Monday, February 8, 2016

First fossil chamaeleonid from Greece

Chameleo chameleo from Samos, Greece.. Benny Trapp
Chameleons  constitute a diverse clade of lizards with more than 200 species that are distributed in Africa, Madagascar and several Indian Ocean islands, southern Asia, Cyprus and southern parts of Mediterranean Europe. Cryptic diversity is common within the group. Several new species having been described in the current decade, mostly on the basis of molecular data. The size range of chamaeleonids is astonishing, with the larger members of the family surpassing 600 mm in total length, and the smallest species rank well among the tiniest known reptiles, the extant Brookesia micra, attaining only 29 mm and the extinct Jucaraseps grandipessimilar of similar size.

The Chamaeleonidae fossil record is very scarce and any new specimen is therefore considered important for our understanding of the evolutionary and biogeographic history of the group. In a new paper Georgalis et al. (2016) report on new specimens from the early Miocene of Aliveri (Evia Island) in Greece. These are the only fossils chamaeleons  from southeastern Europe. Although skull bones are tentatively attributed to the Czech species Chamaeleo cf. andrusovi, revealing a range extension for this taxon, the tooth-bearing bones are described as indeterminate chamaeleonids. The Aliveri fossils rank well among the oldest known reptiles from Greece, provide evidence for the dispersal routes of chameleons out of Africa towards the European continent and, additionally, imply strong affinities with coeval chamaeleonids from Central Europe.

Citation
Georgalis, G. L., Villa, A., & Delfino, M. (2016). First description of a fossil chamaeleonid from Greece and its relevance for the European biogeographic history of the group. The Science of Nature, 103(1-2), 1-12.

Friday, January 22, 2016

A new species of high elevation Liolaemus (Family Liolaemidae)

Liolaemus uniformis. Photo credit:  Jaime Troncoso-Palacios
During a field trip at 3000 metres above sea level, a group of scientists, led by Jaime Troncoso-Palacios, Universidad de Chile, discovered a new endemic lizard species, in the mountains of central Chile, scientists. Noticeably different in size and scalation, compared to the rest of the local lizards, what initially grabbed the biologists' attention was its colouration. Not only was it unlike the already described ones, but also appeared surprisingly consistent within the collected individuals, even regardless of their sex. Eventually, it was this peculiar uniformity that determined the lizard's name Liolaemus uniformis. The study is published in the open-access journal ZooKeys.

The researchers found the lizards quite abundant in the area, which facilitated their observations and estimations. Apart from a thorough description of the new iguana along with its comparisons to its related species, the present paper also provides an in-depth discussion about the placement of the new taxon, which had been confused with other species in the past.

While most of the other lizards from the area and its surroundings often vary greatly in colouration and pattern between populations and sexes, such thing is not present in the new species. Both males and females from the observed collection have their bodies' upper side in brown, varying from dark on the head, through coppery on the back and light brown on the tail. The down side of the body is mainly yellowish, while the belly -- whitish. The only variables the scientists have noticed in their specimens are slight differences in the shade with two females demonstrating unusual olive hues on their snouts. These differences in morphology were also strongly supported by the molecular phylogeny through the analysis of mitochondrial DNA, which was performed by Dr. Alvaro A. Elorza, from Universidad Andres Bello.

Accustomed to life in highland rocky habitats with scarce greenery, these lizards spend their active hours, estimated to take place between 09:00 h and 18:00 h hidden under stones. However, they might not be too hard to find due to their size of about 8.5 cm for the males and their abundance in the studied area. The females are more slender and measure 7 cm in length on average.

Having caught one of their specimens while holding a yellow flower in its mouth, the scientists conducted further examination of the stomach contents of the studied individuals and concluded that the species is omnivorous, feeding mainly on plants as well as insects and roundworms.

In conclusion, the researchers showed that there is still a huge gap in the knowledge of the close relatives of the newly described species and their "challenging taxonomy."

Citation
Jaime Troncoso-Palacios, Alvaro A. Elorza, German I. Puas, Edmundo Alfaro-Pardo. A new species of Liolaemus related to L. nigroviridis from the Andean highlands of Central Chile (Iguania, Liolaemidae). ZooKeys, 2016; 555: 91 DOI: 10.3897/zookeys.555.6011

Tuesday, January 19, 2016

Rapoport's rule & lizards

Left. Anna Pintor with a flap-footed lizards (Pygopodiae). Photo credit: Image 
courtesy of James Cook University.Right pygopodids are legless geckos. JCM

James Cook University scientists have found lizards exposed to rain, hail and shine may cope better with extreme weather events predicted as a result of climate change than their fair-weather cousins.

A new study by JCU PhD student Anna Pintor, published in the journal Ecological Monographs, is one of the first to test the Climatic Variability Hypothesis (CVH) -- which proposes that animals living in environmentally variable areas should be able to tolerate more environmental fluctuations as a result.

This idea is a key assumption of the controversial Rapoport's Rule -- which states that a species at higher latitudes with variable weather conditions leads to the evolution of wider environmental tolerances which leads to a requirement for a larger range size.

Ms Pintor, along with supervisors Professor Lin Schwarzkopf and Professor Andrew Krockenberger from the Centre for Tropical Biodiversity and Climate Change, used three groups of Australian skinks for their analysis.

Their results confirm, in all three groups, that species living in regions with greater temperature variability have both greater environmental tolerances and wider ranges -- both in terms of latitude and altitude.

Andrew Krockenberger explains the importance of this result to advancing scientific thought "The literature is full of examples of species that do and don't fit Rapoport's rule," he said. "We've shown what is important is the actual underlying mechanism -- that species that can deal with a high degree of variability at a single site also end up with more extensive geographic ranges.

"Arguing about whether or not Rapoport's rule is valid is irrelevant and misses the point -- let's start making sure we understand the underlying process instead."

Lead author Anna Pintor said if we want to understand impacts of climate change in the future, we need to know how species' current distributions come about it the first place.

"Understanding underlying mechanisms like the CVH is one way to do that, but we need to do a lot more before we can tell exactly how species will be impacted and how to best help them deal with climate change."

Citation

Anna F. V. Pintor, Lin Schwarzkopf, Andrew K. Krockenberger. Rapoport's Rule: Do climatic variability gradients shape range extent? Ecological Monographs, 2015; 85 (4): 643 DOI: 10.1890/14-1510.1

Sunday, January 10, 2016

Death by constriction, a fourth possible cause

A juvenile Burmese Python constricting a rat.
The evolution of constriction  was undoubtedly very important milestone in the evolution and radiation of snakes. Killing large prey quickly and reducing the chance of injury to a snake allowed snakes to subdue otherwise unobtainable, larger prey. Constricting snakes exert pressure by coiling around and squeezing their prey, usually killing it before swallowing. The process of constriction takes energy and time, and risks injury to the snake. A snake's ability to constrict and kill quickly is important because it impacts feeding success, and thus growth and fitness. Constriction pressures are generated by forces from the snake’s axial musculature applied to the prey. These forces are proportional to the cross-sectional area of active muscle, and therefore to the snake's diameter. In a new paper Penning et al. (2015) describe the ontogeny of constriction performance in Reticulated and Burmese Pythons. The authors also discuss the implications for the cause of prey death during constriction.

The study found both species constrict prey vigorously using coils of 1–4 loops. Reticulated Pythons exerted maximum pressures of 8.27–53.77 kPa, with larger individuals exerting significantly higher peak pressures than smaller individuals. Burmese Pythons constricted with maximum pressures of 18.0–42.93 kPa, with larger individuals also exerting significantly higher peak pressures than smaller individuals  The species or the number of loops in a coil did not significantly affect peak
pressure in either species.

Constriction pressures exerted by both pythons scale differently from those of other snakes, many of the highest pressures were probably enough to force blood into the brain at high pressure in mammalian prey. In addition to suffocation, circulatory arrest and spinal dislocation, the authors propose the ‘red-out effect’  as a fourth possible mechanism of prey death by constriction. The redout effect describes the effect of negative gravity on jet pilots during extreme flight manoeuvres, in which vision becomes reddened by uncontrollable blood flow to the brain and eyes. When fighter pilots experience negative gravitational accelerations (G-forces), they incur a rush of blood to the brain that causes rapid loss of consciousness. Constriction pressures above the venous blood pressure of the prey will impede blood flow and oxygen delivery to tissues.  Pressure from constriction  dramatically higher than the prey’s blood pressure could force blood away from the site of constriction and into the extremities, including the head and brain. Blood being pushed into the brain during peak constriction could cause the same red-out effect described above for pilots, and could cause extensive ruptures in cranial blood vessels.

Citation
Penning, D. A., Dartez, S. F., & Moon, B. R. (2015). The big squeeze: scaling of constriction pressure in two of the world's largest snakes, Python reticulatus and Python molurus bivittatus. Journal of Experimental Biology,218(21), 3364-3367.

Friday, January 1, 2016

Sex chromosomes in snakes

In two recently published articles Rovatsos et al. (2015 a, b) highly differentiated heteromorphic ZZ/ZW sex chromosomes with a heterochromatic W are  basic among the advanced snakes, Colubroidea, while other snake lineages generally lack them. The authors examined the dragonsnake, Xenodermus javanicus (family Xenodermatidae), which is phylogenetically nested between snake lineages with and without differentiated sex chromosomes. Although most snakes have a karyotype with a stable 2n chromosomal number of  36, the dragonsnake has an unusual, derived karyotype  2n = 32 chromosomes. The found that heteromorphic ZZ/ZW sex chromosomes with a heterochromatic W are present in the dragonsnake, which suggests that the emergence of a highly differentiated W sex chromosome within snakes predates the split of Xenodermatidae and the clade including families Pareatidae, Viperidae, Homalopsidae, Lamprophiidae, Elapidae, and Colubridae (the Colubroidae). Although accumulations of interstitial telomeric sequences have not been previously reported in snakes, by using FISH with a telomeric probe they discovered them in six pairs of autosomes as well as in the W sex chromosome of the dragonsnake. Similarly to advanced snakes, the sex chromosomes of the dragonsnake have a significant accumulation of repeats containing a (GATA)n sequence. The results facilitate the dating of the differentiation of sex chromosomes within snakes back to the split between Xenodermatidae and other advanced snakes, about 40-75 mya. In a second  article they document the stability of sex chromosomes in advanced snakes based on the testing of Z-specificity of genes using quantitative PCR (qPCR) across 37 snake species (their qPCR technique is suitable for molecular sexing all advanced snakes). They found that at least part of the sex chromosomes is homologous across all families of caenophidian snakes (Acrochordidae, Xenodermatidae, Pareatidae, Viperidae, Homalopsidae, Colubridae, Elapidae and Lamprophiidae). The emergence of differentiated sex chromosomes can be dated to about 60 Ma, a date that preceded the extensive diversification of advanced snakes, a group with more than 3000 species. The Z-specific genes of caenophidian snakes are (pseudo)autosomal in the snake families Pythonidae, Xenopeltidae, Boidae, Erycidae and Sanziniidae, as well as in outgroups with differentiated sex chromosomes such as monitor lizards, iguanas and chameleons. Along with iguanas, advanced snakes are therefore another example of ectothermic amniotes with a long-term stability of sex chromosomes comparable with endotherms.

Citations
Rovatsos, M., Johnson Pokorná, M., & Kratochvíl, L. (2015). Differentiation of Sex Chromosomes and Karyotype Characterisation in the Dragonsnake Xenodermus javanicus (Squamata: Xenodermatidae). Cytogenetic and genome research.

Rovatsos, M., Vukić, J., Lymberakis, P., & Kratochvíl, L. (2015). Evolutionary stability of sex chromosomes in snakes. In Proc. R. Soc. B (Vol. 282, No. 1821, p. 20151992). The Royal Society.


Tuesday, December 22, 2015

New range and habitat records for threatened Australian sea snakes


The rare short nosed sea snake discovered 
on Ningaloo reef, Western Australia. Photo 
Credit: Grant Griffin, W.A. Dept. Parks and 
Wildlife
Scientists from James Cook University have discovered two critically endangered species of sea snakes, previously thought to be extinct, off the coast of Western Australia.

It's the first time the snakes have been spotted alive and healthy since disappearing from their only known habitat on Ashmore Reef in the Timor Sea more than fifteen years ago.

"This discovery is really exciting, we get another chance to protect these two endemic Western Australian sea snake species," says study lead author Blanche D'Anastasi from the ARC Centre of Excellence for Coral Reef Studies at JCU.

"But in order to succeed in protecting them, we will need to monitor populations as well as undertake research into understanding their biology and the threats they face."

The discovery of the critically endangered short nose sea snake was confirmed after a Western Australia Parks and Wildlife Officer, Grant Griffin, sent a photo of a pair of snakes taken on Ningaloo Reef to Ms D'Anastasi for identification.

"We were blown away, these potentially extinct snakes were there in plain sight, living on one of Australia's natural icons, Ningaloo Reef," says Ms D'Anastasi.

"What is even more exciting is that they were courting, suggesting that they are members of a breeding population."

The researchers also made another unexpected discovery, uncovering a significant population of the rare leaf scaled sea snake in the lush seagrass beds of Shark Bay.

The discovery was made 1700 kilometres south of the snakes only known habitat on Ashmore Reef.

"We had thought that this species of sea snake was only found on tropical coral reefs. Finding them in seagrass beds at Shark Bay was a real surprise," says Ms D'Anastasi.

Both leaf scaled and short nosed sea snakes are listed as Critically Endangered under Australia's threatened species legislation, which means they have special protection.

Despite the good news of the find, sea snake numbers have been declining in several marine parks, and scientists are at a loss to explain why.

"Many of the snakes in this study were collected from prawn trawl by-catch surveys, indicating that these species are vulnerable to trawling," says Dr Vimoksalehi Lukoschek from the Centre of Excellence for Coral Reef Studies.

"But the disappearance of sea snakes from Ashmore Reef, could not be attributed to trawling and remains unexplained.

"Clearly we need to identify the key threats to their survival in order to implement effective conservation strategies if we are going to protect these newly discovered coastal populations," Dr Lukoschek says.

Citation
B.R. D'Anastasi, L. van Herwerden, J.A. Hobbs, C.A. Simpfendorfer, V. Lukoschek. New range and habitat records for threatened Australian sea snakes raise challenges for conservation. Biological Conservation, 2016; 194: 66 DOI: 10.1016/j.biocon.2015.11.032


Tuesday, December 8, 2015

Sea snake diversity in the Indo-Australian Archipelago

The Indo-Australian Archipelago is a marine biodiversity hotspot centred in Southeast Asia that contains many of the extant viviparous sea snakes. Points of origin of for snake radiations are of interest  in understanding the distribution of current diversity. In an early on-line view of a new paper in the Journal of Biogeography, Ukuwela and colleagues (2015) note that previouis studies found the ancestral area for viviparous sea snakes was Australasian about 6.9 million years ago. The Aipysurus group also originated and speciated in Australasia. However, of the Aipysurus group species, only the specialist fish egg-eaters (Emydocephalus ijimae, E. szczerbaki and A. eydouxii) have colonized Southeast Asia and none have expanded into the Indian Ocean beyond the coast of Western Australia. A Beast analyses recovered a Southeast Asian origin for the core Hydrophis group, and all three methods used indicated that subsequent diversification in this rapidly speciating clade occurred primarily in Southeast Asia, with subsequent dispersals into the Indian Ocean and re-colonization of Australasia.

Ukuwela et al. (2015) found evidence for 34 divergences between lineages older than 0.5 Ma (candidate speciation events); 22 of these have > 0.7 posterior probabilities of occurring in Southeast Asia, 10 in Australasia, and 2 in the Indian Ocean. This implies most sea snake diversity in South East Asia originated from a period of rapid in situ evolution. While viviparous sea snakes originated in Australasia, Southeast Asia and its Indo-Australian Archipelago appears to be their primary centre of speciation. This is contrary to predictions of the overlap or accumulation models. Taxa are not more likely to disperse into, rather than out of, Southeast Asia and the Indo-Australian Archipelago.

The majority of sea snake diversification, including the rapid core Hydrophis radiation, occurred during major climatic and geological events that drove vicariant population and species divergence in many of the region’s marine groups. Viviparous sea snakes might be particularly influenced by ‘soft’ biogeographical barriers (such as incomplete and thus permeable land bridges) because they give birth to live young and thus lack the dispersing planktonic larval stage that is expected to promote population connectivity in most other marine groups (many fish and invertebrates). Several sea snake species accordingly show strong intraspecific genetic structure corresponding to deep-water and historical land barriers. However, biogeographical patterns and the diversification dynamics of the entire sea snake radiation have not previously been quantitatively investigated.

Citation
Ukuwela, Kanishka DB, Michael SY Lee, Arne R. Rasmussen, Anslem Silva, Bryan G. Fry, Parviz Ghezellou, Mohsen Rezaie‐Atagholipour, and Kate L. Sanders. 2015. Evaluating the drivers of Indo‐Pacific biodiversity: speciation and dispersal of sea snakes (Elapidae: Hydrophiinae). Journal of Biogeography (2015).

Monday, November 30, 2015

Dinilysia's inner ear suggests it was a burrowing species, implications for the evolution of snakes

Modern snake skull, with inner ear shown in orange. 
Photo Credit: Hongyu Yi
Modern snakes probably originated as habitat specialists, but it is controversial unclear whether they were ancestrally terrestrial burrowers or marine swimmers. In a new paper Yi and Norell (2015)  use x-ray virtual models of the inner ear to predict the habit of Dinilysia patagonica, a stem snake closely related to the origin of modern snakes. Previous work has shown that modern snakes perceive substrate vibrations via their inner ear. The study's  data show that D. patagonica and modern burrowing squamates share a unique spherical vestibule in the inner ear, as compared with swimmers and habitat generalists. The authors built predictive models for snake habitats based on their vestibular shape, which estimated D. patagonica and the hypothetical ancestor of crown snakes as burrowers with high probabilities. This study provides an extensive comparative data set to test fossoriality quantitatively in stem snakes, and it shows that burrowing was predominant in the lineages leading to modern crown snakes.

Comparisons between CT scans of the fossil and modern reptiles indicate that snakes lost their legs when their ancestors evolved to live and hunt in burrows, which many snakes still do today.

The findings suggest snakes did not lose their limbs in order to live in the sea, as has been previously suggested.

Scientists used CT scans to examine the bony inner ear of Dinilysia patagonica, a 2-metre long reptile closely linked to modern snakes. These bony canals and cavities, like those in the ears of modern burrowing snakes, controlled its hearing and balance.

They built 3D virtual models to compare the inner ears of the fossils with those of modern lizards and snakes. Researchers found a distinctive structure within the inner ear of animals that actively burrow, which may help them detect prey and predators. This shape was not present in modern snakes that live in water or above ground.

The findings help scientists fill gaps in the story of snake evolution, and confirm Dinilysia patagonica as the largest burrowing snake ever known. They also offer clues about a hypothetical ancestral species from which all modern snakes descended, which was likely a burrower.

Dr Hongyu Yi, of the University of Edinburgh's School of GeoSciences, who led the research, said: "How snakes lost their legs has long been a mystery to scientists, but it seems that this happened when their ancestors became adept at burrowing. The inner ears of fossils can reveal a remarkable amount of information, and are very useful when the exterior of fossils are too damaged or fragile to examine."

Mark Norell, of the American Museum of Natural History, who took part in the study, said: "This discovery would not have been possible a decade ago -- CT scanning has revolutionised how we can study ancient animals. We hope similar studies can shed light on the evolution of more species, including lizards, crocodiles and turtles."

Citation

Yi, H. &  M.A. Norell. The burrowing origin of modern snakes. Science Advances, 2015; 1 (10): e1500743 DOI: 10.1126/sciadv.1500743

Sunday, November 29, 2015

Eggshell Porosity Provides Insight on Evolution of Nesting in Dinosaurs

A dinosaur nest. Photo credit: Kohei Tanaka
Extinct archosaurs' eggshell porosity may be used as a proxy for predicting covered or exposed nest types, according to a study published November 25, 2015 in the open-access journal PLOS ONE by Kohei Tanaka from the University of Calgary and colleagues.

Knowledge about dinosaur nests may provide insight into the evolution of nesting and reproductive behaviors among archosaurs, a group that includes living birds and crocodilians, as well as extinct dinosaurs. Unfortunately, little remains of prehistoric nests, and most information on extinct archosaurs is only gleaned indirectly through comparison with living relatives. Among extant archosaurs, two general types of nests are observed: open nests, where the eggs are uncovered and built by species that brood their eggs; and covered nests, built by species that incubate their eggs using external heat sources. Scientists try to infer the type of nest by looking at different characteristics of the eggs and the nest setting. The authors of this particular study proposed a statistically rigorous approach to infer nest type based on large datasets of eggshell porosity and egg mass compiled for over 120 extant archosaur species and 29 extinct archosaur taxa.

The researchers found a strong correlation between eggshell porosity and covered or exposed nest types among extant archosaurs, which indicates that eggshell porosity may be used as a proxy for nest type, which may help predict nest type in extinct taxa. Their results show that covered nests were likely used by more primitive dinosaurs, and the transition of theropods from covered to uncovered nests may have allowed the exploitation of alternate nesting locations. These changes in nesting styles may have lessened the odds of nesting failure due to predation, flooding, or torrential rainfall, and may have played a role in the evolutionary success of maniraptorans, including birds.

Citation
Kohei Tanaka, Darla K. Zelenitsky, François Therrien. Eggshell Porosity Provides Insight on Evolution of Nesting in Dinosaurs. PLOS ONE, 2015; 10 (11): e0142829 DOI: 10.1371/journal.pone.0142829

Tuesday, November 10, 2015

The evolution of venom, a new perspective


This is an Anderson's Pitviper (Trimeresurus andersoni), a venomous 
snake in the Andaman Islands of India. Photo Credit: Dr. Kartik Sunagar

In a new study published in  PLOS Genetics, scientists at the Hebrew University of Jerusalem have revealed new discoveries about the evolution of venom. The research points to a 'two-speed' evolution of animal venom, showing for the first time the significant roles played by different forces of natural selection.

Venom is a complex mixture of proteins and other toxic chemicals produced by animals such as snakes and spiders, either to incapacitate their prey or to defend against predators. The influence of positive selection (the process by which a protein changes rapidly over evolutionary time scales) in expanding and diversifying animal venoms is widely recognized.

This process was hypothesized to result from an evolutionary chemical arms race, in which the invention of potent venom in the predatory animals and the evolution of venom resistance in their prey animals, exert reciprocal selection pressures.

In contrast to positive selection, the role of purifying selection (also known as negative selection, which is the selective removal of deleterious genetic changes from a population) has rarely been considered in venom evolution.

Moreover, venom research has mostly neglected ancient animal groups in favor of focusing on venomous snakes and cone snails, which are both "young" animal groups that originated only recently in evolutionary timescales, approximately 50 million years ago. Consequently, it was concluded that venom evolution is mostly driven by positive selection.

In the new study, Dr. Yehu Moran at the Hebrew University's Department of Ecology, Evolution and Behavior and the guest scientist Dr. Kartik Sunagar examined numerous venom genes in different animals in order to unravel the unique evolutionary strategies of toxin gene families.

The researchers analyzed and compared the evolutionary patterns of over 3500 toxin sequences from 85 gene families. These toxins spanned the breadth of the animal kingdom, including ancient venomous groups such as centipedes, scorpions, spiders, coleoids (octopus, cuttlefish and squids) and cnidarians (jellyfish, sea anemones and hydras).

Unexpectedly, despite their long evolutionary histories, ancient animal groups were found to have only accumulated low variation in their toxins.

The analysis also revealed a striking contrast between the evolution of venom in ancient animal groups as compared to evolutionarily "young" animals. It also highlighted the significant role played by purifying selection in shaping the composition of venoms.

According to Dr. Yehu Moran, "Our research shows that while the venoms of ancient lineages evolve more slowly through purifying selection, the venoms in more recent lineages diversify rapidly under the influence of positive selection."

The findings enable the postulation of a new theory of venom evolution. According to this theory, toxin-producing genes in young venomous groups that enter a novel ecological niche, experience a strong influence of positive selection that diversifies their toxins, thus increasing their chances to efficiently paralyze relevant prey and predatory species in the new environment.

However, in the case of the ancient venomous groups, where the venom is already "optimized" and highly suitable for the ecological niche, the venom's rate of accumulating variations slows down under the influence of purifying selection, which preserves the potent toxins generated previously.

The proposed "two-speed" mode of venom evolution highlights the fascinating evolutionary dynamics of this complex biochemical cocktail, by showing for the first time the significant roles played by different forces of natural selection in shaping animal venoms.

According to Drs. Moran and Sunagar, "The 'two-speed' mode of evolution of animal venoms involves an initial period of expansion, resulting in the rapid diversification of the venom arsenal, followed by longer periods of purifying selection that preserve the now potent toxin pharmacopeia. However, species that have entered the stage of purification and fixation may re-enter the period of expansion if they experience a major shift in ecology and/or environment."


Citation

Kartik Sunagar & Yehu Moran. The Rise and Fall of an Evolutionary Innovation: Contrasting Strategies of Venom Evolution in Ancient and Young Animals. PLOS Genetics, 2015; 11 (10): e1005596 DOI: 10.1371/journal.pgen.1005596

Sunday, November 8, 2015

The origin of large body size and herbivory in giant Canary Island lacertids

Gallotia galloti. Photographer's Credit: Petermann
2005, via Wikimedia Commons
The Island Rule on body size claims big animals  evolve smaller body sizes due to the limited resource of food and limited habitat; while smaller animals that have no natural enemies in islands evolve larger body sizes.

 Andrej Čerňanský and colleagues discovered a fossil related to the genus Gallotia which is endemic to the  Canary Islands. They named it Janosikia ulmensis, after the Slovak national hero, outlaw Juraj Jánošík. Zoological Journal of the Linnean Society reports the results. The genus Gallotia has not been growing in size on the island – quite the contrary. The Gallotia ancestor came to the island with a large body size.

Until now, the genus Gallotia was considered a clear example of island gigantism; scientists supposed that a small lizard resembling the North African species Psammodromus colonised the Canary islands 20 to 18 million years ago. As it did not have any natural enemies, it supposedly gradually increased its body size several times. But the fossil record illustrating this  was absent.

“Currently, we have been able to do research, for the first time, on fossils and almost complete findings from about 22 million years old which are in the line leading to the lizards from the Canary Islands. Our fossil comes from Germany and precedes the period of the islands’ colonisation. It also shows us a completely different story, proving that the evolution of body size is much more complex than we had originally thought,” Čerňanský explained.

This stems from a whole set of anatomic features – like the huge size, as the skull alone was almost five centimetres long, the Slovak researcher said. This shows that this line had already grown to this size on the continent before colonising the islands; some other current species from the islands, on the other hand, represent markedly smaller animals. Thus, Janosikia turned the original idea upside down.

The fossil is crucial for understanding the island rule of evolution of body size, and also the herbivory of today’s large species of lizards. It also confirms the assumption of molecular biologists that the line leading to the genus Gallotia has its origin on the European continent; and, last but not least, it is one of the best preserved lizards from the Tertiary that reveals many important, so far unknown aspects of the evolution of dominant group of reptiles in Europe – the family Lacertidae, Čerňanský summed up.

Janosikia ulmensis is from the early Miocene of Ulm, Germany (∼22 Mya). The authors show that this species and the Oligocene Pseudeumeces cadurcensis (Filhol, 1877) are in fact crown lacertids, and the first known pre-Quaternary record of the total clade of Gallotia. Pseudeumeces confirms the early origin of crown Lacertidae in the Palaeogene of Europe. More importantly, these fossil taxa show that large body size was already achieved on the European mainland by the early Miocene. Furthermore, Pseudeumeces and Janosikia were faunivorous, thus demonstrating that insularity, not large body size, was crucial to the evolution of herbivory in this lineage. Body size change in Gallotia was more complex than previously thought, encompassing size increase [e.g. in the extinct Gallotia goliath (Mertens, 1942)], but more commonly involving miniaturization. The physical environment may play a crucial role in modulating the evolution of body size.

Čerňanský, A., Klembara, J. and Smith, K. T. (2015), Fossil lizard from central Europe resolves the origin of large body size and herbivory in giant Canary Island lacertids. Zoological Journal of the Linnean Society. doi: 10.1111/zoj.12340.



Friday, October 30, 2015

The diet of Gasperetti’s sand viper

By Zuhair Amr via Wikimedia Commons
Gasperetti’s sand viper, Cerastes gasperetti, is the most common snake in Saudi Arabia. However, this snake remains poorly studied. It is distributed throughout many deserts in Egypt, Jordan and Saudi Arabia. Horned viper is a nocturnal, true desert snake and prefers sandy soil with some vegetation. Horned vipers are generally considered opportunistic predators with varied diets. However no study has specifically addressed the diet of Cerastes gasperettii.  Al-Sadoom et al. (2015) examined 238 specimens from Al-Thumama area, in the central region of Saudi Arabia collected over a period of one year May, 1998 – April, 1999. The digestive system was examined. Eighty specimens of both sexes were studied for gut content analysis. They found larger specimens of Gasperetti’s sand viper feeds mostly on rodents (Gerbillus cheesmani and Mus musculus) which were found in snakes with larger size and formed 70% of the stomach contents. Arthropods (beetles) constituted 15% of the contents and lizards (Acanthodactylus schmiditi and Stenodactylus slevinii) form 10% of the total diet. The remaining 5% of the stomach content was completely digested and could not be identified.


Citation
Al-Sadoon, M. K., & Paray, B. A. (2015). Ecological Aspects of the Horned viper, Cerastes cerastes gasperettii in the Central Region of Saudi Arabia. Saudi Journal of Biological Sciences.

Wednesday, October 14, 2015

The Cuban Racer in the Bahamas


Cubophis cantherigerus cantherigerus. Photo by Lisa Ferguso
Dipsadidae is one of the largest snake families with more than 754 species, mostly distributed in the Neotropics. The subfamily Xenodontinae is exclusive to South American to Mexico and the West Indies. Mexico, and the West Indies, and highly diverse in both morphology and natural history. The Tribe Alsophiini holds about 43 species restricted to the West Indies. These are typically slender, fast-moving, and active diurnal foragers often commonly called racers. While taxonomic classifications of xenodontines were historically based on hemipenial, dentition, external morphology, and color pattern, recent molecular analyses of Alsophiini are not necessarily in agreement regarding monophyly of the group In 2012, Krysto et al. (2015) collected the first known dipsadid snake on the Cay Sal Bank, The Bahamas. Only two snake species have been previously recorded from any island on the Cay Sal Bank: the Bahamian Slender Blindsnake, Typhlops biminiensis, on Elbow Cay; and the Northern Bahamas Trope, Tropidophis curtus (Garman 1887), on both Elbow Cay and Double Headed Shot Cay.

Krysto et al. examine the external morphology, dentition, and color pattern, and conduct molecular analyses of Caribbean Alsophiine snakes to determine the species identity and phylogenetic placement of the Cay Sal Bank snake. They analyze 3,426 base pairs (bp) of sequence data derived from five mitochondrial loci and one nuclear locus using Maximum Likelihood (ML) and Bayesian Inference (BI) methods. Our molecular data agree with some aspects of morphology (e.g., scale counts, dentition, and color pattern) supporting identification of this specimen as the Cuban Racer, Cubophis cantherigerus cantherigerus (Bibron 1840), a species previously regarded as endemic to Cuba. This discovery provides another example of the strong Cuban affinities of the terrestrial vertebrate fauna of the Bahamian islands.

Citation
KRYSKO, K. L., STEADMAN, D. W., NUÑEZ, L. P., & LEE, D. S. (2015). Molecular phylogeny of Caribbean dipsadid (Xenodontinae: Alsophiini) snakes, including identification of the first record from the Cay Sal Bank, The Bahamas. Zootaxa, 4028(3), 441-450.

Wednesday, September 30, 2015

New Book, Natural History of Neotropical Treeboas (genus Corallus)

Nine species comprise the arboreal boid genus Corallus. Combined, they range from Guatemala in northern Central America to southeastern Brazil in South America, and two species occur on islands in the West Indies. Based on extensive fieldwork by the author extending over 25 years, observations from colleagues, and the literature, Natural History of Neotropical Treeboas (Genus Corallus) summarizes, often in great detail, our current knowledge of treeboa habitats, activity, diet, foraging strategies, defensive behaviors, predators, reproduction, population characteristics, and the shared history of humans and treeboas and the impact humans have had on treeboa natural history. In addition to more than 270 photos depicting treeboa color variation, habitats, predation, and mating, Natural History of Neotropical Treeboas (Genus Corallus) also includes maps, numerous graphs, 26 tables, and more than 400 literature references.

"Robert W. Henderson has conducted research on Neotropical treeboas for nearly 25 years, elucidating aspects of their natural history and monitoring changes in populations over time, emphasizing in particular how these snakes have adjusted in light of human-mediated changes to their habitat, prey base, and predators. In this book, Henderson provides insights into habitat, activity, diet and foraging, predators and defense, and reproduction, with each chapter providing insights, a large percentage of them firsthand, into what we know about these intriguing snakes. I take great pride in seeing a boa before Bob does (it happens rarely), but then he has undoubtedly encountered more treeboas in their natural habitat than anyone."
– Robert Powell

Saturday, September 26, 2015

Fluctuating sea levels and global cooling reduced crocodylian species over millions of years

The giant Sarcosuchus, an extinct crocodilian. Illustrators Credit: Imperial
 College London and Robert Nicholls (Paleocreations)
Crocodylians include present-day species of crocodiles, alligators, caimans and gavials and their extinct ancestors. Crocodylians first appeared in the Late Cretaceous period, approximately 85 million years ago, and the 250 million year fossil record of their extinct relatives reveals a diverse evolutionary history.

Extinct crocodylians and their relatives came in all shapes and sizes, including giant land-based creatures such as Sarcosuchus, which reached around 12 metres in length and weighed up to eight metric tonnes. Crocodylians also roamed the ocean -- for example, thalattosuchians were equipped with flippers and shark-like tails to make them more agile in the sea.

Many crocodylians survived the mass extinction that wiped out almost all of the dinosaurs 66 million years ago, but only 23 species survive today, six of which are classified by the International Union for Conservation of Nature as critically endangered and a further four classified as either endangered or vulnerable.

In a new study published in Nature Communications, researchers from Imperial College London, the University of Oxford, the Smithsonian Institution and the University of Birmingham compiled a dataset of the entire known fossil record of crocodylians and their extinct relatives and analysed data about Earth's ancient climate. They wanted to explore how the group responded to past shifts in climate, to better understand how the reptiles may cope in the future.

Crocodylians are ectotherms, meaning they rely on external heat sources from the environment such as the Sun. The researchers conclude that at higher latitudes in areas we now know as Europe and America, declining temperatures had a major impact on crocodylians and their relatives.

At lower latitudes the decline of crocodylians was caused by areas on many continents becoming increasingly arid. For example, in Africa around ten million years ago, the Sahara desert was forming, replacing the vast lush wetlands in which crocodylians thrived. In South America, the rise of the Andes Mountains led to the loss of a proto-Amazonian mega wetland habitat that crocodylians lived in around five million years ago.

Marine species of crocodylians were once widespread across the oceans. The team found that fluctuations in sea levels exerted the main control over the diversity of these creatures. For example, at times when the sea level was higher it created greater diversity because it increased the size of the continental shelf, providing the right conditions near the coast for them and their prey to thrive.

Interestingly, the Cretaceous-Paleogene mass extinction event, which wiped out many other creatures on Earth nearly 66 million years ago including nearly all of the dinosaurs, had positive outcomes for the crocodylians and their extinct relatives. The team found that while several groups did go extinct, the surviving groups rapidly radiated out of their usual habitats to take advantage of territories that were now uninhabited.

In the future, the team suggest that a warming world caused by global climate change may favour crocodylian diversification again, but human activity will continue to have a major impact on their habitats.

Dr Philip Mannion, joint lead author from the Department of Earth Science and Engineering at Imperial College London, said: "Crocodylians are known by some as living fossils because they've been around since the time of the dinosaurs. Millions of years ago these creatures and their now extinct relatives thrived in a range of environments that ranged from the tropics, to northern latitudes and even deep in the ocean. However, all this changed because of changes in the climate, and crocodylians retreated to the warmer parts of the world. While they have a fearsome reputation, these creatures are vulnerable and looking back in time we've been able to determine what environmental factors had the greatest impact on them. This may help us to determine how they will cope with future changes."

The next step for the researchers will be for them to look at similar patterns in other fossil groups with long histories, such as mammals and birds to determine how past climate influenced them.


Citation

Philip D. Mannion, Roger B. J. Benson, Matthew T. Carrano, Jonathan P. Tennant, Jack Judd, Richard J. Butler. Climate constrains the evolutionary history and biodiversity of crocodylians. Nature Communications, 2015; 6: 8438 DOI: 10.1038/ncomms9438