Academic literature on the topic 'Southern corroboree frog (Pseudophryne corroboree)'

Reproductive compatibility and population genetic structure were examined in the corroboree frog, Pseudophryne corroboree, a species restricted to montane and subalpine environments in south-eastern Australia. The species comprises three geographic populations, represented by two morphological forms. Hybridisation experiments showed that the allopatric populations are interfertile, although crosses between the Snowy Mountains population (southern form) and each of the two northern populations (northern form) resulted in a significantly higher number of tadpoles with growth abnormalities. An electrophoretic examination of metamorphlings indicated that there was considerable genetic divergence between the two forms, with several loci approaching fixation of alternate alleles. The Snowy Mountains population also had substantially reduced levels of genetic variation compared to the two northern populations. Although genetic distances generally correlate with geographic distance, the genetic differences between the northern and southern populations form a pronounced step, not explicable by geographic distance alone. These findings have taxonomic implications which should be taken into account when considering the conservation management of this uncommon species.

Abstract Dietary antioxidants can improve escape-response performance in adult vertebrates, but whether juveniles receive similar benefits remains untested. Here, we investigated the effect of two dietary carotenoids (β-carotene and lutein) on the escape-response of juvenile corroboree frogs (Pseudophryne corroboree) at two developmental points (early and late larval development). We found that burst speed was lower during late larval development compared to early larval development, particularly in the low- and high-dose lutein treatments. These findings suggest that performance decreased over time, and was reduced by lutein consumption. At each developmental point we found no treatment effect on escape-response, providing no evidence for carotenoid benefits. A previous study in corroboree frogs demonstrated that carotenoids improved adult escape-response, so our findings suggest that benefits of carotenoids in this species may be life-stage dependent. Continued investigation into how carotenoids influence escape-response at different life-stages will provide insights into mechanistic links between nutrition and behaviour.

The extent of divergence in morphology and colour-pattern between allopatric populations of the corroboree frog, Pseudophyrne corroboree, was assessed over three breeding seasons by examination of eggs, tadpoles and adults throughout the distributional range of the species. Advertisement calls of individuals from each of the populations also were recorded and analysed. The mean size of adults was found to vary considerably between years; however, within any one year individuals from the Snowy Mountains (southern form) were significantly larger than individuals from the Brindabella Range and Fiery Range (northern form), with the differences apparently not simply related to environmental influences. Multivariate analysis of quantitative morphological characters and colour-pattern separated the frogs into two distinct geographic groups corresponding with the northern form and southern form. Analysis of advertisement calls indicated that there were slight differences in the structure of the calls of the two forms, with the main differences being in call duration and number of pulses. These results, combined with the previously described genetic differences, support their recognition as separate species. It is recommended that the name P. corroboree be restricted to the southern form and that the northern form be referred to as P. pengilleyi Wells & Wellington.

Context Translocations are becoming an increasingly important conservation tool to combat rising levels of species extinction. Unfortunately, many translocation efforts fail; yet, the timing and cause of failure often remain unknown. Monitoring individuals in the days and weeks following release can provide valuable information on their capacity to survive this initial hurdle. In Australia, breeding programs have been established for the endangered northern corroboree frog, Pseudophryne pengilleyi, to enable reintroduction to the wild via captive-reared individuals, typically, early life stages such as eggs or juvenile frogs that cannot be monitored via traditional survey methods that target adult frogs (e.g. shout–response). Environmental DNA (eDNA) detects trace amounts of DNA that organisms release into their environment and could provide a means to infer population persistence for wildlife releases and translocations. Aims In the present study, we aim to develop an eDNA assay capable of detecting both sexes of P. pengilleyi across multiple life stages, and use it to monitor their survival. Methods An eDNA assay was developed to target the two corroboree frog species (P. pengilleyi and P. corroboree, the southern corroboree frog) and was tested for its sensitivity and specificity in silico and in vitro. Pseudophryne pengilleyi eggs were released into three naturally occurring ponds and water samples were, subsequently, collected from each pond on several occasions over a period of 78 days. Quantitative polymerase chain reaction was used to detect P. pengilleyi eDNA from water samples. Key Results The developed assay was shown to be sensitive and specific to corroboree frogs. eDNA monitoring of reintroduced P. pengilleyi detected the species’ DNA at three of three release ponds and DNA remained detectable until at least 78 days post-release at two of three ponds. Conclusions We show how the development of a corroboree frog-specific assay allowed us to monitor the post-release survival of P. pengilleyi in naturally occurring pools. Implications eDNA surveys may provide a useful tool to monitor post-release survival of translocated populations in a non-invasive manner, with the potential to identify the timing and causes of failure. Such knowledge can be used to inform the management of translocated populations and future release strategies.

Abstract Many animals hibernate to survive winter conditions, however, arousal from hibernation generates reactive oxygen species (ROS) that can cause oxidative stress. Dietary antioxidants, like carotenoids, may reduce oxidative stress during arousal from hibernation, and assist with post-hibernation recovery and performance. We tested the effect of carotenoid supplementation on exercise performance (escape-response and activity) in southern corroboree frogs (Pseudophryne corroboree) following initial arousal from hibernation (24–48 h post-arousal) and post-recovery (six weeks post-hibernation). Carotenoids did not affect performance following initial arousal. However, carotenoids improved escape-response six weeks post-hibernation, with carotenoid-supplemented frogs hopping faster and further in their first hop than unsupplemented frogs. Carotenoids also affected post-recovery activity, with carotenoid-supplemented frogs being less mobile than unsupplemented frogs. Carotenoids may affect post-hibernation performance by reducing oxidative stress or by increasing diet quality. Our study provides novel evidence for an effect of carotenoids on performance post-hibernation and highlights the importance of nutrition to hibernating organisms.

Context One of the major drivers of the current worldwide amphibian decline and extinction crisis is the spread of the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd). Captive assurance colonies may be the only lifeline for some species. Current antifungal chemotherapies can be effective for clearing infection but may have detrimental side effects. The only non-chemotherapeutic treatment that has been clinically tested is heat, which is impractical for cold-adapted species. The fungus does not survive desiccation, and therefore a plausible alternative non-chemotherapeutic treatment would be a low-humidity regimen. Aims We tested the efficacy of a low-humidity treatment regimen for treating Bd-infected animals of the critically endangered species Pseudophryne corroboree. This species has high tolerance of dry environments, and is thus an ideal candidate for this treatment trial. Methods Forty frogs were exposed to 1 × 106 zoospores. At three weeks after exposure access to water was reduced to once daily for 10 days for 20 animals. Ten of these animals were also rinsed daily with the aim of removing zoospores. Key results The drying regimen neither increased survival nor decreased infection load, and treatment may have hastened mortality. All infected frogs died between 21 and 80 days after exposure, except one untreated frog. Conclusions Our results suggest that a drying regimen is not a viable treatment for chytridiomycosis. Infection may decrease the host’s ability to cope with water stress. Implications The failed drying treatment in P. corroboree suggests that drying is not an appropriate treatment for chytridiomycosis and treatment efforts should be focussed on chemotherapies for cold-adapted species. P. corroboree is a critically endangered species for which chytridiomycosis is the primary cause of decline, yet few experiments have been carried out on this species with regards to chytridiomycosis. All experimental information about this species and disease will benefit the management and protection of the species.

To protect Australian amphibian biodiversity, we have identified and prioritised frog species at an imminent risk of extinction from chytridiomycosis, and devised national management and research priorities for disease mitigation. Six Australian frogs have not been observed in the wild since the initial emergence of chytridiomycosis and may be extinct. Seven extant frog species were assessed as needing urgent conservation interventions because of (1) their small populations and/or ongoing declines throughout their ranges (southern corroboree frog (Pseudophryne corroboree, New South Wales), northern corroboree frog (Pseudophryne pengilleyi, Australian Capital Territory, New South Wales), Baw Baw frog (Philoria frosti, Victoria), Litoria spenceri (spotted tree frog, Victoria, New South Wales), Kroombit tinkerfrog (Taudactylus pleione, Queensland), armoured mist frog (Litoria lorica, Queensland)) or (2) predicted severe decline associated with the spread of chytridiomycosis in the case of Tasmanian tree frog (Litoria burrowsae, Tasmania). For these species, the risk of extinction is high, but can be mitigated. They require increased survey effort to define their distributional limits and to monitor and detect further population changes, as well as well-resourced management strategies that include captive assurance populations. A further 22 frog species were considered at a moderate to lower risk of extinction from chytridiomycosis. Management actions that identify and create or maintain habitat refugia from chytridiomycosis and target other threatening processes such as habitat loss and degradation may be effective in promoting their recovery. Our assessments for some of these species remain uncertain and further taxonomical clarification is needed to determine their conservation importance. Management actions are currently being developed and trialled to mitigate the threat posed by chytridiomycosis. However, proven solutions to facilitate population recovery in the wild are lacking; hence, we prioritise research topics to achieve this aim. Importantly, the effectiveness of novel management solutions will likely differ among species due to variation in disease ecology, highlighting the need for species-specific research. We call for an independent management and research fund of AU$15 million over 5 years to be allocated to recovery actions as determined by a National Chytridiomycosis Working Group of amphibian managers and scientists. Procrastination on this issue will likely result in additional extinction of Australia’s amphibians in the near future.

The documented decline of amphibian populations over the past two decades has increased attention towards amphibian conservation. Much of this attention has been focused on testing hypotheses as to the causal factors of these declines, however providing convincing data to support any of these hypotheses has proved difficult. The testing of these hypotheses and the implementation of endangered species recovery programs has been restricted by a lack of knowledge of the ecology and population demography of amphibian species that have suffered dramatic declines. This thesis presents aspects of the research phase of the recovery program for the Southern Corroboree Frog, Pseudophryne corroboree, a species that declined to very low numbers during the early 1980's. In particular, this research aimed to determine the distribution, abundance, population dynamics and demography of this rare species. A complete reassessment of the conservation status of P. corroboree was undertaken and the nature of the persistence of this species across the landscape was analysed. Temporal trends in abundance and its relationship with population size were also investigated. Early life-history survivorship and recruitment to metamorphosis were studied at the scale of individual nest sites and populations, and the adult male population age structure and annual mortality were investigated using skeletochronology. The shout/response survey technique was used to survey and monitor the number of breeding male P. corroboree during this study. This method was found to provide consistent results when the surveys were conducted over a short (two week) period during the peak breeding season in January. Neither time of day, nor the number of males present at a pool, was found to influence the level of responsiveness of male P. corroboree to the shout/response technique. Variation in the number of responding males to the shout/response technique through the breeding season, assessed at a single site over two seasons, was unimodal with the peak responding period occurring during the last two weeks of January during both the 1998 and the 1999 breeding seasons. A systematic survey covering 213 sites across the entire historic distribution of P. corroboree found this species to be persisting at 79 sites. The majority of these sites were in the northwestern portion of the species former range, around the Jagungal Wilderness area, while no extant sites were found in the south-eastern portion of the species former range in the Smiggin Holes and Perisher Blue ski resorts area. The overall abundance of males at persistent sites was extremely low, with 92 percent of sites having fewer than ten responding males. Only one site was found to support greater than fifty responding males. A logistic regression analysis found the persistence of P. corroboree to be associated with increased number of pools within a site, decreased distance to nearest extant population and geographic position (latitude and longitude) in the landscape. While annual variation was observed in the number of breeding males for individual sites, there was no overall trend for an increase or decrease in the number of males, regardless of population size. The average annual extinction rate for local populations was five percent during this study, with those populations becoming extinct having very few breeding males (between one and three) during the previous season. Embryonic and tadpole survivorship was monitored for individual nests at three sites across three years. Recruitment to metamorphosis for P. corroboree was characterised by high variation in survivorship between nest sites, populations and years, while overall recruitment for nest sites was skewed towards lower survivorship. Average nest survivorship to metamorphosis across all sites and years was ten percent but the skewed nature of this survivorship meant that the majority of nest sites attained very low or no survivorship. The low proportion of nest sites that did attain high survivorship provided the greatest contribution to overall recruitment. The levels of embryonic and tadpole mortality observed in this study would be providing a considerable contribution to the regulation of current population sizes. The greatest level of early life-history mortality was observed during the late autumn/winter egg and tadpole stage, with high survivorship during the summer and early autumn egg stage and the post-winter tadpole stage. The estimated sex ratio for seven populations, based on the number of eggs within male nest sites, indicated that for most populations, regardless of population size, there was a greater proportion of females to males. In general, the estimated sex ratio of smaller populations showed greater annual variation and had a lower average number of females to males than the single large population. Tadpole surveys conducted across remnant populations during both 1998 and 1999 found recruitment to metamorphosis to be very low for the majority of populations. A third of all populations during both years attained no recruitment to metamorphosis, with those populations that did attain recruitment typically having fewer than 20 tadpoles. While sites with more frogs generally recruited more tadpoles, there was no strong relationship between population size and the number of tadpoles recruited per male at the scale of either pool or site. There was also no significant difference in recruitment levels between the two years. Tadpole surveys across breeding pools within the single large population also found very low tadpole abundance. There was no strong relationship between the number of male frogs at a pool and the number of tadpoles per male and there was no significant difference in tadpole abundance between the two years. Based on the low density of males at pools and sites (typically less than five), and the skewed nature of nest survivorship identified from monitoring individual nest sites, it seems likely that both deterministic and stochastic factors are influencing recruitment levels in remnant populations of P. corroboree. This study determined that adult male P. corroboree could be accurately aged using the technique of skeletochronology, and this technique was used to determine the adult male population age structure for three populations. The results indicated that adult male P. corroboree can reach sexual maturity from metamorphosis in three years, but the majority of individuals take four years. The oldest individual identified in this study was nine years old from metamorphosis. The adult male age structure at the single large site showed very little annual variation, whereas the two smaller populations showed highly pulsed age structures from one year to the next. The size of adult males was found to be a poor predictor of age. Annual adult male survivorship, calculated by following cohorts from one year to the next, was 55 percent. Based on this calculation of annual adult male survivorship, it seems likely that the initial decline in P. corroboree involved increased levels of adult mortality. The results of this study indicate that the persistence of. corroboree in the wild is precarious in the short-term. For this reason, it is recommended that efforts be undertaken to secure this species ex situ. Attempts to increase population numbers in the wild would greatly benefit from determining the factor(s) that have caused the decline in this species, however, failure to do so should not preclude field experimental management aimed at developing technique to increase the size of remnant populations. This is because it is likely that small population stochasticity is contributing to the current regulation of population size and it is possible that the factors that caused the decline in this species cannot be removed from the environment.

The decline and extinction of amphibian species over the past three decades is widely acknowledged as one of the greatest biodiversity crises of modem time. Providing convincing data to support hypotheses about these declines has proved difficult, which has greatly restricted the development and implementation of management actions that may prevent further amphibian declines and extinctions from occurring. In this thesis, I present research that was undertaken as part of the recovery programs for the southern corroboree frog (Pseudophryne corroboree), and the Booroolong frog (Litoria booroolongensis); two species that underwent very rapid declines in distribution and abundance during the 1980's. More specifically, I investigated potential causal factors in the declines of both species using experimental and correlative studies, and examined the mechanisms by which one threatening process (chytridiomycosis) may be causing continued decline and extinction in P. corroboree. I also examined the implications of population dynamics for monitoring L. booroolongensis, and suggest a possible monitoring strategy that may reliably facilitate the implementation of recovery objectives for this species. I also tested one possible reintroduction technique aimed at preventing the continued decline and extinction of P. corroboree populations. In Chapters 2 and 3, I present the results from a series of experiments in artificial enclosures designed to examine whether the tadpoles of L. booroolongensis are susceptible to predation by co-occurring introduced predatory fish species; brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss), European carp (Cyprinus carpio), redfin perch (Percafluviatilis), and mosquito fish (Gambusia holbrooki). I demonstrated that the tadpoles of L. booroolongensis, and a closely related species Litoria lesueuri, were palatable to non-native trout species, but not to two native predatory fish species, Gadopsis bispinosus and Galaxias olidus. A pond breeding frog species included in this experiment, Limnodynastes tasmaniensis, was palatable to both the native and non-native fish species. In a separate experiment I also demonstrated that the tadpole of L. booroolongensis is palatable to the three other introduced fish species examined in this study; C. carpio, P. fluviatilis, and G. holbrooki. In three of the experiments, the provision of rock within enclosures as a potential refuge habitat did not afford protection to L. booroolongensis tadpoles from predation by any of the five introduced fish species examined. While all the introduced fish species tested here did consume L. booroolongensis tadpoles, the results also suggested that chemical unpalatability might afford some level of protection against some of these fish species. Firstly, the addition of alternative prey items in one of the experiments reduced the proportion of tadpoles consumed, suggesting that L. booroolongensis may not be a preferred prey item. Secondly, the proportion of tadpoles consumed varied greatly among the different fish species examined, suggesting differing levels of palatability. Overall, this study supports previous research in suggesting that chemical unpalatability may be an important strategy for the tadpoles of riverine frog species in south-eastern Australia to avoid predation by native fish species, and that this strategy is less effective against introduced fish species. While L. booroolongensis currently persists in streams inhabited by a number of introduced fish species, this study supports the likelihood that these species are having a negative impact on populations of L. booroolongensis in the wild. In Chapter 4, I present the results of a study aimed at examining potential monitoring techniques for L. booroolongensis. The results of a mark-recapture exercise demonstrated that L. booroolongensis may exhibit large fluctuations in abundance from one year to the next, and through a prospective power analysis approach, I demonstrated that it would be difficult to confidently identify population trends of interest using either indices or estimates of abundance for this species. An assessment of the capacity to identify the presence or absence of L. booroolongensis using nighttime spotlight surveys demonstrated the high detectability of this species using this technique, at both the scale of 300-meter sections of stream and individual breeding areas (typically less than 10-meters of stream). This study suggests that the monitoring objectives of the L. booroolongensis recovery program would be most effectively achieved using presence/absence surveys at different scales. In Chapter 5, I present the results of a field survey aimed at determining the current distribution and habitat requirements of L. booroolongensis in the South West Slopes region of New South Wales. Of the 163 sites I surveyed across 49 streams,I located L. booroolongensis along 77 of these sites from 27 streams. Based on population and habitat connectivity, this study identified 18 populations of L. booroolongensis that are likely to be operating as independent populations. Twelve of these populations are not represented in conservation reserves, but rather occur along streams that flow through the agricultural landscape. A broad scale habitat analysis identified a positive relationship between extent of rock structures along the stream and the occurrence of L. booroolongensis, and a negative relationship between the proportion of canopy cover and this species' occurrence. At the breeding habitat scale, this study identified a positive relationship between the presence of breeding males and; number of rock crevices in the aquatic environment, extent of emergent rocks, and proportion pool. This analysis also detected a negative relationship between occupancy and water depth. These results confirm previous work suggesting the importance of rocky stream habitats to the persistence of L. booroolongensis, but also suggest how disturbance processes, such as increasing sedimentation and weed invasion, may reduce the suitability of rocky structures as breeding sites. In Chapter 6, I investigated current levels of amphibian chytrid fungus (Batrachochytrium dendrobatidis) infection in corroboree frog populations, and used retrospective screening of museum specimens to assess the possibility that this pathogen was implicated in the initial decline of the corroboree frogs. Using histology, I did not detect any B. dendrobatidis infections in corroboree frog populations prior to their decline, however using the same technique, moderate levels of infection were detected in post-decline populations of both species. Real-time PCR screening of skin swabs identified much higher overall infection rates in post-decline populations of P. corroboree (between 44% and 59%), while significantly lower rates of infection were observed in P. pengilleyi populations (14%). These results suggest that the initial and continued decline of the corroboree frogs may well be attributed to the emergence of B. dendrobatidis in populations of these species. In Chapter 7, I investigated how B. dendrobatidis may be causing the continued decline of P. corroboree through the presence of an abundant reservoir host for this pathogen. I found that populations of adult C. signifera in sub-alpine bogs carry high B. dendrobatidis infection rates (86%), but appear unaffected by this infection. An experiment involving the release of P. corroboree tadpoles into 15 natural pools resulted in metamorphs from seven of these pools testing positive for B. dendrobatidis, with all these individuals dying soon after metamorphosis. These results support the possibility that B. dendrobatidis infection in P. corroboree populations is being facilitated by the presence of large numbers of infected C. signifera in the shared environment. Chapter 8 presents the results of a population augmentation study for P. corroboree. I investigated the extent to which increasing recruitment to metamorphosis may result in population recovery in this species. This was undertaken by harvesting eggs from the field and rearing them through to mid stage tadpoles over the winter period prior to being released back to their natal ponds in spring. While I was able to increase recruitment to metamorphosis by an average of 20 percent, this did not result in a noticeable influence on the subsequent adult population size, as both manipulated and non-manipulated sites declined over the course of this study by an average of 80 percent. I observed a positive relationship between natural recruitment to a late tadpole stage and subsequent adult male population size, however there was considerable variation associated with this relationship. The relationship between recruitment and subsequent population size at the augmentation sites was consistent with the relationship observed at the non-manipulated sites. These results suggest that recruitment to metamorphosis may not be the most important life stage restricting the population recovery of P. corroboree, but that mortality during post-metamorphic stages may be more important in regulating current population size. Hence, further attempts to use captive rearing to increase P. corroboree populations in the wild should focus on the release of post-metamorphic frogs. Overall, this thesis demonstrates the value of quantitative research to the implementation and progress of threatened species recovery programs. While this research will specifically contribute to the recovery programs for L. booroolongensis and P. corroboree, it more broadly contributes to the understanding and capacity to respond to the concerning levels of amphibian extinctions currently occurring throughout the world.