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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.

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"

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."

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.

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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August 3, 2007

Catfish beats Columbus to America

So did the ancestors of American Indians, of course, but a catfish seems to have beat them by about 50 million years. "Discovery of African roots for the Mesoamerican Chiapas catfish, Lacantunia enigmatica, requires an ancient intercontinental passage" by John Lundberg, John Sullivan, Rocio Rodiles-Hernandez, and Dean Hendrickson, was published in Proceedings of the Academy of Natural Sciences of Philadelphia.

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March 21, 2007

Splitting species: sneak attacks from strategic hamlets

This week's paper is "Colour pattern as a single trait driving speciation in Hypoplectrus coral reef fishes?" by Oscar Puebla (Smithsonian Tropical Research Institute, Panama) and colleagues in Canada and the UK, published on-line (no volume or page number yet) in Proceedings of the Royal Society. (I was planning to review a paper on the evolutionary history of genetic differences between chimps and humans, suggested by a reader, but decided I didn't understand it well enough myself to explain it clearly. Is there a volunteer guest blogger out there?)

Actually, there's a bit of a connection between the two papers. At some point, the ancestors of humans must have stopped having babies with the ancestors of chimps. Otherwise, we'd still be one species. We might have evolved a lot from our common ancestor, but we'd be evolving together, not separately. Interbreeding is a problem for the production of new species in general; the resulting "gene flow" can prevent differentiation into separate species.

One easy solution is geographic separation. Finches on different islands in the Galapagos group rarely interbreed with each other, and never with their ancestral species on the mainland. So natural selection, working in different directions on the different islands, isn't swamped by interbreeding. This eventually produced enough change that the finches would at least hesitate to mate if brought back together.

But can species separate without being physically separated? There are already a few known examples of this, but the authors of this week's paper may have caught "sympatric" speciation in reef fish known as hamlets red-handed. Uh, finned.

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February 20, 2007

Evolutionary trade-offs: how are soybeans like salmon?

Answer: they're both semelparous (reproduce once, then die), so evolutionary trade-offs between number and size of offspring are expected to be similar.

This week's paper is "Evolutionary aspects of the trade-off between seed size and number in crops" (Field Crops Research 100:125-138) by Victor Sadras. You can read the abstract on the web for free. For the full version, you can pay $30 to download, visit your nearest agricultural research library (in the U.S., often at a state university), or email the author at: sadras.victor@saugov.sa.gov.au. My discussion is mostly based on a shorter version presented at the Australian Agronomy Conference.

Demand for grain is increasing, to feed growing human and livestock populations and more recently for ethanol production. Unless those trends are reversed, we will either need to expand the land area used for agriculture or increase grain yields per unit area. Grain yield is the product of plants per area, seeds per plant, and weight per seed. Unfortunately, increasing any one of these (by increasing seeding rate, or through plant breeding) tends to decrease the others.

This paper looks at how natural selection (in the wild ancestors of crop plants and in fish) and plant breeding (especially in maize and sunflower) shape trade-offs between seed number per plant and seed size. The similar patterns in plants and fish show that, as predicted by the relevant aspects of evolutionary theory, we are dealing with fundamental constraints that we are unlikely to change.

Continue reading "Evolutionary trade-offs: how are soybeans like salmon?" »