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.