Altitudinal variation in body size and resistance to stress in Drosophila melanogaster and D. simulans (Diptera: Drosophilidae) in southern Turkey

Tolerance of cold and heat and body size are traits that are important in thermal selection. Latitudinal and altitudinal transects include environments that gradually change in temperature. However, while there are studies on the effects on body size and cold tolerance in natural populations sampled mostly along latitudinal transects, there are few such studies along altitudinal transects. Resistance to starvation and desiccation, which are also thought to be affected by temperature, are the focus of studies on clines. In this study, we measured the variation in tolerance of cold (chill coma recovery time), body size, resistance to starvation and desiccation in isofemale lines of Drosophila melanogaster and D. simulans that originated from four locations (50 m – 1500 m) along an altitudinal transect in the southern part of Turkey. This revealed clines in the tolerance of cold and body size along the altitudinal transect with some degree of difference between these two species, whereas there were no clines in resistance to starvation and desiccation. This study revealed some differences and similarities between the sibling species D. melanogaster and D. simulans. * Corresponding author; e-mail: ergideniz.ozsoy@hacettepe.edu.tr INTRODUCTION Distribution of species and their phenotypic variation in many quantitative traits are shaped by different environmental factors (temperature, air pressure, humidity etc.). Spatially or temporally changing environmental conditions act as selective agents driving the evolution of traits. Organisms cope with these varying selective pressures by local adaptation to different environmental conditions, which eventually generates clines in traits (Endler, 1977). Temperature is one of the most important environmental factors affecting various traits, especially in ectotherms (Cossins & Bowler, 1987) and thus thermal limits are reported for many species (Stillman & Somero, 2000; Duarte et al., 2012; van Heerwaarden et al., 2012). The reproducibility of the latitudinal clines for many traits, including body size (Calboli et al., 2003) and cold tolerance, suggests that natural selection is more important than demographic or other stochastic processes. Similarly, the environmental variation along altitudinal transects is very similar to that along latitudinal transects. However, latitudinal and altitudinal transects show a remarkable difference in terms of geographic scales; the difference between the lowest and highest latitude can cover thousands of kilometres, whereas it can be only a few kilometres in Eur. J. Entomol. 119: 140–147, 2022 doi: 10.14411/eje.2022.015