Wednesday, April 29, 2015

Tracking Python bivittatus in Everglades National Park

The largest and longest Burmese Python tracking study of its kind -- here or in its native range -- is providing researchers and resource managers new information that may help target control efforts of this invasive snake, according to a new study led by the U.S. Geological Survey.

Among the findings, scientists have identified the size of a Burmese python's home range and discovered they share some "common areas" that multiple snakes use.

"These high-use areas may be optimal locations for control efforts and further studies on the snakes' potential impacts on native wildlife," said Kristen Hart, a USGS research ecologist and lead author of the study. "Understanding habitat-use patterns of invasive species can aid resource managers in designing appropriately timed and scaled management strategies to help control their spread."
Using radio and GPS tags to track 19 wild-caught pythons, researchers were able to learn how the Burmese python moved within its home range. The 5,119 days of tracking data led researchers to conclude that python home ranges are an average of 22 square kilometers, or roughly an area 3 miles wide-by-3 miles long, all currently within the park.

The study found pythons were concentrated in slough and coastal habitats, with tree islands being the principal feature of common-use areas, even in areas where they were not the predominant habitat type. The longest movements of individual pythons occurred most often during dry conditions, but took place during "wet" and "dry" seasons.

Burmese pythons are long-lived, large-bodied constricting snakes native to Southeast Asia. Highly adaptable, these ambush predators can reach lengths greater than 19 feet and produce large clutches of eggs that can range from eight to 107 eggs. Burmese pythons were first observed in South Florida's Everglades National Park in 1979. Since then, they have spread throughout the park. Although recent research indicates the snakes may be having a significant effect on some populations of mid-sized mammals, it has also shown there is little risk to people who visit Everglades National Park.

Invasive species compete with native wildlife for food, and they threaten native biodiversity across the globe. With nearly 50 percent of the imperiled species in the US being threatened by exotic species, a major concern for land managers is the growing number of exotics that are successfully invading and establishing viable populations.

Florida is home to more exotic animals than any other state. Snakes in particular have been shown to pose a high risk of becoming invasive species. The establishment of Burmese pythons in South Florida poses a significant threat to both the sensitive Everglades ecosystem and native species of conservation concern. For example, in the park, wood storks, Florida panthers and Cape Sable seaside sparrows are all species of conservation concern that have home ranges near the common-use areas of the radio-tracked pythons.

Citation
Kristen M Hart, Michael S Cherkiss, Brian J Smith, Frank J Mazzotti, Ikuko Fujisaki, Ray W Snow, Michael E Dorcas. 2015. Home range, habitat use, and movement patterns of non-native Burmese pythons in Everglades National Park, Florida, USA. Animal Biotelemetry, 3 (1) DOI: 10.1186/s40317-015-0022-2


Monday, April 27, 2015

The endemic freshwater snake Parahelicops boonsongi moved to a new genus

Isanophis boonsongi new comb., preserved 
holotype (FMNH 135328). From top to 
bottom: Dorsal view - Ventral view - 
Lateral view of the head and neck, left side. 
Photographs by Patrick David.
There is little doubt that Southeast Asia harbors the most diverse assemblage of living snake species. And, a number of species from the Indochinese region, including Thailand, are still poorly known only, in some cases known only from their holotype or type series, or at best a handful of specimens. Natricid snakes are particularly diverse in Southeast Asia and three genera contain species that seem to be restricted to very small ranges, they are all aquatic and despite being described in the mid-20th century have remained enigmatic.
Angel’s stream snake, Paratapinophis praemaxillaris described by Angel in 1929, has been known from two syntypes from northern Laos, and six other specimens from China and Thailand. Two other natricine species, Pararhabdophis chapaensis and Parahelicops annamensis both described by Bourret in 1934, were previously known from their respective holotypes. However, Stuart (2006) described a second specimen of P. annamensis, from Laos in 2006. Recently, intensive fieldwork in northern Vietnam and Laos, recovered about 10 specimens of Parahelicops annamensis and Pararhabdophis chapaensis each. Another rare species, Parahelicops boonsongi described by Taylor and Elbel in 1958 was described on the basis of a single specimen from Loei Province in northeastern Thailand. Subsequently, two additional specimens, also from Loei Province were found by Cox in 1995.

Taylor and Elbel placed their new species to the genus Parahelicops because of morphological similarities with P. annamensis, such as the single prefrontal. However, the generic status of Parahelicops has been controversial since its description. It was established by Bourret for a new species, Parahelicops annamensis, on the basis of a single specimen with the following characters: 25 subequal maxillary teeth, the last two enlarged; head quite distinct from the neck; eye small with a round pupil; nostrils directed upwards; two internasals, a single prefrontal; elongated body, slightly laterally compressed; dorsal scales keeled, without apical pits, in 15 rows; tail long; subcaudals paired; hypapophyses developed throughout the vertebral column. Bourret (1934b) also noted its similarity to Opisthotropis but differed in dentition, having its head distinct from the neck, and its elongated body.

Parahelicops boonsongi was described by Taylor and Elbel in 1958 and is known from only three specimens from Thailand. It has been placed either in the genus Parahelicops Bourret, 1934, along with Parahelicops annamensis, as well as the genus Opisthotropis G√ľnther, 1872. In a new paper David et al. (2015) compared its morphological characters with those of P. annamensis and with three other relevant genera, Opisthotropis, Pararhabdophis Bourret, 1934, and Paratapinophis Angel, 1929. Parahelicops boonsongi is phenotypically distinct from Parahelicops annamensis, Opisthotropis, and all other natricine genera. The authors erect a new genus, Isanophis gen. nov., to accommodate Parahelicops boonsongi. How these snakes are related to each other and other natricids remains to be determined.

Citation

David, P., Pauwels, O. S., Nguyen, T. Q., & Vogel, G. (2015). On the taxonomic status of the Thai endemic freshwater snake Parahelicops boonsongi, with the erection of a new genus (Squamata: Natricidae). Zootaxa, 3948(2), 203-217.

Friday, April 17, 2015

The sea snake assemblage in the Muar estuary

Enhydrina schistosa. Photo credit: Aaron Lobo
The first major survey of marine snakes were published by Malcolm Smith and covered the coastal areas of the Gulf of Thailand and the Malay Peninsula between 1915 and 1918 and yielded a collection of 548 sea snakes representing 17 species. These snakes were obtained as by-catch from local coastal fisherman using a variety of fishing techniques. In the late 1930’s and early 1940’s Bergman reported on another large collection of marine snakes from coastal areas near Sourabaya (Surabaya, Java). The collections were made by local fisherman between 1936 and 1942, and consisted of 984 specimens representing six species (3 or more additional species were “disregarded” due to rarity). This collection may represent the first major collection of marine snakes in which all specimens from a single coastal area were caught, retained and identified, thus providing both the species richness and some data on relative abundance.

After World War II the use of mechanized diesel-powered bottom trawlers expanded in Southeast Asia and as the demersal fish harvest increased, so must have the marine snake by-catch. This technology allowed for numerous sea snake surveys that covered very large geographic areas (80,000 to more than 120,000 km2) such as Tonking Bay, the South China Sea, the Sahul Shelf , the Gulf of Carpentaria and northern coast of Australia, the Gulf of Thailand, and coastal areas of Borneo. Although many of these surveys resulted in both a species count and the relative abundance of each species, they lacked value at the level of ecological communities because the areas sampled were vast and often ill defined.  

Now, Voris (2015) reports on an extensive collection of marine snakes obtained from a few stationary stake nets in one locally defined area of about two square kilometers. Each captured snake was identified to species and tallied over a period of nine months to allow for overall estimates of species diversity as well as comparisons of diversity between collections from different stake nets within the area, and between collections made during different tidal cycles. This survey of marine snakes in the mouth of the Muar River had two goals. First, it aimed to determine the overall marine snake diversity in the river mouth. Second, it sought to determine if there might be differences in species diversity on a small spatial scale.

He found the marine snakes that inhabit the mouth of the Muar River have adapted to a very dynamic tidal environment that is relatively small in area and spatially restricted by shorelines on two sides. In addition to the hourly changes in salinity, turbidity, speed of the current and direction of flow, the river also varies in depth. Extensive sampling over many months at Muar revealed an assemblage of marine snakes that included one very common species, three common species, four rare species, and three very rare species that likely represent waifs. These collections strongly support the view that the numerical marine snake species richness for the mouth of the Muar River is eight species.

The 968 adult marine snakes collected at the stake nets at Muar belonged to 11 species in three snake families: Acrochordidae (Acrochordus granulatus), Homalopsidae (Cerberus schneiderii), and Elapidae (Hydrophiini, true sea snakes). This assemblage was strongly dominated by the beaked sea snake, Enhydrina schistosa, with, E. schistosa and three species of Hydrophis (H. melanosoma, H. brookii, and H. torquatus) make up 98% of the snakes.

Although the Muar River sample represents an assemblage from only one river mouth, the eight species observed at Muar falls in the middle of the range of 5 to 12 species recorded in other surveys. Yet, when it comes to relative abundance the strong dominance of E. schistosa in the Muar River mouth community makes the Muar assemblage the least diverse of all comparable surveys. The comparisons highlight the unique nature of the marine snake survey at the mouth of the Muar River, the only discreet estuarial location in the world that has been surveyed for relative abundances of marine snakes.


Citation

Voris, H. K. (2015). Marine Snake Diversity in the Mouth of the Muar River, Malaysia. Tropical Natural History 15:1-20.

Dehydration and drinking in sea snakes

A new article (Lillywhite et al. 2015) in the Journal of Zoology reports on the drinking behavior a sea snakes. It had been assumed sea snakes had a salt gland located under their tongue and that it was involved in the regulation of sodium ions,allowing the snakes to drink sea water. However, experimental work suggested that sea snakes, while in sea water do not drink. Instead, marine snakes dehydrate at sea and are dependent on environmental sources of fresh water to maintain water balance. They may drink freshwater off the surface of the ocean that comes from rain, or from the mouths of rivers (freshwater being less dense that salt water tends to stay on top until it is mixed with sea water; but only if it is available. Lillywhite et al (2015) investigated the dehydration and drinking responses of five species of hydrophiin sea snakes collected during the dry season in northern Australia. None of these snakes would drink sea water, even when dehydrated. Dehydrated individuals of Hydrophis curtus, H. elegans and H. zweifeli drank fresh water, and the mean threshold levels of dehydration that first elicited drinking were deficits of −26, −29 and −27% of body mass, respectively. Individuals of Aipysurus mosaicus and H. peronii did not drink fresh water when similarly dehydrated. Few snakes they collected following more than four months of drought drank fresh water immediately after capture. Species of Hydrophiin appear to have a high resistance to dehydration, which they evidently tolerate in marine habitats for extended periods during drought. Thirst in these species is significantly less sensitive than in other species, suggesting that marine snakes have variable requirements for drinking fresh water. The results illustrate that sea snakes are characterized by diverse responses to dehydration and likely have different osmoregulatory strategies for survival, with implications for better understanding the evolutionary success of secondarily marine vertebrates and their potential responses to future changes in tropical precipitation.

Citation

Lillywhite, H. B., Heatwole, H. and Sheehy, C. M. (2015), Dehydration and drinking behavior in true sea snakes (Elapidae: Hydrophiinae: Hydrophiini). Journal of Zoology. doi: 10.1111/jzo.12239

Thursday, April 16, 2015

Coyote refuses to eat a dead kingsnake


The very short video below shows a coyote attempting to scavenge a dead California Kingsnake (Lampropeltis californiae) in southeastern Arizona. The canid picked it up with its mouth and then dropped it - apparently because it tasted bad. The snake was one of two killed by a human and left to rot. The kingsnake is shown below.

video


Friday, April 3, 2015

Ancient over-water dispersal of amphisbaenia

Tiny, burrowing reptiles known as worm lizards or amphisbaenians became widespread long after the breakup of the continents, leading scientists to conclude that they must have dispersed by rafting across oceans soon after the extinction of the dinosaurs, rather than by continental drift as previously thought.
Scientists at the Universities of Bath, Bristol, Yale University and George Washington University used information from fossils and DNA from living species to create a molecular clock to give a more accurate timescale of when the different species split apart from each other.
The team studied fossils of worm lizards (Amphisbaenia), a type of burrowing lizards that live almost exclusively underground. The six families of worm lizards are found in five different continents, puzzling biologists as to how these creatures became so widespread.
They found that the worm lizards evolved rapidly and expanded to occupy new habitats around 65 million years ago, just after the impact of an asteroid that caused the mass extinction of about 75% of living things on Earth, including the dinosaurs.
Since this event occurred after the break-up of the super-continent Pangaea, the researchers conclude that these animals could not have dispersed across the globe using land bridges.
Instead they argue that this evidence supports a theory proposed by Charles Darwin and Alfred Russell Wallace in the 19th Century that creatures crossed from continent to continent crossing land bridges or floating across oceans -- in this case being carried across the oceans on floating vegetation.
Dr Nick Longrich, from the University of Bath, explained: "Continental drift clearly can't explain the patterns we're seeing. Continental breakup was about 95 million years ago, and these animals only become widespread 30 million years later.
"It seems highly improbable not only that enough of these creatures could have survived a flood clinging to the roots of a fallen tree and then travelled hundreds of miles across an ocean, but that they were able to thrive and flourish in their new continent.
"But having looked at the data, it is the only explanation for the remarkable diversity and spread of not just worm lizards, but nearly every other living thing as well.
"Once you eliminate the impossible, whatever you're left with, no matter how improbable, must be the truth."
The researchers suggest that mass extinction actually helped the survivors of the asteroid hit colonize new places and diversify because there was less competition for food from other species.
Dr Jakob Vinther, from the University of Bristol, said: "The asteroid hit would have killed most of the plants, meaning there was no new food.
"However, scavengers like worm lizards that live off dead and decaying matter were able to survive and thrive. Their tunnels would have acted like bomb shelters, allowing them to withstand the asteroid impact and without any competition for food and space, they flourished."
Their study, published in the Proceedings of the Royal Society B, describes the earliest definitive fossil evidence of worm lizards, around 100-1000 years after the asteroid hit and long after the break-up of Pangaea. The data suggest that the lizards must have travelled across the oceans at least three times: from North America to Europe, from North America to Africa and from Africa to South America.

Citation
Longrich NR, Vinther J, Pyron RA, Pisani D, Gauthier JA. 2015. Biogeography of worm lizards (Amphisbaenia) driven by end-Cretaceous mass extinction. Proceedings of the Royal Society B, 2015 DOI:10.1098/rspb.2014.3034