Morphological and genetic differentiation of Bufo toads: two cryptic species in Western Europe (Anura, Bufonidae)
Auteur : Arntzen (Jan)
Année de publication : 2013
Publication : Contributions to Zoology
Volume :
82
Fascicule : 4
Pagination : 147-169
Résumé :
The Common toad Bufo bufo sensu lato is a widespread, morphologicallyconserved taxon. Recent studies have uncovered deep genetic differentiation between population groups, highlighting the need to revise the current taxonomy of the group and recognize additional species. Here we investigate patterns of variation in molecular (a mitochondrial DNA restrictionenzyme assay and sequence data for two nuclear DNA fragments totalling 979 bp) and 17 morphological variables in Northern France where two of these groups meet (B. bufo sensu stricto and B. spinosus), in order to delineate their contactzone and uncover characters that would allow discriminationof the two taxa. Mitochondrial DNA data show an abrupttransition from areas where B. bufo is present to those inhabitedby B. spinosus, with a narrow area of overlap east of thecity of Caen. Morphometric characters, particularly those relatedto the positioning of the parotoid glands and metatarsaltubercle shape and size, proved useful in discriminating betweenspecies (AUC ≥ 0.97, kappa ≥ 0.79). We then used thedifferentiating character states to allocate over 300 museumspecimens from Western Europe to either species with consistentresults, including comparable values of AUC and kappaof the identification models, indicating that models could successfullybe applied across datasets. We summarize availableevidence relevant to the delineation of the distribution of B.bufo and B. spinosus in France and discuss the characters differentiatingboth species in an evolutionary context. In view ofthe observed morphological and genetic differentiation andthe absence of unequivocal evidence for widespread hybridizationwe support the view that B. bufo and B. spinosus arebest considered different species. Finally, we propose that‘parotoids in parallel position’ and a thin and smooth skin arederived character states for B. bufo over the northern part ofits range.