Eliciting conditioned taste aversion in lizards: Live toxic prey are more effective than scent and taste cues alone

© 2016 International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd Conditioned taste aversion (CTA) is an adaptive learning mechanism whereby a consumer associates the taste of a certain food with symptoms caused by a toxic substance, and thereafter avoids eating that type of food. Recently, wildlife researchers have employed CTA to discourage native fauna from ingesting toxic cane toads (Rhinella marina), a species that is invading tropical Australia. In this paper, we compare the results of 2 sets of CTA trials on large varanid lizards (“goannas,” Varanus panoptes). One set of trials (described in this paper) exposed recently-captured lizards to sausages made from cane toad flesh, laced with a nausea-inducing chemical (lithium chloride) to reinforce the aversion response. The other trials (in a recently-published paper, reviewed herein) exposed free-ranging lizards to live juvenile cane toads. The effectiveness of the training was judged by how long a lizard survived in the wild before it was killed (fatally poisoned) by a cane toad. Both stimuli elicited rapid aversion to live toads, but the CTA response did not enhance survival rates of the sausage-trained goannas after they were released into the wild. In contrast, the goannas exposed to live juvenile toads exhibited higher long-term survival rates than did untrained conspecifics. Our results suggest that although it is relatively easy to elicit short-term aversion to toad cues in goannas, a biologically realistic stimulus (live toads, encountered by free-ranging predators) is most effective at buffering these reptiles from the impact of invasive toxic prey

Could biodiversity loss have increased Australia’s bushfire threat

Ecosystem engineers directly or indirectly affect the availability of resources through changing the physical state of biotic and/or abiotic materials. Fossorial ecosystem engineers have been hypothesized as affecting fire behaviour through altering litter accumulation and breakdown, however, little evidence of this has been shown to date. Fire is one of the major ecological processes affecting biodiversity globally. Australia has seen the extinction of 29 of 315 terrestrial mammal species in the last 200 years and several of these species were ecosystem engineers whose fossorial actions may increase the rate of leaf litter breakdown. Thus, their extinction may have altered the rate of litter accumulation and therefore fire ignition potential and rate of spread. We tested whether a reduction in leaf litter was associated with sites where mammalian ecosystem engineers had been reintroduced using a pair-wise, cross-fence comparison at sites spanning the Australian continent. At Scotia (New South Wales), Karakamia (Western Australia) and Yookamurra (South Australia) sanctuaries, leaf litter mass ( 24%) and percentage cover of leaf litter ( 3%) were significantly lower where reintroduced ecosystem engineers occurred compared to where they were absent, and fire behaviour modelling illustrated this has substantial impacts on flame height and rate of spread. This result has major implications for fire behaviour and management globally wherever ecosystem engineers are now absent as the reduced leaf litter volumes where they occur will lead to decreased flame height and rate of fire spread. This illustrates the need to restore the full suite of biodiversity globally.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1469-17952017-12-31hb2016Centre for Wildlife Managemen

The implications of biodiversity loss for the dynamics of wildlife in Australia

Our study aimed to identify the broad effects of native fossorial species on leaf litter, and make inferences about their mechanistic influence on fire behavior using simulation models (Hayward et al., 2016). This conceptual link has long been hypothesized, but here we present empirical evidence to support it; our results suggest that native fossorial mammals have fire-suppressive effects because their activity results in higher levels of litter decomposition, and a reduced fuel load across the landscape. The expert commentaries build on this study and raise pertinent points for further consideration.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1469-17952017-12-31hb2016Centre for Wildlife Managemen

New weapons in the toad toolkit: A review of methods to control and mitigate the biodiversity impacts of invasive cane toads (rhinella marina)

© 2017 by The University of Chicago Press. All rights reserved. Our best hope of developing innovative methods to combat invasive species is likely to come from the study of high-profile invaders that have attracted intensive research not only into control, but also basic biology. Here we illustrate that point by reviewing current thinking about novel ways to control one of the world’s most well-studied invasions: that of the cane toad in Australia. Recently developed methods for population suppression include more effective traps based on the toad’s acoustic and pheromonal biology. New tools for containing spread include surveillance technologies (e.g., eDNA sampling and automated call detectors), as well as landscape-level barriers that exploit the toad’s vulnerability to desiccation— a strategy that could be significantly enhanced through the introduction of sedentary, rangecore genotypes ahead of the invasion front. New methods to reduce the ecological impacts of toads include conditioned taste aversion in free-ranging predators, gene banking, and targeted gene flow. Lastly, recent advances in gene editing and gene drive technology hold the promise of modifying toad phenotypes in ways that may facilitate control or buffer impact. Synergies between these approaches hold great promise for novel and more effective means to combat the toad invasion and its consequent impacts on biodiversity

The ecological and life history correlates of boldness in free-ranging lizards

In many animal populations, individuals exhibit repeatable behavioral traits across a range of contexts, and similarly, individuals differ in ecological traits such as habitat use, home range sizes, growth rates, and mating success. However, links between an individual\u27s positions on behavioral vs. ecological axes of variation remain relatively unstudied in the wild. In the course of fieldwork on a remote floodplain in tropical Australia, we quantified boldness and ecological traits in 86 free-ranging (radio-tracked) monitor lizards (Varanus panoptes). These large (up to 7 kg) lizards exhibited a spectrum of boldness, as reflected in correlated scores of responses to approach, handling, and novel prey. Bolder lizards had larger core home ranges and higher mating success and spent more time in areas of high predator abundance, and their seasonal regimes of predation-induced mortality differed from those of shyer lizards. Thus, behavioral differences among lizards underpin much of the variation in ecological traits and individual fitness within this population. Analyses of ecology and microevolution in natural populations cannot afford to ignore the complex covariation between behavior, ecology, and evolution in the wild

Genetic influence on scar height and pliability after burn injury in individuals of European ancestry: A prospective cohort study

After similar extent of injury there is considerable variability in scarring between individuals, in part due to genetic factors. This study aimed to identify genetic variants associated with scar height and pliability after burn injury. An exome-wide array association study and gene pathway analysis were performed on a prospective cohort of 665 patients treated for burn injury. Outcomes were scar height (SH) and scar pliability (SP) sub-scores of the modified Vancouver Scar Scale (mVSS). DNA was genotyped using the Infinium® HumanCoreExome-24 BeadChip. Associations between genetic variants (single nucleotide polymorphisms) and SH and SP were estimated using an additive genetic model adjusting for age, sex, number of surgical procedures and % total body surface area of burn in subjects of European ancestry. No individual genetic variants achieved the cut-off threshold of significance. Gene regions were analysed for spatially correlated single nucleotide polymorphisms and significant regions identified using comb-p software. This gene list was subject to gene pathway analysis to find which biological process terms were over-represented. Using this approach biological processes related to the nervous system and cell adhesion were the predominant gene pathways associated with both SH and SP. This study suggests genes associated with innervation may be important in scar fibrosis. Further studies using similar and larger datasets will be essential to validate these findings

Invasive species as drivers of evolutionary change: cane toads in tropical Australia

The arrival of an invasive species can have wide-ranging ecological impacts on native taxa, inducing rapid evolutionary responses in ways that either reduce the invader's impact or exploit the novel opportunity that it provides. The invasion process itself can cause substantial evolutionary shifts in traits that influence the invader's dispersal rate (via both adaptive and non-adaptive mechanisms) and its ability to establish new populations. I briefly review the nature of evolutionary changes likely to be set in train by a biological invasion, with special emphasis on recent results from my own research group on the invasion of cane toads (Rhinella marina) through tropical Australia. The toads’ invasion has caused evolutionary changes both in the toads and in native taxa. Many of those changes are adaptive, but others may result from non-adaptive evolutionary processes: for example, the evolved acceleration in toad dispersal rates may be due to spatial sorting of dispersal-enhancing genes, rather than fitness advantages to faster-dispersing individuals. Managers need to incorporate evolutionary dynamics into their conservation planning, because biological invasions can affect both the rates and the trajectories of evolutionary change

Curbing catastrophe: ecology and conservation of the Yellow-spotted Monitor (Varanus panoptes) in tropical Australia

Worldwide, one of the most catastrophic impacts of invasive species is to imperil populations of apex predators, thereby inducing trophic cascades that can substantially modify ecosystem function. Management strategies generally focus on controlling the invader; but we can, instead, manipulate the behavioural response of vulnerable native taxa to render them more resilient to the invader’s arrival. In Australia, large varanid lizards (“goannas”) are fatally poisoned when they ingest invasive cane toads (Rhinella marina). As a result, the spread of cane toads has caused catastrophic population declines in these important predators. My PhD investigated the potential for an adaptive learning mechanism, Conditioned Taste Aversion (CTA), to conserve populations of tropical Australia’s largest lizard, the Yellow-spotted Monitor (Varanus panoptes). Ahead of the cane toad invasion, I exposed free-ranging goannas to small, live, non-lethal toads to assess the influence of training on lizard survival post-invasion. After cane toads arrived, trained goannas had significantly higher survival than their untrained (control) counterparts. I investigated mechanisms underpinning CTA to clarify how best to apply it in the field; for example, Yellow-spotted Monitors develop stronger aversions to live prey than sausages laced with chemicals, and an individual’s behavioural phenotype influences the effectiveness of CTA. I documented a behavioural syndrome that correlates with aspects of an individual’s ecology, life history and microevolutionary fitness. Furthermore, some individuals are inherently toad-averse; therefore some goannas (or populations) may not need CTA training. This behavioural diversity demonstrates how inter-individual variation can shape a population’s response to a novel pressure. Identifying and exploiting pre-existing behavioural mechanisms to deal with new challenges holds great promise for amplifying the tools available for conservation efforts globally