Genetic basis of wing size differences between two Drosophila cactophilic sibling species

VALERIA CARREIRA,; SOTO, IGNACIO; EDUARDO SOTO,; JOSÉ FANARA, JUAN; ESTEBAN HASSON,

Florianopolis, Brasil

Congreso; 50° Congresso Brasileiro de Genética; 2004

Sociedad Brasilera de Genética

Drosophila buzzatii (Db) and D. koepferae (Dk) are two sibling species which breed and feed on the decaying tissues of several cactus species. Although sympatric in arid regions of southern South America, Db is mainly associated with tunas (species of the genus Opuntia), while Dk breeds primarily on columnar cacti of the genera Cereus and Trichocereus.Necrotic tunas are abundant but decay faster than cardons, which are spatially scarce but their greater biomass provides resources for the growing larvae for longer periods of time than tunas. On average, Db has a smaller body size and developes faster than Dk when raised in the same substrate. Therefore, the coexistence of these species in nature could be explained by different adaptive strategies related to the characteristics of their host cacti. In order to asses the causes of phenotypic differences between species, we analyzed the genetic basis and phenotypic plasticity of wing size variation in flies derived from a locality, where both species coexist. Flies of fifteen isofemale linesof each species wereraised intwo types of cacti,Opuntia sulphurea (Os) and Trichocereus terscheki(Tt). We measured proximal wing length (WLp), distal wing length(WLd) and wing width (WW) of both wings in both sexes of both species. The general analysis revealed that: 1) Dk was larger than Db, 2) females were larger than males and the sexual dimorphism was more evident in Db and 3) flies reared in Os were larger than those emerging in Tt vials. The sex-specific ANOVAs showed: that both sexes present phenotypic plasticity for all the traits studied, the existence of substantial genetic variation for almost all traits, and a significant line by cactus interaction (GxE) in most cases. The present results suggest thatenvironmental heterogeneity (i.e. different cactus hosts) can explain, at least in part, the maintenance of genetic variation in these species.