title: The dual role of Andean topography in primary divergence: functional and neutral variation among populations of the hummingbird, Metallura tyrianthina.
abstract: BACKGROUND
  The ridges and valleys of the Andes create physical barriers that limit animal dispersal and cause deterministic local variation in rainfall. This has resulted in physical isolation of animal populations and variation in habitats, each of which has likely contributed to the evolution of high species diversity in the region. However, the relative influences of geographic isolation, ecoclimatic conditions, and their potential interactions remain poorly understood. To address this, we compared patterns of genetic and morphological diversity in Peruvian populations of the hummingbird Metallura tyrianthina.
  
  
  RESULTS
  Phylogenetic and variation partitioning analyses showed that geographic isolation rather than climatic dissimilarity explained the greatest proportion of genetic variance. In contrast, bill length variation was explained by climatic seasonality, but not by genetic divergence. We found that mutation-scaled migration rate (m) between persistently humid and semi-humid environments was nearly 20 times higher when the habitats were contiguous (m = 39.9) than when separated by a barrier, the Cordillera de Vilcanota (m = 2.1). Moreover, the population experiencing more gene flow exhibited a lesser degree of bill length divergence despite similar differences in climate.
  
  
  CONCLUSIONS
  Geographic isolation is necessary for genetic divergence. Ecological differences, represented here by climate characteristics, are necessary for functional divergence. Gene flow appears to hinder the evolution of functional traits toward local adaptive optima. This suggests that functional diversification requires geographic isolation followed or accompanied by a shift in ecological conditions. Andean topography causes both isolation and climatic variation, underscoring its dual role in biotic diversification.
authors.affiliation: Department of Biology and Museum of Southwestern Biology, University of New Mexico, 167 Castetter Hall MSC03 2020, 1 University of New Mexico, Albuquerque, NM, 87131, USA. phred.benham@umconnect.umt.edu.|Present address: Division of Biological Sciences, University of Montana, 32 Campus Dr. HS104, Missoula, MT, 59812, USA. phred.benham@umconnect.umt.edu.
authors.forename: Phred M
authors.initials: PM
authors.lastname: Benham
authors.affiliation: Department of Biology and Museum of Southwestern Biology, University of New Mexico, 167 Castetter Hall MSC03 2020, 1 University of New Mexico, Albuquerque, NM, 87131, USA. cwitt@unm.edu.
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Witt
mesh_terms: D063147:Animal Distribution; D000818:Animals; D005075:Biological Evolution; D001717:Birds / Q000145:classification / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000235:genetics; D004463:Ecology; D017753:Ecosystem; D005260:Female; D051456:Gene Flow; D040961:Genetic Drift; D014644:Genetic Variation; D005828:Genetics, Population; D008297:Male; D010802:Phylogeny; D013020:South America
chemical_list: D004272:DNA, Mitochondrial