Embryonic and post‐embryonic responses to high‐elevation hypoxia in a low‐elevation lizard

Low‐elevation species can migrate toward higher elevations to survive in a warming world. However, animals’ responses to hypoxia when migrating to high elevations have rarely been addressed. To identify the response of low‐elevation lizards to high‐elevation hypoxia, we collected field body temperatures (T_fb) and operative temperatures (T_e) of lizards (Eremias argus) from a low‐elevation population (1036 m) and a high‐elevation population (2036 m), and then determined adult thermal physiology, embryonic development, and hatchling phenotypes after acclimating low‐elevation lizards and incubating their eggs in conditions mimicking the low‐elevation oxygen condition (18.5% O₂) and high‐elevation oxygen (hypoxic) condition (16.5% O₂). Our study revealed that T_fb and T_e were higher for the low‐elevation population compared to the high‐elevation population. We also found adults from low elevation acclimated to hypoxia preferred lower body temperatures, but did not show changes in locomotor performance or growth. In addition, hypoxia did not affect embryonic development (hatching time and success) or hatchling phenotypes (body size and locomotor performance). These results suggest that adult lizards from low elevations can respond to hypoxia‐induced stress when migrating to high elevations by behaviorally thermoregulating to lower body temperatures in order to sustain normal functions. Similarly, low‐elevation embryos can develop normally (with unchanged hatching success and offspring phenotypes) under the high‐elevation hypoxic condition. This study highlights that low‐elevation populations of a species that inhabits a range of elevations can buffer the impact of high‐elevation hypoxic conditions to some degree and thus attain similar fitness to the source population.     

An investigation of links between metabolic rate and feed efficiency in European sea bass Dicentrarchus labrax

Feed efficiency (FE) is the amount of body weight gain for a given feed intake. Improving FE through selective breeding is key for sustainable finfish aquaculture but its evaluation at individual level is technically challenging. We therefore investigated whether individual routine metabolic rate (RMR) was a predictor of individual FE in the European sea bass Dicentrarchus labrax, a major species in European mariculture. The European sea bass has three genetically distinct populations across its geographical range, namely Atlantic (AT), West Mediterranean (WM), and East Mediterranean (EM). We compared FE and RMR of fish from these three populations at 18 or 24 °C. We held 200 fish (62 AT, 66 WM, and 72 EM) in individual aquaria and fed them from ad libitum down to fasting. FI was assessed for an ad libitum feeding rate and for a fixed restricted ration (1% of metabolic body weight·day⁻¹, with metabolic body weight = body weight^0.8). After being refed 12 wk in a common tank, individual RMR was measured over 36 h by intermittent flow respirometry. There was a significant effect of temperature whereby fish at 18 °C had greater mean FE (P < 0.05) and lower RMR (P < 0.001). There was also a significant effect of population, where AT fish had lower FE (P < 0.05) and greater RMR (P < 0.001) than WM and EM, at both temperatures. Despite these differences in temperature and population means, individual FE and RMR were not significantly correlated (P > 0.05). Therefore, although the results provide evidence of an association between metabolic rate and FE, RMR was not a predictor of individual FE, for reasons that require further investigation.     

High rodent abundance increases seed removal but decreases scatter-hoarding and seedling recruitment along an elevational gradient

The distributions of small rodents in mountainous environments across different elevations can provide important information regarding the effects of climate change on the dispersal of plant species. However, few studies of oak forest ecosystems have compared the elevational patterns of sympatric rodent diversity, seed dispersal, seed bank, and seedling abundance. Thus, we tested the differences in the seed disperser composition and abundance, seed dispersal, seed bank abundance, and seedling recruitment for Quercus wutaishanica along 10 elevation levels in the Taihang Mountains, China. Our results provide strong evidence that complex asymmetric seed dispersal and seedling regeneration exist along an elevational gradient. The abundance of rodents had a significant negative correlation with the elevation and the seed removal rates peaked and then declined with increasing elevation. The seed removal rates were higher at middle and lower elevations than higher elevations but acorns were predated by 5 species of seed predators at middle and lower elevations, and thus, there was a lower likelihood of recruitment compared with those dropped beneath mother oaks at higher elevations. More importantly, the number of individual seeds in the seed bank and seedlings increased with the elevation, although dispersal services were reduced at sites lacking rodents. As conditional mutualists, the rodents could possibly act as antagonistic seed predators rather than mutualistic seed dispersers at low and middle elevations, thereby resulting in the asymmetric pattern of rodent and seedling abundance with increasing elevation to affect the community assembly and ecosystem functions on a large spatial scale.     

The relation of fasting and resting metabolic rates to heat tolerance in the domestic fowl

1. Resting metabolic rate (RMR) and fasting metabolic rate (FMR) were periodically determined, using an open air circuit master system, from January to September in 10 White Leghorn, 10 Plymouth Rock and 20 New Hampshire × White Leghorn mature laying birds fed ad libitum.

2. The relationship of metabolic rate (l.O2/hr.) to body weight (kg.) in the pooled data followed the 0.795 W0.61 equation for the fasting level, and 0.916 W0.59 for the resting level. The expression of metabolic rates as litres oxygen per kg. body weight can lead to serious errors if birds of differing body weights are compared.

3. Heat increments of feeding (estimated by RMR‐FMR) gradually increased with rising environmental temperature, with only slight initial change in the FMR, followed by marked reductions in both the FMR and the RMR at the higher temperatures. It is suggested that a decrease in the FMR may allow for a reduction in the RMR in the hotter season, without this necessarily being linked with a depression in the heat increment of feeding and productivity.

4. In the lower temperature range the three breeds had similar metabolic rates. At the highest temperatures the White Leghorns and New Hampshire x White Leghorn had lower FMR than the Plymouth Rocks, thereby maintaining similar heat increments, but at lower RMR. It is suggested that this may be the basis for their better heat tolerance.     

Main factors affecting lacertid lizard thermal ecology

The thermal ecology of ectotherms has been studied for almost 2 centuries, but additional attention is currently being paid to it, to understand how organisms deal with the environment in a climate change context. A consensus is still far away due to the large number of factors involved and their complex interactions. In this context, 3 analyses in lacertid lizards were carried out: (i) a meta‐analysis, to test for differences between body and air temperatures from 71 populations; (ii) a meta‐analysis concerning correlations between body and air temperatures from 60 populations; and (iii) a multimodel inference of thermoregulation effectiveness indices from 45 populations. The importance of different factors, including body size, habitat, insularity, altitude, climate and season, was evaluated in all analyses to model the response variables. A strong seasonality effect was observed, with a consistent pattern of less effective thermoregulation in summer compared to other seasons. Altitude was the second most important factor, with a consistent higher thermoregulation effort in populations occurring at high elevations (>1000 m above sea level). Other factors, such as insularity or body size, can also be important, but did not exhibit a clear pattern. Finally, thermoregulation was less affected by climate and habitat type.     

Would behavioral thermoregulation enable pregnant viviparous tropical lizards to cope with a warmer world?

Sceloporus lizards depend on external heat to achieve their preferred temperature (T_sel) for performing physiological processes. Evidence both in the field and laboratory indicates that pregnant females of this Genus select body temperatures (T_b) lower than 34 °C as higher temperatures may be lethal to embryos. Therefore, thermoregulation is crucial for successful embryo development. Given the increase in global air temperature, it is expected that the first compensatory response of species that inhabit tropical climates will be behavioral thermoregulation. We tested whether viviparous Sceloporus formosus group lizards in the wild exhibited differences in thermoregulatory behavior to achieve the known T_sel for developing embryos regardless of local thermal conditions. We quantified field active body temperature, thermoregulatory behavior mechanisms (time of sighting, microhabitat used and basking time) and available microhabitat thermal conditions (i.e. operative temperature) for 10 lizard species during gestation, distributed along an altitudinal gradient. We applied both conventional and phylogenic analyses to explore whether T_b or behavioral thermoregulation could be regulated in response to different thermal conditions. These species showed no significant differences in field T_b during gestation regardless of local thermal conditions. In contrast, they exhibited significant differences in their behavioral thermoregulation associated with local environmental conditions. Based on these observations, the differences in thermoregulatory behavior identified are interpreted as compensatory adjustments to local thermal conditions. We conclude that these species may deal with higher temperatures predicted for the tropics by modulating their thermoregulatory behavior.     

Thermal biology and locomotor performance in Phymaturus calcogaster: are Patagonian lizards vulnerable to climate change?

Behavioral and physiological traits of ectotherms are especially sensitive to fluctuations of environmental temperature. In particular, niche-specialist lizards are dependent on their physiological plasticity to adjust to changing environmental conditions. Lizards of the genus Phymaturus are viviparous, mainly herbivorous, and inhabit only rock promontories in the steppe environments of Patagonia and the Andes. Herein, we examine the vulnerability of the southernmost Phymaturus species to global warming: the endemic Phymaturus calcogaster, which lives in a mesic environment in eastern Patagonia. We studied body temperatures in the field (T_b), preferred body temperatures in a thermogradient (T_pref), the operative (T_e) and environmental temperatures, and the dependence of running performance on body temperature. P. calcogaster had a mean T_b (27.04°C) and a mean T_e (31.15°C) both lower than their preferred temperature (T_pref = 36.61°C) and the optimal temperature for running performance (T_o = 37.13°C). Lizard activity seems to be restraint during the early afternoon due high environmental temperatures. However, both, the high safety margin and warming tolerance suggest that the expected increase in environmental temperatures due to global warming (IPCC report in 2018) would not threaten, but indeed enhance locomotor performance in this population.     

Relationship Between Seed Mass and Young-Seedling Growth and Morphology Among Nine Bluebunch Wheatgrass Populations

To better match plant materials to ecological sites for the purpose of rangeland seedling establishment, we examined the relationship between seed size and growth and morphological traits in young seedlings of bluebunch wheatgrass (BBWG) (Pseudoroegneria spicata [Pursh.] Á. Löve), a perennial Triticeae bunchgrass native to the Intermountain West. Traits examined included onset of germination, seedling biomass traits, and seedling surface-area traits. We grew seeds of nine BBWG populations that varied for seed size and were produced in a common environment under 2 contrasting d/n temperature regimes (20/15°C; 10/5°C). Lighter-seeded populations germinated and initiated shoots earlier. Heavier-seeded populations displayed high levels of biomass-related traits (e.g., shoot and root biomass and shoot length), while lighter-seeded populations displayed high levels of surface area ? related traits (e.g., specific leaf area and specific root length [SRL]). Correlations between seed size and young-seedling traits were mostly similar under the two temperature regimes. However, root length ? related traits showed more positive correlations with seed size under the low-temperature regime, which is more similar to actual field-emergence conditions during early spring. P-24, a light-seeded population, originated from the most arid site and exhibited the highest SRL at low temperature, while T-17t, a heavy-seeded population, originated from the most mesic site and exhibited moderate SRL. Three populations used for rangeland revegetation, “Whitmar,” “Goldar,” and Anatone Germplasm, all exhibited low seed mass and high SRL. However, only Anatone displayed high root-to-shoot length ratio under both temperature regimes, perhaps explaining its wide and successful use in rangeland seedings.     

Evolution for extreme living: variation in mitochondrial cytochrome c oxidase genes correlated with elevation in pikas (genus Ochotona)

The genus Ochotona (pikas) is a clade of cold‐tolerant lagomorphs that includes many high‐elevation species. Pikas offer a unique opportunity to study adaptations and potential limitations of an ecologically important mammal to high‐elevation hypoxia. We analyzed the evolution of 3 mitochondrial genes encoding the catalytic core of cytochrome c oxidase (COX) in 10 pika species occupying elevations from sea level to 5000 m. COX is an enzyme highly reliant on oxygen and essential for cell function. One amino acid property, the equilibrium constant (ionization of COOH), was found to be under selection in the overall protein complex. We observed a strong relationship between the net value change in this property and the elevation each species occupies, with higher‐elevation species having potentially more efficient proteins. We also found evidence of selection in low‐elevation species for potentially less efficient COX, perhaps trading efficiency for heat production in the absence of hypoxia. Our results suggest that different pika species may have evolved elevation‐specific COX proteins, specialization that may indicate limitations in their ability to shift their elevational ranges in response to future climate change.     

内蒙古贺兰山啮齿动物种类组成及海拔梯度分布研究

贺兰山独特的地势地貌和植被垂直分布特点,为啮齿类动物的群落结构和分布特征研究提供了良好条件。在2013年分春、夏、秋3个季节,采用铗日法对内蒙古贺兰山的啮齿动物种类组成和海拔梯度分布情况进行了细致研究。调查选取了8条典型沟道,共布设有效铗日18 748个,捕获啮齿动物235只,隶属2目5科11属13种。捕获种类最多的为哈拉乌沟(11种),最少的是雪岭子沟和甘树湾沟,各捕获2种。啮齿动物多样性垂直分布特点总体上呈现中间高两头低的趋势,符合"驼峰形"格局。     

Reproductive strategies in males of the world's southernmost lizards

Reproductive and life history patterns in reptiles are tightly related to the environmental conditions, so male reproductive cycles have been historically characterized as continuous, for tropical lizards, or seasonal, for temperate lizards. However, males of Liolaemus and Phymaturus lizards (Liolaemidae), from cold temperate climates of high altitudes or latitudes in Argentina and Chile, have developed a variety of reproductive cycles to coordinate with the short female reproductive season and to deal with the low frequency of reproductive females in the population. Using gonadal histology and morphological analysis, we describe the male reproductive biology, fat storage and sexual dimorphism of the viviparous lizards Liolaemus sarmientoi and Liolaemus magellanicus that inhabit an austral grass steppe at 51°S, in the southern limit of the American continent. Males of L. sarmientoi and L. magellanicus are reproductively available during the entire activity season of approximately 5 months. In addition, males of both species exhibit greater body sizes than females in morphological variables relevant in sexual selection. Meanwhile, females of both species exhibit larger inter‐limb length than conspecific males, which suggests fecundity selection to increase space for a larger litter size. The continuous sperm production throughout the activity season allows these liolaemids to mate at any time when females ovulate, representing a selective advantage to deal with the short activity season and the adversities of the cold environment they inhabit.     

Morphological characteristics of blood cells in monitor lizards: is erythrocyte size linked to actual body size?

Blood cell morphology and count are not uniform across species. Recently, between‐species comparisons revealed that the size of red blood cells is associated with body size in some lizard taxa, and this finding was interpreted in the context of the metabolic theory. In the present study, we examined the numbers and the size of blood cells in 2 species of monitor lizards, the mangrove‐dwelling monitor (Varanus indicus) and the savannah monitor (V. exanthematicus), and we compared these traits in individuals of different body size. The results revealed that during the course of ontogeny, the size of red blood cells increases with body mass. Because the mass‐specific metabolic rate decreases with body size and the cell volume‐to‐surface ratio decreases with the cell size, changes in the erythrocyte size might be the result of oxygen transport adjustment.     

Environmental and host factors associated with seropositivity to New Jersey and Indiana vesicular stomatitis viruses in Costa Rican cattle

A cross-sectional study was conducted in Costa Rican cattle to identify host risk factors and endemic foci for vesicular stomatitis virus New Jersey (VSV NJ) and indiana (VSV IND) serotype The effects of age, gender, breed, residence at specific levels of mean annual rainfall, temperature, relative evapotranspiration potential, and elevation on the risk of seropositivity for VSV NJ and VSV IND were evaluated using a random-effects logistic-regression model which adjusted for overdispersion between herds. A total of 2232 cattle from 348 farms located throughout Costa Rica were examined.

Total seroprevalences of 46% and 21% were found for VSV NJ and VSV IND, respectively. When environmental risk factors were considered, cattle residing in areas between 500 and 1500 m (pre-montane or lower montane moist forest) had a higher risk of seropositivity to VSV BNJ compared with cattle living at lower elevations (odds ratio (OR) ≥ 3.6). In addition, cattle residing at 0–500 m and less than 2 m of annual raifall (tropical dry forest) were also at a higher risk of seropositivity to VSV NJ compared with cattle living at other regions (OR ≥ 10). This evidence suggests that at least two transmission cycles may exist for VSV NJ: one located at a higher elevation and the other found at regions of lower elevation and lower rainfall. These regions may indicate the location of different arthropod vectors of viral reservoirs. Antibody prevalence increased with age, suggesting a relationship between lenght of residence in an endemic area and the likelihood of being seropositive to VSV NJ.

No factors were associated with VSV IND seropositivity. The lack of environmental associations with VSV IND seropositivity suggested that the transmission cycle for this serotype is different than that for SV NJ.     

艾美尔球虫对高原鼠兔个性与生理特征的影响

对30只高原鼠兔(Ochotona curzoniae)分别灌喂艾美尔球虫(Eimeria)卵囊(2 × 106个·mL?1)、驱虫剂以及生理盐水(对照),测定艾美尔球虫对高原鼠兔食物摄入量、体重、粪便皮质醇浓度、静止代谢率以及探索性的影响。结果发现：1)试验第5天时,艾美尔球虫卵囊数达到最大值,且灌喂艾美尔球虫组的艾美尔球虫卵囊数显著高于驱虫组和对照组 (P < 0.05);2)试验第18天时,灌喂艾美尔球虫组与对照组高原鼠兔的食物摄入量无显著差异(P > 0.05),但均显著低于驱虫组(P < 0.05);3)第8天时,灌喂艾美尔球虫组和驱虫组高原鼠兔粪便皮质醇浓度显著高于对照组(P < 0.05);第18天时,灌喂艾美尔球虫组和对照组高原鼠兔粪便皮质醇浓度、静止代谢率均显著高于驱虫组(P < 0.05);4)第5 天时,灌喂艾美尔球虫组高原鼠兔探索性显著低于对照组和驱虫组(P < 0.05)。高原鼠兔感染艾美尔球虫后,其皮质醇浓度升高、静止代谢率降低、探索性减弱,降低了被捕食风险,增大了艾美尔球虫在高原鼠兔种群内的传播率。本研究结果可为应用艾美尔球虫作为潜在的高原鼠兔生物防治制剂以及控制高原鼠兔种群数量提供了新的依据。     

青藏高原高寒草甸种子萌发行为沿海拔梯度的分异特征

为探究海拔梯度上高寒草甸植物种子萌发行为的分异特征及温度对不同海拔种群萌发行为的影响，本研究选取青藏高原东缘高寒草甸为研究区，选用31种常见植物种，沿海拔梯度共采集79个种群的种子，设置昼夜温度15℃/5℃和25℃/10℃开展萌发试验，探讨高寒草甸植物种子萌发行为与海拔的关系。研究结果表明：温度对种子萌发行为影响显著，25℃/10℃比15℃/5℃处理下的半数萌发时间（The time to achieve 50% germination，T₅₀）缩短7.20 d，萌发率（Germination percentage，GP）增加12.83%。萌发行为与海拔间的关系与萌发温度有关，15℃/5℃处理下，海拔对T₅₀的影响不显著，GP随海拔的升高显著增加；但在25℃/10℃处理下，T₅₀随海拔升高而显著延长，GP随海拔升高显著下降。温度升高时，部分高海拔种群中的种子倾向选择延迟萌发。延迟萌发对策能够促进有限的环境资源在时间和空间尺度上分化，有利于避免不可预测环境下大量同步萌发所面临的灭绝风险，对物种更新和续存起到重要作用。     

Temperature-induced plasticity at cellular and organismal levels in the lizard Anolis carolinensis

Among ectotherms, individuals raised in cooler temperatures often have larger body size and/or larger cell size. The current study tested whether geographic variation in cell size and plasticity for cell size exist in a terrestrial, ectothermic vertebrate, Anolis carolinensis Voigt, 1832. We demonstrated temperature-induced plasticity in erythrocytes and epithelial cells of hatchlings lizards derived from the eggs of females sampled from four populations and incubated at multiple temperatures. Larger cells were produced in hatchlings from cooler treatments; however, hatchling body size was unaffected by temperature. Therefore, temperature-induced plasticity applies at the cellular, but not organismal, level in A. carolinensis. In addition, reaction norms for cell size differed among populations. There was a latitudinal trend in cell size and in plasticity of cell size among our study populations. The two southernmost populations showed plasticity in cell size, whereas the two northernmost ones did not. We suggest that selection pressure for larger cell size in northern, cooler environments has restricted plasticity in A. carolinensis applied at the cellular level in response to variable incubation environments.     

Selection for feed efficiency does not change the selection for growth and carcass traits in Nellore cattle

The objectives were to conduct a genetic evaluation of residual feed intake (RFI) and residual feed intake adjusted for fat (RFIFat) and to analyse the effect of selection for these traits on growth, carcass and reproductive traits. Data from 945 Nellore bulls in seven feed efficiency tests in a feedlot were analysed. Genetic evaluation was performed using an animal model in which the feed efficiency test and age of the animal at the beginning of the test were considered as a systematic effect. Direct additive genetic and residual effects were considered as random effects. Correlations and genetic gains were estimated by two‐trait analysis between feed efficiency measures (RFI and RFIFat) and other traits. Feed conversion showed low heritability (0.06), but dry matter intake (DMI), average daily gain, RFI, RFIFat, metabolic body weight and scrotal circumference measured at 450 days of age (SC450) showed moderate to high heritability (0.49, 0.28, 0.33, 0.36, 0.38 and 0.80, respectively). Similarly, ribeye area, backfat thickness, rump cap fat thickness, marbling score and subcutaneous fat thickness also had high heritability values (0.46, 0.37, 0.57, 0.51 and 0.47, respectively). Genetic correlations between RFI and SC450 were null, and between RFIFat and SC450 were strongly positive. Genetic and phenotypic correlations of RFI and RFIFat with carcass traits were not different from zero, as correlated responses for carcass traits were also not different from zero. The Nellore selection for feed efficiency by RFI or RFIFat allows the recognition of feed efficient animals, with DMI reduction and without significant changes in growth and carcass traits. However, because of the observed results between RFIFat and SC450, selection of animals should be analysed with caution and a preselection for reproductive traits is necessary to avoid reproductive impairments in the herd.     

Latitudinal and seasonal variation in reproductive effort of the eastern fence lizard (Sceloporus undulatus)

Geographic variation in life‐history traits among populations of wide‐ranging species is influenced by both spatial and temporal aspects of the environment. Rarely, however, are the effects of both aspects examined concurrently. We collected gravid female lizards (Sceloporus undulatus) from northern (Indiana), central (Mississippi) and southern (Florida) populations, spanning nearly the full latitudinal range of the species, to examine amongpopulation differences in strategies of reproductive energy allocation. Adult females from the southern population were smaller, and produced fewer and smaller eggs in their first clutches than did females from the more northern populations. Southern females were more likely to produce a second clutch, and second clutches were smaller than first clutches for females from the 2 northern populations. Together these trends eliminated population differences in overall reproductive output after accounting for body size. The trend for greater reproductive energy to be allocated to first clutches at higher latitudes, and to later clutches at lower latitudes is corroborated by published data from field studies on multiple populations. Distributing reproductive effort by producing more clutches of smaller eggs may be an adaptive response to the long season available for egg incubation and lizard activity in sub‐tropical southern environments. In contrast, allocating greater resources to early reproduction may enhance maternal fitness in the relatively short activity seasons that characterize more northern sites.     

Living on the edge: morphological and behavioral adaptations to a marginal high-elevation habitat in an arboreal mammal

Habitats are characterized by different local environmental conditions that influence both behavior and morphology of species, which can result in habitat-dependent phenotypic differences among animals living in heterogeneous environments. We studied 3 alpine populations of Eurasian red squirrels (Sciurus vulgaris), 1 living in a marginal high-elevation habitat at the edge of the species’ altitudinal distribution, and 2 occurring in higher-quality habitats. Here, we investigated whether squirrels living in the marginal area differed in 2 morphological parameters (body size and body mass) and/or in the expression of 4 personality traits estimated with an open field test and a mirror image stimulation test (activity, exploration, activity-exploration, and social tendency). Furthermore, we tested whether within-individual variance of the traits (behavioral plasticity) was higher in the edge habitat. Male squirrels in the edge habitat were smaller and weighed less than in the other study areas, while among females, size–habitat relationships were less marked. These sex-specific patterns were explained by a strong association between body mass and reproductive success in female squirrels. Squirrels in the marginal habitat were more active, explorative, and had a more social personality than in the other habitats. However, in contrast to our predictions, behavioral plasticity was smaller in the marginal habitat, but only for the trait exploration. Our results suggest that animals choose the habitat that best fits their personality, and that habitat-related differences in selective pressures may shape animals’ morphology.