The evolution of reproductive and genomic diversity in ray-finned fishes
Mank, Judith Elizabeth
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Using comparative phylogenetic methods, I examined several current hypotheses and patterns in the evolution of reproductive and genomic diversity on a supertree for the ray-finned (Actinopterygii) fishes. The topics examined include the evolution of parental care and the implication of viviparity, the evolution of male mating strategies, the evolution of sex determining mechanisms and the relationship between sex chromosomes and male ornaments, evolutionary genomics and the role of genome dynamics in cladogenesis, and the role of sexual selection in increasing taxonomic diversity. Regarding reproductive diversity, the Actinopterygii show remarkable convergence in all traits examined (parental care, internal gestation, male alternative reproductive strategies, and sex determining mechanisms). Similar parental care and male reproductive behaviors in diverse species may be caused by convergent selection on the same suite of gonadotropic hormones. Sexual selection is a major force in the evolution of both parental care and male mating strategies, though sexual selection is not correlated with sex determining mechanisms, it generally acts to increase taxonomic diversity. Internal gestation, though a complex adaptions, has originated multiple independent times throughout the Actinopterygii, and there is no evidence that, once evolved, it has ever been lost from a lineage. This may be because the evolution of viviparity is correlated with cladogenetic expansions. Genomically, actinopterygiian fishes exhibit highly dynamic genomes, possibly due to transposon activity, changes in insertion to deletion ratios, cytogenetic rearrangement, origin and dissolution of sex chromosomes, and gene and genome duplication. This dynamicism may be a factor in the radiation of the teleosts, either by fostering adaptive radiations or via reciprocal silencing. Unexpectedly, the genome dynamics of this clade do not seem to effect higher-level genomic scaffolding, as assessed by somatic chromosome counts. Chromosome complements in the ray-finned fishes are quite stable over vast stretches of evolutionary time.