Abstract
Gene exchange between species occurs in areas of secondary contact, where two species have the opportunity to hybridize. If heterospecific males are more common than conspecific males, females will experience more encounters with males of other species. These encounters might increase the likelihood of heterospecific matings, and lead to the production of hybrid progeny. I studied the mating behavior of two pairs of sibling species endemic to Africa: Drosophila yakuba/Drosophila santomea and Drosophila simulans/Drosophila sechellia. Drosophila yakuba and D. simulans are cosmopolitan species widely distributed in the African continent, while D. santomea and D. sechellia are island endemics. These pairs of species hybridize in nature and have the potential to exchange genes in natural conditions. I used these two pairs of Drosophila species, and constructed mating communities of different size and different heterospecific:conspecific composition. I found that both the total number of potential mates and the relative frequency of conspecific versus heterospecific males affect female mating decisions in the cosmopolitan species but not in the island endemics. These results suggest that the population characteristics, in which mating occurs, may affect the magnitude of premating isolation. Community composition might thus facilitate, or impair, gene flow between species.
Highlights
When different animal species come together in the same geographical location and share at least part of their habitat, biological traits associated with mate choice can prevent interbreeding (Coyne and Orr 2004; Price 2007)
No heterospecific matings were observed with D. sechellia for either 1-h or 24-h trials. These results indicate that, as was the case for D. santomea, the mating behavior of D. sechellia females is not affected by the presence of heterospecific males regardless of the ratio of heterospecific to conspecific males and the mating population size
This study explores how relative frequency and population size, individually and interacting, influence mating behavior in at least two species of Drosophila
Summary
When different animal species come together in the same geographical location and share at least part of their habitat, biological traits associated with mate choice can prevent interbreeding (Coyne and Orr 2004; Price 2007). Premating behavioral isolation occurs when one or both partners discriminate against the other, precluding mating and gene flow (Kaneshiro 1980; Safran et al 2013). Because of their greater investments of resources during and after mating, females usually are the ones that exert the choice and discriminate against heterospecific males. One potential outcome is that the production of unfit hybrids might impose selection to make premating isolation stronger. In this process, termed reinforcement, the enhancement of premating isolation occurs as a byproduct of selection against maladaptive hybridization (reviewed in Servedio and Noor 2003). In rare instances, the production of hybrids can lead to the origin of a new lineage that shows reproductive isolation toward the parentals and constitutes a new hybrid species (Arnold and references therein, Schumer et al 2014)
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