UBC Theses and Dissertations
The genetics of adaptation and speciation in threespine stickleback species pairs (Gasterosteus aculeatus species complex) Conte, Gina Louise
Ecological speciation appears to be a common process by which new species arise and the genetics underlying the process can substantially affect its outcome. Replicate ‘benthic and limnetic’ pairs of threespine stickleback species are an ideal system with which to study the genetics underlying ecological speciation. My first question was: what genetic mechanisms link divergent natural selection to reproductive isolation during ecological speciation? In chapter 2, I present an experiment designed to determine what genetic mechanism links divergent selection on body size to assortative mating by body size in the Paxton Lake species pair. I found that body size functions as a mate signal trait and determines female mate preference via phenotype matching. This implies that genes under divergent selection are the same as those underlying both components of assortative mating, a mechanism that should facilitate ecological speciation with gene flow. My second question was: what is the genetic architecture of adaptation during ecological speciation? In chapter 4, I used QTL mapping to discover the genetic architecture underlying a large number of parallel morphological differences in the Paxton and Priest Lake species pairs and found it to be polygenic and widespread throughout the genome in both. This suggests that many loci underlying ecologically important traits have diverged (and/or divergence has persisted) during ecological speciation despite homogenizing gene flow. My third question was: how predictable are the genetics of adaptation during ecological speciation and in general? Chapters 3 and 4 describe the first studies to quantitatively address this question. In chapter 4, I found that about 50% of QTL for parallel morphological differences are parallel in the two species pairs. Also, on average, the proportional similarity of QTL use underlying individual traits is about 0.4. In Chapter 3, I present the results of a meta-analysis of the genetics underlying repeated phenotypic evolution in natural populations. Using an impartial literature review, I found that the average probability of gene reuse was 0.32 - 0.55. I also found that the probability of gene reuse declined with increasing age of the taxa compared.
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