Rapid diversification and dispersal during periods of global warming by plethodontid salamanders

Vieites, D.R.; Min, M.S.; Wake, D.B.

A phylogeny and timescale derived from analyses of multilocus nuclear DNA sequences for Holarctic genera of plethodontid salamanders reveal them to be an old radiation whose common ancestor diverged from sister taxa in the late Jurassic and underwent rapid diversification during the late Cretaceous. A North American origin of plethodontids was followed by a continental-wide diversification, not necessarily centered only in the Appalachian region. The colonization of Eurasia by plethodontids most likely occurred once, by dispersal during the late Cretaceous. Subsequent diversification in Asia led to the origin of Hydromantes and Karsenia, with the former then dispersing both to Europe and back to North America. Salamanders underwent rapid episodes of diversification and dispersal that coincided with major global warming events during the late Cretaceous and again during the Paleocene–Eocene thermal optimum. The major clades of plethodontids were established during these episodes, contemporaneously with similar phenomena in angiosperms, arthropods, birds, and mammals. Periods of global warming may have promoted diversification and both inter- and transcontinental dispersal in northern hemisphere salamanders by making available terrain that shortened dispersal routes and offered new opportunities for adaptive and vicariant evolution.

Developmental processes underlying the evolution of a derived foot morphology in salamanders

Jaekel, M.; Wake, D.B.

Interdigital webbing has evolved repeatedly in tropical salamanders (bolitoglossines). This derived foot morphology is only one of many homoplastic traits in this diverse amphibian clade. Indeed, few if any morphological traits sort lineages within this clade. We investigate the processes underlying the homoplastic evolution of morphological characters in these salamanders by analyzing selective and developmental processes that generate interdigital webbing. We show that a pedomorphic developmental change generates the new foot morphology and that pedomorphosis affects a number of morphological traits, thus creating a developmental correlation among them. This correlation among traits is maintained across most species, thus facilitating the repeated evolution of traits. Although we find evidence that the changes in foot morphology are adaptive in one species, the evolution of webbing in all other species does not carry an adaptive signature. The new foot morphology therefore evolves repeatedly, even in the apparent absence of a direct selective advantage.

Anatomy of Eocaecilia micropodia, A Limbed Caecilian of the Early Jurassic

Jenkins, F.A.; Walsh, D.M.; Carroll, R.L.

Eocaecilia micropodia, an Early Jurassic caecilian from the Kayenta Formation of northeastern Arizona, is structurally comparable to Recent gymnophionans in numerous aspects but also possesses characters that are primitive or appear to be uniquely derived. The skull of Eocaecilia exhibits such distinctively caecilian features as (1) a sulcus along the orbital rim indicating the presence of a ten-taculum; (2) an os basale representing consolidation of the supraoccipital, exoccipital, basisphenoid, basioccipital, pleurosphenoid, and parasphenoid elements; (3) an internal naris posterior to the premaxillary–maxillary suture and medial to the tooth rows on the vomer and palatine; (4) enlarged nasal capsules; and (5) an olfactory eminence on the vomer. As in Recent caecilians, the lower jaw comprises a pseudodentary and pseudoangular that are joined along an elongate, oblique suture. The pseudoangular bears a robust internal process and an elongate re-troarticular process. The teeth are bicuspid and pedicellate, but are minute in size and are more numerous than in most living caecilians.

Speciation, Species Boundaries and Phylogeography of Amphibians

Vences, M.; Wake, D.B.

A. Species Concepts, Theories on Speciation and their Application in Amphibians

A RESULT of intense interest in species concepts during the past decade is the recognition that controversy has been focused more upon criteria for determining what species to recognize rather than upon what species, in general, are. The intellectual framework presented by de Queiroz (1998, 1999) suggested that despite the appearance of disagreement, there is fundamental agreement among the diverse definitions employed for species. De Queiroz argued that nearly all contemporary biologists accept the idea that species are segments of population-level evolutionary lineages. There remains the large question of what the defining properties of the taxonomic category "species" might be, but the primary issue is to discover when such lineages diverge and when lineages are finally split. The many species definitions — May den (1997) lists more than 20 — become criteria for species recognition under this perspective. The issue of delimiting species remains, but there can be agreement on the goal — an understanding of when evolutionary lineages have irretrievably diverged. As de Queiroz (1998) noted, there are still unresolved issues relating to whether successive species can exist in unbranched lineages, and whether asexual organisms form species, but an intellectual advance has been achieved.

The Amphibian Tree of Life: Ideology, chaos or biological reality?

Vences, M.

Amphibian classification is undergoing major rearrangements. Rates of discovery and descriptions of new species are increasing due to intensified fieldwork. Comprehensive proposals of changes at genus and family levels have been brought forward based on mainly molecular phylogenies. Here I argue that the classificatory proposals of FROST et al. (2006) altogether constitute a great advance in our understanding of amphibian relationships despite many avoidable analytical shortcomings and problems of data quality. For the German fauna, I propose to accept the genus level changes for Rana (usage of Pelophylax for water frogs) but to keep all three species of Bufo in this genus in a preliminary way. Partitioning of Triturus is warranted at well.