Simon Clulow

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

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, range-core 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.

Cryptic and Complex Nesting in the Yellow-Spotted Monitor, Varanus panoptes

Abstract Despite the general importance of nest site choice in reproductive success in taxa with little or no parental care, little is known for reptiles other than turtles. Here we report on the nesting ecology of the Yellow-Spotted Monitor, Varanus panoptes, a large tropical lizard that utilizes warrens (concentrated groups of burrows) in northern Australia. We used radio-telemetry, remote photography, and the complete excavation of a warren to test the hypotheses that 1) warrens are used by multiple individual V. panoptes; and if so, 2) they are used for communal nesting; or alternatively 3) they are used for communal estivation during the dry season. At least six individual V. panoptes utilized the warren system including four females and two males, and burrows were excavated by both sexes. Excavation of the warren revealed no estivating lizards at a time when four radio-telemetered V. panoptes had begun estivation. However, we found two nests in the warren, indicative of either communal nesting or multiple clutches of the same female. Nests were deeper than that recorded for any other reptile and were structurally complex. We discuss the implications of the depth and structure of the nesting burrow for the thermal and hydric environment of the eggs and for hatchling emergence. The warrens usage by multiple individuals raises the possibility that the severe declines in V. panoptes caused by invasive Cane Toads (Bufo marinus) may have important implications for the V. panoptes social structure.

Cryopreservation and other assisted reproductive technologies for the conservation of threatened amphibians and reptiles: bringing the ARTs up to speed

Amphibians and reptiles are experiencing serious declines, with the number of threatened species and extinctions growing rapidly as the modern biodiversity crisis unfolds. For amphibians, the panzootic of chytridiomycosis is a major driver. For reptiles, habitat loss and harvesting from the wild are key threats. Cryopreservation and other assisted reproductive technologies (ARTs) could play a role in slowing the loss of amphibian and reptile biodiversity and managing threatened populations through genome storage and the production of live animals from stored material. These vertebrate classes are at different stages of development in cryopreservation and other ARTs, and each class faces different technical challenges arising from the separate evolutionary end-points of their reproductive biology. For amphibians, the generation of live offspring from cryopreserved spermatozoa has been achieved, but the cryopreservation of oocytes and embryos remains elusive. With reptiles, spermatozoa have been cryopreserved in a few species, but no offspring from cryopreserved spermatozoa have been reported, and the generation of live young from AI has only occurred in a small number of species. Cryopreservation and ARTs are more developed and advanced for amphibians than reptiles. Future work on both groups needs to concentrate on achieving proof of concept examples that demonstrate the use of genome storage and ARTs in successfully recovering threatened species to increase awareness and support for this approach to conservation.

Optimization, validation and efficacy of the phytohaemagglutinin inflammation assay for use in ecoimmunological studies of amphibians

Amphibians are in the midst of an extinction crisis, yet there are few tools available to study amphibian immunocompetence under conditions of changing environments, disease and stress. We developed, validated and optimised a practical assay for studying amphibian immunocompetence and tested its efficacy in a real-world scenario of varying environmental conditions.

Optimisation of an oviposition protocol employing human chorionic and pregnant mare serum gonadotropins in the Barred Frog Mixophyes fasciolatus (Myobatrachidae)

BackgroundProtocols for the hormonal induction of ovulation and oviposition are essential tools for managing threatened amphibians with assisted reproduction, but responses vary greatly between species and even broad taxon groups. Consequently, it is necessary to assess effectiveness of such protocols in representative species when new taxa become targets for induction. The threatened genus Mixophyes (family Myobatrachidae) has amongst the highest proportion of endangered species of all the Australian amphibians. This study developed and optimised the induction of oviposition in a non-threatened member of this taxon, the great barred frog (Mixophyes fasciolatus).MethodsGravid female M. fasciolatus were induced to oviposit on one or more occasions by administration of human chorionic gonadotropin (hCG) with or without priming with pregnant mare serum gonadotropin (PMSG). Treatments involved variations in hormone doses and combinations (administered via injection into the dorsal lymph sacs), and timing of administration. Pituitary homogenates from an unrelated bufonid species (Rhinella marina) were also examined with hCG.ResultsWhen injected alone, hCG (900 to 1400 IU) induced oviposition. However, priming with two time dependent doses of PMSG (50 IU, 25 IU) increased responses, with lower doses of hCG (200 IU). Priming increased response rates in females from around 30% (hCG alone) to more than 50% (p = 0.035), and up to 67%. Increasing the interval between the first PMSG dose and first hCG dose from 3 to 6 days also produced significant improvement (p<0.001). Heterologous pituitary extracts administered with hCG were no more effective than hCG alone (p = 0.628).ConclusionsThis study found that M. fasciolatus is amongst the few amphibian species (including Xenopus (Silurana) and some bufonids) that respond well to the induction of ovulation utilising mammalian gonadotropins (hCG). The optimal protocol for M. fasciolatus involved two priming doses of PMSG (50 IU and 25 IU) administered at 6 and 4 days respectively, prior to two doses of hCG (100 IU), 24 hours apart. This study is also the first to demonstrate in an amphibian species that responds to mammalian gonadotropins that an increase in the ovulation rate occurs after priming with a gonadotropin (PMSG) with FSH activity.

Finding a place to live: conspecific attraction affects habitat selection in juvenile green and golden bell frogs

Conspecific attraction plays an important role in habitat selection of several taxa and can affect and determine distribution patterns of populations. The behaviour is largely studied and widespread among birds, but in amphibians, its occurrence seems limited to breeding habitats of adults and gregarious tadpoles. The Australian green and golden bell frogs (Litoria aurea) have suffered considerable shrinking of their original distribution in south-eastern Australia since the 1970s. Currently, with only about 40 populations remaining, the species is considered nationally threatened. In natural conditions, these frogs are aggregated in the landscape and do not seem to occupy all suitable ponds within the occurrence area. To date, studies focusing on the frogs’ habitat have failed in finding a general habitat feature that explains current or past occupancy. This led us to the hypothesis that social cues may play a key role in habitat selection in this species. Using two choice experiments, we tested the preference of juvenile green and golden bell frogs for habitats containing cues of conspecifics of similar size versus habitats without conspecific cues. Tested frogs did not show a preference for habitats containing only scent from conspecifics but did prefer habitats where conspecifics were present. Our results show that conspecific attraction is a determining factor in juvenile green and golden bell frog habitat selection. To our knowledge, this is the first time the behaviour is shown to occur in juvenile frogs in the habitat selection context. From a conservation management point of view, the behaviour may help to explain the failure of reintroductions to areas where the frogs have been extinct, and the non-occupation of suitable created habitats in areas where they still inhabit and develop appropriated management strategies.

Deliberate Insectivory by the Fruit Bat Pteropus poliocephalus by Aerial Hunting

The diet of the Old World fruit bats (Pteropodidae) has been well studied with a large inventory of nectar and fruit bearing plant species known to be consumed. It is far less certain, however, whether pteropodid bats intentionally supplement their diet with insects in a similar fashion to many other frugivorous and nectivorous species, including some New World fruit bats of the family Phyllostomidae. Several reports of pteropodid bats consuming insects in captivity exist, and insects have been found in the faeces and digestive tracts of some wild pteropodid bats, although their ingestion was initially thought to be accidental. However, more recent observations of large insects in faeces of wild bats, coupled with two reports (one anecdotal) of observed intentional insectivory in the wild, suggest that intentional insectivory by pteropodid bats may be more common than previously thought. In addition, reports of intentional insectivory to date have been of bats catching insects from a stationary position, and a large question still remains as to the ability of pteropodid bats to catch insects in flight without the use of laryngeal echolocation. Here, we report on an observation of intentional insectivory by a group of grey-headed flying foxes (Pteropus poliocephalus) actively preying on, and consuming, numerous (> 20) cicadas (Psaltoda sp.) by aerial hunting in southeastern Australia. We conclude that deliberate insectivory is likely an evolved and fixed component of the grey-headed flying foxs dietary ecology, and suggest that this may be an adaptation more common among pteropodid bats than previously thought.

Amphibians on the brink

Preemptive policies can protect amphibians from devastating fungal diseases Over the past three decades, the emergence of a globalized pandemic lineage of chytrid fungus (Batrachochytrium dendrobatidis) has caused declines of amphibian species in Central America, Europe, Australia, and North America (see the figure). By 2004, where documented, 43.2% of amphibian species globally experienced some level of population decrease, and the amphibian chytrid fungus was identified as a major contributing factor for hundreds of species (1). The recent discovery of a related but functionally distinct chytrid fungus, Batrachochytrium salamandrivorans, that has begun exterminating salamanders in Europe (2) fulfills predictions that further infectious fungal pathogens will continue to emerge (3). The threat of chytrids and similar fungal pathogens to areas where they have not yet emerged—for example, in New Guinea—is of critical conservation concern.

Salinity tolerances of two Australian freshwater turtles, Chelodina expansa and Emydura macquarii (Testudinata: Chelidae)

Two species of Australian freshwater turtle were submerged in either water of 0‰ or 15‰ over 50 days. Turtles in 15‰ water reduced feeding and had raised plasma ionic concentrations of sodium, chloride, urea and uric acid to decrease dehydration and enable survival.

Predator presence and vegetation density affect capture rates and detectability of Litoria aurea tadpoles: wide-ranging implications for a common survey technique

Trapping is a common sampling technique used to estimate fundamental population metrics of animal species such as abundance, survival and distribution. However, capture success for any trapping method can be heavily influenced by individuals’ behavioural plasticity, which in turn affects the accuracy of any population estimates derived from the data. Funnel trapping is one of the most common methods for sampling aquatic vertebrates, although, apart from fish studies, almost nothing is known about the effects of behavioural plasticity on trapping success. We used a full factorial experiment to investigate the effects that two common environmental parameters (predator presence and vegetation density) have on the trapping success of tadpoles. We estimated that the odds of tadpoles being captured in traps was 4.3 times higher when predators were absent compared to present and 2.1 times higher when vegetation density was high compared to low, using odds ratios based on fitted model means. The odds of tadpoles being detected in traps were also 2.9 times higher in predator-free environments. These results indicate that common environmental factors can trigger behavioural plasticity in tadpoles that biases trapping success. We issue a warning to researchers and surveyors that trapping biases may be commonplace when conducting surveys such as these, and urge caution in interpreting data without consideration of important environmental factors present in the study system. Left unconsidered, trapping biases in capture success have the potential to lead to incorrect interpretations of data sets, and misdirection of limited resources for managing species.