Colson, Isabelle Brigitte; (2001) The genetic bases of adaptation and reproductive isolation in the Drosophila melanogaster species complex. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The genetic bases of adaptation and speciation, and the interactions between adaptation and speciation in natural systems are still poorly understood. Here, we investigated the genetic bases of intra- and interspecific adaptation in the Drosophila melanogaster species complex. The species pair D. simulans/D. sechellia was used as a model to study the genetic interactions between loci responsible for D. sechellia's adaptation to a toxic resource and loci involved in reproductive isolation between the two species. We developed microsatellite markers for interspecific mapping of D. simulans and D. sechellia. In the course of characterising the molecular markers, we investigated the sequence structure of microsatellite alleles in order to gain insights about the mechanisms of microsatellite mutation and evolution. We used our microsatellite markers to evaluate the effect of strong local selection on genetic differentiation in populations of D. simulans and D. melanogaster. We investigated the possibility of indirectly studying the adaptation of D. sechellia to a toxic resource by the development of an experimental protocol to select D. simulans populations for resistance to octanoic acid. The response to selection was weak compared to the interspecific differences observed, possibly because mutations of large effect only occurred in the lineage leading to D. sechellia. The mapping of hybrid sterility factors in the D. simulans/D. sechellia species pair supports the dominance and faster male evolution theories. Male sterility factors were mapped at similar locations to reported factors responsible for D. sechellia's resistance to octanoic acid. The implications of this linkage for the understanding of speciation process in the D. simulans/D. sechellia system are discussed.

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