Patterns of niche diversification in south-east Asian crocodile newts

Morphological variation in the vomer of aquatic and terrestrial spelerpini salamanders

The vomer is an important tooth-bearing cranial bone in the lungless salamanders (Caudata: Plethodontidae) that serves different functional roles in aquatic versus terrestrial feeding. Vomerine tooth rows that run parallel with the maxillary teeth are thought to help grasp prey while expelling water from the mouth, while posterior extensions of the tooth row may help terrestrial taxa bring prey down the throat. We hypothesize that these two general morphological types will correlate with the habitat (aquatic vs. terrestrial) of adult salamanders. Alternatively, variation in form may be due to taxonomic effects, such that closely related species will have similar vomer morphology regardless of adult habitat. To test this hypothesis, we examined vomer shape on a set of species of the morphologically diverse tribe Spelerpini, in which two of the five genera (Eurycea and Gyrinophilus) include both aquatic and terrestrial species. Data were collected using micro computed tomography (micro-CT) scans from specimens from the Field Museum of Natural History and the Illinois Natural History Survey; additional data was obtained from public online repositories including Morphosource.org. Two-dimensional geometric morphometric analyses were performed to capture shape variation of both the vomer and the vomerine tooth row. We found clear separation between aquatic and terrestrial taxa, with most of the variation due to differences in the vomerine tooth row. Differences ascribed to habitat use likely correspond to feeding behavior, and the functional role of the vomer in prey processing warrants further investigation in this species-rich salamander family.

A new species of the genus Tylototriton (Urodela, Salamandridae) from western Thailand

We describe a new species of the newt genus Tylototriton from Umphang Wildlife Sanctuary, Tak Province, western Thailand based on molecular and morphological evidence and named here as Tylototritonumphangensissp. nov. The new species is assigned to the subgenus Tylototriton and differs from other species in having dark-brown to blackish-brown body and limbs, truncate snout, prominent antero-medial ends of the expansion of the dentary bones, laterally protruding quadrate regions, indistinct and small rib nodules, a well-segmented vertebral ridge, and rough dorsolateral bony ridges, which are steeper anterior, and curved medially at the posterior ends. The molecular data show that Tylototritonumphangensissp. nov. differs from T.uyenoi sensu stricto by a 5% genetic sequence divergence of the mitochondrial NADH dehydrogenase subunit 2 region gene. The new species and T.uyenoi are both endemic to Thailand, distributed along the Northwest Thai (Dawna) Uplands of Indochina. To clarify the species boundary between Tylototritonumphangensissp. nov. and T.uyenoi, additional field research is needed in adjacent areas. Tylototritonumphangensissp. nov. is restricted to evergreen hill forests in Umphang Wildlife Sanctuary. We suggest that the new species should be classified as Endangered (EN) in the IUCN Red List.

Integrative taxonomy reveals three new taxa within the Tylototriton asperrimus complex (Caudata, Salamandridae) from Vietnam

The Tylototritonasperrimus complex from northern Vietnam is reviewed based on morphological comparisons and analysis of the mitochondrial marker NADH dehydrogenase subunit 2 (ND2). Based on molecular divergences, which were revealed to be higher than in other congeners, in concert with morphological differences, two new species and one subspecies are described herein: Tylototritonpasmansisp. nov. differs from T.asperrimussensu stricto by 3.2 to 3.6 % genetic divergence and a combination of distinct morphological characters, such as head slightly longer than wide, distinct mid-dorsal ridge, relatively wide distance between the eyes, tips of fingers reaching the eye when foreleg is laid forward, labial and gular folds present, central belly skin with tubercles shaped like transverse wrinkles and distinct, pointy to round rib nodules. The population of T.pasmansisp. nov. consists of two subclades, the nominotypic one occurring on the eastern side of the Da River (or Black River, including Hoa Binh and Phu Tho provinces), and another occurring on the western side (including Son La and Thanh Hoa provinces). These two subclades differ by 2.5 to 3.1 % genetic divergence and distinct morphological characters. The western subclade is herein described as Tylototritonpasmansiobstissp. nov., which differs from the nominotypic form by a wider head, longer and narrower snout, shorter femur length, and an overall less granulose skin, without an increased concentration of warts on the body sides.

A second new species, Tylototritonsparreboomisp. nov. is described from Lai Chau Province. It differs from T.asperrimussensu stricto by 4.1 to 4.2 % and from Tylototritonpasmansisp. nov. by 3.6 to 4.5 % genetic divergences as well as by a combination of distinct morphological characters, such as head longer than wide, tips of fingers reaching nostril when foreleg adpressed along head, rib nodules distinct, round and relatively enlarged, and wide distance between the eyes.

Cranial shape evolution of extant and fossil crocodile newts and its relation to reproduction and ecology

The diversity of the vertebrate cranial shape of phylogenetically related taxa allows conclusions on ecology and life history. As pleurodeline newts (the genera Echinotriton, Pleurodeles and Tylototriton) have polymorphic reproductive modes, they are highly suitable for following cranial shape evolution in relation to reproduction and environment. We investigated interspecific differences externally and differences in the cranial shape of pleurodeline newts via two‐dimensional geometric morphometrics. Our analyses also included the closely related but extinct genus Chelotriton to better follow the evolutionary history of cranial shape. Pleurodeles was morphologically distinct in relation to other phylogenetically basal salamanders. The subgenera within Tylototriton (Tylototriton and Yaotriton) were well separated in morphospace, whereas Echinotriton resembled the subgenus Yaotriton more than Tylototriton. Oviposition site choice correlated with phylogeny and morphology. Only the mating mode, with a random distribution along the phylogenetic tree, separated crocodile newts into two morphologically distinct groups. Extinct Chelotriton likely represented several species and were morphologically and ecologically more similar to Echinotriton and Yaotriton than to Tylototriton subgenera. Our data also provide the first comprehensive morphological support for the molecular phylogeny of pleurodeline newts.