Trinidad & Tobago Have More Amphibians & Reptiles Species Than Expected

The diversity of the Trinidad and Tobago herpetofauna is exceptional. Both islands contain more species of frogs, lizards and snakes that would be expected given their geographic areas. The islands on the x axis are arranged by area in kilometers squared. The explanation for the exceptionally rich fauna remains to be determined, but given that they are the only continental islands associated with mainland South America it seems likely that this situation is at least in part responsible for the greater diversity of the herpetofauna.

Data for the graph was obtained from Murphy (unpublished data and this website), the CaribHerp Website, Feunmayor et al. 2005. Caribbean J. Sci. 41:346-351.

Trinidad's Coastal Swamps and Snakes

Top: Liophis cobella, Middle: Helicops 

angulatus, Bottom: Hydrops triangularis. JCM

Caroni Swamp is an 8000 hectare wetland complex composed of marshes, mangrove, brackish lagoons, and tidal marshes. It is perhaps best known for its bird fauna which draws a considerable number of tourists and birders each year. However, it also supports a herpetofauna and some its members are frequently a part of the ecotours. The most obvious species are Ruschenberger's Treeboa, Corallus ruschenbergeri, and the Specteled Caiman, Caiman crocodilus. Taylor et al. (2011) conducted a survey of Ruschenberger's Treeboa over more than 115 km of transects, observed 32 individuals, and estimated the density at about 11 snakes  per km². Treeboas are a favaorite of the tour guides, the birders and ecotourists who cruise the mangroves to see the Scarlet Ibis and the local herons. However, Caroni holds other species of snakes that are of less interest to tourists but of greater interest to science. 


Of the 3300 snakes species known, less than 80 have successfully invaded the ocean, that is about 2.4% of the snake fauna. Yet the oceans cover about 70% of the Earth's surface, so why haven't more species invaded the oceans? To add to the problem there are no mairne snakes in the Caribbean or the Atlantic. All marine snakes are in the Eastern Hemisphere. Yet, Trinidad has three aquatic species that  live in close proximity to each other, species that tolerate the brackish waters in both Caroni and Nariva swamps: Liophis cobella, Helicops angulatus, and Hydrops triangularis (Murphy, 1997). All three have been reported to feed on fishes and frogs and show a variety of adaptations to aquatic ecosystems. Caroni's brackish waters and the presence of these snakes suggests these are species are on a trajectory to adapt to life in the ocean. And, it is not difficult to imagine how aquatic snakes living in places like Caroni and Nariva swamps could transition to life in full salt water over time. 


On 20 June 2011, the Glasgow Zoological Expedition and I did a transect through Caroni, starting at the landward edge and heading west along the main channel after dark. We saw two treeboas, a few caimans, but aquatic snakes were absent. Realizing something was wrong, we took some salinity readings using a hydrometer, the first reading was 28 ppt, then it was 30, and the highest reading was 32 ppt. Full sea water is 36 ppt, and it seemed to me that while these snakes could handle brackish water, this was much to saline for the snakes I was looking for.


So, we took the hydrometer to a small villlage near Nariva Swamp on the east coast of Trinidad. The village has numerous canals and we found two of the three species (Liophis cobella and Helicops angulatus) almost immediately. We found salinity readings between 8 and 12 ppt. These three snakes are of great interest because they may hold clues as to how snakes have transitioned and adapted to marine environments.


References
Murphy, J. C. 1997. Amphibians and Reptiles of Trinidad and Tobago. Krieger Publishing, Malabar, Fl.

Taylor, K., H. P. Nelson, and A. Lawrence. 2011. Population Density of the Cook's tree Boa (Corallus ruschenbergerii) in the Caroni Swamp, Trinidad. Pages 8-18 In: Proceedings of the 1st Research Symposium on Biodiversity in Trinidad and Tobago (A. Lawrence and H. P. Nelson eds.). University of the West Indies Department of Life Sciences.

Further Evidence for Phytotriades Jowers et al.

Phytotriades auratus. JCM

Jowers et al. (2009) erected the genus Phytotriades for Amphodus auratus Boulenger on the basis of two golden longitudinal stripes on its dorsum, lack of vocalization and molecular data (partial sequences of mitochondrial 12S and 16S rDNA). They recovered auratus as the sister to Argenteohyla siemersi, a bromeliad dwelling species from lowland eastern Argentina. Recently Pyron and Wiens (in press, 2011) present data that auratus is the sister to Itapotihyla langsdorffii, an arboreal, lowland species from southeast Brazil, northesatern Argenitina, and Paraguay. Their data suggests that P. auratus and I. landsdorffii  form a clade and are the sister to a suite of arboreal treefrogs including Argenteohyla already mentioned; the South American Aparasphenodon, Corythomantis, Nyctimantis, Osteocephalus, Trachycephalus, Tepuihyla; and the Caribbean Osteopilus. Many of these frogs are called "casqheaded treefrogs" because the skin over the skull is ossified a trait often associated with habitats that have an extended dry period during the year and frogs that dwell in holes, has also been shown to be assocaited with defense (Jared et al. 2005). Phyllodytes luteolus is the type species for the genus and it also turns up in this clade, but as the sister to Osteopilus. Thus, Pyron and Weins (and Weins et al. 2010) have supported Jower's assertion that Phyllodytes was polyphletic and that auratus needed to be placed in its own genus, the remining question - are there other frogs that are also members of the genus Phytotriades?Until they are discovered the genus remains a Trinidad endemic.

Literature
Jared, C. et al. 2005. Head co-ossification, phragmosis and defense in the casque-headed tree frog Corythomantis greebingi. Journal of Zoology 265:1-8.


Jowers, M. J., J. R. Downie, and B. L. Cohen . 2009. The Golden Tree Frog of Trinidad, Phyllodytes auratus (Anura: Hylidae): systematic and conservation status. Studies on Neotropical Fauna and Environment. 43:181-188.


 Pyron R. A. and J. J. Wiens   2011. (in press) A large-scale phylogeny of Amphibia including over 2800 species, and a revised classification of extant frogs, salamanders, and caecilians. Molecular Phylogenetics and Evolution doi:10.1016/j.ympev.2011.06.012.

Wiens, J. J., C. A. Kuczynski, X. Hua, and D. S. Moen . 2010. An expanded phylogeny of treefrogs (Hylidae) based on nuclear and mitochondrial sequence data. Molecular Phylogenetics and Evolution 55: 871-882.

A Declining T&T Herpetofauna?

The advantage of field notes over time is that they allow you to compare data from year to year. Recently I realized that I had the data to compare the Trinidad and Tobago herpetofauna from 1982, 1983, 1984, 2010, and 2011. The number of species I had seen on each of these trips at the same time of years for approximately the amount of time. So, I scoured my notes and built a table that compares the number of species of frogs, lizards and snakes I had seen on each of five trips. The trips were all made during June-July, the rainy season and lasted 3 to 4 weeks. At the end of each day I always tried to write a list of the species I had seen, a practice that I had started on the first trip. So, totaling the species seen on each trip was relatively easy, assuming omissions are about equal for each year. While I would often note seeing or hearing a particular species of frog I did not keep tract of the number of individuals of each species. The same was true for lizards - not wanting to count the ubiquitous Gonatodes vittatus or Ameiva ameiva. Snakes on the other hand are a different story. I did try to keep tract of the number of individual snakes seen on each trip - so they provide another aspect of the herpetofauna at two points in time (the early 1980s and the early 2010's). Table 1. shows the number of species of each higher category seen on each trip. Table 2 shows the number of individual snakes seen on each trip. One could argue that the declining numbers reflects a change in effort - afterall I am 30 years older. However, on each trip I had people assisting me, in the case of the most recent two trips we had The Glasgow Zoological Society Expedition (more than 12 people each year) looking for snakes which substantially increased the effort over the the 3 or 4 people who were with me on the 1980 trips. In the early 1980's many of the specimens recorded were road kills, in the two most recent trips road killed were exceptionally uncommon. There was a large DOR Pseudoboa on Tobago and a DOR Epicrates maurus on Trinidad in 2011 - finding only two road killed snakes in four weeks is not reassuring. Looking at my field notes it was not uncommon to find three to five road kills per night in the 1980's. 


Table 1. Number of species observed each year.

	1982	1983	1984	2010	2011
Frogs	21	13	21	15	17
Lizards	10	11	13	13	14
Snakes	20	24	20	5	10
Totals	61	48	54	33	41

Table 2. Number of snake specimens observed each year.

	1982	1983	1984	2010	2011
Snakes	63	57	40	8	28