Summer Temperature and Photoperiod Induce Physiological, Life History, and Gene Expression Changes in Drosophila Mojavensis

Abstract

Seasonal environmental changes act as a selective force. Across insects, there are many adaptations to unfavorable seasons. Aestivation is one such adaptation that allows insects to survive hot and dry periods experienced in summer seasons. Drosophila mojavensis is a cactophilic Drosophila species that inhabits the Sonoran Desert. Much work has been done on understanding their ecology, and their taxonomic closeness to the model system Drosophila melanogaster allows us to easily use established molecular tools. In this study, a laboratory-generated population of D. mojavensis was established and raised for four generations in conditions mimicking the field conditions of spring and summer in its natural habitat. Currently, it is unknown what physiological, behavioral and/or metabolic mechanisms allow D. mojavensis to over-summer in this hot desert environment. Collecting individuals in this region during the summer months is rare. Generating a lab raised population allowed me to manipulate temperature and photoperiod and observe changes over multiple generations in a controlled setting. Physiological changes over the generations approaching summer showed increases in heat and desiccation resistance, and overall lower activity levels. Drosophila mojavensis continued to lay eggs during the summer generations, but died much earlier than individuals from spring generations. mRNA expression data revealed sets of genes that were overrepresented in categories such as chaperones, heat response, metabolic processes, and protein synthesis/degradation. Genes that control high energy costing processes were highlighted in this study. This is the first study that systematically attempted to investigate the physiological, life history, behavioral and molecular basis of summer survival in D. mojavensis, and although the mechanism of survival appears complex, it has provided a better understanding of seasonal responses, such as continued egg production and lowered longevity, in this Sonoran Desert endemic species.