Week Two of Developmental Biology!

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I saw this article that pertained to some of the mutations that we saw in class. Adapting to Darkness: How Behavioral and Genetic Changes Helped Cavefish Survive Extreme Environment is about how changes in environment lead to evolutionary changes. In this study Mexican Cave Fish were studied since "other than the loss of eyes and lack of pigmentation" you can't tell the two fish apart. In the study they found that in the cave eyes weren't useful since everything was dark, instead they develop and exhibit a Vibration Attraction Behavior (VAB) which has sensory cell masses on the lateral line. This VAB isn't effective for the surface fish since swimming into a disturbance could be a danger since there are more predators towards the surface. I just thought this tied into the other examples we talked about in class where changes in the environment can lead to eventual evolutionary changes. It was interesting how these two fish really do look the same if you can look past the color difference and the cave fish lacks eyes!

The link to the article is here http://www.sciencedaily.com/releases/2010/09/100914171325.htm

10 Comments

I saw this too. Very interesting and it's nice to have the two species to compare. A rare gem.

Ok. I want you to succeed. So I'm going to be critical and hold you standards that, maybe you think are not "fair." But I'm not interested in "fair," but, as I said, in your success.

1. These are Mexican blind cave fish. It's a trivial omission on the face of it, but in many cases trivial differences can make a world of difference in communication. In my profession, the difference between "and" and "or" in the Internal Revenue Code can mean the difference between a felony tax-evasion charge and good tax planning.

2. You introduce one fish, then talk about comparing fish. You do not tell us about the ancestral fish being compared. This is a critical element, yet it is omitted.

3. Paragraphs are your friend. They add clarity to your writing.

4. Of course eyes aren't useful in the dark. If any of the above omitted information was omitted due to space constraints, you made a suspect editorial choice.

Think about what is most important in this article. It's not just another blind cave fish that's figured out a way to make a living in a hostile environment article.

The hook, though there is little in the way of column inches dedicated to it, is that we have a new species that has evolved from an existent ancestral species in one of the speciation methods proposed by evo-devo. This is a fantastic find. A real-life species of evolved fish with its ancestor still alive.

It's the fish equivalent of finding a population of living Homo erectus in Java...

I agree with Moseszd's comments about presentation. It is important to think what people who know little about the subject need to know.

It is well worth looking at other cases where two species are very similar. In my teens (over 50 years ago) I was involved in some research into bats which hibernated in caves in Devon, England. At the time the commonest non-cave bat was the pipistrelle. Some years later, when electronic bat detectors started to be used to reduce the bat's hunting calls to something humans can hear, it was discovered that the pipistrelle had two different hunting calls.
On no they didn't. When DNA testing came along it was realised that there were two different species which were visually indistinguishable - but used different hunting calls. I am not up with the literature (I retired as an academic over 20 years ago - and this was not my specialist area) and it may be that by now someone has published something about different diets or different hunting habits.

When studying it is always useful to look for examples which your tutor has not mentioned - and perhaps has never heard of.

My main question after reading this would have to be, why in the world are their eyes totally gone? I mean bats don't really use their eyes much, but they still have them. Do you think bats might lose their eyes? Why didn't their eyes get big like some nocturnal creatures? It just doesn't make sense, I mean I get it, lived in a cave all the time don't need eyes, but we don't need appendixes?

I'm just not seeing the significance of this or of what we can learn from it outside of one kind of tetra.

I did like the fact that you pointed out how the reliance on their lateral lines could be a disadvantage in other environments.

Can the eyeless tetras produce viable offspring with those uppity eye having tetras?

Haters gonna hate ; )

I like the way you chose to blog about something that illustrates a point made in class - and an interesting one too.
You might want to think about blogging as if you were telling a story to a reader who isn't in your class (like me). For example, there is a cool idea that you want to blog about - evolutionary changes in response to the environment. If you start with a single sentence that describes what you want to say, and then formulate questions about that sentence, you will find the answers to those question pretty much will tell the story you want to tell.

Following caseyhov's comments let me make it clear that the pipistrelle is a very small insect eating bat (between 3 and 8 grams) which catches very large numbers of small insects using echo-location – which allows it to hunt when light levels are so low that it not at risk from predation from carnivorous birds. Large eyes which were sufficiently far apart to provide binocular vision to see insects the size of a gnat in very low light levels would mean a much larger head which would mean a heavier body which means it would need to catch more and possibly bigger insects – so why bother when it can catch them using echo-location. The bat has found a niche where it can hunt successfully with the minimum of predation. What more could a species ask for?

In the case of the Mexico blind fish you have two species which are very similar – but because of very obvious difference in environment their sensory mechanisms have developed (or failed to develop) in different ways.

In the case of the pipistrelle bat you have two species (Pipistrellus pipistrallus and Pipistrellus pygmaeus) which look virtually identical to the extent that experts were fooled in thinking they were one species. However one of their sensory mechanisms has developed in different directions in the two species. Why? Such a difference is probably because they exploit the environment in different ways, as did Darwin's Finches and the Mexican Cave Fish. So what are the differences in the behaviour that lead to the split into two species and what other effects has the change caused? I would expect some changes in both the nasal cavities (which generate the ultrasonic pulses) and the ears which need to be sensitive to different frequencies in the two species (45 and 55 kHz). I suspect that those working on the problem have already identified some differences of this nature – the name of the “new” species suggests that it is the smaller of the two - but I don't know if any details have been published yet.

I assume that as a UMM student you have access to the original article in Current Biology as well. The Science Daily link is to a news article, not a scientific article. In general, it's good to go directly to the primary material. Do you think the news article adequately summarizes the Current Biology one?

I know that both the blind and non-blind fishes have lateral lines and superficial neuromasts, but the article you linked to didn't make it clear whether the difference between the two types of fish were purely behavioral or reflected in the anatomy of the two fish. Does the original article have anything to say about that?

Neat. I realize that morphologically these two fish are identical outside but I was wondering if anyone has looked at any phenotype differences in their brains? I would suspect that if truly blind the visual areas of their little fish brains have been co-opted for use in enhancing other sensory processing - similar to the adaptation demonstrated in humans who are blind recruiting visual neurons for processing information from other senses. If that is the case, then the next question is would any re-wiring be due to physiologic or phylogenetic adaptation? Of course, the visual areas of their brains may have simply attrophied but what an awful waste of good neural tissue that would be.

Astyanax fasciatus would also appear to have an unexpectedly good spatial mapping ability, which is quite handy if the range of its perceptions is about 1/600 of its ranging requirements.

It's interesting that the one of the references on the paper with an author that I recognise is actually a spatial cognition expert rather than a developmental biologist - an example of the what (her paper on spatial mapping) contributing to a slightly different why (the paper in sciencedaily)

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This page contains a single entry by kochx215 published on September 21, 2010 7:47 PM.

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