Genetic structure is determined by stochastic factors in a natural population of Drosophila buzzatii in Argentina

Abstract

D. buzzatii is a cactophilic species associated with several cactaceae in Argentina. This particular ecological niche implies that this species is faced with a non-uniform environment constituted by discrete and ephemeral breeding sites, which are colonized by a finite number of inseminated females. The genetic consequences of this population structure upon the second chromosome polymorphism were investigated by means of F-statistics in a natural endemic population of Argentina. The present study suggests that differentiation of inversion frequencies in third instar larvae among breeding sites has taken place mainly at random and selection is not operating to determine the structure of this population. The average number of parents breeding on a single pad seems to be similar to the number colonizing Opuntia ficus indica rotting cladodes in Carboneras, a derived population from Spain. There is no significant excess of heterokaryotypes within pads or in the population as a whole. The results obtained in the present study suggest that the potential role of selective versus stochastic factors relative to the among pad heterogeneity in the population here studied is different from that of the Spanish population previously reported. Potential mechanisms responsible for these differences are discussed.