The comparative energetics of the turtles and crocodiles

The Add‐my‐Pet collection of data on energetics and Dynamic Energy Budget parameters currently contains 92 species of turtles and 23 species of crocodiles. We discuss patterns of eco‐physiological traits of turtles and crocodiles, as functions of parameter values, and compare them with other taxa. Turtles and crocodiles accurately match the general rule that the life‐time cumulated neonate mass production equals ultimate weight. The weight at birth for reptiles scales with ultimate weight to the power 0.6. The scaling exponent is between that of amphibians and birds, while that for mammals is close to 1. We explain why this points to limitations imposed by embryonic respiration, the role of water stress and the accumulation of nitrogen waste during the embryo stage. Weight at puberty is proportional to ultimate weight, and is the largest for crocodiles, followed by that of turtles. These facts explain why the precociality coefficient, sHbp—approximated by the ratio of weight at birth and weight at puberty at abundant food—decreases with ultimate weight. It is the smallest for crocodiles because of their large size and is smaller for turtles than for lizards and snakes. The sea turtles have a smaller sHbp than the rest of the turtles, linked to their large size and small offspring size. We link their small weight and age at birth to reducing risks on the beach. The maximum reserve capacity in both turtles and crocodiles clearly decreases with the precociality coefficient. This relationship has not been found that clearly in other taxa, not even in other reptiles, with the exception of the chondrichthyans. Among reptiles, crocodiles and sea turtles have a relatively large assimilation rate and a large reserve capacity.

Assisted colonisation trials for the western swamp turtle show that juveniles can grow in cooler and wetter climates

Species with restricted ranges and long generation times are vulnerable to climate change due to limited opportunity to disperse or adapt. Australia’s rarest reptile, the western swamp turtle Pseudemydura umbrina, persists naturally in only one seasonal swamp that holds water in the Austral winter and spring. A marked reduction in winter rainfall in recent decades has shortened the swamp hydroperiod, restricting when turtles are able to feed, grow and reproduce. To mitigate possible future loss of reproductive capacity in the native habitat, assisted colonisation was trialled in 2016 using 35 captive-bred juveniles. Here, we report the outcomes of this 6 mo trial, which compared the growth of turtles released approximately 300 km south of the species’ indigenous range with growth of turtles released at an existing northern translocation site. We showed that growth rates comparable to those at warmer northern translocation sites can be achieved in the south, even in an atypically cool spring as occurred in 2016. Microclimates available to P. umbrina at 2 southern sites were suitable for foraging and growth in late spring and early summer, but juvenile growth at one southern site was significantly better than at the other, likely due to higher prey biomass when water temperatures were suitable for foraging. These early results suggest that introduction of P. umbrina to seasonal wetlands near the south coast of Western Australia could be considered in the immediate future, but further trials are recommended to assess growth and survivorship over longer periods.

Resolution of the enigmatic phylogenetic relationship of the critically endangered Western Swamp Tortoise Pseudemydura umbrina (Pleurodira: Chelidae) using a complete mitochondrial genome

Pseudemydura umbrina is one of the most endangered turtle species in the world, and the imperative for its conservation is its distinctive morphology and relict status among the Chelidae. We use Illumina sequencing to obtain the complete mitogenome for resolving its uncertain phylogenetic position. A novel nuclear paralogue confounded the assembly, and resolution of the authentic mitogenome required further Sanger sequencing. The P. umbrina mitogenome is 16,414bp comprising 37 genes organized in a conserved pattern for other vertebrates. The nuclear paralogue is 547bp, 97.8% identity to the corresponding mitochondrial sequence. Particular features of the mitogenome include an nd3 174+1A frameshift, loss of DHC loop in tRNA^Ser (AGN), and a light-strand replication initiation site in Wancy region that extends into an adjacent tRNA gene. Phylogenetic analysis showed that P. umbrina is the monotypic sister lineage to the remaining Australasian Chelidae, a lineage probably dating back to the Cretaceous.

Factors influencing occurrence of a freshwater turtle in an urban landscape: a resilient species?

Context Species vary broadly in their ability to adapt to urbanisation. Freshwater turtles are vulnerable to the loss and degradation of terrestrial and aquatic habitat in urban environments. There have been few publications investigating impacts of urbanisation on freshwater turtles in Australia. Aims We investigated the effects of urbanisation on the distribution and abundance of the eastern long-necked turtle (Chelodina longicollis) in greater Melbourne. Methods We examined occurrence and relative abundance of C. longicollis at 55 wetlands across an urban–rural gradient in relation to site- and landscape-level factors. Occupancy was modelled using the program PRESENCE, and incorporated landscape and habitat covariates. A negative binomial regression model was used to examine the influence of landscape and habitat factors on relative abundance by using WinBUGS. Key results C. longicollis occupied 85% of the 55 wetlands we surveyed, and we found no evidence that wetland occupancy was influenced by the variables we measured. However, relative abundance was highest at wetlands with low water conductivity and heavy metal pollution, and in wetlands furthest from rivers. Conclusions C. longicollis appears to be resilient to urbanisation and is likely to persist in urban landscapes, possibly because of the creation of new wetlands in Australian cities. However, long-term studies focussed on demographic parameters, or survivorship, may elucidate as yet undetected effects of urbanisation. Although no specific management recommendations may be necessary for C. longicollis in urban areas at this time, this species may be in decline in non-urban areas as a result of climatic changes and wetland drying. Implications Our findings suggest that caution is required before drawing generalised conclusions on the impacts of urbanisation on turtles, as the effects are likely to be species-specific, dependent on specific ecology and life-history requirements. Further studies are required to ascertain these relationships for a wider array of species and over longer time spans.

Linking Eco-Energetics and Eco-Hydrology to Select Sites for the Assisted Colonization of Australia's Rarest Reptile

Assisted colonization-the deliberate translocation of species from unsuitable to suitable regions-is a controversial management tool that aims to prevent the extinction of populations that are unable to migrate in response to climate change or to survive in situ. The identification of suitable translocation sites is therefore a pressing issue. Correlative species distribution models, which are based on occurrence data, are of limited use for site selection for species with historically restricted distributions. In contrast, mechanistic species distribution models hold considerable promise in selecting translocation sites. Here we integrate ecoenergetic and hydrological models to assess the longer-term suitability of the current habitat of one of the world's rarest chelonians, the Critically Endangered Western Swamp Tortoise (Psuedemydura umbrina). Our coupled model allows us to understand the interaction between thermal and hydric constraints on the foraging window of tortoises, based on hydrological projections of its current habitat. The process can then be repeated across a range of future climates to identify regions that would fall within the tortoise's thermodynamic niche. The predictions indicate that climate change will result in reduced hydroperiods for the tortoises. However, under some climate change scenarios, habitat suitability may remain stable or even improve due to increases in the heat budget. We discuss how our predictions can be integrated with energy budget models that can capture the consequences of these biophysical constraints on growth, reproduction and body condition.

Skin disease affecting the conservation of the western swamp tortoise (Pseudemydura umbrina)

OBJECTIVE

To review the present position of the western swamp tortoise (Pseudemydura umbrina) as an endangered species and significant health issues affecting efforts to save it from extinction.

PROCEDURE

A retrospective analysis of the husbandry, hospital and pathology records of the western swamp tortoise captive breeding program at Perth Zoo.

RESULTS

In 1987 a captive breeding project was developed to prevent the extinction of the western swamp tortoise but an outbreak of a necrotising dermatitis in 1989 threatened the survival of the captive bred hatchlings. Less severe outbreaks occurred in 1990 and 1993, with isolated cases in between. Of 283 tortoises that were born in captivity or came into captivity from the wild, 37 (13.1%) were affected, comprising 37% of all males, 26% of all females and 13% of animals of unknown gender. Of the affected animals, 70% were less than 2 years of age and 29% were older. Males were 1.6 times more likely to be infected than females but this difference was not statistically significant (P = 0.27). Culture of the lesions consistently yielded unidentified Pseudomonas sp.

CONCLUSION

Improved husbandry, such as strict maintenance of water quality and temperature conditions similar to that of the animal's natural habitat, and monitoring the health of individual tortoises have successfully controlled skin disease in the captive breeding of the western swamp tortoise.