The Evolution of Cutaneous Senses in Marine Snakes (Hydrophiinae)

Front-fanged elapid snakes (subfamily: Hydrophiinae) have invaded marine habitats twice: the oviparous sea kraits that diverged approximately 18 million years ago and the viviparous sea snakes that diverged approximately six million years ago. Due to these recent marine transitions, marine hydrophiine snakes are embedded within closely-related and extant terrestrial lineages. Within this phylogenetic context, I investigated two questions concerning two cutaneous senses in marine snakes: 1) How has the sense of touch evolved in the transition from land to sea? and 2) How has a novel phototactic trait arisen in sea snakes? Marine snakes possess small scale organs (‘sensilla’) that are presumptive mechanoreceptors widely thought to be co-opted for detecting water motion (i.e. hydrodynamic reception in homoplasy with the lateral line of fish). To test this hypothesis and infer ancestral and derived functions for scale sensilla, I used morphological techniques (quadrate sampling, scanning electron microscopy) to quantify sensilla traits (number, density, area, coverage) among 19 species of terrestrial and marine elapids. After accounting for effects of allometry (head size) and phylogeny (shared descent), I used Bayesian analyses to reconstruct ancestral sensilla traits in sea kraits and sea snakes. I also characterised ultrastructure (histology, immunohistochemistry, transmission electron microscopy) of scale sensilla on the head and tail of two species of sea snakes, Aipysurus laevis and Hydrophis stokesii, which indicate interspecific variation but overall structural similarities with mechanosensory sensilla in terrestrial snakes. These results provide the first evidence for a mechanosensory function for scale sensilla among sea snakes, and a basis for further studies to test for physiological and behavioural responses to water motion among marine snakes. In addition to scale mechanoreceptors, many lineages of sea snakes have conspicuous scale protuberances (e.g. spines, rugosities) with various purportedly sensory and non-sensory adaptive functions. I examined the morphology (scanning electron microscopy, histology) of sexually-dimorphic scale protuberances in turtle-headed sea snakes, Emydocephalus annulatus. Taken together with behavioural data, these morphological results suggest complex mechanosensory roles related to courtship and mating behaviours in this species. Finally, I investigated the evolution and molecular basis of a novel phototactic trait in sea snakes. The movement of tail in response to light detection via the skin (‘tail phototaxis’) is a sensory trait shared by aquatic vertebrates with secretive habits, elongate bodies and paddle-shaped tails, i.e. hagfish, lamprey, aquatic amphibians and sea snakes. I conducted behavioural tests in eight species of sea snakes, developing a preliminary hypothesis for the evolutionary origin of this trait within a small clade of Aipysurus sea snakes. I also quantified tail damage in museum specimens to test whether the probability of sustaining tail injuries is influenced by tail phototactic ability in snakes. I then profiled skin transcriptomes of phototactic snakes to identify candidate phototaxis genes, which can be used to understand the parallel evolution of this trait among vertebrates. This thesis provides the basis for future research on the sensory ecology and evolution of marine snakes. The integrative methods employed speaks to power of these approaches in resolving fundamental questions in evolutionary biology, particularly how novel traits can arise from existing variation.Thesis (Ph.D.) -- University of Adelaide, School of Biological Sciences, 201

Drinking by sea snakes from oceanic freshwater lenses at first rainfall ending seasonal drought

Acquisition of fresh water (FW) is problematic for FW-dependent animals living in marine environments that are distant from sources of FW associated with land. Knowledge of how marine vertebrates respond to oceanic rainfall, and indeed the drinking responses of vertebrates generally following drought, is extremely scant. The Yellow-bellied Sea Snake (Hydrophis platurus) is the only pelagic species of squamate reptile and ranges across the Indo-Pacific oceans, having one of the largest geographic distributions of any vertebrate species. It requires FW and dehydrates at sea during periods of drought. Here we report drinking behaviors of sea snakes precisely at the transition from dry to wet season when rainfall first impacted the ocean following 6 months of seasonal drought. We show that the percentage of sea snakes that voluntarily drank FW in the laboratory when captured over eight successive days decreased from 80% to 13% before and after rainfall commenced, respectively. The percentage of snakes that drank immediately following capture exhibited a significant linear decline as the earliest rains of the wet season continued. Drinking by snakes indicates thirst related to dehydration, and thus thirsty snakes must have dehydrated during the previous six months of drought. Hence, the progressive decline in percentage of thirsty snakes indicates they were drinking from FW lenses associated with the first rainfall events of the wet season. These data reinforce the importance of accessing oceanic FW from precipitation, with implications for survival and distribution of pelagic populations that might be subjected to intensifying drought related to climate change

Evolution of Three-Finger Toxin Genes in Neotropical Colubrine Snakes (Colubridae)

Snake venom research has historically focused on front-fanged species (Viperidae and Elapidae), limiting our knowledge of venom evolution in rear-fanged snakes across their ecologically diverse phylogeny. Three-finger toxins (3FTxs) are a known neurotoxic component in the venoms of some rear-fanged snakes (Colubridae: Colubrinae), but it is unclear how prevalent 3FTxs are both in expression within venom glands and more broadly among colubrine species. Here, we used a transcriptomic approach to characterize the venom expression profiles of four species of colubrine snakes from the Neotropics that were dominated by 3FTx expression (in the genera Chironius, Oxybelis, Rhinobothryum, and Spilotes). By reconstructing the gene trees of 3FTxs, we found evidence of putative novel heterodimers in the sequences of Chironius multiventris and Oxybelis aeneus, revealing an instance of parallel evolution of this structural change in 3FTxs among rear-fanged colubrine snakes. We also found positive selection at sites within structural loops or “fingers” of 3FTxs, indicating these areas may be key binding sites that interact with prey target molecules. Overall, our results highlight the importance of exploring the venoms of understudied species in reconstructing the full evolutionary history of toxins across the tree of life

Learned recognition of brood parasitic cuckoos in the superb fairy-wren Malurus cyaneus

Cuckoo hosts defend themselves against parasitism by means of mobbing, egg rejection, and chick rejection. However, each of these defenses is prone to costly recognition errors, and hosts are therefore more likely to deploy these defenses if they observ

A guide for optimal iodine staining and high- throughput diceCT scanning in snakes

Diffusible iodine- based contrast- enhanced computed tomography (diceCT) visualizes soft tissue from micro- CT (µCT) scans of specimens to uncover internal features and natural history information without incurring physical damage via dissection. Unlike hard- tissue imaging, taxonomic sampling within diceCT datasets is currently limited. To initiate best practices for diceCT in a nonmodel group, we outline a guide for staining and high- throughput µCT scanning in snakes. We scanned the entire body and one region of interest (i.e., head) for 23 specimens representing 23 species from the clades Aniliidae, Dipsadinae, Colubrinae, Elapidae, Lamprophiidae, and Viperidae. We generated 82 scans that include 1.25% Lugol’s iodine stained (soft tissue) and unstained (skeletal) data for each specimen. We found that duration of optimal staining time increased linearly with body size; head radius was the best indicator. Postreconstruction of scans, optimal staining was evident by evenly distributed grayscale values and clear differentiation among soft- tissue anatomy. Under and over stained specimens produced poor contrast among soft tissues, which was often exacerbated by user bias during - digital dissections- (i.e., segmentation). Regardless, all scans produced usable data from which we assessed a range of downstream analytical applications within ecology and evolution (e.g., predator- prey interactions, life history, and morphological evolution). Ethanol destaining reversed the known effects of iodine on the exterior appearance of physical specimens, but required substantially more time than reported for other destaining methods. We discuss the feasibility of implementing diceCT techniques for a new user, including approximate financial and temporal commitments, required facilities, and potential effects of staining on specimens. We present the first high- throughput workflow for full- body skeletal and diceCT scanning in snakes, which can be generalized to any elongate vertebrates, and increases publicly available diceCT scans for reptiles by an order of magnitude.We present the first high- throughput workflow for full- body skeletal and soft- tissue (dice) CT scans in preserved snakes. These methods increase publicly available diceCT scans for reptiles by an order of magnitude and can be generalized to any elongate vertebrates.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/170293/1/ece37467.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/170293/2/ece37467_am.pd

Data for: Shape and size variation in elapid snake fangs, and the effects of phylogeny and diet

 DietRates_BEAST.zip contains: DietRates_con.tre DietRates_con.tre.pdf DietRates.xml LeeEtAl.tree GM_data_and_code.zip contains: Elapid fangs analyses.Rproj Elapid fangs analyses.R digit.curves.ES.r Diet.csv disparity.csv gpa.csv sliders.csv usrMat.anterior.csv usrMat.lateral.csv  Dem_ves.ply landmark data for each species as .nts formatted files (x70) </p

First records of sea snakes (Elapidae: Hydrophiinae) diving to the mesopelagic zone (>200 m)

Viviparous sea snakes (Elapidae: Hydrophiinae) are fully marine reptiles distributed in the tropical and subtropical waters of the Indian and Pacific Oceans. Their known maximum diving depth ranges between 50 and 100 m and this is thought to limit their ecological ranges to shallow habitats. We report two observations, from industry-owned remotely operated vehicles, of hydrophiine sea snakes swimming and foraging at depths of approximately 250 m in the Browse Basin on Australia's North West Shelf, in 2014 and 2017. These observations show that sea snakes are capable of diving to the dim-lit, cold-water mesopelagic zone, also known as the 'twilight' zone. These record-setting dives raise new questions about the thermal tolerances, diving behaviour and ecological requirements of sea snakes. In addition to significantly extending previous diving records for sea snakes, these observations highlight the importance of university-industry collaboration in surveying understudied deep-sea habitats

Divergent Specialization of Simple Venom Gene Profiles among Rear-Fanged Snake Genera (<i>Helicops</i> and <i>Leptodeira</i>, Dipsadinae, Colubridae)

Many venomous animals express toxins that show extraordinary levels of variation both within and among species. In snakes, most studies of venom variation focus on front-fanged species in the families Viperidae and Elapidae, even though rear-fanged snakes in other families vary along the same ecological axes important to venom evolution. Here we characterized venom gland transcriptomes from 19 snakes across two dipsadine rear-fanged genera (Leptodeira and Helicops, Colubridae) and two front-fanged genera (Bothrops, Viperidae; Micrurus, Elapidae). We compared patterns of composition, variation, and diversity in venom transcripts within and among all four genera. Venom gland transcriptomes of rear-fanged Helicops and Leptodeira and front-fanged Micrurus are each dominated by expression of single toxin families (C-type lectins, snake venom metalloproteinase, and phospholipase A2, respectively), unlike highly diverse front-fanged Bothrops venoms. In addition, expression patterns of congeners are much more similar to each other than they are to species from other genera. These results illustrate the repeatability of simple venom profiles in rear-fanged snakes and the potential for relatively constrained venom composition within genera

Future Directions in the Research and Management of Marine Snakes

Marine snakes represent the most speciose group of marine reptiles and are a significant component of reef and coastal ecosystems in tropical oceans. Research on this group has historically been challenging due to the difficulty in capturing, handling, and keeping these animals for field- and lab-based research. Inexplicable declines in marine snake populations across global hotspots have highlighted the lack of basic information on this group and elevated multiple species as conservation priorities. With the increased interest in research on marine snakes, we conducted a systematic survey of experts to identify twenty key questions that can direct future research. These questions are framed across a wide array of scientific fields to produce much-needed information relevant to the conservation and management of marine snakes