Kyle J. Shaney

Snakes possess many extreme morphological and physiological adaptations. Identification of the molecular basis of these traits can provide novel understanding for vertebrate biology and medicine. Here, we study snake biology using the genome sequence of the Burmese python (Python molurus bivittatus), a model of extreme physiological and metabolic adaptation. We compare the python and king cobra genomes along with genomic samples from other snakes and perform transcriptome analysis to gain insights into the extreme phenotypes of the python. We discovered rapid and massive transcriptional responses in multiple organ systems that occur on feeding and coordinate major changes in organ size and function. Intriguingly, the homologs of these genes in humans are associated with metabolism, development, and pathology. We also found that many snake metabolic genes have undergone positive selection, which together with the rapid evolution of mitochondrial proteins, provides evidence for extensive adaptive redesign of snake metabolic pathways. Additional evidence for molecular adaptation and gene family expansions and contractions is associated with major physiological and phenotypic adaptations in snakes; genes involved are related to cell cycle, development, lungs, eyes, heart, intestine, and skeletal structure, including GRB2-associated binding protein 1, SSH, WNT16, and bone morphogenetic protein 7. Finally, changes in repetitive DNA content, guanine-cytosine isochore structure, and nucleotide substitution rates indicate major shifts in the structure and evolution of snake genomes compared with other amniotes. Phenotypic and physiological novelty in snakes seems to be driven by system-wide coordination of protein adaptation, gene expression, and changes in the structure of the genome.

Snake venom gene evolution has been studied intensively over the past several decades, yet most previous studies have lacked the context of complete snake genomes and the full context of gene expression across diverse snake tissues. We took a novel approach to studying snake venom evolution by leveraging the complete genome of the Burmese python, including information from tissue-specific patterns of gene expression. We identified the orthologs of snake venom genes in the python genome, and conducted detailed analysis of gene expression of these venom homologs to identify patterns that differ between snake venom gene families and all other genes. We found that venom gene homologs in the python are expressed in many different tissues outside of oral glands, which illustrates the pitfalls of using transcriptomic data alone to define "venom toxins." We hypothesize that the python may represent an ancestral state prior to major venom development, which is supported by our finding that the expansion of venom gene families is largely restricted to highly venomous caenophidian snakes. Therefore, the python provides insight into biases in which genes were recruited for snake venom systems. Python venom homologs are generally expressed at lower levels, have higher variance among tissues, and are expressed in fewer organs compared with all other python genes. We propose a model for the evolution of snake venoms in which venom genes are recruited preferentially from genes with particular expression profile characteristics, which facilitate a nearly neutral transition toward specialized venom system expression.

Abstract IUCN Red List assessments are important for conservation and management initiatives. However, status assessments are often challenging because of poor sampling between biogeographical regions. Researchers sometimes assess poorly known species, which can have unforeseen ramifications, including the trade of rare and cryptic species under common species names. Here, we address this issue in relation to economically important reptile species in Indonesia. We reviewed examples of single species categorized as Least Concern for which the assessments probably encompassed multiple closely related species. We also examined Red List assessments that utilized species distribution modelling techniques, and identified biogeography as a major barrier to using such methods. To test how biogeography may affect status assessments we used our own model lizard system from Indonesia, taking an integrative phylogeographical approach to quantify status assessments under contrasting scenarios. We show that failure to account for biogeographical breaks leads to significant variation in Red List status. Our model system fluctuates from Least Concern to Endangered, depending upon whether biogeographical boundaries are considered in taxonomic evaluations. We identify Sauria (lizards) and Serpentes (snakes) as major lineages requiring taxonomic and conservation attention in Indonesia. We also make the following recommendations: (1) Indonesia's trade quotas should further subdivide management zones to account for gaps in taxonomic evaluations; (2) genetic sampling should be considered a high priority during wildlife exportation processes from poorly studied geographical areas; and (3) continuation of thorough biological inventory is critical for conservation initiatives across heterogeneous mountain and island landscapes.

We describe a new species of Pseudocalotes from montane forests of the central, western coast of Sumatra. The combination of 3 or 4 interoculabials, slightly enlarged and heavily keeled scales on the lower flanks, a white scapular spot, a relatively long fifth toe, bicarinate lamellae at the base of Toe III, absence of a postrictal modified scale, and three rows of paravertebrals directed dorsally and posteriorly distinguishes the new species from its congeners on Sumatra and Java. Among the new characters defined in this study, counts of subdigital lamellae within the "span of Toe V" proved particularly useful for diagnosing species of Pseudocalotes. Phylogenetic analysis of DNA sequences identified a monophyletic group containing the Sumatran and Javan Pseudocalotes. Based on the phylogeny, we define a P. cybelidermus Group containing P. cybelidermus and P. guttalineatus and a P. tympanistriga Group containing P. tympanistriga, P. rhammanotus, and the new species. Combinations of five morphological characters define each of these two clades. As currently defined, Pseudocalotes is polyphyletic; Javan and Sumatran species are more closely related to other draconines such as Dendragama boulengeri than they are to some mainland species.

We describe three new species of Pseudocalotes from the Bukit Barisan Range of southern Sumatra, Indonesia. Pseudocalotes cybelidermus, P. guttalineatus, and P. rhammanotus differ from most congeners in having serrate dorsal crests that extend to the base of the tail and a dorsolateral series of enlarged heavily keeled scales. In these new species, subdigital lamellae of Toe III have prominent preaxial keels and lack or have greatly reduced postaxial keels. In contrast, P. rhammanotus resembles P. tympanistriga by having bicarinate subdigital lamellae at the base of Toe III. Like most congeners, these new species appear to be restricted to humid forests above 1000 m. We report several new morphological characters for Pseudocalotes and discuss their diagnostic value. Future systematic studies of this genus should assess presence/absence of interparietals, four different kinds of modified scales on the neck, a dorsolateral series of heavily keeled scales, and unicarinate lamellae under the distal phalanges of most fingers and toes. Our comparisons among congeners demonstrate the diagnostic value of width of the gap between the nuchal and dorsal crests and frequency data for contact between the nasal and supralabials and between the postmentals and infralabials. Finally, we discuss variation in morphology of subdigital lamellae at the base of Toe III and describe new conditions intermediate between the serrate fringe of most Indochinese species and the bicarinate lamellae of the P. tympanistriga.