EVOLUTIONARY GENETICS OF DEATH-VALLEY PUPFISH POPULATIONS - MITOCHONDRIAL-DNA SEQUENCE VARIATION AND POPULATION-STRUCTURE

The pupfishes of Death Valley (genus: Cyprinodon) are a classic exampl e of rapid (post-Pleistocene) allopatric divergence with several popul ations exhibiting striking morphological, physiological, and behaviour al differences. However, genetic changes accompanying or causing this divergence have been poorly resolved and/or difficult to detect. In or der to investigate the phylogeography of the system and infer historic al effective population sizes, mtDNA sequence variation was assessed w ithin and among populations. In total, mtDNA D-loop sequences revealed 11 haplotypes among 278 individuals from 16 populations. Genetic dive rsity within populations was generally low (1-3 haplotypes per populat ion) suggesting relatively small effective population sizes. Most vari ation occurred among populations, resulting in extensive genetic struc ture. The genealogical relationships of mtDNA haplotypes were determin ed by a combined phylogenetic analysis of both D-loop and ND2 sequence s. These relationships revealed that the present distribution of haplo types in Death Valley has probably resulted from stochastic, and in so me cases, incomplete sorting of ancestral variation. The presence of h ighly diver gent haplotypes in some populations may indicate that ance stral population sizes were substantially larger, perhaps rivalling po pulation sizes observed in contemporary coastal pupfish species. In co ntrast, other Death Valley populations of equal contemporary size appe ared monomorphic suggesting historical genetic bottleneck events. The Death Valley pupfishes provide an important example of the limitations inherent in defining evolutionarily significant units (ESUs) for cons ervation purposes based on mtDNA sequence variation alone.