Biogeography of Greater Antillean freshwater fishes, with a review of competing hypotheses

Abstract

ABSTRACTIn biogeography, vicariance and long-distance dispersal are often characterized as competing scenarios. However, they are related concepts, both relying on reciprocal illumination from geological, ecological, and phylogenetic evidence. This can be illustrated for freshwater fishes, which may immigrate to islands when freshwater connections are temporarily present (vicariance), or by unusual means when oceanic gaps are crossed (long-distance dispersal). Marine barriers have a strong filtering effect, limiting immigrants to those most capable of oceanic dispersal. The roles of landspans and oceanic dispersal are being debated for freshwater fishes of the Greater Antilles. We review three active hypotheses (Cretaceous vicariance, GAARlandia, long-distance dispersal) and propose long-distance dispersal to be an appropriate null model due to a lack of reciprocal illumination for landspan hypotheses. Greater Antillean freshwater fishes have six potential source bioregions (defined from faunal similarity): Northern Gulf of México, Western Gulf of México, Maya Terrane, Chortís Block, Eastern Panamá, and Northern South America. Faunas of the Greater Antilles are composed of taxa immigrating from many of these bioregions, but there is strong compositional disharmony between island and mainland fish faunas (>90% of the species are cyprinodontiforms, compared to <10% in Northern Gulf of México and Northern South America, and ≤50% elsewhere), consistent with a hypothesis of long-distance dispersal. Ancestral area analysis indicates there were 16 or 17 immigration events over the last 51 my, 14 or 15 of these by cyprinodontiforms. Published divergence estimates and evidence available for each immigration event suggest they occurred at different times and by different pathways, possibly with rafts of vegetation discharged from rivers or washed to sea during storms. If so, ocean currents likely provide critical pathways for immigration when flowing from one landmass to another, but create dispersal barriers when flowing perpendicular between landmasses. In addition to high salinity tolerance, cyprinodontiforms (collectively) display a variety of adaptations that could enhance their ability to live with rafts (small body size, viviparity, low metabolism, amphibiousness, diapause, self-fertilization). These adaptations likely also helped immigrants establish island populations after arrival and persist long term thereafter. Cichlids may have used a pseudo bridge (Nicaragua Rise) to reach the Greater Antilles, persisting only on the largest islands (Cuba, Hispaniola). Gar (Lepisosteidae) may have crossed the Straits of Florida to Cuba, a relatively short crossing that is not a barrier to gene flow for several cyprinodontiform immigrants. Indeed, widespread distributions of Quaternary migrants (Cyprinodon,Gambusia,Kryptolebias), within the Greater Antilles and among neighbouring bioregions, imply long-distance dispersal is not necessarily inhibitory for well-adapted species, even though it appears to be virtually impossible all other freshwater fishes.