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

Although salamanders are characteristic amphibians in Holarctic temperate h abitats, in tropical regions they have diversified evolutionarily only in t ropical America. An adaptive radiation centered in Middle America occurred late in the history of a single clade, the supergenus Bolitoglossa (Plethod ontidae), and large numbers of species now occur in diverse habitats. Subli neages within this clade decrease in number from the northern to southern p arts of Middle America, and in Costa Rica, there are but three. Despite thi s phylogenetic constraint, Costa Rica has many species; the number of salam ander species on one local elevational transect in the Cordillera de Talama nca may be the largest for any such transect in the world. Extraordinary va riation in sequences of the mitochondrial gene cytochrome b within a clade of the genus Bolitoglossa in Costa Rica reveals strong phylogeographic stru cture within a single species, Bolitoglossa pesrubra. Allozymic variation i n 19 proteins reveals a pattern largely concordant with the mitochondrial D NA phylogeography, More species exist than are currently recognized. Divers ification occurs in restricted geographic areas and involves sharp geograph ic and elevational differentiation and zonation. In their degree of genetic differentiation at a local scale, these species of the deep tropics exceed the known variation of extratropical salamanders, which also differ in bei ng 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 physiological differentiation that may contribute importantly to morphological divergence and species formation.