title: Physiological basis of starvation resistance in Drosophila leontia: analysis of sexual dimorphism.
abstract: Geographically varying starvation stress has often been considered as a natural selector that constrains between-population differences for starvation resistance (SR) in Drosophila species. On the Indian subcontinent, a dozen Drosophila species have shown clinal variations in SR across latitude, but the evolved physiological basis of such contrasting adaptations is largely unknown. In the present study, I untangled the physiological basis of sex-specific as well as between-population divergence for SR in D. leontia, collected across a latitudinal transect of the Indian subcontinent (11°45'-31°19'N). Secondly, I tested the assumptions that hardening to starvation stress facilitates an increased survival under subsequent lethal levels of starvation, and such plastic effects differ between the sexes. I observed several interesting results. In contrast to a steeper cline of starvation-related traits with latitude in females, a shallower gradient was observed for males. Females stored higher (~1.3-fold) dry-mass-specific levels of body lipids and glycogen contents, and utilized these both of these energy resources under starvation stress, whereas the starved males metabolized only body lipids as a source of energy. Conversely, the rate of body lipid utilization and threshold need were considerably higher in females as compared with males. Between-population differences were significant for storage levels of energy reserves only, but not for other avenues (rate of metabolite utilization and threshold need) of SR for both sexes. These findings indicate that multiple pathways shape the physiological basis of sexual dimorphism for SR in D. leontia. Further, single or multiple bouts of starvation hardening conferred an increased longevity (~4-9 h; P<0.001) under subsequent lethal levels of starvation stress for females only, and such plastic responses were consistent with a decrease in rate of metabolite utilization. Nevertheless, between-population effects were non-significant for absolute hardening capacity (AHC=KSR-C). Altogether, these findings suggest that similar evolutionary constraints have resulted in divergent genetic as well as plastic responses to evolve adaptations under starvation stress, and account for the observed sexual dimorphism for basal SR in D. leontia.
authors.affiliation: Institute of Evolution, University of Haifa, 31905 Haifa, Israel Department of Genetics, Maharshi Dayanand University, Rohtak 124001, India ddgenetics@gmail.com.
authors.forename: Dau Dayal
authors.initials: DD
authors.lastname: Aggarwal
mesh_terms: D000818:Animals; D004330:Drosophila / Q000378:metabolism / Q000502:physiology*; D004734:Energy Metabolism; D005260:Female; D005843:Geography; D006003:Glycogen / Q000378:metabolism; D007194:India; D008136:Longevity; D008297:Male; D010641:Phenotype; D012727:Sex Characteristics; D013217:Starvation / Q000378:metabolism*
chemical_list: D006003:Glycogen
keywords: D. leontia; Energy metabolites; Sexual dimorphism; Starvation hardening; Starvation resistance