The role of immigrants in the assembly of the South American rainforest tree flora

The Amazon lowland rainforest flora is conventionally viewed as comprising lineages that evolved in biogeographic isolation after the split of west Gondwana (ca. 100 Myr ago). Recent molecular phylogenies, however, identify immigrant lineages that arrived in South America during its period of oceanic isolation (ca. 100-3 Myr ago). Long-distance sweepstakes dispersal across oceans played an important and possibly predominant role. Stepping-stone migration from Africa and North America through hypothesized Late Cretaceous and Tertiary island chains may have facilitated immigration. An analysis of inventory plot data suggests that immigrant lineages comprise ca. 20% of both the species and individuals of an Amazon tree community in Ecuador. This is more than an order of magnitude higher than previous estimates. We also present data on the community-level similarity between South American and palaeotropical rainforests, and suggest that most taxonomic similarity derives from trans-oceanic dispersal, rather than a shared Gondwanan history.     

A likelihood framework for inferring the evolution of geographic range on phylogenetic trees

Abstract At a time when historical biogeography appears to be again expanding its scope after a period of focusing primarily on discerning area relationships using cladograms, new inference methods are needed to bring more kinds of data to bear on questions about the geographic history of lineages. Here we describe a likelihood framework for inferring the evolution of geographic range on phylogenies that models lineage dispersal and local extinction in a set of discrete areas as stochastic events in continuous time. Unlike existing methods for estimating ancestral areas, such as dispersal‐vicariance analysis, this approach incorporates information on the timing of both lineage divergences and the availability of connections between areas (dispersal routes). Monte Carlo methods are used to estimate branch‐specific transition probabilities for geographic ranges, enabling the likelihood of the data (observed species distributions) to be evaluated for a given phylogeny and parameterized paleogeographic model. We demonstrate how the method can be used to address two biogeographic questions: What were the ancestral geographic ranges on a phylogenetic tree? How were those ancestral ranges affected by speciation and inherited by the daughter lineages at cladogenesis events? For illustration we use hypothetical examples and an analysis of a Northern Hemisphere plant clade (Cercis), comparing and contrasting inferences to those obtained from dispersal‐vicariance analysis. Although the particular model we implement is somewhat simplistic, the framework itself is flexible and could readily be modified to incorporate additional sources of information and also be extended to address other aspects of historical biogeography.     

Cryptic diversity in the lizard genus Plica (Squamata): phylogenetic diversity and Amazonian biogeography

Intra‐ and interspecific genetic diversity of the lizard species Plica plica (9 localities) and Plica umbra (19 localities) from the Brazilian Amazon was analysed using two mitochondrial (16S rDNA and CO1) and one nuclear (prolactin receptor – PRLR) genes. We generated a maximum‐likelihood and Bayesian hypotheses of phylogenetic relationships, and using the bPTP and ABGD lineage delimiting methods inferred the most likely number of lineages within each species. Both methods delimited five distinct lineages in Plica plica and six lineages within Plica umbra. The nominal subspecies of Plica umbra was comprised of one lineage, while Plica umbra ochrocollaris was comprised of five lineages. In majority of the cases, lineages were restricted to the interfluves of major Amazonian rivers, and different lineages occupied distinct areas of endemism. Phylogenetic relationships of the lineages are largely concordant with the hypothesized formation of the areas of endemism. The geographic structuring of the clades and the delimitation of these clades as distinct lineages suggest the possibility that these lineages represent species. If the observed diversity of lineages within the genus Plica is characteristic of squamate reptiles of the Amazon region, the diversity of squamates is grossly underestimated.     

Molecular systematics,biogeography and taxonomy of forest‐falcons in the Micrastur ruficollis species complex (Aves: Falconidae)

We gathered molecular data to assess phylogenetic and phylogeographic patterns for widespread lineages of Neotropical forest falcons in the genus Micrastur to: 1) investigate the comparative phylogeography of four species from the M. ruficollis complex (M. ruficollis, M. gilvicollis, M. plumbeus and M. mintoni), to identify the temporal and spatial context of the group's diversification; and 2) to reevaluate, based on molecular characters, the taxonomic status and interspecific boundaries within this complex. Molecular phylogenies were based on sequences of the mitochondrial genes ND2 and Cyt b and the nuclear genes FIB5 and MUSK from 119 specimens, including M. mirandollei and M. semitorquatus as outgroups. The phylogenetic trees obtained by BI and a Species Tree analysis recovered the monophyly of currently accepted species belonging to the M. ruficollis complex. The dates in our tree indicate that the separation of species within the complex occurred 2–4 million yr ago, initiating during the Neogene (Pliocene). However, when compared to most such widely distributed Neotropical lineages, the diversification within the M. ruficollis complex appears more recent (i.e. centered in the Late Pleistocene). Our results demonstrate the existence of eleven geographic lineages (subclades) in M. ruficollis, M. gilvicollis and M. mintoni, which differ genetically from each other and therefore can be interpreted as distinct evolutionary lineages and possibly separate species under lineage‐based species concepts. However, BPP results failed to recognize with strong statistical support any of these subclades as distinct species. Distinct subclades in the M. ruficollis complex are limited by the principal tributaries of the Amazon River and the Andes, suggesting that these modern barriers limit gene flow and thereby could have promoted differentiation mostly during the Pleistocene. However, our results indicate widely disparate responses to individual barriers across subclades, supporting lineage‐specific histories throughout the Neotropics.     

Five Cryptic Species in the Amazonian Catfish Centromochlus existimatus Identified Based on Biogeographic Predictions and Genetic Data

Accurately quantifying biodiversity is fundamental for both evolutionary theory and conservation strategies. DNA-based studies are exposing high cryptic diversity irrespective of taxonomic group or environmental setting, and increasing the ever-growing estimates of global biodiversity. This has severe implications for under-sampled and species-rich tropical regions, such as the Amazon Basin. We used biogeographic predictions derived from geomorphological history and contemporary hydrochemical and genetic data to examine cryptic diversity in the Amazonian driftwood catfish Centromochlus existimatus. Using both nuclear and mitochondrial DNA markers, five deeply divergent cryptic lineages are reported, for which at least three are sympatric in distribution. These lineages appear relatively old, with divergence times dating back to middle Miocene. Diversification events appear to be chronologically associated with the formation of the modern Amazon River system, and perhaps influenced by hydrochemical gradients between tributaries. The cause of apparent morphological stasis in the C. existimatus species complex is speculated within the context of hydrochemistry and non-visual mating cues and a full taxonomic revision is recommended. Our findings suggest that the diversity of Amazonian ichthyofauna is vastly underestimated and highlight the relevance of biogeographic predictions to guide sampling efforts in ecologically complex and under-studied ecosystems.     

A molecular phylogeny of the neotropical butterfly genus Anartia (Lepidoptera: Nymphalidae)

While Anartia butterflies have served as model organisms for research on the genetics of speciation, no phylogeny has been published to describe interspecific relationships. Here, we present a molecular phylogenetic analysis of Anartia species relationships, using both mitochondrial and nuclear genes. Analyses of both data sets confirm earlier predictions of sister species pairings based primarily on genital morphology. Yet both the mitochondrial and nuclear gene phylogenies demonstrate that Anartia jatrophae is not sister to all other Anartia species, but rather that it is sister to the Anartia fatima-Anartia amathea lineage. Traditional biogeographic explanations for speciation across the genus relied on A. jatrophae being sister to its congeners. These explanations invoked allopatric divergence of sister species pairs and multiple sympatric speciation events to explain why A. jatrophae flies alongside all its congeners. The molecular phylogenies are more consistent with lineage divergence due to vicariance, and range expansion of A. jatrophae to explain its sympatry with congeners. Further interpretations of the tree topologies also suggest how morphological evolution and eco-geographic adaptation may have set species range boundaries.     

PHYLOGENIES WITHOUT FOSSILS

Phylogenies that are reconstructed without fossil material often contain approximate dates for lineage splitting. For example, particular nodes on molecular phylogenies may be dated by known geographic events that caused lineages to split, thereby calibrating a molecular clock that is used to date other nodes. On the one hand, such phylogenies contain no information about lineages that have become extinct. On the other hand, they do provide a potentially useful testing ground for ideas about evolutionary processes. Here we first ask what such reconstructed phylogenies should be expected to look like under a birth-death process in which the birth and death parameters of lineages remain constant through time. We show that it is possible to estimate both the birth and death rates of lineages from the reconstructed phylogenies, even though they contain no explicit information about extinct lineages. We also show how such phylogenies can reveal mass extinctions and how their characteristic footprint can be distinguished from similar ones produced by density-dependent cladogenesis.     

Phylogeny and comparative biogeography of Pionopsitta parrots and Pteroglossus toucans

Studies of Neotropical birds, and their distributions and areas of endemism, in particular, have been central in the formulation of hypotheses proposed to explain the high species diversity in the Neotropics. We used mtDNA sequence data (ATPase 6 and 8, COI, and cyt b) to reconstruct the species-level phylogenies for two genera, Pionopsitta (Aves: Psittacidae) and Pteroglossus (Aves: Ramphastidae), compare our results with previous morphology-based phylogenetic analyses, and estimate the absolute timing of lineage and biogeographic divergences. Both the Pionopsitta and Pteroglossus phylogenies support a hypothesis of area relationships in which a divergence of the Serra do Mar (Atlantic Forest, Brazil) region of endemism is followed by the divergence of cis- and trans-Andean regions, then a split between the upper and lower Amazon basin, next the divergence of the Guyana area, and finally diversification of taxa in the upper Amazon basin's areas of endemism. Phylogenies of both genera support a hypothesis of area relationships that is similar to that proposed by Prum [XIX International Ornithological Congress (1988), 2562] for high-vagility species, but while they agree on the relative timing of area divergence (vicariance) events, they yield different absolute time estimates for those divergences when the typical avian mtDNA clock calibration is used. Taken at face value, the time estimates indicate that both genera began to diversify before the start of the Pleistocene, and that climatic and habitat shifts alone do not account for the diversification of these taxa.     

From shallow to deep divergences: mixed messages from Amazon Basin cichlids

Cichlids are a conspicuous component of Amazonian ichthyofauna, filling a wide range of niches. Yet taxonomy of many groups is still poorly known in the Amazon, and most of the yet-to-be discovered species are concentrated there. We analyzed 230 individuals sampled from six major Amazonian River Basins representing 56 morpho-species, 34 nominal and 22 undescribed species in 18 cichlid genera. We used four different single-locus species-discovery (SLSD) methods, delimiting between 53 (mPTP) and 57 (GMYC) species/lineages. When detected, species/lineages are hierarchically geographically structured. Many groups such as the Geophaginae and the Cichlinae have recently diversified, and species of genera such as Cichla and Symphysodon hybridize or have a history of hybridization; thus, these species will not be detected by SLSD methods. At the same time, for example, the genera Apistogramma and Biotodoma harbor cryptic species. For all these reasons, species/lineage diversity of Amazonian cichlids is significantly underestimated. The diversity of Amazonian cichlids is particularly remarkable given that the 570 species of Neotropical cichlids, many of which are from the Amazon Basin, are found in just 1.7% of the freshwater aquatic habitat in which the ~ 2,000 species of the East African rift lake cichlids evolved.

     

Correlating early evolution of parasitic platyhelminths to Gondwana breakup

Investigating patterns and processes of parasite diversification over ancient geological periods should involve comparisons of host and parasite phylogenies in a biogeographic context. It has been shown previously that the geographical distribution of host-specific parasites of sarcopterygians was guided, from Palaeozoic to Cainozoic times, mostly by evolution and diversification of their freshwater hosts. Here, we propose phylogenies of neobatrachian frogs and their specific parasites (Platyhelminthes, Monogenea) to investigate coevolutionary processes and historical biogeography of polystomes and further discuss all the possible assumptions that may account for the early evolution of these parasites. Phylogenetic analyses of concatenated rRNA nuclear genes (18S and partial 28S) supplemented by cophylogenetic and biogeographic vicariance analyses reveal four main parasite lineages that can be ascribed to centers of diversity, namely Australia, India, Africa, and South America. In addition, the relationships among these biogeographical monophyletic groups, substantiated by molecular dating, reflect sequential origins during the breakup of Gondwana. The Australian polystome lineage may have been isolated during the first stages of the breakup, whereas the Indian lineage would have arisen after the complete separation of western and eastern Gondwanan components. Next, polystomes would have codiverged with hyloid sensu stricto and ranoid frog lineages before the completion of South American and African plate separation. Ultimately, they would have undergone an extensive diversification in South America when their ancestral host families diversified. Therefore, the presence of polystome parasites in specific anuran host clades and in discrete geographic areas reveals the importance of biogeographic vicariance in diversification processes and supports the occurrence and radiation of amphibians over ancient and recent geological periods.     

Deep-sea squat lobster biogeography (Munidopsidae: Leiogalathea) unveils Tethyan vicariance and evolutionary patterns shared by shallow-water relatives

The ecology, abundance and diversity of galatheoid squat lobsters make them an ideal group to study deep-sea diversification processes. Here, we reconstructed the evolutionary and biogeographic history of Leiogalathea, a genus of circum-tropical deep-sea squat lobsters, in order to compare patterns and processes that have affected shallow-water and deep-sea squat lobster species. We first built a multilocus phylogeny and a calibrated species tree with a relaxed clock using StarBEAST2 to reconstruct evolutionary relationships and divergence times among Leiogalathea species. We used BioGeoBEARS and a DEC model, implemented in RevBayes, to reconstruct ancestral distribution ranges and the biogeographic history of the genus. Our results showed that Leiogalathea is monophyletic and comprises four main lineages; morphological homogeneity is common within and between clades, except in one; the reconstructed ancestral range of the genus is in the Atlantic and Indian oceans (Tethys). They also revealed the divergence of the Atlantic species around 25 million years ago (Ma), intense cladogenesis 15–25 Ma and low levels of speciation over the last 5 million years (Myr). The four Leiogalathea lineages showed similar patterns of speciation: allopatric speciation followed by range expansion and subsequent stasis. Leiogalathea started diversifying during the Oligocene, likely in the Tethyan. The Atlantic lineage then split from its Indo-Pacific sister group due to vicariance driven by closure of the Tethys Seaway. The Atlantic lineage is less speciose compared with the Indo-Pacific lineages, with the Tropical Southwestern Pacific being the current centre of diversity. Leiogalathea diversification coincided with cladogenetic peaks in shallow-water genera, indicating that historical biogeographic events similarly shaped the diversification and distribution of both deep-sea and shallow-water squat lobsters.     

Avian host composition,local speciation and dispersal drive the regional assembly of avian malaria parasites in South American birds

Identifying the ecological factors that shape parasite distributions remains a central goal in disease ecology. These factors include dispersal capability, environmental filters and geographic distance. Using 520 haemosporidian parasite genetic lineages recovered from 7,534 birds sampled across tropical and temperate South America, we tested (a) the latitudinal diversity gradient hypothesis and (b) the distance–decay relationship (decreasing proportion of shared species between communities with increasing geographic distance) for this host–parasite system. We then inferred the biogeographic processes influencing the diversity and distributions of this cosmopolitan group of parasites across South America. We found support for a latitudinal gradient in diversity for avian haemosporidian parasites, potentially mediated through higher avian host diversity towards the equator. Parasite similarity was correlated with climate similarity, geographic distance and host composition. Local diversification in Amazonian lineages followed by dispersal was the most frequent biogeographic events reconstructed for haemosporidian parasites. Combining macroecological patterns and biogeographic processes, our study reveals that haemosporidian parasites are capable of circumventing geographic barriers and dispersing across biomes, although constrained by environmental filtering. The contemporary diversity and distributions of haemosporidian parasites are mainly driven by historical (speciation) and ecological (dispersal) processes, whereas the parasite community assembly is largely governed by host composition and to a lesser extent by environmental conditions.     

Gene trees,species and species trees in the <Emphasis Type="Italic">Ctenosaura palearis</Emphasis> clade

The growing use of molecular systematics in conservation has increased the importance of accurate resolution of taxonomic units and relationships. DNA data relate most directly to genealogies, which need not have perfect relationships with species limits and phylogenies. We used a multilocus gene tree approach to elucidate the relationships between four endangered Central American iguanas. We found support for the proposition that the described species taxa correspond to distinct evolutionary lineages warranting individual protection. We combined gene trees to estimate a phylogeny using Bayesian Estimation of Species Trees (BEST), minimizing deep coalescence, Species Trees from Average Ranks (STAR), and traditional concatenation. The estimate from concatenation conflicted with the other methods, likely owing to the disproportionate effect of mtDNA on concatenated analyses. This illustrates the importance of appropriate treatment of multilocus sequence data in phylogenetics. Our results indicate that these species have gone through recent and rapid speciation, resulting in four closely related narrow-range endemics.     

Molecular systematic analysis reveals cryptic tertiary diversification of a widespread tropical rain forest tree

The broad geographic range of many Neotropical rain forest tree species implies excellent dispersal abilities or range establishment that preceded the formation of current dispersal barriers. In order to initiate historical analyses of such widespread Neotropical trees, we sequenced the nuclear ribosomal spacer (ITS) region of Symphonia globulifera L. f. (Clusiaceae) from populations spanning the Neotropics and western Africa. This rain forest tree has left unmistakable Miocene fossils in Mesoamerica (15.5-18.2 Ma) and in South America ( approximately 15 Ma). Although marine dispersal of S. globulifera is considered improbable, our study establishes three marine dispersal events leading to the colonization of Mesoamerica, the Amazon basin, and the West Indies, thus supporting the paleontological data. Our phylogeographic analysis revealed the spatial extent of the three Neotropical S. globulifera clades, which represent trans-Andes (Mesoamerica+west Ecuador), cis-Andes (Amazonia+Guiana), and the West Indies. Strong phylogeographic structure found among trans-Andean populations of S. globulifera stands in contrast to an absence of ITS nucleotide variation across the Amazon basin and indicates profound regional differences in the demographic history of this rain forest tree. Drawing from these results, we provide a historical biogeographic hypothesis to account for differences in the patterns of beta diversity within Mesoamerican and Amazonian forests.     

Temporal and spatial diversification of Pteroglossus araçaris (AVES: Ramphastidae) in the neotropics: constant rate of diversification does not support an increase in radiation during the Pleistocene

We use the small-bodied toucan genus Pteroglossus to test hypotheses about diversification in the lowland Neotropics. We sequenced three mitochondrial genes and one nuclear intron from all Pteroglossus species and used these data to reconstruct phylogenetic trees based on maximum parsimony, maximum likelihood, and Bayesian analyses. These phylogenetic trees were used to make inferences regarding both the pattern and timing of diversification for the group. We used the uplift of the Talamanca highlands of Costa Rica and western Panama as a geologic calibration for estimating divergence times on the Pteroglossus tree and compared these results with a standard molecular clock calibration. Then, we used likelihood methods to model the rate of diversification. Based on our analyses, the onset of the Pteroglossus radiation predates the Pleistocene, which has been predicted to have played a pivotal role in diversification in the Amazon rainforest biota. We found a constant rate of diversification in Pteroglossus evolutionary history, and thus no support that events during the Pleistocene caused an increase in diversification. We compare our data to other avian phylogenies to better understand major biogeographic events in the Neotropics. These comparisons support recurring forest connections between the Amazonian and Atlantic forests, and the splitting of cis/trans Andean species after the final uplift of the Andes. At the subspecies level, there is evidence for reciprocal monophyly and groups are often separated by major rivers, demonstrating the important role of rivers in causing or maintaining divergence. Because some of the results presented here conflict with current taxonomy of Pteroglossus, new taxonomic arrangements are suggested.     

Molecular studies of photobionts of selected lichens from the coastal vegetation of Brazil

A light microscopic and molecular analysis of photobionts in Ramalina and Cladonia from coastal habitats of Brazil is presented. A Bayesian phylogenetic analysis of ITS rDNA sequences suggests a Trebouxia lineage which is preferentially tropical in geographic distribution. This highly diverse clade also includes the morphological similar species Trebouxia higginsiae and galapagensis. Within the predominantly tropical clade of Trebouxia we distinguish several subclades, three of which are represented in our samples of Ramalina species. Since sexuality has not been recognized in coccal lichenised photobionts until recently, we cannot apply a biological species concept, but when compared with the sequence diversity between known species we conclude that several new species need to be described in this clade. The mutually exclusive presence of other Trebouxia lineages in temperate samples of Ramalina suggests an evolution towards higher selectivity in this genus. A strictly tropical lineage is not conspicuous in the photobionts of the genus Asterochloris sampled from Cladonia so far.     

Inferring species networks from gene trees in high-polyploid North American and Hawaiian violets (Viola, Violaceae)

The phylogenies of allopolyploids take the shape of networks and cannot be adequately represented as bifurcating trees. Especially for high polyploids (i.e., organisms with more than six sets of nuclear chromosomes), the signatures of gene homoeolog loss, deep coalescence, and polyploidy may become confounded, with the result that gene trees may be congruent with more than one species network. Herein, we obtained the most parsimonious species network by objective comparison of competing scenarios involving polyploidization and homoeolog loss in a high-polyploid lineage of violets (Viola, Violaceae) mostly or entirely restricted to North America, Central America, or Hawaii. We amplified homoeologs of the low-copy nuclear gene, glucose-6-phosphate isomerase (GPI), by single-molecule polymerase chain reaction (PCR) and the chloroplast trnL-F region by conventional PCR for 51 species and subspecies. Topological incongruence among GPI homoeolog subclades, owing to deep coalescence and two instances of putative loss (or lack of detection) of homoeologs, were reconciled by applying the maximum tree topology for each subclade. The most parsimonious species network and the fossil-based calibration of the homoeolog tree favored monophyly of the high polyploids, which has resulted from allodecaploidization 9-14 Ma, involving sympatric ancestors from the extant Viola sections Chamaemelanium (diploid), Plagiostigma (paleotetraploid), and Viola (paleotetraploid). Although two of the high-polyploid lineages (Boreali-Americanae, Pedatae) remained decaploid, recurrent polyploidization with tetraploids of section Plagiostigma within the last 5 Ma has resulted in two 14-ploid lineages (Mexicanae, Nosphinium) and one 18-ploid lineage (Langsdorffianae). This implies a more complex phylogenetic and biogeographic origin of the Hawaiian violets (Nosphinium) than that previously inferred from rDNA data and illustrates the necessity of considering polyploidy in phylogenetic and biogeographic reconstruction.     

Population analysis using the nuclear white gene detects Pliocene/Pleistocene lineage divergence within Anopheles nuneztovari in South America

Anopheles (Nyssorhynchus) nuneztovari Gabaldón (Diptera: Culicidae), a locally important malaria vector in some regions of South America, has been hypothesized to consist of at least two cryptic incipient species. We investigated its phylogeographic structure in several South American localities to determine the number of lineages and levels of divergence using the nuclear white gene, a marker that detected two recently diverged genotypes in the primary Neotropical malaria vector Anopheles darlingi Root. In An. nuneztovari, five distinct lineages (1-5) were elucidated: (1) populations from northeastern and central Amazonia; (2) populations from Venezuela east and west of the Andes; (3) populations from Colombia and Venezuela west of the Andes; (4) southeastern and western Amazonian Brazil populations, and (5) southeastern and western Amazonian Brazil and Bolivian populations. There was a large amount of genetic differentiation among these lineages. The deepest and earliest divergence was found between lineage 3 and lineages 1, 2 and 4, which probably accounts for the detection of lineage 3 in some earlier studies. The multiple lineages within Amazonia are partially congruent with previous mtDNA and ITS2 data, but were undetected in many earlier studies, probably because of their recent (Pleistocene) divergence and the differential mutation rates of the markers. The estimates for the five lineages, interpreted as recently evolved or incipient species, date to the Pleistocene and Pliocene. We hypothesize that the diversification in An. nuneztovari is the result of an interaction between the Miocene/Pliocene marine incursion and Pleistocene climatic changes leading to refugial isolation. The identification of cryptic lineages in An. nuneztovari could have a significant impact on local vector control measures.     

Mitochondrial DNA phylogeography of Caiman crocodilus in Mesoamerica and South America

The Neotropical crocodylian species, Caiman crocodilus, is widely distributed through Mesoamerica, northern South America, and the Amazon basin. Four subspecies are recognized within C. crocodilus, suggesting some geographic variation in morphology. In this study, we utilized mitochondrial DNA (mtDNA) sequence data from 45 individuals of C. crocodilus throughout its range to infer its evolutionary history and population structure, as well as to evaluate genealogical support for subspecies and their geographic distributions. Our molecular phylogenetic results identified five mtDNA haplotype clades with a mean sequence divergence of 3.4%, indicating considerable evolutionary independence among phylogeographic lineages. Our results were also broadly consistent with current subspecific taxonomy, with some important additional findings. First, we found substantial genetic structuring within C. c. fuscus from southern Mesoamerica. Second, though we confirmed the existence of a widespread Amazonian clade, we also discovered a cryptic and divergent mtDNA lineage that was indistinguishable from C. c. crocodilus based on external morphology. Third, we confirm the status of C. c. chiapasius as a distinct evolutionary lineage, and provide evidence that C. c. fuscus may be moving northward and hybridizing with C. c. chiapasius in northern Mesoamerica. Finally, our results parallel previous phylogeographic studies of other organisms that have demonstrated significant genetic structure over shorter geographic distances in Mesoamerica compared with Amazonia. We support conservation efforts for all five independent lineages within C. crocodilus, and highlight the subspecies C. c. chiapasius as a unit of particular conservation concern.     

Molecular systematics and phylogeography of Amazonian poison frogs of the genus Dendrobates

The study of Amazonian biodiversity requires detailed knowledge of the phylogenetic relationships of closely related taxa distributed across Amazonia. The Amazonian poison frogs of the genus Dendrobates have undergone many taxonomic revisions, but the phylogenetic relationships within this group remain poorly understood. Most previous classifications were based on morphology and skin toxin analyses, with limited use of DNA sequence data. Using mtDNA sequence data from four gene regions (cytochrome b, cytochrome oxidase I, 16S rRNA, and 12S rRNA), we present a molecular phylogenetic analysis of the evolutionary relationships within a representative group of Amazonian Dendrobates. We use the resulting phylogenetic hypothesis to investigate different biogeographic hypotheses concerning genetic divergence and species diversity in Amazonia. The results of the analysis support the presence of ancient paleogeographic barriers to gene flow between eastern and western Amazonia, and indicate substantial genetic divergence between species found in the northern and southern regions of western Amazonia.