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Effects of temperature and exercise on metabolism of three species of Australian freshwater turtles: Implications for responses to climate change
Abstract
Oxygen consumption (ZO18062-E1a.gif) of Chelodina expansa, C. longicollis and Emydura macquarii (Pleurodira: Chelidae) was measured at rest and during induced exercise at 8, 13, 18, 22, 26, 30 and 34°C. Resting ZO18062-E1a.gif varied significantly among species, being lowest in C. expansa, which is the most sedentary of the three species in nature, and highest in E. macquarii, which is the most energetic, but active ZO18062-E1a.gif did not differ significantly among the three species overall. For both Chelodina species, resting ZO18062-E1a.gif was appreciably lower than expected from regression of ZO18062-E1a.gif on body mass for non-marine turtles globally, a result that reinforces previous evidence of low resting metabolism in Australian chelid turtles. Active ZO18062-E1a.gif of all three species at higher temperatures was similar to ZO18062-E1a.gif reported for active freshwater cryptodires. Resting ZO18062-E1a.gif of all three species increased similarly with temperature, but active ZO18062-E1a.gif and aerobic scope did not. In C. expansa and E. macquarii, active ZO18062-E1a.gif and aerobic scope increased over the full temperature range assessed but in C. longicollis these variables reached a plateau above 22°C. Projected increases in freshwater temperatures in south-eastern Australia as a result of global warming are likely to enhance activity, feeding and growth of the three species (subject to food availability), especially in cooler seasons for C. longicollis and warmer seasons for C. expansa and E. macquarii. However, other aspects of predicted climate change, especially increased drought, are likely to be detrimental.
... Determining maintenance costs is an important step in understanding adaptive strategies employed by species that use habitats with greater rates of environmental stochasticity. Whether or not to aestivate can be influenced by the relative energetic costs of aestivating versus traveling overland, which are in turn affected by the relative proximity of nearby wetlands and the magnitude of the difference between resting versus active metabolic rates Chessman 2019). For example, overland travel was 1.6-1.7 more costly than aestivation in eastern long-necked turtles (Chelodina longicollis) and the energy saved by not traveling overland could support up to 134 d of aestivation . ...
... When the aquatic habitat starts drying, however, turtles are exposed to increased risk of predation and desiccation as well as temperatures that exceed their normal thermal activity range, forcing them to leave the wetland. While some species or individuals elect to travel overland in search of more permanent aquatic habitats, overland travel can be risky, energetically costly, anddepending on inter-wetland distance and species-specific EWL ratesprohibitive Chessman 2019). Furthermore, in a landscape dominated by seasonal wetlands, the nearest aquatic habitats are also likely to be dry, particularly during extended droughts (Buhlmann et al., 2009). ...
... Aestivation sites can reduce a turtle's risk of predation, rate of desiccation, as well as both overall temperatures and temperature variability (Bennett et al., 1970;Steen et al., 2007;. The lower temperatures in terrestrial aestivation sites relative to water temperatures in drying wetlands, combined with quiescent behavior while aestivating, reduce metabolic maintenance costs even without considering any additional physiological adjustments that turtles might be capable of making (Ligon and Peterson 2002;Chessman 2019). ...
Physiological maintenance of ectotherms is largely dependent on temperature. Abrupt changes in environmental conditions can cause shifts in energy budgets, with higher temperatures requiring more energy be devoted to maintenance functions, making less energy available for other activities. As a group, freshwater turtles are of conservation concern; thus, it is important to understand their physiological responses to temperature shifts, particularly given current climate change predictions. We quantified metabolic rates (MR) for three species of semi-aquatic turtles that vary in their degree of terrestriality and propensity to aestivate: chicken turtles (Deirochelys reticularia), eastern mud turtles (Kinosternon subrubrum), and eastern musk turtles (Sternotherus odoratus). Metabolic trials were performed using a flow-through respirometer at three environmentally-relevant temperatures: 25 °C, 30 °C, and 35 °C. As expected, MRs of turtles were significantly and positively associated with increases in mass and temperature. Pairwise comparisons revealed that D. reticularia exhibited significantly higher oxygen consumption rates (VO2) relative to K. subrubrum, which had significantly higher VO2 than S. odoratus. The combination of higher metabolic rates, the tendency to terrestrially aestivate, and declining quantity of high quality thermal habitats may place some semi-aquatic turtles at a disadvantage when considering future climate scenarios. Our findings, when combined with knowledge of other ecological traits, may be a useful tool for predicting relative sensitivities of turtle species to predicted climate change, particularly those species inhabiting seasonal wetlands.
... Average air and water temperatures in south-eastern Australia are projected to increase by~2 C by the late 21st century (van Vliet et al. 2013;Olson et al. 2016). Such environmental warming could present both opportunities and threats to freshwater turtles: enhanced activity, feeding and growth when in the water, subject to availability of aquatic habitat and food, but increased risk of overheating and dehydration when on land (Chessman 2018). The current results suggest that, of the three species studied, C. longicollis will have the greatest capacity to behaviourally exploit the opportunities and avoid the threats, and C. expansa the least. ...
... Increases in water temperatures are unlikely to be sufficient to threaten C. expansa, C. longicollis and E. macquarii at the warmer and more arid extremes of their ranges (Chessman 2018). However, given their critical thermal maxima of onlỹ 40 C, higher air temperatures may be hazardous to turtles dispersing or sheltering terrestrially, for example as a result of water bodies drying under projected increases in the frequency and intensity of drought (Dai 2013;Feng et al. 2019). ...
... These observations do not conflict with Chessman's (1978) predictions because temperature and humidity adjacent to the aestivating turtles were not reported, and they probably had intermittent opportunities to drink pooled rainwater (Roe et al. 2008). Since both metabolism and evaporative water loss of C. longicollis are positively related to temperature (Chessman 1984a(Chessman , 2018, its apparent ability to select cooler microenvironments for aestivation (Chessman 1983a;Beck 1991), and the availability of such microenvironments, could substantially affect its survival of prolonged drought. ...
The abilities of freshwater turtles to control their body temperatures by behavioural means have implications for activity, food ingestion and digestion, growth, reproduction and potential responses to climate change. I compared various forms of basking in nature, and responses to aquatic and aerial photothermal gradients in the laboratory, among three species of Australian chelid turtles: Chelodina expansa, C. longicollis and Emydura macquarii. Proclivity for behavioural thermoregulation varied substantially among these species, being highest in C. longicollis and lowest in C. expansa. However, C. expansa had a thermophilic response to feeding. For C. longicollis and E. macquarii, behavioural thermoregulation may enhance colonisation of more southerly latitudes or higher elevations as climatic warming proceeds. However, increasing air temperatures may pose a hazard to turtles dispersing or sheltering terrestrially (for example, when water bodies dry during drought). C. longicollis appears the best placed of the three species to avoid this hazard through its abilities to thermoregulate behaviourally and to aestivate in terrestrial microenvironments that are buffered against temperature extremes.
... showing temporal dietary shifts. Plasma is the most enriched tissue, tracking recent diet: November/January in the southern hemisphere spring and summer, although, over a space of only 2 months, δ 15 N was significantly more enriched in turtle plasma in spring than in summer, perhaps indicating a need to feed in spring after coming out of winter inactivity, when metabolic activity drops and basking is reduced (Chessman, 2019(Chessman, , 2020. Plasma δ 15 N analyses showed that turtles fed at high trophic levels during spring, compared with a less enriched 'averaged' diet reflected by the nails, tracking a longer period (up to a year) (Seminoff et al., 2007). ...
Australian freshwater turtles are declining, reflecting global turtle trends. Understanding variation in turtle diets and habitat requirements can guide protection and restoration of ecosystems. Diet and niche overlap were investigated in three co‐existing species of turtle—the broad‐shelled turtle Chelodina expansa , the eastern long‐necked turtle C. longicollis and the Macquarie turtle Emydura macquarii , in three rivers in the Murray–Darling Basin, Australia, in relation to environmental variables.
Dietary variation in relation to water quality (salinity) and macrophyte cover was investigated using stable isotope analyses (δ ¹⁵ N and δ ¹³ C) of turtle tissues (plasma, red blood cell, whole blood and nail) representing food assimilation over different antecedent periods. These stable isotope results were consistent with current dietary understanding based on stomach flushing, indicating that isotope analyses are a non‐invasive method for obtaining dietary information.
There were temporal dietary differences, with strong shifts between spring and summer sampling periods, particularly in the blood plasma. Intraspecific variation in diets reflected in δ ¹⁵ N and δ ¹³ C related to body size. There was evidence of high dietary overlap among the three species, potentially creating competition, particularly when they co‐occur or resources might be limited.
Continued degradation of turtle habitats and water quality affects turtle diet and reduces habitat availability, forcing the three species of turtle to co‐exist in diminishing refugia, increasing interspecific competition for food. Protecting and restoring freshwater ecosystems, including maintaining freshwater refugia, is essential to conserve already declining populations of the three Australian freshwater turtle species.
... Reduced foraging success lowers the amount of energy E. macquarii can allocate to various biological demands (e.g., [4,14]). Second, adult E. macquarii have the highest resting metabolic rates of the three species [10], and are most susceptible to losing body mass due to low foraging success. The lack of a difference in male body condition may be because males do not invest in egg production [44]. ...
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.
The Sailfin Catfish of the genus Pterygoplichthys is a popular aquarium pet distributed and sold globally through the ornamental pet trade. Pterygoplichthys spp. have established stable populations in various freshwater ecosystems following aquarium pet owners' deliberate introduction in the regions outside their native range (South America). Colonisations of Pterygoplichthys spp. in multiple areas of India and Bangladesh were reported along with frequent catches with the aquacultural fish hauls and subsequent adverse effects on the socio-economy and ecosystem functions. In the present study, we identified the suitable habitats of Pterygoplichthys spp. using species distribution modelling (SDM) based on global and regional occurrence data considering India and Bangladesh as focal areas. Along with literature surveys and online databases, we used social media platforms to gather additional occurrence data for SDM. In addition, the social media platforms were used to conduct an online survey to assess the public perception regarding using Ptery-goplichthys spp. as an aquarium pet and subsequent release to natural waterbodies. The results of SDM indicated that several areas of India and the whole of Bangladesh are high to moderately suitable for Pterygoplichthys spp. colonisation and range expansion which can be prioritised for effective restoration and management. It is evident from people's perception that raising awareness among the public about the potential impacts of invasive species on the concerned ecosystems may help reduce or stop further deliberate non-native species introductions to natural habitats.
Freshwater turtles face many threats, including habitat loss and river regulation reducing occupancy and contributing to population decline. Limited knowledge of hydrological conditions required to maintain viable turtle populations in large floodplain wetlands hinders effective adaptive management of environmental water in regulated rivers. We surveyed three turtle species over 4 years across the Lower Murrumbidgee River floodplain, a large wetland complex with a long history of water resource development. Using site and floodplain metrics and generalized linear models, within a Bayesian Model Averaging framework, we quantified the main drivers affecting turtle abundance. We also used a hierarchical modeling approach, requiring large sample sizes, quantifying possible environmental effects while accounting for detection probabilities of the eastern long-necked turtle (Chelodina longicollis). The three species varied in their responses to hydrological conditions and connectivity to the main river channel. Broad-shelled turtles (Chelodina expansa) and Macquarie River turtles (Emydura macquarii macquarii) had restricted distributions, centered on frequently inundated wetlands close to the river, whereas the eastern long-necked turtles were more widely distributed, indicating an ability to exploit variable habitats. We conclude that turtle communities would benefit from long-term management strategies that maintain a spatiotemporal mosaic of hydrological conditions. More specifically, we identified characteristics of refuge habitats and stress the importance of maintaining their integrity during dry periods. Neighboring habitats can be targeted during increased water availability years to enhance feeding and dispersal opportunities for freshwater turtles.
Evidence for a circadian rhythm in the oxygen consumption of resting angulate tortoise (Chersina angulata))
Author(s): Setlalekgomo MR and PED Winter
Abstract: Some ectotherms show daily fluctuations in their metabolic rate (MR) within their experienced temperature range. The rhythms may disappear or persist in constant conditions in the laboratory. The resting oxygen consumption (RVO2) of resting Chersina angulata was measured using open flow through respirometry over 24 hours to detect the presence of daily fluctuations in MR. The tortoises were acclimated in an environmentally controlled room to an ambient temperature of 26 ± 1 °C and a 14L:10D light regime prior to the resting VO2 measurements. The VO2 was measured when tortoises were resting at a constant temperature of 26 ± 1 °C and at three different light regimes, 14L:10D, DD and LL. Daily rhythms in the MR were detected at all three light regimes. However, the rhythm was more pronounced at 14L:10D than at DD and LL. Higher values of resting MR were registered in the early hours of the day, followed by a decrease as the day progressed, while the lowest values were recorded in the late hours of the day. Under constant conditions, the rhythmic pattern persisted, but wi
Australia was not always arid, and the freshwater turtles that have survived to this day are either relicts residing in river systems that have themselves had a history or continuity through the drying of the continent, or they are species that have adapted in some way to meet the challenges of drought. In this chapter, we report on how Australian freshwater turtles cope with periodic loss of habitat through drought at a range of spatial and temporal scales, and consider how they might fare under changing climates predicted to occur through global warming. Global warming is not occurring in isolation of other environmental changes at a landscape scale, and we look at what interactions there might be between climate change and the increasing demands of agriculture, industry and our cities for water, in presenting challenges for our unique freshwater turtle fauna.
Chelodina longicollis occupies a wide range of ephemeral and permanent waters in the Jervis Bay Territory of coastal New South Wales. As ephemeral waters dry up during periods of low rainfall, which may span several years, the turtles retreat to the refuge of two permanent dune lakes. High population densities in these lakes coupled with low productivity lead to a sharp decline in growth, and reproduction ceases almost entirely. Differences between the lakes in the growth rates and body conditions of turtles coincide with differences in food availability. When rainfall increases, the turtles disperse once more to the ephemeral swamps where they growth faster and are in better condition; and reproductive output is considerably greater than in the permanent water. The propensity of the species for overland migration following rain is explained by the advantages of colonizing highly productive ephemeral waters, reinforced by the severe disadvantages of remaining in the permanent water of overcrowded drought refuges. -Authors
Water diversions can disrupt flows and alter thermal regimes changing seasonal patterns that signal the onset of life-history functions of native organisms and compromise the fitness of their populations. We compared size, growth,relative mass, volumetric body condition, and reproductive status of Western Pond Turtles (Actinemys marmorata) across a decade on two forks of California’s Trinity River, one regulated and the other free-flowing. Turtles on the regulated fork experienced flows designed to accommodate anthropocentric demands, whereas those on the free-flowing fork experienced natural hydrologic cycles and seasonal warming. July water temperatures averaged 8.66C colder on the regulated fork due to hypolimnetic releases. Turtles on the colder regulated fork grew more slowly and were smaller at similar ages compared with those on the free-flowing fork, a pattern that was exacerbated across the decade. Female relative mass (RM) across the decade did not differ between forks, whereas male RM was greater on the free-flowing fork only in the 1990s. In the 2000s volumetric body condition of females on the regulated fork differed significantly from males on both forks and females on the free-flowing fork. Females on the regulated fork appeared to be assimilating more resources possibly in response to colder water. Fewer females on the regulated fork were gravid and, due to smaller size, likely carried fewer eggs. The percent of gravid females on both forks declined significantly across the decade. We found additional evidence of a wider regional effect with differences in RM shifting from positive to negative for both sexes on both forks. We did not collect evidence that would explain these phenomena but these strongly suggest that trophic relationships of the turtles in the greater region are being adversely influenced.
Counter‐gradient growth, where growth per unit temperature increases as temperature decreases, can reduce the variation in ectothermic growth rates across environmental gradients. Understanding how ectothermic species respond to changing temperatures is essential to their conservation and management due to human‐altered habitats and changing climates.
Here, we use two contrasting populations of western pond turtles ( Actinemys marmorata ) to model the effect of artificial and variable temperature regimes on growth and age at reproductive maturity. The two populations occur on forks of the Trinity River in northern California, U.S.A. The South Fork Trinity River (South Fork) is unregulated, while the main stem of the Trinity River (Main Stem) is dammed and has peak seasonal temperatures that are approximately 10 °C colder than the South Fork.
Consistent with other studies, we found reduced annual growth rates for turtles in the colder Main Stem compared to the warmer South Fork. The South Fork population matured approximately 9 year earlier, on average, and at a larger body size than the Main Stem population.
When we normalised growth rates for the thermal opportunity for growth using water‐growing degree‐days ( GDD ), we found the reverse for growth rates and age at reproductive maturity. Main Stem turtles grew approximately twice as fast as South Fork turtles per GDD . Main Stem turtles also required approximately 50% fewer GDD to reach their smaller size at reproductive maturity compared to the larger South Fork turtles.
We found we could accurately hindcast growth rates based on water temperatures estimated from the total volume of discharge from the dam into the Main Stem, providing a management tool for predicting the impacts of the dam on turtle growth rates.
Given the importance of size and age at reproductive maturity to population dynamics, this information on counter‐gradient growth will improve our ability to understand and predict the consequences of dam operations for downstream turtle populations.
Atmospheric demand for moisture and dry days are expected to increase, leading to drying over land in the twenty-first century. Here, the magnitude and key drivers of this drying are investigated using model simulations under a low-moderate scenario, RCP4.5. The self-calibrated Palmer drought severity index with the Penman-Monteith potential evapotranspiration (PET) (sc_PDSI_pm), top 10-cm soil moisture (SM), and runoff (R) from 14 models are analyzed. The change patterns are found to be comparable while the magnitude differs among these measures of drought. The frequency of the SM-based moderate (severe) agricultural drought could increase by 50%-100% (100%-200%) in a relative sense by the 2090s over most of the Americas, Europe, and southern Africa and parts of East and West Asia and Australia. Runoff-based hydrological drought frequency could also increase by 10%-50% over most land areas despite increases in mean runoff. The probability density functions (PDFs) flatten, enhancing the drought increases induced primarily by decreases in the mean. Precipitation (P) and evapotranspiration (E) changes contribute to the SM change; whereas decreases in sc_PDSI_pm result from ubiquitous PET increases of 10%-20% with contributions from decreased P over subtropical areas. Rising temperatures and vapor deficits explain most of the PET increase, which in turn explains most of the E increases over Asia and northern North America while decreased SM leads to lower E over the rest of the world. Radiation and wind speed changes have only small effects on future PET and drought. Globally, runoff ratio changes little while P, E, and R all increase by about 4%-5% in the twenty-first century.
SHORTER COMMUNICATIONS SHORTER COMMUNICATIONS relationship to body size. Herpetologica 41:194-205. , AND. 1987. Morphological constraints on egg size: a challenge to optimal egg size theory. Proc. Nat. Acad. Sci. 84:4145-4147. GEORGES, A. 1984. Observations on the nesting and natural incubation of the long-necked tortoise Chel-odina expansa in southeast Queensland. Herpeto-fauna 15:27-31. ,C.
Thermal performance curves are useful for predicting how organisms might respond to environmental change, and are becoming increasingly applicable for ectothermic animals threatened by climate change. Here we present a thermal performance curve for the critically endangered western swamp turtle (Pseudemydura umbrina) based upon measurements of O2 consumption and CO2 production obtained by flow-through respirometry at temperatures between 15 and 30°C. Standard metabolic rate was significantly higher at 30°C (0.030mLg-1h-1 O2, 0.021mLg-1h-1 CO2) than at 20°C (0.007mLg-1h-1 O2, 0.006mLg-1h-1 CO2) and the 20-30°C Q10 for O2 and CO2 were 4.60 and 3.55 respectively. Oxygen consumption rates at 15°C and 25°C were 0.002 (±0.000) and 0.018 (±0.000)mLg-1h-1, with a corresponding Q10 of 9.21. Beyond ∼30°C there was a decline in physiological performance, which was supported by activity patterns reported for P. umbrina in the literature.
This study monitored natural nest temperatures and examined the effect of incubation temperature on hatchling phenotype of the freshwater turtle Elseya albagula to determine the optimal temperature for a potential head-start program. Eggs were incubated at constant temperatures (26°C, 28°C and 30°C) to determine the influence of temperature on incubation period, hatchling morphology, swimming performance and post-hatching growth rate. Hatchlings incubated at 26°C had longer plastrons than hatchlings from 30°C and swam faster, three days after hatching, than did hatchlings incubated at either 28°C or 30°C. Incubation temperature also provided a source of variation in hatchling scute patterns. Clutch of origin influenced hatchling mass and size, growth at 184 days after hatching, and the swimming performance of 3-day and 75-day post-hatch hatchlings. Constant temperatures of 26°C and 28°C produced the highest hatching success and highest-quality hatchlings and are therefore recommended for incubation of eggs in a head-start program. In the field, unshaded nests experienced greater daily fluctuations in temperature and higher temperatures overall compared with shaded nests, such that unshaded nest temperatures approached the upper thermal limit to development.
An investigation of the habitat and dietary pret'erences of freshwater turtles inhabiting ephemeral billabongs on the Ovens River State Forest floodplain at Killawarra, Victoria, was conducted over the summer of 1997/1998. Two species of turtle, Chelodina longicollis and Emydura mucquarii, were captured. Analysis of turtle stomach contents provided confirmation of their diets with other published literature, with the exception of Chelodina longicollis which consumed large amounts of plant matter although it has been classified as an obligate carnivore. Field observations revealed that turtles prefened more complex macrophyte habitats, when available, over less complex snag and clear water areas.
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.
It is unclear how predicted rises in ambient temperature associated with climate change will impact upon the survivorship of oviparous reptiles. Given that the incubation temperature can influence hatchling phenotype, understanding how elevated temperatures during development can affect the ability of hatchlings to undertake routine behaviours is important, especially for threatened species. Here we tested if raising mean incubation temperature above natural levels altered the physiology of hatchlings to an extent that behavioural function was impaired. Firstly, incubation temperatures were recorded from nests of the freshwater turtle (Elusor macrurus) in the wild, and the observed thermal range (26–31 °C) used to define the experimental protocol. Then, freshly laid E. macrurus eggs were collected and incubated at three constant temperatures (26, 29 and 32 °C). Embryos incubated at 32 °C had the lowest hatching success. Those that did hatch were smaller than the other groups and had a reduced post-hatch growth rate. On land, the ability of hatchling turtles to right themselves is critical, and the turtles incubated at 32 °C took 30-times longer to do this than those incubated at 26 °C. Once in the water, hatchling turtles must be able to swim effectively to evade predation and obtain food items. During swimming trials the 32 °C group exhibited a lower mean stroke force (10.5±0.3 mN) and spent less time swimming (133.7±17.7 s) compared with hatchlings incubated at 29 °C (13.4±0.4 mN, 281.3±25.7 s) and 26 °C (15.7±0.5 mN, 270.8±28.5 s). The results of the present study illustrate that even slight rises in the mean incubation temperature, over that observed in the wild, can impact upon a hatchling's performance.
summaRy. – The eastern long-necked turtle, Chelodina longicollis (Family Chelidae), has a wide distribution throughout southeastern Australia. It occupies a broad range of freshwater aquatic habitats but is more abundant in shallow, ephemeral wetlands often remote from permanent rivers. Its propensity for long distance overland migration, coupled with a low rate of desiccation and the capacity to estivate on land, enable it to exploit highly-productive ephemeral habitats in the absence of competition from fish and other turtle species. In wetter periods, such habitats provide optimal conditions for growth and reproduction. In drier periods, however, turtles may need to seek refuge in permanent water where high population densities and low productivity can lead to reduced growth rates and reproductive output. The species is an opportunistic carnivore that feeds on a broad range of plankton, nekton and benthic macro-invertebrates, carrion, as well as terrestrial organisms that fall upon the water. It is relatively slow to mature (7–8 yrs for males and 10–12 yrs for females), lays between 6 and 23 hard-shelled eggs during spring and late summer, and can produce up to 3 clutches per year. Although currently considered common and not under major threat, the most widespread conservation concern for C. longicollis is high nest predation from the introduced fox (Vulpes vulpes), and roads, pest fencing, and habitat changes brought about by prolonged drought and climate change, which present localized and potential future threats for certain populations. distRibution. – Australia. Found throughout southeastern Australia, including southeastern Queensland, New South Wales, Victoria, and southeastern South Australia. synonymy. – Testudo longicollis Shaw 1794, Emys longicollis, Chelodina longicollis, Hydraspis longicollis, Chelys (Chelodina) longicollis, Chelydura longicollis, Chelodina longicollis longicollis, Chelodina novaehollandiae Duméril and Bibron 1835, Chelodina sulcata Gray 1856a, Chelodina longicollis sulcata, Chelodina sulcifera Gray 1856b, Chelodina longicollis sulcifera. subspecies. – None currently recognized. status. – IUCN 2008 Red List: Not Listed (= Least Concern, LR/lc) (assessed 1996, needs updating); CITES: Not Listed; Australian EPBC Act: Not Listed.
Australia's largest snake-necked turtle, Chelodina (Macrochelodina) expansa (Family Chelidae), occurs broadly through the inland rivers and billabongs of eastern and southeastern Australia. The species is cryptic in habit, yet occupies waters heavily exploited and regulated by humans. Traditionally considered a riverine species, recent studies demonstrate that it is more frequently represented in permanent lakes and billabongs connected to main river channels. Typical of many freshwater turtles, C. expansa displays delayed maturity and high adult survivorship. It is carnivorous and feeds primarily on fast-moving prey such as crustaceans and fish, but will also consume carrion. The reproductive biology of C. expansa sets it apart from most other turtles; in response to low temperatures, embryos enter a diapause, which enable them to survive over winter in nests, resulting in a year-long incubation period. Chelodina expansa has lower population densities than sympatric turtle species, which may increase its vulnerability to threats. Persistence of C. expansa relies on habitat quality and longitudinal connectivity of freshwater systems in southeastern Australia.
Adult sex ratios vary considerably among populations of single species and across years, but the best evidence is drawn from species with temperature-dependent sex determination. It is difficult to disentangle the effects of bias in the production of the sexes and the effects of a range of other factors contributing to biased adult sex ratios. In this paper, we survey sex ratios across populations of a species constrained to produce 1:1 offspring sex ratios by genotypic sex determination and show considerable variation in adult sex ratios. Raw adult sex ratios of Emydura macquarii emmottii were significantly biased in nine of the 11 populations examined. In all but one case, the bias was strongly in favour of males. Part of the bias in sex ratio was attributed to the differing ages of maturity of males and females-males mature younger than females-which leads to more male cohorts being included in the calculations of sex ratio than female cohorts. However, correcting for this effect brought the sex ratios of the populations closer to parity, as expected, and accounted for an overall 62% of the male surplus evident in the adult sex ratio. Even so, it was insufficient to explain the strong male bias (1.2-2.9) in five of the nine populations initially showing such bias. This provides support to those who advise caution in interpreting adult sex ratio data for freshwater turtles in the context of demography, sex allocation or evaluating the impact of climate change.
Chelodina longicollis is an opportunistic carnivore that obtains its food from a wide variety of sources— plankton, nekton, benthic macro-organisms, carrion, and terrestrial organisms that fall upon the water. Although there are some quantitative differences between the littoral components of the diet and the composition of the littoral fauna, these can be attributed to differences in accessibility or ‘noticeability’ among prey species. There is no evidence to suggest that C. longicollis is selective in what it eats, within the confines of carnivory. Comparison of the diet of C. longicollis with those of other sympatric chelids reveals considerable overlap; the relevance of this to geographic variation in abundance of the species is discussed.
Understanding the evolutionary history of diversifying lineages and the delineation of evolutionarily significant units and species remain major challenges for evolutionary biology. Low cost representational sampling of the genome for single nucleotide polymorphisms (SNPs) shows great potential at the temporal scales that are typically the focus of species delimitation and phylogeography. We apply these markers to a case study of a freshwater turtle, Emydura macquarii, whose systematics has so far defied resolution, to bring to light a dynamic system of substantive allopatric lineages diverging on independent evolutionary trajectories, but held back in the process of speciation by low level and episodic exchange of alleles across drainage divides on various timescales. In the context of low‐level episodic gene flow, speciation is often reticulate, rather than a bifurcating process. We argue that species delimitation needs to take into account the pattern of ancestry and descent of diverging lineages in allopatry together with the recent and contemporary processes of dispersal and gene flow that retard and obscure that divergence. Underpinned by a strong focus on lineage diagnosabilty, this combined approach provides a means for addressing the challenges of incompletely isolated populations with uncommon, but recurrent gene flow in studies of species delimitation, a situation likely to be frequently encountered. Taxonomic decisions in cases of allopatry often require subjective judgements. Our strategy, which adds an additional level of objectivity before that subjectivity is applied, reduces the risk of taxonomic inflation that can accompany lineage approaches to species delimitation.
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Turtles face a variety of threats (e.g. habitat destruction, introduced predators) that are pushing many species towards extinction. Vehicle collisions are one of the main causes of mortality of adult freshwater turtles. To conceptualise the level of threat that roads pose to Australians turtles, we analysed data gathered through the citizen science project TurtleSAT along the Murray River. We recorded 124 occurrences of turtle road mortality, which included all three local species (Chelodina expansa, Chelodina longicollis, and Emydura macquarii). Chelodina longicollis was the most commonly reported species killed on roads. We found that rain and time of year affect the likelihood of C. longicollis being killed on roads: increased turtle mortality is associated with rain events and is highest during the month of November, which coincides with their nesting season. Chelodina longicollis was most likely to be killed on the Hume Highway and roads around major urban centres therefore, we recommend that governing bodies focus management practices and increase awareness at these locations. The degree of road mortality that we detected in this study requires mitigation, as it may contribute to the decline of C. longicollis along the Murray River.
Consumers usually respond to variations in prey availability by altering their foraging strategies. Generalist consumers forage on a diversity of resources and have greater potential to 'switch' their diet in response to fluctuations in prey availability, in comparison to specialist consumers. We aimed to determine how the diets of two specialist species (the eastern long-necked turtle (Chelodina longicollis) and the broad-shelled turtle (Chelodina expansa) and the more generalist Murray River short-necked turtle (Emydura macquarii) respond to variation in habitat and prey availability. We trapped and stomach-flushed turtles, and compared their diets along with environmental variables (turbidity, macrophyte and filamentous green algae cover, and aquatic invertebrate diversity and abundance) at four wetlands in north-central Victoria. Diets of E. macquarii differed from those of both Chelodina species, which overlapped, across all four sites. However, samples sizes for the two Chelodina species were too small to compare among-wetland variation in diet. Dietary composition of E. macquarii was variable but did not differ statistically among sites. Emydura macquarii preferentially selected filamentous green algae at three of the four sites. Where filamentous green algae were rare, total food bolus volume was reduced and E. macquarii only partially replaced it with other food items, including other vegetation, wood, and animal prey. Many turtles at these sites also had empty stomachs. Thus, filamentous green algae may be a limiting food for E. macquarii. Although E. macquarii has previously been described as a generalist, it appears to have limited ability to replace filamentous green algae with other food items when filamentous green algae are rare.
Turtles have persisted for over 220 million years, despite facing threats at every life-history stage. In Australia, nest predation by introduced foxes has driven severe declines in some populations. Our project quantified the nesting habitat of the endangered broad-shelled turtle (Chelodina expansa) to facilitate protection of critical nesting grounds. We determined the nesting preferences of C. expansa at five distinct wetlands on the Murray River from 2011 to 2014. We identified environmental variables associated with nest sites in different habitats and compared those at nests and non-nest sites to determine nesting preferences. Kernel density estimates were used to identify important nesting grounds. Our study has important implications for conservation of C. expansa. Habitat preferences for nest sites of C. expansa are predictable both within and across sites, with females preferring to nest ∼50 m from shore (∼4 m elevation), in open habitat with little vegetation. Based on these habitat preferences, kernel density estimates showed that C. expansa may select the same nesting beaches in subsequent years. Fox depredation of nests (and nesting adults) drives turtle declines in Australia, so identifying nesting areas for protection is a first step in turtle conservation.
Environmental flows (e-flows) are a common management tool to improve the health of flow-regulated river systems and their biota. The effect of e-flows on fish, waterbirds and vegetation has been assessed in Australia, but their influence on turtles remains largely unstudied. We opportunistically examined the effect of e-flows on the eastern longnecked turtle (Chelodina longicollis), a species that occupies ephemeral aquatic habitats, by measuring an index of abundance (catch per unit effort) and body condition before and after an environmental watering event that replenished a severely contracted creek in the mid-Murray region. We found that average body condition increased after watering. Abundance decreased markedly after watering, but the change was not statistically significant. While the causal inference of our study was limited by the opportunistic nature of our before-after experimental design, this study provides preliminary evidence that environmental flows may improve the health of turtles occupying ephemeral floodplain habitats.Weencourage further research into the effect of e-flows on turtles to confirm the hypothesis that the increase in average body condition recorded in the current study was a function of e-flows.
The embryos of many egg-laying species develop under the environmental conditions selected by one or both parents, and these conditions may cease to be optimal under a changed climate. Assisted colonization is an emerging option to relocate species that are threatened by unfavourable changes in the local climate, but the incubation requirements of embryos are rarely considered in conservation translocations despite suggestions that relocation of early life stages could be more effective than relocating older animals. Here we review examples and outcomes of relocations of reptile eggs, and the decision tools currently available for guiding translocation decisions from an embryonic perspective. We then demonstrate a mechanistic approach, using the modelling framework NicheMapR, for assessing the optimal translocation range for the Western Swamp Turtle (Pseudemydura umbrina), a Critically Endangered reptile with an extremely restricted natural distribution. We determine thermal reaction norms and critical thermal limits for embryonic development based on laboratory and field data, and model soil temperatures at typical nest depths, simulate embryonic development at these depths, and map the probability of survival of P. umbrina embryos within the major bioregions of south-western Australia. The same model forced by future climates for 2050–70 demonstrates a southerly shift in the regions where embryos would be viable. However, if P. umbrina is to be translocated in the near future to regions 300–400 km south of its natural range, females will need to nest in relatively unshaded sites to achieve temperatures that are high enough to promote hatchling success.
The dynamics of bimodal respiration, diving behaviour and blood acid-base status in the softshell turtle Trachemys scripta and the pond slider Apalone ferox were investigated at rest and under conditions of stress induced by exercise and forced submergence. During periods of forced submergence, only A. ferox doubled its aquatic gas exchange rate. Both A, fel ox and T, scripta increased their aerial gas exchange profoundly following exercise and forced submergence, a pattern indicative of increased anaerobic respiration. Emersion duration increased significantly in A. ferox following forced submergence, and mean apnoeic time decreased significantly in A. ferox following exercise, indicating that a larger proportion of time at the surface was spent ventilating. Also, A. ferox maintained a one-breath breathing bout regardless of treatment. Submergence produced a respiratory acidosis in the plasma of approximately 0.2 pH units in magnitude in T, scripta and a mixed respiratory/metabolic acidosis of 0.4 pH units in A. ferox. Exercise induced an acidosis of 0.2 pH units of primarily metabolic origin in both species. Intra-erythrocyte pH was also reduced in both species in response to submergence and exercise, Both intracellular and extracellular acidoses were more severe and longer lasting in A, ferox after each treatment, Plasma [HCO3-] decreased by 25 % in both species following exercise, but only in A. ferox following submergence. Plasma lactate concentrations increased by equal amounts in each species following exercise; however, they returned to resting concentrations sooner in T, scripta than in A. ferox, A, ferox had significantly higher lactate levels than T, scripta following forced submergence as well as a slower recovery time. A, ferox, which is normally a good bimodal gas exchanger at rest, utilizes aerial respiration to a greater extent when under respiratory and/or metabolic stress. T, scripta, although almost entirely dependent on aerial respiration, is physiologically better able to deal with the respiratory and metabolic stresses associated with both forced submergence and exercise.
The thermal acclimatory capacity of a particular species may determine its resilience to environmental change. Evaluating the physiological acclimatory responses of economically important species is useful for determining their optimal culture conditions. Here, juvenile Chinese three-keeled pond turtles (Mauremys reevesii) were acclimated to one of three different temperatures (17, 25 or 33°C) for four weeks to assess the effects of thermal acclimation on some physiological traits. Thermal acclimation significantly affected thermal resistance, but not thermal preference, of juvenile M. reevesii. Turtles acclimated to 17°C were less resistant to high temperatures than those acclimated to 25°C and 33°C. However, turtles increased resistance to low temperatures with decreasing acclimation temperature. The acclimation response ratio of the critical thermal minimum (CTMin) was lower than that of the critical thermal maximum (CTMax) for acclimation temperatures between 17 and 25°C, but slightly higher between 25 and 33°C. The thermal resistance range (i.e., the difference between CTMax and CTMin) was widest in turtles acclimated to the intermediate temperature (25°C), and narrowest in those acclimated to low temperature (17°C). The standard metabolic rate increased as body temperature and acclimation temperature increased, and the temperature quotient (Q10) between acclimation temperatures 17 and 25°C was higher than the Q10 between 25 and 33°C. Our results suggest that juvenile M. reevesii may have a greater resistance under mild thermal conditions resembling natural environments, and better physiological performance at relatively warm temperatures.
Chelodina longicollis in the vicinity of Armidale, NSW show typical temperate-zone chelonian gametogenic patterns. Mating is in September and ovulation occurs during late October and November. A single clutch is laid in November or December. The nesting season lasts c1 months although commencement date varies each year. There are significant positive correlations between female size/clutch size and female size/egg diameter. Natural incubation period is 110-120 days (nest temperature 21.5oC; range 12.5-32.0oC). Minimum estimate of nest predation at one study site was 49%. Nest predation in the general study area was probably greater. Hatchlings emerge from the nest in late March and go directly to water. Data indicated a Slobodkin Type IV survivorship curve with mortality primarily affecting eggs, hatchlings and juveniles. Estimated non-juvenile mortality was <2% per annum. -from Author
Growth rates of juveniles and age at maturity of males were examined in a population of painted turtles, Chrysemys picta, inhabiting a marsh in southwestern Michigan (approximately 42 degrees 24'N, 85 degrees 24'W) to compare temporal variation in these two important life history traits within a decade. Elongation of the third right foreclaw was used as an indicator of incipient sexual maturity of males. Males in the late 1980s reached maturity at least a year earlier than did those in the early 1980s. Analysis of climatological data revealed that growing seasons in the late 1980s were typically warmer and longer than in the early years of the decade. The observed changes in juvenile growth rates and age at maturity of male C. picta are in accord with recent field and laboratory studies of emydid turtles. They also support predictions of life history theory, and may serve as working hypotheses that can be tested with data from other long-term projects. If substantiated, these patterns may indicate how some freshwater turtle populations in temperate latitudes might respond to predicted global warming trends.
We determined the effects of dietary protein and on growth rates, food consumption rates, digestion rates, and digestive efficiencies of juvenile slider turtles (Trachemys scripta). Results from this study provide a clearer understanding of how these environmental factors interact in influencing body sizes and growth rates of individuals in wild slider turtle populations. Changes in plastron length, carapace length, and body mass were significantly greater for T. scripta eating 25% and 40% crude protein diets than for those eating 10% crude protein. Those consuming 10% crude protein showed significant decreases in body mass and plastron length over a 13-wk period. Individuals at of 15°, 22°, 28°, or 34° C had food ingestion rates (kJ wk⁻¹) that increased markedly with an increase in . Increasing dietary crude protein concentration increased turtle ingestion rates and influenced the positive effect of . Increasing dietary crude protein concentration alone did not significantly affect turtle consumption rates but did significantly influence the positive effect of . Digestive efficiencies were very high (because of the pelleted diet). Those turtles that ate at 15° C had a digestive efciency of 99.5%, as compared with 98.3% at 22° C, 94.8% at 28° C, and 95.8% at 34° C. Dietary protein concentration did not influence the digestive efficiencies of T. scripta. These data suggest that dietary protein is an important nutritional component to the growth of juvenile slider turtles and that elevated thermal conditions, combined with a high dietary protein availability, may explain the very high growth rates of slider turtles in some wild populations.
When painted turtles engage in a two minute period of intense exercise in a dry metabolic chamber at 25 C, their rate of consumption of oxygen from chamber air rises from a resting level of 0.0302 cm3 O2 g-1 h-1 to a maximal level of 0.1837 cm3 O2 g-1 h-1, their total body lactate content increases from 0.145 to 0.255 mg lactate g-1, and their lung oxygen concentration remains unchanged. In contrast, a two minute burst of swimming by painted turtles in 18 cm of water at 25 C is associated with a statistically insignificant change in oxygen uptake, a rise in total body lactate content from 0.188 to 0.487 mg lactate g-1, and a decline in lung oxygen concentration from 17.18 to 13.26%. These results suggest that 56% of the ATP liberated during maximal activity by a painted turtle in a terrestrial environment comes from anaerobic pathways whereas 71% of the ATP provided during burst swimming comes from this source. The total metabolic scope for activity for painted turtles in water is over twice that of animals in a dry metabolic chamber. Thus, the energetics of muscular activity of painted turtles differs considerably between land and water. These results suggest that measurement of the depletion of oxygen stores is important in assessing the relative importance of aerobic and anaerobic metabolism during activity in aquatic species.
The female reproduction of Chrysemys scripta elegans was compared in natural lakes and a lake receiving thermal effluent from a coal-fired power plant. Upon maturation turtles from the heated lake were younger and larger than those from the natural lake. The nesting season began earlier with mean clutch size being larger for the females in the heated lake. Reproductive potential was much greater in the heated lake, giving that population a much larger rate of natural increase.
Maternal ability to match nest characteristics with environmental conditions can influence offspring survival and quality, and may provide a mechanism by which animals can keep pace with climate change. In species with temperature-dependent sex determination that construct subterranean nests, the depth of the nest may affect incubation temperatures, and thus offspring sex ratio. Maternal adjustment of nest depth may be a mechanism by which climate change-induced sex ratio skews could be prevented in globally imperiled taxa such as turtles. We experimentally manipulated nest depth within a biologically relevant range in nests of the model turtle species Chrysemys picta. We then quantified the effects of nest depth on incubation regime, offspring sex ratio and offspring performance. We found no effect of nest depth on six parameters of incubation regime, nor on resultant offspring survival, size or sex ratio. However, deeper nests produced hatchlings that weighed less, and were faster at righting themselves and swimming, than hatchlings from shallower nests. We suggest that cues used by females in adjusting nest depth are unreliable as predictors of future incubation conditions, and the adjustment in nest depth required to affect sex ratio in this species may be too great to keep pace with climate change. Therefore, maternal adjustment of nest depth seems unlikely to compensate for climate change-induced sex ratio skews in small-bodied, freshwater turtles.
How are organisms responding to climate change? The rapidity with which climate is changing suggests that, in species with long generation times, adaptive evolution may be too slow to keep pace with climate change, and that alternative mechanisms, such as behavioural plasticity, may be necessary for population persistence. Species with temperature-dependent sex determination may be particularly threatened by climate change, because altered temperatures could skew sex ratios. We experimentally tested nest-site choice in the long-lived turtle Chrysemys picta to determine whether nesting behaviour can compensate for potential skews in sex ratios caused by rapid climate change. We collected females from five populations across the species′ range and housed them in a semi-natural common garden. Under these identical conditions, populations differed in nesting phenology (likely due to nesting frequency), and in nest depth (possibly due to a latitudinal cline in female body size), but did not differ in choice of shade cover over the nest, nest incubation regime, or in resultant nest sex ratios. These results suggest that choice of nest sites with particular shade cover may be a behaviourally plastic mechanism by which turtles can compensate for change in climatic temperatures during embryonic development, provided that sufficient environmental variation in potential nest microhabitat is available.
1.1. Oxygen consumption of resting and active snapping turtles at 10, 20 and 30°C was measured following acclimation to 10 and 25°C.2.2. Cold acclimation results in depressed resting and active rates of oxygen consumption and in a decreased aerobic metabolic scope for activity; these changes facilitate hibernation.3.3. Warm-acclimated animals have a high aerobic capacity which supports aquatic and terrestrial activity.
The complexity of instrumentation sometimes requires data analysis to be done before the result is presented to the control room. This tutorial reviews some of the theoretical assumptions underlying the more popular forms of data analysis and presents simple examples to illuminate the advantages and hazards of different techniques. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Individual yellow-bellied turtles (Pseudemys scripta) in Par Pond, a thermally polluted reservoir on the Savannah River Plant, Aiken, South Carolina, U.S.A., reach exceedingly large body sizes and maintain extraordinary juvenile growth rates when compared with turtles of this species from other populations in the vicinity. Increased water temperatures are not directly responsible for the observed size and growth differences. Diet differences resulting from increased productivity at lower trophic levels as a result of the hot-water effluent may be the cause of the observed growth and size phenomena. The increased growth rates and larger body sizes in the Par Pond turtles result in changes in reproductive rate which may have interesting consequences on the demography of the population.
Incubation periods and nest contents of three species of chelid tortoises in
northern Victoria were recorded. Mean incubation period for eggs of Emydura macquari
(Cuvier) was 75 days and average number of eggs per nest was 15.7; for Chelodina
longicollis (Shaw), 138 days and 10.7 eggs per nest; for Chelodina expansa Gray,
normally exceeding 324 days and 15.4 eggs per nest. In abnormal seasons C. expansa
hatchlings may emerge from the nest in less than 193 days or more than 522 days after
eggs were deposited.
Eggs artificially incubated at 30°C consistently develop more quickly than those
at lower temperatures under natural conditions. In the field nest temperatures closely
approximate the mean daily air temperature.
Embryos of C. expansa are tolerant to nest temperatures ranging from 4.9°C
minimum to 29.6°C maximum. The other species are subject to variations of about
15 degC with up to 8.5 degC variation being recorded in 1 day.
Development of early embryos approximated that recorded for cryptodire
tortoises. However, there are large individual differences in the period of incubation
needed for specific stages to be reached, especially between embryos of the short-necked
and long-necked species of these pleurodire tortoises.
It is suggested that differences in the anatomy of their eggs are the main factors
in the different incubation periods between short-necked and long-necked species.
Climate change will affect hydrologic and thermal regimes of rivers, having a direct impact on freshwater ecosystems and human water use. Here we assess the impact of climate change on global river flows and river water temperatures, and identify regions that might become more critical for freshwater ecosystems and water use sectors. We used a global physically based hydrological-water temperature modelling framework forced with an ensemble of bias-corrected general circulation model (GCM) output for both the SRES A2 and B1 emissions scenario. This resulted in global projections of daily river discharge and water temperature under future climate. Our results show an increase in the seasonality of river discharge (both increase in high flow and decrease in low flow) for about one-third of the global land surface area for 2071–2100 relative to 1971–2000. Global mean and high (95th percentile) river water temperatures are projected to increase on average by 0.8–1.6 (1.0–2.2) 8C for the SRES B1–A2 scenario for 2071–2100 relative to 1971–2000. The largest water temperature increases are projected for the United States, Europe, eastern China, and parts of southern Africa and Australia. In these regions, the sensitivities are exacerbated by projected decreases in low flows (resulting in a reduced thermal capacity). For strongly seasonal rivers with highest water temperatures during the low flow period, up to 26% of the increases in high (95th percentile) water temperature can be attributed indirectly to low flow changes, and the largest fraction is attributable directly to increased atmospheric energy input. A combination of large increases in river temperature and decreases in low flows are projected for the southeastern United States, Europe, eastern China, southern Africa and southern Australia. These regions could potentially be affected by increased deterioration of water quality and freshwater habitats, and reduced water available for human uses such as thermoelectric power and drinking water production.
Rates of oxygen consumption of Scaphiopus hammondii were measured during rest, forced activity, and recovery from activity. Similar measurements were taken from Bufo cognatus, Rana pipiens, and R. catesbeiana for comparison. Aerobic metabolic scope for activity strictly increased with temperature in all species tested. Maximum absolute scopes of B. cognatus (1.36 cc O2/g·hr) and S. hammondii (1.22 cc O2/g·hr) were comparable only to those of the most active ectothermal vertebrates in the literature and were considerably greater than the scopes of R. pipiens (0.32 cc O2/g·hr) and R. catesbeiana (0.16 cc O2/g·hr). High aerobic scopes of the toads may be correlated with both the natural occurrence of long periods of sustained burrowing activity and the absence of behavioral thermoregulation. S. hammondii and B. cognatus failed to show signs of fatigue after long periods of exercise. R. pipiens and R. catesbeiana, however, apparently fatigued rapidly. The relative magnitude of the oxygen debts suggested that anaerobic metabolism during exercise is of greater importance in R. pipiens and R. catesbeiana than in S. hammondii. Within about one hour, S. hammondii repaid oxygen debts which amounted to 15-29% of the total oxygen consumed for the support of activity. At temperatures between 20 and 32.5 C, the apparent importance of anaerobic metabolism was less than at lower temperatures, possibly reflecting high metabolic scopes within this temperature range. Rates of oxygen consumption of S. hammondii were determined while the toads burrowed in soil. Digging was intermittent at all temperatures tested. Comparison of the calculated oxygen demand during the bouts of burrowing to the maximum rate of supply during forced activity revealed that slight oxygen debts were repaid during periods of inactivity between bouts of digging. This conclusion was substantiated by low blood lactate levels observed following burrowing as compared to high levels following forced activity. S. hammondii may be able to utilize energy more economically by burrowing intermittently and avoiding a large oxygen debt than it could by burrowing continuously.
Observations of natural populations and captives over a period of 6 years provide preliminary information on the ecology of a poorly known and secretive species. Included are observations on habitat partitioning in small pools where two other chelid species occur and notes on the carnivorous diet and manner of feeding. Head bobbing and self-grooming behavior are described.
Activity cycles of Chelodina expansa, C. longicollis and Emydura macquarii were inferred from captures
in baited traps set in the Murray River and Lake Boga. C. expansa and E, macquarii were caught
only from October to April, while C. longicollis was taken in all months but June and July. Minimum
water temperatures at capture were highest for C. expansa and lowest for C. longicollis. Diel cycles of
catch rate were often weak, but tended to be bimodal for all species, with peaks near dawn and in
the afternoon or evening. Unlike the Chelodina species, E. macquarii was ofen caught near midnight.
In the laboratory (at c. 24'C with light : dark 12 : 12 h), the average diel pattern of locomotor activity
was weakly bimodal in C. expansa, strongly bimodal in C. longicollis and unimodal in E. macquarii.
Preferences of Chelodina expansa, Chelodina longicollis and Emydura macquarii (Testudines : Chelidae)
for different types of aquatic habitat on the Murray River flood plain in south-eastern Australia were
inferred from catch statistics. E. macquarii was the species most often caught in the river itself and river
backwaters, whereas C. longicollis formed the majority of captures from oxbow lakes, anabranches,
ponds, rain pools and a swamp. Relative abundance of E. macquarii was significantly positively
correlated with water body depth, transparency, persistence during dry conditions and flow speed, and
negatively correlated with remoteness from the river. C. longicollis demonstrated the opposite pattern,
and the proportional catch of C. expansa was weakly correlated with environmental variables. The
capacity of C. longicollis for colonising and surviving in small, remote and ephemeral ponds and pools
relates to its ability to aestivate and resist desiccation and its propensity for overland migration.