Abstract
BackgroundThe contribution of North Africa to the assembly of biodiversity within the Western Palaearctic is still poorly documented. Since the Miocene, multiple biotic exchanges occurred across the Strait of Gibraltar, underlying the high biogeographic affinity between the western European and African sides of the Mediterranean basin. We investigated the biogeographic and demographic dynamics of two large Mediterranean-adapted snakes across the Strait and assess their relevance to the origin and diversity patterns of current European and North African populations.ResultsWe inferred phylogeographic patterns and demographic history of M. monspessulanus and H. hippocrepis, based on range-wide multilocus data, combined with fossil data and species distribution modelling, under present and past bioclimatic envelopes. For both species we identified endemic lineages in the High Atlas Mountains (Morocco) and in eastern Iberia, suggesting their persistence in Europe during the Pleistocene. One lineage is shared between North Africa and southern Iberia and likely spread from the former to the latter during the sea-level low stand of the last glacial stage. During this period M. monspessulanus shows a sudden demographic expansion, associated with increased habitat suitability in North Africa. Lower habitat suitability is predicted for both species during interglacial stages, with suitable areas restricted to coastal and mountain ranges of Iberia and Morocco. Compiled fossil data for M. monspessulanus show a continuous fossil record in Iberia at least since the Pliocene and throughout the Pleistocene.ConclusionsThe previously proposed hypothesis of Pleistocene glacial extinction of both species in Europe is not supported based on genetic data, bioclimatic envelopes models, and the available fossil record. A model of range retraction to mountain refugia during arid periods and of glacial expansion (demographic and spatial) associated to an increase of Mediterranean habitats during glacial epochs emerges as a general pattern for mesic vertebrates in North Africa. Moreover, the phylogeographic pattern of H. hippocrepis conforms to a well-established biogeographic partition between western and eastern Maghreb.
Highlights
The contribution of North Africa to the assembly of biodiversity within the Western Palaearctic is still poorly documented
Predictive modelling We evaluated the suitability of Iberian and North African environments for Malpolon monspessulanus and Hemorrhois hippocrepis under present, Holocene (6 thousand years ago, kya), Last Glacial Maximum (LGM; 23–18 kya) and Last Interglacial (LIG; 140–120 kya) bioclimatic
For both H. hippocrepis and M. monspessulanus, the cyt-b and the concatenated mtDNA alignments were resolved into a single statistical parsimony network (Figs. 2a, b, 3a, b; Additional file 1: Fig. S2, 3)
Summary
The contribution of North Africa to the assembly of biodiversity within the Western Palaearctic is still poorly documented. While for Europe it is well established that glacial periods represented a phase of demographic (and range) contraction for thermophilic species, with expansion phases associated with interglacial periods [3, 4, 8], less is known regarding the demographic and range dynamics of North African species during Pleistocene climatic cycles. In reptiles many species show shallow genetic differentiation between “European” and “African” populations, suggesting that they have independently crossed the Strait of Gibraltar, in both directions and on different occasions, throughout the Pleistocene [14, 20,21,22] For many of these species the relative role of Iberia and North Africa as glacial or interglacial refugia is still unclear, as well as their role as sources of colonization toward the other side of the Strait
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