Phylogenetic relationships within the aquatic snail genus Tryonia: Implications for biogeography of the North American southwest

We examined the phylogenetic relationships among 23 species of the North Am erican aquatic snail genus Tryonia (Hydrobiidae), 10 additional representat ives of the subfamily Cochliopinae, and two outgroups. Maximum parsimony an alysis of a 601-base-pair sequence from the mitochondrial COI gene did not support monophyly of the genus nor its subgenus Paupertryonia. A clade comp osed of the type species of Tryonia and 16 congeners was strongly supported by the COI data and congruent with recently discovered variation in female genitalic morphology. This "true Tryonia" clade included two large western subclades having a sister-group relationship. The phylogenetic: structure of one of these subclades is congruent with vicariant events associated wit h late Neogene history of the lower Colorado River drainage. The other subc lade mirrors development of the modern Rio Grande rift and inception of mod ern topography in the southwestern Great Basin during the late Neogene, Bot h subclades are represented in the composite Tryonia fauna of the Amargosa River basin, whose assembly is attributed to the complex geological history of the Death Valley region. (C) 1999 Academic Press.