孵化温度对王锦蛇胚胎代谢和幼体适合度的影响

孵化温度所驱动的爬行动物的表型变异是生理生态学研究的热点。本研究以王锦蛇(Elaphe carinata)为实验动物,检验了24℃和28℃孵化温度对王锦蛇胚胎代谢速率、孵化过程中的卵重量、孵出幼体代谢和行为的影响。研究结果显示:卵重和胚胎的呼吸代谢均与孵化时间呈正相关;28℃下胚胎代谢速率大于24℃;幼蛇孵出15 d内体重随着生长时间的延长而减小,24℃孵出幼体的代谢速率大于28℃孵出幼体,两温度下孵出幼体的呼吸代谢速率和生长时间无显著关系;28℃孵出幼体的疾游速和吐信频次均大于24℃;两孵化温度孵出幼体的选择体温无显著差异,但在消耗完体内的剩余卵黄后28℃孵出幼体有60%的个体摄食,而24℃孵出幼体无摄食个体。总体而言,王锦蛇28℃孵出幼体适合度优于24℃孵出幼体。     

孵化温度对乌龟胚胎能量利用及矿物质代谢的影响

在24℃、27℃、30℃和33℃条件下孵化乌龟(Chinemysreevesii)卵,检测温度对胚胎利用卵内能量和矿物质的影响。孵化温度显著影响乌龟胚胎的能量利用。卵在温和温度下(27℃和30℃)比在高温(33℃)和低温(24℃)孵化有较高的干物质、脂肪和能量转化率。因而,27℃和30℃新生幼体的总能量高于33℃和24℃下孵出的幼体。新生幼体内剩余卵黄随温度升高而增大。27℃下新生幼体的躯干能量显著高于其它温度。此外,孵化温度显著影响乌龟胚胎钙代谢,但对镁和钾代谢影响微弱。24℃下胚胎从卵黄和卵壳吸收的总钙量小于其它温度条件下胚胎,与之相对应,24℃下孵出卵卵壳内残留较多的钙。由此可见,温和温度(27-30℃)可提高胚胎能量转化效率,促进胚胎从卵黄和卵壳吸收较多的矿物质,有利于孵出发育良好的乌龟幼体     

孵化温度对赤链蛇胚胎代谢和幼体行为的影响

研究了赤链蛇(Dinodon rufozonatum)在孵化过程中卵的生长、孵化期、胚胎代谢和孵出幼体行为表现的热依赖性。结果显示:孵化温度对孵化期、卵增重、孵化过程中消耗的总能量和孵出幼体的运动表现有显著影响,但不影响胚胎代谢率、孵化成功率和幼体吐信频次。孵化期随着孵化温度的升高而缩短,孵化过程中,24℃终末卵重和胚胎代谢率显著大于30℃,而27℃与其他两个温度没有差异;27℃孵出幼体游速较24℃快,30℃孵出幼体与其他两个温度孵出幼体的游速无显著差异。上述结果显示:24—30℃是赤链蛇适合的孵化温度范围,与赤链蛇所处的生境温度相近。     

孵化温度对白条草蜥孵出幼体大小、形态和运动表现的影响

实验用白条草蜥(Takydrous wolteri）卵由1999年和2000年4月捕自安徽滁州的19条成年雌体产出。用4个恒定温度（24-33℃）孵化白条草蜥卵,检测孵化温度对孵出幼体大小、形态和运动表现的影响。孵化卵从环境中吸不导致生量增加,卵重量增加与卵初始重量和孵化温度有关。24、27、30和33℃孵化期的平均值分别为41.9、30.6、6.25和22.6d。温度显著影响孵化成功率及孵出幼体的湿重、躯干干重和剩余卵黄干重,但对孵出幼体的性别、体长、尾长和干重无显著影响。24℃和27℃孵出幼体湿重和躯干干重大于33℃孵出幼体,剩余卵黄干则小于33℃孵出幼体;30℃和33℃孵出幼体的湿重、躯干干重和剩余卵黄干重无显著差异。孵化温度显著影响孵出幼体一些局部形态特征：24℃和27℃孵出幼体头长和头宽矫正值显著大于高温（33℃）孵出幼体,24℃孵出幼体耳径正值一般小于较高温度孵出的幼体。疾跑速与幼体体长成正相关,与幼体尾长和状态无关。高温孵出幼体运动能力较差。雄笥幼体腹鳞行数少于雌性幼体,尾长和后肢长大于雌性幼体,这些特征的两性差异与孵化温度无关。孵化热环境能诱导白条草蜥部分表型特征的变异,这些特征的变异可能对个体的适应性具有长期的影响。     

滑鼠蛇的繁殖输出及孵化热环境对孵出幼体表型特征的影响

用15条2002年6月中旬捕自浙江丽水的怀卵滑鼠蛇研究繁殖输出及孵化热环境对孵出幼体表型特征的影响。母体在捕后3周内各产一窝柔性卵。窝卵数、窝卵重和卵大小均随母体体长增加而增大,平均值分别为13．3(枚卵)、332．4g和24．8g。窝卵数和卵大小的变异系数分别为0．18和0．13。窝卵数与产后母体状态呈正相关,卵数量和大小无关。每窝部分可孵卵分别用恒温(24、27、30、33℃)和21．0-39．0℃(平均28．3℃)范围内的波动温度孵化,每隔5d记录恒温孵化卵的重量。孵化热环境对卵与环境之间的水分交换有显著影响,并影响孵化卵重量的时间变化。24、27、30、33℃和波动温度的平均孵化期分别为105．4、78．0、57．8、51．3和58．6d。不同热环境下的孵化成功率和幼体畸形率有一定差别,但统计上不显著。24℃和30℃孵出幼体雄性比例较高,27℃、33℃和波动温度孵出幼体雌性比例较高,但没有证据表明孵化温度能决定滑鼠蛇性别。除孵出幼体灰分含量外,孵化温度对其它幼体特征均有显著影响。33℃孵出幼体SVL较小,但剩余卵黄和其中的灰分含量大于其它温度孵出的幼体。24℃和30℃孵出幼体的总干重、总能量、躯干干重、脂肪体干重总体上小于27℃和波动温度孵出幼体。24℃孵出幼体特征性具有最小的剩余卵黄,33℃孵出幼体则特征性地具有最大的剩余卵黄。24℃和30℃孵出幼体特征较为接近,27℃和波动温度孵出幼体较为接近。对9个幼体特征变量做主成分分析发现,第一和第二主成分共解释81．2％的变异。幼体SVL、湿重、干重、脂肪含量、能量、躯干干重和脂肪体干重在第一主成分有较高的正负载系数(解释56．9％变异),剩余卵黄干重在第二主成分有较高的正负载系数(解释24．3％变异),第一和第二主成分的分值均差异显著。主成分分析进一步显示,24、30和33℃孵出幼体总体上小于27℃和波动温度孵出幼体[动物学报50(4)：541-550,2004]。     

恒定和波动温度下丽斑麻蜥孵出幼体的表型变异

作者以丽斑麻蜥(Eremias argus)为模型动物研究恒定和波动孵化温度对孵化成功率和孵出幼体表型的影响。卵在四个恒定[24 ,27 ,30 and 33 (±0·3)℃]、一个波动温度下孵化。不同温度处理下的孵化成功率相同,但孵出幼体表型不同。孵化期随孵化温度升高呈指数式缩短;在相同平均温度下,波动温度孵化卵的孵化期比恒温孵化卵长。在所有被检表型特征中,幼体的干重、剩余卵黄干重和运动表现更易受孵化温度影响。总体而言,低温(24℃、27℃)孵出幼体运动表现最佳,高温(33℃)孵出幼体最差、温和温度(30℃和波动温度)孵出幼体居中。本文研究数据显示: (1)丽斑麻蜥卵每日短期暴露于潜在致死的极端温度下对孵化成功率和孵出幼体形态特征无明显的不利效应; (2)温度波动对孵出幼体运动表现无促进作用,对孵化期的影响则不同于平均值相同的恒定温度。     

孵化温度对灰鼠蛇卵孵化期、孵化成功率和孵出幼体特征的影响

用4个恒定温（24－32℃）孵化灰鼠蛇卵,检测温度对孵化期,孵化成功率和孵出幼体特征的影响。在24－32℃范围内,孵化温度显影响孵化期及孵出幼体的体长和剩余卵黄大小,但不影响孵化成功率和孵出幼体的性别,体重,躯干重和脂肪体重。24,26,30和32℃孵化期分别为99．0,72．2,54．7和48．7d。24℃和26℃孵出幼体的体筮大于30℃和32℃孵出幼体;24℃和32℃孵同幼体内的卵黄较多。不同温度下发育的胚胎对卵内物质和能量的利用一定的差异,但差异不显。雌性幼体的体长,尾长和总长均大于雄性幼体,这些两性差异与孵化温度无关。孵出幼体和新生卵内容的灰分含量无显差异,孵化前后卵壳灰分含量也无显差异,表明灰鼠蛇的卵黄可提供胚胎发育所需的所有无机物。     

孵化温度对中华鳖胚胎物质和能量利用的影响

用多重温度组合[7个恒温（23、24、27、28、30、33和34℃）和1个波动温度（22．3－32．8℃）]孵化中华鳖（Pellodiscus sinensis）卵,检测温度对胚胎利用卵内物质和能量的影响。卵在波动温度和温和温度下（27℃和28℃）孵化有较高的干物质、脂肪和能量转化率,卵出幼体因而含有较多的无机物,幼体躯干和脂肪体含有较高的能量。卵在极端高温（34℃和33℃）或极端低温（23℃）下孵化物质和能量转化率较低,使得孵出幼体中无机物较少,幼体射干和脂肪中含能量较低。孵化温度显著影响中华鳖孵出幼体内的能量分配;27℃和28℃孵出幼体含能量较高且相似,但27℃孵出幼体剩余卵黄能量小于28℃孵出幼体;34℃和23℃孵出幼体含能量较低且相似,但23℃孵出幼体剩余卵黄能量大于34℃孵出幼体。波动温度拓宽存活孵化温度范围。     

温度和卵大小对尖吻蝮幼蛇孵化及存活率影响的研究

目的研究尖吻蝮（Dienagkistrodon acutus）幼蛇成活率低的原因,观察不同温度条件和不同卵大小对尖吻蝮幼蛇的孵化、幼体特征、转化率、幼蛇存活率的影响。方法将不同窝尖吻蝮蛇卵按产卵日期相差不超过1天分为同一组,每组随机选择不同的温度进行孵化,采用隔水式恒温培养箱进行控温,以常温孵化作为对照试验,幼蛇出壳后采集相关试验数据并进行分析。在环境条件、养殖模式和养殖方法相同情况下对幼蛇饲养3个月,然后统计各组成活率。结果尖吻蝮幼体的孵化和幼体特征及存活率与孵化温度条件有明显相关性,孵化温度越高,孵化期越短,畸形率越高,蛇卵重量转化为幼体体重的转化率越低,3月龄幼蛇存活率越低。较大的尖吻蝮蛇卵孵出的幼蛇个体较大,生存力较强,存活率较高。结论尖吻蝮幼蛇的存活率与孵化温度条件及蛇卵重量大小有明显相关性,较适宜的孵化温度为24-26℃,蛇卵越大幼蛇存活率越高。     

南草蜥胚胎生长及物质和能量动用

用3种水热条件下(3温度×1湿度)孵化南草蜥(Takydomus sexlineatusDaudiin)卵以观测孵化卵质量变化、卵大小、孵化期、胚胎发育及孵出幼体特征。孵化过程中, 每5 d测定卵质量和大小。初生幼体称重后冰冻处死, 解剖分离为躯干、剩余卵黄和腹脂肪体, 65 ℃恒温干燥后称重。不同孵化温度对孵化期的长短有明显影响, 孵化期随孵化温度升高而缩短, 24 ℃平均41.8 d、27 ℃平均35.4 d、30 ℃平均34.0 d。卵孵化到14 d肉眼可见胚胎, 此后胚胎发育变化明显加速。孵化温度显著影响孵出幼体的质量、大小。本实验的受精卵在24 ℃、27 ℃中孵出的幼体质量较大。24 ℃、27 ℃发育的胚胎对卵黄的利用最充分, 剩余卵黄少。     

Thermal variability in body temperature in an ectotherm: Are cloacal temperatures good indicators of tortoise body temperature?

Historically, studies of reptilian thermal biology have compared ambient temperatures (T_a) to body temperatures (T_b) from the animal under study, with T_b usually taken from the cloaca and various instruments being used to measure T_b. The advent of surgically implanted miniature temperature loggers has offered the opportunity to test the efficacy of cloacal T_b as a measurement in thermoregulatory studies. We expected that there was a difference between skin, cloacal, and core T_b's. Temperatures were measured from various positions on leopard tortoises (Stigmochelys pardalis) using thermocouples and miniature temperature loggers, including surgically implanted temperature loggers. Measurements of temperature from various positions on and in the tortoise were significantly different from T_a. Cloacal T_b's were significantly lower than all other body temperatures measured, and core T_b's were significantly different from cloacal T_b, skin and carapace temperatures. In addition, significant differences were found between measures of temperature from other parts of the body. The variations between core T_b, cloacal T_b and other measures of T_b indicated that there are large thermal gradients within the body of a relatively large tortoise at any given time with cloacal T_b not an accurate measure of core T_b.     

Thermal preference,tolerance and oxygen consumption of adult white shrimp Litopenaeus vannamei (Boone) exposed to different acclimation temperatures

Final temperature preferendum of white shrimp adults were determined with acute and gravitation methods. The final preferendum was similar, independent of method (26.2–25.6 °C). A direct relationship was determined between the critical thermal maxima values and the acclimation temperatures (P<0.05). The end point of Critical Thermal Maxima (CTMax) for adults was defined as the loss of righting response (LRR). The acclimation response ratio (ARR) for adults of white shrimp had an interval of 0.36–0.76, values that agreed with others obtained for crustaceans from tropical and subtropical climates. The oxygen consumption rates increased significantly (P<0.05) from 39.6 up to 90.0 mg O₂ kg⁻¹ h⁻¹ wet weight (w.w.) as the acclimation temperature increased from 20 to 32 °C. The range of temperature coefficient (Q₁₀) of the white shrimp between 23 and 26 °C was the lower 1.60. The results obtained in this work are discussed in relation to the species importance in the reproductive scope and maintenance of breeders.     

驯化温度与急性变温对南方鲇幼鱼皮肤呼吸代谢的影响

为了考查鱼类皮肤呼吸代谢的温度反应特征,在不同驯化温度(10、20、30℃)及双向急性变温(10→20℃、20→30℃、10→30℃;20→10 ℃、30→20℃、30→10℃)条件下采用自行设计的皮肤呼吸代谢装置测定麻醉后南方鲇(Silurus meridionalis)幼鱼的皮肤耗氧率(MO2skin)及鳃部耗氧率(MO2gill),并计算整体耗氧率(MO2total).研究显示:南方鲇幼鱼的MO2skin占MO2total 的16.4％-19.0％,随着驯化温度的升高,MO2skin上升的幅度显著低于MO2total(P＜0.05),MO2skin占MO2total的比例则呈下降趋势;急性升(降)温组的MO2skin与升(降)温前驯化温度组相比显著升高(降低)(P＜0.05),却与相应温度驯化组的MO2skin无显著性差异(P＞0.05);急性变温组MO2skin的Q10值与驯化温度组的差异不显著(P＞0.05),却显著低于MO2total的Q10值(P＜0.05).通过相关资料比较发现,南方鲇幼鱼MO2skin占MO2total的比例处于中上水平.研究表明,在驯化温度和急性变温条件下,实验鱼的MO2total分别存在代谢补偿反应和急性胁迫反应;MO2skin与MO2total的温度反应不同,它既不是一个完全的化学反应过程,也不是生物反应过程,而更倾向于是一个物理的扩散过程.     

Effects of acclimation and egg-incubation temperature on selected temperature by hatchling western painted turtles (Chrysemys picta bellii)

The ability of hatchling turtles to detect environmental temperature differences and to effectively select preferred temperature is a function that critically impacts survival. In some turtle species, temperature preference may be influenced by embryonic and post-hatching conditions, such as egg-incubation and acclimation temperature. We tested for effects of embryonic incubation temperature (27.5 °C, 30 °C) and acclimation temperature (20 °C, 25 °C) on the selected temperature and movement patterns of 32 Chrysemys picta bellii (Reptilia: Emydidae) hatchlings in an aquatic thermal gradient of 14-34 °C and in single-temperature (20 °C, 25 °C) control tests. Among 10-11 month old hatchlings, acclimation temperature and egg-incubation temperature influenced temperature selection and movement patterns. Acclimation temperature affected activity and movement: in thermal gradient and single-temperature control tests, 25 °C-acclimated turtles relocated between chambers significantly more frequently than individuals acclimated to 20 °C. Acclimation temperature also affected temperature selection: 20 °C-acclimated turtles selected a specific temperature during gradient tests, but 25 °C-acclimated turtles did not. Among 20 °C-acclimated turtles, egg-incubation temperature was inversely related to selected temperature: hatchling turtles incubated at 27.5 °C selected the warmest temperature available (34 °C); individuals incubated at 30 °C selected the coldest temperature (14 °C). These results suggest that interactions of environmental conditions may influence post-hatching thermoregulatory behavior in C. picta bellii, a factor that ultimately affects fitness.     

Consequences of thermal acclimation for the mating behaviour and swimming performance of female mosquito fish

The mating system of eastern mosquito fish (Gambusia holbrooki) is dominated by male sexual coercion, where all matings are forced and females never appear to cooperate and actively avoid all attempts. Previous research has shown that male G. holbrooki offer a model system for examining the benefits of reversible thermal acclimation for reproductive success, but examining the benefits to female avoidance behaviour has been difficult. In this study, we examined the ability of non-male-deprived female G. holbrooki to avoid forced-coercive matings following acclimation to either 18 or 30 degrees C for six weeks (12h light:12h dark photoperiod). Thermal acclimation of burst and sustained swimming performance was also assessed, as these traits are likely to underlie their ability to avoid forced matings. There was no influence of thermal acclimation on the burst swimming performance of female G. holbrooki over the range 18-30 degrees C; however, sustained swimming performance was significantly lower in the warm- than the cool-acclimation group. For mating behaviour, we tested the hypothesis that acclimation would enhance the ability of female G. holbrooki to avoid forced matings at their host acclimation temperature relative to females acclimated to another environment. However, our hypothesis was not supported. The rate of copulations was almost three times greater for females acclimated to 30 degrees C than 18 degrees C when tested at 30 degrees C, indicating that they possess the ability to alter their avoidance behaviour to 'allow' more copulations in some environments. Coupled with previous studies, female G. holbrooki appear to have greater control on the outcome of coercive mating attempts than previously considered and can alter their propensity to receive forced matings following thermal acclimation. The significance of this change in female mating-avoidance behaviours with thermal acclimation remains to be explored.     

Penetration and Development of Meloidogyne hapla in Resistant and Susceptible Alfalfa Under Differing Temperatures

Studies were conducted to examine under differing temperatures (12, 16, 20, 24, 28, and 32 C) the penetration anti development of Meloidogyne hapla in resistant lines ''298'' and ''Nev. Syn XX'', and susceptible ''Lahontan'' and ''Ranger'' hardy-type alfalfas. The results indicated that resistance to M. hapla was similar to that previously described for M. incognita in nonhardy alfalfa. Although initial penetration in resistant seedlings was similar to that of susceptible seedlings, nematode larvae failed to establish and develop in root tissues and nematode numbers subsequently declined. In susceptible seedlings, nematode development proceeded rapidly, and egg production began after 5 weeks. Temperature had little influence on the nematode development except to slow the response at the lower temperatures. Other studies were conducted to verify a previously reported immune (no penetration) reaction to M. hapla by the ''Vernal'' selection ''M-4''. When compared to the resistant (penetration without nematode development) Vernal selection ''M-9'' under differing temperatures (20, 24, 28, and 32 C), each selection was equally penetrated by M. hapla but at a lower level than in susceptible Ranger cuttings. Generally, no root galling was observed in either M-4 or M-9; however, very slight galling was found 35 days after inoculation on about 50% of these cuttings when grown at 32 C.     

The use of small subcutaneous transponders for quantifying thermal biology and torpor in small mammals

Remote measurements of body temperature (T_b) in animals require implantation of relatively large temperature-sensitive radio-transmitters or data loggers, whereas rectal temperature (T_rec) measurements require handling and therefore may bias the results. We investigated whether ∼0.1 g temperature-sensitive subcutaneously implanted transponders can be reliably used to quantify thermal biology and torpor use in small mammals. We examined (i) the precision of transponder readings as a function of temperature and (ii) whether subcutaneous transponders can be used to remotely record subcutaneous temperature (T_sub). Five adult male dunnarts (Sminthopsis macroura, body mass 24 g) were implanted with subcutaneous transponders to determine T_sub as a function of time and ambient temperature (T_a), and in comparison to thermocouple readings of T_rec. Transponder temperature was highly correlated with water bath temperature (r²=0.96–0.99) over a range of approximately 10.0–40.0 °C. Transponders provided reliable data (±0.6 °C) over the T_sub of 21.4–36.9 °C and could be read from a distance of up to 5 cm. Below 21.4 °C, accuracy was reduced to ±2.8 °C, but individual transponder accuracy varied. Consequently, small subcutaneous transponders are useful to remotely quantify thermal physiology and torpor patterns without having to disturb the animal and disrupt torpor. Even at T_sub<21.4 °C where the accuracy of the temperature readings was reduced, transponders do provide reliable data on whether and when torpor is used.     

Metabolic heat estimation of the sea turtle Lepidochelys olivacea embryos

Several studies have reported the importance of metabolic heat on the increment of temperature in the sea turtle nests; however, the metabolic heat has not been calculated for sea turtle eggs. In this study, the metabolic heat generated by embryos of the sea turtle Lepidochelys olivacea was estimated from a thermal balance model by means of three measured temperatures—one in the center of the nest, and the others in the sand above and beside the nest. An experiment was conducted with a sample of 100 eggs from a Lepidochelys olivacea nest collected in the Baja Peninsula, Mexico. The results showed that during the incubation period, no metabolic heat was detected before day 19 but it increased from that day until a maximum of 0.84 W at day 34, when the incubation process was interrupted due to rain. This value corresponds to 31 emerged hatchlings. The novel model is a suitable framework to predict the temperature and metabolic heat within the nest.     

低温导致中华蜜蜂后翅翅脉的新变异

在封盖发育期,将中华蜜蜂Apis cerana cerana封盖子放入24℃低温环境中分别处理24、48、72 h,再恢复到正常的发育温度35℃至羽化,或将封盖子放在30℃低温中培养至羽化,发现羽化后的蜜蜂后翅翅脉发生明显变异。发现翅脉变异有3种类型,翅脉增加、翅脉突出和翅脉缺失。后翅翅脉增加的变异只发现一种,基室、缘室共有的径分脉与基室、盘室共有的中脉之间,新增径中横脉。新增的径中横脉发生的程度不同,有的在径分脉和中脉相对的位置相向伸出,有的形成完整的新脉,新增的径中横脉与原径中横脉相似,在末端均有"弱化点"。由于原有径中横脉较短,一直忽略其存在,这次径中横脉的确定,可以判定原来公认的"中脉分叉"应分别是径分脉和中脉延伸出来的两条翅脉。后翅突出的变异有2种,中脉向基室突出,径分脉向基室突出。翅脉突出的程度不同,有的略突出,有的明显突出,有的伸出翅脉较长。中脉突出均发生在中脉的转折点上,且此类翅脉变异,仅发生在雄蜂样本中,在工蜂样本中还未见。后翅翅脉缺失的变异有2种,发生在肘臀横脉和中脉。肘臀横脉"弱化点"处缺失。将中华蜜蜂雄蜂封盖子放入低温30℃恒温培养箱中发育,发现2个羽化的雄蜂样本发生肘臀横脉在"弱化点"处缺失。中脉向盘室伸出的部分发生缺失。翅脉缺失的程度不同,有的明显缩短,有的仅存痕迹,有的缺失大部分或完全缺失。中脉向盘室伸出的部分是东方蜜蜂Apis cerana区别于西方蜜蜂Apis mellifera的主要形态特征之一,如果东方蜜蜂这段翅脉全部缺失,此部位的形态与西方蜜蜂完全相同。这意味着这个翅脉作为区分东方蜜蜂和西方蜜蜂的翅脉特征将面临挑战。对蜜蜂种质资源鉴定,蜜蜂的系统发育和进化生物学等领域的研究将具有重要影响。温度影响翅脉发育的深入研究,为研究蜜蜂翅脉发育过程,揭示翅脉发育调控机制,以及蜜蜂发育的温度适应生理机制提供一个新思路。     

Lizards in the slow lane: Thermal biology of chameleons

1.

Field body temperatures (T_b's) of Chamaeleo chamaeleon in southwestern Spain averaged 28 °C in October and 30 °C in June. Slopes of regressions of T_b on T_a (ambient temperature at perch height) indicated that individuals were able to maintain a preferred body temperature of about 30 °C in June but not in October.