Terrestrial Ectotherms Research Articles

Seed dispersal by Galápagos tortoises

AbstractAim Large‐bodied vertebrates often have a dramatic role in ecosystem function through herbivory, trampling, seed dispersal and nutrient cycling. The iconic Galápagos tortoises (Chelonoidis nigra) are the largest extant terrestrial ectotherms, yet their ecology is poorly known. Large body size should confer a generalist diet, benign digestive processes and long‐distance ranging ability, rendering giant tortoises adept seed dispersers. We sought to determine the extent of seed dispersal by Galápagos tortoises and their impact on seed germination for selected species, and to assess potential impacts of tortoise dispersal on the vegetation dynamics of the Galápagos.Location Galápagos, Ecuador.Methods To determine the number of seeds dispersed we identified and counted intact seeds from 120 fresh dung piles in both agricultural and national park land. To estimate the distance over which tortoises move seeds we used estimated digesta retention times from captive tortoises as a proxy for retention times of wild tortoises and tortoise movement data obtained from GPS telemetry. We conducted germination trials for five plant species to determine whether tortoise processing influenced germination success.Results In our dung sample, we found intact seeds from > 45 plant species, of which 11 were from introduced species. Tortoises defecated, on average, 464 (SE 95) seeds and 2.8 (SE 0.2) species per dung pile. Seed numbers were dominated by introduced species, particularly in agricultural land. Tortoises frequently moved seeds over long distances; during mean digesta retention times (12 days) tortoises moved an average of 394 m (SE 34) and a maximum of 4355 m over the longest recorded retention time (28 days). We did not find evidence that tortoise ingestion or the presence of dung influenced seed germination success.Main conclusions Galápagos tortoises are prodigious seed dispersers, regularly moving large quantities of seeds over long distances. This may confer important advantages to tortoise‐dispersed species, including transport of seeds away from the parent plants into sites favourable for germination. More extensive research is needed to quantify germination success, recruitment to adulthood and demography of plants under natural conditions, with and without tortoise dispersal, to determine the seed dispersal effectiveness of Galápagos tortoises.

Acceleration data reveal the energy management strategy of a marine ectotherm during reproduction

Abstract1. Maintaining a high and stable body temperature is often critical for female ectotherms during reproduction. Yet this strategy may be energetically costly, and therefore challenging, during this period of already high‐energy demand.2. Here, the 6‐week deployment of tri‐axial accelerometers (n = 6) on a marine ectotherm, the loggerhead turtle (Caretta caretta), reproducing at the northern limit of the species’ breeding range (i.e. in a thermally dynamic environment) revealed the behavioural mechanisms underlying its energy management strategy during the breeding season.3. The estimated activity levels of female loggerheads using overall dynamic body acceleration (ODBA) were high during the breeding season, suggesting that marine turtles may not be able to remain inactive for long periods in the same manner as terrestrial ectotherms, because of the thermally dynamic nature of their environment.4. However, activity levels were not constant throughout the season, being impacted by both ambient water temperature and female reproductive status. In cold water at the beginning of the nesting season, high levels of activity suggested that females behaviourally thermoregulated by seeking out warm water patches along the shoreline. Interactions with male turtles (courtship and/or avoidance) may also explain this high level of activity. As sea temperatures warmed up and the amount of energy devoted to reproduction probably increased, the turtles spent more time resting during long sequential flat‐bottomed dives, and reduced any unnecessary locomotory activity.5. Turtles may therefore adjust their activity patterns in response to seasonal variations in abiotic (i.e. ambient temperature) and biotic (i.e. reproductive status) factors. This may help minimize activity‐linked metabolic rate and maximize reproductive output over a season while breeding in thermally dynamic environments.6. A mechanistic model gave support to these empirical results. The model revealed that actively maintaining high and stable body temperature is of clear benefit to female turtles at temperate breeding sites. While energetically costly, such active thermoregulatory behaviour may speed up egg maturation, allowing turtles to initiate nesting earlier in the season, and hence maximize reproductive output.

Tissue Carbon Incorporation Rates and Diet-to-Tissue Discrimination in Ectotherms: Tortoises Are Really Slow

Abstract Understanding carbon incorporation rates and diet-to-tissue discrimination (Δ(13)C(tissue-diet)) in animals is necessary to interpret stable isotope data collected from animals in the field. Our current understanding of the carbon dynamics in terrestrial ectotherms such as snakes, lizards, and turtles is poorly developed. Here we use a diet switch experiment to estimate carbon incorporation rates and diet-to-tissue discrimination factors in growing desert tortoises (Gopherus agassizii). Average carbon retention times for red blood cells (RBCs) and plasma were 126.7 ± 40.3 and 32.9 ± 14.5 days, respectively. Tissue carbon incorporation rates were affected by both growth and metabolism, with growth accounting for 50% of the carbon turnover in RBCs and 13% of carbon turnover in plasma. At equilibrium, scute keratin (0.8 ± 0.1) and plasma (1.0 ± 0.2) showed enriched discrimination values (Δ(13)C) compared to the test diet, but RBC Δ(13)C values were indistinguishable from diet (0.2 ± 0.3). We also found that new keratin continued to contribute significant material to previously grown keratin rings on the tortoise's shell. Changes in the δ(13)C of previously laid down growth rings indicated that the old rings closest to the region of new growth received about 73% of the carbon from the current diet; these data suggest that the interpretation of dietary history using growth rings must recognize that each ring may represent the weighted average of the diet over several seasons. These results continue to highlight the importance of laboratory experiments in interpreting isotopic data derived from field studies.

A snake of a different color: physiological color change in Arizona black rattlesnakes

Coloration may serve a variety of behavioral (e.g., crypsis, communication) and physiological (e.g., thermoregulation, protection) functions for terrestrial ectotherms. However, optimal coloration for a given function may vary over environments (spatial or temporal) or conflict with other functions. Physiological color change (rapid change due to movement of pigment granules within chromatophores) may be an adaptation to resolve conflicting selective pressures on coloration. The proximate factors related to physiological color change are well known in many animals, but few studies have investigated the ecological or evolutionary implications of this behavior. Here, we present alternative hypotheses for physiological color change and discuss biotic and abiotic factors that may have led to the maintenance and/or loss of this behavior among populations of Arizona black rattlesnakes (Crotalus cerberus). We discuss what is known about this behavior and propose to investigate the function and evolution of coloration and color change in C. cerberus.

A snake of a different color: physiological color change in Arizona black rattlesnakes

AbstractColoration may serve a variety of behavioral (e.g., crypsis, communication) and physiological (e.g., thermoregulation, protection) functions for terrestrial ectotherms. However, optimal coloration for a given function may vary over environments (spatial or temporal) or conflict with other functions. Physiological color change (rapid change due to movement of pigment granules within chromatophores) may be an adaptation to resolve conflicting selective pressures on coloration. The proximate factors related to physiological color change are well known in many animals, but few studies have investigated the ecological or evolutionary implications of this behavior. Here, we present alternative hypotheses for physiological color change and discuss biotic and abiotic factors that may have led to the maintenance and/or loss of this behavior among populations of Arizona black rattlesnakes (Crotalus cerberus). We discuss what is known about this behavior and propose to investigate the function and evolution of coloration and color change in C. cerberus.

Intraspecific Variation of Reproductive Traits in a Mediterranean Lizard: Clutch, Population, and Lineage Effects

Widely distributed terrestrial ectotherms from the southern European peninsulas show patterns of subdivision (related to isolation in temperate refugia) that allow us to test the relative importance of phylogeographic lineage, population of origin and familial effects as sources of variation for life-history traits. We collected gravid females from 15 geographically separated populations of the lacertid lizard Psammodromus algirus, a widely distributed species with well differentiated eastern and western lineages. We incubated eggs under two treatments of constant (28°C) and fluctuating (28 ± 4°C) temperature, and we examined clutch, population, and lineage effects on several traits of females, eggs, and hatchlings. Incubation time was mainly explained by differences between lineages, but it was also influenced by population and female effects. Within each lineage, incubation was shorter at cooler and wetter sites, and for a given climate it was shorter for eastern than for western populations, suggesting that countergradient variation has evolved independently in the two lineages. Female size, clutch size, and relative fecundity were primarily influenced by inter-population differences, a pattern that seemed attributable to environmental differences in productivity, because mean female size was positively correlated with a gradient of increasing precipitation and decreasing temperature. Clutch size was mainly, but not entirely, dependent on female SVL, suggesting both a proximate effect of local conditions and intrinsic differences among populations. Females from drier and warmer sites produced larger hatchlings. Mean egg mass was mainly determined by familial effects. Eggs incubated at a constant temperature hatched earlier than did their siblings incubated at fluctuating temperatures, a fact that could be explained by considering that in Mediterranean environments developmental rate might increase at a lower speed above average incubation temperature than it does decrease below it.

Metabolic theory, life history and the distribution of a terrestrial ectotherm

Summary1. Life histories, population dynamics and geographic range limits are fundamentally constrained by the way organisms acquire and allocate energy and matter. Metabolic theories provide general, parameter‐sparse frameworks for understanding these constraints. However, they require the accurate estimation of body temperature which can be especially challenging in terrestrial environments.2. Here, I integrate a metabolic theory (Dynamic Energy Budget theory, DEB) with a biophysical model for inferring field body temperatures and activity periods of terrestrial ectotherms and apply it to study life‐history variation and geographic range limits in a widespread North American lizard, Sceloporus undulatus.3. The model successfully predicted trait co‐variation (size at maturity, maximum size, reproductive output and length‐mass allometry) through changes in a single parameter. It also predicted seasonal and geographic variation in field growth rates, age at first reproduction, reproductive output and geographic range limits (via rmax estimates), all as a function of spatial climatic data. Although variation in age at maturity was mostly explained by climate, variation in annual reproduction was largely a product of local body size.4. Dynamic Energy Budget metabolic theory is concluded to be a powerful and general means to mechanistically integrate the dynamics of growth and reproduction into niche models of ectotherms.

The Effects of Climate Modes on Growing-Season Length and Timing of Reproduction in the Pacific Northwest as Revealed by Biophysical Modeling of Lizards

Abstract The effects of climate change on environments are increasingly obvious and are leading to stronger and more varied biological responses as organisms compensate. To understand better the responses of terrestrial ectotherms to climate oscillations we created a biophysical model based on the degree-days concept to predict relevant life-history events. By studying side-blotched lizards, Uta stansburiana, we were able to calculate the timing and length of the growing season as well as the timing of the breeding season for this species at a site in the Pacific Northwest based primarily on temperature data. We then used historical meteorological data to test for the effects of short- and long-term fluctuations in climate modes on lizards using indices for the El Nino-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Results indicate that these two climate modes affect different aspects of life history and that their effects, either alone or in combination, have the potential to alte...

Is Aquatic Life Correlated with an Increased Hematocrit in Snakes?

BackgroundPhysiological adaptations that allow air-breathing vertebrates to remain underwater for long periods mainly involve modifications of the respiratory system, essentially through increased oxygen reserves. Physiological constraints on dive duration tend to be less critical for ectotherms than for endotherms because the former have lower mass-specific metabolic rates. Moreover, comparative studies between marine and terrestrial ectotherms have yet to show overall distinct physiological differences specifically associated with oxygen reserves.Methodology/Principal FindingsWe used phylogenetically informed statistical models to test if habitat affects hematocrit (an indicator of blood oxygen stores) in snakes, a lineage that varies widely in habitat use. Our results indicate that both phylogenetic position (clade) and especially habitat are significant predictors of hematocrit. Our analysis also confirms the peculiar respiratory physiology of the marine Acrochordus granulatus.Conclusion/SignificanceContrary to previous findings, marine snakes have significantly–albeit slightly–elevated hematocrit, which should facilitate increased aerobic dive times. Longer dives could have consequences for foraging, mate searching, and predation risks. Alternatively, but not exclusively, increased Hct in marine species might also help to fuel other oxygen-demanding physiological adaptations, such as those involved in osmoregulation.

Global analysis of thermal tolerance and latitude in ectotherms.

A tenet of macroecology is that physiological processes of organisms are linked to large-scale geographical patterns in environmental conditions. Species at higher latitudes experience greater seasonal temperature variation and are consequently predicted to withstand greater temperature extremes. We tested for relationships between breadths of thermal tolerance in ectothermic animals and the latitude of specimen location using all available data, while accounting for habitat, hemisphere, methodological differences and taxonomic affinity. We found that thermal tolerance breadths generally increase with latitude, and do so at a greater rate in the Northern Hemisphere. In terrestrial ectotherms, upper thermal limits vary little while lower thermal limits decrease with latitude. By contrast, marine species display a coherent poleward decrease in both upper and lower thermal limits. Our findings provide comprehensive global support for hypotheses generated from studies at smaller taxonomic subsets and geographical scales. Our results further indicate differences between terrestrial and marine ectotherms in how thermal physiology varies with latitude that may relate to the degree of temperature variability experienced on land and in the ocean.

Toward a General Theory for How Climate Change Will Affect Infectious Disease

Toward a General Theory for How Climate Change Will Affect Infectious Disease

Tissue‐Carbon Incorporation Rates in Lizards: Implications for Ecological Studies Using Stable Isotopes in Terrestrial Ectotherms

Carbon stable isotope (delta(13)C) analysis can be used to infer the origin and to estimate the flow of nutrient resources through animals and across ecological compartments. These applications require knowledge of the rates at which carbon is incorporated into animal tissues and diet-to-tissue discrimination factors (Delta(13)C). Studies of carbon dynamics in terrestrial vertebrates to date have focused almost solely on endothermic animals; ectotherms such as reptiles have received little attention. Here we determined carbon incorporation rates and Delta(13)C in tissues of prairie lizards (Sceloporus undulatus consobrinus) and collared lizards (Crotaphytus collaris). The smaller lizard, S. undulatus, had carbon retention times of 25 and 61 d in plasma and red blood cells (RBC), respectively, compared with 44 and 311 d for the larger C. collaris. Liver, muscle, and skin carbon retention times for S. undulatus were 21, 81, and 94 d. Growth contributed 9%-19% of the carbon incorporated into these tissues. This contribution is similar to endotherms measured at comparable developmental stages. Mean Delta(13)C for plasma (-0.2 per thousand +/- 0.4 per thousand Vienna Pee Dee Belemnite Standard) and RBCs (-1.3 per thousand +/- 0.8 per thousand) were similar to values reported for other vertebrates. Carbon incorporation rates for these ectotherms, however, are seven times slower than in similarly sized adult endotherms. Although a limited comparison with data for warm-water fishes suggests comparable incorporation rates between aquatic and terrestrial ectotherms, this study highlights the lack of experimental data for isotope dynamics in ectotherms across a range of temperatures, body sizes, and developmental stages.

Non-climatic thermal adaptation: implications for species' responses to climate warming

There is considerable interest in understanding how ectothermic animals may physiologically and behaviourally buffer the effects of climate warming. Much less consideration is being given to how organisms might adapt to non-climatic heat sources in ways that could confound predictions for responses of species and communities to climate warming. Although adaptation to non-climatic heat sources (solar and geothermal) seems likely in some marine species, climate warming predictions for marine ectotherms are largely based on adaptation to climatically relevant heat sources (air or surface sea water temperature). Here, we show that non-climatic solar heating underlies thermal resistance adaptation in a rocky-eulittoral-fringe snail. Comparisons of the maximum temperatures of the air, the snail's body and the rock substratum with solar irradiance and physiological performance show that the highest body temperature is primarily controlled by solar heating and re-radiation, and that the snail's upper lethal temperature exceeds the highest climatically relevant regional air temperature by approximately 22°C. Non-climatic thermal adaptation probably features widely among marine and terrestrial ectotherms and because it could enable species to tolerate climatic rises in air temperature, it deserves more consideration in general and for inclusion into climate warming models.

Physiological and behavioural responses to seasonal changes in environmental temperature in the Australian spiny crayfish Euastacus sulcatus

The strategies used by ectotherms to minimise the detrimental effects of suboptimal thermal environments on physiological performance are often related to whether they inhabit a terrestrial or aquatic environment. Most terrestrial ectotherms use thermoregulatory strategies to maintain body temperature within an optimal range, while many aquatic ectotherms utilise thermal acclimation to maintain performance over varying seasonal temperatures. This study aimed to elucidate the relative contributions of acclimation and behavioural thermoregulation to maintaining whole-animal performance over varying seasonal temperatures in the semi-terrestrial Lamington spiny crayfish (Euastacus sulcatus). Crayfish activity and surface temperatures were determined by means of radio tracking and behavioural observations. Field studies demonstrated that E. sulcatus is exposed to stable daily temperatures, varying only between seasons from 10 degrees C in late winter to over 20 degrees C in summer. Also, terrestrial behaviour corresponded to a small portion of crayfish time (1.13%), much lower than predicted, indicating that E. sulcatus has limited opportunity for behavioural thermoregulation. We also tested the effect of acclimation to either 10 or 20 degrees C on chela strength and stamina. We found acclimation had a more marked effect on chela stamina than maximum strength measures; however, overall acclimatory capacity was limited in E. sulcatus. Thus, we found that the semi-terrestrial crayfish E. sulcatus used neither thermoregulatory behaviours nor physiological strategies to deal with seasonal changes in environmental temperature.

The Well‐Temperatured Biologist

Temperature provides a powerful theme for exploring environmental adaptation at all levels of biological organization, from molecular kinetics to organismal fitness to global biogeography. First, the thermodynamic properties that underlie biochemical kinetics and protein stability determine the overall thermal sensitivity of rate processes. Consequently, a single quantitative framework can assess variation in thermal sensitivity of ectotherms in terms of single amino acid substitutions, quantitative genetics, and interspecific differences. Thermodynamic considerations predict that higher optimal temperatures will result in greater maximal fitness at the optimum, a pattern seen both in interspecific comparisons and in within-population genotypic variation. Second, the temperature-size rule (increased developmental temperature causes decreased adult body size) is a common pattern of phenotypic plasticity in ectotherms. Mechanistic models can correctly predict the rule in some taxa, but lab and field studies show that rapid evolution can weaken or even break the rule. Third, phenotypic and evolutionary models for thermal sensitivity can be combined to explore potential fitness consequences of climate warming for terrestrial ectotherms. Recent analyses suggest that climate change will have greater negative fitness consequences for tropical than for temperate ectotherms, because many tropical species have relatively narrow thermal breadths and smaller thermal safety margins.

Functional and Numerical Responses of Predators: Where Do Vipers Fit in the Traditional Paradigms?

Snakes typically are not considered top carnivores, yet in many ecosystems they are a major predatory influence. A literature search confirmed that terrestrial ectotherms such as snakes are largely absent in most discussions of predator-prey dynamics. Here, we review classical functional and numerical responses of predator-prey relationships and then assess whether these traditional views are consistent with what we know of one group of snakes (true vipers and pitvipers: Viperidae). Specifically, we compare behavioural and physiological characteristics of vipers with those of more commonly studied mammalian (endothermic) predators and discuss how functional and numerical responses of vipers are fundamentally different. Overall, when compared to similar-sized endotherms, our analysis showed that vipers have: (i) lower functional responses owing primarily to longer prey handling times resulting from digestive limitations of consuming large prey and, for some adults, tolerance of fasting; (ii) stronger numerical responses resulting from higher efficiency of converting food into fitness currency (progeny), although this response often takes longer to be expressed; and (iii) reduced capacity for rapid numerical responses to short-term changes in prey abundance. Given these factors, the potential for viperids to regulate prey populations would most likely occur when prey populations are low. We provide suggestions for future research on key issues in predator-prey relationships of vipers, including their position within the classical paradigms of functional and numerical responses.

Impacts of climate warming on terrestrial ectotherms across latitude

The impact of anthropogenic climate change on terrestrial organisms is often predicted to increase with latitude, in parallel with the rate of warming. Yet the biological impact of rising temperatures also depends on the physiological sensitivity of organisms to temperature change. We integrate empirical fitness curves describing the thermal tolerance of terrestrial insects from around the world with the projected geographic distribution of climate change for the next century to estimate the direct impact of warming on insect fitness across latitude. The results show that warming in the tropics, although relatively small in magnitude, is likely to have the most deleterious consequences because tropical insects are relatively sensitive to temperature change and are currently living very close to their optimal temperature. In contrast, species at higher latitudes have broader thermal tolerance and are living in climates that are currently cooler than their physiological optima, so that warming may even enhance their fitness. Available thermal tolerance data for several vertebrate taxa exhibit similar patterns, suggesting that these results are general for terrestrial ectotherms. Our analyses imply that, in the absence of ameliorating factors such as migration and adaptation, the greatest extinction risks from global warming may be in the tropics, where biological diversity is also greatest.

Transient Receptor Potential Ion Channels Control Thermoregulatory Behaviour in Reptiles

Biological functions are governed by thermodynamics, and animals regulate their body temperature to optimise cellular performance and to avoid harmful extremes. The capacity to sense environmental and internal temperatures is a prerequisite for the evolution of thermoregulation. However, the mechanisms that enable ectothermic vertebrates to sense heat remain unknown. The recently discovered thermal characteristics of transient receptor potential ion channels (TRP) render these proteins suitable to act as temperature sensors. Here we test the hypothesis that TRPs are present in reptiles and function to control thermoregulatory behaviour. We show that the hot-sensing TRPV1 is expressed in a crocodile (Crocodylus porosus), an agamid (Amphibolurus muricatus) and a scincid (Pseudemoia entrecasteauxii) lizard, as well as in the quail and zebrafinch (Coturnix chinensis and Poephila guttata). The TRPV1 genes from all reptiles form a unique clade that is delineated from the mammalian and the ancestral Xenopus sequences by an insertion of two amino acids. TRPV1 and the cool-sensing TRPM8 are expressed in liver, muscle (transversospinalis complex), and heart tissues of the crocodile, and have the potential to act as internal thermometer and as external temperatures sensors. Inhibition of TRPV1 and TRPM8 in C. porosus abolishes the typically reptilian shuttling behaviour between cooling and heating environments, and leads to significantly altered body temperature patterns. Our results provide the proximate mechanism of thermal selection in terrestrial ectotherms, which heralds a fundamental change in interpretation, because TRPs provide the mechanism for a tissue-specific input into the animals' thermoregulatory response.

Comparison of erythrocyte osmotic fragility among amphibians, reptiles, birds and mammals

Erythrocyte osmotic fragility (EOF) is a measure of erythrocyte strength and its ability to withstand varying osmotic gradients. Erythrocyte osmotic fragility was compared among a variety of terrestrial ectotherms, aquatic/semiaquatic ectotherms and endotherms. We hypothesized that EOF should be lowest in those animals that are aquatic and whose red blood cells would likely be exposed to hypotonic conditions (i.e., some amphibians and reptiles). The greatest erythrocyte osmotic resistance (i.e., least fragile erythrocytes) was found in the bullfrog (Rana catesbeiana), followed in decreasing order by the larval tiger salamander (Ambystoma tigrinum), marine toad (Bufo marinus), ornate box turtle (Terrepene ornata ornata), painted turtle (Chrysemys picta bellii), red-eared slider (Trachemys scripta elegans), red-sided garter snake (Thamnophis sirtalis parietalis), domestic chicken (Gallus gallus), cotton rat (Sigmodon hispidus), Sprague-Dawley rat (Rattus norvegicus), and eastern woodrat (Neotoma floridana). A significantly higher erythrocyte osmotic resistance was detected in the aquatic/semiaquatic amphibians (R. catesbeiana and A. tigrinum) than in the terrestrial amphibian (B. marinus). However, among reptilian species, no significant differences were noted between terrestrial and aquatic/semiaquatic species. The erythrocytes of ectotherms possessed a greater osmotic resistance than those of endotherms. Such differences might be necessary because of exposure to wide temperature ranges in ectotherms and/or the long erythrocyte life span of ectothermic red blood cells relative to those of endotherms. Nucleated erythrocytes were more osmotically resistant than were non-nucleated erythrocytes. Additionally, erythrocyte osmotic resistance was correlated with erythrocyte mean cell volume. Larger erythrocytes were more osmotically resistant than smaller erythrocytes. Polynomial regression equations computed to approximate these data showed the cubic polynomial to be an excellent fit when data for the larval tiger salamander were excluded. Our data suggest that erythrocyte volume may play a significant role in erythrocyte osmotic resistance.

Protecting embryos from stress: corticosterone effects and the corticosterone response to capture and confinement during pregnancy in a live-bearing lizard ( Hoplodactylus maculatus)

Hormones in the embryonic environment, including those of the hypothalamo–pituitary–adrenal (HPA) axis, have profound effects on development in eutherian mammals. However, little is known about their effects in reptiles that have independently evolved viviparity. We investigated whether exogenous corticosterone affected embryonic development in the viviparous gecko Hoplodactylus maculatus, and whether pregnant geckos have a corticosterone response to capture and confinement that is suppressed relative to that in non-pregnant (vitellogenic) females and males. Corticosterone implants (5 mg, slow-release) administered to females in mid-pregnancy caused a large elevation of corticosterone in maternal plasma ( P<0.001), probable reductions in embryonic growth and development ( P=0.069–0.073), developmental abnormalities and eventual abortions. Cool temperature produced similar reductions in embryonic growth and development ( P⩽0.036 cf. warm controls), but pregnancies were eventually successful. Despite the potentially harmful effects of elevated plasma corticosterone, pregnant females did not suppress their corticosterone response to capture and confinement relative to vitellogenic females, and both groups of females had higher responses than males. Future research should address whether lower maternal doses of corticosterone produce non-lethal effects on development that could contribute to phenotypic plasticity. Corticosterone implants also led to increased basking in pregnant females ( P<0.001), and basal corticosterone in wild geckos (independent of reproductive condition) was positively correlated with body temperature ( P<0.001). Interactions between temperature and corticosterone may have broad significance to other terrestrial ectotherms, and body temperature should be considered as a variable influencing plasma corticosterone concentrations in all future studies on reptiles.