Overwintering under ice: A novel observation for an Australian freshwater turtle

Frozen water bodies provide a physiological challenge to fauna by physically limiting access to atmospheric oxygen. To tolerate low temperatures, reptiles use brumation as a physiological strategy in winter. Cryptodira vary in their tolerance to freezing conditions but the extent of tolerance in pleurodirans is largely unknown. Australia's freshwater turtles inhabit warmer regions with less severe winters and have well-developed mechanisms to cope with high temperatures and drying waterbodies, rather than extreme cold tolerance. Chelodina longicollis is a widespread Australian freshwater turtle species that tolerates high temperatures and desiccation during hot, dry periods while also undergoing brumation during winter months. Despite extensive research, limited observations exist on their behaviour during severe winter periods at the extremes of their range. In an 11-month tracking study, we monitored adult C. longicollis, noting their movements, locations, and temperature weekly. We observed an adult female C. longicollis which, during a seven-month period within a single creek pool, survived brumation in extreme cold water including a 15-day period of total freezing of the surface water. After the ice melted following a rain event, the turtle was recaptured alive. This marks the first observation of brumation for an Australian chelid species under ice.

No Ranaviral DNA Found in Australian Freshwater Turtles, 2014-19, Despite Previous Serologic Evidence

Ranaviruses are pathogens of ectothermic vertebrates (fish, amphibians, and reptiles). Turtles are the most common group of reptiles reported with ranaviral infections. However, there have been no surveys for wild ranaviral infection in any turtles from the suborder Pleurodira, despite ranaviral distributions and experimentally susceptible pleurodiran turtle populations overlapping in several areas, including Australia. We assayed 397 pooled blood samples from six Australian freshwater turtle species collected from five different sites in northern Australia between 2014 and 2019. Historical serologic surveys in the area had found antiranaviral antibodies; however, we did not detect any ranaviral DNA in our samples. Discrepancies between historical serologic and our molecular results may be explained by low viral prevalence during the years that these samples were collected, survivorship bias, or possibly an age class bias in sampling.

Characterisation of Nematoda and Digenea in selected Australian freshwater snails

Freshwater snails are integral to local ecosystems as a primary food source for various vertebrate species, thereby contributing significantly to ecological food webs. However, their role as intermediate hosts also makes them pivotal in the transmission of parasites. In Australia, research on freshwater snails has predominantly focused on their role as intermediate hosts for livestock parasites, while there has been limited exploration of the impact of these parasites on snail health and population dynamics. The aim of this study was to determine parasitic infection in freshwater snails. This study was conducted in the south-eastern region of Australia, in 2022. A total of 163 freshwater snails from four different species were collected and examined in the Murrumbidgee catchment area in the southeastern part of Australia during the Southern Hemisphere summer and autumn months (February to May). The species included Isidorella hainesii, Glyptophysa novaehollandica, Bullastra lessoni (endemic species), and Physella acuta (an introduced species). Through the analysis of sequence data from the various regions of the nuclear ribosomal DNA, we determined that the Digenea species in this study belonged to three distinct species, including Choanocotyle hobbsi, Petasiger sp. and an unidentified species belonging to Plagiorchioidea. Additionally, analysis of the sequences from Nematoda found in this study, revealed they could be categorized into two separate taxa, including Krefftascaris sp. and an unidentified nematode closely associated with plant and soil nematodes. This research holds significant implications for the future understanding and conservation of Australian freshwater ecosystems. Most parasites found in the present study complete their life cycle in snails and turtles. As many of freshwater snail and turtle species in Australia are endemic and face population threats, exploring the potential adverse impacts of parasitic infections on snail and turtle health, is crucial for advancing our understanding of these ecosystems and also paving the way for future research and conservation efforts. While none of the native snail species in the present study have been listed as endangered or threatened, this may simply be attributed to the absence of regular population surveys.

Maternal diet influences fecundity in a freshwater turtle undergoing population decline

Food availability determines the amount of energy animals can acquire and allocate to reproduction and other necessary functions. Female animals that are food limited thus experience reduced energy available for reproduction. When this occurs, females may reduce frequency of reproductive events or the number or size of offspring per reproductive bout. We assessed how maternal diet affects reproductive output in adult female Murray River short-necked turtles, Emydura macquarii, from four wetlands in Victoria. We previously found that turtle diets differ in the composition of plants and animals between our study wetlands. In this study, we tested whether differences in turtle diet composition (i.e. plants and animals) at these wetlands were associated with differences in clutch mass, individual egg mass, bulk egg composition and hatching success. We found total clutch mass increased with maternal body size at each site. At sites where filamentous green algae were scarce and E. macquarii were carnivorous, females produced smaller clutches relative to body size compared to females from sites where algae were abundant, and turtles were more herbivorous. Individual egg mass, bulk egg composition and hatching success did not differ across wetlands. Isotopic analysis revealed significant positive relationships between the carbon and nitrogen isotopes (δ13C, δ15N) of the eggs and those of the mothers, indicating that mothers allocated ratios of carbon and nitrogen isotopes to their eggs similar to those present in their tissues. Our study suggests that at sites where females are more carnivorous due to a relative absence of algae, females produce smaller clutches, but other aspects of their reproduction are not significantly impacted. The reduction in clutch size associated with differences in the availability of dietary plants and animals may have long-term consequences for E. macquarii and other freshwater turtle species that are experiencing population declines.

Partitioning of PFAS to serum, tissues, eggs, and hatchlings of an Australian freshwater turtle

Turtles are a potential sentinel species of aquatic ecosystem health as they inhabit aquatic ecosystems, are long lived, and potentially have high exposure to anthropogenic chemicals via food and water. This study investigated per- and polyfluoroalkyl substances (PFAS) tissue partitioning in female Emydura macquarii macquarii turtle, and the maternal offloading of (PFAS) into eggs and then hatchlings as well as the accumulation of PFAS in male and female Emydura macquarii macquarii serum. Significantly higher levels of perfluorosulfonic acids (PFSAs) and perfluorocarboxylic acids (PFCAs) were measured in the male serum compared to the female turtle serum, whereas perfluoroalkane sulfonamides (FASAs) were significantly higher in the female turtle serum. Perfluorooctane sulfonate (PFOS) was the predominant PFAS in the turtles whereas PFHxA was the predominant PFAS found in the surrounding water. PFHxA was not reported in any turtle tissue or the serum. The short-chain PFSAs and FASAs appeared to be highly associated with blood; long-chain PFSAs and PFCAs were more likely to be associated with tissue. Half of the PFHxS and all the long-chain PFSAs and PFCAs reported in the yolks were transferred into the hatchlings (by mass), suggesting a potential intergenerational effect.

Pathogenesis of Bohle iridovirus infection in Krefft's freshwater turtle hatchlings (Emydura macquarii krefftii)

Ranaviruses have been detected in over 12 families of reptiles including many genera of turtles, tortoises, and terrapins, but the pathogenesis of these infections is still poorly understood. Krefft's river turtle hatchlings (N = 36; Emydura macquarii krefftii) were inoculated intramuscularly with Bohle iridovirus (BIV, Ranavirus, isolate) or saline, and euthanized at 9 timepoints (3 infected and 1 control per timepoint) over a 24-day period. Samples of lung, liver, kidney, and spleen were collected for quantitative polymerase chain reaction (PCR); internal organs, skin, and oral cavity samples were fixed for histopathological examination. The earliest lesions, at 8 days postinoculation (dpi), were lymphocytic inflammation of the skin and fibrinoid necrosis of regional vessels at the site of inoculation, and mild ulcerative necrosis with lymphocytic and heterophilic inflammation in the oral, nasal, and tongue mucosae. Fibrinonecrotic foci with heterophilic inflammation were detected in spleen and gonads at 16 dpi. Multifocal hepatic necrosis, heterophilic inflammation, and occasional basophilic intracytoplasmic inclusion bodies were observed at 20 dpi, along with ulcerative lymphocytic and heterophilic tracheitis and bronchitis. Tracheitis, bronchitis, and rare bone marrow necrosis were present at 24 dpi. Of the viscera tested for ranaviral DNA by PCR, the liver and spleen had the highest viral loads throughout infection, and thus appeared to be major targets of viral replication. Testing of whole blood by qPCR was the most-effective ante-mortem method for detecting ranaviral infection compared with oral swabs. This study represents the first time-dependent pathogenesis study of a ranaviral infection in turtles.

Optimising the hatching success of artificially incubated eggs for use in a conservation program for the western saw-shelled turtle (

Artificial incubation of eggs and the release of hatchlings into the wild is a common conservation intervention designed to augment threatened turtle populations. We investigate a range of incubation temperatures to establish an optimal temperature for maximum hatching success of western saw-shelled turtle (Myuchelys bellii) eggs. We report on the influence of incubation temperature on incubation duration and hatching success and describe two experimental incubation methods which, for the same incubation temperature (27°C), resulted in 77% and 97% hatching success, respectively. Eggs were incubated at constant temperatures (27°C, 28°C and 29°C) to determine the influence of temperature on incubation period, hatchling morphology and external residual yolk. Incubation duration was negatively correlated with incubation temperature. We report on the morphology of eggs and hatchlings and show that their dimensions are positively correlated with maternal adult size and mass. A constant incubation temperature of 27°C produced the highest hatching success and smallest external residual yolk on hatching and is therefore recommended for incubation of eggs for population reinforcement programs. Our study is the first to optimise artificial incubation procedures for M. bellii and will be a valuable resource for M. bellii and other threatened freshwater turtle conservation initiatives.

Adaptive Management to Reduce Nest Inundation of a Critically Endangered Freshwater Turtle: Confirming the Win-win

Inundation of Australian freshwater turtle nests has been identified as a threat to recruitment and long-term viability of species such as the critically endangered white-throated snapping turtle (Elseya albagula). Water level fluctuations within water storage infrastructure can inundate significant proportions of E. albagula nests in any year. Using an ecological risk assessment framework, operating rules for a water storage in the Burnett River (South East Queensland, Australia) were implemented to support nesting of E. albagula. Turtles were encouraged to nest at higher elevations on riverbanks by maintaining higher water levels in the impoundment during the nesting season, followed by lowering of water levels during the incubation period to minimise rates of nest inundation from riverine inflows. To verify the success of the new rules, a three-year confirmation monitoring program of nest heights and water levels was undertaken. Results of confirmation monitoring showed that 3% (2018), 11% (2019) and 0% (2020) of E. albagula nests were inundated under the new operating rules, compared to previously estimated nest inundation rates of >20% in ~24% of years of a 118-year simulation period (1890-2008) under previous storage operating rules. Emergency releases from an upstream storage in 2019 and 2020 for dam safety did not affect the success of the rule, demonstrating its resilience to natural and artificial flow regimes. This study demonstrates the importance of confirmation monitoring in verifying the efficacy of targeted changes to water management, and highlights potential application across other water storage infrastructure with threatened freshwater turtle populations requiring adaptive management.

Prey-switching does not protect a generalist turtle from bioenergetic consequences when its preferred food is scarce

BACKGROUND

Optimal foraging theory explains how animals make foraging decisions based on the availability, nutritional content, and handling times of different food types. Generalists solve this problem by consuming a variety of food types, and alter their diets with relative ease. Specialists eat few food types, and may starve if those food types are not available. We integrated stable isotope analyses with previously-published stomach contents and environmental data to investigate how the foraging ecologies of three sympatric freshwater turtle species vary across four wetlands that differ in turbidity and primary producer abundance.

RESULTS

We found that the generalist Emydura macquarii consumes a varied diet (but mostly filamentous green algae) when primary producers are available and water is clear, but switches to a more carnivorous diet when the water is turbid and primary producers are scarce, following the predictions of optimal foraging theory. In contrast, two more-specialized carnivorous species, Chelodina expansa and Chelodina longicollis, do not differ in diet across wetlands, and interspecific competition may increase where E. macquarii is carnivorous. When forced to be more carnivorous, E. macquarii exhibits higher rates of empty stomachs, and female turtles have reduced body condition, but neither Chelodina species are affected.

CONCLUSIONS

Our results provide support for optimal foraging theory, but also show that the ability to change diet does not protect the generalist from experiencing lower foraging success when its preferred food is rare, with direct consequences for their energy budgets. Our results have conservation implications because wetlands in the Murray-Darling river system are increasingly turbid and have low macrophyte abundance, and all three species are declining.

Cutaneous Lesions in Freshwater Turtles (Emydura macquarii krefftii and Myuchelys latisternum) in a Rainforest Creek in North Queensland, Australia

Freshwater turtles inhabit most rivers and creeks on the east coast of Australia, but some species are only found in specific catchments, which makes them vulnerable to extinction. During annual fieldtrips to Alligator Creek, North Queensland, the resident population of Myuchelys latisternum and Emydura macquarii krefftii in a natural pond, just outside Bowling Green National Park, have been surveyed for a number of years and demographic data recorded against tagged turtles. Rounded, cutaneous lesions on individual animals were first noted in August 2016, three years after the first survey of the population. Turtles living in the upstream sections of the creek were not affected. An initial investigation into the cause of the lesions ruled out pollutants and although the bacterial communities appeared to be different on turtles with lesions, a causative agent was not identified. Attempts to isolate virus in culture was not successful and specific PCRs for ranavirus, papillomavirus, adenovirus and herpesvirus did not identify their presence. Blood biochemical parameters, body condition and activity levels were not significantly different between affected turtles and those without lesions. The turtles in this pond were monitored regularly over the following three years with 249 M. latisternum and 192 E. m. krefftii captured, tagged and released. The prevalence of the lesions fluctuated with season from 0 to 77 and 68% respectively, but did not vary significantly between species or sex in adults. There was a tendency for larger animals to be more likely to have lesions. The position of the lesions on the turtles was mostly on dorsal surfaces, distally on the legs and proximal on the tales of males, indicating that the initial lesion may have been associated with a behaviourally induced trauma. Recaptured animals (n = 43) during this period, provided records of lesion progression over time and while some healed up between capture events, others persisted for up to 24 months. Some turtles were repeatedly captured without lesions. Intra-species aggression associated with seasonal behaviours could potentially be the primary cause of skin trauma, followed by a secondary invasion of an unusual pathogen present in the environment.

Conservation implications of turtle declines in Australia's Murray River system

Conservation requires rapid action to be effective, which is often difficult because of funding limitations, political constraints, and limited data. Turtles are among the world’s most endangered vertebrate taxa, with almost half of 356 species threatened with extinction. In Australia’s Murray River, nest predation by invasive foxes (Vulpes vulpes) was predicted to drive turtle declines in the 1980s. We assessed populations of the broad-shelled turtle (Chelodina expansa), eastern long-necked turtle (C. longicollis), and Murray River turtle (Emydura macquarii) in the Murray River and some of its associated waterways. Our results suggest that the predicted decline is occurring. All three species are rare in the lower Murray River region, and were undetected in many locations in South Australia. Moreover, E. macquarii had considerable population aging almost everywhere, possibly due to comprehensive nest destruction by foxes. Chelodina longicollis also had population aging at some sites. Sustained low recruitment has potential to lead to collapses as turtles age, which is particularly worrying because it was predicted over 30 years ago and may have already occurred in South Australia. Our results show that turtle declines were not mitigated since that prediction. If the crash continues, a vertebrate guild responsible for considerable nutrient cycling in the aquatic ecosystem will disappear. Our results highlight a worst-case outcome when species declines are predicted, but insufficiently mitigated.