The Early Stages of Speciation in Amazonian Forest Frogs: Phenotypic Conservatism Despite Strong Genetic Structure
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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.
KeywordsGenetic drift Integrative phylogeography Isolation by distance Mitochondrial DNA River barrier Sexual signals
We thank Anelise Montanarin, Francisco C. de Freitas, Irene da S. Melo, Maria A. Carvalho, Moisés da S. Melo and Raimundo N. Amorim for fieldwork assistance; Daniela Leroy e Waleska Gravena for help in laboratory procedures; Adolfo Amézquita, Adrian Garda, Andrew J. Crawford, Camila Ribas, Heike Pröhl, Janet W. Reid, Jeffrey Podos, Luciana K. Erdtmann, Marcelo Gordo, Marcelo Menin, Marina Anciães, Pedro Ivo Simões, Tomas Hrbek, Vanessa Verdade and Walter Hödl for valuable suggestions during this study. We extend thanks to two anonymous reviewers whose observations led to further improvements in the text. We also thank the Brazilian Conselho de Desenvolvimento Científico e Tecnológico for financial support (CNPq-CT Amazônia 553997/2006-8 and 575572/2008-6).
Conflict of interest
The authors declare that they have no conflict of interest.
This study complies with the current Brazilian laws and was allowed by RAN-ICMBio/IBAMA (licences 13777-2, 18516-1, 20065-2, and 21950-1).
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