Detection of Glacial Refugia and Post-Glacial Colonization Routes of Morphologically Cryptic Marsh Frog Species (Anura: Ranidae: <i>Pelophylax</i>) Using Environmental Niche Modeling

Studying the distribution of morphologically cryptic animal species is always a very difficult task. Because most marsh frog species (the <i>Pelophylax ridibundus</i> complex) are cryptic, we used molecular markers to identify them. Three marsh frog species (<i>P. ridibundus</i>, <i>P. kurtmuelleri</i> and <i>P.</i> cf. <i>bedriagae</i>) inhabit the northern part of Western Palearctic. We created a database of localities and built models of their modern distribution. These models showed that the most suitable habitats are on the north of the Mediterranean region for <i>P</i>. cf. <i>bedriagae</i>, temperate Europe for <i>P. ridibundus</i>, and the Balkan coastal areas for <i>P. kurtmuelleri</i>. The projection of the modern ecological niches under the late-Quaternary climatic conditions showed that the range of <i>P. kurtmuelleri</i> remained largely unchanged during the period, whereas the ranges of <i>P.</i> cf. <i>bedriagae</i> and especially <i>P. ridibundus</i> changed greatly over time. During the Last Glacial Maximum, the presumed range of <i>P.</i> cf. <i>bedriagae</i> covered a relatively large area in the north of the Mediterranean region and the south of European Russia. Glacial refugia of <i>P. ridibundus</i> were apparently located in the northern Balkans, the northern coast of the Black and Azov seas, and possibly in Western Europe. The northward long-distance post-glacial dispersal of <i>P. ridibundus</i> occurred from refugia in the northeastern Balkans and the Black-Azov seas region. Since the Late Pleistocene, suitable habitats for <i>P.</i> cf. <i>bedriagae</i> in southern Russia began to decline, but local habitats for <i>P. ridibundus</i> become more suitable. Therefore, a mosaic of populations consisting of these both species and their hybrids has now been found here.