Hypotheses Concerning Algal Adaptation to Periodic Environmental Factors

A new lower-dimension ecological–evolutionary model of algae was proposed to describe the simultaneous dynamics of variables (population biomass) and parameters (limits of the temperature tolerance interval [a – d, a + d]). In a given periodic temperature regime, the parameters tend to certain final values, which are called evolutionarily stable (ES) values. Calculations showed that ES parameters form a rainbow structure on the plane (a, d); the farthest points of the rainbow correspond to psychrophilic (diatom) and thermophilic (blue–green) algae. Algal adaptation to two periodic environmental factors, temperature and salinity, was carried out within preset temperature and salinity tolerance ranges [a – d, a + d] and [b – c, b + c]. The domain of evolutionarily stable parameters in the plane (a, b) was found to depend on the degree of synchronism of environmental factors. The parameters lay on a linear segment in some cases, while their location on a nonlinear oval was unexpectedly possible in some other cases.

     

黄土-古土壤原核生物群落对古气候变化的响应

【目的】黄土-古土壤序列是记录第四纪气候环境变化的良好载体,其内部的土壤微生物特征是蕴含土壤环境变化的重要信息。由于黄土与古土壤成壤环境的气候差异,微生物群落结构特征可能会有不同的响应,但针对该问题的研究还十分有限。【方法】选择任家坡(R)和九州台(J)两地黄土(RL和JL)-古土壤(RS和JS)序列,运用高通量测序技术和线性判别分析效应大小(linear discriminant analysis effect size, LEfSe)识别土壤原核生物群落结构和类群差异,基于原核生物分类单元功能注释(functional annotation of prokaryotic taxa, FAPROTAX)数据库进行群落功能预测,以及利用Mantel test探讨影响土壤原核生物群落稳定的环境因子。【结果】土壤中碳氮营养物质与气候变化的代用指标磁化率、Rb/Sr变化趋势一致,含量整体表现为古土壤(RS和JS)高,对应的黄土(RL和JL)低,这一特征在任家坡古土壤(RS)中尤为显著;在同一气候时期,九州台较任家坡更为干冷,并且九州台古土壤沉积阶段也受到较强冬季风的影响,使其气候冷干与暖湿转变呈渐变型。原核生物群落结构中酸杆菌门(Acidobacteria)、泉古菌门(Crenarchaeota)、绿弯菌门(Chloroflexi)等具有嗜热嗜温性质的细菌和古菌在任家坡黄土-古土壤(RL和RS)中丰度较高,芽单胞菌门(Gemmatimonadetes)、放线菌门(Actinobacteria)、厚壁菌门(Firmicutes)、广古菌门(Euryarchaeota)、异常球菌-栖热菌门(Deinococcus-Thermus)等耐旱、适宜极端环境中生存的细菌和古菌在九州台黄土-古土壤中(JL和JS)丰度较高。同时,生命产能、氮、锰、铁、氯元素循环相关功能基因在任家坡古土壤(RS)中表达量最高,而碳、氢、硫元素循环相关功能基因在任家坡黄土(RL)中表达量最高。与任家坡相比,九州台原核生物群落具有物种多样性高、功能种类少的特点。Mantel test分析进一步表明,有机碳(soil organic carbon, SOC)、含水率(soil water content, SWC)、总氮(total nitrogen, TN)和硝态氮(nitrate nitrogen, NO₃^--N)是影响任家坡原核生物群落和功能稳定的关键环境因子,而TN、SOC、pH值和铵态氮(NH₄⁺-N)是影响九州台原核生物群落和功能稳定的关键环境因子。【结论】在暖湿期,微生物群落分化出更多的功能种类,具有更旺盛的生命活动;在冷干期,微生物群落通过提高物种多样性来完成主要的生命活动功能,通过协同共生维持群落生存和稳定来适应环境胁迫。研究成果对认识气候变化对土壤微生物多样性和功能的影响具有重要意义。     

Atmospheric CO2 concentration does not directly affect leaf respiration in bean or poplar

It is a matter of debate if there is a direct (short‐term) effect of elevated atmospheric CO₂ concentration (C_a) on plant respiration in the dark. When C_a doubles, some authors found no (or only minor) changes in dark respiration, whereas most studies suggest a respiratory inhibition of 15–20%. The present study shows that the measurement artefacts – particularly leaks between leaf chamber gaskets and leaf surface, CO₂ memory and leakage effects of gas exchange systems as well as the water vapour (‘water dilution’) effect on DCO₂ measurement caused by transpiration – may result in larger errors than generally discussed. A gas exchange system that was used in three different ways – as a closed system in which C_a increased continuously from 200 to 4200 mmol (CO₂) mol^‐1 (air) due to respiration of the enclosed leaf; as an intermittently closed system that was repeatedly closed and opened during C_a periods of either 350 or 2000 mmol mol^‐1, and as an open system in which C_a varied between 350 and 2000 mmol mol^‐1– is described. In control experiments (with an empty leaf chamber), the respective system characteristics were evaluated carefully. When all relevant system parameters were taken into account, no effects of short‐term changes in CO₂ on dark CO₂ efflux of bean and poplar leaves were found, even when C_a increased to 4200 mmol mol^‐1. It is concluded that the leaf respiration of bean and poplar is not directly inhibited by elevated atmospheric CO₂.     

Succinate oxidation by coupled potato tuber mitochondria followed by rapid scan spectrometry

Oxidation of succinate by potato tuber mitochondria has been investigated from aerobiosis to complete anuerobiosis. Difference spectra of the various steps were recorded by a rapid scan spectrometer delivering averaged spectra every 3 s in the range 380 to 630 mm. The transitions between state 3 and 4 resulted in large redox changes, essentially for the b cytochromes, and in significant changes in the spectral baseline (light scattering). At anaerobiosis the cytochromes c, c₁ and a were reduced while cytochrome a, remained oxidized. – Addition of uncouplers in aerobiosis induced oxidation of the b cytochromes, and when anaerobiosis occurred cytochromes c, c₁a and a₃ were reduced simultaneously. When uncouplers were added in anaerobiosis a partial oxidation of the b cytochromes and the reduction of cytochrome a₃ were observed. These results are interpreted as the building up of a membrane potential, maximal in state 4 and stable after anaerobiosis. The cytochromes buried in the membrane equilibrate with the membrane potential, and their redox states are sensitive to the changes. Variations of membrane potential also induce changes in the light scattering by the mitochondrial membrane.     

Can we predict ectotherm responses to climate change using thermal performance curves and body temperatures?

Thermal performance curves (TPCs), which quantify how an ectotherm's body temperature (T_b) affects its performance or fitness, are often used in an attempt to predict organismal responses to climate change. Here, we examine the key – but often biologically unreasonable – assumptions underlying this approach; for example, that physiology and thermal regimes are invariant over ontogeny, space and time, and also that TPCs are independent of previously experienced T_b. We show how a critical consideration of these assumptions can lead to biologically useful hypotheses and experimental designs. For example, rather than assuming that TPCs are fixed during ontogeny, one can measure TPCs for each major life stage and incorporate these into stage‐specific ecological models to reveal the life stage most likely to be vulnerable to climate change. Our overall goal is to explicitly examine the assumptions underlying the integration of TPCs with T_b, to develop a framework within which empiricists can place their work within these limitations, and to facilitate the application of thermal physiology to understanding the biological implications of climate change.     

Intermolt development reduces oxygen delivery capacity and jumping performance in the American locust (<Emphasis Type="Italic">Schistocerca americana</Emphasis>)

Among animals, insects have the highest mass-specific metabolic rates; yet, during intermolt development the tracheal respiratory system cannot meet the increased oxygen demand of older stage insects. Using locomotory performance indices, whole body respirometry, and X-ray imaging to visualize the respiratory system, we tested the hypothesis that due to the rigid exoskeleton, an increase in body mass during the intermolt period compresses the air-filled tracheal system, thereby, reducing oxygen delivery capacity in late stage insects. Specifically, we measured air sac ventilation frequency, size, and compressibility in both the abdomen and femur of early, middle, and late stage sixth instar Schistocerca americana grasshoppers. Our results show that late stage grasshoppers have a reduced air sac ventilation frequency in the femur and decreased convective capacities in the abdomen and femur. We also used X-ray images of the abdomen and femur to calculate the total proportion of tissue dedicated to respiratory structure during the intermolt period. We found that late stage grasshoppers had a lower proportion of their body dedicated to respiratory structures, especially air sacs, which convectively ventilate the tracheal system. These intermolt changes make oxygen delivery more challenging to the tissues, especially critical ones such as the jumping muscle. Indeed, late stage grasshoppers showed reduced jump frequencies compared to early stage grasshoppers, as well as decreased mass-specific CO₂ emission rates at 3 kPa PO₂. Our findings provide a mechanism to explain how body mass changes during the intermolt period reduce oxygen delivery capacity and alter an insect’s life history.     

Anti-inflammatory and anti-tumor-promoting effects of 5-deprenyllupulonol C and other compounds from Hop (Humulus lupulus L.)

A new phloroglucinol derivative, 5‐deprenyllupulonol C ( 1 ), along with four other phloroglucinol derivatives, 2 – 5 , five chalcones, 6 – 10 , four flavanones, 11 – 14 , two flavonol glycosides, 15 and 16 , and five triterpenoids, 17 – 21 , were isolated from the female inflorescence pellet extracts of hop (Humulus lupulus L.). Upon evaluation of these compounds against the Epstein? Barr virus early antigen (EBV‐EA) activation induced by 12‐O‐tetradecanoylphorbol 13‐acetate (TPA) in Raji cells, twelve compounds, i.e., 1 – 4, 11 – 14, 17 – 19 , and 21 , showed potent inhibitory effects on EBV‐EA induction, with IC₅₀ values in the range of 215–393 mol ratio/32 pmol TPA. In addition, eleven compounds, i.e., 1 – 4, 6, 11, 12, 14, 17, 18 , and 20 , were found to inhibit TPA‐induced inflammation (1 μg/ear) in mice, with ID₅₀ values in the range of 0.13–1.06 μmol per ear. Further, lupulone C ( 2 ) and 6‐prenylnaringenin ( 14 ) exhibited inhibitory effects on skin‐tumor promotion in an in vivo two‐stage mouse‐skin carcinogenesis test based on 7,12‐dimethylbenz[a]anthracene (DMBA) as initiator and with TPA as promoter.     

Development and ageing of etioplast structures in dark grown leaves ofAvena sativa (L.)

Summary Etioplasts of dark grown plants contain a large paracrystalline prolamellar body (PLB) and, attached to this there are prothylakoid membranes (PTs).PLB-tubules inAvena are composed mainly of two saponins and include only a low percentage of other lipids, protochlorophyll(ide) and proteins.Following the development of etioplasts in darkness from the very beginning until plants loose turgescence one can observe marked changes in ultrastructure. In the early stage of development predominantly PTs are seen in small etioplasts. Wide-type PLBs are small. After eight days there is a well developed stage with the well-known big and highly crystalline PLBs, which are connected to many long PT-membranes. After 13 days the PLBs are not significantly changed, while number and length of PTs are strongly reduced.These morphological observations are quantified by measurements of PLB-area and PT-length per plastid section. Saponin content as a marker for PLB-tubules and protochlorophyll(ide)-content as a marker for PT-membranes were measured. Both methods of determination show in good agreement a peak of development for PTs around day 6–7, and for PLBs around 9–10. Beginning senescence affects PT-membranes and PChl(ide) strongly, while saponins resp. PLBs persist better. These results are presented in view of thylakoid formation during greening, starting from the different etioplast stages.Abbreviations Chl(ide) chlorophyll(ide) - EM electron-microscope - PChl(ide) protochlorophyll(ide) - PLB prolamellar body - PT prothylakoid - TLC Thin layer chromatography A preliminary report has been presented at the V. Intern. Congress on Photosynthesis at Chalkidiki, Greece 1980.     

Seasonal control of energy requirements for thermoregulation in the djungarian hamster (Phodopus sungorus), living in natural photoperiod

Summary Djungarian dwarf hamsters,Phodopus s. sungorus, were kept in natural photoperiodic conditions throughout the year, either inside at a constantT _a of 23°C or outside subjected to seasonally varyingT _a. Comparisons were made between hamsters from both conditions to evaluate the significance of seasonal changes in photoperiod and/orT _a as environmental cues for seasonal acclimatization inPhodopus. Basal metabolic rate was lowest in July (1.68 ml/g·h) and highest in January (2.06 ml/g·h inPhodopus living outside), combined with a decrease inT _1c from 26°C in July to 20°C in January. This was parallelled by seasonal changes in body weight (summer 42 g, winter 25g), fur colouration, fur depth and the occurrence of short daily torpor.AtT _a below thermoneutrality total energy requirements for thermoregulation in winter acclimatizedPhodopus were found 36% lower than summer values (e.g. at O°CT _a in summer 1,160 mW, in winter 760 mW), which were effected by a combined strategy of reducing body weight (19%) together with improvements of thermal insulation of the body surface (17%). All seasonal changes were similar inPhodopus living inside or outside, suggesting that seasonal changes in photoperiod and not seasonal changes inT _a is the overriding controller for the environmental cueing of seasonality in energy requirements for thermoregulation.This research was supported by the Deutsche Forschungsgemeinschaft (He 990)     

Hypothermia after chronic mild stress exposure in rats with a history of postnatal maternal separations

The circadian system develops and changes in a gradual and programmed process over the lifespan. Early in life, maternal care represents an important zeitgeber and thus contributes to the development of circadian rhythmicity. Exposure to early life stress may affect circadian processes and induce a latent circadian disturbance evident after exposure to later life stress. Disturbance of the normal regulation of circadian rhythmicity is surmised to be an etiological factor in depression. We used postnatal maternal separation in rats to investigate how the early life environment might modify the circadian response to later life unpredictable and chronic stress. During postnatal days 2–14, male Wistar rats (n?=?8 per group) were daily separated from their mothers for a period of either 180?min (long maternal separation; LMS) or 10?min (brief maternal separation; BMS). In adulthood, rats were exposed to chronic mild stress (CMS) for 4 weeks. Body temperature, locomotor activity and heart rate were measured and compared before and after CMS exposure. LMS offspring showed a delayed body temperature acrophase compared to BMS offspring. Otherwise, adult LMS and BMS offspring demonstrated similar diurnal rhythms of body temperature, locomotor activity and heart rate. Exposure to CMS provoked a stronger and longer lasting hypothermia in LMS rats than in BMS rats. The thermoregulatory response appears to be moderated by maternal care following reunion, an observation made in the LMS group only. The results show that early life stress (LMS) in an early developmental stage induced a thermoregulatory disturbance evident upon exposure to unpredictable adult life stressors.     

Seasonal changes in daily metabolic patterns of Lacerta viridis

Summary Lacerta viridis maintained under natural photoperiodic conditions show daily and seasonal changes in metabolic rates and body temperature (T _b) as well as seasonal differences in sensitivity to temperature change. At all times of the year lizards have a daily fluctuation in oxygen consumption, with higher metabolic rates during the light phase of the day when tested at a constant ambient temperature (T _a) of 30°C. Rhythmicity of metabolic rate persists under constant darkness, but there is a decrease in the amplitude of the rhythm.Oxygen consumption measured at various T_as shows significant seasonal differences at T _as above 20°C. Expressed as the Arrhenius activation energy, metabolic sensitivity of Lacerta viridis shows temperature dependence in autumn, which changes to metabolic temperature independence in spring at T _as above 20°C. The results indicate a synergic relationship between changing photoperiod and body temperature selection, resulting in seasonal metabolic adjustment and seasonal adaptation.Abbreviations ANOVA analysis of variance - LD long day (16 h light) - SD short day (8 h light) - T _a ambient temperature - T _b body temperature     

Chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence transient during freezing and recovery in winter wheat

Chlorophyll (Chl) a fluorescence measurements as evaluators of plant freezing tolerance are frequently insufficiently sensitive to detect the early metabolic changes that are initiated following exposure to freezing temperatures. Using cold-acclimated winter wheat, I analysed the polyphasic transience (from 50 μs to 1 s) of Chl a fluorescence. This enabled detailed studies of the progressive energy flows and efficiencies within the photosystem 2 (PS2) complex that ensue following initial exposure to freezing temperatures right through to the plant recovery stage. The initial consequences of mild frosts that may cause primary damage involve a disturbance to the energy transfer subsequent to Q_A (the primary quinone electron acceptor of PS2). Lower freezing temperatures, on the other hand, may deter energy flow between the PS2 reaction centre (RC), Chl, and Q_A. All primary damage could only be repaired partially. Further freezing-triggered dysfunction of the electron transfer between the PS2 RCs and Q_A was connected with secondary damage that could lead to PS2 deactivation. Both primary and secondary freezing damages were reflected in decreased PI_ABS, the Performance Index based on equal absorption that characterizes all energy bifurcations in PS2. PI_ABS also differentiated cultivars with contrasting freezing-tolerance either subsequent to the onset of freezing or during the recovery stage. In contrast, the potential quantum yield of PS2 (F_v/F_m), which characterizes efficiency of energy trapping in the PS2 RCs, was only different in cultivars with contrasting freezing-tolerance during the recovery stage.     

Photosynthetic and biochemical activities in flag leaves of a newly developed superhigh-yield hybrid rice (<Emphasis Type="Italic">Oryza sativa</Emphasis>) and its parents during the reproductive stage

Responses of net photosynthetic rates to intercellular CO₂ concentration (P _n/C _i curves) and photochemical characteristics were investigated in flag leaves of newly developed superhigh-yield hybrid rice (Oryza sativa L.) LiangYouPeiJiu (LYPJ) and its maternal PeiAi64S (PA64S) and paternal WuMang9311 (WM9311) lines grown in the field during the reproductive stage. The results showed that photosynthetic functions, such as the electron transport activities of photosystems and photophosphorylation, assessed in vivo from P _n/C _i curves under field conditions declined more or earlier than those obtained in vitro. The degradation of polypeptides of thylakoid membranes was slower than those for P _Ca=360 (light-saturated net photosynthetic rate measured at 360 μmol mol⁻¹) and CE (carboxylation efficiency, obtained from the initial slope of the P _n/C _i curve). The initial inhibition of the PSII electron transport and oxygen-evolving activity induced by senescence occurred before the degradation of the oxygen-evolving complex. In comparison, LYPJ had intermediate photosynthetic functions in the early stage of leaf development, but greater photochemical activities in the mid and late stages. WM9311 showed a similar pattern of changes but lower values, and PA64S had higher values in the early stage but showed a faster rate of senescence than LYPJ. These findings implied that the hybrid LYPJ demonstrated intermediate photosynthetic activities between its parents in the early stage of leaf development, whereas it had higher photosynthetic activities than its parents in the mid and late stages, which may be responsible for its high yield.     

Gene and whole genome analyses reveal that the mycobacterial strain JS623 is not a member of the species Mycobacterium smegmatis

Unexpected differences were found between the genome of strain JS623, used in bioremediation studies, and the genome of strain mc²155, a model organism for investigating basic biology of mycobacteria. Both strains are currently assigned in the databases to the species Mycobacterium smegmatis and, consequently, the environmental isolate JS623 is increasingly included as a representative of that species in comparative genome‐based approaches aiming at identifying distinctive traits of the different members of the genus Mycobacterium. We applied traditional molecular taxonomic procedures – inference of single and concatenated gene trees – to re‐evaluate the membership of both strains to the same species, adopting the latest accepted cut‐off values for species delimitation. Additionally, modern whole genome‐based in silico methods where performed in a comprehensive molecular phylogenetic analysis of JS623 and other members of the genus Mycobacterium. These analyses showed that all relevant genome parameters of JS623 clearly separate this strain from M. smegmatis. The strain JS623 should be corrected as Mycobacterium sp. not only in the literature but, even more importantly, in the database entries, as inclusion of the genome wrongly attributed to the M. smegmatis species in comparative studies will result in misleading conclusions.     

Influence of circadian disruption on neurotransmitter levels,physiological indexes,and behaviour in rats

Brain monoamines – such as noradrenaline (NA), dopamine (DA) and serotonin (5-HT) – regulate several important physiological functions, including the circadian rhythm. The purpose of this study was to examine changes in NA, DA and 5-HT levels in various brain regions and their effect on core body temperature (T_c), heart rate (HR) and locomotor activity (Act) in rats following exposure to an artificial light/dark (LD) cycle. For this, male Wistar rats were housed at an ambient temperature (T_a) of 23?°C and 50% relative humidity with free access to food and water. Rats were exposed to either natural (12?h:12?h) or artificial (6?h:6?h) LD cycles for 1 month, after which each brain region was immediately extracted and homogenized to quantify the amounts of NA, DA and 5-HT by high-performance liquid chromatography. Behavioural changes were also monitored by the ambulatory activity test (AAT). Notably, we found that artificial LD cycles disrupted the physiological circadian rhythms of T_c, HR and Act. Although the 5-HT levels of rats with a disrupted circadian rhythm decreased in cell bodies (dorsal and median raphe nuclei) and projection areas (frontal cortex, caudate putamen, preoptic area and suprachiasmatic nucleus) relative to the control group, NA levels increased both in the cell body (locus coeruleus) and projection area (paraventricular hypothalamus). No significant changes were found with respect to DA. Moreover, circadian rhythm-disrupted rats also showed anxious behaviours in AAT. Collectively, the results of this study suggest that the serotonergic and noradrenergic systems, but not the dopaminergic system, are affected by artificial LD cycles in brain regions that control several neural and physiological functions, including the regulation of physiological circadian rhythms, stress responses and behaviour.     

Timing of torpor bouts during hibernation in European hamsters (Cricetus cricetus L.)

Body temperature (T _b) of seven European hamsters maintained at constant ambient temperature (T _a = 8 °C) and constant photoperiod (LD 8:16) was recorded throughout the hibernating season using intraperitoneal temperature-sensitive HF transmitters. The animals spent about 30% of the hibernation season in hypothermia and 70% in inter-bout normothermy. Three types of hypothermia, namely deep hibernation bouts (DHBs), short hibernation bouts (SHBs), and short and shallow hibernation bouts (SSHBs), were distinguished by differences in bout duration and minimal body temperature (T _m). A gradual development of SSHBs from the diel minimum of T _b during normothermy could be seen in individual hamsters, suggesting a stepwise decrease of the homeostatic setpoint of T _b regulation during the early hibernation season. Entry into hibernation followed a 24-h rhythm occurring at preferred times of the day in all three types of hypothermia. DHBs and SHBs were initiated approximately 4 h before SSHBs, indicating a general difference in the physiological initiation of SSHBs on the one hand and DHBs and SHBs on the other. Arousals from SHBs and SSHBs also followed a 24-h rhythm, whereas spontaneous arousals from DHBs were widely scattered across day and night. Statistical analyses of bout length and the interval between arousals revealed evidence for a free-running circadian rhythm underlying the timing of arousals. The results clearly demonstrate that entries into hypothermia are linked to the light/dark-cycle. However, the role of the circadian system in the timing of arousals from DHBs remains unclear. Accepted: 11 December 1996     

Isolation and characterization of butachlor‐catabolizing bacterial strain Stenotrophomonas acidaminiphila JS‐1 from soil and assessment of its biodegradation potential

Aims: Isolation, characterization and assessment of butachlor‐degrading potential of bacterial strain JS‐1 in soil. Methods and Results: Butachlor‐degrading bacteria were isolated using enrichment culture technique. The morphological, biochemical and genetic characteristics based on 16S rDNA sequence homology and phylogenetic analysis confirmed the isolate as Stenotrophomonas acidaminiphila strain JS‐1. The strain JS‐1 exhibited substantial growth in M9 mineral salt medium supplemented with 3·2 mmol l^?1 butachlor, as a sole source of carbon and energy. The HPLC analysis revealed almost complete disappearance of butachlor within 20 days in soil at a rate constant of 0·17 day^?1 and half‐life (t_½) of 4·0 days, following the first‐order rate kinetics. The strain JS‐1 in stationary phase of culture also produced 21·0 μg ml^?1 of growth hormone indole acetic acid (IAA) in the presence of 500 μg ml^?1 of tryptophan. The IAA production was stimulated at lower concentrations of butachlor, whereas higher concentrations above 0·8 mmol l^?1 were found inhibitory. Conclusions: The isolate JS‐1 characterized as Stenotrophomonas acidaminiphila was capable of utilizing butachlor as sole source of carbon and energy. Besides being an efficient butachlor degrader, it substantially produces IAA. Significance and Impact of the Study: The bacterial strain JS‐1 has a potential for butachlor remediation with a distinctive auxiliary attribute of plant growth stimulation.     

Variation in nestling body condition and wing development predict cause‐specific mortality in fledgling dickcissels

Phenotypic traits developed in one life‐history stage can carryover and affect survival in subsequent stages. For songbirds, carryover effects from the pre‐ to post‐fledging period may be crucial for survival but are poorly understood. We assessed whether juvenile body condition and wing development at fledging influenced survival during the post‐fledging period in the dickcissel Spiza americana. We found pre‐ to post‐fledging carryover effects on fledgling survival for both traits during the ‘early part’ – first four days – of the post‐fledging period. Survival benefits of each trait depended on cause‐specific sources of mortality; individuals in better body condition were less likely to die from exposure to adverse environmental conditions, whereas those with more advanced wing development were less likely to be preyed upon. Fledglings with more advanced wing development were comparatively more active and mobile earlier in the post‐fledging period, suggesting they were better able to avoid predators. Our results provide some of the first evidence linking development of juvenile phenotypic traits to survival against specific sources of post‐fledging mortality in songbirds. Further investigation into pre‐ to post‐fledging carryover effects may yield important insights into avian life‐history evolution.     

Energetics and thermoregulation during digging in the rodent tuco-tuco (Ctenomys talarum)

For subterranean rodents, searching for food by extension of the tunnel system and maintenance of body temperature are two of the most important factors affecting their life underground. In this study we assess the effect of ambient temperature on energetics and thermoregulation during digging in Ctenomys talarum. We measured V˙o₂ during digging and resting at ambient temperature (T_a) below, within, and above thermoneutrality. Digging metabolic rate was lowest at T_a within the thermoneutral zone and increased at both lower and higher temperatures, but body temperature (T_b) remained constant at all T_as. Below thermoneutrality, the cost of digging and thermoregulation are additive. Heat production for thermoregulation would be compensated by heat produced as a by-product of muscular activity during digging. Above thermoneutrality, conduction would be an important mechanism to maintain a constant T_b during digging.