Abstract
Comparative phylogeography can elucidate the influence of historical events on current patterns of biodiversity and can identify patterns of co-vicariance among unrelated taxa that span the same geographic areas. Here we analyze temporal and spatial divergence patterns of cloud forest plant and animal species and relate them to the evolutionary history of naturally fragmented cloud forests–among the most threatened vegetation types in northern Mesoamerica. We used comparative phylogeographic analyses to identify patterns of co-vicariance in taxa that share geographic ranges across cloud forest habitats and to elucidate the influence of historical events on current patterns of biodiversity. We document temporal and spatial genetic divergence of 15 species (including seed plants, birds and rodents), and relate them to the evolutionary history of the naturally fragmented cloud forests. We used fossil-calibrated genealogies, coalescent-based divergence time inference, and estimates of gene flow to assess the permeability of putative barriers to gene flow. We also used the hierarchical Approximate Bayesian Computation (HABC) method implemented in the program msBayes to test simultaneous versus non-simultaneous divergence of the cloud forest lineages. Our results show shared phylogeographic breaks that correspond to the Isthmus of Tehuantepec, Los Tuxtlas, and the Chiapas Central Depression, with the Isthmus representing the most frequently shared break among taxa. However, dating analyses suggest that the phylogeographic breaks corresponding to the Isthmus occurred at different times in different taxa. Current divergence patterns are therefore consistent with the hypothesis of broad vicariance across the Isthmus of Tehuantepec derived from different mechanisms operating at different times. This study, coupled with existing data on divergence cloud forest species, indicates that the evolutionary history of contemporary cloud forest lineages is complex and often lineage-specific, and thus difficult to capture in a simple conservation strategy.
Highlights
Cloud forest is among the most threatened types of vegetation in northern Mesoamerica
Ethics statement We obtained collecting permits to conduct this work from the Secretarıa de Medio Ambiente y Recursos Naturales, Instituto Nacional de Ecologıa, Direccion General de Vida Silvestre and the Guatemalan Government through the Universidad del Valle de Guatemala herbarium (UVAL) collecting permits granted to Jose Juan Vega (Universidad San Carlos de Guatemala) and Ana Lu MacVean (Universidad del Valle de Guatemala)
Phylogeny and divergence time estimation The phylogenies of all 15 species recovered varying levels of sequence divergence between populations separated by a geographic barrier, ranging from 0.118% in R. baccifera populations separated by the Isthmus of Tehuantepec, to 7–13% in rodent populations separated by this barrier, with intermediate values between populations of bird species (Table S3)
Summary
Cloud forest is among the most threatened types of vegetation in northern Mesoamerica. Throughout its geographic distribution, cloud forest habitat is influenced by fog during the winter dry season, and precipitation ranging from 1000 to 3000 mm of annual precipitation, and average daily temperatures from 12 to 23 uC and an annual mean around 18 uC [4]. These conditions favor the development of exuberant vegetation, including large tree ferns, a great variety of epiphytes and vines, and a mixed canopy of temperate deciduous trees and tropical broadleaved-evergreen trees [5]. Cloud forest recognized for its high endemism of epiphytes, has the highest biotic diversity per unit area in Mexico with cloud forests accounting for 10% of all Mexican flora (2500 vascular plant species) and 12% of the terrestrial vertebrates [2,3,4,6,7,8]
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