Abstract at:

http://www.americans...l/assetid/56469

link to full article on that page

Death Valley seems an unlikely spot to go fishing. Nonetheless, seven species of pupfish survive in North America's lowest, hottest spot as remnants from the cooler, damper Pleistocene Epoch. For the most part, these species exist in isolation and have been left to adapt to minute details of their local environment—sort of the fish version of Darwin's finches. Surprisingly, however, even within a species, when environmental variables such as water temperature or food supply vary, morphological changes are evident within a few generations. This phenotypic plasticity calls into question not only environmental management practices for species preservation but also just what it is to be a species.

Camped out there when I was in the Air Force and when there, took some tour with a ranger and walked over a board walk and he said if you look down you can see some fish that only live here and no where else on earth. I mean the place is an alkaline haven and can get to 130 degrees or more but there you have fish. I am amazed at these pup fish. But then you go a few miles and there is one a little different.

We had a slight rain when there and the tarantulas came out of the ground that was a neat experience also.

The phenotypic plasticity shown by these pupfish species and populations doesn't so much call into question the concept of a species, as it does to clarify what is a species. A purely morphological definition won't work, and that's true for many other organisms. It's a question of who mates with whom on a regular basis, and/or shared ancestry.

People worry about the various pupfishes changing in artificial refugia. But I would guess that if you take those refugia populations and reintroduce them to their original or very similar habitat, the phenotype would shift back to the original form within a few generations. Talk is cheap, of course, federal managers don't seem to have done such an experiment and maybe for good reason.

But I would guess that if you take those refugia populations and reintroduce them to their original or very similar habitat, the phenotype would shift back to the original form within a few generations.

Now, that's what I've always said (opinions are cheap, especially mine!), and I've been roundly pooh-poohed for saying it. So, now I have an ally in the pupfish war as well as the hybrid war! Now, about those F. "notatus"...

People worry about the various pupfishes changing in artificial refugia. But I would guess that if you take those refugia populations and reintroduce them to their original or very similar habitat, the phenotype would shift back to the original form within a few generations.

I'd agree with that. I'm thinking the Devil Hole pupfish grew because, in an effort to save them, they probably feed them. Over fed fish, just like over fed people, get bigger! Consider the average height and weight of the average American a hundred years ago to today. I think we're a good foot taller than the pilgrams! I know in my own tank, despite my efforts to NOT over feed my fish, they are all larger than "the book" says they are suppose to be.

And thank you Kraft, that was an interesting article.

There are other examples of morphological polymorphism that are similar to the desert pupfish situation. These include the troglobitic Astyanax in Mexico, the benthic morph sticklebacks in Canadian lakes, the neotenic Eurycea salamanders in Alabama and Texas, and nearly all poeciliid species.

Depending on who is writing, these polymorphisms are explained by either phenotypic plasticity or incipient speciation. What's interesting to me is that the patterns are not accurately described by phenotypic plasticity, nor do they necessarily indicate a speciation event. True phenotypic plasticity is observed within a single generation (alligator sex determination, sneaker male lepomis, red midas cichlids). The variation observed in these groups is less discrete. Additionally, natural experiments suggest that the variants (benthic sticklebacks, blind tetras etc) return to the mode relatively quickly over evolutionary time, suggesting that speciation has not taken place. This conclusion is supported by a lack of genetic differentiation among phenotypes, in most cases.

It seems to me that the retention of phenotypic variation through time is an evolutionarily stable strategy, which adapts a species to more than a single niche via pleiotropy. The result is a species which is able to adapt to gradual or cyclic environmental change through time. Over the long term this strategy would actually counteract speciation, not promote it.

Edited by Elassoman, 25 July 2008 - 10:55 PM.

sneaker male lepomis

Pardon my ignorance, but does this refer to cuckolding behavior? I understand that there are salmon males that never return to the ocean and fertilize females that return. Would "sneaker male lepomis" refer to a male that is a cuckolding specialist?

"Sneaker males" are males that are phenotypically female but have functional testes. They rush into alpha males' nests at the moment of spawning and release their own gametes, then quickly skedaddle.

Gotta love cryptocopulators.

Blake

Gotta love cryptocopulators.

That's me! "Who was that masked man, anyway?"

"Sneaker males" are males that are phenotypically female but have functional testes. They rush into alpha males' nests at the moment of spawning and release their own gametes, then quickly skedaddle.

That's freaking awesome.

Don't try this at home!

If anyone took the phrase "phenotypically female" as a personal challenge...

I read a paper a while ago (will link later when I find it) about morphological variation in pupfish; I think Pecos Pupfish. After measuring (I think) eight characteristics, they found that morphological variation was the least amongst breeding males. Non-breeding males and all females had similar, higher rates of variation. This suggests that a major driver for selection in pupfishes is female sexual preference. They've done other experiments with females of one species favoring males of another, and then looked at hybrid selection by females-details are foggy in my mind, but unfortunately sheepshead minnows are popular mates. I think that is the main driver in many of these similar systems that show high rates of pupfish variation, but hopefully I'll find some more answers to this soon.

In anthropogenic terms, pupfish colonies are like high schools, and the breeding males are the popular kids. Not much variation, but gettin all the action.

I think the preserving the species as a static entity approach is BS... I think it's very possible that female selective preferences change more quickly than we think in these guys in ways that we don't understand yet-maybe even environmental triggers, and their phenotypes are changing almost like an evolutionary fashion show. It would be interesting to find a fossil record of pupfish in the same location of an extant population and see how bone structure has changed over time... Anyone know of any finds like this?

Hope this ramble makes sense. Two days in the field electroshoking on slick bedrock have made me loopy and sore.

What you say about variable phenotype is true. The linked article by Sean Lema that started this thread discusses how he and associates were able to manipulate behavioral phenotypes in two different populations of pupfish by rearing them in slightly different environments, a steady temperature vs. variable temperature and elevated salt level vs. low salt level. This changed the aggerssiveness of males in the two populations by tweaking the size and function of different neuronal nuclei in the prefrontal cortex of the hypothalamus, affecting release of the neuropeptide AVT which in turn directly affects the hypothalamo-pituitary-gonadal axis that drives sexual function and behavior. This isn't too big a surprise when you think about it; the environment shapes behavior, and at the microevolutionary level shapes what are successful behaviors especially in terms of reproductive fitness. So a successful phenotype is a moving target as the environment may change for a given population/species, and what females see as an attractive male phenotype (sexual selection) would be expected to change as a specific type of coevolution.

My lab group has been working with scarlet shiners (Lythrurus fasciolaris) and telescope shiners (Notropis telescopus). We're interested in the neurological aspects of reproduction such as levels of the male hormone 11-ketotestosterone and "male" features such as intensity of coloration. Scarlets are strongly sexually dimorphic, with larger, brighter males, while telescopes aren't, and the males are smaller than females. Two things we've found bounce off what rjmtx mentioned in his post. For one thing, we've found that successful alpha males have very similar phenotypes with little variation (especially in scarlet shiners). And we've also found that males in both species have relatively larger brains than females, at a strong level of statistical significance. What does this mean? We're still not exactly sure; but in scarlet shiners the brain region that's most different from females is the optic tectum, two large lobes that process visual information (we're still working on the telescope shiner data).

So these are two notropine species that live in the same streams, with different reproductive phenotype strategies, that share the feature of larger-brained males. Would this change if these fish were in different environments? I'd guess so, although one could imagine a range of plausible outcomes.