Thursday, August 29, 2013

Diet overlap in aquatic snake assemblages

Competition for prey is thought to be important in structuring snake assemblages. However, given the secretive behavior and low detectability of many snake species, this generalization is based on a limited number of studies, most of which focus on a single study site. In a forthcoming paper in the Journal of Zoology Durso et al (2013) examined differences in diet composition, trophic niche overlap, site occupancy and detectability of five sympatric aquatic snake species [eastern mud snake, Farancia abacura; banded watersnake, Nerodia fasciata; Florida green water snakes, N. floridana; glossy crayfish snakes, Regina rigida; and black swamp snakes, Seminatrix pygaea] between two different habitat types in the southeastern US. They studies  permanent wetlands with fishes (n = 13) and isolated, often ephemeral wetlands without fishes (n = 10). More than 3700 prey items were collected from snakes and compared diet composition among snake species to examine niche breadth and overlap, correcting for relative availability of prey captured independently in the same wetlands. They also evaluated evidence for competitive exclusion by estimating the probability of co-occupancy for pairs of snake species in each habitat type using occupancy modeling. In wetlands with fishes, niche overlap was low, suggesting resource partitioning. Conversely, in wetlands without fishes, niche overlap was high, with most species feeding on larval or paedomorphic ambystomatid salamanders, but competitive exclusion did not occur. They suggest that high co-occupancy of aquatic snakes in wetlands without fishes, despite the apparent lack of resource partitioning, is due to a combination of seasonally high abundance of high quality amphibian prey, unique aspects of predator physiology and stochastic abiotic processes that prevent these systems from reaching equilibrium. The results demonstrate that snake diets can be highly context (e.g. habitat) specific.

Citation
Durso AM, Willson J D, & Winne CT. (2013)  Habitat influences diet overlap in aquatic snake assemblages. Journal of Zoology. DOI: 10.1111/jzo.12061

Social female copperheads found to be non-kin

Recent observations suggest snakes may be far more social than previously thought, including the ability to recognize and group with kin, and provide parental care (defense) for young. Inclusive fitness theory predicts that benefits of such groupings should be greater when groups are composed of related individuals. Although the ability required to recognize kin under this theory has been observed in a wide range of vertebrates, it has only recently been reported in snakes. Li et al. (2013) tested competing hypotheses for aggregation behavior in female neonate copperhead snakes, female aggregations are common in nature; male aggregations have not been observed.  They asked is (1) aggregation is mediated by genetic relatedness, or is (2) aggregation is mediated by familiarity, i.e. learned. The authors found no effect of learning on neonate aggregation. With regard to relatedness, contrary to  expectation they found  unrelated individuals tended to aggregate more than related individuals. The authors suggest that the lack of aggregation behavior in related individuals may be due to selection for dispersal and/or reduced effects of predation or disease.

Citation
Li M., Moeller JF,  Smith CF. (2013). Family and Friends: What Factors Influence Aggregation in Female Copperhead Snakes?. Lander University 9: 15-9: 27.

Monday, August 26, 2013

Eastern coral snake venom found to contain molecules from 15 toxin families

Snake venom is shaped by the ecology and evolution of the species that makes it. Evidence of positive selection in toxins have been consistently documented, reflecting the role of venoms as an ecologically critical phenotype. New World coral snakes (Elapidae) are represented by three genera and over 120 species and subspecies that are capable of causing significant human morbidity and mortality, yet coral-snake venom composition is poorly understood in comparison to that of Old World elapids.

In a recently published article Mark Margres of Florida State University and colleagues used high-throughput sequencing to identify thousands of loci, while providing characterizations of expression patterns and the molecular evolutionary forces acting within the venom gland.

The authors describe the de novo assembly and analysis of the venom-gland transcriptome of the eastern coral snake (Micrurus fulvius). The identified 1,950 nontoxin transcripts and 116 toxin transcripts. These transcripts accounted for 57.1% of the total reads, with toxins accounting for 45.8% of the total reads. Phospholipases A2 and three-finger toxins dominated expression, accounting for 86.0% of the toxin reads. A total of 15 toxin families were identified, revealing venom complexity previously unknown from New World coral snakes. Toxins exhibited high levels of heterozygosity relative to nontoxins, and overdominance may favor gene duplication leading to the fixation of advantageous alleles. Phospholipase A2 expression was uniformly distributed throughout the class while three-finger toxin expression was dominated by a handful of transcripts, and phylogenetic analyses indicate that toxin divergence may have occurred following speciation. Positive selection was detected in three of the four most diverse toxin classes, suggesting that venom diversification is driven by recurrent directional selection.

The new research describe the most complete characterization of an elapid venom gland to date. Toxin gene duplication may be driven by heterozygote advantage, as the frequency of polymorphic toxin loci was significantly higher than that of nontoxins. Diversification among toxins appeared to follow speciation reflecting species-specific adaptation, and this divergence may be directly related to dietary shifts and is suggestive of a co-evolutionary arms race.


Citation
Margres MJ, Aronow K, Loyacano J, Rokyta DR 2013.The venom-gland transcriptome of the eastern coral snake (Micrurus fulvius) reveals high venom complexity in the intragenomic evolution of venoms. BMC Genomics 2013, 14:531.

Saturday, August 17, 2013

Female mate choice in Hyla chrysoscelis

From frogs to humans, selecting a mate is complicated.  Females of many species judge suitors based on many indicators of health or parenting potential. But it can be difficult for males to produce multiple signals that demonstrate these qualities simultaneously.

In a study of gray tree frogs, a team of University of Minnesota researchers discovered that females prefer males whose calls reflect the ability to multitask effectively.  In this species (Hyla chrysoscelis) males produce "trilled" mating calls that consist of a string of pulses.

Typical calls can range in duration from 20-40 pulses per call and occur between 5-15 calls per minute. Males face a trade-off between call duration and call rate, but females preferred calls that are longer and more frequent, which is no simple task.

The findings were published in August issue of Animal Behavior.

"It’s kind of like singing and dancing at the same time," says Jessica Ward, a postdoctoral researcher who is lead author for the study. Ward works in the laboratory of Mark Bee, a professor in the College of Biological Sciences’ Department of Ecology, Evolution and Behavior.

The study supports the multitasking hypothesis, which suggests that females prefer males who can do two or more hard-to-do things at the same time because these are especially good quality males, Ward says.  The hypothesis, which explores how multiple signals produced by males influence female behavior, is a new area of interest in animal behavior research.

By listening to recordings of 1,000 calls, Ward and colleagues learned that males are indeed forced to trade off call duration and call rate. That is, males that produce relatively longer calls only do so at relatively slower rates.

"It's easy to imagine that we humans might also prefer multitasking partners, such as someone who can successfully earn a good income, cook dinner, manage the finances and get the kids to soccer practice on time."

The study was carried out in connection with Bee’s research goal, which is understanding how female frogs are able to distinguish individual mating calls from a large chorus of males. By comparison, humans, especially as we age, lose the ability to distinguish individual voices in a crowd. This phenomenon, called the "cocktail party" problem, is often the first sign of a diminishing ability to hear. Understanding how frogs hear could lead to improved hearing aids.

College of Biological Sciences faculty conduct research in all areas of biology, from molecules to ecosystems, which supports applications in medicine, renewable energy, agriculture and biotechnology. The college offers degree programs in biochemistry, molecular biology and biophysics; genetics, cell biology and development; ecology, evolution and (animal) behavior; plant biology; microbiology and neurosciences. Admission to undergraduate programs is highly competitive.

Citation
Ward JL, Love EK, Vélez A, Buerkle NP, O'Bryan LR, Bee MA. 2013. Multitasking males and multiplicative females: dynamic signalling and receiver preferences in Cope's grey treefrog. Animal Behaviour, 2013; 86(2):231 DOI: 10.1016/j.anbehav.2013.05.016

Thursday, August 15, 2013

Sea snakes disappear at Ashmore Reef despite protection


The Ashmore Reef National Nature Reserve was established in 1983 and covers 583 kmAshmore Reef  contains seagrass beds, intertidal sand flats, coral reef flats, and lagoons, and supports an important and diverse range of species, including 14 species of sea snakes, a population of dugong that may be genetically distinct, a diverse marine invertebrate fauna, and many endemic species, especially of sea snakes and molluscs. Feeding and nesting sites for loggerhead, hawksbill and green turtles are present. And, it is an Important Bird Area with 50,000 breeding pairs of seabirds.

Malcolm Smith recognized the high diversity and abundance of  sea snakes in his  1926 Monograph of Sea Snakes. In 1973  Alpha Helix expedition collected more than 350 sea snakes representing nine species in less than two weeks and observed many more In 2005 the  standing stock of sea snakes was estimated at about 40,000  snakes on the 174 kmreef flat of Ashmore Reef.

Besides high species diversity and abundance, there are high levels of sea snake endemism at Ashmore Reef. Half of the species (3/6) from the Aipysurus lineage recorded from Ashmore Reef are restricted to the Timor Sea. Endemics that almost certainly evolved in the Timor Sea highlighting the  role this region has played in the evolutionary history of the Aipysurus lineage. Additionally four of the nine resident species and three of the five vagrant species are Australasian endemics.

In a new study, Lukoschek et al. (2013) report on surveys conducted between 1973 and 2010. They recorded the highest abundances (average 42–46 snakes day)  and species richness (nine species) in 1973 and 1994. In 2002 abundance had declined by more than 50% (21 snakes day) and only five species were recorded. Since 2005 abundances have been consistently low (1–7 snakes per day) with just two species, Aipysurus laevis and Emydocephalus annulatus, recorded in significant numbers. Extensive searches since 2005 (especially in 2010) five species of sea snake historically abundant at Ashmore Reef have not been observed and are presumed  locally extinct. These species include three Timor Sea endemics Aipysurus apraefrontalis, Aipysurus foliosquama, Aipysurus fuscus, and one Australasian endemic Aipysurus duboisii. Declines in sea snake abundance and diversity at Ashmore Reef cannot be attributed to differences in survey methods over time.

The authors discuss habitat loss, illegal harvesting, decline in prey, disease, invasive species, and pollution as possible causes for the decline. But it is important to note the declines happened in spite of Ashmore Reef's National Nature Reserve (IUCN Category 1a) status that was declared in 1983 and, although the causes for the declines are not known, this protection has not prevented their disappearance.

Citation
Lukoschek V, Beger M, Ceccarelli  D,  Richards Z,  Pratchett M, 2013. Enigmatic declines of Australia’s sea snakes from a biodiversity hotspot, Biological Conservation, 166, 191-202, ISSN 0006-3207,

Tuesday, August 6, 2013

The beaded lizard reassed

The beaded lizard (Heloderma horridum) has a fragmented distribution in Mesoamerica that extends from northwestern Mexico to eastern Guatemala.  Locally known as the “escorpión” its natural history is surrounded by mystery, notoriety and misconception. Consequently, it is frequently slaughtered when encountered. Adding to this anthropogenic pressure, beaded lizard populations, with rare exceptions  occur primarily in seasonally dry tropical forests,  the most endangered biome in Mesoamerica owing to persistent deforestation for agriculture, cattle ranching, and a burgeoning human population. Drought and fires escalate the above threats and recent predictive models of climate change suggest  persistence of seasonally dry tropical forests in this region is highly dubious.

Despite its large size and charismatic nature, knowledge of the ecology, geographic distribution, and status of beaded lizard populations remains limited.

Reiserer et al. (2013) reassess the taxonomic status of the beaded lizard populations using morphology, biogeography, and a recent molecular-based analysis conducted by Douglas et al. (2010).

The authors found the greatest divergence between H. h. charlesbogerti and H. h. exasperatum (9.8%), and the least between H. h. alvarezi and H. h. charlesbogerti (1%). The former clade represents populations that are widely separated in distribution (eastern Guatemala vs. southern Sonora, Mexico), while  in the latter clade the populations are much closer (eastern Guatemala vs. Chiapas, Mexico). The nominate subspecies (Heloderma h. horridum) differed from the other subspecies of H. horridum by 5.4% to 7.1%.

The new study suggests beaded lizards diverged from a most-recent common ancestor about 35 million years ago in the Late Eocene, and subsequent diversification occurred during the late Miocene (9.71 mya), followed by a lengthy stasis of up to five million years, more recent diversification  extended into the Pliocene and Pleistocene. In both beaded lizards and seasonally dry tropical forests, the tempo of evolution and diversification was uneven, and their current distributions are fragmented. Based on multiple lines of evidence, including a review of the use of trinomials in taxonomy, the authors elevated the four subspecies of beaded lizards to full species: Heloderma alvarezi (Chiapan beaded lizard), H. charlesbogerti (Guatemalan beaded lizard), H. exasperatum (Río Fuerte beaded lizard), and H. horridum (Mexican beaded lizard), with no changes in their vernacular names. The full article is available on-online.

Citations
Reiserer RS, Schuett GW, Beck DD. 2013. Taxonomic reassessment and conservation status of the beaded lizard, Heloderma horridum (Squamata: Helodermatidae). Amphibian & Reptile Conservation 7(1): 74–96.

Douglas ME, Douglas MR, Schuett GW, Beck DD, Sullivan BK. 2010. Conservation phylogenetics of helodermatid lizards using multiple molecular markers and a supertree approach. Molecular Phylogenetics and Evolution 55: 153–167.

Friday, August 2, 2013

A second specimen of the bush viper, Atheris hirsuta

 Atheris hirsuta
The viper, Atheris hirsuta was described by Ernst & Rödel in  2002, based on a single specimen found near the ecological research station in the Taï National Park, Côte d’Ivoire. The holotype was found in secondary rainforest between a field station and the town of Taï. It was collected on a dirt road during heavy rain, however, it is clearly adapted to an arboreal lifestyle.

Recently a short survey of the herpetofauna of Mt. Swa in Nimba County, Liberia (~200 km west of the type locality) revealed a second specimen of this species. The mountain does harbour good secondary forests and altitude stays below 600 m above seal level. The specimen was found around 2100 h on the 26 September 2012. The individual was observed climbing in secondary vegetation about 2 m above ground on the ridge of the mountain at about 585 m. No water bodies of any kind were found on top of the ridge. Weather was windy, cloudy but without rain.

Tai National Park holds the largest protected rainforest in West Africa. The forest habitat outside the national park is fragmented and being degraded by agricultural and human population expansion. Eventually  these pressures are expected to extend into the national park.

Citation
Penner J,  Gonwouo NL &  Rodel M-O1 2013. Second record of the West African hairy bush viper
Atheris hirsuta Ernst & Rödel, 2002 (Serpentes: Viperidae). Zootaxa 3694 (2): 196–200.

Suizo Report -- Thanks and July 2013

Howdy Herpers,                                                                                                               07/31/13

Thank you cards are slugging their way toward the nine kind souls who gave our fiscal situation a jump start. Thanks to their efforts, we can not only keep the animals in the game that we have, but also add a few more. I do not wish to embarrass anybody by mentioning names here. Just know that when the acks are presented, your names will be enshrined. And that ought to add numerous zeros to your paychecks, open the gates of heaven for you and yours, and massively improve your love lives.

As for the rest of you--see what you missed? But it's never too late!

Ok, enough with the BS.

On the evening of 3 July, Typing Boy here was tracking  our pregnant female CM17. This was one of those rare nights when Marty Feldner was at my side, instead of being on the other side of the hills mowing down a line of snakes. Whenever we track together, Marty lets me track. There is no sense in him doing the tracking, as he'll leave me in his dust. So he happily weaves a herpetological tapestry around me as we move. Typing Boy was following the path of least resistance, following the cattle trails that line the berm of an arroyo that flows from the bowels of a slot canyon. Marty was a couple climate zones above me, when he yells down to me: "Got a hatchling tortoise."

Tortoises of any size will cause a break from tracking, but all the more so for hatchlings. Sluggo made his way upslope to view the find.

Sure enough, once I gave pause to forcibly eject some black lung tissue shaken loose from the arduous climb, I saw Marty's hatchling tortoise.

Its head was up, one foreleg poised as if to take the next step. We both took several photos, marveling over how cooperative the little gogger was being. At some point later, Marty morphed into a poopsock by proclaiming "I think it's dead." Inspired by this statement, I gave it a poke with my walking stick. This did nothing to disturb the status quo, not to mention the tortoise. The poopsock was correct, the little gogger was quite dead.

A couple of strands of spider web were strung across its head, and one of the strands had also snagged its right forelimb. We eventually broke the hapless thing out of the web, noting that the strands had the tensile strength of thin steel wire. There is only one spider that spins webs like that in these parts--the black widow.

The most likely cause of death is that it was merely stuck, and baked its brains out in the sun. There were some signs of trauma to the head, which could have been from a bite. In any case, this event has stumped many a tortoise Jedi. There is more info that could be shared--but I won't.

Marty and I WILL go Hollywood with this observation, and reveal the rest therein. (If I do it here, all chance of a natural history note dies. Why publish it here--where people will actually read it?)

That, my friends, is what image 1 is all about. Cool--huh?

As most of the images are labeled, it makes no sense for me to beat them to death with lengthy descriptions. A few highlights include our newest male tiger CT16 with rain drops on his coiled form, the shed skin of an atrox that looks very much like a living snake, one of the neonate tigers shown in our last missive at its release site, and the face of God closes this missive.














Best to all, roger