Spotlight on islands: on the origin and diversification of an ancient lineage of the Italian wall lizard Podarcis siculus in the western Pontine Islands

Abstract

Groups of proximate continental islands may conceal more tangled phylogeographic patterns than oceanic archipelagos as a consequence of repeated sea level changes, which allow populations to experience gene flow during periods of low sea level stands and isolation by vicariant mechanisms during periods of high sea level stands. Here, we describe for the first time an ancient and diverging lineage of the Italian wall lizard Podarcis siculus from the western Pontine Islands. We used nuclear and mitochondrial DNA sequences of 156 individuals with the aim of unraveling their phylogenetic position, while microsatellite loci were used to test several a priori insular biogeographic models of migration with empirical data. Our results suggest that the western Pontine populations colonized the islands early during their Pliocene volcanic formation, while populations from the eastern Pontine Islands seem to have been introduced recently. The inter-island genetic makeup indicates an important role of historical migration, probably due to glacial land bridges connecting islands followed by a recent vicariant mechanism of isolation. Moreover, the most supported migration model predicted higher gene flow among islands which are geographically arranged in parallel. Considering the threatened status of small insular endemic populations, we suggest this new evolutionarily independent unit be given priority in conservation efforts.

The comparative biogeography of Philippine geckos challenges predictions from a paradigm of climate-driven vicariant diversification across an island archipelago

“…A "species-pump" model of diversification (Jetz et al, 2004;Fjeldså and Rahbek, 2006;Kozak and Wiens, 2010;Sedano and Burns, 2010;Schoville et al, 2012;Papadopoulou and Knowles, 2015) via repeated vicariance predicts that divergences across taxa that occur on historically connected "island archipelagos" should be clustered around times of historical isolating mechanisms. This model can be relevant to a diversity of structured environments, including deep-ocean (Ricklefs and Bermingham, 2008;Brown et al, 2013;Papadopoulou and Knowles, 2015) and coastal (Papadopoulou and Knowles, 2017;Senczuk et al, 2018) islands, and mountain tops (i.e., "sky" islands; Knowles, 2000Knowles, , 2001McCormack et al, 2008) Within the Philippines, this model predicts that divergences among taxa distributed across islands within the same PAIC should be associated with times of rising sea levels that fragmented PAICs into the islands of today. Therefore, if we compare the divergence times of multiple pairs of populations or closely related species that occur on two islands that were connected during glacial periods of lower sea levels, we expect some to be contemporaneous with interglacial fragmentation events.…”

The comparative biogeography of Philippine geckos challenges predictions from a paradigm of climate‐driven vicariant diversification across an island archipelago

“…; Papadopoulou and Knowles ) and coastal (Papadopoulou and Knowles ; Senczuk et al. ) islands, and mountain tops (i.e., “sky” islands; Knowles , ; McCormack et al. ).…”

“…A "species-pump" model of diversification (Jetz et al 2004;Fjeldså and Rahbek 2006;Kozak and Wiens 2010;Sedano and Burns 2010;Schoville et al 2012;Papadopoulou and Knowles 2015) via repeated vicariance predicts that divergences across taxa that occur on historically connected "island archipelagos" should be clustered around times of historical isolating mechanisms. This model can be relevant to a diversity of structured environments, including deep ocean (Ricklefs and Bermingham 2008;Brown et al 2013;Papadopoulou and Knowles 2015) and coastal (Papadopoulou and Knowles 2017;Senczuk et al 2018) islands, and mountain tops (i.e., "sky" islands; Knowles 2000Knowles , 2001Mc-Cormack et al 2008). Within the Philippines, this model predicts that divergences among taxa distributed across islands within the same PAIC should be associated with times of rising sea levels that fragmented PAICs into the islands of today.…”

The role of island physiography in maintaining genetic diversity in the endemic Tyrrhenian wall lizard (Podarcis tiliguerta)

“…Such circumstances may have favoured relict populations to persist and differentiate in situ during the Mid‐Pleistocene marine transgressions (Malatesta & Zarlenga, ; Carrara et al ., ). A similar explanation was also suggested for other Mediterranean insular Podarcis to explain their genetic Mid‐Pleistocene make up (Brown et al ., ; Senczuk et al ., ). The mitochondrial genetic admixture found for the populations within La Maddalena Archipelago, characterized by a high number of shared haplotypes, would suggest the relevant role of the LGM coastal expansions in favouring diffusion processes.…”

“…These marine transgressions caused a sea level rise of 55–120 m (Malatesta & Zarlenga, ; Carrara, Cremaschi & Dai Pra, ). Such strong episodes of sea level rise have been suggested to be the main cause of local extinctions of insular vertebrate populations (Brown et al ., ; Senczuk et al ., ).…”