The genetic basis of morphological change in convergent evolution of natural populations: identifying candidate genes behind convergent evolution in blind cavefish astyanax mexicanus

Abstract

Understanding the genetic basis of adaptive phenotypic variation is central to our understanding of the origins and maintenance of biological diversity. Repeated occurrence of the same phenotypes in closely or distantly related populations is a very powerful tool for testing the role of natural selection in maintenance of those phenotypes. Research into the molecular basis behind similar phenotypic change provides the best opportunity to unite long-standing ideas about the extent to which evolutionary change is constrained. Do similar phenotypes always diversify by the same genetic bases or does selection uses many alternative genomic routes to the same phenotypic ends? Do these changes mainly occur from already available variation in the genome or is adaptation dependent on the incoming mutation? In this dissertation we address these questions using different populations of Mexican blind cavefish (Astyanax mexicanus) as our model, and by taking an integrative approach using the tools of population genetics, quantitative genetics and genomics. This species is very unique, with 30 different cave populations derived from surface populations. There are numerous morphological differences between the cave adapted and closely related surface forms, including reduction in pigmentation and eye size, hypertrophy of nonoptic sensory organs, reduced metabolic rate, increased numbers of taste buds, changes in numbers of ribs as well as multiple behavioral changes. First we asked how many independent times did these morphological traits repeatedly evolved in the cave populations. We assessed genetic structure and differentiation within and among the populations using genetic data from 568 fishes from 10 cave and 11 surface localities, and 26 genetically unlinked microsatellite loci.(...)