Gene flow, kinship, and source population assignment in Chrysomya blow flies

Blow flies of the genus Chrysomya are among the earliest colonizers of human remains and are important forensic indicators in Africa and the Middle East. However, the population genetic structure of Old World Chrysomya species in North Africa remains poorly understood. We conducted the first amplified fragment length polymorphism (AFLP)-based population genetic analysis of Chrysomya albiceps and Chrysomya marginalis in Egypt to assess geographic and temporal structure and to evaluate their forensic utility for population assignment. Adult flies were collected from multiple localities in Egypt and across consecutive years, and AFLP profiles were generated using four primer combinations. All individuals yielded unique multilocus genotypes. In C. albiceps, most genetic variation occurred within populations (93%), with only weak but significant among-population differentiation (Fst = 0.045), no isolation by distance, and no geographically coherent clustering, indicating near-panmixia at the regional scale. In C. marginalis, spatial differentiation was negligible, whereas temporal comparison of samples from Giza revealed modest year-to-year structuring. Within-sample relatedness was consistently positive in both species, suggesting nonrandom kin associations within collection events. Although simulation-based assignment success was high, empirical reallocation performance was substantially lower, indicating that assignment accuracy depends strongly on the level of genetic differentiation and may not yet be robust for routine forensic inference. This apparent paradox reflects fine-scale structuring driven by kin aggregation within sampling events, despite overall high gene flow at the regional scale.