Biodiversity of Costa Rican salamanders: Implications of high levels of genetic differentiation and phylogeographic structure for species formation

摘要

Although salamanders are characteristic amphibians in Holarctic temperate habitats, in tropical regions they have diversified evo- lutionarily only in tropical America. An adaptive radiation centered in Middle America occurred late in the history of a single clade, the supergenus Bolitoglossa (Plethodontidae), and large numbers of species now occur in diverse habitats. Sublineages within this clade decrease in number from the northern to southern parts of Middle America, and in Costa Rica, there are but three. Despite this phylogenetic constraint, Costa Rica has many species: the number of salamander species on one local elevational transect in the Cordillera de Talamanca may be the largest for any such transect in the world. Extraordinary variation in sequences of the mito- chondrial gene cytochrome b within a clade of the genus Bolito- glossa in Costa Rica reveals strong phylogeographic structure within a single species, Bolitoglossa pesrubra. Allozymic variation in 19 proteins reveals a pattern largely concordant with the mitochondriaI DNA phylogeography. More species exist than are currently recognized. Diversification occurs in restricted geo- graphic areas and involves sharp geographic and elevational dif- ferentiation and zonation. In their degree of genetic differentia- tion at a local scale, these species of the deep tropics exceed the known variation of extratropical salamanders. which also differ in being less restricted in elevational range. Salamanders display "tropicality" in that although speciose. they are usually local in distribution and rare. They display strong ecological and physio- logical differentiation that may contribute importantly to morpho- logical divergence and species formation.