Biogeography of the Tropical Eastern Pacific: distribution and phylogeny of chaenopsid fishes

The Tropical Eastern Pacific Biogeographic Region (TEP) is delimited by sle ep thermal gradients to the north and south, by a wide expanse of open ocea n (the East Pacific Barrier) to the west, and by the Central American land mass to the east. Four provinces within the TEP have been recognized based on the distribution of rocky shore fishes and marine invertebrates: the Cor tez, Mexican, Panamic, and Galapagos Provinces. For rocky shore fishes, hyp othesized barriers between these provinces are areas lacking rocky outcropp ings, specifically the Central American Gap between the Panamic and Mexican Provinces, the Sinaloan Gap between the Mexican and Cortez Provinces: and the Pelagic Gap between the mainland and the Islas Galapagos. The occurrenc e of 33 chaenopsid fish species within these provinces, as well as other oc eanic islands or archipelagos in the TEP (Isla de Malpelo, Isla del Coco, a nd Islas Revillagigedo) were tallied based on literature records and observ ations of museum specimens. Chaenopsid distributions within the TEP support these hypothesized provinces and their intervening gaps. Twenty-one specie s (64% of the TEP chaenopsid fauna) are restricted to a single mainland pro vince or one of the oceanic islands or archipelagos. Of the mainland provin ces, the Cortez and Panamic exhibit similar Iea els of endemism (50%), but the Mexican Province has only one endemic (10%). Of the remaining chaenopsi ds in the Mexican Province, three are widespread, occurring in all three ma inland provinces, four are shared only with the Cortez Province? and two ar e shared only xith the Panamic Province. Within the TEP, the Pelagic Gap is the most effective (crossed by only 3 of 33 species adjacent to it), follo wed by the Central American Gap (crossed by 5 of 21 species), and the Sinal oan Gap (crossed by 7 of 17 species). Only one species, Chaenopsis alepidot a, which is found off southern California and in the Cortez Province, cross es a barrier delimiting the TEP. Species-level phylogenetic hypotheses for the Chaenopsidae imply exclusively allopatric speciation for these fishes i n the TEP. Of the barriers delimiting the TEP, the most important in the re cent evolution of chaenopsids is the Isthmian Barrier which is implicated i n six speciation events. Within the TEP, the Central American Gap and Sinal oan Gap are each implicated in three speciation events, while the Pelagic G ap is implicated in three speciation events of island endemics from mainlan d populations and one inter-island speciation event. (C) 2000 The Linnean S ociety of London.