Molecular Phylogenetic Relationships Among Crested-tailed Mice (Genus <Emphasis Type="Italic">Habromys</Emphasis>)

We examined genealogical relationships among six of seven species of crested-tailed mice (Habromys chinanteco, H. delicatulus, H. ixtlani, H. lepturus, H. lophurus, and H. simulatus) using DNA sequence data from the cytochrome-b gene. Gene trees based on maximum likelihood, Bayesian inference and maximum parsimony were largely congruent in that H. lepturus and H. ixtlani were closely related and formed the sister group to H. lophurus. All analyses also arranged H. chinanteco and H. simulatus as sister taxa. These results are concordant with the phenetic groupings of Carleton et al. (2002) based on morphology. Our unweighted maximum parsimony trees did not resolve placement of H. delicatulus relative to other taxa. However, analyses using weighted maximum parsimony, maximum likelihood and Bayesian inference optimality criteria recovered a sister group relationship between H. delicatulus and the clade comprised of ((H. lepturus H. ixtlani)(H. lophurus)). This relationship differs from the overall phenetic similarity of H. delicatulus with H. simulatus and H. chinanteco, influenced by the small size of these three taxa, but is consistent with some derived features of the phallus (Carleton et al., 2002). Based on our sequence data, a specimen from Michoacán, México, recently assigned to Peromyscus sagax likely was inadvertently misidentified (Tiemann-Boege et al., 2000) and actually represents a new locality record for H. delicatulus. Finally, we comment on the conservation status of species of Habromys.     

Fundamental biogeographic patterns across the Mexican Transition Zone: an evolutionary approach

Transition zones, located at the boundaries between biogeographic regions, represent events of biotic hybridization, promoted by historical and ecological changes. They deserve special attention, because they represent areas of intense biotic interaction. In its more general sense, the Mexican Transition Zone is a complex and varied area where Neotropical and Nearctic biotas overlap, from southwestern USA to Mexico and part of Central America, extending south to the Nicaraguan lowlands. In recent years, panbiogeographic analyses have led to restriction of the Mexican Transition Zone to the montane areas of Mexico and to recognize five smaller biotic components within it. A cladistic biogeographic analysis challenged the hypothesis that this transition zone is biogeographically divided along a north‐south axis at the Transmexican Volcanic Belt, as the two major clades found divided Mexico in an east‐west axis. This implies that early Tertiary geological events leading to the convergence of Neotropical and Nearctic elements may be younger (Miocene) than those that led to the east‐west pattern (Paleocene). The Mexican Transition Zone consists of five biogeographic provinces: Sierra Madre Occidental, Sierra Madre Oriental, Transmexican Volcanic Belt, Sierra Madre del Sur, and Chiapas. Within this transition zone, at least four cenocrons have been identified: Paleoamerican, Nearctic, Montane Mesoamerican, and Tropical Mesoamerican. Future studies should continue refining the identification of cenocrons and the reconstruction of a geobiotic scenario, as well as integrating ecological biogeographic studies, to allow a more complete understanding of the patterns and processes that have caused the biotic complexity of this transition zone.     

Phylogeography of the bark beetle Dendroctonus mexicanus Hopkins (Coleoptera: Curculionidae: Scolytinae)

Dendroctonus mexicanus is polyphagous within the Pinus genus and has a wide geographical distribution in Mexico and Guatemala. We examined the pattern of genetic variation across the range of this species to explore its demographic history and its phylogeographic pattern. Analysis of the mtDNA sequences of 173 individuals from 25 Mexican populations allowed to us identify 53 geographically structured haplotypes. High haplotype and low nucleotide diversities and Tajima’s D indicate that D. mexicanus experienced rapid population expansion during its dispersal across mountain systems within its current range. The nested clade phylogeographic analysis indicates that the phylogeographic pattern of D. mexicanus is explained by continuous dispersion among lineages from the Sierra Madre Occidental, the Sierra Madre Oriental and the Trans-Mexican Volcanic Belt. However, we also observed isolation events among haplotypes from the Cofre de Perote/Trans-Mexican Volcanic Belt/Sierra Madre Oriental and the Trans-Mexican Volcanic Belt/Sierra Madre del Sur, which is consistent with the present conformation of mountain systems in Mexico and the emergence of geographical barriers during the Pleistocene.     

Do the Oaxacan Highlands represent a natural biotic unit? A cladistic biogeographical test based on vertebrate taxa

Aim  We analysed the distributional patterns of six terrestrial vertebrate taxa from the Oaxacan Highlands (Sierra Mazateca, Nudo de Zempoaltépetl and Sierra de Juárez) through a cladistic biogeographical approach, in order to test their naturalness as a biotic unit.
Location  The Oaxacan Highlands, Mexico.
Methods  The cladistic biogeographical analysis was based on the area cladograms of the Pseudoeurycea bellii species group (Amphibia: Plethodontidae), the genus Chlorospingus (Aves: Thraupidae), the genera Microtus , Reithrodontomys and Habromys , and the Peromyscus aztecus species group (Mammalia: Rodentia). We obtained paralogy-free subtrees, from which the components were coded in a data matrix for parsimony analysis. The data matrix was analysed with N ona through W in C lada .
Results  The parsimony analysis resulted in a single general area cladogram in which areas were fragmented following the sequence Sierra Madre Occidental, Trans-Mexican Volcanic Belt, Chiapas, Sierra Madre Oriental + Sierra Mazateca, Sierra Madre del Sur, Nudo de Zempoaltépetl and Sierra de Juárez.
Main conclusions  The general area cladogram shows that the Oaxacan Highlands do not constitute a natural unit. The Sierra Mazateca is the sister area to the Sierra Madre Oriental, whereas the Nudo de Zempoaltépetl and the Sierra de Juárez are closely related to the Sierra Madre del Sur. The events that might have caused these patterns include cycles of expansion and contraction of mountain pinyon, juniper and oak woodlands during the Pleistocene.     

Historical biogeography of the genus Rhadinaea (Squamata: Dipsadinae)

Multiple geological and climatic events have created geographical or ecological barriers associated with speciation events, playing a role in biological diversification in North and Central America. Here, we evaluate the influence of the Neogene and Quaternary geological events, as well as the climatic changes in the diversification of the colubrid snake genus Rhadinaea using molecular dating and ancestral area reconstruction. A multilocus sequence dataset was generated for 37 individuals of Rhadinaea from most of the biogeographical provinces where the genus is distributed, representing 19 of the 21 currently recognized species, and two undescribed species. Our analyses show that the majority of the Rhadinaea species nest in two main clades, herein identified as “Eastern” and “Southern”. These clades probably diverged from each other in the early Miocene, and their divergence was followed by 11 divergences during the middle to late Miocene, three divergences during the Pliocene, and six divergences in the Pleistocene. The ancestral distribution of Rhadinaea was reconstructed across the Sierra Madre del Sur. Our phylogenetic analyses do not support the monophyly of Rhadinaea. The Miocene and Pliocene geomorphology, perhaps in conjunction with climate change, appears to have triggered the diversification of the genus, while the climatic changes during the Miocene probably induced the diversification of Rhadinaea in the Sierra Madre del Sur. Our analysis suggests that the uplifting of the Trans‐Mexican Volcanic Belt and Chiapan–Guatemalan highlands in this same period resulted in northward and southward colonization events. This was followed by more recent, independent colonization events in the Pliocene and Pleistocene involving the Balsas Basin, Chihuahuan Desert, Pacific Coast, Sierra Madre Occidental, Sierra Madre Oriental, Sierra Madre del Sur, Trans‐Mexican Volcanic Belt, and Veracruz provinces, probably driven by the climatic fluctuations of the time.     

Halffter's Mexican transition zone (1962–2014), cenocrons and evolutionary biogeography

The Mexican transition zone is the complex and varied area in which the Neotropical and Nearctic biotas overlap. In a series of contributions, Gonzalo Halffter provided a coherent theory that explains how sets of taxa that evolved in different geographical areas assembled in this transition zone. Halffter's theory developed gradually, being refined and clarified in successive contributions from him and other authors. After a review of the historical development of the Mexican transition zone, including the characterization of the dispersal or distributional patterns recognized by Halffter, its relevance for evolutionary biogeography is discussed briefly. The Mexican transition zone in the strict sense includes the highlands of Mexico and Guatemala (Sierra Madre Occidental, Sierra Madre Oriental, Transmexican Volcanic Belt, Sierra Madre del Sur and Chiapas Highlands provinces), whereas northern Mexico and the southern United States are clearly Nearctic, and the lowlands of southern Mexico and Central America are clearly Neotropical. The distributional patterns recognized by Halffter are considered to represent cenocrons (sets of taxa that share the same biogeographical history, constituting identifiable subsets within a biota by their common biotic origin and evolutionary history). The development of the Mexican transition zone is summarized into the following stages: (1) Jurassic–Cretaceous: the four Paleoamerican cenocrons extend in Mexico; (2) Late Cretaceous–Palaeocene: dispersal from South America of the Plateau cenocron; (3) Oligocene–Miocene: dispersal from the Central American Nucleus of the Mountain Mesoamerican cenocron; (4) Miocene–Pliocene: dispersal from North America of the Nearctic cenocron; and (5) Pleistocene: dispersal from South America of the Typical Neotropical cenocron.     

Molecular systematics of a speciose, cosmopolitan songbird genus: defining the limits of, and relationships among, the Turdus thrushes

The avian genus Turdus is one of the most speciose and widespread of passerine genera. We investigated phylogenetic relationships within this genus using mitochondrial DNA sequence data from the ND3, ND2 and cytochrome b genes. Our sampling of Turdus included 60 of the 65 extant species currently recognized, as well as all four species from three genera previously shown to fall inside Turdus (Platycichla, Nesocichla, and Cichlherminia). Phylogenetic trees based on maximum likelihood and maximum parsimony algorithms were congruent. Most of the Turdus taxa sampled fall into one of four clades: an African clade, a Central American-Caribbean clade, a largely South American clade, and a Eurasian clade. Still other taxa are placed either at the base of Turdus, or as links between clades. In no instance is any continent reciprocally monophyletic for the species distributed on it. A general lack of nodal support near the base of the phylogeny seems related to a rapid intercontinental establishment of the major clades within Turdus very early in the history of the genus. The monotypic genus Psophocichla is distantly related to, but clearly the sister of, Turdus rather than a constituent member of it.     

Cenozoic biogeography and evolution in direct-developing frogs of Central America (Leptodactylidae: Eleutherodactylus) as inferred from a phylogenetic analysis of nuclear and mitochondrial genes

We report the first phylogenetic analysis of DNA sequence data for the Central American component of the genus Eleutherodactylus (Anura: Leptodactylidae: Eleutherodactylinae), one of the most ubiquitous, diverse, and abundant components of the Neotropical amphibian fauna. We obtained DNA sequence data from 55 specimens representing 45 species. Sampling was focused on Central America, but also included Bolivia, Brazil, Jamaica, and the USA. We sequenced 1460 contiguous base pairs (bp) of the mitochondrial genome containing ND2 and five neighboring tRNA genes, plus 1300 bp of the c-myc nuclear gene. The resulting phylogenetic inferences were broadly concordant between data sets and among analytical methods. The subgenus Craugastor is monophyletic and its initial radiation was potentially rapid and adaptive. Within Craugastor, the earliest splits separate three northern Central American species groups, milesi, augusti, and alfredi, from a clade comprising the rest of Craugastor. Within the latter clade, the rhodopis group as formerly recognized comprises three deeply divergent clades that do not form a monophyletic group; we therefore restrict the content of the rhodopis group to one of two northern clades, and use new names for the other northern (mexicanus group) and one southern clade (bransfordii group). The new rhodopis and bransfordii groups together form the sister taxon to a clade comprising the biporcatus, fitzingeri, mexicanus, and rugulosus groups. We used a Bayesian MCMC approach together with geological and biogeographic assumptions to estimate divergence times from the combined DNA sequence data. Our results corroborated three independent dispersal events for the origins of Central American Eleutherodactylus: (1) an ancestor of Craugastor entered northern Central America from South American in the early Paleocene, (2) an ancestor of the subgenus Syrrhophus entered northern Central America from the Caribbean at the end of the Eocene, and (3) a wave of independent dispersal events from South America coincided with formation of the Isthmus of Panama during the Pliocene. We elevate the subgenus Craugastor to the genus rank.     

Phylogeny of South American Bufo (Anura: Bufonidae) inferred from combined evidence

Despite the considerable research that has focused on the evolutionary relationships and biogeography of the genus Bufo, an evolutionary synthesis of the entire group has not yet emerged. In the present study, almost 4 kb of DNA sequence data from mitochondrial (12S, tRNA^Val, and 16S) and nuclear (POMC; Rag-1) genes, and 83 characters from morphology were analysed to infer a phylogeny of South American toads. Phylogenies were reconstructed with parsimony and maximum likelihood and Bayesian model-based methods. The results of the analysis of morphological data support the hypothesis that within Bufo , some skull characters (e.g. frontoparietal width), correlated with the amount of cranial ossification, are prone to homoplasy. Unique and unreversed morphological synapomorphies are presented that can be used to diagnose recognized species groups of South American toads. The results of all phylogenetic analyses support the monophyly of most species groups of South American Bufo . In most DNA-only and combined analyses, the South American (minus the B. guttatus and part of the ' B. spinulosus ' groups), North American, Central American, and African lineages form generally well-supported clades: ((((((((South America) (North America + Central America)) Eurasia) Africa) Eurasia) South America) West Indies) South America). This result confirms and extends prior studies recovering South American Bufo as polyphyletic. The biogeographical results indicate that: (1) The origin of Bufo predates the fragmentation of Gondwana; (2) Central and North American species compose the sister group to a large, 'derived' clade of South American Bufo ; and (3) Eurasian species form the sister group to the New World clade.  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 146 , 407–452.     

Evolution of Galapagos Island Lava Lizards (Iguania: Tropiduridae: Microlophus)

Nucleotide sequences of mitochondrial genes (ND1, ND2, COI, and tRNAs) were determined for 38 samples representing 15 taxa of tropidurid lizards from the Galapagos Islands and mainland South America. Phylogenetically informative characters (759 of 1,956) were analyzed under Bayesian, maximum likelihood, and parsimony frameworks. This study supports the hypothesis that tropidurid lizards dispersed to the Galapagos on at least two separate occasions. One dispersal event involved an eastern Galapagos clade (Microlophus habelii and M. bivittatus, on Marchena and San Cristobal islands, respectively) the sister taxon of which is M. occipitalis from coastal Ecuador and Peru; the closest mainland relative of the western Galapagos clade was not unambiguously identified. The wide-ranging M. albemarlensis is revealed to be a complex of weakly divergent lineages that is paraphyletic with respect to the insular species M. duncanensis, M. grayii, and M. pacificus.     

Species delimitation in the continental forms of the genus Epicrates (Serpentes, Boidae) integrating phylogenetics and environmental niche models

Until recently, the genus Epicrates (Boidae) presented only one continental species, Epicrates cenchria, distributed in Central and South America, but after a taxonomic revision using morphologic characters five species were recognized: E. cenchria, E. crassus, E. maurus, E. assisi, and E. alvarezi. We analyzed two independent data sets, environmental niche models and phylogeny based on molecular information, to explore species delimitation in the continental species of this genus. Our results indicated that the environmental requirements of the species are different; therefore there are not evidences of ecological interchangeability among them. There is a clear correlation between species distributions and the major biogeographic regions of Central and South America. Their overall distribution reveals that allopatry or parapatry is the general pattern. These evidences suggest that habitat isolation prevents or limits gene exchange among them. The phylogenetic reconstruction showed that the continental Epicrates are monophyletic, being E. alvarezi the sister species for the remaining two clades: E. crassus-E. assisi, and E. maurus-E. cenchria. The clade grouping the continental Epicrates is the sister taxon of the genus Eunectes and not of the Caribbean Epicrates clade, indicating that the genus is paraphyletic. There is a non-consistent pattern in niche evolution among continental Epicrates. On the contrary, a high variation and abrupt shifts in environmental variables are shown when ancestral character states were reconstructed on the sequence-based tree. The degree of genetic and ecological divergence among continental Epicrates and the phylogenetic analyses support the elevation to full species of E. cenchria, E. crassus, E. maurus, E. assisi, and E. alvarezi.     

Local origin and diversification among Lampornis hummingbirds: a Mesoamerican taxon

The huge biodiversity found in Mesoamerica is often explained by its geographic situation as a natural bridge between two large biogeographic regions. Often overlooked, however, are the high levels of speciation and diversification in the area. Here we assess the phylogenetic relationships within a Mesoamerican group of hummingbirds (Lampornis). We sequenced both mtDNA (1,143 bp of cyt b and 727 bp of ND5) and nuclear genes (505 bp of AK-5 intron and 567 bp of c-mos) for each of the seven recognised species and outgroups. We find two or three clades of similar age within this genus: L. clemenciae and L. amethystinus (singly or as each other's sister taxa) and a Central American clade. This Central-American clade presents a clear bipartition between northern (L. viridipallens and L. sybillae) and southern Mesoamerica, which is shared with many other Mesoamerican organisms. Our analyses suggest that L. hemileucus does not belong in the genus Lampornis. While we refrain to apply a time-scale to our data because of the lack of an appropriate calibration, our results indicate that the genus Lampornis predates the uprising of the Panama land-bridge, and that diversification among the isthmian species (L. castaneoventris and L. calolaema) is a very recent event. Our results strongly suggest a local Mesoamerican origin for this genus.     

Priority areas for the conservation of the genus Abies Mill. (Pinaceae) in North America

Fir forests (Abies, Pinaceae) are dominant in temperate regions of North America; however, they have experienced high degradation rates that can threaten their long-term continuity. This study aimed to identify the priority areas for the conservation of the genus Abies in North America. First, we modeled the species distribution of the 17 native species through ecological niche modeling, considering 21 environmental variables. Then, we defined the priority areas through multi-criteria analysis, considering the species richness, geographic rareness, irreplaceability, habitat degradation, and risk extinction. We also built six scenarios, giving more priority to each criterion. Finally, we identified the proportion of the extent of the priority areas covered by protected areas. Elevation, precipitation seasonality, and winter precipitation influenced the distribution of most of the Abies species. When considering equal weights to each criterion, the priority areas summed up 6% of the total extent covered by the Abies species in North America. Most priority areas were located on the West Coast of the United States, the Eastern Sierra Madre, Southern Sierra Madre, Sierras of Chiapas and Central America, and the Trans-Mexican Volcanic Belt ecoregions. In these ecoregions, the Abies species are restricted to small areas facing high degradation levels. Only 16% of the area covered by the Abies species in North America is protected, mainly under restrictive schemes such as National Parks and Wilderness Areas. The priority areas identified could be the basis for establishing or enlarging protected areas. The preservation of the genus Abies could also maintain other ecological features and processes such as biodiversity, forest resources, and environmental services.     

Molecular systematics of the African snake family Lamprophiidae Fitzinger, 1843 (Serpentes: Elapoidea), with particular focus on the genera Lamprophis Fitzinger 1843 and Mehelya Csiki 1903

The snake family Lamprophiidae Fitzinger (Serpentes: Elapoidea) is a putatively Late Eocene radiation of nocturnal snakes endemic to the African continent. It incorporates many of the most characteristic and prolific of Africa's non-venomous snake species, including the widespread type genus Lamprophis Fitzinger, 1843 (house snakes). We used approximately 2500 bases of mitochondrial and nuclear DNA sequence data from 28 (41%) of the approximately 68 recognised lamprophiid species in nine of the eleven genera to investigate phylogenetic structure in the family and to inform taxonomy at the generic level. Cytochrome b, ND4 and tRNA gene sequences (mitochondrial) and c-mos sequences (nuclear) were analysed using Maximum Likelihood, Bayesian Inference and Maximum Parsimony methods. The genus Mehelya Csiki, 1903 was paraphyletic with respect to Gonionotophis Boulenger, 1893. To address this, the concept of Gonionotophis is expanded to include all current Mehelya species. The genus Lamprophis emerged polyphyletic: the enigmatic Lamprophis swazicus was sister to Hormonotus modestus from West Africa, and not closely related to its nominal congeners. It is moved to a new monotypic genus (Inyoka gen. nov.). The remaining Lamprophis species occur in three early-diverging lineages. (1) Lamprophis virgatus and the widely distributed Lamprophis fuliginosus species complex (which also includes Lamprophis lineatus and Lamprophis olivaceus) formed a clade for which the generic name Boaedon Duméril, Bibron & Duméril, 1854 is resurrected. (2) The water snakes (Lycodonomorphus) were nested within Lamprophis (sensu lato), sister to Lamprophis inornatus. We transfer this species to the genus Lycodonomorphus Fitzinger, 1843. (3) We restrict Lamprophis (sensu strictissimo) to a small clade of four species endemic to southern Africa: the type species of Lamprophis Fitzinger, 1843 (Lamprophis aurora) plus Lamprophis fiskii, Lamprophis fuscus and Lamprophis guttatus.     

Phylogenetic relationships of North American garter snakes (Thamnophis) based on four mitochondrial genes: how much DNA sequence is enough?

The clade of garter snakes (Thamnophis) includes some of the most abundant and well-studied snakes in North America. However, phylogenetic relationships within this group have been little studied. We used DNA sequences of four mitochondrial genes (cytochrome b and NADH dehydrogenase subunits 1, 2, and 4) to estimate relationships among 29 of the 31 recognized species of Thamnophis plus the related species Adelophis foxi. Both maximum parsimony (MP) and maximum-likelihood (ML) analyses of all these genes combined produced well-resolved trees with moderate (70-89%) to strong (90-100%) bootstrap support for most clades. MP and ML trees were very similar, with no strongly supported conflict between the two analyses. These analyses identify a clade of 12 species largely restricted to México (the "Mexican clade"), and a clade containing 15 species that collectively range from Central America to southern Canada (the "widespread clade"). These two groups are identified as sister taxa in both MP and ML analyses. A clade consisting of the ribbon snakes (T. sauritus and T. proximus) and the common garter snake (T. sirtalis) is placed as the sister group to all other Thamnophis (i.e., the Mexican + widespread clades) in our analyses. High bootstrap proportions at several levels in the tree support the inclusion of both Thamnophis validus, which has traditionally been placed in the genus Nerodia, and the poorly known species Adelophis foxi within Thamnophis. We used randomly sampled characters (i.e., standard bootstrapping) and randomly sampled contiguous blocks of characters to examine the effect of number of characters on resolution of and support for relationships within Thamnophis using MP. In general, these analyses indicate that we have reached a point of strongly diminishing returns with respect to the effect of adding mtDNA sequence characters for the current set of taxa; our sample of 3809 mtDNA characters is apparently "enough." The next steps to improve the phylogenetic estimate may be to add nuclear DNA sequences, morphology, or behavior, or to sequence additional mtDNA lineages within species.     

Molecular phylogenetic relationships of Xiphidiopicus percussus, Melanerpes, and Sphyrapicus (Aves: Picidae) based on cytochrome B sequence

The endemic woodpecker, Xiphidiopicus percussus, from Cuba has been postulated as the sister taxon to the Hispaniolan woodpecker (Melanerpes striatus) and its relationships to the genera Sphyrapicus and Melanerpes have been speculated. We used mitochondrial cytochrome b sequences from a collection of New World picids to investigate the phylogenetic relationships among these species using maximum parsimony and maximum likelihood approaches. Our data suggest that X. percussus is the sister taxon to the Melanerpes woodpeckers, which appear to group into a single distinct clade. Xiphidiopicus percussus is not the sister taxon to M. striatus as has been postulated [Olson, S., 1972. The generic distinction of the Hispaniolan Woodpecker, Chryserpes striatus (Aves: Picidae). Proc. Biol. Soc. Wash. 85, 499-508]. The genus Sphyrapicus appears to have diverged earlier than Xiphidiopicus. Divergence estimates from the cytochrome b sequences indicate that Xiphidiopicus probably diverged sometime in the late Miocene-early Pliocene, and the endemic contemporary species X. percussus on Cuba may be a relict from a group that originated in Central America or North America.     

Phylogeography of the Buarremon brush-finch complex (Aves, Emberizidae) in Mesoamerica

The Buarremon brush-finches represent a complex suite of populations distributed in the montane New World Tropics from Mexico south to South America. Traditional taxonomic arrangements have separated populations of this genus into three species, based on plumage variation, although plumage patterns are well known to exhibit homoplasy. We present a first detailed phylogeographic and phylogenetic study, focused on Mesoamerican populations, and signal the existence of strong differentiation among populations with a clear geographic structure. We find well differentiated clades for (1) the Sierra Madre Oriental and Sierra Madre del Sur in Oaxaca, (2) western Mexican populations, including the B. brunneinucha populations in the Sierra Madre del Sur and B. virenticeps, (3) Sierra Madre Oriental and Sierra de los Tuxtlas, (4) northern Central America, (5) southern Central America, (6) middle Central America, and (7) South America. We demonstrate a lack of concordance with plumage patterns, and argue for several additional species to be recognized in the complex.     

Molecular phylogenetics of Atlantic Shield Platynectes diving beetles (Coleoptera: Dytiscidae): a first glance at the evolution of the genus in the Amazon Basin

Neotropical diving beetles of the genus Platynectes are distributed across Central America, the Andes and different Precambrian shields in the Amazon Basin. Species from the northern Guiana Shield form a monophyletic clade, yet the phylogenetic relationships of the eastern Atlantic Shield species remain unknown. Here, we augmented an existing molecular dataset with a species from the Atlantic Shield that was not previously sampled. We reconstructed the phylogenetic relationships and estimated divergence times to understand the evolution of lineages dwelling in this region. The newly sampled specimens from the Atlantic Shield are recovered as sister taxa to Guiana Shield species. The dating analyses suggest a split between these two lineages in the late Oligocene to mid-Miocene, contemporary with the Miocenic geological remodeling of the Amazon Basin. Additional sampling in the Atlantic and Central Brazilian Shields will be determinant to test the monophyly of Platynectes species distributed in these ancient shields, and to fully understand the biogeographical history of diving beetles in the Amazon Basin.     

The diversification of Nearctic mammals in the Mexican transition zone

The boundary between the Nearctic and Neotropical regions has been delineated using different approaches, methods and taxa. Using a panbiogeographical approach, identification of nodes can help understand the dynamics and evolution of the boundary. We analysed the distribution patterns of 46 Mexican land mammal species belonging to the Nearctic biotic component and delineated generalized tracks and nodes, in order to determine the southernmost boundary of the Nearctic region in Mexico. We found six generalized tracks and nine nodes; the latter located largely in the Sierra Madre Oriental, Transmexican Volcanic Belt, Sierra Madre del Sur and Chiapas biogeographical provinces. The highlands of Chiapas were found to represent the southernmost area inhabited by Nearctic taxa. The other biogeographical provinces, together with the Sierra Madre Occidental and Balsas Basin provinces, represent the Mexican transition zone in the strict sense. Instead of a classic static boundary, this transition zone represents an evolutionarily 'active' zone, where several speciation events have taken place in the past.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 327–339.     

Relative roles of Neogene vicariance and Quaternary climate change on the historical diversification of bunchgrass lizards (Sceloporus scalaris group) in Mexico

Neogene vicariance during the Miocene and Pliocene and Quaternary climate change have synergistically driven diversification in Mexican highland taxa. We investigated the impacts of these processes on genetic diversification in the widely distributed bunchgrass lizards in the Sceloporus scalaris group. We searched for correlations between timing in diversification and timing of (1) a period of marked volcanism across the Trans-Mexican Volcanic Belt in central Mexico 3-7.5 million years ago (Ma) and (2) a transition to larger glacial-interglacial cycles during the mid-Pleistocene. From our phylogenetic analyses of mitochondrial DNA we identified two major clades that contained 13 strongly supported lineages. One clade contained lineages from the two northern sierras of Mexico, and the other clade included lineages associated with the Trans-Mexican Volcanic Belt and Central Mexican Plateau. Results provided support for Neogene divergences within the S. scalaris group in response to uplift of the Trans-Mexican Volcanic Belt, a pattern observed in several co-distributed taxa, and suggested that Quaternary climate change likely had little effect on diversification between lineages. Uplift of the Trans-Mexican Volcanic Belt during specific time periods appears to have strongly impacted diversification in Mexican highland taxa.