Adapting to deserts: Searching for genes contributing to desiccation resistance in the cactophilic Drosophila mojavensis

The ability to adapt to water stress can be a major contributor influencing the distribution of insects. Understanding how desiccation resistance evolves at a genetic level can help more precisely predict the future distribution of insects as climate change continues at an unprecedented rate. Cactophilic Drosophila naturally living in the deserts of the southwestern United States and northern Mexico are a powerful system to identify genes that contribute to desiccation resistance. Here we examined three species of cactophilic Drosophila (D. mojavensis, D. arizonae, and D. navojoa) to identify genes involved with desiccation resistance. We first performed an assay to assess the variation across species and populations in desiccation resistance.  We observed that D. mojavensis had higher desiccation resistance than D. arizonae and D. navojoa. Within D. mojavensis the Mojave Desert (MOV) and Sonoran Desert (SON) populations had significantly higher desiccation resistance times than the Baja (BC) and Catalina Island (CI) populations. Using two populations of D. mojavensis from distinct environments (SON and CI) we assessed the transcriptome at three different time points, lethal time (LT) to death for the 15^th (LT15), 50^th (LT50), and 75^th (LT75) percentiles. In comparison to a no-food and humidity control (ie. starvation resistance), we observed a total of 1913 and 1798 upregulated genes and 1853 and 2076 downregulated genes in SON and CI populations respectively. The number of differentially expressed genes found within a previously identified the D. mojavensis desiccation quantitative trait locus region was 30 and 43 for SON and CI populations respectively.