Phylogeography of a cryptic speciation continuum in Eurasian spadefoot toads (Pelobates)

Christophe Dufresnes*, Ilias Strachinis, Nataliia Suriadna, Galyna Mykytynets, Dan Cogălniceanu, Paul Székely, Tanja Vukov, Jan W. Arntzen, Ben Wielstra, Petros Lymberakis, Eli Geffen, Sarig Gafny, Yusuf Kumlutaş, Çetin Ilgaz, Kamil Candan, Edvárd Mizsei, Márton Szabolcs, Krzysztof Kolenda, Nazar Smirnov, Philippe GéniezSimeon Lukanov, Pierre André Crochet, Sylvain Dubey, Nicolas Perrin, Spartak N. Litvinchuk, Mathieu Denoël

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Cryptic phylogeographic diversifications provide unique models to examine the role of phylogenetic divergence on the evolution of reproductive isolation, without extrinsic factors such as ecological and behavioural differentiation. Yet, to date very few comparative studies have been attempted within such radiations. Here, we characterize a new speciation continuum in a group of widespread Eurasian amphibians, the Pelobates spadefoot toads, by conducting multilocus (restriction site associated DNA sequencing and mitochondrial DNA) phylogenetic, phylogeographic and hybrid zone analyses. Within the P. syriacus complex, we discovered species-level cryptic divergences (>5 million years ago [My]) between populations distributed in the Near-East (hereafter P. syriacus sensu stricto [s.s.]) and southeastern Europe (hereafter P. balcanicus), each featuring deep intraspecific lineages. Altogether, we could scale hybridizability to divergence time along six different stages, spanning from sympatry without gene flow (P. fuscus and P. balcanicus, >10 My), parapatry with highly restricted hybridization (P. balcanicus and P. syriacus s.s., >5 My), narrow hybrid zones (~15 km) consistent with partial reproductive isolation (P. fuscus and P. vespertinus, ~3 My), to extensive admixture between Pleistocene and refugial lineages (≤2 My). This full spectrum empirically supports a gradual build up of reproductive barriers through time, reversible up until a threshold that we estimate at ~3 My. Hence, cryptic phylogeographic lineages may fade away or become reproductively isolated species simply depending on the time they persist in allopatry, and without definite ecomorphological divergence.

Original languageEnglish
Pages (from-to)3257-3270
Number of pages14
JournalMolecular Ecology
Volume28
Issue number13
DOIs
StatePublished - Jul 2019

Keywords

  • amphibia
  • anuran
  • hybrid zones
  • population genomics
  • reproductive isolation
  • speciation continuum

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