Sneaky Copulation

In terms of reproduction, size matters. In most species larger dominant males are preferred by the females, and perform better in male to male competition. And as a result they get to spread their ‘king-size’ genes around. But not always. Sometimes smaller is preferred as can be witnessed in the mating behaviour of several dwarfed animal species. Andrea Pilaster of the Sexual Selection Group at the University of Padova found that in terms of male dwarfism the mosquitofish are an interesting species because their reproduction is based on a little bit of both strategies. The larger dominant mosquitofish males are still preferred by the opposite sex, (taking into account that in mosquitofish the females are considerably larger than all males). At the same time the subordinate smaller males, in order to make sure their ’small-size’ genes get a chance at dissemination, sneak-copulate. They sneak in around the unfertilised eggs and release their sperm before the bigger male can respond. The behavioural data indicate that the advantages to small males are two-fold: 1. They have a greater chance to approach females from behind without being detected, and 2: They manoeuvre better when inserting the monopodium into the female’s gonoduct, which is not saying they’re better lovers but in terms of reproductive success at least they don’t miss out. The selective advantage of small size might explain male dwarfism in poeciliids. Similar strategies have been witnessed in flat lizardsburying beetles and long-tailed macaques.

Sneaky copulation is a strategy often used by aquatic organisms who portray sexual mimicry. In this rather obscure reproductive strategy small male fish will look and behave like the females of their species to gain access to female territory and copulate with them. They’re often successful. Perhaps in the grand scheme of life and making sure your genetic material gets spread around it doesn’t make a difference if you fight for it, or steal it. With a little imagination we can speak of a highly developed form of shrink activism. Mosquitofish are the Oscar Matzerath of the animal world.

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