The goal of this project is to identify the genes underpinning dormancy on a population scale in wild Drosophila populations. A genome-wide scan for dormancy has not been reported. Our goal will be accomplished by using Pool-GWAS, a genotype-phenotype mapping in which extreme individuals across a phenotypic gradient are grouped and sequenced as pools. However, the success of such a protocol depends on the right phenotyping of the trait of interest. Thus, the first step in achieving our goal is familiarizing with dormancy, identifying extreme dormancy phenotypes and developing strategies for efficient screening of the trait.
According to the literature, dormancy in D. melanogaster is phenotyped by dissection of ovaries from virgin female flies, that eclosed under normal conditions (LD 12:12, 25oC) and were transferred and maintained for several days (usually 28 days) under dormancy-inducing conditions (usually LD 10:14, 10 – 12oC). The egg chambers are then classified according to criteria established by King (1970). Most studies classify flies with exclusively previtellogenic egg chambers (stages ≤ 7) as dormant, while non-dormant flies have vitellogenic egg chambers or mature eggs (stages 8 – 14, where stage 14 represents the mature egg).
Our experiments included isofemale lines from recently collected population from Vienna and South Africa, and several inbred lines from around the world. The two extreme dormancy phenotypes observed in our assays deviate from published data. We also identified a strong effect of larval density on dormancy, suggesting that larval density should be controlled during dormancy screening. We screened Sub-Saharan Africa isofemale lines too, in order to examine the ancestral state of the trait. These lines seem to be dormant, challenging the adaptive nature of the trait, as it is described above.