A group of researchers in the United States decided to do an experiment with water striders, in which they observed the mating success of prudent, "nice" males versus aggressive, "psychopathic" males. The latter group tried often to mate with the females very aggressively, and in previous experiments they had the most reproductive success. But these scientists discovered that the success of the psychopaths depended on very specific laboratory conditions

It turned out that other studies of sex among water striders had kept the population contained in a limited area, where females had access to very few males. When the researchers opened up the insects' habitat, allowing the females to roam freely, they discovered that the less aggressive males attracted the highest number of mates.

According to a release about the research, published yesterday afternoon in Science:

"The presence of psychopaths dramatically reduced the productivity of the population," [biologist David Sloan] Wilson said. "When all the males were gentlemen, the females laid about three times more eggs than they did when all the males were psychopaths. And yet within each group the psychopaths were doing better than the gentlemen. How do the gentlemen persist if they're disadvantaged within the group?"

Once the females could move between groups, the researchers had their answer. [Researcher Omar Tonsi] Eldakar and Michael J. Dlugos, then also a Binghamton graduate student, devised a wading pool equipped with special doors that could restrict movement between groups or allow the insects to move freely.

"When they opened the doors, the females would leave whenever a psychopath came around," Wilson said. "The whole thing resulted in a heterogeneity in which the females were clustered with the gentlemen. It's the movement of individuals that creates these differences between groups that favor nonaggressive males."

Who knows how much research into sexual selection has been flawed because researchers forgot the crucial ingredient of female freedom?

Ultimately, what's interesting about this study is that it shows why isolated populations might engage in a different mode of sexual selection than a free-ranging population that has a lot of contact with outside groups.

via Science

Published this week in Nature, the new study shows that even when a group of creatures is not separated by mountain ranges, and isn't forced to find a niche in the ecosystem via natural selection, new species will evolve over hundreds of generations. The researchers created a mathematical model of speciation, when one species evolves into many, which tracks emergence of species over 2,000 generations. The model was based on scientific observation of how new species have evolved all over the Earth.

Above, you can see the model, showing how species transform over time. Each color represents a species. What begins as a uniform single-color group slowly evolves into several distinct species. But this occurs via mutation and sexual selection, not from the creatures growing distant from each other geographically. And not from competing for different niches in the environment. In this model, there are no niches and no geographical boundaries.

So what's the big deal? In short, it means that new species can arise without competion for environmental resources. Sexual selection alone is enough to produce species diversity.

According to the New England Complex Systems Institute, which funded the study:

The study found that over generations the genetic distance between organisms in different regions increases, and groups of organisms spontaneously form groups that can no longer mate, causing a patchwork of species across the area. The number of species increases rapidly until it reaches a relatively steady state.

"One can think about the creation of species on the genetic level in the same way we think about the appearance of many patterns, including traffic jams," said [researcher] Yaneer Bar-Yam. "While the spatial environment may vary, specific physical barriers aren't necessary. Just as traffic jams can form from the flow of traffic itself without an accident, the formation of many species can occur as generations evolve across the organisms' spatial habitat."

The study authors are not claiming that enviroment is unimportant. They are simply saying that under some circumstances, it is not a necessary ingredient for evolutionary transformation.

Nevertheless, this study overturns the typical view of evolution. It turns out that we don't need adaptation to a hostile natural environment to evolve new forms of life. We can do it just by having offspring and mutating over time.

via Nature and New England Complex Systems Institute

A study published today in Science details a series of careful experiments Swedish researchers conducted on mating seed beetles (pictured). They want to find out what the benefits were to females who mated with multiple males, given that multiple matings could be dangerous to their health for a variety of reasons. The accepted wisdom is that females mate with many men because they can choose which sperm fertilize their eggs after mating. Basically, more men equals a bigger and better smorgasbord to choose from in the genetics department.

If this hypothesis were true, females would always choose sperm from the fittest males to fertilize their eggs. But they didn't. If you measure male fitness as the ability to produce a great number of offspring who themselves produce a great number of offspring, then the fittest males always lost. Inevitably, the females chose sperm from unfit males.

Why would these insects have sex with so many different men, only to choose the crappiest sperm? The researchers admit that they are baffled. Their experiment was only intended to determine whether females favored sperm from fit males – not to plumb the depths of the psychology behind female insect promiscuity.

However, what these Swedish researchers have done is eliminate one possible reason why female insects mate with multiple males. They're not doing it because of genetic benefits that come from the males. They are not picking sperm that have direct or indirect benefits on their offspring, as far as the researchers could tell. Though they do float the possibility that these females may be choosing sperm that are beneficial exclusively to female offspring. In other words, genes that make fathers fit may not make daughters who are fit.

According to researcher Göran Arnqvist:

The results support the suggestion that genes that are good for males may often be bad for their mates. Therefore, in beetles at least, multiple mating does not award females with genetic benefits.

So if multiple mating does not award females with genetic benefits, what exactly does it award them with? Is it possible that they're sleeping around just for fun?

via Science and Uppsala University

The new study, conducted by a team of researchers from the UK, France, and China, used genomic analysis to determine at whether married couples were more likely to be "MHC-dissimilar." The results showed that European couples were overwhelmingly MHC-dissimilar, while African couples were neither similar nor dissimilar (in other words, they were just as likely to be similar as dissimilar). The researchers concluded that in the European population, mate selection may be driven more by biology than in other populations.

Conclude the researchers in their paper:

At the molecular level, we found that the European American couples we studied are significantly more MHC-dissimilar than random pairs of individuals, and that this pattern of dissimilarity is extreme when compared to the rest of the genome, both globally and when broken into windows having the same length and recombination rate as the MHC . . . Such dissimilarity, observed from both molecular and serological data, cannot be explained by demographic processes, since such effects would affect the whole genome.

They're saying that the MHC-dissimilarity is not just caused by demographic factors like geographical location.

Even more interesting was that the offspring of the MHC-dissimilar couples "were not more MHC-diverse than expected by random selection." So the marry-by-smell method may not actually be creating more robust offspring. More research is needed to discover why Europeans are more likely to marry for biological reasons than other populations are.

Is Mate Choice in Humans MHC-Dependent? [via PLoS Genetics]

Among these hopping insects, it's not uncommon for the males to travel up to 90 meters per night searching for a mate, which would be the equivalent of a human man walking 7 kilometers per night in search of a lady friend. Size does matter among the weta — it's just that being lightweight allows the male to show off his walking prowess much better than a large body would. Female wetas tend to walk much less, and when they do find a little male they like, they spend the whole next day mating with him nonstop.

How do we know this, you ask? Apparently our group of researchers, who hail from Toronto, put microchips on male and female wetas and tracked them. Then, when these researchers found the mating wetas, they counted the empty sperm packets called "spermatophores" that were piled up around them. Then they could estimate whether weta who walked further got more chances with the old spermataphores. Know what I mean? Wink, wink, nudge, nudge?

Said researcher Clint Kelly:

Our findings are a rare example of sexual selection favoring a suite of traits that promote greater mobility in one sex only. This is exciting because it suggests that sexual selection for smaller, more mobile males could be responsible for some of the impressive sexual difference in body size in this species.

It also shows why sometimes a small man and a big woman make the very best pair. Weta portrait via New Zealand Department of Conservation.

Sexual Selection for Male Mobility [via American Naturalist]