Category Archives: adaptation

Beware: The Sneaky Grass Goby

by Amy Dapper
Grass Gobies

Grass Goby (Zosterisessor ophiocephalus) – Wikipedia Commons

Competition for mates drives the evolution of many of the exaggerated male traits, such as the bright plumage of tropical birds or the intricate horns of dung beetles, that are so easily appreciated (and photographed).  However, the elaborate consequences of competition for mates continue even after mate choice and copulation has taken place, inside of the female reproductive tract.  Much of the research on sperm competition has focused, for obvious reasons, on the quantity and morphology of the sperm produced by males with results that are no less fascinating or extreme.  For example, the fruit fly, Drosophila bifurca, produce sperm that are around 2.3 inches long, which is more than 20 times their body length and 1000 times the length of human sperm!

However, sperm constitute only a small portion of the male ejaculate transferred to females during mating.  The rest, up to 90%, is composed of a myriad of proteins and other compounds that constitute the seminal fluid.  In addition to being produced in abundance, seminal fluid proteins are also diverse.  For example, scientists have found that males, of many species, produce dozens, if not hundreds, of different types of seminal fluid proteins.  So, what then, do all these proteins do?  It turns out that these protein are involved in many different processes that indirectly influence male reproductive success, including influencing female physiology and interacting with a male’s own, as well as rival, sperm.

A recent study by Locatello et al., published in Proceedings of the Royal Society B, has taken advantage of some useful characteristics of the mating system of the grass goby, Zosterisessor ophiocephalus, (pictured above) to investigate how alternative male mating strategies may be paired with alternative sperm competition strategies to help level the playing field between males that vary in their ability to directly compete for mates.

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Carnival of Evolution: We’re hosting!

by Yoder

Evolution

Step right up, step right up, ladies and gentlemen, to submit your fine evolution-related blog posts to the 58th edition of the Carnival of Evolution, the one and only community-assembled, community-supported, community-hosted aggregation of the finest online writing on the illustrious topic of Descent With Modification and all its manifold modified descendents.

On the first day of March, this glorious Carnival will be found right here at Nothing in Biology Makes Sense!, the better to showcase the work of everyone from students to scientists to great fans of science, everyone and anyone, ladies and gentlemen, who believes and can demonstrate in mellifluous prose, captivating videos, eye-catching infographics, or hilarious LOLcats that bedrock principle of the modern life sciences, that nothing—no, ladies and gentlemen, not a gosh-darned thing—in the whole of biology makes sense, except in the light of evolution.

Think you’ve got what it takes to join this revolutionary celebration of evolutionary science? Send us links to your blog posts, essays, videos, and webcomics at this elegant and convenient form (it requires a log-in, but then what doesn’t these days?) or simply e-mail them direct to Jeremy Yoder, our local curator of carnivalian content. Please do send’em before the 26th of February, though, to ensure proper packaging and adequate care of all your delightful and illuminating work.

We thank you humbly and vociferously for your contributions, one and all—and we look forward to seeing you right here, at this very URL, for the Carnival of Evolution, in less than the span of one short month!

Is epigenetics totally gay?

by Yoder

… epigenetics is why I love you? (Photos from the ONE National Gay & Lesbian Archive.)

In the light of much of what we know about evolution, human homosexuality doesn’t make a lot of sense. Available data suggests that sexual orientation has some inborn, probably genetic, basis. But it’s hard to reconcile that with the fact that gay men and lesbians aren’t, by definition, particularly interested in doing what it takes to pass on any genes that might have contributed to creating their orientation. Natural selection is, all things being equal, pretty good at eliminating genes that make people less likely to make babies.

I’m gay. I’m also an evolutionary biologist. You could say this particular puzzle is tailor-made to attract my interest.

It turns out that there are a number of ways that human populations might accommodate gene variants for same-sex attraction without suspending the rules of natural selection. But it’s also possible that human sexual orientation has a biological basis without being genetic. Natural selection can’t do anything about a trait if variation in that trait isn’t linked to variation at the genetic level. So I was immediately interested by the recent announcement that a team of biologists at NIMBioS, the National Institute for Mathematical and Biological Synthesis, had found that human homosexuality is due not to genetics, but to epigenetics.

However, as soon as I secured a copy of the study itself (available in PDF format here), I was disappointed to find out that the reports of a solution to this particular evolutionary enigma are somewhat exaggerated. The paper doesn’t present any new data that directly links a specific developmental process to human sexual orientation — it’s a review article, gathering existing results in support of a hypothesis that isn’t, at its most basic level, entirely new. But it’s not the job of a review article to present new data; reviews are supposed to gather up what is already known on a topic and identify what new research could do to better answer the questions that remain. And that’s exactly what the new study does.

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Many genes, but two major roads to adaptation

by Yoder

Cross-posted at Denim and Tweed.

In the course of adaptive evolution — evolutionary change via natural selection — gene variants that increase the odds of survival and reproduction become more common in a population as a whole. When we’re only talking about a single gene variant with a strong beneficial effect, that makes for a pretty simple picture: the beneficial variant becomes more and more common with each generation, until everyone in the population carries it, and it’s “fixed.” But when many genes are involved in adaptation, the picture isn’t so simple.

This is because the more genes there are contributing to a trait, the more the trait behaves like a quantitative, not a Mendelian, feature. That is, instead of being a simple question of whether or not an individual has the more useful variant, or allele, at a single gene — like a light switch turned on or off — it becomes possible to add up to the same trait value with different combinations of variants at completely different genes. As a result, advantageous alleles may never become completely fixed in the course of an adaptive evolutionary response to, say, changing environmental conditions.

That principle is uniquely well illustrated by a paper published in the most recent issue of Molecular Ecology, which pairs classic experimental evolution of the fruitfly Drosophila melanogaster with modern high-throughput sequencing to directly observe changes in gene variant frequencies during the course of adaptive evolution. It clearly demonstrates that when many genes contribute to adaptation, fixation is no longer inevitable, or even necessary.

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