Two extremely rare new species of fossorial salamanders of the genus Oedipina (Plethodontidae) from northwestern Ecuador

We describe two new species of salamanders of the genus Oedipina, subgenus Oedopinola, from two localities on the northwestern foothills of Ecuador, at elevations between 921 and 1,067 m. These are the southernmost members of the genus. We examined different museum collections and we found just three specimens of Oedipina from Ecuador, obtained throughout the history of herpetological collections in the country. We identify two of the three specimens as new species, but refrain from assigning a specific identity to the third, pending further study. Oedipina villamizariorum sp. n. is a medium-sized member of the genus, with a narrow, relatively pointed head and blunt snout; dorsolaterally oriented eyes, moderate in size; and digits that are moderately long and having pointed tips. Oedipina ecuatoriana sp. n., somewhat larger, has a narrow head and broadly rounded snout; this new species differs from all known Oedipina by the distinctive presence of paired prefrontal bones and a reduced phalangeal formula: 0-0-1-0; 0-1-2-1-1. We provide detailed descriptions of the osteology of both new species. Finally, we present a phylogenetic hypothesis for the genus, including one of the two new species, based on partial sequences of mitochondrial DNA.

Osteological Variation among Extreme Morphological Forms in the Mexican Salamander Genus Chiropterotriton (Amphibia: Plethodontidae): Morphological Evolution And Homoplasy

Osteological variation is recorded among and within four of the most distinctive species of the Mexican salamander genus Chiropterotriton. Analysis of the data is consistent with the monophyletic status of the genus and documents previously unrecorded intraspecific and interspecific variation. Most of the recorded variation involves qualitative and quantitative proportional differences, but four fixed differences constitute autapomorphic states that affirm and diagnose some species (C. dimidiatus, C. magnipes). Osteological variation in 15 characters is analyzed with respect to predictions generated from four hypotheses: 1) phylogeny, 2) adaptation to specific habitats (the four species include cave-dwelling, terrestrial, and arboreal forms), 3) size-free shape, and 4) size. High levels of intraspecific variation suggest that the characters studied are not subject to rigid functional constraints in salamanders, regardless of size. The pattern predicted by the hypothesis based on size differences seen among these four Chiropterotriton species matches most closely the observed pattern of relative skull robustness. Since size change and heterochrony are often associated in plethodontid evolution, it is likely that changes in developmental timing play a role in the morphological transitions among these morphologically diverse taxa. Webbed feet, miniaturization, body shape, and an unusual tarsal arrangement are morphologies exhibited in species of Chiropterotrition that are shown to be homoplastic with other clades of tropical plethodontids. Although extensive homoplasy in salamanders might be seen as a roadblock to unraveling phylogenetic hypotheses, the homologous developmental systems that appear to underlie such homoplasy may reveal common and consistent evolutionary processes at work.

Morphology and posthatching ontogeny of the autopodial skeleton of Bolitoglossa nicefori (Caudata: Plethodontidae)

Webbed foot morphology is a highly homoplastic character in species of Bolitoglossa and has been assumed to be pedomorphic. This study examines the morphology and posthatching ontogeny of the autopodial skeleton of Bolitoglossa nicefori and compares the descriptive and morphometric results with other species of the genus. We show that the autopodial morphology of B. nicefori coincides with the generalized pattern of the genus; webbed foot morphology is produced by pedomorphosis that affect the phalange length of the digits, resulting in a synchronized growth of digits (length and ossification rates) and the fleshy web. Although the webbed foot morphology of B. nicefori might be explained by the pervasive pedomorphic developmental trend observed in the genus, the large degree of variation encountered in the morphology of the distal phalanges indicates that the pedomorphic processes acting in this species are neither a simple truncation of the autopodial developmental program during early posthatching development nor a global process acting over the whole body plan. Instead, this morphological pattern is probably a result of the modular nature of limb development.

Phylogenetic history underlies elevational biodiversity patterns in tropical salamanders

Elevational variation in species richness is ubiquitous and important for conservation, but remains poorly explained. Numerous studies have documented higher species richness at mid-elevations, but none have addressed the underlying evolutionary and biogeographic processes that ultimately explain this pattern (i.e. speciation, extinction and dispersal). Here, we address the evolutionary causes of the mid-elevational diversity hump in the most species-rich clade of salamanders, the tropical bolitoglossine plethodontids. We present a new phylogeny for the group based on DNA sequences from all 13 genera and 137 species. Using this phylogeny, we find no relationship between rates of diversification of clades and their elevational distribution, and no evidence for a rapid 'species pump' in tropical montane regions. Instead, we find a strong relationship between the number of species in each elevational zone and the estimated time when each elevational band was first colonized. Mid-elevation habitats were colonized early in the phylogenetic history of bolitoglossines, and given similar rates of diversification across elevations, more species have accumulated in the elevational zones that were inhabited the longest. This pattern may be widespread and suggests that mid-elevation habitats may not only harbour more species, but may also contain more phylogenetic diversity than other habitats within a region.

Phylogeny, biogeography, and evolution of two Mediterranean snakes, Malpolon monspessulanus and Hemorrhois hippocrepis (Squamata, Colubridae), using mtDNA sequences

Variation in 815bp of mitochondrial DNA from two gene fragments (300bp of cytochrome b and 395-515bp of 12S rRNA) for 26 Malpolon monspessulanus, and cytochrome b for a further 21 individuals, indicates that this species originated in the Maghreb area of Northwest Africa. Here, an estimated 3.5-6Mya, it divided into the western M. m. monspessulanus, and an eastern clade including M. m. insignitus and M. m. fuscus. The very limited genetic differentiation between Maghreb and Southwest European populations of this form suggests that it arrived in the Iberian Peninsula only recently. Population genetics and demographic tests indicate subsequent expansion in this area around 83,000-168,000 year ago. Because present populations of Malpolon arrived recently, mid-Pliocene and at least some Pleistocene fossils of the genus Malpolon in Southwest Europe are probably derived from an earlier invasion from the Maghreb, possibly as early as the end of the Miocene period, 5.3-5.9Mya, when there was a temporary land bridge across the site of the Strait of Gibraltar and the Mediterranean Sea desiccated. The descendants of this earlier invasion must have eventually become extinct, perhaps during one of the Pleistocene glaciations. In contrast to the western M. m. monspessulanus, the greater genetic divergence found in the eastern clade of M. monspessulanus suggests that it dispersed at an earlier date and probably over a longer period, spreading eastwards through northern Libya and Egypt to Syria, Iraq, and Iran, and around the Mediterranean Sea through Turkey into the Aegean archipelagos and the Balkan peninsula. The western and eastern units of M. monspessulanus have different dorsal color pattern, differences in skull structure and exhibit an 8.4% uncorrected genetic divergence in the combined gene fragments investigated here. It is consequently recommended that they should be treated as separate species: M. monspessulanus (sensu stricto) and Malpolon insignitusstat. nov., the latter including the subspecies Malpolon insignitus fuscuscomb. nov. The same combined mitochondrial gene fragments used in Malpolon were investigated in 20 individuals of Hemorrhois hippocrepis, and of cytochrome b alone in a further 17. They indicate that this species also originated in the Maghreb and again invaded the Iberian Peninsula quite recently. Some of the most recent invasions of the Iberian Peninsula by reptiles and amphibian taxa could probably be anthropogenic in origin. Some other species including M. monspessulanus and H. hippocrepis, may have crossed naturally, by "hopping" across the Strait of Gibraltar via temporary islands on the shallowest parts that were exposed during sea-level fall associated with Pleistocene glaciations.

Phylogenetic relationships of the genus Chiropterotriton (Caudata: Plethodontidae) based on 16S ribosomal mtDNA

The genus Chiropterotriton contains only 12 described species but includes a rich variety of morphological and ecological forms ranging from diminutive to large cave-dwelling species, as well as a number of terrestrial and arboreal forms. Although morphological diversification has taken place during the evolution of this genus, morphological stasis and parallelism also characterize the evolution of this group, generating complexes of cryptic species. I obtained sequences of the 16S ribosomal mtDNA gene from most of the species. Mitochondrial DNA shows great diversification, with genetic divergence among taxa as high as 12.5%. The 531-bp mtDNA data matrix contained 121 parsimony-informative characters. Basal relationships are poorly supported by maximum parsimony analyses. There is, however, support for a clade that includes all of the samples of the C. chiropterus group. The maximum-likelihood and Bayesian topologies differ from maximum-parsimony topologies mainly in the arrangement of the basal relationships. Based on the results, the genus Chiropterotriton comprises 12 species with available names: C. arboreus, C. chiropterus, C. chondrostega, C. cracens, C. dimidiatus, C. lavae, C. magnipes, C. mosaueri, C. multidentatus, C. orculus, C. priscus, and C. terrestris, plus 7 additional undescribed species for which allozyme and mitochondrial data sets are congruent.

Dwarfism in insular sloths: biogeography, selection, and evolutionary rate

The islands of Bocas del Toro, Panama, were sequentially separated from the adjacent mainland by rising sea levels during the past 10,000 years. Three-toed sloths (Bradypus) from five islands are smaller than their mainland counterparts, and the insular populations themselves vary in mean body size. We first examine relationships between body size and physical characteristics of the islands, testing hypotheses regarding optimal body size, evolutionary equilibria, and the presence of dispersal in this system. To do so, we conduct linear regressions of body size onto island area, distance from the mainland, and island age. Second, we retroactively calculate two measures of the evolutionary rate of change in body size (haldanes and darwins) and the standardized linear selection differential, or selection intensity (i). We also test the observed morphological changes against models of evolution by genetic drift. The results indicate that mean body size decreases linearly with island age, explaining up to 97% of the variation among population means. Neither island area nor distance from the mainland is significant in multiple regressions that include island age. Thus, we find no evidence for differential optimal body size among islands, or for dispersal in the system. In contrast, the dependence of body size on island age suggests uniform directional selection for small body size in the insular populations. Although genetic drift cannot be discounted as the cause for this evolution in body size, the probability is small given the consistent direction of evolution (repeated dwarfism). The insular sloths show a sustained rate of evolution similar to those measured in haldanes over tens of generations, appearing to unite micro- and macroevolutionary time scales. Furthermore, the magnitude and rate of this example of rapid differentiation fall within predictions of theoretical models from population genetics. However, the linearity of the relationship between body size and island age is not predicted, suggesting that either more factors are involved than those considered here, or that theoretical advances are necessary to explain constant evolutionary rates over long time spans in new selective environments.

Molecular phylogenetic relationships of neotropical salamanders of the genus Pseudoeurycea

Pseudoeurycea, with 34 described species, is one of the most diversified groups of neotropical salamanders. I generated a phylogenetic hypothesis of relationships for Pseudoeurycea and related taxa, based on DNA sequences of 16S, Cyt b, and ND4 mitochondrial genes. The analyses include 27 species of Pseudoeurycea and samples from the monotypic Lineatriton, Ixalotriton, and Parvimolge. All phylogenetic analyses resulted in a paraphyletic Pseudoeurycea. Ixalotriton and Pseudoeurycea parva always form a monophyletic group. P. parva is transferred to Ixalotriton based on morphological and molecular grounds. The phylogenetic position of the newly defined Ixalotriton clade is uncertain since it is part of an unresolved basal polytomy. Parvimolge is closely related to Pseudoeurycea, and it is also part of the basal polytomy. Lineatriton, a highly specialized taxon, is deeply nested within Pseudoeurycea. In order to provide a taxonomic arrangement consistent with the monophyly of the different units that reflects both evolutionary history and morphological specialization, Pseudoeurycea should be split into several taxonomic units.

Extreme morphological and ecological homoplasy in tropical salamanders

Fossorial salamanders typically have elongate and attenuated heads and bodies, diminutive limbs, hands and feet, and extremely elongate tails. Batrachoseps from California, Lineatriton from eastern México, and Oedipina from southern México to Ecuador, all members of the family Plethodontidae, tribe Bolitoglossini, resemble one another in external morphology, which has evolved independently. Whereas Oedipina and Batrachoseps are elongate because there are more trunk vertebrae, a widespread homoplasy (parallelism) in salamanders, the genus Lineatriton is unique in having evolved convergently by an alternate "giraffe-neck" developmental program. Lineatriton has the same number of trunk vertebrae as related, nonelongated taxa, but individual trunk vertebrae are elongated. A robust phylogenetic hypothesis, based on sequences of three mtDNA genes, finds Lineatriton to be deeply nested within a clade characterized by generalized ecology and morphology. Lineatriton lineolus, the only currently recognized taxon in the genus, shows unanticipated genetic diversity. Surprisingly, geographically separated populations of L. lineolus are not monophyletic, but are sister taxa of different species of the morphologically generalized genus Pseudoeurycea. Lineatriton, long thought to be a unique monospecific lineage, is polyphyletic. Accordingly, the specialized morphology of Lineatriton displays homoplasy at two hierarchical levels: (i) with respect to other elongate lineages in the family (convergence), and (ii) within what is currently recognized as a single taxon (parallelism). These evolutionary events are of adaptive significance because to invade the lowland tropics salamanders must be either arboreal or fossorial; the repeated evolution of elongation and attenuation has led to multiple lowland invasions.

Biodiversity of Costa Rican salamanders: implications of high levels of genetic differentiation and phylogeographic structure for species formation

Although salamanders are characteristic amphibians in Holarctic temperate habitats, in tropical regions they have diversified evolutionarily only in tropical America. An adaptive radiation centered in Middle America occurred late in the history of a single clade, the supergenus Bolitoglossa (Plethodontidae), and large numbers of species now occur in diverse habitats. Sublineages within this clade decrease in number from the northern to southern parts of Middle America, and in Costa Rica, there are but three. Despite this phylogenetic constraint, Costa Rica has many species; the number of salamander species on one local elevational transect in the Cordillera de Talamanca may be the largest for any such transect in the world. Extraordinary variation in sequences of the mitochondrial gene cytochrome b within a clade of the genus Bolitoglossa in Costa Rica reveals strong phylogeographic structure within a single species, Bolitoglossa pesrubra. Allozymic variation in 19 proteins reveals a pattern largely concordant with the mitochondrial DNA phylogeography. More species exist than are currently recognized. Diversification occurs in restricted geographic areas and involves sharp geographic and elevational differentiation and zonation. In their degree of genetic differentiation at a local scale, these species of the deep tropics exceed the known variation of extratropical salamanders, which also differ in being less restricted in elevational range. Salamanders display "tropicality" in that although speciose, they are usually local in distribution and rare. They display strong ecological and physiological differentiation that may contribute importantly to morphological divergence and species formation.