Sunday, January 29, 2017

Oldest, most complete iguanian in the Americas

The lizard Magnuviator ovimonsensis is a newly discovered species at Egg
 Mountain in Montana,  US, at a site rich in fossils from the Cretaceous Period. 
The lizard is thought to have lived 75 million years ago. Artist credit: 
Misaki Ouchida
Paleontologists picking through a bounty of fossils from Montana have discovered something unexpected -- a new species of lizard from the late dinosaur era, whose closest relatives roamed in faraway Asia.

This ancient lizard, which lived 75 million years ago in a dinosaur nesting site, is described from stem to stern in a paper published Jan. 25 in the Proceedings of the Royal Society B. Christened Magnuviator ovimonsensis, the new species fills in significant gaps in our understanding of how lizards evolved and spread during the dinosaur era, according to paleontologists at the University of Washington and the Burke Museum of Natural History & Culture who led the study.

"It is incredibly rare to find one complete fossil skeleton from a relatively small creature like this lizard," said David DeMar, lead author and postdoctoral research associate in the UW biology department and the Burke Museum. "But, in fact, we had two specimens, both from the same site at Egg Mountain in Montana."

Right out of the gate, Magnuviator is reshaping how scientists view lizards, their biodiversity and their role in complex ecosystems during this reptile's carefree days in the Cretaceous Period 75 million years ago.

Based on analyses of the nearly complete fossil skeletons, Magnuviator was an ancient offshoot of iguanian lizards -- and they're actually the oldest, most complete iguanian fossils from the Americas. Today, iguanians include chameleons of the Old World, iguanas and anoles in the American tropics and even the infamous water-walking basilisk -- or "Jesus Christ" -- lizards. But based on its anatomy, Magnuviator was at best a distant relative of these modern lizard families, most of which did not arise until after the non-avian dinosaurs -- and quite a few lizards and other creatures -- went extinct 66 million years ago.

The team came to these conclusions after meticulous study of both Egg Mountain specimens over four years. This included a round of CT scans at Seattle Children's Hospital to narrow down the fossil's location within a larger section of rock and a second round at the American Museum of Natural History to digitally reconstruct the skull anatomy. The fact that both skeletons were nearly complete allowed them to determine not only that Magnuviator represented an entirely new species, but also that its closest kin weren't other fossil lizards from the Americas. Instead, it showed striking similarities to other Cretaceous Period iguanians from Mongolia.

"These ancient lineages are not the iguanian lizards which dominate parts of the Americas today, such as anoles and horned lizards," said DeMar. "So discoveries like Magnuviator give us a rare glimpse into the types of 'stem' lizards that were present before the extinction of the dinosaurs."

But Magnuviator's surprises don't end with the Mongolian connection. The site of its discovery is also eye-popping.

Egg Mountain is already famous among fossil hunters. Over 30 years ago, paleontologists discovered the first fossil remains of dinosaur babies there, and it is also one of the first sites in North America where dinosaur eggs were discovered.

"We now recognize Egg Mountain as a unique site for understanding Cretaceous Period ecosystems in North America," said senior author Greg Wilson, UW associate professor of biology and curator of paleontology at the Burke Museum. "We believe both carnivorous and herbivorous dinosaurs came to this site repeatedly to nest, and in the process of excavating this site we are learning more and more about other creatures who lived and died there."

The team even named their new find as homage to its famous home and its close lizard relatives in Asia. Magnuviator ovimonsensis means "mighty traveler from Egg Mountain."

Through excavations at Egg Mountain led by co-author David Varricchio at Montana State University and meticulous analysis of fossils at partner institutions like the UW and the Burke Museum, scientists are piecing together the Egg Mountain ecosystem of 75 million years ago. In those days, Egg Mountain was a semi-arid environment, with little or no water at the surface. Dinosaurs like the duck-billed hadrosaurs and the birdlike, carnivorous Troodon nested there.

Researchers have also unearthed fossilized mammals at Egg Mountain, which are being studied by Wilson's group, as well as wasp pupae cases and pollen grains from plants adapted for dry environments. Based on the structure of Magnuviator's teeth, as well as the eating habits of some lizards today, the researchers believe that it could have feasted on wasps at the Egg Mountain site. Though based on its relatively large size for a lizard -- about 14 inches in length -- Magnuviator could have also eaten something entirely different.

"Due to the significant metabolic requirements to digest plant material, only lizards above a certain body size can eat plants, and Magnuviator definitely falls within that size range," said DeMar.

Whatever its diet, Magnuviator and its relatives in Mongolia did not make it into the modern era. DeMar and co-authors hypothesize that these stem lineages of lizards may have gone extinct along with the non-avian dinosaurs. But given the spotty record for lizards in the fossil record, it will take more Magnuviator-level discoveries to resolve this debate. And, unfortunately, part of the excitement surrounding Magnuviator is that it is a rare find.

Citation
David G. DeMar, Jack L. Conrad, Jason J. Head, David J. Varricchio, Gregory P. Wilson. A new Late Cretaceous iguanomorph from North America and the origin of New World Pleurodonta (Squamata, Iguania). Proceedings of the Royal Society B: Biological Sciences, 2017; 284 (1847): 20161902 DOI: 10.1098/rspb.2016.1902

Sunday, January 15, 2017

The hormonal basis for parental care in rattlesnakes

Pigmy Rattlesnakes, Sistrurus miliarius.
Rattlesnakes have been documented to show parental care, a complex social behavior that is widespread among vertebrates. This behavior has been linked to neuroendocrine regulation in mammals, and, to a lesser extent, birds and fish. However, its influence on reptiles is poorly known. In mammalian species and humans, the posterior pituitary hormones in the  oxytocin and vasopressin families mediate parental care behaviors. In a forthcoming paper in Biology Open, Lind et al. (2017) test the hypothesis that the regulatory role of posterior pituitary neuropeptides is conserved in a viviparous squamate reptile. The researchers pharmacologically blocked the vasotocin receptor in postparturient Pigmy Rattlesnakes, Sistrurus miliarius, and monitored the spatial relationship between females and their offspring relative to controls. Mothers in the control group demonstrated spatial aggregation with offspring, with mothers having greater postparturient energy stores aggregating more closely with their offspring. Blockade of vasotocin receptors eliminated evidence of spatial aggregation between mothers and offspring and eliminated the relationship between maternal energetic status and spatial aggregation. The results are the first to implicate posterior pituitary neuropeptides in the regulation of maternal behavior in a squamate reptile and are consistent with the hypothesis that the neuroendocrine mechanisms underlying social behaviors are broadly conserved among vertebrates.

Citation
Lind CM, Birky NK, Porth AM, Farrell TM. Vasotocin receptor blockade disrupts maternal care of offspring in a viviparous snake, Sistrurus miliarius. Biology Open. 2017 Jan 1:bio-022616.

Low cost method for surveying Eastern Massasauga Rattlesnake

Adult female Eastern Massasauga (Sistrurus catenatus). The rattle was painted with nail polish to 
aid with individual identification. Photo credit Danielle Bradke.
Monitoring populations of rare and endangered species is a priority for management and conservation. However, rare and endangered species have low detection probabilities. Low detection rates may be the result of small populations at low densities, misidentification, cryptic behavior, inefficiency of survey method and difficult survey conditions such as dense vegetation or weather. In a recent paper, Bartman et al. (2016)explored the effectiveness of using artificial cover objects (AOCs) and funnel traps to supplement visual survey methods for the Eastern Massasauga Rattlesnake (Sistrurus catenatus) at a site in southwestern Michigan. They found the funnel traps (2.64 snakes/h) were about six times more efficient than visual surveys (0.41 snakes/h) for capturing both sexes combined, and approximately 28 times more efficient for capturing males. Wooden coverboards (1.11 snakes/h) were approximately 3.5 times more efficient than visual surveys (0.32 snakes/h) for capturing females. The authors recommend the use of these trapping techniques, in addition to visual surveys, as efficient methods for capturing and monitoring Eastern Massasaugas.

Citation
Bartman JF, Kudla N, Bradke DR, Otieno S, Moore JA. 2016. Work Smarter, Not Harder: Comparison of Visual and Trap Survey Methods for the Eastern Massasauga Rattlesnake (Sistrurus catenatus). Herpetological Conservation and Biology 11:451-8.

Saturday, January 14, 2017

An introduced snake on Ibiza Island, the Horseshoe Whip Snake

Hemorrhois hippocrepis Photo credit: Accipiter (R. Altenkamp)
Island ecosystems may be more vulnerable to invasive species than any other ecosystems. Island species have often evolved in isolation with reduced competition and predation from mainland species. When new species invade an island they are often able to out-compete the local endemics resulting in serious population declines or extinctions. The Mediterranean's Balearic Islands have been isolated from the continent for 5.33 million of years. Human-mediated introductions started by the end of the third millennium BCE, when humans colonized the islands and alien species introductions began. Two mammals, the European Pine Marten, Martes martes, and the Least Weasel, Mustela nivalis, together with an introduced snake, False Smooth Snake, Macroprotodon cucullatus, have been considered responsible for the extinction of the native lizard Podarcis lilfordi on the main islands.
Podarcis pityusensis Wikimedia Commons

Until quite recently, all except two of the larger 63 Mediterranean islands larger than 75 km2 harbored at least one snake species. The exception were the westernmost Balearic islands, also known as the Pityusic islands, Ibiza, and Formentera, which were never colonized by snakes. This absence of snakes was recognized by Pliny the Elder two thousand years ago. Between 12 and 13 years ago, three species of snakes (Horseshoe Whip Snake, Hemorrhois hippocrepis; Ladder Snake, Rhinechis scalaris; and the Montpellier snake, Malpolon monspessulanus) were introduced in Ibiza when old ornamental olive trees were imported from the southern Iberian Peninsula. However, there have not been any records of the Montpellier snake in Ibiza during the last six years. The Ladder Snake has been captured infrequently which might mean that it is struggling to establish a population. The Horseshoe Whip Snake, however, is expanding in Ibiza. It is a large, slender-bodied, long-tailed colubrid distributed throughout the Western Mediterranean. It was first reported on Ibiza in 2003.

In a new paper Hinkey et al. (2017) report that specimens of the Horseshoe Whip Snake obtained from an early eradication campaign showed a rapid expression of phenotypic plasticity and acquired larger body sizes than those of the source population. This was probably due to a high prey availability and few snake predators. the Horseshoe Whip Snake is thriving at the expense of a small variety of native and non-native prey. However, the predation pressure on the endemic Ibiza wall lizard, Podarcis pityusensis, the only native reptile on the island, is very high.  The Ibiza Wall Lizard represents 56% of the prey taken by the Horseshoe Whip Snake and the heavy predation may threaten its survival.

The authors conclude the Horseshoe Whip Snake threatens the biodiversity of Ibiza and that the threat may extend to smaller populations of lizards on  surrounding islands. The snake has been observed swimming in the sea and a shed skin was found on one islet. It seems that an eradication effort is needed.

Citation
Hinckley A, Montes E, Ayllón E, Pleguezuelos JM. 2017. The fall of a symbol? A high predation rate by the introduced horseshoe whip snake Hemorrhois hippocrepis paints a bleak future for the endemic Ibiza wall lizard Podarcis pityusensis. European Journal of Wildlife Research. 63(1):13.

Friday, January 13, 2017

Rattlesnakes strike faster in the wild — compared to laboratory observations

Biologists from the University of California at Riverside used high-speed cameras to study predator-prey interactions in the wild. They found that the rattlesnakes strike faster in the wild — compared to laboratory observations conducted in prior studies — but the kangaroo rats' "sling shot" tendons give them a good chance at evasion.


Feeding is paramount to the survival of almost every animal, and just about every living organism is eaten by another. Not surprisingly, the animal kingdom shows many examples of extreme specialization -- the chameleon's tongue, fox diving into snow, cheetah sprinting -- for capturing prey or escaping predators.

The antagonistic predator-prey relationship is of interest to evolutionary biologists because it often leads to extreme adaptations in both the predator and prey. One such relationship is seen in the rattlesnake-kangaroo rat system -- a model system for studying the dynamics of high-power predator-prey interactions that can be observed under completely natural conditions.

Curiously, however, very little is known about the strike performance of rattlesnakes under natural conditions. But that is now about to change because technological advances in portable high-speed cameras have made it possible for biologists like Timothy Higham at the University of California, Riverside to capture three-dimensional video in the field of a rattlesnake preying on a kangaroo rat.

"Predator-prey interactions are naturally variable -- much more so than we would ever observe in a controlled laboratory setting," said Higham, an associate professor of biology, who led the research project. "Technology is now allowing us to understand what defines successful capture and evasion under natural conditions. It is under these conditions in which the predator and prey evolve. It's therefore absolutely critical to observe animals in their natural habitat before making too many conclusions from laboratory studies alone."

A question Higham and his team are exploring in predator-prey relationships is: What factors determine the success/failure of a strike or escape? In the case of the rattlesnake and kangaroo rat, the outcome, they note, appears to depend on both the snake's accuracy and the ability of the kangaroo rat to detect and evade the viper before being struck.

"We obtained some incredible footage of Mohave rattlesnakes striking in the middle of the night, under infrared lighting, in New Mexico during the summer of 2015," Higham said. "The results are quite interesting in that strikes are very rapid and highly variable. The snakes also appear to miss quite dramatically -- either because the snake simply misses or the kangaroo rat moves out of the way in time."

Many studies have examined snake strikes, but the new work is the first study to quantify strikes using high-speed video (500 frames per second) in the wild.


In the paper, Higham and his coauthors conclude that rattlesnakes in nature can greatly exceed the defensive strike speeds and accelerations observed in the lab. Their results also suggest that kangaroo rats might amplify their power when under attack by rattlesnakes via "elastic energy storage."

"Elastic energy storage is when the muscle stretches a tendon and then relaxes, allowing the tendon to recoil like an elastic band being released from the stretched position," Higham explained. "It's equivalent to a sling shot -- you can pull the sling shot slowly and it can be released very quickly. The kangaroo rat is likely using the tendons in its lower leg -- similar to our Achilles tendon -- to store energy and release it quickly, allowing it to jump quickly and evade the strike."

To collect data, the team radio-tracked rattlesnakes by implanting transmitters. Once the rattlesnake was in striking position, the team carried the filming equipment to the location of the rattlesnake (in the middle of the night) and set up the cameras around the snake. The team then waited (sometimes all night) for a kangaroo rat to come by for the snake to strike.

"We would watch the live view through a laptop quite far away and trigger the cameras when a strike occurred," Higham said.

Next, the researchers plan to expand the current work to other species of rattlesnake and kangaroo rat to explore the differences among species.
Citation
 Higham TE, Clark RW, Collins CE, Whitford MD, Freymiller GA. 2017. Rattlesnakes are extremely fast and variable when striking at kangaroo rats in nature: Three-dimensional high-speed kinematics at night. Scientific Reports, 2017; 7: 40412 DOI: 10.1038/srep40412

Tuesday, January 3, 2017

Rhynchocalamus a poorly known clade of snakes from southwest Asia

The colubrid snake genus Rhynchocalamus composed of three small, gracile snakes distributed in Southwest Asia. While, these snakes are sometimes called Kikuri snakes, a name sometimes applied to the members of the genus Oligodon, they also tend to have blackheads and are sometimes called the blackheaded snakes, a name that may confuse them with the North American genus Tantilla. Their secretive fossorial lifestyle has resulted in them being poorly known and under studied. Only recently Šmíd et al. (2015) found Rhynchocalamus to be a member of the the Western Palearctic clade of Colubrinae and the sister to the awl-headed snakes of the genus  Lytorhynchus.

Three species of Rhynchocalamus are currently recognized, R. satunini (Turkey eastwards to Iran), R. arabicus (Yemen and Oman), and R. melanocephalus (from the Sinai Peninsula northwards to Turkey). Tamar et al. (2016) recently completed a comprehensive study on all known Rhynchocalamus species in order to review the intra-generic phylogenetic relationships and historical biogeography of the genus and describe a fourth species from Israel.

The molecular results found Rhynchocalamus monophyletic, and last shared an ancestor with Lytorhynchus in Late Oligocene. The three recognized species of Rhynchocalamus comprise four independently lineages with the genus diverge during the Middle Miocene. They discovered R. melanocephalus is paraphyletic. A population from the Negev Mountain area in southern Israel is phylogenetically closer to R. arabicus from Oman than to the northern populations of the species from Israel, Syria and Turkey and they describe this population as the new species Rhynchocalamus dayanae.

A) R. dayanae sp. nov. specimen from  Mitzpe Ramon, Negev Mountain, Israel; photo by Simon Jamison); (B) R. melanocephalus (Tartus, Syria; photo by Bayram Göçmen); (C) R. satunini (Artuklu, Mardin province, Turkey; photo by Bayram Göçmen); (D) R. arabicus (Wadi Ayoun, Dhofar Governorate, Oman; photo by Gabriel Martínez).

Citations

Šmíd, J;  Martínez G, Gebhart J, Aznar J,  Gállego J, Göçmen B, De Pous P, Tamar K & Carran-za S. 2015. Phylogeny of the genus Rhynchocalamus (Reptilia; Colubridae) with a first record from the Sultanate of Oman Zootaxa 4033 (3): 380–392.

Tamar K, Šmíd J, Göçmen B, Meiri S, Carranza S. (2016) An integrative systematic revision and biogeography of Rhynchocalamus snakes (Reptilia, Colubridae) with a description of a new species from Israel. PeerJ 4:e2769 https://doi.org/10.7717/peerj.2769.