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.

A. - (e.g., Haffer 1974, Hackett and Lehn 1997, Eberhard and Bermingham 2005.The "green" toucanets in the genus Aulacorhynchus are almost completely restricted to Neotropical humid montane forests from southern and eastern Mexico south to Bolivia. Currently, they are placed in six to seven highly polytypic species (Haffer 1974, Sibley 5 E-mail: fernandopuebla@hotmail.com The Auk, Vol. 125, Number 1, pages 39-50. ISSN 0004-8038, electronic ISSN 1938-4254. c Press's Rights and Permissions website, http://www.ucpressjournals.com/reprintInfo.asp. DOI: 10.1525/auk.2008.125.1.39 and Monroe 1990). Aulacorhynchus spp. show discrete variation in coloration and size, and several populations isolated on single mountain ranges are surprisingly distinct. However, systematic study of this genus has been slowed by the paucity of specimens throughout its range (Navarro-Sigüenza et al. 2001) by The American Ornithologists' Union. All rights reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California

Aim We used mitochondrial DNA sequences to reconstruct the phylogenetic relationships of Mesoamerican Amazilia hummingbirds (Trochilidae). The phylogeny was used to identify vicariance scenarios, reconstruct ancestral biogeographical areas, and investigate the role of geological events in generating genetic divergence through vicariance events.Location Mesoamerica.Methods Molecular sequence data were gathered from three mitochondrial genes (ND2, ND5 and 12S) for samples taken within the Mesoamerican region and analysed using maximum parsimony, maximum-likelihood and Bayesian approaches. Statistical dispersal-vicariance analysis (S-DIVA) was used to reconstruct biogeographical areas and changes in distribution during the evolutionary history of Amazilia. The phylogeny was calibrated using fossil dates, mean substitution rates and coalescent-based divergence time inference.Results Amazilia can be split into two divergent lineages, with high levels of sequence divergence within some Mesoamerican species. Ancestral area reconstructions favour an ancestral distribution west of the Isthmus of Tehuantepec, with subsequent dispersals east of the isthmus and to South America. Divergence time estimations suggest that major diversification events occurred in the Miocene and Pliocene, corresponding temporally and geographically to the formation of the mountain systems and establishment of the major biomes in Mesoamerica. Main conclusionsThe diversification of Amazilia corresponds to vegetation shifts in combination with regional orogenesis. Intriguingly, the timing of the major diversification events and dispersal into South America pre-dates the completion of the Panamanian isthmus c. 4 Ma before present.

The costs of bird song incurred in a diversity of ways may result in trade‐offs in the production and maintenance of elaborate plumage ornaments. In this paper, we examine evolutionary trade‐offs between acoustic and visual signalling in trogon birds (Trogonidae). Using multiple regressions with phylogenetically independent contrasts, we found that interspecific variation in male plumage coloration was not significantly predicted by song traits (reduced by PCA) or altitude. Although plumage coloration is expected to decrease with increases in song elaboration, both groups of variables were not related. Given that song and plumage coloration traits are likely targets of sexual selection, we also examined their relationships with sexual plumage dimorphism. We found that male carotenoid‐derived coloration was positively related to sexual plumage dimorphism, suggesting that sexual selection on male carotenoid‐derived coloration may be stronger than on melanin‐ or structurally based coloration, or than on acoustic traits. Comparative studies on other bird families accounting for the effects of phylogeny as well as environmental covariates are required to test the generality of our findings in trogons.

The differentiation of the bipotential 02Aprogenitor cell into an oligodendrocyte or a type 2 astrocyte has been well documented in cell cultures of various regions of the central nervous system. The appropriate tools to prove its existence in vivo have been lacking. We report on an in vitro-in vivo approach that combines stable labeling of an enriched population of cultured 02A progenitors by the fluorescent dye fast blue, followed by their transplantation into neonatal rat brains, which allowed us to study the influence of the brain microenvironment on their lineage decision. Recently, the existence of type 2 astrocytes in vivo has been questioned (6, 7). Raffand coworkers (5) have estimated the in vivo appearance of type 1 astrocytes, oligodendrocytes, and type 2 astrocytes in the rat optic nerve to be at postnatal day 0 (PO), P4, and P15, respectively. However, a light and electron microscopic immunocytochemical analysis of [3H]thymidine pulse-labeled developing rats has revealed only two periods of astrocyte and oligodendrocyte generations, the earliest being that of GFAP+ cells near PO followed by a wave of oligodendrocytes at P4-P8 (6, 7). A major obstacle to resolve this controversy has been the lack of appropriate markers to identify type 2 astrocytes in the brain (5). The antibody A2B5 is not a reliable marker in tissue sections because it stains unrelated cell types and intracellular structures (for review, see refs. 7 and 8).In this study, we propose an approach to compare the fate of 02A progenitors in the in vivo vs. in vitro environment. An enriched population of 02A progenitors in culture was labeled with the fluorescent dye fast blue (FB) and transplanted into neonatal rat brains. The phenotypic differentiation of 02A cells was studied in tissue sections by single and double immunolabeling and examined by fluorescence microscopy to visualize grafted cells and their progeny. We have reported (9) that FB-labeled cultured glial cells transplanted into normal and myelin-deficient (md) Wistar rats remain identifiable in immunostained tissue sections up to 6 months after grafting (9). We now report that transplanted 02A progenitors in vivo develop into oligodendrocytes but not astrocytes. MATERIALS AND METHODSAnimals. Normal Wistar and md Wistar rat pups were raised in our breeding colonies. Rats were housed in a restricted-access temperature-controlled vivarium on a 12-h light/12-h dark cycle, with free access to food and water. Fifty percent of pups born to previously identified female carriers of the md trait are genetically normal (+/y) and 50% carry the md trait (md/y). Males ofboth genotypes were used at P5 as recipients for cell transplants.Cell Culture. Primary cultures were prepared from newborn rat brains as described (10). These cultures were maintained in Waymouth medium supplemented with 10% (vol/ vol) fetal calf serum. After 9 days in culture, 02A cells growing on top ofthe astrocyte monolayer (type 1 astrocytes) were removed by a modification of the method of McCarthy and de Vel...