A reassessment of the diversity of green toads (Bufotes) in the circum‐Aegean region

Abstract

The dynamic biogeography of glacial refugia may cause complex patterns of genetic admixture between parapatric taxa, which in turn can mislead their systematics, diversity, and distributions. We investigated this issue for green toads (Bufotes) inhabiting the circum-Aegean region, a biodiversity hotspot of the Eastern Mediterranean.A previous phylogeographic study based on mitochondrial and microsatellite loci identified the hybrid zone between the European (viridis) and Anatolian (sitibundus) lineages of B. viridis all over the Balkan Peninsula, but subsequent range-wide genomic analyses (>1000 SNPs) located this transition in Turkey, a thousand kilometers eastwards. In order to clarify the diversity and taxonomy of the circum-Aegean populations, we reconciled these conflicting findings by integrating previous data with pure sitibundus individuals. Our results confirmed that the viridis/sitibundus hybrid zone extends in Western Anatolia, but that southeastern European populations feature cytonuclear discordances and a high and structured microsatellite diversity. This remarkable situation may stem from a massive geographic displacement of the hybrid zone during the last glacial fluctuations, an underappreciated yet seemingly common feature among the herpetofauna of the region. Our study thus contributes to the rising view that mitochondrial DNA can be a poor predictor of current phylogeographic structure, hence the need for genomic data, especially for narrowly distributed taxa. Finally, the analyses unambiguously support the distinction of a micro-endemic clade of green toads unique to some Cyclades islands, for which we provide a formal taxonomic description.

Low neutral and immunogenetic diversity in northern fringe populations of the green toad Bufotes viridis: implications for conservation

“…However, the comparatively high genetic diversity in southern Europe may have been inflated by the diffusion of alleles from the closely related B. sitibundus. This taxon forms a wide hybrid zone with B. viridis across Western Anatolia, which could have been previously located in the Balkans (Dufresnes et al 2021). The occurrence of foreign alleles through past introgression, as seen at least from mtDNA, would obviously obscure the comparisons.…”

“…Moreover, it is worth mentioning that Swedish green toads have been affected by taxonomic and even nomenclatural changes in recent years (Dufresnes et al 2019). Bufotes systematics are complicated by far reaching introgression of B. sitibundus (previously "B. variabilis") mt-DNA into the range of B. viridis (Stöck et al 2006;Dufresnes et al 2019Dufresnes et al , 2021. As a consequence, Swedish populations used to be called "B. variabilis" (as still listed on the Swedish red list, following Stöck 2005), even though they actually correspond to B. viridis, the only species present in continental Europe -expect in Ukraine-Russia (B. sitibundus), Italy and Spain (B. balearicus) (Dufresnes et al 2019).…”

“…The following thermocycling conditions were applied: 95 °C for 15′, 35 cycles of 94 °C for 30″, 53 °C for 45″ and 72 °C for 1′; 72 °C for 5′. Amplicons were Sanger-sequenced in a single direction (CytbA-L) and sequences were assigned to one of the two main mitochondrial lineages found in B. viridis: the viridis lineage and the sitibundus lineage, the latter having spread in Europe through past mtDNA introgression by the Anatolian taxon B. sitibundus (Dufresnes et al 2019(Dufresnes et al , 2021. To visualize lineage distributions, our new data was combined to the mtDNA dataset recently compiled for all major Bufotes lineages by Dufresnes et al (2019), and which encompasses 162 localities where the viridis and/or sitibundus mtDNA occur.…”

Phylogeography and systematics of Algyroides (Sauria: Lacertidae) of the Balkan Peninsula

“…Alexandri et al., 2012, 2016; Tryfonopoulos et al., 2010), amphibians (e.g. Dufresnes, Strachinis, Suriadna, et al., 2019, Dufresnes, Berroneau, 2020, Dufresnes, Probonas, 2020; Pabijan et al., 2017; Wielstra & Arntzen, 2014) and reptiles such as lizards (e.g. Gvoždík et al., 2010; Kornilios et al., 2020; Marzahn et al., 2016; Psonis et al., 2018; Sagonas et al., 2014) and snakes (e.g.…”

Small‐scale dams deplete frogs and toads

“…The Earth's biodiversity is in severe decline, and amphibians seem particularly vulnerable to environmental changes as they are among the worst affected animal groups (Barnosky et al, 2011;Dufresnes et al, 2021;Jetz & Pyron, 2018;Stuart et al, 2004). They are declining faster than birds and mammals and today almost 41% of amphibians are threatened with extinction (International Union for Conservation of Nature [IUCN]).…”