From Science Daily:
Researchers at Michigan State University, with the help of some stickleback fish, have shown that intense competition among males most definitely has a big say in creating new species. The results, featured in the January issue of Ecology Letters, also show that such competition can reverse the process, actually erasing boundaries between species.
“Our paper is of special interest because this is the first time that researchers have shown that intense competition between males for the chance to mate with females can have this kind of influence on splitting populations in two or fusing them together,” said Janette Boughman, MSU integrative biologist and the paper’s senior author.More.
Good heavens, not the threespine sticklebacks again? Two stories blew through here last week about them. In one case, two ”species“ hybridized, which was classed as two extinctions. And in the other, a probable hybrid colony appears to be splitting, “into two separate species before our eyes, and at rapid speeds.”
This study argues for sexual selection as a driver for speciation:
“We show that sexual selection causes speciation in an unexpected way,” she said. “It’s happening by male-directed competition — fighting with each other and essentially deciding which males are able to enter the mating pool. Our results show that male competition is a key driver of speciation — by a factor that is five times greater than results on which other, more-traditional theories of natural selection causing speciation are based.”
These effects do not depend on natural selection, either. In these observations, literally thousands of hours of watching stickleback fish guarding nests and mating, there weren’t any changes in food sources, environment or predation — factors involved in natural selection.
This is unusual because stickleback fish have long been held as the poster children for natural selection, Boughman added.
Well that’s valuable to know but come back in a decade or so and the sticklebacks might be back together again. All the more so if male behavior, not key environment changes, is driving the trend.
(Apparently, they are swift in reverse gear too.)
These fish are interesting to study but it’s not clear that they are separate species in any meaningful sense.
See also: New study: Contra Darwin, females don’t choose mates. If this finding is often replicated, it is a serious blow not only to the Darwinian theory of sexual selection, but to the pop mag evolutionary psychology theories of human behaviour based on that.
Can sex explain evolution?
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Here’s the abstract:
Speciation is facilitated when selection generates a rugged fitness landscape such that populations occupy different peaks separated by valleys. Competition for food resources is a strong ecological force that can generate such divergent selection. However, it is unclear whether intrasexual competition over resources that provide mating opportunities can generate rugged fitness landscapes that foster speciation. Here we use highly variable male F2 hybrids of benthic and limnetic threespine sticklebacks, Gasterosteus aculeatus Linnaeus, 1758, to quantify the male competition fitness landscape. We find that disruptive sexual selection generates two fitness peaks corresponding closely to the male phenotypes of the two parental species, favouring divergence. Most surprisingly, an additional region of high fitness favours novel hybrid phenotypes that correspond to those observed in a recent case of reverse speciation after anthropogenic disturbance. Our results reveal that sexual selection through male competition plays an integral role in both forward and reverse speciation. (Public access) – Jason Keagy, Liliana Lettieri, Janette W. Boughman. Male competition fitness landscapes predict both forward and reverse speciation. Ecology Letters, 2016; 19 (1): 71 DOI: 10.1111/ele.12544