Wednesday, November 23, 2011

Thoughts on the Origins of the Tobago Herpetofauna

Three species of frogs from 
Tobago with close relatives in 
northern Venezuela. Top to 
bottom: Hylinobatrachium 
orientale, Pristimantis 
charllottvilensis, and 
Mannophryne olmonae.
Currently the H. orientale is
thought to be the same species
present in Venezuela. P. 
charllottvillensis is very
similar to P. Pristimantis 
terraebolivaris  a
species with which it was
long confused. And. M.
olmonae's sister species
is M. riveroi. See Map.
Look at a map of northern South America and most people assume that the coastal Cordillera of Venezuela, Trinidad and Tobago were continuous and that Tobago forms the eastern most end of the mountain range. The flora and fauna of Tobago have some Lesser Antillean species, but most of the fauna is continental. So, the assumption that Tobago is in fact part of South America's Northern Andes is quite reasonable, but one that is proving to be incorrect.

Tobago has Mesozoic rocks of two quite different types: (1) an oceanic-arc rock sequence (about 105 mya) and (2) older North Coast Schist (about 120 mya). The schist layer has been melted and cooled - probably multiple times - its metamorphic. The structural rock overlying Tobago Volcanic Group has also undergone some metamorphosis and has been titled by faulting. The time difference (~15 million years) suggests something dramatic happened in the island's development. Fossils are uncommon in igneous and metamorphic rocks but ammonites and radiolarians recovered from the Spring Gardens quarry and Bacolet in Tobago are of middle and early Albian (112.0 to 99.6 mya) age (Snoke and Nobel, 2001).

Several authors have hypothesized that Mesozoic oceanic-arc rocks scattered along the northern and southern margins of the Caribbean plate were once part of the Great Arc of the Caribbean (see Pindell and Kennan, 2007). This oceanic arc entered the Caribbean region of today from the Pacific and through intra-arc rifting and back arc spreading expanded greatly to form the Caribbean Plate of the present day as well as much of Middle America.

Today, Tobago lies within the southern plate-boundary zone between the South American and Caribbean plates. Its present geographic position is the structural high point at the northeast corner of the South American continental shelf and it reflects a long and complex history of tectonic displacement - in other words Tobago (or at least pieces of it) as well as Little Tobago, have traveled a considerable distance from their point of origin, which was far to the west of its current position.
The Venezuelan distributions of three species of frogs with close ties to frogs on Tobago.

So how did the continental flora and fauna present today come to be there if it's not the eastern end of the Coastal Cordillera of Venezuela? Tobago has some very cool frogs: glass frogs (Hyalinobatrachium), at least two species of endemic Pristimantis, and an endemic Mannophryne. But it also has some widespread frogs, like Leptodactylus fuscus, Rhinella marina, and Trachycephalus typhonius. All the frogs suggest a close relationship with Venezuela. There are also some very interesting endemic squamates: Gonatodes ocellatusErythrolamprus ocellatus, and Mastigodryas dunni. But there are also widespread squamates like Spilotes pullatus and Pseudoboa neuwiedii, and the gecko Thecadactylus rapicauda.

The influences of the Lesser Antilles are really very minimal in the herpetofauna, the large Anolis richardii is the only one that immediately comes to mind. And, that raises the question often asked by people who study Anoles - why are there so few anoles on Tobago? A. richardii  is generally thought to have been introduced from the Grenada Bank. So Tobago (and Little Tobago) have no native Anolis or even widespread Anolis associated with mainland South America - this is very strange. It's very difficult to find any piece of neotropical real estate - no matter how small - that does not have native anoles.

In the 1997 book I placed an emphasis on changing sea levels in the Pleistocene in an attempt to explain how and why Trinidad and Tobago have the species they do. At the time I wrote the book, Haffner's forest refugia hypothesis was being used to explain the distribution of many South American organisms, particularly vertebrates and butterflies. But, 25 years later it is clear that while the forest refugia may have been influential, they are by no means the whole story. In South America, the changing course of the Amazon and Orinoco Rivers combined with marine intrusions into continental South America during the Miocene play an important role in biogeographical theories. Trinidad and Tobago were most certainly impacted by these Miocene events.

Clues as how how Tobago got its mainland fauna (and flora) are going to be found in the DNA of those species living there today as well as their relatives found on mainland South America and Trinidad. In fact this has already started to happen. Camarego et al. (2009)  found that Leptodactylus validus colonized Trinidad a mere 1.025 mya, and only arrived in Tobago 219,000 years ago. Gamble et al. 2008 found Gonatodes ceciliae (a Trinidad endemic) and Gonatodes ocellatus (a Tobago endemic) shared an ancestor about 3.8 mya. So, from these dates it appears that there is not going to be a single event to explain how Tobago got its continental fauna. However, it seems probable that there will be some event to explain the origin of a large number of the species present on the island.

Two years ago I started to take a second, very careful look at the species on Trinidad and Tobago and compare their morphology to relatives on the mainland, the results have been startling. Many of what are believed to be widespread species are not, they are endemic species, often cryptic in appearance, suggesting that, while the islands have been connected to the mainland many times in the Pleistocene as sea level rose and fell with glacial cycling, there was considerable speciation prior to Pleistocene, and the islands were invaded and re-invaded by different lineages of mainland species. So the extant fauna is the result of both dispersal and vicariance, speciation and extinction.

Thus, the stream frogs of the genus Mannophryne on Trinidad and Tobago are not sisters, that is they are not each others closest relatives as might be expected if Tobago was the eastern end of the Venezuela's Coastal Andes. Manzanilla et al. (2009) used partial sequences of mitochondrial 16S and cytochrome oxidase and analysed 1.2 kb from 13 of the 15 described species of Mannophryne at the time and found three deeply differentiated clades that split from each other in a relatively short period of time. The evolution of the frog clades occurred well before the glacial-interglacial periods of the Quaternary. Also they found the Tobago Mannophryne olmonae to be more closely related to the Venezuelan species M. riveroi ( from Cerro Azul on the Península de Paria, Sucre, Venezuela, between 400–1000m ) than to the Trinidad island endemic M. trinitatis which is more closely related to M. venezuelensis (from the slopes of the Peninsula de Paria, Sucre, Venezuela from sea level to 600 m) .

Santos et al. (2009) wrote, "Interestingly, the contemporaneous divergence of the Trinidad and Tobago species (Mannophryne trinitatis and M. olmonae) from Venezuelan relatives at 8.3 MYA suggests a global period of high sea level."

There seems to be a problem here, because trinitatis and olmonae are not sisters and they did not necessarily diverge at the same point in time from their respective sisters in Venezuela.

Pindell and Kennan (2007) describe the Gulf of Paria as a pull-apart basin formed in the late Miocene. Assuming that this was in part responsible for the opening of the the channel between Trinidad's northern Peninsula and the Paria Peninsula, as well as the formation of the Bocas Islands this event would have effectively separated the two sister species of M. trinitatis and M. venezuelensis (or their ancestors). But, the separation of M. olmonae and M. riveroi. How did this happen? One possibility, that no longer seems viable, is that M. riveroi was widespread and ranged from Venezuela, across Trinidad's Northern Range and right out on to Tobago and then became extinct on Trinidad - but Tobago was not in its present location it was moving on the Caribbean plate towards its current position.

Also, sea level has undergone dramatic changes over the past 30 my. Below, is a graph that shows sea level changes, note that in the Oligocene there were times when sea level was ~200 m above present levels and in the Miocene there was a point when it was ~75 m below present levels. Directly above the graph are maps of T&T showing elevations. When sea level rises a substantial part of the islands are covered by seas, greatly restricting the area of land available for terrestrial vertebrates, and when sea level drops the amount of land available of terrestrial organisms expands. I have attempted to color code the graph to the maps. Assuming Tobago did not rise or sink due to tectonics, when sea level rose 150 m there was only 150.7 km2 of exposed land on Tobago, when sea level was up 200 m there was only 73.6 km2 of land surface exposed.

Tobago's movement is shown in the bottom pane of the attached figure taken from Pindell and Kennan (2007) - the red line.  Tobago is moving on the Caribbean plate and 11 mya (towards the end of the middle Miocene) Tobago is located about 50 km north of the Paria Peninsula, at a time when sea level is low - about 75 m lower than it is today. Thus, it is entirely possible that there was a dry land connection between Tobago and the Paria Peninsula, or perhaps Tobago was pushed directly up to the continent and made contact with it directly. In either case the fauna from northern Venezuela could have moved directly onto Tobago and as the island continued its travels towards its present location it may have by-passed Trinidad completely without contact. Sea level was also low at various time during the last 3 my, but by that time it had moved passed the Venezuelan coast well on its way to its present position.

This hypothesis can be tested with DNA.



References
Camargo A, W. R. Heyer, R. O. de Sá. 2009. Phylogeography of the frog Leptodactylus validus (Amphibia: Anura): patterns and timing of colonization events in the Lesser Antilles. Molecular Phylogenetics and Evolution 53:571-579.

Castroviejo-Fisher, S., J. C. Señaris, J. Ayarzagüena, and C. Vilà . 2009 "2008". Resurrection of Hyalinobatrachium orocostale and notes on the Hyalinobatrachium orientale species complex (Anura: Centrolenidae). Herpetologica 64: 472-484.

Eberli, G. P. 2000. The record of Neogene sea-level chances in the prograding carbonates along the Bahamas Transect - Leg 166 Syntheisis. Pages 167-177 In: Swart, P.K., Eberli, G.P., Malone, M.J., and Sarg, J.F. (Eds.), 2000. Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 166.

Gamble, T., A. M. Bauer, E. Greenbaum, and T.R. Jackman. 2008. Evidence for Gondwanan vicariance in an ancient clade of gecko lizards. Journal of Biogeography 35: 88-104

Manzanilla, J., M. J. Jowers, E. La Marca, and M. García-París . 2007. Taxonomic reassessment of Mannophryne trinitatis (Anura: Dendrobatidae) with a description of a new species from Venezuela. Herpetological Journal, 17: 13-42.

Murphy, J. C. 1997. Amphibians and Reptiles from Trinidad and Tobago. Krieger Publishing Company. Malabar. 245 pp.

Pindell, J. and  Kennan, L. 2007. Cenozoic kinematics and dynamics of oblique collision between two convergent plate margins: the Caribbean-South America collision in eastern Venezuela, Trinidad, and Barbados. In: Kennan, L., Pindell, J. L. & Rosen, N. C. (eds) Transactions of the 27th GCSSEPM Annual Bob F. Perkins Research Conference: The Paleogene of the Gulf of Mexico and Caribbean
Basins: Processes, Events and Petroleum Systems, 458-553.

Pindell, J. and Kennan, L. 2009. Tectonic evolution of the Gulf of Mexico, Caribbean and northern South America in the mantle reference frame: an update. In: James, K., Lorente, M. A. & Pindell, J. (eds) The geology and evolution of the region between North and South America. Geological Society of London, Special Publication.

Santos J.C., L. A. Coloma, K. Summers, J. P. Caldwell, R. Ree, et al. 2009. Amazonian Amphibian Diversity Is Primarily Derived from Late Miocene Andean Lineages. PLoS Biology 7(3): e1000056. doi:10.1371/journal.pbio.1000056.


Snoke, A. and P. J. Noble. 2001. Ammonite-radiolarian assemblage, Tobago Volcanic Group, Tobago, West Indies—Implications for the evolution of the Great Arc of the Caribbean. GSA Bulletin, 113: 256–264



Sunday, November 6, 2011

Patrons Needed for the New Trinidad & Tobago Herpetofauna Volume

Several years ago Roger Downie, at the University of Glasgow, started talking to me about a new book on Trinidad and Tobago herps. In 2010 we had a meeting with people interested in working on the project. After that the project was stalled because I was side tracked by other projects. Now, I have returned to look at designing an outline for a new herpetology volume that focuses on the islands' environments, biogeography, and how they relate to the herpetofauna. Preliminary field work was done in 2010 and 2011, and plans are being made for additional field work in the summer of 2012. We are only getting started at this time, but the book will have multiple authors and contributors from at least four different countries. Much of the nomenclature has changed since the 1997 book was published (and is available on this web site), recent ecological and systematic work as been done, new species have been added to the islands' fauna and there are more taxa to be discovered and described. We are also working on collecting new photographs of animals and habitats. Note that the cover above is for illustration purposes only.

We need patrons for this project. Funding for additional field work would help move things along. But more importantly money to underwrite the final cost of the book would allow us to keep the price low on the final volume, allow us to include more color plates, and make the book more readily available to a wider audience. If you are interested in helping send me an email at serpentresearch@gmail.com JCM

Friday, September 30, 2011

New Frog Added to Trinidad's Herpetofauna

Scarthyla vigilans from southwestern Trinidad. JCM

The tiny, grass-dwelling frog, Scarthyla vigilans (Hylidae) has been officially added to the herpetofauna of Trinidad. The frog avoided detection of previous researchers investigating the fauna of the continetal island until 2006 when J. Roger Downie and Joanna M. Smith collected striped tadpoles from an irrigation ditch in a coconut plantationin the southwest peninsula of the island. The tadpoles positioned themselves vertically in the water adjacent to submerged grass stems.The tadpoles did not match any of the known species from Trinidad.The tads weighed only 0.26 g and measured about 29 mm. Two adults were collected in 2007, and more were added in 2010. The frogs were discovered in Venezuela's Orinoco Delata in 2008, but were previously known from northeast Colombia and northwest Venezuela. The small size (14-19 mm) of adults, their very insect-like call, and their superficial similarity to the very common and widespread Scinax rubra has contributed to them going undiscovered. The full paper is available on-line.

Citation
Smith, J.M.; J.R. Downie; R.F. Dye; V. Ogilvy; D.G. Thornham; M.G. Rutherford; S.P. Charles; J.C. Murphy.2011. Amphibia, Anura, Hylidae, Scarthyla vigilans (Solano, 1971): Range extension and new country record for Trinidad, West Indies, with notes on tadpoles, habitat, behavior and biogeographical significance. Check List 7(5):574-577.

Friday, September 9, 2011

Epicrates maurus

Epicrates maurus. JCM
The Rainbow Boas of the genus Epicrates are widespread in the Caribbean with nine species and another five species that range from Costa Rica to Argentina. Recent molecular work shows the genus to be paraphyletic, and the mainland species will undoubtedly remain in the genus Epicrates while the West Indian forms will probably be placed in another genus, perhaps Fischer's genus Homalochilus that is now in the synonymy of Epicrates striatus.

Recently, Rivera et al. (2011) have analyzed two independent data sets, environmental niche models and phylogeny based on molecular information, to explore species delimitation in the continental species of this genus. Their results indicated that the environmental requirements of the species are different and are not ecological interchangeable. The authors found a correlation between species distributions and the major biogeographic regions of Central and South America. The distribution of the five species reveals that allopatry or parapatry is the general pattern suggesting that habitat isolation prevents or limits gene flow between the species. Their phylogenetic reconstruction shows that the mainland Epicrates are monophyletic and the sister to the anacondas (Eunectes). E. maurus shows a disjunct distribution, and is present in the dry forest of the biogeographic regions Pacific Coast, Venezolana, Savanna, Guajira and some areas in the Amazonic domain, in Central America and Northern South America. On Trinidad and Tobago this snake does quite well in the presence of humans and can be found in urban and agriculture areas, habitat use that might be expected of a species that uses dry forests.

Citation
Rivera PC, Di Cola V, Martínez JJ, Gardenal CN, Chiaraviglio M (2011) Species Delimitation in the Continental Forms of the Genus Epicrates (Serpentes, Boidae) Integrating Phylogenetics and Environmental Niche Models. PLoS ONE 6(9): e22199. doi:10.1371/journal.pone.0022199

Sunday, August 28, 2011

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.

Friday, August 5, 2011

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.






Monday, August 1, 2011

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


Monday, July 11, 2011

Monday, May 16, 2011

Welcome

This is the beginning of the Herpetology of Trinidad and Tobago web site and blog, its purposes are to advance knowledge of the T&T herpetofauna, educate the public, and promote an appreciation for the diverse nature of the fauna. Conservation of these unique animals and their habitats needs to be a priority. While many of the Trinidad and Tobago species have populations in mainland South America, many do not.

Please note that this is not a commercial web site, however we will advertise natural history books related to this site and the Eastern Caribbean. If you are an author and would like your book shown on this web site, contact us. There is no charge. We will also provide a list of businesses that service ecotourists. Trinidad and Tobago are excellent locations for observing many neotropical ecosystems, amphibians, reptiles, birds, and mammals. Ecotourism can be a valuable tool for conservation.