Patterns of activity and body temperature of Aldabra giant tortoises in relation to environmental temperature

100 million years of turtle paleoniche dynamics enable the prediction of latitudinal range shifts in a warming world

Past responses to environmental change provide vital baseline data for estimating the potential resilience of extant taxa to future change. Here, we investigate the latitudinal range contraction that terrestrial and freshwater turtles (Testudinata) experienced from the Late Cretaceous to the Paleogene (100.5-23.03 mya) in response to major climatic changes. We apply ecological niche modeling (ENM) to reconstruct turtle niches, using ancient and modern distribution data, paleogeographic reconstructions, and the HadCM3L climate model to quantify their range shifts in the Cretaceous and late Eocene. We then use the insights provided by these models to infer their probable ecological responses to future climate scenarios at different representative concentration pathways (RCPs 4.5 and 8.5 for 2100), which project globally increased temperatures and spreading arid biomes at lower to mid-latitudes. We show that turtle ranges are predicted to expand poleward in the Northern Hemisphere, with decreased habitat suitability at lower latitudes, inverting a trend of latitudinal range contraction that has been prevalent since the Eocene. Trionychids and freshwater turtles can more easily track their niches than Testudinidae and other terrestrial groups. However, habitat destruction and fragmentation at higher latitudes will probably reduce the capability of turtles and tortoises to cope with future climate changes.

Evaluation of locomotor activity in female Chelonoidis chilensis (Testudinidae, Gray 1870) in response to artificial photoperiod and temperature treatments

Turtles as many other reptiles are capable of orientating their bodies toward the sun. This conduct requires the presence of an internal biological chronometer in the organism that regulates this behavior. Thus, a description of the internal clock in these reptiles is of interest. The assessment of locomotor activity can be considered a reliable indicator of biological clock function. This study aimed to investigate the effect of different artificial photoperiod and ambient temperature schedules on total locomotor activity of female Chelonoidis chilensis and its rhythmicity. Six C. chilensis specimens were exposed to different artificial photoperiods and temperature regimes each fixed for seven days. It was observed that the activity period during the different experimental schedules was close to the 24 hours indicating a daily rhythmicity. Moreover, all tortoises showed a similar total locomotor activity pattern displaying the most of motion during light phase. Under the condition of constant light tortoises exhibited a self-sustaining rhythm not entrained to light and temperature zeitgebers, thus, suggesting its possible endogenous periodicity. Though this study deepens the knowledge on the rhythmic system of C. chilensis, further investigations are needed to achieve a more detailed understanding of tortoise biological clock.

Cardiovascular contributions and energetic costs of thermoregulation in ectothermic vertebrates

Ectothermic vertebrates use a suite of physiological and behavioral mechanisms to thermoregulate, which result in various thermoregulatory strategies from thermoconformity to thermoregulation. Here, we present a novel synthesis of theoretical and empirical methods to determine cardiovascular contributions to heat transfer in free-living ectothermic vertebrates. We start by identifying the fundamental components of heat transfer and the cardiovascular mechanisms for physiological modulation of heat exchange, and then integrate these components into a single, integrative framework: the cardiovascular heat exchange framework (CHEF). We demonstrate that this framework can identify details of the thermoregulatory strategy in two turtle species, most notably the preponderance of instances where turtles use physiological mechanisms to avoid overheating, suggesting vulnerability to climate change. As modulated physiological contributions to heat flow incur a greater energy demand than relying on unmodulated passive heat transfer, we then asked whether we could characterize the energetic costs of thermoregulation. We measured field metabolic rate (FMR) in free-living turtles and used the CHEF to determine FMR while actively or passively thermoregulating. Comparing an individual's actual FMR to the rate calculated assuming absence of thermoregulation revealed that painted turtles, a partial thermoregulator, elevate their daily energy expenditure (DEE) by about 25%, while box turtles, a thermoconformer, have a DEE that is nearly unchanged as a result of thermoregulation. This integrative framework builds a new paradigm that provides a mechanism to explain correlations between energy demand and thermoregulatory strategy, quantifies the energetic costs of thermoregulation, and identifies the role of cardiovascular contributions to thermoregulation in free-living animals.

Investigating the Behavior and Personality Structure of the Aldabra Tortoise during Human Interactions and Training Events

Simple Summary

There are many studies that suggest that a range of animal species have personalities, and that animals can benefit from interactions with their human caregivers. However, many of these previous studies have focused only on mammals, with fewer studies focusing on reptiles. Research was undertaken at the Faunistic Park Le Cornelle, Italy, to investigate the effects of approach tests and food interaction events on 5 male and 5 female Aldabra tortoises’ (Aldrabrachelys gigantea) behavior. There were differences in behavior between tortoises, and in response to different types of events. The tortoises also responded differently to their own keepers, vets, or unfamiliar people. The personality of the tortoises were also quantified using principal component analysis. Overall, the study revealed that individuals acted significantly differently to one another, and that while females initially appeared to display a greater number of shy behaviors, this was not consistent across the group. PCA revealed two personality dimensions in the tortoises, boldness and avoidance. Overall, the study revealed that the tortoises possessed personalities that were independent of sex or scenario. The study also revealed that many tortoises chose to interact with their keepers during training and approach tests: this suggests that human-tortoise interactions may have some enrichment value. Future research could quantify tortoise personality in other scenarios, such as in social interactions with other tortoises.

Abstract

Human–animal interaction (HAI) can be valuable for captive animals, and many zoo-housed species benefit from interactions with their keepers. There is also an increasing body of evidence that some animal species possess personalities that are temporally consistent. However, the majority of zoo research, particularly on personality and HAI, traditionally has focused on mammals, and there are comparatively fewer studies on reptiles. Research was undertaken at the Faunistic Park Le Cornelle, Italy, to investigate the effects of approach tests and food interaction events on 5 male and 5 female Aldabra tortoise (Aldrabrachelys gigantea) behavior. During human–tortoise interactions, continuous focal sampling of behavior took place. The behavioral differences between individual tortoises, interaction type (approach or training) and person involved in the interaction (keeper, vet, or observer) were analysed using general linear mixed-effects models. The personality components of the tortoises were also quantified using principal component analysis. Overall, the study revealed that individuals acted significantly differently to one another, and that while females initially appeared to display a greater number of shy behaviors, this was not consistent across the group. PCA revealed two personality dimensions in the tortoises: boldness and avoidance. Overall, the study revealed that the tortoises possessed personalities that were independent of sex or scenario. The study also revealed that many tortoises chose to interact with their keepers during training and approach tests: this suggests that human–tortoise interactions may have some enrichment value. Future research could quantify tortoise personality in other scenarios such as in social interactions with other tortoises.

Detectability and impact of repetitive surveys on threatened West African crocodylians

West African crocodylians are among the most threatened and least studied crocodylian species globally. Assessing population status and establishing a basis for population monitoring is the highest priority action for this region. Monitoring of crocodiles is influenced by many factors that affect detectability, including environmental variables and individual- or population-level wariness. We investigated how these factors affect detectability and counts of the critically endangered Mecistops cataphractus and the newly recognized Crocodylus suchus. We implemented 195 repetitive surveys at 38 sites across Côte d'Ivoire between 2014 and 2019. We used an occupancy-based approach and a count-based GLMM analysis to determine the effect of environmental and anthropogenic variables on detection and modeled crocodile wariness over repetitive surveys. Despite their rarity and level of threat, detection probability of both species was relatively high (0.75 for M. cataphractus and 0.81 for C. suchus), but a minimum of two surveys were required to infer absence of either species with 90% confidence. We found that detection of M. cataphractus was significantly negatively influenced by fishing net encounter rate, while high temperature for the previous 48 h of the day of the survey increased C. suchus detection. Precipitation and aquatic vegetation had significant negative and positive influence, respectively, on M. cataphractus counts and showed the opposite effect for C. suchus counts. We also found that fishing encounter rate had a significant negative effect on C. suchus counts. Interestingly, survey repetition did not generally affect wariness for either species, though there was some indication that at least M. cataphractus was more wary by the fourth replicate. These results are informative for designing future survey and monitoring protocols for these threatened crocodylians in West Africa and for other endangered crocodylians globally.

Factors influencing distributional shifts and abundance at the range core of a climate-sensitive mammal

Species are frequently responding to contemporary climate change by shifting to higher elevations and poleward to track suitable climate space. However, depending on local conditions and species' sensitivity, the nature of these shifts can be highly variable and difficult to predict. Here, we examine how the American pika (Ochotona princeps), a philopatric, montane lagomorph, responds to climatic gradients at three spatial scales. Using mixed-effects modeling in an information-theoretic approach, we evaluated a priori model suites regarding predictors of site occupancy, relative abundance, and elevational-range retraction across 760 talus patches, nested within 64 watersheds across the Northern Rocky Mountains of North America, during 2017-2020. The top environmental predictors differed across these response metrics. Warmer temperatures in summer and winter were associated with lower occupancy, lower relative abundances, and greater elevational retraction across watersheds. Occupancy was also strongly influenced by habitat patch size, but only when combined with climate metrics such as actual evapotranspiration. Using a second analytical approach, acute heat stress and summer precipitation best explained retraction residuals (i.e., the relative extent of retraction given the original elevational range of occupancy). Despite the study domain occurring near the species' geographic-range center, where populations might have higher abundances and be at lower risk of climate-related stress, 33.9% of patches showed evidence of recent extirpations. Pika-extirpated sites averaged 1.44℃ warmer in summer than did occupied sites. Additionally, the minimum elevation of pika occupancy has retracted upslope in 69% of watersheds (mean: 281 m). Our results emphasize the nuance associated with evaluating species' range dynamics in response to climate gradients, variability, and temperature exceedances, especially in regions where species occupy gradients of conditions that may constitute multiple range edges. Furthermore, this study highlights the importance of evaluating diverse drivers across response metrics to improve the predictive accuracy of widely used, correlative models.

Design of SNP markers for Aldabra giant tortoises using low coverage ddRAD-seq

The Aldabra giant tortoise (Aldabrachelys gigantea) is one of only two remaining giant tortoise species worldwide. Captive-bred A. gigantea are being used in rewilding projects in the Western Indian Ocean to functionally replace the extinct endemic giant tortoise species and restore degraded island ecosystems. Furthermore, large-scale translocations may become necessary as rising sea levels threaten the only wild population on the low-lying Aldabra Atoll. Critical management decisions would be greatly facilitated by insights on the genetic structure of breeding populations. We used a double-digest restriction-associated DNA sequencing (ddRAD-seq) approach to identify single nucleotide polymorphisms (SNP) among the wild population and two additional captive populations of A. gigantea. A total of 1674 unlinked, putatively neutral genome-wide SNPs were identified. The values of expected heterozygosity ranged from 0.33 to 0.5, whereas the minor allele frequency ranged from 0.20 to 0.5. These novel SNP markers will serve as useful tools for informing the conservation of A. gigantea.

Frugivory and seed dispersal by chelonians: a review and synthesis

In recent years, it has become clear that frugivory and seed dispersal (FSD) by turtles and tortoises is much more common than previously thought. We here review published and unpublished records of chelonian FSD, and assess the role of chelonians as seed dispersers, from individual species to the community level. We first discuss the distribution of chelonian FSD and the characteristics of the fruit and/or seed species eaten and dispersed by chelonians. We then use the seed dispersal efficiency framework to explore the quantitative and qualitative components of seed dispersal by tortoises and turtles, embarking on a journey from when the fruits and/or seeds are consumed, to when and where they are deposited, and assess how efficient chelonians are as seed dispersers. We finally discuss chelonian FSD in the context of communities and of chelonians as megafauna. A substantial proportion of the world's aquatic and terrestrial turtles and a major part of testudinid tortoises (71 species in 12 families) include fruits and/or seeds in their diet; fruits of at least 588 plant species in 121 families are ingested and/or dispersed by chelonians. For some chelonians, overall or in certain seasons, fruit may even form the largest part of their diet. Contrary to seed dispersal by lizards, the other major reptilian frugivores, chelonian FSD is not an island phenomenon in terms of geographic distribution. Nevertheless, on islands tortoises are often among the largest native terrestrial vertebrates - or were until humans arrived. We synthesise our knowledge of chelonian FSD, and discuss the relevance of our findings for conservation and restoration, especially in relation to rewilding with large and giant tortoises.

Frugivory and seed dispersal by chelonians: a review and synthesis

In recent years, it has become clear that frugivory and seed dispersal (FSD) by turtles and tortoises is much more common than previously thought. We here review published and unpublished records of chelonian FSD, and assess the role of chelonians as seed dispersers, from individual species to the community level. We first discuss the distribution of chelonian FSD and the characteristics of the fruit and/or seed species eaten and dispersed by chelonians. We then use the seed dispersal efficiency framework to explore the quantitative and qualitative components of seed dispersal by tortoises and turtles, embarking on a journey from when the fruits and/or seeds are consumed, to when and where they are deposited, and assess how efficient chelonians are as seed dispersers. We finally discuss chelonian FSD in the context of communities and of chelonians as megafauna. A substantial proportion of the world's aquatic and terrestrial turtles and a major part of testudinid tortoises (71 species in 12 families) include fruits and/or seeds in their diet; fruits of at least 588 plant species in 121 families are ingested and/or dispersed by chelonians. For some chelonians, overall or in certain seasons, fruit may even form the largest part of their diet. Contrary to seed dispersal by lizards, the other major reptilian frugivores, chelonian FSD is not an island phenomenon in terms of geographic distribution. Nevertheless, on islands tortoises are often among the largest native terrestrial vertebrates - or were until humans arrived. We synthesise our knowledge of chelonian FSD, and discuss the relevance of our findings for conservation and restoration, especially in relation to rewilding with large and giant tortoises.

Drop it like it's hot: Interpopulation variation in thermal phenotypes shows counter-gradient pattern

Ectotherms utilise a complex array of behavioural and physiological mechanisms to cope with variation in suboptimal thermal environments. However, these mechanisms may be insufficient for population persistence under contemporary climate change, resulting in a greater need to understand how local populations respond to geographic variation in climate. In this study, we explored the potential for local adaptation and acclimation in thermal traits and behaviours using wild and captive populations of a small agamid lizard (the jacky lizard, Amphibolurus muricatus). We predicted that wild lizards from a high elevation site would have cooler thermal preferences compared to those at low elevation sites to match the more restricted thermal resources at higher, cooler elevations. We additionally explored whether variation in thermal traits was due to recent acclimation or fixed population differences, such as due to developmental plasticity or local adaptation. In contrast to our predictions, we found high-elevation lizards began panting at higher temperatures and had higher thermal preferences relative to lower elevation lizards. When allowed to bask freely, there was no difference in the intensity of basking or daily duration of time spent basking between lizards from different elevations. Although the high-elevation lizards appeared to show stronger acclimation to recent air temperatures compared to low-elevation lizards, this difference was not significant. Similarly, captive lizards acclimated under long and short basking regimes showed no major differences in thermal traits or basking behaviour. Our results are consistent with the presence of counter-gradient variation in thermal phenotypes of lizards, and suggest that these are driven by local adaptive responses or developmental effects rather than recent acclimation.

Evaluation of artificial heating sources for the thermoregulation of Aldabra giant tortoises (Aldabrachelys gigantea) in Zurich zoo

We recorded the thermoregulatory patterns of five Aldabra giant tortoises (Aldabrachelys gigantea) (25-193 kg) during spring (ZRH spring trial), after the installation of a heating area (concrete heat pad and basking lamp) at Zurich Zoo, Switzerland. The measurements were compared to published results on the same tortoises observed prior to the installation of the heater (ZRH summer and winter trials), and on wild tortoises on Aldabra Atoll. The mean environmental temperature outside the heating area was 23.3 °C, significantly lower compared to Aldabra Atoll (30.3 °C; range: 23.8-43.8 °C), and to the environmental temperature range at which tortoises maximize their activity in the wild (T_a-opt ; 25.8-31.7 °C). The heating area exhibited a mean temperature of 36.3 °C, and tortoises that made use of the heating area were able to maintain a mean core body temperature (T_bc ) of 30.0 °C, which was comparable to the T_bc of tortoises during ZRH summer and on Aldabra trials, and an improvement over the mean T_bc recorded during the ZRH winter trial (21.2 °C). The smaller individuals reached the upper limits of T_bc recommended for the species, probably due to heating pad temperatures above T_a-opt . We discuss current practices to provide external heating sources for tortoises and how this method can be used to provide an adequate thermal environment for large captive reptiles. Finally, we provide recommendations for the installation of artificial heating sources for tortoises and large reptiles.

Island rewilding with giant tortoises in an era of climate change

Replacing recently extinct endemic giant tortoises with extant, functional analogues provide the perhaps best examples of island rewilding to date. Yet, an efficient future application of this conservation action is challenging in an era of climate change. We here present and discuss a conceptual framework that can serve as a roadmap for the study and application of tortoise rewilding in an uncertain future. We focus on three main ecological functions mediated by giant tortoises, namely herbivory, seed dispersal and nutrient cycling, and discuss how climate change is likely to impact these. We then propose and discuss mitigation strategies such as artificial constructed shade sites and water holes that can help drive and maintain the ecosystem functions provided by the tortoises on a landscape scale. The application of the framework and the mitigation strategies are illustrated with examples from both wild and rewilded populations of the Aldabra giant tortoise, Aldabrachelys gigantea, in the Western Indian Ocean.This article is part of the theme issue 'Trophic rewilding: consequences for ecosystems under global change'.