Beyond the river: Underlying determinants of population acoustic signal variability in Amazonian direct-developing Allobates (Anura: Dendrobatoidea)

The multidimensional nature of animal signals makes acoustic traits potentially subject to different determinants. The Amazonian frogs Allobates nidicola and Allobates masniger have an allopatric distribution, occurring along the left and right sides of the Madeira River, respectively. These are two sister, phenotypically similar species whose eggs are deposited and develop entirely in a terrestrial nest. In this study, we analyzed 2,000 advertisement calls recorded from ten localities across Central Amazonia, in order to understand the role of determinants of acoustic signal variability at the population and species levels. We assessed, through nested analyses of variance, the differentiation of six characters of this sexual signal among populations and between interfluves. Moreover, we measured the degree of variability and the extent of temperature- and body size-induced plasticity in call traits. We also tested for isolation-by-distance effects in phenotypic differentiation through Mantel tests. Coefficients of variation were higher among than within populations for all call measurements. Spectral call properties were more distinctive than temporal traits among populations and species. Advertisement call traits showed strong temperature-induced plasticity (e. g., 45 % of the variation in note duration). In contrast, the effects of body size were restricted to frequency-related characters. The river barrier effect was significant among all the acoustic variables analyzed even after controlling for male body size. Geography (sampling locality) and body size also jointly affected call variability. No correlation between geographical and acoustic distances among populations was observed, suggesting that local stabilizing selective pressures have an important role in the evolution of call differentiation. © 2012 Springer-Verlag and ISPA

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

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

The Early Stages of Speciation in Amazonian Forest Frogs: Phenotypic Conservatism Despite Strong Genetic Structure

Phylogeographic perspectives incorporating multiple classes of characters, especially those relating to sexual signals, are promising for the elucidation of recent evolutionary mechanisms driving speciation. Here, forest frogs were used as a model system to access distinct stages in the process of evolutionary differentiation. We studied 280 individuals assigned to three species: Allobates paleovarzensis, A. nidicola and A. masniger. Samples were collected at 20 localities arranged in two study systems, along the middle Amazon and the lower Madeira Rivers, in Central Amazonia. Mantel tests, analyses of molecular variance, and the spatial distribution of haplogroups indicated that the distribution of genetic variability, as inferred from a mitochondrial DNA marker, was determined by a combination of isolation-by-distance effects and the transposition of large Amazonian rivers. These two factors had contrasting relative influences in each of the study systems, which also differed regarding the estimated time of the major cladogenetic events. Pronounced population genetic structure was observed. However, multivariate discriminant function analyses revealed that the phenotypic (morphological and acoustic) divergence was loosely related with genetic differentiation and did not successfully predict assignment of individuals to genetic groups. The observed distribution of genetic variability showed the important role of genetic drift in the diversification of the mitochondrial marker studied. The phenotypic conservatism among populations was surprising in view of the high genetic structuring observed, and indicates a prevailing role of stabilizing selective forces in the process of sexual signal and morphological differentiation. © 2012 Springer Science+Business Media New York