Cryopreservation Cooling Rate Impacts Post-Thaw Sperm Motility and Survival in Litoria booroolongensis

The cryopreservation and storage of gametes (biobanking) can provide a long-term, low-cost option for the preservation of population genetic diversity and is particularly impactful when applied to manage selective breeding within conservation breeding programs (CBPs). This study aimed to develop a sperm cryopreservation protocol for the critically endangered Booroolong frog (Litoria booroolongensis) to capture founder genetics within the recently established (est. 2019) CBP for this species. Hormone-induced sperm release was achieved using established protocols, and spermic urine samples were collected over a 6-h period. Pooled spermic urine samples (n = 3 males) were divided equally between two cryoprotectant (CPA) treatments and diluted by 1:5 (sperm:CPA) with either 15% (v/v) dimethyl sulfoxide + 1% (w/v) sucrose in simplified amphibian Ringer's (SAR; CPAA) or 10% (v/v) dimethylformamide + 10% (w/v) trehalose dihydrate in SAR (CPAB). The samples were cryopreserved in 0.25 mL straws using either a programmable freezer (FrA) or an adapted dry shipper method (FrB). The thawed samples were activated via dilution in water and assessed for viability and motility using both manual assessment and computer-assisted sperm analysis (CASA; 0 h, 0.5 h post-thaw). Upon activation, the survival and recovery of motility (total motility, forward progression and velocity) of cryopreserved sperm suspensions were higher for sperm preserved using FrB than FrA, regardless of CPA composition. This work supports our long-term goal to pioneer the integration of biobanked cryopreserved sperm with population genetic management to maximize restoration program outcomes for Australian amphibian species.

Variability in prey field structure drives inter-annual differences in prey encounter by a marine predator, the little penguin

Understanding how marine predators encounter prey across patchy landscapes remains challenging due to difficulties in measuring the three-dimensional structure of pelagic prey fields at scales relevant to animal movement. We measured at-sea behaviour of a central-place forager, the little penguin (Eudyptula minor), over 5 years (2015-2019) using GPS and dive loggers. We made contemporaneous measurements of the prey field within the penguins' foraging range via boat-based acoustic surveys. We developed a prey encounter index by comparing estimates of acoustic prey density encountered along actual penguin tracks to those encountered along simulated penguin tracks with the same characteristics as real tracks but that moved randomly through the prey field. In most years, penguin tracks encountered prey better than simulated random movements greater than 99% of the time, and penguin dive depths matched peaks in the vertical distribution of prey. However, when prey was unusually sparse and/or deep, penguins had worse than random prey encounter indices, exhibited dives that mismatched depth of maximum prey density, and females had abnormally low body mass (5.3% lower than average). Reductions in prey encounters owing to decreases in the density or accessibility of prey may ultimately lead to reduced fitness and population declines in central-place foraging marine predators.

A comparison of nutritional value of native and alien food plants for a critically endangered island flying-fox

Habitat loss and alteration are two of the biggest threats facing insular flying-foxes. Altered habitats are often re-vegetated with introduced or domestic plant species on which flying-foxes may forage. However, these alien food plants may not meet the nutritional requirements of flying-foxes. The critically endangered Christmas Island flying-fox (CIFF; Pteropus natalis) is subject to habitat alteration and the introduction of alien food plants, and therefore is a good model species to evaluate the potential impact of alien plant species on insular flying-foxes. In this study, we evaluated nutritional content of native food plants to determine how flying-foxes historically met their nutritional requirements. Furthermore, we compared the nutritional content of native and alien fruits to predict possible impacts of alien plants on insular flying-foxes. Native and alien fruits and flowers, and native foliage (leaves, petals, and petioles) commonly consumed by the CIFF were collected and evaluated for soluble sugars, crude protein, non-fiber carbohydrates, and nine minerals. Evaluation of native food plants suggests that flying-foxes meet energy requirements by consuming fruit and nectar. However, fruit and nectar are low in protein and essential minerals required for demanding life periods; therefore, flying-foxes likely supplement their diets with pollen and foliage. Thus, flying-foxes require a diverse array of plants to meet their nutritional requirements. Compared to native fruits, alien fruits contained significantly higher non-fiber carbohydrates, and this may provide an important energy source, particularly from species that bear fruit year-round. Median mineral concentrations in alien fruit species, however, were deficient compared to native fruits, suggesting major (or even seasonal) shifts in the proportion of alien species in the CIFF diet could lead to nutritional imbalances. This study confirms the need to quantify nutritional parameters in addition to feeding ecology when evaluating habitat quality to inform conservation actions that can be applied both locally and globally.

Does detection range matter for inferring social networks in a benthic shark using acoustic telemetry?

Accurately estimating contacts between animals can be critical in ecological studies such as examining social structure, predator-prey interactions or transmission of information and disease. While biotelemetry has been used successfully for such studies in terrestrial systems, it is still under development in the aquatic environment. Acoustic telemetry represents an attractive tool to investigate spatio-temporal behaviour of marine fish and has recently been suggested for monitoring underwater animal interactions. To evaluate the effectiveness of acoustic telemetry in recording interindividual contacts, we compared co-occurrence matrices deduced from three types of acoustic receivers varying in detection range in a benthic shark species. Our results demonstrate that (i) associations produced by acoustic receivers with a large detection range (i.e. Vemco VR2W) were significantly different from those produced by receivers with smaller ranges (i.e. Sonotronics miniSUR receivers and proximity loggers) and (ii) the position of individuals within their network, or centrality, also differed. These findings suggest that acoustic receivers with a large detection range may not be the best option to represent true social networks in the case of a benthic marine animal. While acoustic receivers are increasingly used by marine ecologists, we recommend users first evaluate the influence of detection range to depict accurate individual interactions before using these receivers for social or predator-prey studies. We also advocate for combining multiple receiver types depending on the ecological question being asked and the development of multi-sensor tags or testing of new automated proximity loggers, such as the Encounternet system, to improve the precision and accuracy of social and predator-prey interaction studies.

Emergent multisystemic Enterococcus infection threatens endangered Christmas Island reptile populations

Multisystemic infections with a morphologically unusual bacterium were first observed in captive critically endangered Lister’s geckos (Lepidodactylus listeri) on Christmas Island in October 2014. Since then the infection was identified in another captive critically endangered lizard species, the blue-tailed skink (Cryptoblepharus egeriae) and two species of invasive geckos; the four clawed gecko (Gehyra mutilata) and Asian house gecko (Hemidactylus frenatus), in a wide geographic range across the east side of the island. The Gram and periodic acid-Schiff positive cocci to diplococci have a propensity to form chains surrounded by a matrix, which ultrastructurally appears to be formed by fibrillar capsular projections. The bacterium was associated with severe and extensive replacement of tissues, but minimal host inflammatory response. Attempts to grow the organism in culture and in embryonated eggs were unsuccessful. Molecular characterisation of the organism placed it as a novel member of the genus Enterococcus. Disease Risk Analyses including this organism should now be factored into conservation management actions and island biosecurity.