Monday, August 31, 2015

Digestive system's adaptations to island life in Lacerta trilineata


Balkan Green Lizard. Lacerta trilineata.Photo Credit: 
Kostas Sagonas
Life on an island isn't always easy. To make the most of the little there is to eat on many Greek islands, the digestive system of s has evolved considerably compared to family members on the mainland. Surprisingly, many of these insect-eating lizards even have special valves that help to digest plants. These are some of the findings¹ from a study led by Konstantinos Sagonas of the National and Kapodistrian University of Athens in Greece, published in Springer's journal The Science of Nature².
Reptiles can adjust their digestive system and food preferences due to adverse circumstances such as low rainfall and poor food supply. Previous studies, for instance, show that insect-eating Balkan green lizards (Lacerta trilineata) surviving in the harsh environments of various Greek islands have broadened their diet to include more plants. To extend this research, Sagonas' team set out to compare groups of these lizards on the islands of Andros and Skyros with two other populations in mainland Greece.
They found that the island lizards have a longer small intestine and hindgut compared to their mainland counterparts. Those collected from the island of Skyros also have larger stomachs. When the animals were dissected, the researchers made an unusual discovery. Cecal valves, which slow down food passage and provide fermenting chambers, were found in 62 percent of the island-dwelling lizards, compared to 19 percent of the mainland ones. This was a fact not previously known for green lizards.
Cecal valves are typically found in plant-eating lizards, and host micro-organisms that help to ferment and break down plant material into fatty acids.. When these structures do occur in insect-eating lizards, it is generally among populations that have started to eat a varied diet that also includes plants. Sagonas believes the presence of cecal valves among the island lizards therefore reflects their higher consumption of plant material. About 30 percent of their diet consists of plant material, compared to the 10 percent of the mainland reptiles.
Their evolved digestive system therefore makes it possible for island lizards to eat more plants. Because of their longer digestive tract and the presence of cecal valves, it takes up to 26 percent longer for the food of island lizards to pass through their digestive system. In a process which is more common to plant-eating lizards, the ingested food is ultimately exposed far longer to digestive enzymes.
"Such adaptations allow insular populations to take advantage of the limited food resources of the islands and, eventually, overcome food dearth," explains Sagonas. "Energy flow in insular environments, the digestive performance of insular populations and the connections within them, provide insights into how animals are able to colonize islands and maintain viable populations." 


Citation

Sagonas K, Pafilis P., Valakos ED. Effects of insularity on digestion: living on islands induces shifts in physiological and morphological traits in island reptilesThe Science of Nature, 2015; 102 (9-10) DOI: 10.1007/s00114-015-1301-8

Saturday, August 29, 2015

A model for managing the Giant Garter Snake, Thamnophis gigas

Thamnophis gigas. Photo by Dave Feliz
The Giant Gartersnake (Thamnophis gigas) is a highly aquatic species that uses marshes and sloughs, low-gradient streams, ponds, and small lakes, with cattails, bulrushes, willows, or other emergent or water-edge vegetation. Because of the direct loss of natural habitat, this snake now relies heavily on rice fields in the Sacramento Valley, but it also uses managed marsh areas in various national wildlife refuges and state wildlife areas. Essential habitat components consist of adequate water during the snake's active season (early spring through mid-fall) to provide adequate permanent water to maintain dense populations of food organisms; emergent, herbaceous wetland vegetation, such as cattails and bulrushes, for escape cover and foraging habitat during the active season; upland habitat with grassy banks and openings in waterside vegetation for basking; and  higher elevation upland habitats for cover and refuge from flood waters during the snake's inactive season in the winter. The Giant Garter Snake is absent from large rivers and other waters with populations of large, introduced, predatory fishes, and from wetlands with sand, gravel, or rock substrates. Riparian woodlands do not provide suitable habitat because of excessive shade and inadequate prey resources. As of 1992, there were 13 known populations. Not all of have good viability. The adult population size is unknown but presumably is at least a few thousand. Estimates of population size for three local populations in the mid-1990s were in the low 100's. The species is now apparently extirpated or very rare in most of the former range in the San Joaquin Valley. Surveys in the 1970s and 1980s yielded some previously unknown localities and several cases of extirpation or at least severe population declines. The area of occupancy, number of subpopulations, and population size are probably continuing to decline, but the rate of decline is unknown.
 Because more than 90 percent of their historical wetland habitat has been converted to other uses, the species has been listed as threatened by the State of California (California Department of Fish and Game Commission, 1971) and the United States (U.S. Fish and Wildlife Service, 1993). Giant Gartersnakes inhabit a highly modified landscape, with most extant populations occurring in the rice-growing regions of the Sacramento Valley, especially near areas that historically were tule marsh habitat. In ricelands and managed marshes, many operational decisions likely impact the health and viability of Giant Gartersnake populations. Land-use decisions, including the management of water, aquatic vegetation, terrestrial vegetation, and co-occurring species, have the potential to affect giant Gartersnake populations. Little is known, however, about the effects of these types of decisions on the viability of the populations.
In a recent report Halstead et al. (2015) recognized that Bayesian network models are a useful tool to help guide decisions with uncertain outcomes. These models require the articulation of what experts think they know about a system, and facilitate learning about the hypothesized relations. Bayesian networks further provide a clear visual display of the model that facilitates understanding among various stakeholders. Empirical data and expert judgment can be combined, as continuous or categorical variables, to update knowledge about the system. The objective of this project was to develop a conceptual model of site-specific ecology of the Giant Gartersnake in the Sacramento Valley of California. The authors chose to develop the model at a site-specific scale because that is the scale at which most management decisions are made and at which Giant Gartersnake responses can be quantified. They used a Bayesian network model, and also quantified uncertainty associated with different nodes affecting ecology of the Giant Gartersnake, and the strength of influence of different variables on population growth rates of the species. This is a preliminary step in an ongoing process to clarify and quantify the effects of management actions on Giant Gartersnake populations.
They found population growth of the Giant Gartersnake was most influenced by demographic parameters, especially adult survival. Directly managing for increased survival or fecundity, however, generally is not feasible. Habitat quality, was strongly influenced by water availability and emergent vegetation and had a strong influence on both adult and first-year survival. Additional research into the effects of specific habitat attributes on Giant Gartersnake fitness is needed to better quantify the qualitative relations hypothesized in the Bayesian network model. In this regard, habitat quality; predator, parasite, and pathogen effects; and prey availability (particularly as it affects fecundity) all would be productive avenues for future research efforts. Alternatively, research could focus on those nodes for which the least information exists. For example, the scenario analysis indicated that changing Giant Gartersnake population growth from increasing to decreasing resulted in little change in many nodes. Competitor effects, other sources of mortality, and nearly all parents of habitat quality were changed little under increasing and decreasing population growth scenarios. This indicates that these variables either are truly unimportant for determining Giant Gartersnake population growth, or uncertainty in the strength of these relations precludes drawing conclusions about how these variables affect population growth of the Giant Gartersnake. The prudent course of action would be to conduct research into the effects of these variables on Giant Gartersnakes to determine which of these alternatives is correct.

Citation

Halstead, B.J., Wylie, G.D., Casazza, M.L., Hansen, E.C., Scherer, R.D., and Patterson, L.C., 2015, A conceptual model for site-level ecology of the giant gartersnake (Thamnophis gigas) in the Sacramento Valley, California: U.S.Geological Survey Open-File Report 2015-1152, 152 p., http://dx.doi.org/10.3133/ofr20151152.

Friday, August 28, 2015

A reassessment of the conservation status of the Central American herpetofauna

Salamanders like this Costa Rican Bolitoglossa striata are 
more susceptible to environmental disturbances than other
amphibians. JCM
A recently published article by Johnson et al. (2015) takes a second look at the herpetofauna of Central America and its conservation needs. The authors found Mesoamerica (the area composed of Mexico and Central America) is the third largest biodiversity hotspot in the world. The Central American herpetofauna has 493 species of amphibians and 559 species of crocodilians, squamates, and turtles.
The authors use a revised EVS measure to reexamine the conservation status of the herpetofauna using the General Lineage Concept of Species to recognize species-level taxa, and employ phylogenetic concepts to determine evolutionary relationships among the taxa.
Since the publication of Conservation of Mesoamerican Amphibians and Reptiles, in 2010, 92 species of amphibians and squamates have been described, resurrected, or elevated from subspecies to species level, and one species of anuran has been synonymized. The herpetofaunal diversity of Central America is comparable to that of Mexico, a significant finding because the land area of Mexico is 3.75 times larger. The number of amphibian species is 1.3 times greater in Central America, whereas the number of species of turtles, crocodilians, and squamates is 1.5 times greater in Mexico. Endemicity is also significant in Central America (65.6% of amphibians, 46.5% of turtles, crocodilians, and squamates), with a combined average of 55.6%.
The authors regard the IUCN system as expensive, time-consuming, and behind advances in systematics and over-dependent on the Data Deficient and Least Concern categories. Conversely, the EVS measure is economical, it can be applied when species are described, is predictive, simple to calculate, and does not “penalize” poorly known species.
The EVS analysis of amphibians demonstrates that on average salamanders are more susceptible to environmental deterioration, followed by caecilians, and anurans. Among the remainder of the herpetofauna, crocodilians are the most susceptible and snakes the least, with turtles and lizards in between.
Biodiversity decline is an environmental problem of global dimensions, comparable to the more commonly publicized problem of climate change. Both of these environmental super-problems exist because of human action and inaction, exacerbated by humanity’s anthropocentric focus.

Citation

Johnson, J. D., Mata-Silva, V., & Wilson, L. D. (2015). A conservation reassessment of the Central American herpetofauna based on the EVS measure. Amphibian & Reptile Conservation, 9(2), 1-94.

Wednesday, August 26, 2015

Gueragama sulamericana a Late Cretaceous stem iguanid from southern Brazil


Gueragama sulamerica. Credit: Julius Csotonyi
University of Alberta paleontologists have discovered a new species of lizard, named Gueragama sulamericana, in the municipality of Cruzeiro do Oeste in Southern Brazil in the rock outcrops of a Late Cretaceous desert, dated approximately 80 million years ago.

"The roughly 1700 species of iguanas are almost without exception restricted to the New World, primarily the Southern United States down to the tip of South America," says Michael Caldwell, biological sciences professor from the University of Alberta and one of the study's authors. Oddly however, iguanas closest relatives, including chameleons and bearded dragons, are all Old World. As one of the most diverse groups of extant lizards, spanning from acrodontan iguanians (meaning the teeth are fused to the top of their jaws) dominating the Old World to non-acrodontans in the New World, this new lizard species is the first acrodontan found in South America, suggesting both groups of ancient iguanians achieved a worldwide distribution before the final break up of Pangaea.

"This fossil is an 80 million year old specimen of an acrodontan in the New World," explains Caldwell. "It's a missing link in the sense of the paleobiogeography and possibly the origins of the group, so it's pretty good evidence to suggest that back in the lower part of the Cretaceous, the southern part of Pangaea was still a kind of single continental chunk."

Distributions of plants and animals from the Late Cretaceous reflect the ancestry of Pangaea when it was whole. "This Gueragama sulamericana fossil indicates that the group is old, that it's probably Southern Pangaean in its origin, and that after the break up, the acrodontans and chameleon group dominated in the Old World, and the iguanid side arose out of this acrodontan lineage that was left alone on South America," says Caldwell. "South America remained isolated until about 5 million years ago. That's when it bumps into North America, and we see this exchange of organism north and south. It was kind of like a floating Noah's Arc for a very long time, about 100 million years. This is an Old World lizard in the new world at a time when we weren't expecting to find it. It answers a few questions about iguanid lizards and their origin."

The University of Alberta is a world leader in paleontology. This study was a collaboration between the University of Alberta and scientists in Brazil. Caldwell says of the collaboration, "It's providing an opportunity for our students and research groups to expand our expertise and interests into an ever-increasing diversity of organisms within this group of animals called snakes and lizards."

The lead author of the paper is Caldwell's PhD student, Tiago Simoes, a Vanier scholar. "As with many other scientific findings, this one raises a number of questions we haven't previously considered," says Simoes. "This finding raises a number of biogeographic and faunal turnover questions of great interest to both paleontologists and herpetologists that we hope to answer in the future."

In terms of next steps, Caldwell notes "Each answer only rattles the questions harder. The evolution of the group is much older than has been previously thought, which means we can push an acrodontan to 80 million years in South America. We now need to focus on much older units of rock if we're going to find the next step in the process."

The findings, "A stem acrodontan lizard in the Cretaceous of Brazil revises early lizard evolution in Gondwana," were published in the journal Nature Communications, one of the world's top multidisciplinary scientific journals.

Citation

Tiago R. Simões, Everton Wilner, Michael W. Caldwell, Luiz C. Weinschütz, Alexander W. A. Kellner. A stem acrodontan lizard in the Cretaceous of Brazil revises early lizard evolution in Gondwana. Nature Communications, 2015; 6: 8149 DOI: 10.1038/ncomms9149

Wednesday, August 19, 2015

Embryonic lizards may not survive global warming

Currently, three percent of land in the US is inhospitable to 
lizards (orange areas). In the next century, the scientists say 
the areas where lizards may not thrive could grow to 48 
percent (purple area). Map Credit: Ofir Levy; Lizard Photo
 - The Tree Lizard, Urosaurus ornatus. JCM
The expected impact of climate change on North American lizards is much worse than first thought. A team of biologists led by Arizona State University investigators has discovered that lizard embryos die when subjected to a temperature of 110 degrees Fahrenheit even for a few minutes.

The researchers also discovered a bias in previous studies, which ignored early life stages such as embryos. Embryonic lizards are immobile and cannot seek shade or cool off when their surrounding soil becomes hot.

This bias produced overly optimistic forecasts about the fate of lizards during climate change. Given the potential impacts on embryos, many more places in the United States could become uninhabitable for lizards than previously expected.

"Lizards put all of their eggs in one basket, so a single heat wave can kill an entire group of eggs," said Ofir Levy, lead investigator of the study and postdoctoral fellow with ASU School of Life Sciences. "If mothers don't dig deeper nests to lay their eggs, we expect this species to decline throughout the United States."

The findings appear today online in the journal Proceedings of the Royal Society B.

After finding that lizard embryos cannot tolerate 110 degrees Fahrenheit for even a short period, the researchers used a climate model to predict how often heat waves in the past and future would kill developing lizards. Areas in the U.S. reaching lethal temperatures, even in the shade, could spread from 3 percent currently to 48 percent of the country in the next century.

Female lizards lay eggs in spring and summer, digging nests and then leaving their offspring to develop for more than two months. Mothers may choose shadier soils or dig deeper nests to help their offspring avoid the heat. But even if lizards lay eggs in cooler places, nests may still exceed the temperatures that embryonic lizards can tolerate. And, assuming that baby lizards could reach the surface after hatching from a deeper nest, that still may not offer enough protection. Repeated exposure to above average, but not lethal temperatures, can negatively affect a lizard's physiology and behavior.

"Since this year promises to be the hottest on record, we are asking whether organisms, like lizards, can adjust to their warming world," said Michael Angilletta, professor and senior sustainability scientist with ASU School of Life Sciences. "It's critical that we acquire detailed knowledge about what temperatures these lizards and other animals can tolerate throughout the life cycle, not just as adults."

Levy added: "Because lizards are prey for animals such as birds, snakes and mammals, the harmful effects of climate change on embryonic lizards could also negatively affect other species."

Citation
Levy O,  Buckley LB,  Keitt TH,  Smith CD, Boateng KO, Kumar DS,  Angilletta MJ. 2015. Resolving the life cycle alters expected impacts of climate change. Proceedings of the Royal Society B, August  DOI: 10.1098/rspb.2015.0837

Thursday, August 13, 2015

New book: Atlas Serpientes de Venezuela - Price Reduced


Atlas Serpientes de Venezuela by Marco Natera Mumaw, Luis Felipe Esqueda, González and Manuel. The book's size is 32x25, full color, dust jacket, it contains 456 pages,>400 photos, >60 maps on geographic distribution and assembled in four chapters and four thematic appendices. For requests send an email to Luis Felipe Esqueda, Co-author and Editor or directly to Marisol Diaz Astorga (responsible for final acceptance and shipping, see instructions). General cost of book is 60$ + 10$ PayPal or Western Union (charges a commission) + shipping costs depending on the location (certified by Correos de Chile).









Friday, August 7, 2015

Venomous frogs


Corythomantis greeningi greening was found to have spines extending from  its skull that can poke through the skin to deliver poison into potential predators (left). Corythomantis greeningi greening, or Greening's frog (middle). Aparasphenodon brunoi, or Bruno's Casque-headed Frog (right.).
Photo Credit: Carlos Jared.

Venomous animals have toxins associated with delivery mechanisms that can introduce the toxins into another animal.

Although most amphibian species produce or sequester noxious or toxic secretions in the glands of the skin to use as antipredator mechanisms, they have been considered poisonous rather than venomous because delivery mechanisms are absent.

The frogs in question – the Greening’s frog (Corythomantis greeningi) and the Bruno’s casque-headed frog (Aparasphenodon brunoi) – produce potent toxins and also have a mechanism to deliver those harmful secretions into another animal using bony spines on their heads.

“Discovering a truly venomous frog is nothing any of us expected, and finding frogs with skin secretions more venomous than those of the deadly pit vipers of the genus Bothrops was astounding,” said  Edmund Brodie, Jr. from Utah State University, a team member and a co-author on the study.

The Greening’s frog and the Bruno’s casque-headed frog have both been known for many decades, if not centuries. But scientists have known little of their biology.

The team’s calculations suggest that a single gram of the toxic secretion from the Bruno’s casque-headed frog would be enough to kill more than 300,000 mice or about 80 humans.

“It is unlikely that a frog of this species produces this much toxin, and only very small amounts would be transferred by the spines into a wound. Regardless, we have been unwilling to test this by allowing a frog to jab us with its spines,” said lead author Dr Carlos Jared from the Instituto Butantan in São Paulo, Brazil.

The researchers, whose findings are published in the journal Current Biology, only discovered they were venomous while collecting amphibians for study. Jared was injured by a spine from Corythoimantis greeingi while handling it, leading to intense spreading pain in his hand for around five hours. Fortunately for him, the frog was the less toxic of the two. He said: 'The action should be even more effective on the mouth lining of an attacking predator.'

The researchers say they have still to find out exactly how much toxin the frogs can deliver in one go. However, they believe there may be other species of frog that are also venomous. Dr Brodie added: 'It is unlikely that a frog of this species produces this much toxin, and only very small amounts would be transferred by the spines into a wound. 'Regardless, we have been unwilling to test this by allowing a frog to jab us with its spines.'

“The new discovery is important for understanding the biology of amphibians and their interactions with predators in the wild,” the scientists said.

Citation
Jared et al. 2015. Venomous Frogs Use Heads as Weapons. Current Biology, doi: 10.1016/j.cub.2015.06.061

Wednesday, August 5, 2015

Snakes & Palm Oil Plantations in Colombia

The most commonly encountered snake in oil palm plantations
was Ninia atrata.
Rainforest in the tropics is frequent cut to make way for the African oil palms, Elaeis guineensis. The plant is most often grown for cooking oil but has recently attracted the attention of the alternative energy industry as a source of biofuel. While the plant is native to sub-Saharan Africa, it has now spread to tropical Asia and the Neotropics.
Lynch (2015) analyzes the snake species found during student field trips to Colombian oil palm plantations between 2006-2013. They visited 30 palm plantations varying in size from 0.02-20,000 hectares. These include small privately held palm trees groves as well as large commercial plantations. Success-rates varied with less success in the dry season and greater success in the wet season. Thirty-five snake species were found. Widespread lowland species (Boa constrictor, Clelia clelia, Corallus hortulanus, Imantodes cenchoa, Leptophis ahaetulla, Ninia atrata, Oxyrhopus petola, Tantilla melanocephala, and the species pairs of Bothrops asper or B. atrox, Epicrates cenchria or E. maurus, and Leptodeira annulata or L. septentrionalis). Seven other species (Chironius carinatus, Erythrolamprus bizona, Lampropeltis cf. triangulum, Mastigodryas boddaertii, M. pleei, Sibon nebulata, and Typhlops reticulatus) occur across the regions sampled but do not occupy all lowlands of Colombia. All of these except Imantodes cenchoa, Lampropeltis cf. triangulum, and Sibon nebulata were captured in at least one plantation. Of the 35 species of snakes captured in palm trees, fourteen were diurnal activity or crepuscular, the remaining 21 species are exclusively nocturnal.
To date, there are no reliable data on population sizes of any snake species in Colombia. In point of fact, the impression of collectors is that densities are very low. This impressions is contradicted by our work in palm plantations. Collecting in natural habitats by other researchers has produced success rates equivalent or superior to our work in palm trees.
The Colombian African palm oil industry could be a major factor in conserving snakes. Snake mortality from rural workers exceeds 100 million/year and no fewer than 50,000 snakes die/year due to traffic. However, to be a partner in snake conservation will require two changes in the industry: (1) all waste be fronds need to be piled into mounds on the plantation and allowed to decompose slowly. This provides refuges for snakes, easy access to prey, and reduces human encounters, Secondly, stop converting parcels of secondary forest into more monoculture of palms. Leaving patches of secondary forest and scrub increases microhabitats and the prey base.

Citation
Lynch, J. D. (2015). The role of plantations of the African palm (Elaeis guineensis Jacq.) in the conservation of snakes in Colombia. Caldasia, 37(1), 169-182.