Ruchira Somaweera

Genus-level phylogeny of snakes reveals the origins of species richness in Sri Lanka

Snake diversity in the island of Sri Lanka is extremely high, hosting at least 89 inland (i.e., non-marine) snake species, of which at least 49 are endemic. This includes the endemic genera Aspidura, Balanophis, Cercaspis, Haplocercus, and Pseudotyphlops, which are of uncertain phylogenetic affinity. We present phylogenetic evidence from nuclear and mitochondrial loci showing the relationships of 40 snake species from Sri Lanka (22 endemics) to the remaining global snake fauna. To determine the phylogenetic placement of these species, we create a molecular dataset containing 10 genes for all global snake genera, while also sampling all available species for genera with endemic species occurring in Sri Lanka. Our sampling comprises five mitochondrial genes (12S, 16S, cyt-b, ND2, and ND4) and five nuclear genes (BDNF, c-mos, NT3 RAG-1, and RAG-2), for a total of up to 9582bp per taxon. We find that the five endemic genera represent portions of four independent colonizations of Sri Lanka, with Cercaspis nested within Colubrinae, Balanophis in Natricinae, Pseudotyphlops in Uropeltidae, and that Aspidura+Haplocercus represents a distinct, ancient lineage within Natricinae. We synonymize two endemic genera that render other genera paraphyletic (Haplocercus with Aspidura, and Cercaspis with Lycodon), and discover that further endemic radiations may be present on the island, including a new taxon from the blindsnake family Typhlopidae, suggesting a large endemic radiation. Despite its small size relative to other islands such as New Guinea, Borneo, and Madagascar, Sri Lanka has one of the most phylogenetically diverse island snake faunas in the world, and more research is needed to characterize the islands biodiversity, with numerous undescribed species in multiple lineages.

The Role of Predation in Shaping Crocodilian Natural History

Abstract: Although adult crocodilians have few predators (mostly humans and other crocodilians), hatchlings and eggs are killed and consumed by a diverse array of invertebrates, fishes, anurans, reptiles, birds, and mammals. We review published literature to evaluate the incidence of predation in crocodilian populations, and the implications of that mortality for crocodilian life-history evolution. Presumably because predation is size-dependent, small-bodied crocodilian taxa appear to be more vulnerable to predation (across a range of life stages) than are larger-bodied species. Several features of crocodilian biology likely reflect adaptations to reducing vulnerability to predation. For example, the threat of predation may have influenced the evolution of traits such as nest-site selection, maternal care of eggs and hatchlings, crèche behavior in hatchlings, and cryptic coloration and patterning. Even for such large and superficially invulnerable taxa such as crocodilians, the avoidance of predation appears to have been a significant selective force on behavior, morphology, and ecology.

Australian Freshwater Crocodiles (Crocodylus johnstoni) Transport Their Hatchlings to the Water

Abstract Remote video cameras recorded eight instances of nest excavation and parental transport of offspring to the water by Australian freshwater crocodiles (Crocodylus johnstoni) inhabiting Lake Argyle in northwestern Australia. Parental assistance during hatching appears to be vital for successful emergence of hatchlings from nests in this area.

Assessing the potential impact of invasive cane toads on a commercial freshwater fishery in tropical Australia

Context The toxins produced by cane toads (Rhinella marina) are fatal to many Australian predators that ingest these invasive anurans. To date, the potential economic impact of the cane toad invasion has attracted little attention. Toads have recently arrived at a large impoundment (Lake Argyle) in north-eastern Western Australia, that supports a commercial fishery for silver cobbler (shovel-nosed catfish, Arius midgleyi), raising concern that the toads may inflict significant economic damage by killing fish. Aims Our research aimed to clarify the vulnerability of silver cobblers to the eggs and larvae of cane toads by determining (a) whether catfish are adversely affected if they prey on toad eggs or tadpoles, and (b) whether surviving catfish learn to avoid cane toad eggs and tadpoles in subsequent encounters. Methods We conducted laboratory feeding trials to examine feeding responses of catfish to cane toad eggs and tadpoles in early and late developmental stages. Fish that survived exposure to toad eggs and/or tadpoles were re-tested with potential prey of the same sizes and developmental stages four days later. Key results Our laboratory trials confirmed that some catfish eat toad eggs and die; but most catfish avoided the eggs. Catfish readily consumed toad tadpoles at both early and late developmental stages, but without experiencing mortality; and soon learned not to consume this toxic new prey type. Conclusions and implications Despite potential frequent episodes of mortality of small numbers of catfish during the wet season, the overall impacts of cane toads on the Lake Argyle fishery likely will be minimal.

Determinants of Habitat Selection by Hatchling Australian Freshwater Crocodiles

Animals almost always use habitats non-randomly, but the costs and benefits of using specific habitat types remain unknown for many types of organisms. In a large lake in northwestern Australia (Lake Argyle), most hatchling (<12-month-old) freshwater crocodiles (Crocodylus johnstoni) are found in floating vegetation mats or grassy banks rather than the more widely available open banks. Mean body sizes of young crocodiles did not differ among the three habitat types. We tested four potential explanations for non-random habitat selection: proximity to nesting sites, thermal conditions, food availability, and exposure to predation. The three alternative habitat types did not differ in proximity to nesting sites, or in thermal conditions. Habitats with higher food availability harboured more hatchlings, and feeding rates (obtained by stomach-flushing of recently-captured crocodiles) were highest in such areas. Predation risk may also differ among habitats: we were twice as likely to capture a crocodile after seeing it in open-bank sites than in the other two habitat types. Thus, habitat selection of hatchling crocodiles in this system may be driven both by prey availability and by predation risk.

A catalogue and systematic overview of the shield-tailed snakes (Serpentes: Uropeltidae)

ABSTRACT We present a catalogue and systematic overview of Uropeltidae Müller, 1832 based on both new and previously published molecular and morphological data, and a new molecular phylogenetic analysis. We support the monophyly and distinctiveness of Brachyophidium Wall, 1921, Melanophidium Günther, 1864, Platyplectrurus Günther, 1868, Pseudoplectrurus Boulenger, 1890, and Teretrurus Beddome, 1886. We move Uropeltis melanogaster (Gray, 1858), U. phillipsi (Nicholls, 1929), and Pseudotyphlops Schlegel, 1839 to Rhinophis Hemprich, 1820, and re-name Pseudotyphlops philippinus (Müller, 1832) as R. saffragamus (Kelaart, 1853), and U. smithi Gans, 1966 as U. grandis (Beddome, 1867). Thanks to these changes, the taxonomy of all these genera is based on monophyletic entities. Diagnoses based on meristic and mensural characters for external and internal anatomy are provided for the family and all genera, and accounts are given for all currently recognized species, summarizing known morphological variation. We note several taxa that continue to be of uncertain phylogenetic affinity, and outline necessary future studies of variation in systematically valuable characters such as rostral and tail morphology. Cryptic variation is likely present in many species, and additional collection of specimens and DNA-sequence data will likely be needed to provide conclusive resolution for remaining taxonomic issues. Numerous questions remain for the systematics of Uropeltidae, and we hope that this study will provide a platform for ongoing research into the group, including the description of cryptic species, clarifying the phylogenetic placement of some remaining taxa, and quantifying the range of intra- and inter-specific variation in crucial morphological characters.