Dipsas variegata - the 44th species of snake reported from Trinidad

A comparison of Dipsas trinitatis (A 

and c) and Dipsas variegata (B and D).

Thirty six species of the snail-eating snakes in the genus Dipsas are currently recognized. One species, Dipsas trinitatis Parker is known only from Trinidad. The original description of Dipsas trinitatis (Parker, 1926) was based upon a single male specimen from the Trinity Hills and a second specimen without locality data. Parker recognized its close relationship to the mainland South American Dipsas variegata and distinguished the two species using the presence/absence of a preocular, the number of upper labials, and differences in color pattern, characters now known to be variable in both taxa. In an overall review of dipsadine snakes Peters (1960) relegated D. trinitatis to a subspecies of D. variegata based on color differences from the mainland populations. Emsley (1977), Murphy (1997) and Boos (2001) followed this recommendation and discussed this snake as D. v. trinitatis.

Until now, all references to Dipsas on Trinidad have referred to Dipsas trinitatis Parker. Murphy and Rutherford (2014) have now report the presence of Dipsas variegata on Trinidad. Its presence is based upon a single female specimen, identified as Dipsas trinitatis, was found in the collection of The National Museum and Art Gallery of Trinidad & Tobago and now stored in The University of the West Indies Zoology Museum (UWIZM). Its large size (796 mm total length, 607 mm SVL), bulky head, tall upper labials, an eye diameter that is about equal to the eye-mouth distance readily distinguish it from its congener, Dipsas trinitatis. The specimen agrees well with all 16 diagnostic characters for the species listed by Harvey and Embert (2008).

Collection data accompanying the specimen reports it locality as Macqueripe Bay on the north coast of the Chaguaramas Peninsula and adjacent to Tucker Valley.

The smaller head in D. trinitatis has been noted previously, but placed side-by-side the size difference is dramatic and it appears Dipsas variegata is macrocephalic, while D. trinitatis is microcephalic. Microcephalism evolved in several sea snakes (Hydrophis, family Elapidae, Hydrophiinae) that specialize in hunting snake eels in crevices. The smaller head allows the snake to probe holes and crevices to extract the fish. Since Dipsas feeds on snails and extracts them from their shells it seems probable that the difference in head size is adaptive for a specific type of prey, or a specific foraging strategy (possibly removing snail bodies from shells of different sizes or extracting snails from crevices). Feeding behavior and diet in these snakes is poorly known it is unclear as to how head size relates to diet or foraging.

Dipsas variegata is the 44^th species of snake reported from Trinidad and the second species of Dipsas from the island. In addition there is a third species of snake specialized for feeding on gastropods from Trinidad – Sibon nebulata.

Citation

Murphy JC, Rutherford, MG. 2014. The snail-eating snake Dipsas variegata (Duméril, Bibron and Duméril) on Trinidad, and its relationship to the microcephalic Dipsas trinitatis Parker (Squamata, Dipsadidae). Herpetology Notes, 7: 757-760. 

Hyla goughi Boulenger resurrected for the Trinidad & Tobago Dendropsophus minutus population

Dendropsophus goughi Boulenger

In the Neotropics, nominal taxa such as the toad Rhinella margaritifera (Bufonidae), the thin-toed frog Leptodactylus fuscus (Leptodactylidae), and the tree frog Scinax ruber (Hylidae) are prominent examples of anuran species once considered to occur across nearly the entire tropical lowlands of South America. Evidence has accumulated that many such putatively widespread species could in fact be complexes of cryptic taxa. However, given limited genetic sampling and the difficulty in reviewing material from all countries hosting populations, their relationships and systematics remain in many cases as unclear as they were decades ago.

Dendropsophus minutus (Peters, 1872) is a small hylid frog, 21–28 mm snout-vent length, distributed in Cis-Andean South America, including the Andean slopes, the Amazon Basin, the Guiana Shield, down to the Atlantic Forests of southeastern Brazil, with an elevational record from near sea level up to 2,000 m. Variation in coloration, osteology, advertisement calls and larval morphology, along with molecular data from limited parts of the species' distribution suggest the nominal D. minutus might represent a species complex. However, the sheer size of its supposed geographical range along with nomenclatural and taxonomic complexity (six junior synonyms) and unresolved relationships in the D. minutus species group have so far made these frogs inaccessible to revision.

Gehara et al. (2014) use D. minutus to understand to what degree a small-sized, tropical anuran has the potential to be continentally widespread with limited genetic structure within its range, as expected for a single species. In addition to conservation concerns, this question has important implications for South American biogeography in general and amphibian systematics and evolution in particular. Evidence is accumulating that body size in amphibians has a positive correlation with range size, but contrary to this trend many Holarctic amphibians occur with little genetic substructure across the vast ranges they colonized after the last glaciation, despite sometimes moderate to small body sizes. Whether such patterns also exist across vast ranges in tropical regions, with their distinct historical climatic dynamics, is an open question. Deciphering possible cryptic diversity within the nominal D. minutus would also help inform conservation assessments which typically use species' geographic distributions as criteria for conservation status.

The phylogenetic tree based on the 16S gene containing all Dendropsophus for which sequences were available recovered the monophyly of the D. minutus species group. Within the group, the clade containing samples representing lineages 19–43 received a maximal posterior probability (1.0) and is defined here as the D. minutus complex, given that lineage 25 contains samples from the type locality of D. minutus.

Most of the mitochondrial lineages containing more than one sample received strong nodal support. The lineages splitting off from basal nodes of the tree (lineages 1–18) are distributed in the Guiana Shield, and in the Andean region of Peru, Ecuador and Colombia, with an eastern extralimital clade assembling disjunct localities in Mato Grosso and Pará.

The remaining lineages are in general more widely distributed in central and eastern South America Lineages are largely allopatric but several cases of sympatry were observed. The uncorrected pairwise distances between lineages for the 16S gene ranged from 0.7 to 13%, while within-lineage p-distances ranged from 0.0 to 1.8%.

Most of the lineages (45%) were found in only one or two localities. Fifty per cent of the lineages were only found in areas smaller than 10 km², and more than 70% have known ranges smaller than 10,000 km². Eight out of the 43 lineages have a distribution larger than 100,000 km2. Largest range sizes were found in northeastern Brazil (Caatinga domain; 997,262 km², lineage 36), eastern Bolivia and western Brazil (Cerrado, Chaco and Dry Forest domains; 293,321 km², lineage 33) and the Guiana Shield (269,741 km², lineage 2).

Among the D. minutus species group members external to the D. minutus complex, lineages 1–6 are Guianan, while 7–18 are primarily distributed along the Andean foothills, and all show well-pronounced molecular differentiation and divergence. Among lineages 1–6, there is moderate genetic differentiation. Considering mitochondrial reciprocal monophyly and GMYC results as criteria, and being taxonomically conservative, one available name, Hyla goughi Boulenger, 1911 (type locality: Trinidad), should likely be removed from the synonymy of D. minutus and allocated to populations comprised by all or some of lineages 1–6. As a conservative estimate, the authors hypothesize that lineages 7–18 comprise seven distinct species, i.e., five named taxa and two undescribed species (lineages 9+10 and 11+12).

Data presented herein provide conclusive evidence for a strong genetic subdivision of the nominal species Dendropsophus minutus as currently understood. Current taxonomy conservatively assumes a putatively widespread species encompassing a vast area of South America (from approximately latitude 11.0°N to 35.0°S), distributed across several biomes. Our results, however, reveal high genetic diversity within D. minutus that would suggest the existence of numerous distinct species, leading to an important increase in number of species. If this hypothesis is confirmed through further studies, the existence of an increased number of species with decreased range sizes would have important consequences for the definition of centers of endemism and for assessing conservation status.

Citation

Gehara M, Crawford AJ, Orrico VGD, Rodríguez A, Lötters S, et al. (2014) High Levels of Diversity Uncovered in a Widespread Nominal Taxon: Continental Phylogeography of the Neotropical Tree Frog Dendropsophus minutus. PLoS ONE 9(9): e103958. doi:10.1371/