Ecological and biogeographic drivers of speciation in neotropical hognose pit vipers, Porthidium (Squamata, Viperidae)

Abstract

The neotropical hognose pit vipers (Porthidium) represent an ideal system for studying how ecological and geographic factors drive speciation. This genus encompasses nine species distributed across diverse environments in North, Central and northern South America, with two distinct clades suggesting historical ecological differentiation. Using a time-calibrated phylogeny and occurrence data, we tested whether speciation was driven by niche conservatism or divergence, and assessed the role of major biogeographic barriers. Niche overlap analyses revealed no or low similarity between species (mean D = 0.12, I = 0.24, Jaccard full background = 0.02 and Jaccard union background = 0.06). Our null models confirm an indistinct niche overlap between sister species and random species, indicating speciation through ecological divergence. Speciation was shaped by three major barriers: the Nicaraguan Depression (∼10 Mya), the Motagua-Polochic Fault (∼7.7 Mya), and the Isthmus of Tehuantepec (∼3.1–3.5 Mya) indicating an ancestral range in the Pacific dominion by all models, while additionally Páramo and Yucatan Peninsula province by the Bayesian approach. Our findings demonstrate that Porthidium speciation was driven by niche divergence rather than conservatism, with geographic barriers promoting parapatric speciation for non-endemic Porthidium species and sympatric speciation for endemic species. This integrated framework provides new insights into how ecological adaptation and physical barriers interact during rapid radiations in Neotropical vertebrates.