Temperature and the tropical tortoise Kinixys spekii: constraints on activity level and body temperature

Movements of five Kinixys spekii were measured continuously during six weeks of their activity season, by thread-trailing. The mean daily movement distance was negatively correlated with maximum shade air temperature, but not significantly related to minimum temperature, rainfall, or humidity. There was a midday period of inactivity of increasing length as maximum air temperature exceeded 29° C. Temperatures of models suggest that lower activity on hot days was due to the risk of overheating in this small (mean mass 617 g) tortoise. Kinixys spekii had a mean field body temperature (T^b) of 27° C, which is low compared to other tortoises (including sympatric Geochelone pardulis, mean T^b= 32.5° C), but salivated at a similar T^b (38.4° C). This pattern also occurs in other small species; mean and maximum field T^bs of tortoises are positively correlated with body mass, but salivation and critical maximum T_bs do not vary with body mass. Low field T_b provides a wide safety margin before evaporation of water becomes necessary. Kinixys sprkii had a short annual activity period, with about 95% of sightings in four months (December to March). Monthly sightings of K. spekii were correlated with rainfall, but not significantly related to temperature or humidity. Seasonal activity is therefore related to rainfall, but within the rainy season the level and pattern of daily activity is related to temperature.     

Invertebrate prey and predatory behaviour of the omnivorous African tortoise Kinixys spekii

Invertebrates form an important part of the diet in the omnivorous African tortoises of the genus Kinixys. Millipede prey of Kinixys spekii in Zimbabwe had a mean volume of 0.9 ml, and made up 64.7% of invertebrate food by volume; beetles made up most of the remainder and had a mean volume of 1.4 ml. The mean mass of invertebrate prey was 0.19% of tortoise mass, a similar value of relative prey mass to many insectivorous lizards. Tortoises preferentially attacked moving millipedes at or just behind the head, but predatory behaviour was otherwise unspecialized, with tortoises killing millipedes by ingesting them in pieces. Handling times of millipede prey varied significantly with relative prey mass, defensive behaviour, and direction of ingestion. The profitability (mass intake/handling time) of millipedes was maximal at a relative prey mass of 0.2%; the basis on which prey are selected is discussed.     

Low survival rate and high predation in the African hingeback tortoise Kinixys spekii

Live and dead Kinixys spekii were collected in the Sengwa Wildlife Research Area, Zimbabwe over a 12‐year period. Live tortoises were sexable at a midline plastron length of 100 mm; females were considered sexually mature at 140 mm (reached by age 9 years) and males at 120 mm (at age 7 years). Adult females were significantly larger than males, on average by 14 mm in length and by 1.43 times in mass. Mark–recapture analysis in a 2 km² area showed a population density of sexable tortoises of 0.16 ha^?1. The survival rate was estimated by recaptures, by the frequency distribution of age at death, and by the mean age of live tortoises, and averaged 0.74 year^?1. Seventy‐seven to 89% of dead tortoises showed evidence of predation, depending on the criteria used. Damage occurred in characteristic forms, loss of the front or rear of the plastron, or holes in the carapace and plastron, which were attributed to predation by mammals and ground hornbills, respectively. K. spekii had similar body size and sexual size dimorphism to Mediterranean tortoises (Testudo), but population density was much lower and the mortality rate was twice as high, probably due to the abundant African predators. High mortality was offset by a rate of juvenile growth twice that of Testudo.     

Heat stress in tropical birds: behavioural thermoregulation during flight

Pacific Swallows and Blue-throated Bee-eaters in Malaysia commonly exposed their legs when flying. The habit was most frequent around midday and was interpreted as a mechanism to dissipate heat and thereby reduce stress. The main cause of heat stress was thought to be solar radiation combined with high endogenous heat production during flight. Stress was probably increased by high ambient temperature and humidity. The occurrence of leg exposure during flight in a total of 17 species showed the habit was widespread among open habitat species in Malaysia.     

Temporal and spatial complexity of maternal thermoregulation in tropical pythons

Parental care is a widespread adaptation that evolved independently in a broad range of taxa. Although the dynamics by which two parents meet the developmental needs of offspring are well studied in birds, we lack understanding about the temporal and spatial complexity of parental care in taxa exhibiting female-only care, the predominant mode of parental care. Thus, we examined the behavioral and physiological mechanisms by which female water pythons Liasis fuscus meet a widespread developmental need (thermoregulation) in a natural setting. Although female L. fuscus were not facultatively thermogenic, they did use behaviors on multiple spatial scales (e.g., shifts in egg-brooding postures and surface activity patterns) to balance the thermal needs of their offspring throughout reproduction (gravidity and egg brooding). Maternal behaviors in L. fuscus varied by stage within reproduction and were mediated by interindividual variation in body size and fecundity. Female pythons with relatively larger clutch sizes were cooler during egg brooding, suggesting a trade-off between reproductive quantity (size of clutch) and quality (developmental temperature). In nature, caregiving parents of all taxa must navigate both extrinsic factors (temporal and spatial complexity) and intrinsic factors (body size and fecundity) to meet the needs of their offspring. Our study used a comprehensive approach that can be used as a general template for future research examining the dynamics by which parents meet other developmental needs (e.g., predation risk or energy balance).     

Keeping it regular: Development of thermoregulation in four tropical seabird species

The thermoregulatory capacity of a species can determine which climatic niche it occupies. Its development in avian chicks is influenced by numerous factors. Furthermore, it is suggested that altricial chicks develop their thermoregulatory capacity post-hatching, while precocial chicks develop aspects of this in the egg. We investigated the development of thermoregulation of four co-occurring seabird species in the Seychelles; namely white, ground-nesting white-tailed tropicbirds (Phaethon lepturus) and tree-nesting fairy terns (Gygis alba); and dark plumaged, tree-nesting lesser noddies (Anous tenuirostris) and ground- and tree-nesting brown noddies (A. stolidus). White-tailed tropicbirds have semi-altricial chicks, while the remaining species have semi-precocial chicks. Cloacal temperatures (T_b) were measured at five day intervals from newly hatched chicks and compared over time, and with adult T_bs. Initial T_bs of all chicks, except fairy terns, were lower than those taken when chicks were older. Brooding cessation generally coincided with feather development, as did an increase in T_b. Mean chick T_b was significantly lower than mean adult T_b for all species, but only white-tailed tropicbird and brown noddy chicks in tree nests differed significantly from mean adult T_b when chick T_b at five day intervals were considered. There was a significant interactive effect of nest site and age on brown noddy chick T_b, but chick colour did not have a significant effect on T_b. However, brown noddy chicks on dune crests maintained a constant T_b sooner than chicks in tree nests. Our results demonstrate that tropical seabird species have a more delayed onset of thermoregulatory capabilities when compared with those in temperate environments, perhaps as nest sites are less thermally challenging. Nest microhabitats and behavioural thermoregulation, are likely more important during early chick development for these species.     

Behavioral thermoregulation in a tropical gastropod: links to climate change scenarios

Tropical species are vulnerable to global warming because they live at, or near to, their upper thermal threshold limits. Therefore, the predicted increase in the frequency of warming events in the tropics is expected to be critical for the survival of local species. This study explored the major environmental variables which were thought to be correlated with body temperatures (BTs) of the tropical snail Littoraria scabra at the niche level. A correlation between BT and substrate temperature (ST) was detected from field observations which suggests a possible causal relationship between both substrate and BTs. In contrast, there was no correlation between BT and air temperature. Field observations suggest that 33.4 °C may be L. scabra upper limit of substrate surface temperature, although further experiments are needed to assess if the upper limit of physiological tolerance is actually different. As L. scabra individuals were free to choose their substrata, the observed distribution pattern at the niche level is related to L. scabra's behavior. Additionally, substrate surface temperatures were very heterogeneous at centimeter scale (i.e. from 22.5 to 53.1 °C) and L. scabra was shown to select specific STs (i.e. between 22.5 and 33.4 °C) rather than microhabitat type. Therefore, L. scabra did not seem to behaviorally thermoregulate through microhabitat selection nor aggregation. In contrast, behavioral experiments showed that L. scabra has the ability to actively select a thermally favorable site over short temporal scale (i.e. individual average speed of 1.26 cm min^?1) following exposure to high temperatures above 33.4 °C. Hence, this study supports the crucial need to integrate intertidal invertebrate behavioral responses to thermal constraints in climate change studies.     

Effects of heat acclimatisation on work tolerance and thermoregulation in trained tropical natives

This study aimed to investigate the effects of heat acclimatisation on thermoregulatory responses and work tolerance in trained individuals residing in the tropics. Eighteen male trained soldiers, who are native to a warm and humid climate, performed a total of four heat stress tests donning the Skeletal Battle Order (SBO, 20.5 kg) and Full Battle Order (FBO, 24.7 kg) before (PRE) and after (POST) a 10-day heat acclimatisation programme. The trials were conducted in an environmental chamber (dry bulb temperature: 32 °C, relative humidity: 70%, solar radiation: 400 W/m²). Excluding the data sets of which participants fully completed the heat stress tests (210 min) before and after heat acclimatisation, work tolerance was improved from 173±30 to 201±18 min (∼21%, p<0.05, n=9) following heat acclimatisation. Following heat acclimatisation, chest skin temperature during exercise was lowered in SBO (PRE=36.7±0.3 vs. POST=36.5±0.3 °C, p<0.01) and FBO (PRE=36.8±0.4 vs. POST=36.6±0.3 °C, p<0.01). Ratings of perceived exertion were decreased with SBO and FBO (PRE=11±2; POST=10±2; p<0.05) after heat acclimatisation. Heat acclimatisation had no effects on baseline body core temperature, heart rate and sweat rate across trials (p>0.05). A heat acclimatisation programme improves work tolerance with minimal effects on thermoregulation in trained tropical natives.     

Aspects of comparative thermal ecology of sympatric hinge-back tortoises (Kinixys homeana and Kinixys erosa) in the Niger Delta, southern Nigeria

Aspects of the thermal ecology of two sympatric hinge‐back tortoises, Kinixys erosa and Kinixys homeana, were studied in the rainforest zone of south‐eastern Nigeria (West Africa). There were no significant differences in mean body temperatures (T_b) among K. homeana males, K. homeana females, K. erosa males and K. erosa females. In both species, there was a significant correlation between T_b and air temperature (T_a), and the regression line of T_a plotted against T_b differed significantly from the line of ideal poikilothermy. These regressions did not differ significantly between sexes in either species. There were no significant differences in terms of mean T_b in K. homeana during the various day‐hour intervals, whereas the mean T_b of K. erosa varied significantly among the various daytime intervals, attaining the higher values at 11.01–15.00 and 15.01–19.00 hours. In both species, T_bs were nearly always below T_as, and the negative difference ‘T_b ‐ T_a’ increased with increasing T_a. The hourly‐time course of the difference between T_b and T_a showed significant differences in K. homeana (with the higher negative differences at 11.01–15.00 and 15.01–19.00 hours), whereas no such difference was observed in K. erosa. In general, tortoises of both species showed behavioural thermoregulation in their avoidance of overheating in tropical environments, taking advantage of shady forest environments.     

Genetic parameters for thermoregulation and production traits in lactating sows reared in tropical climate

The objective of this study was to estimate the genetic parameters for thermoregulation traits and the relationships with performance of Large White lactating sows reared in a tropical humid climate. The thermoregulation traits were rectal temperature (RT), cutaneous temperature (CT) and respiratory rate (RR) during lactation measured in the afternoon (1200 h) and in the morning (0700 h). The production traits were sow’s average daily feed intake (ADFI), litter BW gain (LBWg) and sow’s proportion of BW change between farrowing and weaning (BWc). Complete data included 931 lactating performance on 329 Large White sows from the INRA experimental unit in Guadeloupe (French West Indies). Random regression models using linear spline functions were used for longitudinal data (RT, CT, RR and daily feed intake). Results showed that when ignoring values at the beginning and the end of lactation, the traits studied can be treated as the same trait throughout days of lactation, with fairly constant heritability and variance. However, largest heritabilities and genetic variances were estimated in mid-lactation. Heritability estimates on average performance during lactation were low to moderate for thermoregulation traits (0.35±0.09 for RT, 0.34±0.12 for CT and 0.39±0.13 for RR). Heritability estimates for production traits were 0.26±0.08 for ADFI, 0.20±0.07 for BWc and 0.31±0.09 for LBWg. Significant genetic correlations between thermoregulation traits and production traits were only obtained for ADFI and RR (0.35±0.12). From this study it can be concluded that thermoregulation traits are heritable, indicating that there are genetic differences in heat stress tolerance in lactating Large White sows.     

Habitat use and activity influence thermoregulation in a tropical lizard, Ameiva exsul

We examined the contributions of alterations in daily activity and behavioral selection of microhabitat to thermoregulation in a population of the lizard, Ameiva exsul (Teiidae), by combining data on lizard activity with data on the availability of sun-shade patches and operative temperatures (T_e). By comparing T_e distributions predicted by “no thermoregulation” and “only thermoregulation” hypotheses to those predicted by random use of thermal habitat, we assessed the relative contributions of microhabitat selection and daily activity to regulation of body temperature (T_b). Over the course of a day lizards maintained T_b very close to optimal temperature (T_sel) despite T_es that deviated substantially from T_sel. Data demonstrating a unimodal daily activity pattern reject the hypothesis of uniform activity throughout the day. Also, lizard activity was not positively correlated with the proportion of T_es within T_sel nor negatively correlated with the absolute deviation of available T_e from T_sel (d_e) (“only thermoregulation”). Microsite use by A. exsul deviated significantly from predictions of the “no thermoregulation” hypothesis, but our data could not reject predictions of the “only thermoregulation” hypothesis that lizards would use sun-shade patches relative to the proportion of microsites where T_e is within T_sel. Also, lizards appeared to actively select sunlit and partially shaded microsites at different times of day. Thus, despite thermal constraints imposed by the habitat, A. exsul maintained high and relatively constant T_bs throughout its daily activity period and thermoregulated effectively. This appears to be generally representative of West Indian species of Ameiva.     

Influence of shell morphometry,microstructure, and thermal conductivity on thermoregulation in two tropical intertidal snails

Tropical intertidal organisms tolerate large fluctuations in temperature and high desiccation rates when exposed during low tide. In order to withstand the short‐term heat stress, intertidal organisms adopt behavioral responses to maximize their survival. Our previous research showed that tropical littorinids found at the upper and lower intertidal shores in Singapore exhibited different behavioral adaptations during low tide. Most of the upper‐shore Echinolittorina malaccana kept a flat orientation, with the aperture against the substrate and the long axis of the shell towards the sun, whereas a majority of the lower‐shore individuals of Echinolittorina vidua stood with the edge of the aperture perpendicular to the substrate on the rocky shore during low tide. This prompted analyses of the shells of these two species to determine whether the differences in the shell morphometry, microstructure, and thermal conductivity of shells of E. malaccana and E. vidua were associated with their respective behavioral responses to thermal stress. Analyses of shell morphometry and thermal conductivity showed that shells of E. malaccana were more likely to minimize heat gain, despite having a higher thermal conductivity on the outer surface, due to their light‐gray, elongated shell. By contrast, the dark‐colored, globose shells of E. vidua probably gain heat more readily through solar radiation. Scanning electron microscopy images of the shells of both littorinid species further revealed that they have cross‐lamellar structure; however, only individuals of E. vidua showed the presence of disjointed rod layers and a pigmented inner shell surface. Individuals of E. malaccana had a rough outer shell surface with holes that inter‐connect to form water‐trapping channels that probably aid cooling. Individuals of E. vidua, however, had a smooth outer surface with rows of kidney‐shaped depressions as microsculptures which probably help to stabilize shell shape. In both Echinolittorina species, behavioral responses were used to overcome thermal stress during low tide that was associated with shell morphometry and shell thermal conductivity. Such combined adaptations increase survivability of the littorinids at their respective tidal levels.