Friday, December 10, 2010

Recently Discovered Diversity in Breviciptid Frogs


Callulina kreffti , Nieden, 1911.  
Photo Credit: Michele Menegon
Frogs of the family Brevicipitidae are endemic to Sub-Saharan Africa from Ethiopia southward to Angola and South Africa and is composed of five genera (Balebreviceps, Breviceps, Callulina, Probreviceps, Spelaeophryne) and more than 26 species. They were long considered part of the family Microhylidae. They are bizarre little frogs, most have rounded bodies with tiny legs, and members of the genus Breviceps (the most specious genus) use sticky skin secretions produced in their numerous skin glands, to hold amplexing pairs together because their legs are too short for the male to clasp the female. Breviceps  eggs are laid in burrows and undergo direct development. Recent investigations of the more arboreal genus Callulina has revealed the sky island clade to have more species than previously thought, and the newly described species have small ranges, and show a high degree of endemism in the Eastern Arc Mountains, a global biodiversity hotspot. The number of species before 2004 was one, C. kreffti was described by Fritz Nieden in 1911. C. kreffti was thought to have a continuous distribution throughout the montane forests of the Eastern Arc Mountains with its type locality at Amani in the East Usambara. However, specimens from other localities have proven not to be conspecific with C. kreffti. The northern Eastern Arc range has turned out to have numerous distinct species restricted to small, limited ranges. Five separate species have been described to date: C. kisiwamsitu de Sá et al., 2004, C. dawida Loader et al., 2009a, C. laphami Loader et al.,2010a, C. shengena Loader et al. 2010a, and C. stanleyi Loader et al., 2010a. Michelle Menegon and colleagues (2008) listed four undescribed species of Callilina from the Nguru Mountains based upon preliminary morphological and molecular data. Now, two of those species have been described by Loader et al. (2010b).  Callulina hanseni is from the Maskati side of the Nguru South Forest Reserve, Tanzania; and Callulina kanga is from the Kanga Forest Reserve, Mwomero District, Morogoro Region, Tanzania. Both species were found in shrubs and trees and C. hanseni was collected as high as 10 m above the ground. Both species inhabit primary montane rainforest. Thus there are now 8 species recognized in the genus Callinia, whereas there was only on prior to 2004; and there are more species in this genus yet to be described.

Literature
de Sá, R., S. P. Loader, and A. Channing. 2004. A new species of Callulina (Anura: Microhylidae) from the West Usambara Mountains, Tanzania. Journal of Herpetology, 38, 219–222.

Loader, S. P., G. J. Measey, R. D. de Sá, and P. K. Malonza. 2009a. A new brevicipitid species (Anura: Brevicipitidae: Callulina) from the fragmented forests of the Taita Hills, Kenya. Zootaxa, 2123, 55–68.

Loader, S. P., D. J. Gower, W. Ngalason,  and M. Menegon. 2010a. Three new species of Callulina (Amphibia: Anura: Brevicipitidae) highlight local endemism and conservation plight of Africa's Eastern Arc forests. Zoological Journal of the Linnean Society, 160, 496–514.

Loader, S. P., D. J. Gower, H. Muller, and M. Menegon. 2010b.  Two new species of Callulina (Amphibia: Anura: Brevicipitidae) from the Nguru Mountains, Tanzania. Zootaxa 2694: 26–42

Menegon, M., N. Doggart, and N. Owen. 2008. The Nguru Mountains of Tanzania, an outstanding hotspot of herpetofaunal diversity. Acta Herpetologica, 3, 107–127.

Thursday, December 9, 2010

Reptile Extinction in the Agean

This is an almost unedited press release from  PhysOrg.com.

A sample group of Aegean wall lizards 
was captured during field work on one 
of the Greek study islands. 
Credit: Johannes Foufopoulos
A wave of reptile extinctions on the Greek islands over the past 15,000 years may offer a preview of the way plants and animals will respond as the world rapidly warms due to human-caused climate change, according to a University of Michigan ecologist and his colleagues.
 
The Greek island extinctions also highlight the critical importance of preserving habitat corridors that will enable plants and animals to migrate in response to climate change, thereby maximizing their chances of survival.

As the climate warmed at the tail end of the last ice age, sea levels rose and formed scores of Aegean islands that had formerly been part of the Greek mainland. At the same time, cool and moist forested areas dwindled as aridity spread through the region.

In response to the combined effects of a shifting climate, vegetation changes and ever-decreasing island size, many reptile populations perished.

To gain a clearer understanding of the past consequences of climate change, Johannes Foufopoulos and his colleagues calculated the population extinction rates of 35 reptile species---assorted lizards, snakes and turtles---from 87 Greek islands in the northeast Mediterranean Sea. The calculated extinction rates were based on the modern-day presence or absence of each species on islands that were connected to the mainland during the last ice age.

Foufopoulos and his colleagues found a striking pattern to the island extinctions. In most cases, reptile populations disappeared on the smallest islands first---the places where the habitat choices were most limited.
Especially hard hit were "habitat specialist" reptiles that required a narrow range of environmental conditions to survive. In addition, northern-dwelling species that required cool, moist conditions showed some of the highest extinction rates. 

The study results appear in the January edition of American Naturalist.

The researchers conclude that a similar pattern of extinctions will emerge at various spots across the globe as the climate warms in the coming decades and centuries. In addition to adapting to a changing climate, plants and animals will be forced to traverse an increasingly fragmented natural landscape. 

Citation
Foufopoulos, J., A. Marm Kilpatrick, and A. R. Ives. 2011. Climate Change and Elevated Extinction Rates of Reptiles from Mediterranean Islands. The American Naturalist 177:19-129.

Wednesday, December 8, 2010

Simosuchus clarki from the Late Cretaceous of Madagascar


The following is an almost unedited press release from the Society of Vertebrate Paleontology.

Bizarre Reptile Challenges Notion of Crocodiles as ‘Living Fossils’
Released: 12/2/2010 3:20 PM EST
Newswise — The 20-odd species of living alligators and crocodiles are nearly all that remains of what was once an incredibly diverse group of reptiles called crocodyliforms. Recent discoveries of fossil crocodyliforms have revealed that some of these reptiles, instead of conforming to traditional crocodile norms (long snout, conical teeth, strong jaw and long tail) possessed a dazzling array of adaptations that resulted in unique and sometimes bizarre anatomy. These discoveries have provided new information about a large and important group of extinct animals, while simultaneously helping to dispel the notion of crocodiles as static, unchanging ‘living fossils.’
Holotype skull and lower jaw of Simosuchus clarki in side vie> Photo credit Jeanne Nevill

The epitome of crocodyliform bizarreness is represented by Simosuchus clarki, which lived in Madagascar at the end of the “Age of Dinosaurs” (about 66 million years ago). First described preliminarily in 2000 from a well-preserved skull and partial skeleton, Simosuchus shattered the crocodyliform mold with its blunt, pug-nosed snout, leaf-shaped teeth, and short, tank-like body covered in a suit of bony armor. Over the next decade, expeditions to Madagascar recovered more skulls and skeletons, now representing nearly every bone of Simosuchus. A reconstruction of this uncommonly complete fossil reptile and an interpretation of its place in the crocodile evolutionary tree became the subject of a newly published Memoir of the Society of Vertebrate Paleontology.

Edited by David W. Krause and Nathan J. Kley of Stony Brook University, the large, densely illustrated volume gives an account of fossil crocodyliform anatomy that is unprecedented in its thoroughness. “The completeness and preservation of the specimens demanded detailed treatment,” said Krause. “It just seemed unconscionable to not document such fantastic fossil material of this unique animal.” A separate chapter is devoted to each of the major parts of the animal – skull, backbone, limbs and armor. “The skull and lower jaw in particular are preserved almost completely,” said Kley. “This, combined with high-resolution CT scans of the most exquisitely preserved specimen, has allowed us to describe the structure of the head skeleton – both externally and internally – in exceptional detail, including even the pathways of the tiniest nerves and blood vessels.”

But while it is easy to lose oneself in the details of these incredible fossils, one of the most amazing features is the overall shape of the animal. Two feet long, pudgy, with a blunt snout and the shortest tail of any known crocodyliform, Simosuchus was not equipped to snatch unsuspecting animal prey from the water’s edge as many modern crocodiles do. “Simosuchus lived on land, and its crouched posture and wide body probably meant it was not very agile or fast,” said Joseph Sertich, who participated in the study. In addition, its short, underslung jaw and weak, leaf-shaped teeth show that it probably munched on a diet of plants. While the idea of a gentle, vegetarian crocodile is unusual to us today, the new memoir makes it easy to imagine Simosuchus ambling through its semi-arid grassland habitat, pausing to nip at plants and crouching low to hide from predators like the meat-eating dinosaur Majungasaurus.

The paleontologists also found evidence that pointed to the evolutionary origin of Simosuchus. “Interestingly, an analysis of evolutionary relationships suggests Simosuchus’ closest relative lived much earlier, in Egypt,” said Sertich. Details like these are crucial to deciphering the pattern of the dispersal of life around the globe, an area of scientific study known as biogeography. Whatever its ancestry, Simosuchus has set a surprising new standard for what constitutes a crocodile. Said Sertich, “It’s probably the most bizarre in an already very strange group of small, terrestrial crocodiles known from the other southern continents during this time.”

Dr. Christopher Brochu of the University of Iowa agreed. “This is easily the most bizarre crocodyliform ever found.” Brochu, who specializes in fossil crocodyliforms but was not directly involved with the study, explained that this strangeness may have been tied to the special niche Simosuchus occupied in its ecosystem. “A lot of the ecological roles filled by dinosaurs in the north were filled by crocs in the south,” he said. “That led to some really weird crocs.” Brochu also drew a striking contrast between Simosuchus and one modern-day crocodyliform. “Think about everything the slender-snouted forms like the Indian gharial do – long snout with needlelike teeth, jaw joint placed as far back as possible – and Simosuchus does the opposite. Its snout is so short the skull is almost cubical. The teeth are anything but needlelike, and the jaw joint is shoved beneath the ear. It’s doing (and this is a metaphorical “do”) everything it can to not be a gharial.”

As strange as Simosuchus was, the incredible completeness and preservation of its fossils, coupled with an equally impressive scientific investigation, have yielded one of the most comprehensive volumes of crocodyliform anatomy ever to be published. “Very few crocodyliforms – even those alive today – have been subjected to this level of analysis,” said Brochu. “This reference is going to be used for decades.”

The article appears in the Journal of Vertebrate Paleontology 30(6, Supplement) published by Taylor and Francis.

Citation: D. W. Krause and N. J. Kley (eds.), Simosuchus clarki (Crocodyliformes: Notosuchia) from the Late Cretaceous of Madagascar. Society of Vertebrate Paleontology Memoir 10. Journal of Vertebrate Paleontology 30(6, Supplement).

Journal Web site: Society of Vertebrate Paleontology: http://www.vertpaleo.org


The following reconstruction was published later.
A reconstruction of Simosuchus clarki as it may have appeared walking through the semi-arid grasslands of Madagascar in the Cretaceous Period. (Credit: Photo of type locality by Raymond Rogers; sculpture of Simosuchus by Boban Filipovic; montage by Lucille Betti-Nash).




Snakes & Snails

Relatively few snakes feed on mollusks, but there are snakes in many lineages that have specialized to feed on gastropods. In North America the natricids in the genus Storeria feed on slugs and earthworms, in the Neotropics some of the dipsidids (Sibon, Dipsas, Tropidodipsas, and Sibynomorphus) tend to specialize in feeding on snails and slugs. In Africa members of the genus Duberria (family Pseudoxyrhophiidae) feed on slugs, However, the Asian family Pareatidae are very specialized for feeding on gastropods, and Pareas iwasakii has been well studied by Masaki Hoso and colleagues (see references below).

Above: Pareas iwasakii grasping a snail. 
Below: The skull and lower jaws of Pareas
iwasakii,  note the different number of teeth 
on each side of the jaw. From Hoso et al. (2010).
Snails with shells that coil counterclockwise have difficulty mating with snails of the same species whose shells coil clockwise because their bodies do not align properly. The snails have traded easy of mating for safety from snakes. The coil direction made mating difficult, and why a mutation causing this reversal would be favored was puzzling. Most snail shells curl clockwise. Studies of Iwasaki's Snail-eater (Pareas iwasakii) demonstrated the snake approaches the snail from behind, grasping the shell with its upper jaw and the soft body with its lower jaw. The snake then works the right and left halves of its lower jaw back and forth to extract the snail's body from the shell.

Since most snail shells turn clockwise, the snakes evolved a specialized lower jaw with more teeth on the right side than on the left. This makes it difficult for the snake to feed on snails coiled counterclockwise. When snakes try and eat snails coiled counterclockwise they frequently fail, and often drop the prey. In one study 87.5 percent of the counterclockwise snails survived the snake, suggesting the spiraling made the difference.

In a follow-up to the previous work Hoso et al. (2010) examined the snails and how genes can spread in a population. The land snails have a single gene for left–right reversal and the authors suggest that this could result in instant speciation, because dextral (shells coiled to the right) and sinistral (shells coiled to the left) snails have difficulty in mating. Hoso and colleagues show that specialized snake predation of the dextral majority drives prey speciation by reversal. Their experiments demonstrate that sinistral Satsuma snails (Stylommatophora: Camaenidae) survive predation by Pareas iwasakii. They found stylommatophoran snail speciation by reversal has been accelerated in the range of pareatid snakes, especially in snails that gain stronger anti-snake defense and reproductive isolation from dextrals by sinistrality. Molecular phylogeny of Satsuma snails further provides intriguing evidence of repetitive speciation under snake predation.

Literature
Hoso, M. 2007. Oviposition and hatchling diet of a snail-eating snake Pareas iwasakii (Colubridae: Pareatinae). Current Herpetology 26:41–43.

Hoso, M. and M. Hori. Divergent shell shape as an antipredator adaptation in tropical land snails. American Naturalist 172:726–732.

Hoso, M. and M. Hori. 2006. Identification of molluscan prey from feces of Iwasaki's slug snake, Pareas iwasakii. Herpetological Review 37:174–176.

Hoso, M., T. Asami, and M. Hori. 2007. Right-handed snakes: convergent evolution of asymmetry for functional specialization. Biology Letters, 3:169-172 DOI: 10.1098/rsbl.2006.0600

Hoso, M.,Y. Kameda, S.-P. Wu, T. Asami, M. Kato, and M. Hori. 2010. A speciation gene for left–right reversal in snails results in anti-predator adaptation. Nature, http://www.nature.com/ncomms/journal/v1/n9/full/ncomms1133.html

Tuesday, December 7, 2010

Detecting A Striking Snake

Fear of snakes has been documented in some primates as well as humans, and snake-phobia is regarded as a global phenomenon.  Lynn Isbell’s study of the human visual system proposes that some aspects of it evolved to facilitate the detection of snakes. Evidence to support her argument included a series of investigations that showed that human adults have an attentional bias for the detection of fear-relevant stimuli such as snakes when compared to neutral stimuli such as flowers and mushrooms. Other recent studies suggest that preschool children, 8- to 14-months old infants, and even non-human primates also detect snakes more quickly than neutral stimuli such as flowers. Nobuo Masataka and colleagues performed an experiment with 74 children 3- to 4-years old and adults. The test subjects were asked to find a single target black-and-white photo of a snake among an array of eight black-and-white photos of flowers as distracters. As target stimuli, the researchers prepared two groups of snake photos, one set in which a typical striking posture was displayed by a snake and the other in which a resting snake was shown. Masataka and colleagues then measured the reaction time to find the snake photo. This was then compared between the resting and striking snakes. The reaction time to find the striking snake had a mean value significantly faster for the photos of snakes displaying a striking posture than for the photos of resting snakes in both the adults and children. These findings suggest the possibility that the human perceptual bias for snakes per se could be differentiated according to the difference of the degree to which their presence acts as a fear-relevant stimulus.

Masataka et al. Figure 2. An example of a 363 matrix used as the stimulus in an experimental trial where a photo of striking posture of a snake was included (Striking), and one where a photo of a resting snake was included (Resting). From doi:10.1371/journal.pone.0015122.g002
Masataka et al. Figure 3. Mean reaction time to detect a snake when striking posture was displayed in the target photo and when a resting snake was shown in the target photo. From doi:10.1371/journal.pone.0015122.g003


Literature
Isbell, L. A. 2009. The Fruit, the Tree, and the Serpent: Why We See So Well. Cambridge: Harvard University Press.

Masataka, N., S. Hayakawa, and N. Kawai. 2010. Human Young Children as well as Adults Demonstrate ‘Superior’ Rapid Snake Detection When Typical Striking Posture Is Displayed by the Snake. PLoS ONE 5(11): e15122. doi:10.1371/journal.pone.0015122

Monday, December 6, 2010

Mimicry can be Imperfect but Effective

British naturalist and explorer, Henry W. Bates is known for his 1848 collecting expedition to the Amazon with Alfred Russel Wallace. Wallace lost most of what he collected in a shipwreck on his way home in 1852. Bates, however, did not return until 1859 and by that date had sent most of the 14,000 species he collected home. Bates' work on Amazonian butterflies led him to develop the concept of mimicry. In 1861, he wrote, "The process by which a mimetic analogy is brought about in nature is a problem which involves that of the origin of all species and all adaptations." Today, Batesian mimicry is the term used to describe the situation when a palatable species looks like (or mimics) an unpalatable or noxious species. One criticism of mimicry theory is that the mimics are often imperfect. Now, David W. Kikuchi and David W. Pfennig at the University of North Carolina have addressed this issue with field experiments, using the venomous Eastern Coral Snake (Micrurus fulvius) and its harmless mimic the Scarlet Kingsnake (Lampropeltis elapsoides). They designed a field experiment to determine if predator cognitive abilities could explain imperfect coral snake mimicry. The Scarlet Kingsnake is an imprecise mimic of the Eastern Coral Snakes.  Both species possess brightly colored rings of red, yellow, and black encircling their bodies, but the rings differ in order: the coral snake has a black-yellow-red-yellow ring order, while the kingsnake has a black-yellow-black-red ring order.  Therefore, the well known rhyme for distinguishing coral snakes models from kingsnakes mimics, “red on yellow, kill a fellow; red on black, venom lack”. They chose a study site in southeastern North Carolina where the two species distributions overlap. To measure selection on different snake phenotypes, they used clay replicas of snakes bearing three different color patterns. The authors asked, would predators avoid perfect mimics (the coral snake) and prey on imperfect mimics (the kingsnake), or a very poor mimic (a kingsnake model that differs from the coral snake in ring order and relative proportions of red and black)? The contrast between predation on the poor mimic and on the good and perfect mimics served as a control. A previous study demonstrated that the poor mimic is attacked significantly more often than the good mimic in an area where the two species overlap. In the field, Kikuchi and Pfennig arranged the replicas in threes (consisting of one of each phenotype) and placed them in transects. These were separated from adjacent sets by about 75 m. Eighteen such transects were placed in natural areas where mimics and snake predators are abundant. After 5 weeks in the field the replicas were collected and scored as having been attacked if it bore a marks suggesting a beak, claw, or carnivore bite marks. Or, if the model was carried off completely. Markings consistent with rodent or insect activity were ignored because they do not pose a threat to snakes. Of 537 replicas available for analysis 66 (12.3%) were attacked. Of these, 10 were attacked by birds and 21 by carnivorous mammals and 35 could not be assigned to a specific predator group. Replicas of the good mimics (based on the kingsnake) were no more likely to be attacked by predators than were replicas of the model (the coral snake). The authors suggest two hypotheses that might explain why selection does not favor improvement in mimicry. First, predators might generalize aposematic signals of models due to an increasingly high probability of incorrectly identifying prey as mimics grow more similar to models in phenotype – this is a widely supported idea. Secondly, with a highly toxic model (like the coral snake) risk taking by predators is disfavored. Consequently, predators should avoid a wide range of trait values, thereby maintaining imprecise mimics. Evidence for the second hypothesis was found in this study. The authors suggest that the difference in predation rates on good and poor mimics can best be reconciled if mimics exploit a limitation in predator cognition. In summary they wrote, "If only certain traits are required to deceive predators, then mimics need not resemble their model exactly.... The fact that good mimics did not suffer any greater predation than perfect mimics...suggests that good mimics achieved complete protection by resembling the model in color proportions alone (or, for deterring attacks by mammalian predators that might lack color vision..., good mimics achieved complete protection by resembling the model in proportions of different shades of gray)."
The model (Eastern Coral Snake) above. 
The mimic (Scarlet Kingsnake) below. JCM



Literature
Bates H. W. 1862. Contributions to an insect fauna of the Amazon Valley. Lepidoptera: Heliconidae. Transactions of the Entomological Society, 23:495-566.

Kikuchi D. W. and David W. Pfennig. 2010. Predator Cognition Permits Imperfect Coral Snake Mimicry. The American Naturalist 176:830-834.

Sunday, December 5, 2010

The Strike of a Snake and Body Size

Body size in animals plays a major role in the animal's biology. John Tyler Bonner wrote that "...size is an aspect of the living that plays a remarkable overreaching role that affects life's matter in all its aspects." In a recent paper Herrell et al (2010) investigate size-related changes in defensive strike performance in the White-lipped Green Pit Viper, Trimeresurus (Crypteletrops) albolabris. T. albolabris is an arboreal pit viper from Southeast Asia this is an ambush specialist. However, in some species juveniles select higher, more open foraging sites, possibly giving them a thermal foraging advantage.Thus juvenile arboreal pit vipers may be more exposed while foraging, and consequently subjected to a larger number of predators. Larger individuals tend to forage more in terrestrial situations and usually eat larger prey. The sexes may also be expected to differ in strike performance capacity if they select different prey types, use different types of habitats, or are simply different in size. Striking fast and far is likely of importance in both (defensive and feeding. Fast, long strikes can deter potential predators as well as allow snakes to capture elusive prey.  The authors used 18 female and 17 male albolabris, housed at the Faculty of Science, University of Zagreb, Croatia. They used a digital high speed  camera set at 400 frames per second and filmed 129 strikes made by 29 individual snakes and examined  how defensive strike performance changes with body size in both male and female. Their data show a significant negative allometry in the scaling of head dimensions and head mass to body mass. However, strike velocity and strike distance are independent of body mass, with juveniles in the sample striking as fast and as far as adults. Contrary to model predictions suggesting that acceleration capacity should decrease with increasing body mass, acceleration capacity increases with snake body mass, and that this is the result of a negative allometric scaling of head mass combined with an isometric scaling of the dorsal epaxial musculature. Finally, the data showed a significant sexual dimorphism in body size and strike velocity with females being heavier and striking faster, independent of the dimorphism in body size. Mean strike velocity was 1.5–1.6ms for males and females, respectively.

Literature
Bonner, J. T., 2006. Why Size Matters. Princeton University Press. 161 pp.

Herrel, A., K. Huyghe, P. Okovic´, D. Lisicˇic´, Z. Tadic. 2010. Fast and furious: effects of body size on strike performance in an arboreal viper Trimeresurus (Cryptelytrops) albolabris. Journal of Experimental Zoology. 313A. DOI: 10.1002/jez.645

Friday, December 3, 2010

Cruising For Food

A cruising forager. JCM
Foraging behavior in lizards has been classically described as either active foraging or ambush (also called sit-and-wait). Both types of foraging behavior have been correlated with morphological, behavioral, and habitat traits. Active foragers, for example, have higher activity levels, caloric intake, and body temperatures compared with ambush foragers.  However, chameleons have unusual morphological and behavioral traits that undoubtedly influence feeding behavior. The moniker, “cruise forager,” was first suggested by Regal (1978) as an intermediate stage between active and ambush foraging. Regal (1983), later defined cruise foraging  as an animal that moves, stops, scans the environment, then moves, stops, and scans again. Observing the chameleon Bradypodion pumilum foraging for food prompted Butler (2005), to propose chameleons compose a third foraging class, the “cruise foragers.”  Hagey et al. (2010) observed Jackson’s chameleon, Chameleo jacksonii xantholophus on the island of Hawai’i. The species is endemic to Mt. Kenya, Kenya, but was introduced to Hawai’i in the early 1970’s and has spread to several other islands in the Sandwich group. The lizards were filmed, measured, and their microhabitat described. The video was used to quantify the lizards’ foraging behavior and it was compared to the behavior reported by Butler (2005). The results suggested that Jackson’s Chameleon exhibits a moderate percent time moving (19.7%), has a low number of moves per minute (the mean was 0.24); and a very slow locomotion speed. This combination is rarely seen in other lizard species, but it is strikingly similar to data from the only other chameleon studied, B. pumilum. The authors suggest that another lizard, other than other true chameleons (family Chamaeleonidae), that may be a cruise forager is the polychrotid, Chamaeleolis, which is in a different lineage than the true chameleons – it is closely related to the anoles. As for “cruise foraging” as a new class of hunting behavior in lizards, these authors agree that it should be recognized.

Literature
Butler, M. A. 2005. Foraging mode of the chameleon, Bradupodion pumilum: A challenge to the sit-and wait versus active forager paradigm? Biological Journal of Linnean Society, 84:797–808.

Hagey, T. J., J. B. Losos, and L. J. Harmon. 2010.  Cruise Foraging of Invasive Chameleon (Chamaeleo jacksonii xantholophus) In Hawai'i. Breviora 519:1-7.

Regal, P. J. 1978. Behavioral differences between reptiles and mammals: An analysis of activity and mental capabilities, pp. 183–202, In N. Greenberg, and P. D. MacLean (eds.), Behavior and Neurology of Lizards. Rockville, Maryland, National Institute of Mental Health.

Regal, P. J. 1983. The adaptive zone and behavior of lizards, pp. 105–118. In R. B. Huey, E. R. Pianka, and T. W. Schoener (eds.), Lizard Ecology: Studies of a Model Organism. Cambridge, Massachusetts, Harvard University Press.

Thursday, December 2, 2010

Reptile Evolution and Rainforest Collapse


Growing-up in northeastern Illinois I became familiar with Coal Swamp Forest fossils at an early age. Roaming the slag piles of strip mines in southern Will County fossil ferns, the occasional horsetail, crustaceans, or the highly sought after Tullymonster (Tullimonstrum gregarium) could be found. The pits were dug by the Peabody Coal Company, and abandoned after they would no longer produce. Today, the slag is covered with dense vegetation making it more difficult to find ancient remains and the pits are filled with water and home to hybrid trout. 

The Coal Forest Diorama, part of which can be viewed in the Life Over Time exhibit at the Field Museum was the result of work done by Bror Eric Dalgren. The exhibit opened in 1931 and was the product of three years of work. © The Field Museum, #GEO75400.

 

In the Middle Pennsylvanian (311-306 millions of years ago -MYA), Coal Swamp Forests were widespread and covered tropical Euramerica, an area that includes what is now Europe, eastern North America, and extreme northwestern Africa. By the Middle Pennsylvanian much of the Euramerican Coal Swamp Forests disappeared. Howard Falcon-Lang of the University of London and William Dimichele of the Smithsonian have proposed that the Coal Swamp Forests responded to alternating glacial and inter-glacial periods (cyclotherms) with the Swamp Forests expanding and thriving during the interglacial periods and Seasonally Dry Forests replacing them during the glacial periods when much of the water was tied up in ice.

About 305.4 MYA, about the boundary of the upper to middle Pennsylvanian there was what Falcon-Land and Dimichele call a hyperconstriction event. This was an abrupt change from coal forests dominated by lycopsids (club mosses) to those dominated by tree ferns that ultimately resulted from an extreme glacial period that produced equatorial refugia.

In a more recent, related paper Sarda Sahney and colleagues (2010) suggest that the evolution of reptiles was stimulated by the cyclic expansion and contraction of the Coal Swamp Forests – habitat fragmentation. In a press release Howard Falcon-Lang explained, "Climate change caused rainforests to fragment into small 'islands' of forest. This isolated populations of reptiles and each community evolved in separate directions, leading to an increase in diversity." And, the other co-author, Mike Benton added, "This is a classic ecological response to habitat fragmentation. You see the same process happening today whenever a group of animals becomes isolated from its parent population. It's been studied on traffic islands between major road systems or, as Charles Darwin famously observed in the Galapagos, on oceanic islands."

The authors discovered changes in tetrapod diversity across the Moscovian-Kasimovian interval, by constructing two late Paleozoic tetrapod databases, comprising records of global and alpha diversity (family diversity) over nine global stages ranging from 346 to 270 MYA. They restrict the analysis to this time span because bracketing Tournaisian and Kungurian (359.2-306.5 MYA) stages were times of very low diversity, which had previously been interpreted as mass extinctions or gaps in the record. They tabulated 67 families from 163 tetrapod sites worldwide into a global database. Stratigraphic ranges were assigned to each family and the associated dates were correlated with the time scale. Each family was given an ecological assignment based on size and diet resulting in 12 ecological niches. Diet was inferred from jaw and tooth structure, patterns of tooth wear, body size, and whether the animal was adapted for a predominantly aquatic or terrestrial lifestyle.

Several patterns emerge from the analysis. They found global diversity steadily increased through the study interval from 6 or 7 families to 39 families. Alpha diversity (the number of families) closely tracked global diversity until the late Moscovian (about 306 MYA), the two curves dramatically diverged across the Moscovian-Kasimovian boundary as alpha diversity collapsed from 20 families to 7 families. The authors saw only one way to reconcile the rise in global diversity at a time when alpha diversity was falling – the number of endemics greatly increased between the Moscovian and Kasimovian-Gzhelian intervals. Confirmation came from the calculations. The ecological data confirmed the diversification, the number of ecological niches occupied by tetrapods increased from 4 to 9.

The authors concluded that the abrupt collapse of the tropical rainforest biome (the Coal Forests) drove rapid diversification of Carboniferous tetrapods (amphibians and reptiles) in Euramerica. Amphibians were devastated because of their dependence on wet environments – their eggs need wet environments for development, while the amniotes ('reptiles') fared better, because they were ecologically adapted to the drier conditions. Amniotes had evolved the “land egg,” an egg where the embryo is protected from desiccation by a series of membranes. The paper demonstrates, for the first time, that Coal Forest fragmentation had a tremendous influence on the ecology and evolution of the terrestrial fauna. And, it illustrates the tight coupling that existed and still exists between vegetation, climate, and trophic webs.

Literature
Falcon-Lang, H. J. and W. A. Dimichele. 2010.  What happened to the Coal Forests during the Pennsylvanian glacial phases? Palaios, 25:611–617.

Sahney. S., M. J. Benton, and H. J. Falcon-Lang. 2010. Rainforest collapse triggered Carboniferous tetrapod diversification in Euramerica. Geology 38(12):1079-1082.



Wednesday, December 1, 2010

The Cost of Making Venom

Acanthophis antarcticus, Petra Karstedt Wikimedia

Speculation and studies on the energy cost of snakes producing venom are of interest because they are tied to the idea that snakes meter their venom during bites. However, only one study has attempted to examine the metabolic cost of replenishing venom in snakes. McCue (2006) showed that venom expenditure increased the metabolic rate in three pit vipers by 11% increase during the first 72 hour of replenishment. Now Anna Pinto and colleagues from James Cook University use flow-through respirometry, to examine changes in the metabolic rate of the Australia elapid known as the Death Adder, Acanthophis antarcticus. They measure metabolism after venom expenditure and feeding as well as during preparation for shedding in an effort to establish a comparison for the energetic expenditures made during these common physiological processes. The snakes used were a captive group of six siblings and their parents. The authors found venom expenditure was associated with an abrupt and distinct increase in metabolism during the first 12 h after venom extraction, followed by a slow return to resting levels and they found that snakes appear to spread out the expenditure of energy of to replace the venom over time and the metabolic rate may stay up for a much longer time period than was measured in the study. However, 54% of total costs are made during the first day first day of venom replenishment, and the metabolic rate stayed only slightly above the resting metabolism during the subsequent five days. Suggesting that the activation of venom gland epithelium including the up regulation of protein synthesis was the main expense in venom production and it occurs in the first day after the venom was expelled.  Pinto and colleagues found that the cost of replenishing venom increased the snake's resting metabolism by 69%, while feeding (minus the venom expenditure) increased the metabolic rate 169%, and his was considerably lower than the cost of shedding, which increased the snake's metabolism 126% above the resting rate for 13 days (this is 17 times greater than the energy used to replace the venom). Thus, their results suggest that total costs of venom replenishment are relatively small when compared to costs of digestion and shedding.

Literature
Pintor, A. F. V., A. K. Krockenberger and J. E. Seymour. 2010. Costs of venom production in the common death adder (Acanthophis antarcticus). Toxicon, 56(6):1035-1042.

McCue, M. D., 2006. Cost of producing venom in three North American pitviper species. Copeia 2006, 818–825.

A Giant in a Genus of Small Snakes


Atractus gigas
Perhaps the most specious genus of snakes is Atractus (Family Dipsididae) with about 130 species.  Atractus are commonly known as ground snakes, and tend to be small to medium snakes that feed on earthworms, arthropods, and mollusks. They are distributed from Panama to Argentina and overall knowledge about their natural history is at best very incomplete. They occur from sea level to 4,500 m in elevation and many, if not most of them, are known only from the type specimens. They are closely related to the Middle American and northern South American fossorial and cryptozoic genera Adelphicos and Geophis. Atractus range in size from snakes that are less than 200 mm at maturity to the giant, Atractus gigas that exceeds 1000 mm. Myers and Schargel (2006) described Atractus gigas from a single specimen collected on the west side of the Ecuadorian Andes, Tolhurst et al. (2010) recently reported a second specimen of A. gigas about 50 km from the type locality on the basis of photographs.  Now, Passos et al (2010) discovered additional specimens of this poorly known snake in museum material and collected new specimens during fieldwork in the northeastern Peruvian Andes. The largest female was 1040 mm in body length, while the largest male was 255 mm in body length (presumably this was a subadult). The female’s body size makes this species the largest in the genus. The authors describe the juvenile and adult color patterns and detail the sexually dimorphic scale counts. They encountered this snake at Santuario Nacional Tabaconas Namballe, San Ignacio, Peru, on a coffee plantation and in nearby montane forest. Individuals were observed from early morning to late afternoon. Thus, Atractus gigas inhabits primary and secondary cloud and montane forest as well as coffee plantations between 600 and 2300 m on both sides of the Andes. The diurnal activity of this snake is also unusual for the genus, since many others ground snake species are known to be nocturnal. One female contained 12 oviductal eggs, this is an exceptionally large clutch size for an Atractus [other Atractus with known clutch sizes, i.e. A. reticulatus and A. trilineatus, have 1-6 eggs]. Many Atractus show sexual dimorphism with large females and smaller males. Thus this clade of snakes may make an excellent study group to test hypotheses about sexual dimorphism in snakes - given the number of species it is likely one or more has males that are larger than females.

Literature
Myers, C. W. and W. E. Schargel. 2006. Morphological extremes – Two new snakes of the genus Atractus from northwestern South America (Colubridae: Dipsadinae). American Museum Novitates, 3532: 1‑13.

Passos, P., M. Dobiey, and P. J. Venegas  2010. Variation and Natural History Notes on Giant Groundsnake, Atractus gigas (Serpentes: Dipsadidae). South American Journal of Herpetology 5(2):73-82.

Tolhurst, B.; M. Peck; J. N. Morales; T. Cane and, I. Recchio. 2010. Extended distribution of recently described dipsadine colubrid snake: Atractus gigas. Herpetology Notes, 3: 73‑75.