Amat, F. A.

Mountains are main drivers of speciation and elevational patterns of species richness in New World pitvipers (Viperidae: Crotalinae). pp. 195-205 plus Supplementary material.

Abstract. New World pitvipers (Agkistrodon, Atropoides, Bothrocophias, Bothriechis, Bothrops, Cerrophidion, Crotalus, Lachesis, Metlapilcoatlus, Mixcoatlus, Ophryacus, Porthidium and Sistrurus) are abundantly distributed in the tropics, where they live from sea level to 4,500 m altitude. I analysed the role of mountains in the diversification of the New World pitvipers by quantifying the orographic patterns of speciation and testing the effect of diversification rates and historical colonizations on elevational pattern of species richness. Using a time-calibrated phylogeny I found 42 speciation events, 68.6% of them involving mountain ranges mostly occurring in North and South America. Speciation restricted to lowlands was less frequent and in 75% of the cases happened by separation of an ancestral species by the emergence of mountain barriers. New World pitvipers underwent diversification from an ancestor living at middle elevation, posteriorly leading to several independent colonizations of high and low altitudes. By combining evidence from several methods, I found high initial speciation rates at medium elevations followed by a progressive slowing down negatively correlated with altitude. The effect of the historical processes seems to be less important and only the number of colonizations was positively associated with species richness when 200 m bands, which were correlated with elevation, and 500 m bands were analysed. Thus, evolutionary and historical processes produced an elevational pattern of species richness characterised by a maximum at medium elevations and a sharp decline at the higher.

Key words. Squamata, Serpentes biogeography, macroevolution, molecular phylogeny, speciation.