Tag Archives: sexual selection

Nothing in Biology Makes Sense: Nature’s Nether Regions, by Menno Schilthuizen, reviewed

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Jewelwing Love

Jewelwing damselflies (Calopteryx maculata) mating. (Flickr: Lisa Brown)

Over at Nothing in Biology Makes Sense, I’ve posted a long-overdue review of a terrific little book about naughty parts. Genitals. Junk. It’s called Nature’s Nether Regions, by evolutionary biologist and entomologist Menno Schilthuizen, and it puts the weird world of (animal) reproductive anatomy on full display, while avoiding the cliches and pitfalls into which so many popular accounts of sex and evolution fall.

The book’s subtitle What the Sex Lives of Bugs, Birds, and Beasts Tell us About Evolution, Biodiversity, and Ourselves, might be a bit ominous to a reader familiar with the many hazards of evolutionary hypothesizing about human behavior, but Schlithuizen’s chatty tour of animals’ sexual anatomy dodges them all. He does this, in large part, by devoting far more time and attention to the “evolution” and “biodiversity” than to “ourselves,” putting the rather pedestrian reproductive arrangements of Homo sapiens in their place amidst the baroque diversity of appendages, receptacles, secretions, and behaviors other animals employ to multiply their kinds.

Go read the whole review, which includes some sampling of the natural history Schilthuizen covers, and then check out the book itself.

The Molecular Ecologist: Sexual selection, natural selection, and pronghorn

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Run antelope, run! Male pronghorn, on the run. Photo by Great Beyond.

Meanwhile, over at The Molecular Ecologist, I interviewed my old friend Stacey Dunn about a study of hers recently published in Science, which presents ten years of data to examine how A.J. Bateman’s principal of sexual selection — that males maximize their evolutionary fitness by mating with lots of females, but females maximize their fitness by mating with just one or a few carefully-chosen males — in pronghorn.

The National Bison Range pronghorn have been studied extensively by John [Byers] and his lab since 1981. Each spring, we captured nearly all fawns born in the population. During captures, we weighed, measured, sexed and tagged the fawns and took a tissue sample for genetic analysis. We genotyped each individual alive since 1999 at 19 microsatellite loci. We determined paternity for all fawns based on genotype. Maternity was known from fawn captures, but was also confirmed genetically. We then used that information to reconstruct a multi-generational pedigree of the pronghorn population.

To learn how the study improves on Bateman’s original work with fruit flies (which has since been called into question for methodological issues), and for Stacey’s tips on how to catch a baby pronghorn, go read the whole thing.◼

The living rainbow: Er, kinda …

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06 Drosophila melanogater Mating Mating fruit flies. Photo by Image Editor.

I just saw this from Christopher Ryan, coauthor of Sex at Dawn, on Twitter:

Foundational Evolutionary Psychology paper called into serious question. Randy males/choosy females? Maybe not. npr.org/blogs/13.7/201…

— Christopher Ryan (@ChrisRyanPhD) December 13, 2012

As I tweeted in response: er, kinda.

Ryan linked to some new discussion of a study I covered back in June. That paper found a major flaw in a 1948 study of Drosophila fruit flies that was the first to clearly support a component of sexual selection theory — the idea that males maximize their evolutionary fitness (i.e., the number of offspring they sire) by having many mates, but females maximize fitness by selecting just a single “best” mate.

The author of the 1948 study, A.J. Bateman, tracked the parentage of flies in his study — which was necessary to tally the offspring of each male and female fly — using visible “marker” mutations. The new study’s authors, Patricia Gowaty et al., tried to replicate Bateman’s experiment, and discovered that some of the marker mutations were so disabling to the flies that they almost certainly biased Bateman’s results.

That knocks the legs out from under Bateman’s experiment. But it doesn’t really deal a knockout punch to sexual selection, much less to evolutionary psychology. Yes, evo psych (especially the kind that I really despise) tends to default to Bateman’s “randy males/choosy females” model. But evo psych, which is primarily about the recent evolutionary history of human behavior, isn’t the same thing as sexual selection theory, which is about the evolution of mating systems in, well, pretty much anything that reproduces sexually.

And, in fact, new studies with better data do support Bateman’s model for other non-human animals. Just a couple weeks ago, Science published a very thorough study on pronghorn antelope that tracked the interaction of Bateman-style sexual selection and regular old natural selection over a decade. (One of that study’s coauthors, Stacey Dunn, is a personal friend — I’ll be running an interview with her over at The Molecular Ecologist next week.) That work is based on modern genetic markers, which have none of the drawbacks of Bateman’s method.

But all of this is sort of beside the point, as far as the rightness or wrongness of evolutionary psychology goes, since fruit flies and pronghorn aren’t humans. There’s a huge diversity of sexual expression across the animal kingdom, and it’s absurd to think that we can make any particular conclusion about recent human evolution based on what works for insects or ruminants.

If evolutionary psychologists would be wrong to use Bateman’s fruit flies to support a particular hypothesis about human sexuality — and they would be — then those of us who disagree with them don’t have any reason to crow about Bateman’s mistakes.◼

References

Byers, J. & Dunn, S. 2012. Bateman in nature: Predation on offspring reduces the potential for sexual selection. Science, 338: 802–804. doi: 10.1126/science.1224660.

Gowaty, P.A., Kim, Y.-K. & Anderson, W.W. 2012. No evidence of sexual selection in a repetition of Bateman’s classic study of Drosophila melanogaster. Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.1207851109.

The living rainbow: A fatal flaw in a classic study of sexual selection

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06 Drosophila melanogater Mating

A mating pair of fruit flies. (Flickr: Image Editor)

ResearchBlogging.orgA key component of classical sexual selection theory is the idea that males maximize their evolutionary fitness—the number of children they ultimately have—by mating with lots of females, while females maximize their fitness by selecting only one or a few high-quality partners. It’s pretty clear that this model works well for some species (like ducks), but also that there are many it doesn’t fit so well. Now it looks like one of the “classic” experimental examples of sexual selection may actually fall into the latter category.

Sexual selection was first proposed by Charles Darwin, in his 1871 follow-up to The Origin of Species, The Descent of Man, and Selection in Relation to Sex; but one of the earliest experimental tests of the model wasn’t published until 1948 [PDF]. The biologist A.J. Bateman allowed small groups of fruit flies—good old Drosophila melanogaster—containing equal numbers of males and females to mate at random, then reared the resulting eggs and reconstructed the parentage of the offspring to determine (1) the number of offspring each of the male and female parent flies had produced and (2) how many parters each parent fly had had.

How did Bateman reconstruct parentage decades before the advent of modern genetic testing? He used mutations with known, visible phenotypic effects as “markers”:

The fertility of individual flies of both sexes was measured by means of dominant marker genes. Several flies of each sex were mated together in one bottle, each fly carrying a different dominant marker gene. In this way, assuming the complete viability of all the marker genes, half the progeny of each fly could be identified.

That’s a pretty clever design given the technological limitations of the time. But it also turns out to be the fatal flaw in Bateman’s experiment.

Continue reading →

The living rainbow: In ducks and geese, do bigger eggs raise the sexual stakes?

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Mandarin ducks. Photo by Steve-h.

ResearchBlogging.orgThe central idea of sexual selection theory is pretty simple: Females, who invest relatively more in making and raising offspring, have an incentive to be choosy about mating. Males, on the other hand, may be able to get away with no more investment that a squirt of semen—so they have an incentive to mate with any female who’ll have them. How widely that model applies in the animal kingdom is very much an open question, but it does make some specific predictions that can be tested in an evolutionary context.

One of those predictions is that, when relatively more resources are at stake in the process of making babies, sexual selection should be stronger. Austin Hughes, a biologist at the University of South Carolina, recently set out to test for that pattern in waterfowl [$a].

Ducks and their relatives already look like a good fit for classic sexual selection. In many duck species mating is coercive, so females have evolved maze-like reproductive tracts to slow down unwelcome penises—and males have, in turn, evolved corkscrewing penises to navigate those mazes. And in many species, the sexes have strikingly different coloration—generally thought to mean that males are vying for female attention with brightly colored plumage, while females are more concerned with staying hidden while sitting on a nest.

However, there are also plenty of waterfowl species where males and females are almost indistinguishable—think of swans or geese, especially. If sexual plumage differences are related to the strength of sexual selection, maybe that reflects differences in the sexual “stakes” at play in each species. Hughes tested this hypothesis by comparing closely related pairs of waterfowl species or subspecies.

As an index of the reproductive effort made by females of each species, he used the mass of the average clutch of eggs laid, as a fraction of the mass of the average female. He then tested whether the species in each pair whose females made the larger “investment” in reproducing was also the species in the pair with more pronounced sexual differences in plumage coloration. And this was, indeed, what he found.

So that looks like a neat confirmation for one predicted effect of sexual selection. A worthwhile follow-up might be to add male parental care—which may be, admittedly, harder to measure—into the mix. If males help feed and protect the brood (which is often the case for waterfowl), that should offset the cost of reproduction from a female’s perspective, which might also reduce the strength of sexual selection.◼

Reference

Hughes, A. (2012). Female reproductive effort and sexual selection on males of waterfowl. Evolutionary Biology DOI: 10.1007/s11692-012-9188-1

Nothing in Biology Makes Sense: Sexual selection and the lek paradox

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A peacock, which made Darwin “sick.” Photo by aussiegal.

This week at the collaborative blog Nothing in Biology Makes Sense!, guest contributor Tom Houslay makes sense of costly mating displays:

Time and again in the animal kingdom, we see exaggerated ornaments, vibrant colours, and fantastic acoustic and visual displays. Frogs and crickets advertise their whereabouts with loud calls, fireflies flash patterns with bioluminescence; greater sage grouse strut brazenly in open pastures. While they undoubtedly brighten up the world around us, these behaviours and morphologies can seem not only unnecessary, but downright detrimental to the survival of an individual. How, then, can their existence be resolved with our knowledge of evolution?

To find out how a single showy trait can come to “capture” all the genetic variation in a population, read the whole thing. On an almost totally unrelated note: if I ever open a gay bar, it will definitely be called Lek. ◼

For wasps’ pheromones, quantity predicts quality

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ResearchBlogging.orgDon’t tell the people behind Axe body spray, but entomologists have shown that the fertility of male Nasonia vitripennis wasps is predicted by how much sex pheromone they produce [$-a].

How many sperm a male wasp can produce turns out to be a big deal for female Nasonia wasps, because the species is haplodiploid — fertilized eggs become females, and unfertilized eggs become males. Because females are the only sex that can fly off to lay more eggs, the number of female offspring a wasp produces strongly determines her reproductive fitness. She wants, therefore, to mate with a male who can fertilize a lot of eggs, and determines who that is by smelling prospective mates.

Reference

Ruther, J., Matschke, M., Garbe, L., & Steiner, S. (2009). Quantity matters: male sex pheromone signals mate quality in the parasitic wasp Nasonia vitripennis. Proc. R. Soc. B DOI: 10.1098/rspb.2009.0738