A new collaborative project among researchers from Uppsala University in Sweden and the University of Cincinnati has, for the first time, demonstrated experimentally the evolutionary force behind the rapid evolution of male genitals, focusing on a species of seed beetle.
This mechanism is revealed in a study published today in the scientific journal Current Biology. The experiments leading to this paper involved a species of seed beetle known as Callosobruchus maculatus. Mating among these beetles involves several males engaging in copulation with individual females.
"When a female mates with several males, the males compete over the fertilization of her eggs," said Michal Polak, associate professor of biological sciences at the University of Cincinnati, one of the co-authors. "Because females mate with multiple males, the function of the male copulatory organ may determine which of the males will fertilize most of her eggs. Our results show that the morphology of the male genitalia affects his fertilization success in these beetles."
The competition to produce offspring is the driving force of evolution. Competition among males occurring after insemination may be an important evolutionary force that has led to the evolution of a diversity of shapes and sizes of male sexual organs, the co-authors assert. This competition among males has generated a great biological diversity that they believe can directly contribute to the formation of new species.
"The reproductive organs of animals with internal fertilization change more rapidly than all other morphological features during evolution," Polak said. "In virtually all groups of animals, from roundworms and molluscs to reptiles and mammals, the male sex organs differ markedly among even closely related species, with female genital traits remaining relatively unchanged."
To experimentally investigate the role of genital shape in reproductive success, the
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University of Cincinnati