Thermogenic responses in Eurasian Tree Sparrow(Passer montanus)to seasonal acclimatization and temperature-photoperiod acclimation

Background:Small birds in temperate habitats must either migrate,or adjust aspects of their morphology,physiology and behavior to cope with seasonal change in temperature and photoperiod.It is,however,difficult to accurately measure how seasonal changes in temperature and photoperiod affect physiological processes such as basal metabolic rate(BMR)and metabolic activity.To address this problem,we collected data in each month of the year on body mass(Mb)and BMR,and conducted a series of experiments to determine the effect of temperature and photoperiod on Mb,BMR and physiological markers of metabolic activity,in the Eurasian Tree Sparrow(Passer montanus).Methods:In one experiment,we measured monthly change in Mb and BMR in a captive group of birds over a year.In another experiment,we examined the effects of acclimating birds to two different temperatures,10 and 30℃,and a long and a short photoperiod(16 h light:8 h dark and 8 h light:16 h dark,respectively)for 4 weeks.Results:We found that these treatments induced sparrows to adjust their Mb and metabolic rate processes.Acclimation to 30℃for 4 weeks significantly decreased sparrows’Mb,BMR,and energy intake,including both gross energy intake and digestible energy intake,compared to birds acclimated to 10℃.The dry mass of the liver,kidneys and digestive tract of birds acclimated to 30℃also significantly decreased,although their heart and skeletal muscle mass did not change significantly relative to those acclimated to 10℃.Birds acclimated to 30℃also had lower mitochondrial state-4 respiration(S4R)and cytochrome c oxidase(COX)activity in their liver and skeletal muscle,compared to those acclimated to 10℃.Birds acclimated to the long photoperiod also had lower mitochondrial S4R and COX activity in their liver,compared to those acclimated to the short photoperiod.Conclusions:These results illustrate the changes in morphology,physiology,and enzyme activity induced by seasonal change in temperature and photoperiod in a small temperate passerine.Both temperature and photoperiod probably have a strong effect on seasonal variation in metabolic heat production in small birds in temperate regions.The effect of temperature is,however,stronger than that of photoperiod.

The role of temperature as a driver of metabolic flexibility in the Red-billed Leiothrix(Leiothrix lutea)

Background:The thermoregulatory ability of animals is strongly influenced by the temperature of their environment.Acclimation to cold requires a range of physiological and morphological adjustments.In this study,we tested the hypothesis that a small passerine,the Red-billed Leiothrix(Leiothrix lutea),can maintain homeothermy in cold conditions by adjusting the physiology and biochemistry of its tissue and organs and return to its former physiological and biochemical state when moved to a warm temperature.Methods:Phenotypic variation in thermogenic activity of the Red-billed Leiothrixs(Leiothrix lutea)was investigated under warm(35℃),normal(25℃)or cold(15℃)ambient temperature conditions.Oxygen consumption was measured using an open-circuit respirometry system.Mitochondrial state-4 respiration and cytochrome-c oxidase(COX)activity in liver,kidney heart and pectoral muscle were measured with a Clark electrode.Results:Birds acclimated to an ambient temperature of 15℃ for 4 weeks significantly increased their basal metabolic rate(BMR)compared to a control group kept at 25℃.Birds acclimated to 35℃ decreased their BMR,gross energy intake(GEI)and digestible energy intake(DEI).Furthermore,birds acclimated to 15℃ increased state-4 respiration in their pectoral muscles and cytochrome-c oxidase(COX)activity in their liver and pectoral muscle,compared to the 25℃ control group.Birds acclimated to 35℃ also displayed lower state-4 respiration and COX activity in the liver,heart and pectoral muscles,compared to those kept at 25℃.There was a positive correlation between BMR and state-4 respiration,and between BMR and COX activity,in all of the above organs except the liver and heart.Conclusions:Our study illustrates that the morphological,physiological,and enzymatic changes are associated with temperature acclimation in the Red-billed Leiothrix,and supports the notion that the primary means by which small birds meet the energetic challenges of cold conditions is through metabolic adjustments.

不同生境内啮齿动物对辽东栎幼苗的频率依赖性捕食及其对幼苗生长与存活的影响

啮齿动物对辽东栎(Quercus wutaishanica)种子的侵袭取决于种子的大小及其捕食频率。然而,啮齿动物对幼苗的捕食是否具有频率依赖性还不清楚。本研究在宁夏六盘山区辽东栎次生林内,选取林窗和林下两种生境,按5个种子大小频率(9:1,7:3,5:5,3:7和1:9)移栽萌发生根的辽东栎幼苗,探究啮齿动物对幼苗子叶的频率依赖性捕食及其对幼苗生长与存活的影响。研究结果表明:(i)幼苗移栽初期(1-7天),啮齿动物更偏好大种子建立幼苗的子叶。然而,移栽后8-60天,啮齿动物更偏好小种子建立幼苗的子叶,即表现为正频率依赖性捕食。(ii)尽管幼苗捕食率在林下高于林窗,但经过一个生长周期后,林窗内幼苗存活率高于林下(分别为5.40%和2.00%)。(iii)捕食子叶对辽东栎幼苗生长无显著影响,但顶芽被咬掉后幼苗各生长参数均显著降低(P<0.05)。这些结果不仅为啮齿动物和不同表型辽东栎幼苗的共存提供了新的见解,还揭示了栎树幼苗的更新策略。