Variationin the ilium of central European water frogs Pelophylax (Amphibia, Ranidae) and its implications for species-level identification of fragmentary anuran fossils.

Hugues-Alexandre Blain,Gottfried Böhme,Iván Lózano-Fernández

doi:10.1186/s40555-014-0094-3

Abstract

In the opinion of all field herpetologists and archaeozoologists, green frogs (living and sub-fossil specimens)are among the most difficult European amphibians to identify. Here, we examine the intra- and interspecific variation in both continuous and discrete iliac characters for refining the criteria for species-level identification among Europeangreen frogs Pelophylaxridibundus,Pelophylaxlessonae andtheir associated klepton Pelophylaxkl.P.esculentus (Amphibia,Ranidae). Atotal of 454 ilia of modern green frogs from the former German Democratic Republic have been studied: 168 for P.lessonae (86of males and 82 of females), 118 for P.ridibundus (44of males and 74 of females) and 168 for P.kl.P.esculentus (86of males and 82 of females). The origin, sex, population structure and phenotype are known for each of the studied specimens. Eight variables have been taken (one angle and seven measurements), mainly on the distal part of the element in order to be able to apply them to fragmentary fossil ilia. Interspecific variations, sexual dimorphism and population structure have been investigated. Results suggest that the secure determination of a single fossil ilium at species level is quite impossible, but that at population level, it may be possible to distinguish between a 'pure' species or a 'pure' species plus its cohabiting hybrid form, as some minor differences have been evidencedin particular in the angle of the tubersuperior inrelation to iliac's main axis (character 2) and the width of the parsascendens (character8); two parameters significantly non size-dependent. No sexual dimorphism has been detected, except for P.lessonae. We propose here a new biometrical method in order to differentiate between the fossil ilia of central European water frogs (genus Pelophylax) at population level.

Highlights

In the opinion of all field herpetologists and archaeozoologists, green frogs are among the most difficult European amphibians to identify
The results of the Mann-Whitney U test (Table 2) suggest that the difference between species and klepton are highly significant for all characters but for character 3 between P. ridibundus and P. kl
The only reliable fossil mention according to Sanchiz (1998) has been made for the Late Pleistocene and Holocene of Pisede (Germany; Böhme 1983a, b), whereas according to Martín and Sanchiz (2014) database, P. lessonae is mentioned since the Late Pliocene of Korotoyak-Belogor'e (Voronezh, Russia; Ratnikov 2001a) and P. ridibundus probably since the Early Pliocene (MN14) of Nurnus (Kotayk, Armenia; Vasilyan 2009)

Summary

Introduction

In the opinion of all field herpetologists and archaeozoologists, green frogs (living and sub-fossil specimens) are among the most difficult European amphibians to identify. Blain et al Zoological Studies (2015)54:5 can live and reproduce in the presence of only one parental species. P. esculentus is more flexible than its parental species and poses fewer demands on its habitat (Günther 1990; Plötner 2005). P. esculentus lives in sympatry with the parental species P. lessonae (LE system). P. esculentus breeds with P. ridibundus forming populations of the RE system, which feature high structural genetic variability (Plötner 2005). P. esculentus stems from hybridogenetic reproduction or primary hybridization between the parental species (Günther 1991; Plötner 2005). There is all-hybrid populations (EE system) that have become reproductively independent of the parental forms owing to polyploidization, i.e. via triploid individuals (Günther 1975; Uzzell and Berger 1975; Ebendal and Uzzell 1982; Regnier and Neveu 1986; Pruvost et al 2013) and which mainly occur in the northern region of the distribution range (Ebendal 1979; Eikhorst 1987)

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Discussion

Conclusion