Morphological divergence among populations of D. buzzatii: geographic isolation and chromosomal rearrangements correlate with genital morphology.

SOTO IM; CARREIRA, VP; HASSON, E

Ribeirao Preto, San Pablo, Brasil

Simposio; V Simpósio de Ecologia, Genética e Evolução de Drosophila; 2007

In the D. buzzatii cluster, the strong association of species with host plants leads to a patchy population structure with different degrees of isolation among demes. Though this effect varies from one species to another, in all cases local conditions, geography and isolation raise a new dimension to the change in morphology.  Selective processes as well as genetic drift interact with gene flow and lead to different degrees of divergence among demes. When populations occupy different habitats, divergent selective pressures might cause differentiation in ecologically relevant traits. Otherwise, gene flow acts as a homogenizing force for all traits slowing down interpopulation divergence. In this sense, recent, reports in several taxa and traits showed an inverse relationship between gene flow and morphological differentiation. We investigated the morphology of the aedeagus, a taxonomic valuable trait, in males of 12 natural populations of D. buzzatii from Argentina. We described genital morphology by means of Elliptic Fourier Descriptors and subsequent Principal Component analysis exploring patterns of variation and the relationship of shape with both geographic isolation and the polymorphic inversion arrangements of chromosome 2. Populations differed both in genital size and, more relevant, in the non-allometric portion of shape change. Phenetic similarities were highly correlated with the matrix of geographic distances. Nevertheless, we detected significant relationships between aedeagus shape and frequencies of the two most common gene arrangements, the derived j and st, the ancestral gene order. Since polymorphic inversions of chromosome 2 are known to affect general body size and other fitness-related traits, these results represent the first report in Drosophila relating inversions and genital morphology and reinforce the idea that evolution of the intromittent organ in the D. buzzatii cluster might be responding mainly to a pleiotropic model.