Tuesday, May 26, 2015

Modeling the first snake

A reconstruction of the ancestral crown-group snake, 
Artwork by Julius Csotonyi.
The original snake ancestor was a nocturnal, stealth-hunting predator that had tiny hind limbs with ankles and toes, according to new research. Snakes show incredible diversity, with over 3,400 living species found in a wide range of habitats, such as land, water and in trees. But little is known about where and when they evolved, and how their original ancestor looked and behaved. The original snake ancestor was a nocturnal, stealth-hunting predator that had tiny hind limbs with ankles and toes, according to research published in the open access journal BMC Evolutionary Biology.
The study, led by Yale University, USA, analyzed fossils, genes, and anatomy from 73 snake and lizard species, and suggests that snakes first evolved on land, not in the sea, which contributes to a longstanding debate. They most likely originated in the warm, forested ecosystems of the Southern Hemisphere around 128 million years ago.
Snakes show incredible diversity, with over 3,400 living species found in a wide range of habitats, such as land, water and in trees. But little is known about where and when they evolved, and how their original ancestor looked and behaved.
Lead author Allison Hsiang said: "While snake origins have been debated for a long time, this is the first time these hypotheses have been tested thoroughly using cutting-edge methods. By analyzing the genes, fossils and anatomy of 73 different snake and lizard species, both living and extinct, we've managed to generate the first comprehensive reconstruction of what the ancestral snake was like."
By identifying similarities and differences between species, the team constructed a large family tree and illustrated the major characteristics that have played out throughout snake evolutionary history.
Their results suggest that snakes originated on land, rather than in water, during the middle Early Cretaceous period (around 128.5 million years ago), and most likely came from the ancient supercontinent of Laurasia. This period coincides with the rapid appearance of many species of mammals and birds on Earth.
The ancestral snake likely possessed a pair of tiny hind limbs, and targeted soft-bodied vertebrate and invertebrate prey that were relatively large in size compared to prey targeted by lizards at the time. While the snake was not limited to eating very small animals, it had not yet developed the ability to manipulate prey much larger than itself by using constriction as a form of attack, as seen in modern Boa constrictors.
While many ancestral reptiles were most active during the daytime (diurnal), the ancestral snake is thought to have been nocturnal. Diurnal habits later returned around 50-45 million years ago with the appearance of Colubroidea -- the family of snakes that now make up over 85% of living snake species. As colder night time temperatures may have limited nocturnal activity, the researchers say that the success of Colubroidea may have been facilitated by the return of these diurnal habits.
The results suggest that the success of snakes in occupying a range of habitats over their evolutionary history is partly due to their skills as 'dispersers'. Snakes are estimated to be able to travel ranges up to 110,000 square kilometers, around 4.5 times larger than lizards. They are also able to inhabit environments that traditionally hinder the dispersal of terrestrial animals, having invaded aquatic habitats multiple times in their evolutionary history.

Hsiang AY, Field DJ, Webster TH, Behlke ADB, Davis MD, Racicot RA, Gauthier JA. 2015. The origin of snakes: revealing the ecology, behavior, and evolutionary history of early snakes using genomics, phenomics, and the fossil record. BMC Evolutionary Biology, 2015; 15 (1) DOI: 10.1186/s12862-015-0358-5

Tuesday, May 19, 2015

Eating-induced changes of the Burmese python's intestines due to changes in gene expression

 The Burmese python's body undergoes massive reconstruction followed by complete deconstruction every time it eats. Within three days of eating, its organs expand up to double in size and its metabolism and digestive processes increase 10- to 44-fold. Ten days after eating, the snake's meal is digested and these changes have reversed, allowing the body to shrink and return back to its pre-meal state. In a new study published in Physiological Genomics, a team of U.S. researchers tracked in detail how this extreme makeover is controlled by changes in gene expression.

The Burmese python's extreme physiology is fascinating to study because it gives unique insight into how vertebrates control organ growth and function, the researchers wrote. Although the Burmese python's body shape is distinct from other vertebrates, including humans, its organs operate the same. This means findings from snakes can be applied to understanding the human body and potentially developing new therapies for human diseases, the researchers said.

In this study, the research team focused on the small intestine, which doubles in mass and nutrient-absorption rate during digestion. The researchers found that the expression of at least 2,000 genes changed after the snake ate. Surprisingly, most of the changes occurred soon after eating -- within six hours. Genes that changed included those involved with the intestine's structure and nutrient absorption, cell division and cell death. The patterns of gene expression matched and often preceded physiological changes in the intestine, the researchers wrote. The gene expression patterns, like the structural changes, then returned to pre-eating state within 10 days after eating, "indicating a tight association between differential gene expression and the rapid and cyclic physiological remodeling of the intestine," the researchers said.

According to the researchers, this is the first study to link the extreme and rapid eating-induced changes of the Burmese python's intestines directly to changes in gene expression, and also the first to show how quickly gene expression changed. The study also found that some of the morphing genes in the python's intestine, notably those in a signaling pathway called WNT, were genes that were involved in intestinal and other cancers. This suggests that "the python intestine may represent a valuable model for studying the interactions of metabolism with the regulation of cell division/death and WNT signaling relevant to cancer," the researchers said.

Andrew AL, Card DC, Ruggiero RP, Schield DR, Adams RH, Pollock DD, Secor SM, Castoe TA. (2015) Rapid changes in gene expression direct rapid shifts in intestinal form and function in the Burmese python after feeding. Physiological Genomics, 47 (5): 147 DOI: 10.1152/physiolgenomics.00131.2014

Saturday, May 16, 2015

tail length in snakes associated with gravity

An arboreal eyelash viper (Bothriechis schlegelii)
 resting on a branch in Costa Rica. Photograph by 
Coleman M. Sheehy III. 
Gravity is a pervasive force that can severely affect blood circulation in terrestrial animals, and these effects can be particularly pronounced in tall or long organisms such as giraffes and snakes. Upright postures create vertical gradients of gravitational pressures within circulatory vessels that increase with depth. In terrestrial animals, this pressure potentially induces blood pooling and edema in the lower-most tissues and decreases blood volume reaching the head and vital organs.

Since their evolutionary origins about 100 million years ago, snakes have diversified into a wide variety of aquatic, burrowing, terrestrial, and arboreal habitats where they experience various levels of gravitational stress on blood circulation. At the extremes, these stresses range from low to none in fully aquatic species living in essentially “weightless” environments, to relatively high in climbing species, especially arboreal forms specialized for climbing trees. As a result, arboreal snakes exhibit many adaptations for countering the effects of gravity on blood circulation, including relatively tight tissue compartments in the tail. However, patterns of tail length in relation to arboreal habitats and gravity have not been previously studied.

We obtained length data for 226 snake species representing almost all snake families to test the hypothesis that arboreal snakes have longer tails than do non-climbing species. We found that average tail length increased and average body length decreased with increasing use of arboreal habitats and that arboreal snake species had average tail lengths 3–4 times longer than those of non-climbing species. Snakes with longer tails have a higher percentage of elongate blood vessels contained within the relatively tight skin of the tail, which counters blood pooling experienced during climbing. Total body length appears to be constrained in arboreal species, and total body length in adult female arboreal snakes appears to be an evolutionary tradeoff that favors longer tail lengths over maximum production of offspring as arboreal habitat-use increases. Our findings provide evidence that long tails of arboreal snakes function, at least in part, as an adaptation to counter cardiovascular stresses on blood circulation imposed by gravity.


Sheehy, C. M., Albert, J. S., & Lillywhite, H. B. (2015). The evolution of tail length in snakes associated with different gravitational environments. Functional Ecology. Early On-line.

Friday, May 1, 2015

Geckos evolved daytime activity multiple times

A diurnal Phelsuma and a nocturnal Cyrtodactylus
Geckos are the only clade of lizards that are mostly nocturnal; 72% of the 1552 described species are active at night. Geckos possess numerous adaptations to low light and low temperatures, suggesting nocturnal activity evolved early in their evolution. These adaptations include the evolution of vocalization and acoustic communication, olfactory specialization, enhanced capability for sustained locomotion at low temperatures, shifts in diet and foraging mode, and the absence of the parietal foramen and pineal eye. Geckos have acute vision and many adaptations for seeing in low light including: large eyes, pupils capable of an extreme degree of constriction and dilation, retinas without foveae, short visual focal length, multifocal color vision, and rod-like photoreceptor cells in the retina that lack oil droplets. However, not all gecko species are nocturnal; more than 430 are diurnal. Many of these diurnal lineages have their own adaptations to living in warm, photopic environments including round pupils, UV-filtering crystallin lens proteins, smaller eyes, partial to complete foveae, cone-like photoreceptor cells in the retina and a return to higher energetic costs of locomotion. Geckos are thought to be ancestrally nocturnal and diurnality evolved multiple times. However, this hypothesis has never been tested in a phylogenetic framework.

Now, in a new paper Gamble et al. (2015) performed comparative analyses using a newly generated gecko phylogeny and examined the evolution of temporal activity patterns to: test the hypothesis of an early origin of nocturnality in geckos; verify repeated subsequent transitions to diurnality; and determine whether the evolution of temporal activity patterns has influenced diversification rates. The results provide the first phylogenetic analysis of temporal activity patterns in geckos and confirm an ancient origin of nocturnality at the root of the gecko tree. Gamble et al. identify multiple transitions to diurnality at a variety of evolutionary time scales and transitions back to nocturnality occur in several predominantly diurnal clades.

The authors found several transitions occurred deep in the phylogeny, including ancestors to the Pygopodidae, the New World sphaerodactyl geckos and the Phelsuma plus Lygodactylus clade. More recent transitions occurred in Rhoptropus, within New Zealand and New Caledonian diplodactylids (Naultinus and Eurydactylodes), and within Gymnodactylus, Ptyodactylus and Mediodactylus. Both Asian Cnemaspis clades seem to include multiple transitions, although additional taxonomic sampling is needed to confirm this. They also identified several well-supported eversions to nocturnality within otherwise diurnal clades, including Sphaerodactylus, Gonatodes, Phelsuma and the Pygopodidae. Their results indicate frequent shifts in temporal activity patterns in geckos at a variety of evolutionary timescales. Determining what factors initiate shifts in individual clades was beyond the scope of the paper, but they suggest three possible causes: climate, predators and competition.

Some shifts in activity pattern may be related to thermoregulation and evading extreme temperatures and desiccation. For example, geckos in the genus Sphaerodactylus appear to overheat easily and several species that inhabit hot, xeric habitats are nocturnal, including: S. leucaster, S. thompsoni and S. ladae in southern Hispaniola; S. roosevelti in south-west Puerto Rico; and S. inaguae from the Bahamas. Similarly, some gecko species living at high altitudes, such as Mediodactylus amictopholis, are thought to have shifted to diurnal activity to facilitate thermoregulation in colder climates. However, there are numerous counter inhabiting extreme environments. Pristurus and Rhoptropus, for instance, are diurnal genera that can be active at extremely high temperatures in arid environments while Homonota darwnii and Alsophylax pipiens live in cold climates at extreme latitudes and remain nocturnal. Furthermore, nocturnal geckos seem quite capable of regulating body temperature while hidden in retreats during the day and thus switching to diurnality solely for thermoregulatory purposes may be uncommon overall.

Predation could also instigate changes in temporal activity patterns in geckos and such shifts are well documented in other vertebrate species. Most predator-induced niche shifts in geckos involve the alteration of the spatial niche. However, the hypothesis that geckos may transition to a more conspicuous, diurnal lifestyle in environments where predators are less abundant or absent, such as on islands. Lack of predators is thought to be responsible for dramatic changes in phenotype and behavior in many island species, such as the evolution of flightlessness in birds. Thus, it is reasonable that similar selective pressures could alter temporal activity in geckos.

Shifts in temporal activity patterns may also be related to competition avoidance and the exploitation of underutilized resources. Temporal resource partitioning helps competitors coexist by avoiding direct confrontation or reducing resource overlap. For example, the early shift to nocturnality in ancient geckos has been attributed to avoiding competition with diurnal lizards and exploiting the relatively open nocturnal niche. The lack of competition with other diurnal lizards, mostly iguanians, is frequently cited as promoting transitions back to diurnality in geckos. Indeed, many diurnal geckos occur in regions with a paucity of iguanian species. The success of Phelsuma and Lygodactylus in Madagascar has been attributed to the lack of arboreal iguanians, with the exception of the extremely specialized chameleons.

The scenario presented here will be useful in reinterpreting existing hypotheses of how geckos have adapted to varying thermal and light environments. These results can also inform future research of gecko ecology, physiology, morphology and vision as it relates to changes in temporal activity patterns.


Gamble T, Greenbaum E, Jackman TR, Bauer AM (2015), Into the light: diurnality has evolved multiple times in geckos. Biological Journal of the Linnean Society. doi: 10.1111/bij.12536

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.

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.


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.


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.


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.


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.

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

Tuesday, March 31, 2015

Bushmaster - a preview of a forthcoming book

Bushmaster - due out on June 2, 2015 - is the story of one man’s obsession with an enigmatic and deadly reptile. Raymond Ditmars (1876-1942), the first curator of reptiles at New York’s world-famous Bronx Zoo, popularised cold-blooded animals as never before. His love for snakes, insects and other misunderstood creatures was conveyed in books, lectures, and pioneering motion pictures. But his expeditions to the South America jungles during the 1930s in search of the legendary bushmaster – the world’s largest viper – really captured the public imagination. In Bushmaster the author, Dan Eatherley, follows in Ditmars’s footsteps and attempts to achieve what Ditmars himself failed to do: find a bushmaster in the wild. Eighty years on, will Dan have any more luck? And will a bushmaster find him first?

Dan Eatherley is a British naturalist, writer and wildlife film-maker with a first class zoology degree from Oxford University. Dan has made a variety of natural history TV documentaries for the BBC, National Geographic, and the Discovery Channel, including credits as an assistant producer on two BBC series hosted by Sir David Attenborough: Life of Mammals and Planet Earth. He has filmed on location in swamps, deserts and jungles around the world. He has written over 100 articles on science and environmental issues for New Scientist, Scientific American and BBC Wildlife magazines. These days, when not hunting giant vipers, he works from his home in southwest England as a consultant in environmental sustainability.

Some advance reviews for Bushmaster:

Bushmaster is a skillful work that combines the author’s own journey of discovery while shadowing the footsteps of one of the world’s most celebrated herpetologists and early pioneers for the conservation of reptiles with a fascinating history of the early evolution and modernization of the Bronx Zoo and herpetology in general.” —Austin Stevens, herpetologist, author, and adventure wildlife filmmaker

"There is perhaps no snake that so captures the imagination as the bushmaster, creature of myth, a real life dragon in serpent form. This quest to find one in the wild is a personal odyssey driven by fascination, and an intriguing read for any herpetologically minded wildlife fiends." —Steve Backshall, naturalist, writer, television presenter

"The world's greatest snakehunter, his quest for a legendary serpent, and a modernBoy's Own adventure, three stories elegantly intertwined in Bushmaster. Beautifully written and meticulously researched, I'm sure like me you won't be able to put it down." —Nigel Marven, television presenter

“A considerable number of persons can trace their interest in herpetology to days reading the many books by Raymond L. Ditmars. Those of us who have worked with bushmasters feel fortunate to have had this wonderful opportunity. Dan Eatherley has captured their essence and the nexus with Ditmars—unearthing a plethora of new information about one of our famous and most productive herpetologists.” —James B. Murphy, research associate zoologist, Division of Amphibians & Reptiles, Smithsonian National Museum of Natural History

“When I was a mere stripling my mother bought me Snakes of the World by Raymond L. Ditmars. My innate fascination for snakes soared to the skies with this book. But I never did realize what an incredible character Ditmars was. InBushmaster Dan Eatherley brings to life this enigmatic hero to uncounted, obsessed herpers.” —Romulus Whitaker, herpetologist, conservationist, and filmmaker

You can find Dan Eatherly's web page at www.daneatherley.com and his Twitter account at: @daneatherley

The book can be ordered early on Amazon .  

 The prologue to Bushmaster: Raymond Ditmars and the Hunt for the World’s Largest Viper

© Dan Eatherley 2015

Summer 1896. The Bronx, New York City.

JUST LIKE A COFFIN. Five feet long, three feet wide, and three feet high, the wooden box dominates the landing.
“The expressmen must have had some job getting it up here,” muses the nineteen-year-old. According to the delivery note, the sender is a “Mr. R. R. Mole, Port-of-Spain.” After three months the consignment finally showed up at port yesterday aboard the SS Irrawaddy of the Trini­dad line, and just a few hours ago the crate was delivered by horse and cart to the large brownstone house on Bathgate Avenue. Dinner seemed to take forever but now it’s over. Insisting that his parents remain two sto­ries below, the young man can at last get to work with hammer and pry bar. He ignores the intermittent buzzes coming from the room adjacent to the landing. Forcing off the lid, he prepares for the draught of fetid air, a sure sign of a dead specimen, but is relieved to detect only a faint nutty odor. Under several inches of brittle straw lie various large burlap sacks, each knotted and labeled. Turning over a tag, he shudders as two words are revealed in a neat script.
Lachesis muta
The sack expands and contracts in response to the breathing of its contents whose rough scales press a distinctive pattern against the fabric.
Like the surface of a pine cone, he thinks.
“Everything all right up there, Ray?” his mother’s voice disturbs the youth’s reverie.
“Fine. Don’t anybody come up!” He needs to get a move on.
Heart pounding, the teenager grasps the bag above the knot and lifts it from the crate. It’s disappointingly light given that Mole’s note describes an animal of “about eight feet long.” Books and articles had led him to expect a specimen of that length to be far heavier. Holding the sack away from his body, he enters a small adjoining room via a door fitted with strong springs. Glass-fronted cages are arranged in two tiers along one wall. Above them stretches the desiccated skin of a large snake, a python maybe.
The buzzing, emanating from one of the upper cages, intensifies. The teenager places the sack in a large empty cage on the lower tier and loosens the knot. He reaches for a broom handle; attached to one end is a piece of stiff wire twisted like a shepherd’s crook. Using this, he inverts and raises the bag, hoping to coax out its tenant from a safe distance, but the animal is not cooperating and instead braces itself against the cloth, defying gravity. The beast does at least offer up a glimpse of alternating salmon-pink and jet-black markings. Impatient to see more, the young man whips away the sack with his hand, spilling the creature out into the cage.
He would never forget the turmoil of impressions etched on his brain in that instant: the snake’s length far exceeding that suggested by its weight; the keeled scales lending the skin a rasp-like quality; the waxy sheen of the animal; the blunt head; and, set above pinkish jowls, the red­dish-brown eyes with their elliptical black pupils. In the moments these features take to register, the front half of the reptile’s body rises to form a huge “S” while the glistening pink tongue forks at the air.
Then the snake advances.
In horror the teenager backs away, knocking over a chair.
The reptile follows.
Never has he encountered a viper actually prepared to pursue him. In his experience, even the most venomous of snakes are cowards and, unless cornered, flee at the first sign of trouble. With the staff he tries ever more forcefully to check the giant reptile’s progress, attempting to lift and push it back, but the limbless body of his adversary slides over the hook like jelly. The snake is between him and the door, cutting off any hope of escape. The buzzing is now an uninterrupted, deafening drone.
Downstairs his mother drops her knitting. “That was definitely a crash I just heard, John.”
“Relax, my dear. Ray seems to know what he’s doing,” responds her husband with little conviction. They both glance nervously at the ceiling.
And still the serpent advances.
The inch-long fangs and excessive amounts of venom for which this species is notorious dominate the young man’s thoughts. Can this snake know its own power? Can that dancing tongue taste his fear?
The teenager has almost nowhere left to go when, in his peripheral vision, he notices a broom. He flicks it behind him with the crook of his staff. Retreating another step, in one motion he grabs the implement and shoves the bristles sharply into the face of his pursuer. The snake pauses, pulls its body into a tight coil and beats out a rhythm against the floor with the strange horny tip of its tail. The youth catches his breath. Saved!
Broom in hand and more confident, he advances on the reptile. Sev­eral additional firm jabs encourage the serpent to turn and creep toward the cage. The teenager gently raises the snake’s chin with his staff ena­bling the viper to glide into its new quarters. He slams shut the glass door to the cage and slumps to the floor, gasping and prickled by sweat.
Now for the boas.
Editor's note. Dan Eatherley spent sometime with me in Trinidad searching for bushmasters. To find out the results of his quest you will need to read the book. JCM

A new squamate phylogeny that resolves from previous problems

Estimated phylogeny of squamate reptiles from 
likelihood analysis of combined morphological 
and molecular data, after removal of four “rogue” 
fossil taxa. Red dots indicate clades with 
bootstrap values from 90–100%, black dots 
indicate values from 70–89% (values <70 nbsp="" span="">
not shown; for bootstrap values for all branches 
see. Fossil taxa are indicated with “” and green 
branches. The four abbreviated fossil taxa in 
gray at the base of the phylogeny are the four rogue 
taxa (Eichstaetisaurus, Huehuecuetzpalli
SineoamphisbaeniaAMNH FR 21444), shown in 
their phylogenetic positions as inferred in the 
combined analysis including all taxa. Photos 
include representatives of Dibamidae (Anelytropsis), 
Gekkota Carphodactylidae:Underwoodisaurus), 
Scincoidea (Scincidae: Plestiodon), Amphisbaenia
(Bipedidae:Bipes), Mosasauria (Tylosaurus), 
Serpentes (Boidae: Exiliboa), Anguimorpha 
(Xenosauridae: Xenosaurus), Polyglyphanodontia 
(Polyglyphanodon), Acrodonta (Agamidae:
 Calotes), and Pleurodonta (Phrynosomatidae: 
Sceloporus). See Acknowledgments in 
original paper for photo credits (except for 
Anelytropsis from T. M. Townsend). 

In a new paper published in PLoS, Reeder et al. (2015) note that squamate reptiles (lizards and snakes) are an important and diverse group of terrestrial vertebrates, with more than 9,000 species and that studies of squamate biology are presently hampered by uncertainty over their phylogeny.
Higher-level squamate phylogeny is currently unresolved because of conflicts between hypotheses based on separate analyses of morphological and molecular datasets. 

Most attention has focused on the placement of iguanians (including iguanas, anoles, chameleons, dragons, and relatives), which are placed at the base of the squamate tree in morphological analyses, and in a clade (called Toxicofera) with snakes and anguimorphs (including monitor and alligator lizards, the Gila monster, and relatives) in molecular analyses. The largest morphological dataset (in characters) included 189 squamate taxa (140 living and 49 fossil; plus 3 outgroup taxa) and 610 characters (~33% missing data; Gauthier et al., GEA hereafter). 

The largest molecular dataset (in terms of characters) included 161 living taxa (plus 10 outgroup taxa) for up to 44 nuclear protein-coding loci (33,717 base pairs/characters; ~20% missing data); Wiens et al., (WEA hereafter). Given the unresolved conflict between these two large datasets over the placement of Iguania, some authors have considered higher-level squamate relationships to be unresolved. Some recent, prominent studies have considered the traditional, morphological tree only, ignoring the molecular hypothesis altogether.

In this study the authors perform an integrated analyses to resolve this conflict and further elucidate the relationships of both living and fossil squamates. First, they generated an expanded morphological dataset with taxon sampling largely matching that of GEA for extant taxa, adding new data from 81 additional characters (primarily from squamation) to the mostly osteological dataset of GEA. This is a 13% increase in characters (to 691), and the largest morphological dataset for squamates. Next, they expanded the molecular dataset of WEA by including published sequences from two additional loci (nuclear c-mos; mitochondrial ND2) for closely matched species yielding up to 46 protein-coding loci and 35,673 characters for each of 161 taxa. We then performed separate and combined analyses of each dataset using likelihood, Bayesian, and parsimony approaches, and evaluated the potential causes of conflict by examining trees from subsets of the molecular and morpohological data. Combined analyses included reweighting the molecular data such that genes were treated as equivalent to morphological characters.

The results resolve higher-level relationships as indicated by molecular analyses, and reveal hidden morphological support for the molecular hypothesis (but not vice-versa). Furthermore, the authors find that integrating molecular, morphological, and paleontological data leads to surprising placements for two major fossil clades (Mosasauria and Polyglyphanodontia), demonstrate the importance of combining fossil and molecular information, and the potential problems of estimating the placement of fossil taxa from morphological data alone. These results caution against estimating fossil relationships without considering relevant molecular data, and against placing fossils into molecular trees (e.g. for dating analyses) without considering the possible impact of molecular data on their placement.

The combined analyses strongly suggest that the phylogenetic hypothesis for living squamates based on the molecular data is correct. Specifically, the results support the hypothesis that Iguania is placed with snakes and anguimorphs, and not at the squamate root (as suggested by morphological data alone). The conclusions are based on several lines of evidence, including: (a) combined analyses of the relevant molecular and morphological data supports the molecular placement of Iguania, even when the molecular dataset is reduced to only 63 characters, less than one tenth the size of the morphological dataset, (b) mapping morphological characters on the combined-data tree shows that there is actually hidden support for the molecular hypothesis in the morphological data (similar to the number of characters supporting the morphological hypothesis), (c) the morphological dataset is dominated by misleading phylogenetic signal associated with convergent evolution of a burrowing lifestyle and associated traits, and a similar problem associated with feeding modes may explain the morphological placement of Iguania, and (d) the morphological hypothesis is unambiguously supported by only one of six subsets of the morphological data. Conversely, we find no evidence for hidden signal supporting the morphological hypothesis among the 46 genes in the molecular dataset; no genes support this hypothesis. Further, the failure of some genes to fully support the molecular placement of iguanians in Toxicofera seems to be associated with sampling error (i.e. shorter genes).


Reeder TW, Townsend TM, Mulcahy DG, Noonan BP, Wood PL Jr, et al. (2015) Integrated Analyses Resolve Conflicts over Squamate Reptile Phylogeny and Reveal Unexpected Placements for Fossil Taxa. PLoS ONE 10(3): e0118199. doi:10.1371/journal.pone.0118199.

Sunday, March 29, 2015

The Python & the Marsh Rabbit in the Florida Everglades

The invasive Burmese python (Python molurus bivittatus or Python bivittatus) has been suspected in the drastic decline of mammal populations in Everglades National Park (ENP) over the last several decades, The park is globally recognized for its unique biotic communities, sits at the southern end of the Greater Everglades Ecosystem (GEE), a vast freshwater wetland (≈10 000 km2) encompassing most of the southern Florida peninsula. The ecological processes, functionality and restoration efforts within this distinct ecosystem are probably being substantially impaired by the disappearance of once common mammalian predators and herbivores. Declines in mammal populations in ENP appear to coincide temporally and spatially with the arrival and spread of invasive Burmese pythons, a large-bodied snake native to Southeast Asia that preys on vertebrates. Pythons were probably introduced into ENP several decades ago via releases or escapes from private ownership. Sightings and removals of pythons in ENP were sporadic in the 1980s and 1990s, and increased sharply in the early 2000s. During this time, gut content analysis of invasive pythons in ENP indicated that mammals accounted for about 75% of their diet.
Previous evidence linking pythons to mammal declines has been indirect, and there are reasons to question whether pythons or any predator could have caused the precipitous declines seen across a range of mammalian functional groups. Introduced predators, including snakes, have reduced or eliminated fauna on islands, yet there are no accounts of a lone introduced apex predator (apart from humans) removing a functionally diverse, continental mammal community. Additionally, ecological theory provides little support for the hypothesis that an apex predator could extirpate small, broadly dispersed, fecund, generalist herbivores.
In a new article in the Proceedings of the Royal Society of London B: Biological Sciences McCleery et al. (2015) test the hypothesis that pythons are driving the decline of mammal populations, and they experimentally manipulated the marsh rabbit (Sylvilagus palustris) populations in ENP.
Marsh rabbits are small (≈1 kg) lagomorphs found near fresh and brackish water throughout the southeastern USA. They are sexually active throughout the year and can produce up to six litters of three to five young annually. Through the 1980s, this species was one of the most commonly seen mammals in ENP. Despite having a wide variety of natural predators, marsh rabbits are still common in areas of the GEE outside of ENP. For these reasons, and because rabbit populations are generally resilient and capable of persisting under considerable predation pressure the authors  chose marsh rabbits as a model to understand the impacts of pythons on mammals in ENP. If pythons caused the declines of marsh rabbits in ENP, they predicted that (i) pythons would be the dominant cause of marsh rabbit mortality in ENP, (ii) mammals would cause more marsh rabbit mortalities in areas of the GEE where pythons were rare or absent, (iii) marsh rabbit populations introduced in ENP would not persist, and (iv) unlike endothermic predators (i.e. mammals), the timing of python-caused mortality would vary with seasonal climate conditions.
The authors experimentally manipulated the marsh rabbit populations to determine the role of pythons in driving mammal declines within ENP. They compared the risk of mortality from different causative agents in areas with established Burmese python populations to similar areas where pythons were rare or absent. The also evaluated the influence of environmental factors on temporal variation in mortality rates from the dominant predators of marsh rabbits (e.g. pythons and mammals) in the GEE.
They captured marsh rabbits from donor populations and randomly assigned them to one of three sites: two sites in ENP and a procedural control site in the GEE, where pythons had not been observed. The purpose of the procedural control was to account for the influence of translocation on mortality events. The also established a control site where pythons were rare or absent to compare causes of mortality in ENP with an established population of marsh rabbits that was not manipulated. At the control site, they captured and released rabbits without trans-locating them.
They captured, released and radiotracked 95 adult marsh rabbits from 14 September 2012 to 19 August 2013 (coastal ENP = 15, freshwater ENP = 16, procedural control = 15, control = 49). Eighty rabbits survived the 10-day adjustment period needed to reduce exploratory movements and acclimate to the sites. Additionally, 10 rabbits were censored after the 10-day adjustment period (e.g. lost signal from predation or equipment failure), and two rabbits were alive at the end of the study, so the study documented 68 rabbit mortalities. Classification of the cause of mortality for 55 rabbits was possible and the remaining 13 rabbit mortalities were listed as being from an unknown endothermic predator. Marsh rabbits in ENP faced the greatest risk of predation from pythons, which accounted for 77% of all mortalities. And, the authors attributed only one rabbit mortality in ENP to mammal predation. This was in stark contrast to results from control sites, where no rabbits were killed by pythons and they attributed 71% of classified mortalities to mammals. Only three rabbits (8%) at the control site were eaten by snakes, all native eastern diamondback rattlesnakes (Crotalus adamanteus).
The loss of marsh rabbits and other mammals from ENP  is probably causing a massive rearrangement of the ENP food web, losses in ecosystem function, and complex and unpredictable cascading effects. As prey and predators at multiple trophic levels, nutrient cyclers and engineers of vegetation, mammals are an indispensable component of the GEE. This research clearly establishes pythons as a causal agent of marsh rabbit declines, a species selected because of its theoretical resilience to predation pressure. Accordingly, pythons are a logical and likely explanation for the observed declines in less fecund mammalian prey found in ENP (raccoon, round-tailed muskrat, bobcat).
Only with the recovery of the parks mammal populations will it be possible to restore the health and functionality of this World Heritage Site. However, it seems unlikely that marsh rabbits and other mammal populations will rebound without action to manage pythons. Because pythons are capable of persisting in the environment by switching to different prey and going long periods without food controlling them is a difficult challenge. Without effective tools and a strategy for reducing the prevalence of these invasive snakes, the dire state of mammals in the Everglades will probably remain unchanged, and spread if python populations expand northward or become established elsewhere in the USA.


McCleery RA., Sovie A, Reed RN, Cunningham MW, Hunter ME, & Hart KM. (2015). Marsh rabbit mortalities tie pythons to the precipitous decline of mammals in the Everglades. Proceedings of the Royal Society of London B: Biological Sciences, 282(1805), 20150120.