Host-related genetic differentiation of a polyxenic avian ectoparasite, Ornithomya avicularia (Hippoboscidae)

Ectoparasites play a key role in ecosystems, affecting the health, behaviour, and reproductive success of their hosts. The parasite-host relationships are complex and dynamic, and selective pressures exerted by the hosts can lead to local adaptations and changes in the genetic structure of the parasite population. Our aim was to investigate how parasitism on a diverse range of avian hosts with varying ecology and habitat preferences shapes the genetic variation of the parasite. For this purpose, we quantified the genetic structure and differentiation of host-related populations of a common polyxenic avian ectoparasite Ornithomya avicularia (Hippoboscidae, Ornithomyinae), a louse fly species parasitizing various bird species occupying diverse ecological niches. Using 20 polymorphic microsatellite markers, we genotyped louse flies collected from four phylogenetically (passerine and non-passerine) and ecologically (wetland vs. forest) divergent avian hosts caught during autumn migration. Despite the ecological and phylogenetic differences among hosts, the genetic differentiation among louse fly populations was modest, indicating ongoing gene flow. Bayesian clustering and discriminant analysis identified two genetic clusters with relatively weak barriers to gene flow, but this clustering reflected neither phylogenetic nor ecological differences between hosts. We suggest that the high dispersal abilities and the specific reproductive strategy of O. avicularia likely contribute to the genetic homogeneity of its populations across ecologically and phylogenetically distant hosts. This study provides novel insights into the population genetics of an understudied ectoparasite, with implications for understanding host-parasite interactions and disease transmission in avian systems.