Desiccation resistance and mating behaviour in laboratory populations of Drosophila simulans originating from the opposing slopes of Lower Nahal Oren (Israel)

Conserved ecophysiology despite disparate microclimatic conditions in a gecko

Microscale differences in the habitats organisms occupy can influence selection regimes and promote intraspecific variation of traits. Temperature-dependent traits can be locally adapted to climatic conditions or be highly conserved and insensitive to directional selection under all but the most extreme regimes, and thus be similar across populations. The opposing slopes of Nahal Oren canyon in the Carmel Mountains, Israel, are strikingly different: the south-facing slope receives intensive solar radiation, is hot and supports mostly annual vegetation, whereas the north-facing slope is ~10°C cooler, more humid, and supports Mediterranean woodland. We examined whether these differences manifest in the thermal physiology of a common gecko species Ptyodactylus guttatus in controlled laboratory conditions. We predicted that geckos from the hotter south-facing slope would prefer higher temperatures, have faster gut passage times, lower metabolic and evaporative water loss rates, and start diel activity earlier compared with north-facing slope conspecifics. Contrary to these predictions, there were no differences between any of the ecophysiological traits in geckos from the opposing slopes. Nevertheless, our data showed that individuals from the north-facing slope were generally more active in earlier hours of the afternoon compared with south-facing individuals. We suggest that P. guttatus individuals disperse between the slopes and either gene-flow or behavioral plasticity deter local adaptation, resulting in similar physiological traits. Perhaps a stronger contrast in climatic conditions and a stronger barrier are needed to result in interpopulation divergence in temperature-dependent traits.

Male pheromone polymorphism and reproductive isolation in populations of Drosophila simulans

The dominant cuticular hydrocarbons (HC) in Drosophila simulans are 7-tricosene (7-T) and 7-pentacosene (7-P). The 7-T is the major HC in East Africa and in other continents. In West Africa, D. simulans is very rare and displays 7-P as the major compound. We studied three D. simulans strains from Egypt (Eg), Sao-Tome (ST), and Cameroon (Cam), with 7-T, intermediary or 7-P phenotypes. HC profiles of ST and Cam female differed slightly from corresponding male profiles; females had more 7-T and less 7-P. Varying temperature affected all HCs (even those with 27 and 29 carbons)-not just 7-T and 7-P; there was no clear relationship between HC phenotype and resistance to desiccation. We report reproductive isolation between Eg and ST and Eg and Cam (but not between ST and Cam), which is due to Eg and Cam female preferences for their own males. In conclusion, our findings do support divergence of D. simulans populations from West Africa for both pheromonal profile and mating preference.