Data from: The magnitude of behavioral isolation is affected by characteristics of the mating community

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/D. santomea and D.
simulans/D. 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 vs. 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.