Thursday, March 27, 2014

Dehydration in sea snakes

Like camels of the sea, a species of sea snake goes without a drink for months on end, gradually dehydrating, before refueling with freshwater when rain falls, new research suggests.

"Perhaps six or seven months of the year, these snakes are living thirsty," said Coleman Sheehy III, an evolutionary biologist at the University of Florida, and a co-author of the study published March 18 in the journal Proceedings of the Royal Society B.

Past studies have found that snakes can dehydrate for short periods of time and then gulp freshwater when it's available, but those snakes typically have access to freshwater sources such as nearby springs. [Image Gallery: Snakes of the World]

The yellow-bellied sea snake, Hydrophis platurus, by contrast, has a vast range and habitat. The 3.3-foot-long snakes drift along ocean currents feeding on fish, and are found in the middle of the vast Indian and Pacific oceans, spending months without any freshwater sources.

To understand exactly how they manage this feat, Sheehy and his colleagues gingerly collected hundreds of the wild sea snakes in the Guanacaste province of Costa Rica. (The sea snakes have a nasty, venomous bite, though no one has died from one, Sheehy said.) In that region, the dry season lasts from December to May or June, and the snakes were collected on several different trips at different points in both seasons.

'They tank up during the rainy season and then it takes a while for them to get thirsty enough to drink.'
 Coleman Sheehy III, an evolutionary biologist at the University of Florida

They then took the snakes back to their lab, towel-dried them, and measured and weighed them.

Next, they placed the snakes in freshwater tanks to see whether the sea creatures drank.

Snakes collected after long dry spells were extremely skinny, because they had been slowly drying out. The slimmest snakes also drank freshwater in the lab aquariums, plumping up and rehydrating.

But many snakes collected during the rainy season and shortly afterward didn't sip a drop of water, suggesting they can go quite a while, even one to two months, before they get the urge to rehydrate.

"They tank up during the rainy season and then it takes a while for them to get thirsty enough to drink," Sheehy told Live Science.

The team suspects that H. platurus has evolved adaptations to prevent freshwater loss through the skin.

But at some point, the sea snakes need to drink, so where do they get their water?

"The only source of freshwater for a marine snake like this species that's living in the middle of the ocean is rainfall," Sheehy said.

During rainy periods, the rainfall floats at the top of the denser saltwater ocean and accumulates in layers known as freshwater lenses. It's these freshwater lenses that provide a drink for the parched yellow-bellied sea snake.

The snakes are hardwired to come up to the surface to drink, even when they are in a freshwater aquarium where a good drinking source is all around them, Sheehy said.

The new study shows that animals that evolved on land but then moved into the seas have developed a unique array of adaptations to their salty home. For instance, whales seals, sea turtles and other animals have evolved not to need any freshwater access at all either by having salt glands that process seawater, or by extracting water from their food, Sheehy said.

"Instead of adapting to marine environments like many other vertebrates have, these animals, sea snakes, have taken a different approach," Sheehy said.

HB Lillywhite, CM. Sheehy III, F Brischoux, and A Grech. 2014. Pelagic sea snakes dehydrate at sea. Proceedings of the Royal Society B.May 7, 2014 281 1782 20140119; doi:10.1098/rspb.2014.0119 1471-2954

Sunday, March 23, 2014

Homing & navigation in the invasive Python bivittatus

Evidence for homing behavior and navigation in snakes has been around for awhile see Stickel and Cope (1947) and such behavior should not be at all surprising in Python bivittatus, so keep this in mind while reading the popular press release below.

By Mickie Andersson, University of Florida News Center

GAINESVILLE — If you pick them up and drop them in a new location, most snakes will move rapidly but erratically, often traversing the same terrain before giving up and settling into their new digs.

A team of researchers including scientists from the University of Florida has discovered that the giant snakes — which have invaded and affected the food chain in Everglades National Park and Big Cypress National Preserve — can find their way home even when moved more than 20 miles.

The findings, published last week by the Royal Society’s Biology Letters, change how researchers understand pythons’ behaviors and intellect.

“This is way more sophisticated behavior than we’ve been attributing to them,” said Frank Mazzotti, a UF wildlife ecology and conservation professor based at the Fort Lauderdale Research and Education Center. “It’s one of those things where nature makes us go ‘wow.’ That is truly the significance of this.”

In 2006 and 2007, researchers captured 12 pythons and surgically implanted radio transmitters that allowed them to track the snakes’ movements. As a control group, they returned six of the snakes to the spot of their capture and turned them loose.

The remaining six snakes were taken to spots ranging from 13 to 22 miles away from where they had been captured and turned loose. To the researchers’ surprise, the snakes oriented themselves toward “home” and maintained their bearings as they traveled.

And although it took between 94 and 296 days for five of the six snakes to get within three miles of home, partly due to it being the snakes’ dormant season, the reptiles kept that orientation — a clear signal to scientists that the snakes have both “map” and “compass” senses.

The relocated snakes appeared to use local cues at the release site to understand their position relative to home (the map sense), and appeared to use cues along the way (their compass sense) to ensure that they remained on track, although the researchers don’t yet know what those cues are: smell, perhaps the stars, light or some kind of magnetic force.

Mazzotti said it’s helpful for researchers to know that the snakes move purposefully through their environment, but in reality, it’s not that much help.

“It amps up a little bit our concern about the snakes, but given all the other things we know about pythons, the amount of increasing concern is minor,” he said.

The Burmese python has been an invasive species in South Florida since about 2000, likely stemming from accidental or purposeful releases by former pet owners. The largest python found in the Everglades area had grown to more than 18 feet.

The snakes suffocate and eat even large animals, such as deer and alligators, and in 2012, a research team that included Mazzotti found severe declines in sightings in python-heavy areas of native animals including raccoons, opossum, bobcats and rabbits.

In 2012, the federal government banned the import and interstate trade of four exotic snake species: the Burmese python, the yellow anaconda, and North and South African python.

Pittman SE, Hart KM, Cherkiss MS, Snow RW, Fujisaki I, Smith BJ, Mazzotti FJ, and Dorcas ME. 2014. Homing of invasive Burmese pythons in South Florida: evidence for map and compass senses in snakes Biol. Lett. March, 2014 10 3 20140040; doi:10.1098/rsbl.2014.0040 1744-957X.

Stickel, WH. Cope JB. 1947. The home ranges and wanderings of snakes. Copeia, 127-136.

Thursday, March 20, 2014

Rukwanyoka holmani; the oldest advanced venomous snake

A vertebrae of the oldest fossil venomous snake 
Rukwanyoka holmani in Africa. Photo Credit:
Ohio University.
Ohio University scientists have found the oldest definitive fossil evidence of modern, venomous snakes in Africa, according to a new study published March 19 in the journal PLOS ONE.

The newly discovered fossils demonstrate that elapid snakes—such as cobras, kraits and sea snakes—were present in Africa as early as 25 million years ago, said lead author Jacob McCartney, a postdoctoral researcher in the Ohio University Heritage College of Osteopathic Medicine. He's part of a team that has been examining the Rukwa Rift Basin of Tanzania over the last decade to understand environmental change through time in the East African Rift System.

Elapids belong to a larger group of snakes known as colubroids, active foragers that use a variety of methods, including venom, to capture and kill prey.

Colubroid fossils are documented as early as 50 million years ago. But they weren't expected to constitute such a large part of the African snake fauna 25 million years ago, as they became dominant in Europe and North America much later.

"In the Oligocene epoch, from about 34 to 23 million years ago, we would have expected to see a fauna dominated by booid snakes, such as boas and pythons. These are generally 'sit and wait' constricting predators that hide and ambush passing prey," McCartney said.

In fact, the recent study includes a description of the oldest evidence of African booid snakes, he said. The researchers have named this new species Rukwanyoka holmani; the genus name combines the Rukwa region name with the Swahili word for snake, and the species name is in honor of J. Alan Holman, a paleontologist and mentor.

However, the team was surprised to discover that the fauna actually revealed more colubroids than booids. That higher-than-expected concentration of colubroid snakes suggests that the local environment became more open and seasonally dry—and, in turn, more hospitable to these active foraging types of snakes that don't require cover to hide and ambush prey—at an earlier time in Africa than in most other parts of the world, as documented in previous studies.

"This finding gives further strength to the idea that tectonic activity in the East African Rift has helped to shape animal habitats in fascinating ways," said Nancy Stevens, an associate professor of biomedical sciences at Ohio University and co-author of the study. "The fossils suggest a fundamental shift toward more active and potentially venomous snakes that could exert very different pressures on the local fauna."

More fossils from additional locations should indicate whether colubroid snakes dominated all of Africa during the Oligocene or just the local region around the Rukwa Rift, McCartney said.

The study published in PLOS ONE describes eight different types of fossil snakes from the Rukwa Rift (five colubroid and three booid), with vertebrae ranging in length from 2.6 mm to just over 5 mm.

McCartney JA, Stevens NJ, O’Connor PM (2014) The Earliest Colubroid-Dominated Snake Fauna from Africa: Perspectives from the Late Oligocene Nsungwe Formation of Southwestern Tanzania. PLoS ONE 9(3): e90415. doi:10.1371/journal.pone.0090415

Monday, March 10, 2014

Jurassic sites link fossil communities of amphibians, reptiles, and mammals

The fossil salamander Chunerpeton shows the
preserved skeleton, the skin, and  external gills.
Photo Credit: Society of Vertebrate Paleontology.

Over the last two decades, huge numbers of fossils have been collected from the western Liaoning Province and adjacent parts of northeastern China, including exceptionally preserved feathered dinosaurs, early birds, and mammals. Most of these specimens are from the Cretaceous Period, including the famous Jehol Biota. However, in recent years many fossils have emerged from sites that are 30 million years earlier, from the Middle-Upper Jurassic Period, providing an exceptional window on life approximately 160 million years ago. A new paper published in latest issue of the Journal of Vertebrate Paleontology shows that several of these Jurassic sites are linked together by shared species and can be recognized as representing a single fossil fauna and flora, containing superbly preserved specimens of a diverse group of amphibian, mammal, and reptile species.

This fossil assemblage, newly named the Daohugou Biota after a village near one of the major localities in Inner Mongolia, China, dates from a time when many important vertebrate groups, including our own group, mammals, were undergoing evolutionary diversification. The Daohugou Biota makes an immense contribution to our understanding of vertebrate evolution during this period, with such notable creatures as the oldest known gliding mammal, another early mammal that may have swum with a beaver-like tail, the oldest dinosaurs preserved with feathers, and a pterosaur that represents an important transitional form between two major groups. As described by Dr. Corwin Sullivan, lead author of the study, "The Daohugou Biota gives us a look at a rarely glimpsed side of the Middle to Late Jurassic -- not a parade of galumphing giants, but an assemblage of quirky little creatures like feathered dinosaurs, pterosaurs with 'advanced' heads on 'primitive' bodies, and the Mesozoic equivalent of a flying squirrel."

Almost more impressive than the diversity of the biota is the preservation of many of the vertebrate specimens, including complete or nearly-complete skeletons associated with preserved soft tissues such as feathers, fur, skin or even, in some of the salamanders, external gills. Dr Yuan Wang, co-author of the study, explained, "The Daohugou amphibians are crucially important in the study of the phylogeny and early radiation of modern amphibian groups."

Dr. Paul Barrett, dinosaur researcher at the Natural History Museum, London, who was not involved with the study, commented, "Daohugou is proving to be one of the key sites for understanding the evolution of feathered dinosaurs, early mammals, and flying reptiles, due largely to the fantastic levels of preservation. Many of the fossils are stunning and offer vast amounts of information. There are only a handful of similar sites elsewhere in the world and this article represents the first comprehensive attempt to draw all of the relevant information together into a single benchmark paper." Because the Daohugou Biota and the much better studied Jehol Biota are similar in preservational mode and geographic location, but separated by tens of millions of years, they give palaeontologists an outstanding, even unique, opportunity to study changes in the fauna of this region over a significant span of geological time and an important period in vertebrate evolution. As Dr. Sullivan further remarked, "The Cretaceous feathered dinosaurs of northeastern China have been astonishing palaeontologists and the public for almost two decades now, and the Daohugou Biota preserves their Jurassic counterparts in the same region. As prequels go, it's pretty exciting."

Corwin Sullivan, Yuan Wang, David W. E. Hone, Yuanqing Wang, Xing Xu, Fucheng Zhang. The vertebrates of the Jurassic Daohugou Biota of northeastern China. Journal of Vertebrate Paleontology, 2014; 34 (2): 243 DOI: 10.1080/02724634.2013.787316

Friday, March 7, 2014

Interspecific aggression in garter snakes

The aquatic garter snake at Sibley Volcanic Regional Preserve, Oakland, CA. 
Photo credit: Sarah Stierch.
Aggressive behavior is used in many vertebrate communities to gain control of resources,  snakes, however, have been thought the exception. Some snake species use male-to-male combat for access to females, but this is intraspecies behavior.  Food partitioning usually thought to shape community structure of snake communities. A new study by Edgehouse and colleagues used two species of garter snakes at the Santa Lucia Preserve in Monterey Co. California. Both the common garter snake,Thamnophis sirtalis, the aquatic garter snake, a T. atratus and western terrestrial garter snake T. elegans coexist with their abundant, toxic prey  the California newt, Taricha torosa. At the study site,  Thamnophis sirtalis and T. atratus are aquatic and demonstrate independently evolved resistance to tetrodotoxin (TTX), a potent neurotoxin, found in the skin of the newt.

Edgehouse et al.  show that the common garter snake (Thamnophis sirtalis) and the aquatic garter snake (Thamnophis atratus) show a strong preference for amphibians and forces these snakes to exploit aquatic habitats. They investigate the aggressive behavior of T. sirtalis and the potential that this aggression displaces T. atratus from its preferred habitat. When individuals from either species were alone, they showed a complete preference for aquatic or near aquatic habitats. In contrast, when these species are together, T. sirtalis occupy the aquatic habitat and T. atratus occupy an area far removed from the water. They found Thamnophis sirtalis often physically force T. atratus from the aquatic habitat through repeated biting and other displays of aggression.

The spatial partitioning documented by the authors is likely a direct result of food availability and aggressive defense of the prey resource. The most abundant amphibian prey found in the snakes at the study site were California newt and the pacific treefrog.

Edgehouse M, Latta LC IV, Brodie ED III, Brodie ED Jr (2014) Interspecific Aggression and Habitat Partitioning in Garter Snakes. PLoS ONE 9(1): e86208. doi:10.1371/journal.pone.0086208

Sunday, March 2, 2014

Herpetofauna of the the Tay Yen Tu Nature Reserve, Vietnam

Rhynchophis boulengeri , one of the colubrids present at Tay Yen Tu. JCM

The Tay Yen Tu Nature Reserve is located in Bac Giang Province, about 100 km northeast of Hanoi, Vietnam and is situated in the western side of theYen Tu massif, which is the largest granitic formation in northeastern Vietnam. The main habitat of the area is evergreen broad-leaved tropical forest. The total area of the reserve is 16 ha and includes two non-contiguous sectors: the Thanh Son-Luc Son sector and the Khe Ro sector. The Thanh Son-Luc Son sector is centered on the 1,068 m high Mount Yen Tu, while the Khe Ro sector is about 886 m on Mount Da Bac. A comprehensive study on the biodiversity has not been conducted in the reserve to date, However, preliminary field research indicates the area supports a number of species of national or global conservation concern. Four new species have been discovered from Yen Tu Mountain in the last decade: Sphenomorphus cryptotis, Scincella devorator, Tylototriton vietnamensis and Odorrana yentuensis. Additionally, three new country records were recently reported from this nature reserve: Shinisaurus crocodilurus, Amphiesmoides ornaticepsm, and Rhacophorus maximus.  The discoveries of new reptiles and amphibians from Yen Tu Mountains underscore the unrealized biodiversity of northeastern Vietnam. Based on the results of recent field surveys Hetch et al. (2014) provide the first list of amphibians and reptiles recorded from Tay Yen Tu Nature Reserve.

A total of 76 species of amphibians and reptiles were recorded, including one caecilian, one newt, 34 species of anurans, 18 species of lizards, and 22 species of snakes. Thirty species are reported for the first time. Among the recorded species, five are currently known only from Vietnam. A high level of species diversity and endemism of the herpetofauna underscores the importance of biodiversity conservation in this nature reserve, which covers a major part of the remaining lowland evergreen forest in northeastern Vietnam.

Hecht, Vera L., Cuong T. Pham, Tao T. Nguyen, Truong Q. Nguyen, Michael Bonkowski, and Thomas Ziegler.  2014. First report on the herpetofauna of Tay Yen Tu Nature Reserve, northeastern Vietnam. Biodiversity Journal, 4 (4): 507–552.

Risk assessment for Burmese pythons in Everglades National Park

A large Burmese python, weighing 162 pounds and more than 15 feet 
long at the time of its capture in 2009. Caught alive in the Everglades, 
it had eaten an American alligator that measured about 6 feet in 
length. University of Florida researchers in the photo: Michael 
Rochford is holding the python's head, and Alex Wolf and Therese 
Walters are holding the python's body. Photo credit USGS.
The estimated tens of thousands of Burmese pythons now populating the Everglades present a low risk to people in the park, according to a new assessment by U.S. Geological Survey and National Park Service scientists.

The human risk assessment looked at five incidents that involved humans and Burmese pythons over a 10-year period in Everglades National Park. All five incidents involved pythons striking at biologists who were conducting research in flooded wetlands.

"Visitor and staff safety is always our highest priority at Everglades National Park," said Superintendent Dan Kimball. "Everglades, as many other national parks, draws many thousands of visitors for the opportunity to view the wildlife that live here in a natural setting. Our guidance to visitors with respect to Burmese pythons is the same as for our native wildlife -- please maintain a safe distance and don't harass the wildlife. With respect to controlling Burmese pythons, we are working diligently with our state, federal, tribal, and local partners to manage this invasive species and educate the public on the importance of not letting invasive species loose in the wild."

Although there have been numerous bites to people provoking Burmese pythons by attempting to capture or kill the snakes, this study examined only unprovoked strikes directed at people.

"The strikes did not appear to be defensive, but were more likely were associated with aborted feeding behavior," said USGS wildlife biologist and herpetologist Bob Reed, the lead author of the study. "Pythons usually direct defensive strikes at the front of a person, not from the side or rear, as all of these strikes were. Additionally, Burmese pythons rely on being secretive and evading detection as their primary means of avoiding interactions with people, and typically don't strike until provoked."

The biologists did not detect any of the snakes before the strikes occurred, making it even more likely that the attacks were related to feeding and not defense, Reed noted. Two of the attacks resulted in very minor injuries from the pythons' teeth and none involved constriction.

Reed and his co-author, retired Everglades National Park scientist Skip Snow, consider the attacks as cases of mistaken identity. In four of five cases the python was small compared to the size of the person, which resulted in the snake likely aborting the attack upon realizing the large size of its prey. Aborting strikes before actual bites with the possible prey indicates that pythons may be able to assess the size of the prey mid-strike and adjust accordingly, the study said.

Although the pythons' threat to people is low, previous studies have shown that this invasive snake species is having a negative effect on many of the native mammals in the South Florida Everglades. One study suggests the population of raccoons, opossums, and bobcats have declined significantly in the regions of Everglades National Park where pythons have been established the longest.

More than one million people visit Everglades National Park every year, often traveling along hiking and canoeing trails where Burmese pythons have been spotted or captured. Despite this close interaction, the study noted that none of the reported incidents involved a park visitor. All of the incidents were directed at biologists moving through remote and flooded areas of the park.

"As people wade through shallow water, they produce ripples that move ahead of them, and these pressure waves may be detectable to a motionless snake in ambush posture," said Reed. "We speculate that detecting these changes in water pressure may alert a python that an animal is approaching, perhaps priming it to strike immediately when a potential prey item is detected."

Burmese pythons became established in Florida several decades ago as a result of the international pet trade. The largest snakes removed from the Everglades have exceeded 18 feet and 150 pounds. Snakes of this size are capable of ingesting large prey like deer and alligators.

This human risk assessment concluded that although the risk of an unprovoked attack by a Burmese python in Everglades National Park is low, it is not non-existent. Available evidence from captive snakes suggests that even those strikes that result from cases of mistaken identity or defensive behavior may still result in constriction, which can prove fatal to people when a large python or a small human is involved.

The study focused only on the risk associated with Burmese pythons, but did not address other invasive constrictor species, such as the Northern African python, which is also known as the African Rock python, which are also known to be established and breeding in South Florida outside of Everglades National Park. USGS scientists continue to work with partners to better understand the impacts on invasive reptiles in the Everglades, help reduce their spread into new areas and help prevent new species from becoming established.

RN Reed, RW Snow. 2014 Assessing risks to humans from invasive Burmese pythons in Everglades National Park, Florida, USA. Wildlife Society Bulletin, DOI: 10.1002/wsb.413