Sexual conflict and sympatric speciation in the Pacific
A project undertaken at the School of Biological, Earth and Environmental Sciences, University of New South Wales, and supervised by Dr Nikolai Tatarnic
Conflict between males and females over mating is thought to fuel intense evolutionary arms races between the sexes, through a process known as sexually antagonistic coevolution (SAC) (Rice 1996; ). SAC is thought to drive rapid evolutionary change in morphology and behaviour (Chapman et al. 2003), and has even been invoked as a vehicle for speciation (Gavriletts 2000; Chapman et al. 2003; Arnqvist and Rowe 2005).
In the plant bug genus Coridromius, mating takes place by traumatic insemination (TI): males bypass the female genital tract, instead stabbing their partners with hypodermic genitalia and ejaculating into their blood (Tatarnic et al. 2006). In response, females of many TI species have evolved elaborate paragenitalia at the site of copulation to reduce the costs of mating. TI was first discovered in bedbugs (Carayon 1966) and is thought to have arisen either as a means for males to circumvent female mating resistance or as a product of male-male competition (Arnqvist and Rowe 2005; Reinhardt and Siva-Jothy 2007). TI is an incontrovertible example of a conflict trait, as males obligatorily damage females to promote their own reproductive success, and females coevolve paragenitalia to reduce these costs.
In our recent revision of Coridromius (Tatarnic and Cassis 2008) we identified several unique and elaborate paragenital forms and increased the number of described species from 11 to 33, with many of these found throughout the South Pacific. Several localities, such as New Guinea and Borneo, have been identified as areas of endemism for the genus, harbouring several species with overlapping distributions. These findings made us question why so many species are sympatric, and how this might reflect underlying mechanisms of evolution.
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