On the origin of the recent herpetofauna of Sicily: Comparative phylogeography using homologous mitochondrial and nuclear genes

Abstract

In contrast to oceanic, continental islands are expected to show less diversification and endemism and thus phylogeographic signatures of multiple colonization events from adjacent continents due to episodic connections by sea level changes. In order to test this situation for the herpetofauna of Sicily, we here focus on three amphibian and four reptile species-groups and investigate their phylogeographic relationships across the Sicily and Messina straits, where Plio-Pleistocene marine transgressions shortened the distances between (or connected) Sicily, North Africa and/or the Italian (Apennine) Peninsula. Using a multi-species, multi-marker phylogeographic approach (mitochondrial cytochrome b; 16S rDNA, nuclear intron of tropomyosin), we apply Bayesian and Maximum Likelihood phylogenetic methods and haplotype networks to examine the phylogenies, and to estimate divergence times from molecular data using the program BEAST. We recognize three colonization patterns: (i) Plio-Pleistocene colonization of Sicily from North Africa for the skinks Chalcides chalcides (1.8Mya) and Chalcides ocellatus (0.61My), (ii) Pleistocene colonization from the Italian Peninsula for the anurans Pelophylax spp. (0.81Mya) and Bufo bufo (late Pleistocene), and (iii) recent (late Pleistocene to Holocene), natural or man-mediated out-of-Africa dispersal for the anuran Discoglossus pictus and out-of-Africa human introduction for the gekkonid lizards Tarentola mauritanica and Hemidactylus turcicus. The Sicilian herpetofauna shows phylogeographic signatures as typical of continental islands, with limited diversification and endemism. Colonization by terrestrial amphibians and reptiles from adjacent continents appears shaped by interactions of the active geo-marine history along with species' ecology and human intervention, including a widely neglected faunal contribution from Africa. On some small islands and in Tunisia, we found isolated local populations significant for conservation. Our results underline how only multispecies approaches involving ecologically diverse taxa are able to reveal the complexity of faunal contributions to large continental islands like Sicily.