RESUMO
Nucleotide sequences at two mitochondrial genes from 57 individuals representing eight species of deep-sea clams (Vesicomyidae) were examined for variation consistent with the neutral model of molecular evolution. One gene, cytochrome oxidase subunit I (COI), deviated from the expectations of neutrality by containing an excess of intraspecific nonsynonymous polymorphism. Additionally, one species, Calyptogena kilmeri, showed a significant excess of rare polymorphism specifically at the COI locus. In contrast, a second mitochondrial gene, the large-subunit 16S ribosomal RNA gene (16S), showed little deviation from neutrality either between or within species. Together, COI and 16S show no deviation from neutral expectations by the HKA test, produce congruent phylogenetic relationships between species, and show correlated numbers of fixed differences between species and polymorphism within species. These patterns of both neutral and nonneutral evolution within the mitochondrial genome are most consistent with a model where intraspecific nonsynonymous polymorphism at COI is near neutrality. In addition to examining the forces of molecular evolution, we extend hypotheses about interspecific relationships within this family for geographical locations previously unexamined by molecular methods including habitats near the Middle Atlantic, the Aleutian Trench, and Costa Rica.
Assuntos
Bivalves/genética , Variação Genética , Mitocôndrias/genética , Filogenia , Animais , Costa Rica , DNA Ribossômico/genética , Complexo IV da Cadeia de Transporte de Elétrons/genética , MéxicoRESUMO
To assess the level of genetic variation in a threatened black howler monkey (Alouatta pigra) population, we examined 36 allozyme loci and restriction fragment profiles of mitochondrial DNA (mtDNA). Mean heterozygosity at allozyme loci was only 0.021 and 5.6 percent of the loci were polymorphic. Analyses of mtDNA also revealed low genetic diversity compared with other primates. F-statistics revealed no significant genetic heterogeneity among troops within the Bermudian Landing preserve, but did indicate a deficiency of heterozygotes at one of the two loci. We explore several explanations for this result, which is unexpected in a socially structured primate. Low genetic diversity in this population may reflect its history of demographic bottlenecks.
Assuntos
Alouatta/genética , DNA Mitocondrial/química , Enzimas/genética , Variação Genética , Polimorfismo Genético , Alelos , Animais , Belize , Mapeamento Cromossômico , DNA Mitocondrial/genética , Evolução Molecular , Heterozigoto , Primatas/genéticaRESUMO
It has been suggested that the patchy distribution of snail susceptibility to schistosomes might be due to genetic drift. Since direct estimation of genes for susceptibility is not feasible in population studies, electrophoretic techniques were used to examine this hypothesis for populations of Biomphalaria glabrata from Puerto Rico. These populations were characterized by relative genetic homogeneity within populations and differentiation among local populations. The data presented are consistent with the hypothesis that random genetic drift and low rates of migration might be responsible for the patchy distribution of small susceptibility to schistosomes.