Thursday, December 25, 2014

Draco's bright coloration mimics falling leaves

Draco cornutus. Photo
credit Devi Stuart-Fox
By mimicking the red and green colors of falling leaves, Bornean lizards avoid falling prey to birds whilst gliding, new research has found. The work suggests that populations of the gliding lizard, Draco cornutus, have evolved extendable gliding membranes, like wings, which closely match the colors of falling leaves to disguise themselves as they glide between trees in the rainforest.

Found throughout South-East Asia, Draco is the only living genus of lizard with extendable gliding membranes -- call patagia -- which allow them to glide between trees in their territories.

Published Dec. 24 in the international journal Biology Letters, the study was conducted by PhD student Ms Danielle Klomp, based at both the University of Melbourne and the University of New South Wales with supervisors Dr Terry Ord and Dr Devi Stuart-Fox and collaborator Dr Indraneil Das from the University of Malaysia.

The team travelled to Borneo and observed two populations of a gliding lizard that have different colored gliding membranes and occupy very different habitats.

One population has red gliding membranes, which match the color of the red falling leaves of their coastal mangrove forest habitat. The other population has dark brown and green gliding membranes, which match the colors of falling leaves in their lowland rainforest habitat.

They determined how the colors would be perceived by a predatory bird and found that the gliding membrane color would be indistinguishable from a falling leaf in the same forest.

Birds can see ultraviolet light as well as the colors that humans see, so it is important to take into account how closely the colors would actually match to a bird, Ms Klomp said.

"It's a cool finding because these gliding lizards are matching the colors of falling leaves and not the leaves that are still attached to the tree. In the mangrove population the leaves on the trees are bright green, but turn red shortly before falling to the ground, and it is this red color that the lizards mimic in their gliding membranes. This allows them to mimic a moving part of the environment- falling leaves -- when they are gliding." Ms Klomp said.

Because some animals have developed color not only for camouflage, but also as a form of communication, we also wanted to watch the lizards interact in the wild and determine whether their gliding membranes were used for communication as well as gliding said Ms Klomp.
The team filmed hours of gliding lizard behavior to observe how often the colors were displayed to other lizards.

"We found that both the red and green/brown gliding membranes seem to have evolved to specifically resemble the falling leaves in each population's particular habitat, and are rarely used for communication," Ms Klomp said.

"Perhaps these populations may have originally had the same gliding membrane colors but as they have moved into different forest types their colors have adapted to closely resemble the colors of falling leaves in the different forests, known as divergent evolution."

Citation
Klomp DA, Stuart-Fox D, Das I, Ord TJ. 2014.  Marked colour divergence in the gliding membranes of a tropical lizard mirrors population differences in the colour of falling leaves. Biology Letters, 10 (12): 20140776 DOI:10.1098/rsbl.2014.0776


Thursday, December 11, 2014

Why does the pelagic sea snake dive?


Note: It is the end of the year and this blog is going to be in hibernation for a short time. So this post may be the last for several weeks. But it will be active again in the near future.

Species that forage exclusively at the sea’s surface but spend much of the rest of their time submerged could offer a rare opportunity to shed light on the evolution of diving behavior that is independent from foraging. The viviparous Yellow-bellied Sea Snake, Hydrophis (formerly Pelamis) platurus (Hydrophiinae), also known as the Pelagic Sea Snake, provides this opportunity.

In a recent paper in Animal Behaviour, Cook and Brischoux (2014) note the Pelagic Sea Snake drifts passively with surface and subsurface currents, spending its entire life cycle at sea. The result is a wide distribution covering the entire tropical Indo-Pacific basin, one of the largest distributions of any squamate reptile. Another remarkable feature of the Pelagic Sea Snake’s unusual life history, is it spends most of its day-to-day life floating in the water column 20 to 50 m deep. Submergence time is interrupted by surfacing, which can be brief to breathe or longer to forage. The foraging strategy of the Pelagic Sea Snake is remarkable for a marine tetrapod, it ambushes larval fish that are concentrated under debris on oceanic labile features such as slicks or drift lines, doing ‘float-and-wait’ foraging at the oceanic surface.  

Hydrophis platurus is the only marine tetrapod foraging specifically at the ocean surface, but spending a considerable proportion of its time budget submerged. An activity pattern offering a unique opportunity to study diving independently from foraging.

The authors found the Pelagic Sea Snake spends 95% of its time underwater, where it can dive to 50 m and stay for 3.5 hours without breathing. Dives are S-shaped, with a long phase of gradual ascent during which the snake is neutrally buoyant. Snake lungs deflate slowly during this phase at a rate that increases with water temperature, and thus metabolism. Dive duration is linked to inferred lung volume at the start of the dive, suggesting aerobic diving.

The pelagic sea snakes dive for multiple reasons, but the primary reason seems to be to avoid sea surface turbulence. Underwater, they can reduce metabolism by targeting cooler water layers. And by hovering in the water column, they reduce energy expenditure and escape both surface and bottom predators. At the same time they can more easily locating their own prey from underneath.

A detailed analysis of the diving behavior of H. platurus shows how this exclusively marine species of tetrapod manages its dive cycle and the influence environmental parameters have upon its diving and surfacing behaviors. This has opened the door to a better understanding of the adaptations developed by this species.

Interestingly, there is an important parallel in behavior between H. platurus and several species of marine turtles. Adaptations in both these lineages of reptiles reflect a response to pressures of the marine environment experienced during the evolutionary transition from terrestrial to oceanic life. Unfortunately, the behavior of sea snakes at sea is still inadequately known compared to that of marine turtles despite being a highly diversified group comprising four families and ca. 90 species.

The authors suggest the study of sea snakes can help interpret diving behavior in other lineages of marine reptiles.

Citation
Cook TR & Brischoux F (2014). Why does the only ‘planktonic tetrapod’dive? Determinants of diving behaviour in a marine ectotherm. Animal Behaviour, 98, 113-123.


Climate change & the ectotherm

Animals that regulate their body temperature through the external environment may be resilient to some climate change but not keep pace with rapid change, leading to potentially disastrous outcomes for biodiversity.

A study by the University of Sydney and University of Queensland showed many animals can modify the function of their cells and organs to compensate for changes in the climate and have done so in the past, but the researchers warn that the current rate of climate change will outpace animals' capacity for compensation (or acclimation).

The research has just been published in Nature Climate Change (Letters), written by Professor Frank Seebacher School of Biological Sciences and Professor Craig Franklin and Associate Professor Craig White from the University of Queensland.

Adapting to climate change will not just require animals to cope with higher temperatures. The predicted increase to fluctuations in temperature as well as to overall temperature would require animals to function across a broader range of conditions. This is particularly important for ectotherms, animals that rely on external sources of heat to control body temperature, and are therefore more influenced by environmental temperatures.

The research showed that many groups of ectotherms, which make up more than 90 percent of all animals, are able to change their physiological function to cope with an altered environment, but the rapid pace and fluctuations of human-induced climate change present serious challenges.

The researchers studied 40 years of published data to assess how biological functions change in response to a sudden fluctuations in environmental temperatures. They found that the physiological rates of ectothermic animals, such as heart rate, metabolism and locomotion, had already increased over the past 20 years with increasing average temperatures.

"It is important that animals maintain the right balance between the large number of physiological functions despite environmental fluctuations. An increase in temperature that leads to changed reaction rates can upset that balance and cause the decline of individuals and species," said Professor Seebacher. "For example, movement requires energy and oxygen to be delivered to muscles. However, if metabolism or the cardiovascular system can't cope with increased temperatures, animals can no longer move to forage, migrate or interact with each other.

"The overall trend in the last 20 years has been to increased physiological rates, and we predict that this would continue to increase with increasing temperature. "Even if animals are able to maintain the balance of their physiological functions in a warmer climate, increased metabolism leads to increases in the food resources needed and could upset the balance in ecosystems, particularly if predator and prey populations respond very differently to the environmental temperature change."

Citation

Seebacher F, White CR, Franklin CE. Physiological plasticity increases resilience of ectothermic animals to climate change. Nature Climate Change, 2014; DOI: 10.1038/nclimate2457

Tuesday, December 9, 2014

The Reptile Database updated


Some new lizard species described in 2014
The Reptile Database (RDB) is a very useful tool for herpetologists, and they released a new version a few days ago. The new version lists 10,119 species (including 139 described this year), up from 10,038 in August, 35,615 references (including 1,203 published this year), up from 34,104 in August, which resulted in almost 200 new and changed names.

The site also is importing references for all of the papers published in Herpetology Notes and BioGecko, and they have about a 1000 papers from Sauria now crossed reference and they can be individually ordered from the RBD.

The RDB Newsletter also noted some selected taxonomic news:

Homalopsidae: Murphy and Voris (2014) suggested a number of new genera and revalidated a few more, leading to 28 genera for just 53 species.

Boidae: Pyron et al. 2014 suggested to split the monophyletic boas into multiple families; we did not follow this suggestion following a discussion with the Scientific Advisory Board (see below). However, the new suggested families (such as “Sanziniidae) can be found in the database.

More species and genera split, including Lampropeltis, Blanus, Crotalus triseriatus, Hemidactylus fasciatus, and Pelomedusa subrufa. Guo et al. (2014) split the fairly large genus Amphiesma (43 species) into 3 genera. Only Amphiesma stolatum remains in the genus.

The RDB recently constituted a Scientific Advisory Board (SAB) to make general strategic decisions as well a decisions on controversial taxonomic issues. One of the first recommendations of the SAB was not to adopt the suggested Boid taxonomy suggested by Pyron et al. (2014, see above). We continue to consult individual experts in more special cases, e.g. on individual species or genera. There is a consensus that all published taxonomic changes should be in the Reptile Database but when it comes to valid names they can only show one “accepted” name for any given species even if several are in use. Instead of flip-flopping between names with each new publication, the result will be a bit more conservative but also more stable. The members of the SAB are listed on a new page at http://www.reptile-database.org/db-info/sab.html.

Some new snake species described in 2014
In order to manage data curation and data import better, we have started to recruit editors for special tasks. 

Paul Freed and Sven Mecke are our first volunteer photo editors. They will receive the photos sent to the RDB, edit them, verify correct identifications with experts, find photos of species not pictured etc. This will also allow us to process photos faster. Thed RBD is looking for a photo editor taking care of turtles.

Similar to the photo editors, RBD is looking for volunteers willing to help with the curation of papers. Initially we will start with editors for turtles, crocodiles, and squamate families (or genera if they have a substantial number of species). The taxonomic editors will receive papers from which they are supposed to extract information that is relevant for the database such as taxonomic or nomenclatural changes, new distribution records, or databasable life history data.

The RBD is asking instructors teaching herpetology or taxonomy to help improve data curation by using it in their classes. Students could curate papers, edit Wikipedia pages link to the Reptile Database, ID species, or find and analyze other information. There is always a large backlog of papers that need to be curated, including simple cases with new distribution data or more complicated ones. Please get in touch if you are interested. They have designed a few exercised and assignment for classroom use: http://www.reptile-database.org/db-info/teaching.html.
RDB has a large number of new photos (>1,500). However, these are added to the database independently of text, and thus have not been updated yet. This will probably take another few weeks or so, just in case you do not see the photos that you have submitted. In any case, more photos are always welcome! Please send photos (with location or coordinates) to info@reptile-database.org.

The RDB often use Google Maps to verify the localities reported in papers. However, Google Maps shows different maps in different countries. For instance, Google Maps in India shows Arunachal Pradesh as part of India. However, Google Maps in China shows Arunachal Pradesh as part of China. The RDB will replace current approximate maps with “real" distribution maps sooner or later, such details are important when you search the Reptile Database for geographic areas (or if you need a list of all Indian or Chinese reptiles). Right now, they treat Arunachal Pradesh as part of India. Finally, there are different names in different Google Maps versions. For instance, in the international version you can see the “Persian Gulf”. However, in Arabian countries it is called the “Arabian Gulf”. There are a number of other contentious borders or names, so please keep this in mind when you search the database.

In the course of history new countries form, such as the new countries that used to be Yugoslavia or North and South Sudan (which used to be Sudan). However, there are also new states, such as the new state of Telangana in India, and the Indian government apparently discusses the creation of another 21 new states (the current states are fairly new too, many formed in 1956). Obviously, this can cause headaches in trying to keep tabs on reptiles in those states, especially when they are species-rich such as those in India. Please let RDB know if you see discrepancies or errors.

A new web service and database, http://journalmap.org/ offers a scientific literature search engine that empowers you to find relevant research based on location and biophysical attributes combined with traditional keyword searches. Give it a try.

The RDB does not have funding. If you plan to submit a grant related to reptile taxonomy or with databasable information, they are asking members to consider including the Reptile Database as a subcontractor or collaborator. Or budget personnel to curate data for the RDB.

Since it is gifting season, the RDB is accepting donations now. Available money is used to buy literature, travel to libraries, or pay students to enter, scan, or process data. You can donate at this link: https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=5EP9QGWFLKA7W.




Monday, December 8, 2014

A new model for the evolution of snake venom

Technology that can map out the genes at work in a snake or lizard's mouth has, in many cases, changed the way scientists define an animal as venomous. If oral glands show expression of some of the 20 gene families associated with "venom toxins," that species gets the venomous label.
But, a new study from The University of Texas at Arlington challenges that practice, while also developing a new model for how snake venoms came to be. The work, which is being published in the journal Molecular Biology and Evolution, is based on a painstaking analysis comparing groups of related genes or "gene families" in tissue from different parts of the Burmese python, or Python molurus bivittatus.
A team led by assistant professor of biology Todd Castoe and including researchers from Colorado and the United Kingdom found similar levels of these so-called toxic gene families in python oral glands and in tissue from the python brain, liver, stomach and several other organs. Scientists say those findings demonstrate much about the functions of venom genes before they evolved into venoms. It also shows that just the expression of genes related to venom toxins in oral glands of snakes and lizards isn't enough information to close the book on whether something is venomous.
"Research on venom is widespread because of its obvious importance to treating and understanding snakebite, as well as the potential of venoms to be used as drugs, but, up until now, everything was focused in the venom gland, where venom is produced before it is injected," Castoe said. "There was no examination of what's happening in other parts of the snake's body. This is the first study to have used the genome to look at the rest of that picture."
Learning more about venom evolution could help scientists develop better anti-venoms and contribute to knowledge about gene evolution in humans
Castoe said that with an uptick in genetic analysis capabilities, scientists are finding more evidence for a long-held theory. That theory says highly toxic venom proteins were evolutionarily "born" from non-toxic genes, which have other ordinary jobs around the body, such as regulation of cellular functions or digestion of food.
"These results demonstrate that genes or transcripts which were previously interpreted as 'toxin genes' are instead most likely housekeeping genes, involved in the more mundane maintenance of normal metabolism of many tissues," said Stephen Mackessy, a co-author on the study and biology professor at the University of Northern Colorado. "Our results also suggest that instead of a single ancient origin, venom and venom-delivery systems most likely evolved independently in several distinct lineages of reptiles."
Castoe was lead author on a 2013 study that mapped the genome of the Burmese python. Pythons are not considered venomous even though they have some of the same genes that have evolved into very toxic venoms in other species. The difference is, in highly venomous snakes, such as rattlesnakes or cobras, the venom gene families have expanded to make many copies of those shared genes, and some of these copies have evolved into genes that produce highly toxic venom proteins.
"The non-venomous python diverged from the snake evolutionary tree prior to this massive expansion and re-working of venom gene families. Therefore, the python represents a window into what a snake looked like before venom evolved," Castoe said. "Studying it helps to paint a picture of how these gene families present in many vertebrates, including humans, evolved into deadly toxin encoding genes."
Jacobo Reyes-Velasco, a graduate student from Castoe's lab, is lead author on the new paper. In addition to Castoe and Mackessy, other co-authors are: Daren Card, Audra Andrew, Kyle Shaney, Richard Adams and Drew Schield, all from the UT Arlington Department of Biology; and Nicholas Casewell, of the Liverpool School of Tropical Medicine.
The paper is titled "Expression of Venom Gene Homologs in Diverse Python Tissues Suggests a New Model for the Evolution of Snake Venom." The abstract is available online at: 
http://mbe.oxfordjournals.org/content/early/2014/11/03/molbev.msu294.abstract.
The research team looked at 24 gene families that are shared by pythons, cobras, rattlesnakes and Gila monsters, and associated with venom. The traditional view of venom evolution has been that a core venom system developed at one point in the evolution of snakes and lizards, referred to as the Toxicofera, and that the evolution of highly venomous snakes, known as caenophidian snakes, came afterward. But little explanation has been given for why evolution picked just 24 genes to make into highly toxic venom-encoding genes, from the 25,000 or so possible.
"We believe that this work will provide an important baseline for future studies by venom researchers to better understand the processes that resulted in the mixture of toxic molecules that we observe in venom, and to define which molecules are of greatest importance for killing prey and causing pathology in human snakebite victims," Casewell said.
When they looked at the python, the team found several common characteristics among the venom-related gene families that differed from other genes. Compared with other python gene families, venom gene families are "expressed at lower levels overall, expressed at moderate-high levels in fewer tissues and show among the highest variation in expression level across tissues," Castoe said.
"Evolution seems to have chosen what genes to evolve into venoms based on where they were expressed (or turned on), and at what levels they were expressed," Castoe said.
Based on their data, the new paper presents a model with three steps for venom evolution. First, these potentially venomous genes end up in the oral gland by default, because they are expressed in low but consistent ways throughout the body. Then, because of natural selection on this expression in the oral gland being beneficial, tissues in the mouth begin expressing those genes in higher levels than in other parts of the body. Finally, as the venom evolves to become more toxic, the expression of those genes in other organs is decreased to limit potentially harmful effects of secreting such toxins in other body tissues.
The team calls its new model the Stepwise Intermediate Nearly Neutral Evolutionary Recruitment, or SINNER, model. They say differing venom levels in snakes and other animals could be traced to the variability of where different species, or different genes within a species, are along the continuum between the beginning and end of the SINNER model.
Castoe said the next step in the research would be to examine the genome of highly venomous snakes to see if the SINNER model bears out. For now, he and the rest of the team hope that their findings about the presence of venom-related genes in other parts of the python change some thinking on what species are labeled as venomous.
"What is a venom and what species are venomous will take a lot more evidence to convince people now," Castoe said. "It provides a brand new perspective on what we should think of when we look at those oral glands."

Citation
Reyes-Velasco J, Card DC, Andrew AL, Shaney KJ, Adams, RH, Schield, DR, Casewell NR, Mackessy SP, Castoe, TA. (2014). Expression of venom gene homologs in diverse python tissues suggests a new model for the evolution of snake venom. Molecular biology and evolution, msu294.


Thursday, December 4, 2014

Humans consume an endangered iguana



The Valle de Aguán spiny-tailed iguana is a critically endangered species found in Honduras. A recent survey of people living in the region shows that, although residents are aware of the endangered status of the species, the iguana continues to be hunted for food. Of particular concern is the preference for the consumption of female iguanas that are gravid (carrying eggs in their body).

"In this study we worked to gain a better understanding of how humans are harvesting the species for food," said Stesha Pasachnik, Ph.D., a lead researcher on the study and a postdoctoral research associate for the San Diego Zoo Institute for Conservation Research. "The information we gained indicates a use that is not only not sustainable but is likely to accelerate this species' extinction due to the loss of gravid females."

Published in the December issue of Herpetological Conservation and Biology, the study gained firsthand information regarding the hunting, harvesting and consumption of the species. Although the study, supported by the Bay Islands Foundation and San Diego Zoo Global, highlights an area of serious concern, it also recommends work to educate residents about the species and ways that harvesting can be made more sustainable.

Bringing species back from the brink of extinction is the mission of San Diego Zoo Global. As a leader in conservation, the work of San Diego Zoo Global includes onsite wildlife conservation efforts (representing both plants and animals) at the San Diego Zoo, San Diego Zoo Safari Park, and San Diego Zoo Institute for Conservation Research, as well as international field programs on six continents. The important conservation and science work of these entities is made possible by the San Diego Zoo Wildlife Conservancy and is supported in part by the Foundation of the Zoological Society of San Diego.

 Citation
Stesha A. Pasachnik, James A. Danoff-Burg, Edoardo E. Antúnez, and Jeffrey P. Corneil. Local Knowledge and Use of the Valle Deaguán Spiny-Tailed Iguana, Ctenosaura melanosterna, in Honduras. Herpetological Conservation and Biology, 2014