Gene could answer age old question: does size really matter?

© iStock/Ivan-balvan

Scientists at Oxford Brookes University have discovered a gene that contributes to differences in the size of male genitalia between different species of flies.

From blue whales to door mice – the size and shape of male genitalia is strikingly diverse amongst animals. The Oxford Brookes researchers have identified a gene that contributes to differences in size of male genitalia between different species of fruit flies.

The findings were published in the journal Proceedings of the National Academy of Sciences (PNAS).

Lead researcher, Dr Daniela Santos Nunes said: “Identifying the genes underlying differences in morphology (the form and structure of organisms) between species, and in particular, differences in size and genital structures that are involved in mating and reproduction, is important for us to be able to understand how biodiversity is generated and maintained.”

Tartan gene

The article in the journal describes the quantitative mapping and functional work that led to the identification of tartan, as one of the genes responsible for the differences in size of the claspers between the species of fruit flies used in the study.

Dr Nunes said: “The claspers are secondary genital structures present in many species of flies. Drosophila mauritiana has much larger and hairier claspers than Drosophila simulans and at least in these species, these structures appear to be important for successful copulation. This is because they lead to the opening of the oviscapt (the copulatory structure in females), either through stimulation or mechanical force.”

The researchers were able to show that flies with the Drosophila mauritiana version of tartan, had larger claspers than flies with the Drosophila simulans version of tartan.

Professor Alistair McGregor, another senior author of the article, said: “Now we need to understand how this gene evolved to lead to the changes we see in the morphology of the claspers, without disrupting the development of these important structures. This will give us important insights into how evolution has modified development.”

Dr Nunes added: “We can also go back to the ultimate causes of male genital evolution. Now we can test if males that only differ in the size and bristle number of their claspers have different reproductive success. Are males with larger claspers more or less likely to mate? And do they have more or less progeny than males with smaller claspers?

“We can finally answer the age old question: does size really matter?”

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