The ecological and evolutionary implications of hybridization
Rosenthal, David M
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Natural hybridization occurs in many organismal groups. Indeed, recent molecular studies confirm that hybridization occurs in numerous plant lineages. However, well-documented cases are rare enough that the ecological and evolutionary implications of natural hybridization are poorly understood. These questions were addressed by studying several well-characterized species of natural hybrid sunflowers in their native desert habitats and in the greenhouse. To better understand the ecological implications we studied habitat differences of two sunflowers of hybrid origin and then determined if ecological differences were associated with specific trait differences. Field surveys of environmental parameters demonstrated that the habitats of the two focal species differed significantly in plant water availability and nutrient content. A combination of field surveys, field experiments and greenhouse studies on natural hybrid plants demonstrated that species differences in drought tolerance mirrored habitat differences in water availability. These findings strongly suggest that these species are adapted to their respective habitats. The evolutionary implications of hybridization were explored by asking whether or not hybridization could produce individuals with phenotypes suitable to colonize and subsist in a hybrid species habitat. Synthetic hybrids between the ancestral parents of the hybrid sunflower species were generated and served as the putative ancestors of the hybrid species. Multivariate analyses of parental, natural hybrid and synthetic hybrid phenotypic data, indicated that certain synthetic hybrids had hybrid species-like phenotypes. This work demonstrates that hybridization can produce individuals with the appropriate multivariate phenotypes in as little as 3 generations. While these results show that natural hybridization can yield individuals with phenotypes approaching that of the hybrid species, selection undoubtedly plays a critical role in fine-tuning hybrid species phenotypes to subsist in the hybrid species habitats.
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