cannot use their mandibles for defense, so they carry hitchhikers to ward off the parasites. (Bottom) The fungus garden in a nest of Atta leaf-cutter ants. Notice the diversity of ant sizes within a colony, from the large red soldier ants to the minute orange ants tending to the garden. Atta ants have some of the most sophisticated caste systems among the social insects. -- photos and captions from Alex Wild (mymercos.net)

"Ant2.jpeg
This week’s paper, “Black yeast symbionts compromise the efficiency of antibiotic defenses in fungus-growing ants" by Ainslie Little and Cameron Currie, was just published in Ecology. Elsa Youngsteadt interviewed me, among others, for a story in Science about this research.

I’ve never done research on the fungal “farms" of ants and termites, but I’ve been interested in them every since a camera company bought a close-up photo (not Photoshopped like this one) of an ant carrying a leaf along a barbed wire “bridge" on its way back to its nest, from my mycologist father, William Denison. Dad was best known for pioneering research in the tops of tall trees, but never had to fight a shaman, as far as I know.

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April 19, 2008

Separate vacations and other sexual differences

Three recent papers in Proceedings of the Royal Society discuss differences between males and females or, in one case, among males.

The costs of risky male behaviour: sex differences in seasonal survival in a small sexually monomorphic primate? by Cornelia Kraus and others, is based on a 10-year study of differences between male and female behavior in grey mouse lemurs. During the breeding season, males had lower survival than females, despite any possible risks associated with pregnancy or raising young. The higher risk for males apparently resulted from their tendency to travel more, looking for females.

The sexes also differ in winter behavior: females hibernate, while males remain active. Is there something about female physiology that makes hibernation healthier for them than it would be for males? Maybe, but there was no difference in winter survival between the sexes, which don’t differ much in size in this lemur species. The authors suggest that hibernation might have longer-term benefits in females, such as increased lifespan, whereas males need to stay active to bulk up in preparation for the breeding season.

This paper reminded me of an earlier paper on albatrosses, in which "in each pair, the male spent the winter just north of the pack ice in Antarctic waters whereas the female stayed south of Madagascar." It’s not hard to understand why males and females might differ in various ways (size, color, etc.) but differences in behavior outside of the breeding season are more interesting.

The second paper addresses an old argument between Charles Darwin and Alfred Russel Wallace, who developed similar explanations of evolution by natural selection at about the same time.

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March 31, 2008

Learning vs. lifespan?

For my first 100 posts, I’ve ignored journals with “evolution? in their names, to make the point that evolution is at the heart of biology, rather than an “appendix.? Much of our DNA can be deleted without obvious ill effect, but taking evolution out of biology would kill it as an explanatory, hypothesis-driven science. Point made? This week I untie my hands and discuss a paper from one of the 30+ scientific journals that focus on evolutionary biology.

“Learning ability and longevity: a symmetrical evolutionary tradeoff in Drosophila? by Joep Burger, Munjong Koss, and others, will appear soon in the journal, Evolution.

The ability to learn is useful under a wide range of conditions, but is it always beneficial? If so, why do most species have limited learning ability? Is there some evolutionary constraint, such as head size, that prevents evolving greater learning ability? Apparently not. Artificial selection for learning ability has been successful in several species. When artificial selection imposed by humans achieves something in months that natural selection has failed to do in millions of years, that suggests that the “improvement? has some cost that exceeds its benefits, at least in nature. But could the ability to learn really have a cost that exceeds its benefits?

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March 9, 2008

Tricky parasites winning the evolutionary arms race

Two papers this week describe recently discovered sophisticated adapatations of two different parasites: Gall insects can avoid and alter indirect plant defenses, published in New Phytologist by John Tooker and colleagues, and Parasite-induced fruit mimicry in a tropical canopy ant, published in American Naturalist by Steve Yanoviak and colleagues (if you're in a hurry, skip to the end for amazing photos).

Various plants recruit "bodyguards" when attacked by insects. For example, when caterpillars start munching on corn (maize) plants, the plants (including uninjured leaves) release gaseous chemicals called terpenoids. These terpenoids attract parasitic wasps, which lay their eggs into the caterpillars. This eventually kills the caterpillars, which presumably benefits the plant. But what if the caterpillars could prevent the plant from signaling to the wasps? As far as I know, caterpillars haven’t evolved this trick (yet), but there are apparently some insects – the Hessian fly, Mayetiola destructor (say) – that do not trigger signaling when they feed on wheat plants. There are at least two possible explanations…

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February 25, 2008

Reversing evolution: conspicuous mimicry vs. camoflage

Two papers this week on the type of mimicry named for Henry Bates, whose book on exploring the Amazon was published shortly after The Origin of Species. Batesian mimic species resemble foul-tasting or dangerous species, thereby avoiding being eaten, even though they are not actually dangerous themselves. Bates worked on butterflies whose wing patterns resembled those of other species. Butterflies are still the best-known examples of mimicry, but there are also examples of mimicry (involving behavior) in snakes and octopi.

The two papers are:
Once a Batesian mimic, not always a Batesian mimic: mimic reverts back to ancestral phenotype when the model is absent
by Kathleen Prudic and Jeffrey Oliver, of the University of Arizona, and
Colour pattern specification in the Mocker swallowtail Papilio dardanus: the transcription factor invected is a candidate for the mimicry locus H
by Rebecca Clark and colleagues in the UK, Australia, Kenya, and Germany. Both were published in Proceedings of the Royal Society.

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February 18, 2008

Natural enemies complicate reproductive tradeoffs

Semelparous plants and animals are those that reproduce only once, whether after a few months of growth (annual plants, like wheat) or after years (“century plant? or most salmon). Iteroparous species iterate. That is, they reproduce repeatedly. For example, perennial grasses may produce seeds every year for a decade or more.

One reason this difference matters is that perennial crops may have some environmental benefits, relative to annual crops. Plowing, traditionally more common with annual than perennial crops, can greatly increase soil erosion, especially on steep slopes. So there is increasing interest in developing perennial grain crops as an alternative to wheat.

However, perennial plants have lower seed yield than their annual relatives, so we would need to devote more land to agriculture to get the same amount of grain. One reason for the yield difference is that an annual plant can transfer most of the carbon (energy) and nitrogen (needed for protein) from its leaves, stem, and roots into its seeds. It’s going to die anyway, so the next generation gets its accumulated wealth. A perennial plant needs to hold back some carbon and nitrogen for winter survival and spring regrowth. The more resources it puts into this year’s seed production, the less it can carry forward to support reproduction next year.

This week’s paper shows that iteroparous plants face additional costs when they reproduce, namely, ecological costs. “Herbivore-mediated ecological costs of reproduction shape the life history of an iteroparous plant? was written by Tom Miller and colleagues at the University of Nebraska (where I’ll be speaking on Darwinian Agriculture in April) and published in American Naturalist.

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January 10, 2008

Ants en't ents

Science advances by disproving previously-tenable hypotheses. For example, "The earth is <10,000 years old" was disproved by annual sediment layers long before we were able to estimate the actual age. Actually, Tom Kinraide and I argued in "Strong inference -- the way of science" that a hypothesis needs to be explanatory as well as falsifiable. So for a young earth to ever have qualified as a hypothesis, it would first have needed to explain at least some real world observations. Right off hand, I can't think of any actual data that an unbiased person would look at and say, "Well, these data would make sense, but only if we assume the earth is <10,000 years old."

Similarly, if someone wanted to convert "intelligent design" from religious whining into a scientific discipline, we'd need some falsifiable hypotheses. Suppose, for example, we hypothesized that current features of plants and animals (not just their single-celled, distant ancestors) were supernaturally-imposed designs to maximize their success. That hypothesis is consistent with the many examples of sophisticated adaptations (err, "design"), but what can we conclude from the many examples of maladaptation ("bad design")? Maladaptation is predicted by evolutionary theory (when current conditions don't match those under which past selection occurred, for example) but if some design team is continuously intervening in evolution, do maladaptations imply that they had a busy week? If so, should we expect the problem to instantly disappear, once they get around to it?

This week's paper is another example of the pattern we see repeatedly in biology: many sophisticated adaptations, but also serious "design flaws." In particular, Acacia trees can be fooled into feeding and housing ants that are harming them.

Breakdown of an Ant-Plant Mutualism Follows the Loss of Large Herbivores from an African Savanna was published this week in Science by Todd Palmer and five coauthors, three of whom I know from my years at UC Davis.

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December 7, 2007

The ghost of infections past, present, and future

Summary: A 39-year record of host-parasite interaction, recovered from sediment layers in a pond, is consistent with rapid coevolution.
Link: Host-parasite /`Red Queen/' dynamics archived in pond sediment

As I've discussed previously, archival samples often prove useful for answering questions that weren't being asked when the samples were collected. But what if nobody collected and preserved the samples you need for your research? Maybe you can find a "natural archive" that has what you need.

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August 31, 2007

Whose genes are these, anyway?

Most of the genome of Wolbachia, a bacterial parasite of fruit flies, has been incorporated into the genome of the fruit-fly itself. Discussion at Not Exactly Rocket Science. Bacteria tend to pass genes around, or (more accurately, perhaps) bacterial genes tend to move themselves around (usually to other bacteria), but this is amazing.

August 17, 2007

Almost a no-brainer

How sophisticated behavior would you expect from an animal with a brain as small as a wasp's? Few, if any, female wasps have read David Lack's classic paper on the optimum number of eggs to lay, or even John Dennehy's clear summary of it. This week's paper asks whether they, nonetheless, adjust egg numbers optimally in response to competition from other wasps and resource availability.

"Encountering competitors reduces clutch size and increases offspring size in a parasitoid with female–female fighting" was written by Marlene Goubault, Alexandra Mack, and Ian Hardy, of the University of Nottingham, and published in Proceedings of the Royal Society.

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July 23, 2007

Diversity, stability, productivity, and policing

This week I will discuss two papers, both of which consider possible benefits of biological diversity. In interpreting the data in the experimental paper, on bees, we need to remember that a given set of data can often be consistent with two or more different hypotheses. This point is reinforced in the review article, which discusses the relationship between diversity and stability of ecosystems.

The experimental paper is "Genetic diversity in honey bee colonies enhances productivity and fitness" by Heather Mattila and Thomas Seeley, of Cornell University (Science 317:362). The review article is "Stability and diversity of ecosystems" by Anthony Ives and Stephen Carpenter, of the University of Wisconsin (Science 317:58).

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May 20, 2007

Rapid evolution of beneficial infections

Given my location halfway between the Twin Cities of Minneapolis and St. Paul, and my childish love of clever acronyms, I sometimes wish I'd named this blog This Week In Natural Selection. But then I suppose I'd have to review a pair of closely related papers each week. I'm going to do that this week, anyway.

This week's twins were both published in PLoS Biology, so both are freely available on-line. Both have new data on bacteria that infect insects. Both help us understand the conditions under which infecting bacteria evolve to be beneficial, rather than harmful. Finally, both disprove, again, the popular idea that any evolutionary change big enough to matter (except antibiotic resistance, which a creationist commenter once claimed always involves "horizontal transfer" of genes among bacteria, even though resistance often evolves in bacteria in a closed container all descended from a single cell) always involves lots of genes and takes millions of years. Evolution is our present and future, not just our past.

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March 31, 2007

Can a selfish gene stop malaria?

A bird that risks her life to lead a fox away from her chicks may be influenced by a "selfish gene" (Dawkins, 1976). Genes can't think, of course. However, a gene causing behavior that risks the loss of one copy of itself (in the mother) will become more common over time, if this same behavior often saves more than one copy of itself (in the chicks). The gene can be considered "selfish", in the sense that the welfare of the mother, her species, or the whole ecosystem only indirectly affect the gene's spread. It's as if each gene were at war with rivals (other versions of the gene, or alleles) for its place on the chromosome.

The selfish gene concept is now being used to design new methods to control the spread of disease. Mosquitoes that resist infection by the malaria parasite can be made by genetic engineering. Unfortunately, the small benefit (to a mosquito) of resistance to this parasite is probably not enough for resistant mosquitoes to take over in the wild, because most of the animals they bite aren't infected. (It would be nice if the laws of nature always favored human welfare, but they don't.)

How can we make such beneficial genes spread through mosquito populations? This week's paper, "A Synthetic Maternal-Effect Selfish Genetic Element Drives Population Replacement in Drosophila" by Chun-Hong Chen and colleagues at Cal Tech and UCLA, published on-line in Science, demonstrates one interesting approach.

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February 28, 2007

Experimental evolution: play dead or fly away?

Last week's paper discussed trade-offs between seed size and seed number. Many such trade-offs (growth vs. reproduction, more seeds vs. taller stem, etc.) follow directly from conservation of matter or energy, but what about other sorts of trade-offs? It has been suggested, for example, that there is a trade-off between competitiveness and dispersal ability. Why should this be? For seeds, at least, a larger seed gives the seedling a head-start against competitors, but smaller seeds travel farther on the wind.

This week's paper proposes another trade-off, for which the mechanism is less obvious. "Drop or fly? Negative genetic correlation between death-feigning ability and flying ability as alternative anti-predator strategies", was written by Tatunori Ohno and Takahisa Miyatake and published in Proceedings of the Royal Society B (vol. 274, p. 555-560).

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