l_raty
laurent raty
Smith, Seeholzer, Harvey, Cuervo, Brumfield. 2017. A latitudinal phylogeographic diversity gradient in birds. PLoS Biol 15(4):e2001073.
[full paper]
Abstract -
High tropical species diversity is often attributed to evolutionary dynamics over long timescales. It is possible, however, that latitudinal variation in diversification begins when divergence occurs within species. Phylogeographic data capture this initial stage of diversification in which populations become geographically isolated and begin to differentiate genetically. There is limited understanding of the broader implications of intraspecific diversification because comparative analyses have focused on species inhabiting and evolving in restricted regions and environments. Here, we scale comparative phylogeography up to the hemisphere level and examine whether the processes driving latitudinal differences in species diversity are also evident within species. We collected genetic data for 210 New World bird species distributed across a broad latitudinal gradient and estimated a suite of metrics characterizing phylogeographic history. We found that lower latitude species had, on average, greater phylogeographic diversity than higher latitude species and that intraspecific diversity showed evidence of greater persistence in the tropics. Factors associated with species ecologies, life histories, and habitats explained little of the variation in phylogeographic structure across the latitudinal gradient. Our results suggest that the latitudinal gradient in species richness originates, at least partly, from population-level processes within species and are consistent with hypotheses implicating age and environmental stability in the formation of diversity gradients. Comparative phylogeographic analyses scaled up to large geographic regions and hundreds of species can show connections between population-level processes and broad-scale species-richness patterns.
Author summary -
The causes of high tropical species diversity remain contentious and disputed. Recent studies have shown that latitudinal differences in speciation and extinction rates give rise to high tropical diversity. However, it is unclear if this gradient is the product of population-level, species-level, or clade-level processes. Here, we used genetic, environmental, and morphological data from hundreds of bird species occurring in the Western Hemisphere to evaluate patterns of within-species diversity. We found that tropical species have greater intraspecific genetic variation, and this diversity persists longer than in temperate species. These results indicate that biodiversity gradients can arise more rapidly than previously thought and that the processes governing these gradients operate on multiple evolutionary timescales.
[full paper]
Abstract -
High tropical species diversity is often attributed to evolutionary dynamics over long timescales. It is possible, however, that latitudinal variation in diversification begins when divergence occurs within species. Phylogeographic data capture this initial stage of diversification in which populations become geographically isolated and begin to differentiate genetically. There is limited understanding of the broader implications of intraspecific diversification because comparative analyses have focused on species inhabiting and evolving in restricted regions and environments. Here, we scale comparative phylogeography up to the hemisphere level and examine whether the processes driving latitudinal differences in species diversity are also evident within species. We collected genetic data for 210 New World bird species distributed across a broad latitudinal gradient and estimated a suite of metrics characterizing phylogeographic history. We found that lower latitude species had, on average, greater phylogeographic diversity than higher latitude species and that intraspecific diversity showed evidence of greater persistence in the tropics. Factors associated with species ecologies, life histories, and habitats explained little of the variation in phylogeographic structure across the latitudinal gradient. Our results suggest that the latitudinal gradient in species richness originates, at least partly, from population-level processes within species and are consistent with hypotheses implicating age and environmental stability in the formation of diversity gradients. Comparative phylogeographic analyses scaled up to large geographic regions and hundreds of species can show connections between population-level processes and broad-scale species-richness patterns.
Author summary -
The causes of high tropical species diversity remain contentious and disputed. Recent studies have shown that latitudinal differences in speciation and extinction rates give rise to high tropical diversity. However, it is unclear if this gradient is the product of population-level, species-level, or clade-level processes. Here, we used genetic, environmental, and morphological data from hundreds of bird species occurring in the Western Hemisphere to evaluate patterns of within-species diversity. We found that tropical species have greater intraspecific genetic variation, and this diversity persists longer than in temperate species. These results indicate that biodiversity gradients can arise more rapidly than previously thought and that the processes governing these gradients operate on multiple evolutionary timescales.
