Multilocus phylogeography of the common midwife toad, Alytes obstetricans (Anura, Alytidae): Contrasting patterns of lineage diversification and genetic structure in the Iberian refugium

Abstract

Recent investigations on the evolutionary history of the common midwife toad (Alytes obstetricans) revealed high levels of geographically structured genetic diversity but also a situation where delineation of major historical lineages and resolution of their relationships are much more complex than previously thought. We studied sequence variation in one mitochondrial and four nuclear genes throughout the entire distribution range of all recognized A. obstetricans subspecies to infer the evolutionary processes that shaped current patterns of genetic diversity and population subdivision. We found six divergent, geographically structured mtDNA haplogroups diagnosing population lineages, and varying levels of admixture in nuclear markers. Given the timeframe inferred for the splits between major lineages, the climatic and environmental changes that occurred during the Pleistocene seem to have shaped the diversification history of A. obstetricans. Survival of populations in allopatric refugia through the Ice Ages supports the generality of the "refugia-within-refugia" scenario for the Iberian Peninsula. However, lineages corresponding to subspecies A. o. almogavarii, A. o. pertinax, A. o. obstetricans, and A. o. boscai responded differently to Pleistocene climatic oscillations after diverging from a common ancestor. Alytes o. obstetricans expanded northward from a northern Iberian refugium through the western Pyrenees, leaving a signal of contrasting patterns of genetic diversity, with a single mtDNA haplotype north of the Pyrenees from SW France to Germany. Both A. o. pertinax and A. o. boscai are widespread and genetically diverse in Iberia, the latter comprising two divergent lineages with a long independent history. Finally, A. o. almogavarii is mostly restricted to the north-eastern corner of Iberia north of the Ebro river, with additional populations in a small region in south-eastern France. This taxon exhibits unparalleled levels of genetic diversity and little haplotype sharing with other lineages, suggesting a process of incipient speciation.

Favourable areas for co‐occurrence of parapatric species: niche conservatism and niche divergence in Iberian tree frogs and midwife toads

“…In this sense, our models captured the present distribution of the four studied species, while showing additional favourable but currently unoccupied areas. This information complements previous and ongoing studies about the evolutionary history of these species (Recuero et al ., ; Gonçalves et al ., , ; I. Martínez‐Solano, unpublished data), although our methodological framework may be applied to other taxa as well.…”

“…). These species diverged at least 10 Ma (Gonçalves et al ., ), and thus it is reasonable to assume that there have been opportunities for secondary contact and hybridization at different times in their evolutionary history, at least in some parts of their ranges. Thus, given that these two species are currently reproductively isolated (hybridization is extremely rare; Rosa, ), and considering their small distributional overlap (Fig.…”

Subterranean termite phylogeography reveals multiple postglacial colonization events in southwestern Europe

“…2002; Hewitt 2004; Gómez and Lunt 2007; Abellán and Svenning 2014; Gonçalves et al. 2015; Rato et al. 2016).…”

“…2013; Gonçalves et al. 2015). This rich endemism can be explained by the heterogeneous topology of the Iberian Peninsula (it is situated at the interface between the Atlantic Ocean and the Mediterranean Sea), its past connections with Africa (Jaeger 1994; Agustí et al.…”

Evolutionary melting pots and reproductive isolation: A ring‐shaped diversification of an odorous frog (Odorrana margaratea) around the Sichuan Basin

“…Recently described complex refugia, such as microrefugia and refugia within refugia (e.g., Gómez & Lunt, ; Rull, ), may further promote genetic diversity within these areas. The Iberian Peninsula is probably the best representative of such areas, which served as a glacial refugium during various glaciations and currently maintains high levels of genetic diversity for numerous species (e.g., Gonçalves et al., ; Rowe, Harris, & Beebee, ). Alternatively, areas of secondary contact, rather than areas of refugia, may possess high levels of genetic diversity.…”