A MOLECULAR PHYLOGENY FOR APLOCHEILOID FISHES (ATHERINOMORPHA, CYPRINODONTIFORMES) - THE ROLE OF VICARIANCE AND THE ORIGINS OF ANNUALISM

Annual aplocheiloid killifish embryos possess a rare ability among ver tebrates to enter stages of developmental arrest (diapause) when subje cted to adverse environmental conditions. Previous morphological analy ses have presented disparate hypotheses regarding the evolution of the intriguing life history associated with this phenomenon. We present a novel hypothesis of aplocheiloid relationships based on 1,099 bp of s equence data from three mitochondrial genes (cytochrome b, 12S rRNA, a nd 16S rRNA). Phylogenetic analysis using maximum parsimony, neighbor- joining, and maximum likelihood produce strongly congruent topologies. Our data confirm the monophyly of the Neotropical family Rivulidae, w hile demonstrating a paraphyletic Old World assemblage. The basal sist er group position of Indo-Malaysian and Madagascaran taxa relative to a monophyletic South American/African dichotomy strongly indicates the role of vicariance in the diversification of these fishes in spite of their definition as secondary freshwater fish. The distribution of an nualism onto this topology implies a single early origin for this suit e of characters, prior to the divergence of South American and African taxa. If so, then annualism has since been lost several times during the evolution of genera now residing in permanent aquatic habitats. Pa leoclimatic knowledge complements this scenario based on molecular cha racters.