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Here’s what you’ll learn when you read this story:
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Sexual selection, which can create diverse speciation as males develop attributes in competition with other males, can change the course of evolution.
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A 40-year-long experiment analyzed the sexual selection of seed beetles—one group was allowed to mate freely (strong sexual selection) while another had one male mated with one female only (weak sexual selection).
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Because of their short lifespans, scientists were able to observe 200 generations throughout this experiment, and noted that distinct changes were occurring between the populations.
Every single life form on Earth is the tireless work of evolution spread across billions of years. Of course, within our measly human lifespans, it’s extremely difficult to observe these genetic changes in real time—but not impossible.
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A new study (led by scientists at Uppsala University in Sweden and the University of Belgrade in Serbia) details an experiment spanning nearly four decades that analyzed the sexual selection of the seed beetle Acanthoscelides obtectus across 200 generations. Split into two groups—one in which males could mate freely and another in which competition for mating was restricted (i.e. one male per one female)—the researchers noticed vast changes between the two groups as they began to evolve in different directions. The results of the study were published in the journal Evolution Letters.
“Previous research has suggested that competition between males plays an important role in the formation of new species,” Göran Arnqvist, lead author of the paper from Uppsala, said in a press statement. “The populations that evolved under conditions of strong sexual selection ended up being far more different from each other—both genetically and in reproductive characteristics. We have also observed that they evolved in different directions more than twice as rapidly when sexual selection was strong.”
With more than 1,600 species spread across 70 genera, the seed beetle (or “bean weevil” as it’s also known) is an annoying pest that is regularly controlled with pesticides. However, for biologists, they’re invaluable tools for studying evolutionary pressures, thanks to their short lifespans and easy adaptability to laboratory conditions.
In this new study, scientists say they began to witness the first inklings of species divergence—the males with in the strong-sexual-selection (meaning many males mated with one female) population transmitted different mixes of peptides and proteins in semen than those in the other, weak-sexual-selection population. This copulation cocktail is how males attempt to outcompete other males. According to Arnqvist, changes were also seen in the receptors inside the females. These changes occurred even through there were no differences in the seed beetles’ surrounding ecosystems.
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“This protein cocktail, but also the beautiful feathers or plumage that males develop in certain animal species, are all characteristics that have to do with reproductive success and can lead to evolution taking off,” Arnqvist said in a press statement. “Two hundred generations are not enough, but when we’re talking about 20,000 or 200,000 generations—in that case the populations may become so different that they can no longer breed with each other.”
Although this study makes a strong case for sexual selection playing a major role in evolutionary change, the authors note that the role of natural selection in this perceived divergence can’t be excluded, and the link between reproductive proteins and sexual selection is inferred rather than demonstrated. They suggest that future studies could employ various methods for strengthening this tenuous-yet-compelling link between the strength of sexual selection and genetic evolution.
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