Chris Hay

Rapid Radiations and the Race to Redundancy: An Investigation of the Evolution of Australian Elapid Snake Venoms.

Australia is the stronghold of the front-fanged venomous snake family Elapidae. The Australasian elapid snake radiation, which includes approximately 100 terrestrial species in Australia, as well as Melanesian species and all the world’s true sea snakes, may be less than 12 million years old. The incredible phenotypic and ecological diversity of the clade is matched by considerable diversity in venom composition. The clade’s evolutionary youth and dynamic evolution should make it of particular interest to toxinologists, however, the majority of species, which are small, typically inoffensive, and seldom encountered by non-herpetologists, have been almost completely neglected by researchers. The present study investigates the venom composition of 28 species proteomically, revealing several interesting trends in venom composition, and reports, for the first time in elapid snakes, the existence of an ontogenetic shift in the venom composition and activity of brown snakes (Pseudonaja sp.). Trends in venom composition are compared to the snakes’ feeding ecology and the paper concludes with an extended discussion of the selection pressures shaping the evolution of snake venom.

Correlation between ontogenetic dietary shifts and venom variation in Australian brown snakes ( Pseudonaja )

Venom is a key evolutionary trait, as evidenced by its widespread convergent evolution across the animal kingdom. In an escalating prey-predator arms race, venoms evolve rapidly to guarantee predatory or defensive success. Variation in venom composition is ubiquitous among snakes. Here, we tested variation in venom activity on substrates relevant to blood coagulation among Pseudonaja (brown snake) species, Australian elapids responsible for the majority of medically important human envenomations in Australia. A functional approach was employed to elucidate interspecific variation in venom activity in all nine currently recognised species of Pseudonaja. Fluorometric enzymatic activity assays were performed to test variation in whole venom procoagulant activity among species. Analyses confirmed the previously documented ontogenetic shift from non-coagulopathic venom in juveniles to coagulopathic venom as adults, except for the case of P. modesta, which retains non-coagulopathic venom as an adult. These shifts in venom activity correlate with documented ontogenetic shifts in diet among brown snakes from specialisation on reptilian prey as juveniles (and throughout the life cycle of P. modesta), to a more generalised diet in adults that includes mammals. The results of this study bring to light findings relevant to both clinical and evolutionary toxinology.

Catch a tiger snake by its tail: Differential toxicity, co-factor dependence and antivenom efficacy in a procoagulant clade of Australian venomous snakes

A paradigm of venom research is adaptive evolution of toxins as part of a predator-prey chemical arms race. This study examined differential co-factor dependence, variations relative to dietary preference, and the impact upon relative neutralisation by antivenom of the procoagulant toxins in the venoms of a clade of Australian snakes. All genera were characterised by venoms rich in factor Xa which act upon endogenous prothrombin. Examination of toxin sequences revealed an extraordinary level of conservation, which indicates that adaptive evolution is not a feature of this toxin type. Consistent with this, the venoms did not display differences on the plasma of different taxa. Examination of the prothrombin target revealed endogenous blood proteins are under extreme negative selection pressure for diversification, this in turn puts a strong negative selection pressure upon the toxins as sequence diversification could result in a drift away from the target. Thus this study reveals that adaptive evolution is not a consistent feature in toxin evolution in cases where the target is under negative selection pressure for diversification. Consistent with this high level of toxin conservation, the antivenom showed extremely high-levels of cross-reactivity. There was however a strong statistical correlation between relative degree of phospholipid-dependence and clotting time, with the least dependent venoms producing faster clotting times than the other venoms even in the presence of phospholipid. The results of this study are not only of interest to evolutionary and ecological disciplines, but also have implications for clinical toxinology.

Endless forms most beautiful: the evolution of ophidian oral glands, including the venom system, and the use of appropriate terminology for homologous structures

The differentiated serous-secreting dental glands of caenophidian snakes are diverse in form despite their developmental homology. This variation makes the elucidation of their evolutionary history a complex task. In addition, some authors identify as many as ten discrete types/subtypes of ophidian oral gland. Over the past decade and a half, molecular systematics and toxinology have deepened our understanding of the evolution of these fascinating and occasionally enigmatic structures. This paper includes a comprehensive examination of ophidian oral gland structure and (where possible) function, as well as new data on rictal glands and their associated anatomy. Following this, appropriate use of terminology, especially that pertaining to homologous structures (including the controversial “venom gland” vs “Duvernoy’s gland” debate), is considered. An interpretation of the evolutionary history of the ophidian venom system, drawing on recent results from molecular systematics, toxinology and palaeontology, concludes the paper.

Proteomic and functional variation within black snake venoms (Elapidae: Pseudechis)

Pseudechis (black snakes) is an Australasian elapid snake genus that inhabits much of mainland Australia, with two representatives confined to Papua New Guinea. The present study is the first to analyse the venom of all 9 described Pseudechis species (plus one undescribed species) to investigate the evolution of venom composition and functional activity. Proteomic results demonstrated that the typical Pseudechis venom profile is dominated by phospholipase A2 toxins. Strong cytotoxicity was the dominant function for most species. P. porphyriacus, the most basal member of the genus, also exhibited the most divergent venom composition, being the only species with appreciable amounts of procoagulant toxins. The relatively high presence of factor Xa recovered in P. porphyriacus venom may be related to a predominantly amphibian diet. Results of this study provide important insights to guide future ecological and toxinological investigations.

The Intracultural Actor: Embracing Difference in Theatre Arts Teaching

Embracing difference in theatre arts teaching and training requires pedagogical as well as philosophical adjustments in classrooms and rehearsal rooms. We propose that the unique cultural context of the individual actor is a rich hinterland for discovery and source of power for the student, and outline our intracultural training practice as a starting point for teachers and trainers seeking to engage with cultural and linguistic diversity. The argument of this chapter is divided into three sections. In the first, we consider the insidious impact of “neutrality” (and its synonyms) on actor training. Theatre arts training too often enables the erasure of difference through predicating teaching and learning on an imagined sameness across our student body. We argue that teachers and trainers must instead acknowledge that this sameness is determined by the hegemonic cultural power, and can therefore be wielded as an exclusionary device against students of diverse identities and diasporic heritages. The second section introduces an intracultural training practice: it first summarizes the ideas that have informed the development of our practice, and then sets out its main principles. In the final section of the chapter, we provide some practical suggestions of exercises and activities to begin implementing intracultural practice in class and rehearsal rooms. Across the chapter, our focus is on how our practice can be implemented by others, with specific reference to actor training.