Diversification of rainforest faunas: An integrated molecular approach

Understanding the evolutionary processes that generate and sustain diversity in tropical faunas has challenged biologists for over a century and should underpin conservation strategies. Molecular studies of diversity within species and relationships among species, when integrated with more traditional approaches of biogeography and paleoecology, have much to contribute to this challenge. Here we outline the current major hypotheses, develop predictions relevant to integrated molecular approaches, and evaluate the current evidence, focusing on central African, Australian, and South American systems. The available data are sparse relative to the scale of the questions. However, the following conclusions can be drawn: (a) in most cases, the divergence of extant sister taxa predates the Pleistocene; (b) areas with high habitat heterogeneity and recent climatic or geological instability appear to harbor more species of recent origin; (c) there is support for both allopatric and gradient models of diversification and more attention should be given to the role of diversifying selection regardless of geographic context; and (d) conservation strategies should seek to protect heterogeneous landscapes within and adjacent to large rainforest areas, rather than rainforests alone

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