Evolutionary response to artificial selection and heritability of ectoparasite resistance in a natural host-parasite association

Abstract

By Harmanpreet Singh, Biological sciences; Joy Bose, University of Cincinnati; Joshua Benoit, University of Cincinnati

Advisor: Michal Polak

Abstract: Ectoparasites are abundant in nature, can exert pronounced deleterious fitness consequences on their hosts, and are important vectors of transmissible diseases. Whereas there is ample information available concerning the mechanisms that animal hosts use to defend themselves against ectoparasitism, there exists only a limited number of studies on the presence and magnitude of heritable genetic variation for ectoparasite resistance. More broadly, even though the evidence indicates that genetic variation for parasite resistance may often be present in natural populations, the extent to which this variation is attributable to heritable genetic differences among host individuals remains unknown. This dearth of information limits our ability to predict evolutionary response to selection pressure imposed by parasites. Here, we test for the presence of additive genetic variation underlying resistance against ectoparasitic mites, Gamasodes queenslandicus, and report replicate estimates of realized heritability for this trait. Artificial selection was applied for 20 generations for increasing behavioral resistance to mites in replicate lines of Drosophila melanogaster, each derived from a common field population. Response after 20 generations consistently but gradually continued to increase up to 34 generations of selection. All replicates responded significantly and similarly to selection, demonstrating the existence of heritable genetic variation for ectoparasite resistance in the original field population. Heritability of resistance was estimated to be approximately 10%. Selection was applied on males only, but females responded to selection similarly to males, suggesting autosomal inheritance for resistance. This study establishes interesting parallels between insects and other animals in their ability to protect themselves.