Significant but not diagnostic: Differentiation through morphology and calls in the Amazonian frogs allobates nidicola and A. masniger

Abstract

Acoustic parameters often usefully supplement the classic morphological approaches used to discriminate between similar species of frogs, and thus provide better assessments about their taxonomy at the species level. Allobates nidicola and A. masniger are known only from their respective type localities in Brazilian Amazonia, and the two species share all the available qualitative diagnostic traits. This study describes and compares a set of quantitative morphometric (external measurements) and acoustic (temporal and spectral parameters) characters of these species in a sampling design that included their type localities, in order to assess whether they are phenotypically distinguishable. The advertisement call of A. masniger is described here for the first time. Both acoustic (including temporal and spectral properties) and morphometric characters overlapped with those found in A. nidicola. The two species differed statistically in acoustic and morphometric characters when we compared between individuals from their type localities, and also when assuming that they are allopatric by the transposition of the Madeira River, the main biogeographic barrier in the study area. However, multivariate analyses failed to prove unambiguous distributional boundaries of these species based on the analysed phenotypic traits. Therefore, further lines of evidence - such as behavioural, developmental and molecular data - are required in order to detect diagnostic characters and thus clarify the taxonomic status of these phenotypically similar species.