Determination of genetic elements determining the effect of larval density on viability in Drosophila melanogaster by genome wide association study

Population density is one of the key factors affecting the fitness of organisms in that population. Many traits, such as viability, lifespan, body size, starvation resistance, and body fat content, vary across different population densities. Competition, environmental dependence, and cooperation factors that lead to natural selection play a major role in explaining the variation in the life history traits of organisms at different population densities. Previous studies have examined how the viability of organisms can vary at low, medium, and high population densities, as well as the variations in other traits that influence an organism's adaptive success across different population densities. However, the genetic components underlying how viability is affected by different population densities remain unknown. In light of this information, the thesis study revealed how differences in population density affect the viability of organisms and which genetic elements are responsible for this effect. In this context, Drosophila melanogaster strainsiv from the Drosophila Genetic Reference Panel (DGRP) were used as model organisms, and genome-wide association analysis (GWAS) was used as the method. In the experiments, the first larval stage (L1) forms of the offspring generated by laying eggs under specific conditions were used, following the maintenance of DGRP strains under optimal laboratory conditions (25°C, ~65% relative humidity). The development processes of L1 larvae into adult flies were examined over a 16-day period after they were transferred to standard culture medium at different densities. Based on the number of larvae that completed their development into adult flies, six different GWAS were conducted to assess viability differences between low, medium, and high densities, as well as between low–medium, low–high, and medium–high densities. As a result of the GWAS, 289 candidate genetic variants potentially associated with viability were identified. These 289 genetic variants correspond to 151 genes in the Drosophila genome. The identified genes have a wide range of functions, from development to nervous system function, behavioral biology to cellular and metabolic pathways. The human orthologs of these genes and the diseases they are associated with are also reported. Essentially, this study is the first comprehensive study to identify candidate genes that play a role in the genetic background of the effect of larval density on viability, which is of evolutionary and ecological importance and has significant implications for population biology in many species. The identified candidate genes will be validated in further studies and then linked to viability, thereby contributing to the literature. This will enable the evaluation of these genes in terms of adult life history traits and their potential to induce changes in population structure.