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

Abstract

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

Understanding the Distribution, Behavioural Ecology, and Conservation Status of Asian Pelophylax

“…However, this consistency in ecological requirements resulted in large shifts in distribution over time; for instance, the ecological niche of P. ridibundus expanded during the late Quaternary. However, the species was restricted to glacial refugia in the northern Balkans on the northern coasts of the Black and Azov Seas and possibly in Western Europe, but post-glacial dispersal routes started from the refugia in the northeastern Balkans and the Black-Azov Seas regions [157]. The mean temperature of the driest quarter had the highest percentage of contribution for the sympatric P. bedriagae, and the range of the species followed the same variations.…”

“…For these lineages, the precipitation of the warmest quarter was of primary importance for the distribution of P. terentievi, and this pattern regulates the distribution of other amphibians, such as Rana graeca in the Balkans [158]. In addition, precipitation of the coldest quarter was important for the P. "Syr Darya" lineage, similar to the variable principally regulating the range of P. kurtmuelleri in Europe [157].…”

“…Precipitation of the coldest quarter was also a limiting factor for the distribution of this lineage. As the region is generally marked by dry winters, the high contribution of this variable highlights an adaptation to wetter winters and low variability in precipitation among seasons [157]. For the P. n. "reinhardtii" lineage, annual mean temperature was the most important variable, representing the temperature fluctuations in comparison with yearly variations [17].…”

“…The mean temperature of the driest quarter had the highest percentage of contribution for the sympatric P. bedriagae, and the range of the species followed the same variations. During the Last Glacial Maximum, the species was mainly distributed in the north of the Mediterranean region and the south of European Russia; however, in the Late Pleistocene, the suitable habitat of P. bedriagae began to decline in southern Russia [157]. The remaining lineages were generally restricted to specific river basins.…”