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The Importance of Parallelism for Evolutionary Theory



The genetic and molecular basis for parallel evolution

Department of Biology, Duke University, Durham, North Carolina, USA

(abstract pending)

Parallel selection and the genetics of adaptation in sticklebacks

Department of Zoology, University of British Columbia, Vancouver, British Columbia, CANADA

Growing knowledge of the molecular basis of adaptation in wild populations is expanding the study of natural selection. I summarize ongoing efforts to infer three aspects of natural selection - mechanism, form, and history - from the genetics of parallel adaptive evolution in threespine stickleback that colonized fresh water after the last ice age. We tested a mechanism of selection for reduced bony armour in fresh water by tracking genotype and allele frequency changes at an underlying major locus (Ectodysplasin) in transplanted stickleback populations. We inferred disruptive selection on genotypes at the same locus in a population polymorphic for bony armour. Finally, we compared the distribution of phenotypic effect sizes of genes underlying changes in body shape to that predicted by models of adaptive peak shifts following colonization of fresh water. Studies of the effects of parallel selection on genes complement efforts to identify the molecular basis of adaptive differences, and improve our understanding of phenotypic evolution.


The inside story on parallelism illustrated by the multiple origins of cartilage

Department of Biology, Dalhousie University, Halifax, Nova Scotia, CANADA

After a brief overview of the concept and term ?parallelism? and its relation to convergence and homoplasy I will turn to an examination of the evolution of a single tissue, cartilage. Although regarded as a vertebrate tissue and synapomorphy, tissues that share many of the features of vertebrate cartilage are found in numerous lineages of invertebrates. Indeed, these tissues may share more features with vertebrate cartilage than the latter shares with cephalochordate (amphioxus) cartilage. Vertebrate cartilage also shares many features with notochord, which is a synapomorphy of chordates. I will discuss the features of these various tissues in the context of parallel evolution between major animal groups and address the issue of whether cartilage had one or multiple evolutionary origins. I will then turn to parallel evolution of cartilage(s) within individual vertebrate taxa, thereby extending the concept of parallelism to the evolution of a homologous tissue from developmentally and evolutionarily independent cell lineages. Examples will include mesodermal and neural crest-derived cartilage, axial and appendicular cartilages, and endoskeletal vs. extraskeletal (sesamoid) cartilages, all of which share the features of cartilage but evolved in parallel.

Supported by NSERC of Canada (Grant A5056)


Parallel evolution of derived modes of reproduction in amphibians

Department of Integrative Biology, University of California, Berkeley, California, USA

Diverse modes of live-bearing reproduction have arisen in amphibians, many using sites of development nearly unique to the class and order (e.g., frogs developing embryos in the vocal sacs of the paternal male, and in the stomach and in and on the skin of the backs of maternal females). Intra-oviductal maintenance of developing embryos through metamorphosis, with maternal nutrition supplied after yolk resorption, has evolved independently in all three orders several times. In addition, maintenance without additional nutrients and with 'birth' at virtually any stage of relatively late development occurs in frogs and in salamanders. Maintenance of developing young in the skin of the back of the maternal female occurs in two rather distantly related lineages of frogs. Adelophagy has arisen, recently, twice in closely related salamander subspecies. Given robust hypotheses of phylogenetic relationships, many kinds of homoplasious conditions have been identified, but few have been assessed in terms of mechanisms of origin, and common and divergent features in those mechanisms. I explore the parallel evolution of the morphology of intra-oviductal and back-skin viviparity in both parents and embryos/fetuses in order to generate hypotheses about physiology, behavior, development, ecology, and patterns of evolution of the systems within and across lineages.


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