Ecological and Geographical Reasons for the Variation of Digestive Tract Length in Anurans

Changes of environmental conditions can shape organs size evolution in animal kingdoms. In particular, environmental changes lead to difference in food resources between different habitats, thereby affecting individual's energy intake and allocation. The digestive theory states that animals consuming food with low contents of digestible materials should result in increasing gut length. In this study, to test the hypothesis of digestive theory, we studied ecological and geographical reasons for variation in digestive tract length among 35 species of anurans distributing in different altitude and latitude. The results showed that ecological type significantly affected digestive tract length among species, with aquatic and terrestrial species having longer digestive tract than arboreal ones. Latitude was positively correlated with digestive tract length. However, altitude, as well as monthly mean temperature and precipitation, did not correlate with digestive tract length among species. Our findings suggest that aquatic and terrestrial species might forage less digestible materials than arboreal species, thereby displaying relatively longer digestive tract than arboreal species.     

Morphological and physiological responses to altitude in deer mice Peromyscus maniculatus.

Individuals within a species, living across a wide range of habitats, often display a great deal of phenotypic plasticity for organ mass and function. We investigated the extent to which changes in organ mass are variable, corresponding to environmental demand, across an altitudinal gradient. Are there changes in the mass of oxygen delivery organs (heart and lungs) and other central processing organs (gut, liver, kidney) associated with an increased sustainable metabolic rate that results from decreased ambient temperatures and decreased oxygen availability along an altitudinal gradient? We measured food intake, resting metabolic rate (RMR), and organ mass in captive deer mice (Peromyscus maniculatus bairdii) at three sites from 1,200 to 3,800 m above sea level to determine whether energy demand was correlated with organ mass. We found that food intake, gut mass, and cardiopulmonary organ mass increased in mice living at high altitudes. RMR was not correlated with organ mass differences along the altitudinal gradient. While the conditions in this study were by no means extreme, these results show that mice living at high altitudes have higher levels of energy demand and possess larger cardiopulmonary and digestive organs than mice living at lower altitudes.     

Changes in reproductive investment with altitude in an alpine plant

Aims In perennial species, the allocation of resources to reproduction results in a reduction of allocation to vegetative growth and, therefore, impacts future reproductive success. As a consequence, variation in this trade-off is among the most important driving forces in the life-history evolution of perennial plants and can lead to locally adapted genotypes. In addition to genetic variation, phenotypic plasticity might also contribute to local adaptation of plants to local conditions by mediating changes in reproductive allocation. Knowledge on the importance of genetic and environmental effects on the trade-off between reproduction and vegetative growth is therefore essential to understand how plants may respond to environmental changes.Methods We conducted a transplant experiment along an altitudinal gradient from 425 to 1?921 m in the front range of the Western Alps of Switzerland to assess the influence of both altitudinal origin of populations and altitude of growing site on growth, reproductive investment and local adaptation in Poa alpina .Important findings In our study, the investment in reproduction increased with plant size. Plant growth and the relative importance of reproductive investment decreased in populations originating from higher altitudes compared to populations originating from lower altitudes. The changes in reproductive investment were mainly explained by differences in plant size. In contrast to genetic effects, phenotypic plasticity of all traits measured was low and not related to altitude. As a result, the population from the lowest altitude of origin performed best at all sites. Our results indicate that in P. alpina genetic differences in growth and reproductive investment are related to local conditions affecting growth, i.e. interspecific competition and soil moisture content.     

Effects of temperature acclimation on body mass and energy budget in the Chinese bulbul Pycnonotus sinensis

Chinese bulbuls(Pycnonotus sinensis) are small passerine birds that inhabit areas of central, southern and eastern China. Previous observations suggest that free–living individuals of this species may change their food intake in response to seasonal changes in ambient temperature. In the present study, we randomly assigned Chinese bulbuls to either a 30 °C or 10 °C group, and measured their body mass(BM), body temperature, gross energy intake(GEI), digestible energy intake(DEI), and the length and mass of their digestive tracts over 28 days of acclimation at these temperatures. As predicted, birds in the 30 °C group had lower body mass, GEI and DEI relative to those in the 10 °C group. The length and mass of the digestive tract was also lower in the 30 °C group and trends in these parameters were positively correlated with BM, GEI and DEI. These results suggest that Chinese bulbuls reduced their absolute energy demands at relatively high temperatures by decreasing their body mass, GEI and DEI, and digestive tract size.     

Proximate causes of adaptive growth rates: growth efficiency variation among latitudinal populations of Rana temporaria

In ectothermic organisms, declining season length and lower temperature towards higher latitudes often select for latitudinal variation in growth and development. However, the energetic mechanisms underlying this adaptive variation are largely unknown. We investigated growth, food intake and growth efficiency of Rana temporaria tadpoles from eight populations along a 1500 km latitudinal gradient across Sweden. To gain an insight into the mechanisms of adaptation at organ level, we also examined variation in tadpole gut length. The tadpoles were raised at two temperatures (16 and 20 degrees C) in a laboratory common garden experiment. We found increased growth rate towards higher latitudes, regardless of temperature treatment. This increase in growth was not because of a higher food intake rate, but populations from higher latitudes had higher growth efficiency, i.e. they were more efficient at converting ingested food into body mass. Low temperature reduced growth efficiency most strongly in southern populations. Relative gut length increased with latitude, and tadpoles at low temperature tended to have longer guts. However, variation in gut length was not the sole adaptive explanation for increased growth efficiency as latitude and body length still explained significant amounts of variation in growth efficiency. Hence, additional energetic adaptations are probably involved in growth efficiency variation along the latitudinal gradient.     

Altitudinal variation in age and body size in Yunnan pond frog (Pelophylax pleuraden)

Large-scale systematic patterns of body size are a basic concern of evolutionary biology. Identifying body size variation along altitudinal gradients may help us to understand the evolution of life history of animals. In this study, we investigated altitudinal variation in body size, age and growth rate in Chinese endemic frog, Pelophylax pleuraden. Data sampled from five populations covering an altitudinal span of 1413 to 1935 m in Sichuan province revealed that body size from five populations did not co-vary with altitudes, not following Bergmann's rule. Average adult SVL differed significantly among populations in males, but not in females. For both sexes, average adult age differed significantly among populations. Post-metamorphic growth rate did not co-vary with altitude, and females grew faster than males in all populations. When controlling the effect of age, body size did not differ among populations in both sexes, suggesting that age did not affect variation in body size among populations. For females, there may be other factors, such as the allocation of energy between growth and reproduction, that eliminated the effect of age on body size. To our minds, the major reason of body size variation among populations in male frogs may be related to individual longevity. Our findings also suggest that factors other than age and growth rate may contribute to size differences among populations.     

洞庭湖区社鼠消化道长度和质量的季节变化

对洞庭湖区社鼠（Niviventer confucianus）自然种群四季的消化道各器官的长度和质量进行了测定。结果表明。消化道指标季节变化明显。总体消化道含内容鲜质量、净鲜质量与干质量均具有显著的季节变化。以冬、春季较高。夏、秋季较低。消化道各器官的变化与总消化道不尽相同。其中,以胃的变化相对比较稳定。仅长度的变化达显著水平,以冬季最短,夏、秋季较长。这是动物为适应繁殖季节能量需求而增加摄食量的反应,也与夏秋季食物丰富度有关。小肠、盲肠、大肠的长度和质量指标（内容鲜质量、净鲜质量和干质量）以冬、春季较高。夏、秋季较低。这是该鼠对冬、春季低温和食物匮乏的适应性反应。总体来说。洞庭湖区社鼠为适应夏、秋季繁殖盛期能量需求增加的主要对策是增加摄食量;而为适应冬、春季低温环境和食物数量和质量减少的主要对策是增大消化道。提高消化效率。     

Reduction in leaf size at higher altitudes across 39 broad-leaved herbaceous species on the northeastern Qinghai-Tibetan Plateau

青藏高原东北部39种阔叶草本植物叶大小随海拔增加而减少 种间或种内的叶大小随环境变化存在很大的差异，但这些差异如何随海拔变化一直都在争论。我们在青藏高原东北缘的冷龙岭和达坂山，沿海拔3200–4400 m的山坡上选取生长在开阔环境下的39种阔叶草本植物，观测了叶大小、叶长、叶宽和比叶重。研究结果表明，随海拔增加叶片显著减小，而且叶片面积的减小主要受叶片长度的影响，即随海拔增加叶长度减小明显。此外，叶片面积与海拔之间的关系随物种、叶倾角和叶表面特征而不同。利用局地环境观测数据驱动的能量平衡模型分析发现：叶温能更密切地追随气温变化，叶大小变化对叶温的影响在高海拔更为强烈。同时，基于上述能量平衡的计算结果，我们认为青藏高原东北部阔叶草本植物的海拔分布上限大约为5400 m。     

温度与光周期对白头鹎体质量、能量收支和消化道形态的影响

温度与光周期是环境季节性变化的最直接表现因子及时间变化指示标志,对动物的形态、生理及行为产生重要的影响.本文以白头鹎为研究对象,探讨了不同温度与光周期对其体质量、能量收支和消化道形态的影响,分析了能量收支与消化道形态特征的关系.将28只白头鹎(12雄16雌)分为4组:暖温长光组(30℃,16 L8 D;3雄4雌)、暖温短光组(30 ℃,8 L16 D;3雄4雌)、低温长光组(10 ℃,16 L8 D;3雄4雌)和低温短光组(10 ℃,8 L16 D;3雄4雌).结果表明: 低温与短光照可促进白头鹎的体质量、摄入能及同化能明显增加,同时温度与光周期的交互作用对白头鹎的摄入能及同化能影响显著.低温条件下,胃、小肠、直肠及总消化道的湿质量及干质量明显增加.残差分析表明,小肠与总消化道的长度及干质量与摄入能和同化能显著相关.表明低温与短光照下白头鹎通过增加体质量、能量摄入和改变消化道形态来应对严酷的环境条件.     

Geographic variation in body size, sexual size dimorphism and fitness components of a seed beetle: local adaptation versus phenotypic plasticity

Variation in body size, growth and life history traits of ectotherms along latitudinal and altitudinal clines is generally assumed to represent adaptation to local environmental conditions, especially adaptation to temperature. However, the degree to which variation along these clines is due to adaptation vs plasticity remains poorly understood. In addition, geographic patterns often differ between females and males – e.g. sexual dimorphism varies along latitudinal clines, but the extent to which these sex differences are due to genetic differences between sexes vs sex differences in plasticity is poorly understood. We use common garden experiments (beetles reared at 24, 30 and 36°C) to quantify the relative contribution of genetically‐based differentiation among populations vs phenotypic plasticity to variation in body size and other traits among six populations of the seed‐feeding beetle Stator limbatus collected from various altitudes in Arizona, USA. We found that temperature induces substantial plasticity in survivorship, body size and female lifetime fecundity, indicating that developmental temperature significantly affects growth and life history traits of S. limbatus. We also detected genetic differences among populations for body size and fecundity, and genetic differences among populations in thermal reaction norms, but the altitude of origin (and hence mean temperature) does not appear to explain these genetic differences. This and other recent studies suggest that temperature is not the major environmental factor that generates geographic variation in traits of this species. In addition, though there was no overall difference in plasticity of body size between males and females (when averaged across populations), we did find that the degree to which dimorphism changed with temperature varied among populations. Consequently, future studies should be extremely cautious when using only a few study populations to examine environmental effects on sexual dimorphism.     

The effect of cold-acclimation on energy strategies of Apodemus draco in Hengduan Mountain region

Environmental factors play an important role in the seasonal adaptation of body mass and thermogenesis in small mammals. The purpose of the present study was to test the hypothesis that ambient temperature triggers adjustments in body mass, body temperature, energy intake, digestible energy intake, metabolic energy intake, and the length and weight of the digestive tract, in Apodemus draco during 42 days of cold exposure. Body mass and body temperature of the cold-acclimated group decreased during the first 28 days and then stabilized at the lower levels. After 14 days of cold acclimation, the body mass of the cold-exposed group was significantly lower and the energy intake, digestible energy intake, and metabolic energy intake were significantly elevated relative to control animals. The differences were maximal after 21 days. The length and weight of the digestive tract (both wet and dry mass of the stomach, small intestine, large intestine, and cecum) changed significantly in response to decreasing temperature. During cold exposure, A. draco was able to maintain physiological functions and reduce its absolute energy demands by reducing the body mass, increasing energy intake, and adjusting the length of the digestive tract.     

新疆干旱环境中褐家鼠消化道长度和重量的季节变化及其适应意义

动物消化道的形态与食性、食物质量以及动物对能量的需求密切关系。本文对新疆干旱环境中生存的褐家鼠在自然环境中消化道长度及重量进行了测定,结果表明,家栖的褐家鼠只有总消化道、小肠和大肠的长度有季节差异,冬、春季高于夏、秋季。同时发现捕自阿拉山口的褐家鼠胃长度和干重有季节差异。     

Intraspecific variation in morphology of spiny pollen grains along an altitudinal gradient in an insect-pollinated shrub

• Intraspecific variations in pollen morphological traits are poorly studied. Interspecific variations are often associated with pollination systems and pollinator types. Altitudinal environmental changes, which can influence local pollinator assemblages, provide opportunities to explore differentiation in pollen traits of a single species over short distances. The aim of this study is to examine intraspecific variations in pollen traits of an insect-pollinated shrub, Weigela hortensis (Caprifoliaceae), along an altitudinal gradient.
• Pollen spine phenotypes (length, number and density), pollen diameter, lipid mass (pollenkitt) around pollen grains, pollen production per flower and pollinator assemblages were compared at four sites at different altitudes.
• Spine length and the spine length/diameter ratio of pollen grains were greater at higher altitudes but not correlated with flower or plant size. Spine number and density increased as flower size increased, and pollen lipid mass decreased as plant size increased. Bees were the predominant pollinators at low-altitude sites whereas flies, specifically Oligoneura spp. (Acroceridae), increased in relative abundance with increasing altitude.
• The results of this study suggest that the increase in spine length with altitude was the result of selection favouring longer spines at higher-altitude sites and/or shorter spines at lower-altitude sites. The altitudinal variation in selection pressure on spine length could reflect changes in local pollinator assemblages with altitude.

     

Longer guts and higher food quality increase energy intake in migratory swans

1. Within the broad field of optimal foraging, it is increasingly acknowledged that animals often face digestive constraints rather than constraints on rates of food collection. This therefore calls for a formalization of how animals could optimize food absorption rates. 2. Here we generate predictions from a simple graphical optimal digestion model for foragers that aim to maximize their (true) metabolizable food intake over total time (i.e. including nonforaging bouts) under a digestive constraint. 3. The model predicts that such foragers should maintain a constant food retention time, even if gut length or food quality changes. For phenotypically flexible foragers, which are able to change the size of their digestive machinery, this means that an increase in gut length should go hand in hand with an increase in gross intake rate. It also means that better quality food should be digested more efficiently. 4. These latter two predictions are tested in a large avian long-distance migrant, the Bewick's swan (Cygnus columbianus bewickii), feeding on grasslands in its Dutch wintering quarters. 5. Throughout winter, free-ranging Bewick's swans, growing a longer gut and experiencing improved food quality, increased their gross intake rate (i.e. bite rate) and showed a higher digestive efficiency. These responses were in accordance with the model and suggest maintenance of a constant food retention time. 6. These changes doubled the birds' absorption rate. Had only food quality changed (and not gut length), then absorption rate would have increased by only 67%; absorption rate would have increased by only 17% had only gut length changed (and not food quality). 7. The prediction that gross intake rate should go up with gut length parallels the mechanism included in some proximate models of foraging that feeding motivation scales inversely to gut fullness. We plea for a tighter integration between ultimate and proximate foraging models.     

Gut length plasticity in perch: into the bowels of resource polymorphisms

Resource polymorphisms, intraspecific variation in morphology due to differential resource use, are common across a wide range of animal taxa. The focus in studies of such polymorphisms has been on external morphology, but the differential use of food resources could also influence other phenotypic traits such as the digestive performance. In the present study, we experimentally demonstrate that Eurasian perch ( Perca fluviatilis L.) display adaptive plasticity in gut length when exposed to different food types. Perch fed a less digestible food type developed relatively longer guts compared to fish fed a more easily digested food type. This divergence in gut length was also apparent under natural conditions because perch inhabiting the littoral and pelagic habitats of a lake differed in resource use and relative gut length. Despite that the digestive system in perch is plastic, we found that individuals switching to a novel food type might experience an initial fitness cost of the diet switch in the form of a temporary reduction in body condition. These results show the importance of gut length plasticity for an ontogenetic omnivore but also a cost that might prevent diet switching in polymorphic populations.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 517–523.     

Phenotypic plasticity of gut structure and function during periods of inactivity in Apostichopus japonicus

Apostichopus japonicus is a common sea cucumber that undergoes seasonal inactivity phases and ceases feeding during the summer months. We used this sea cucumber species as a model in which to examine phenotypic plasticity of the digestive tract in response to food deprivation. We measured the body mass, gross gut morphology and digestive enzyme activities of A. japonicus before, during, and after the period of inactivity to examine the effects of food deprivation on the gut structure and function of this animal. Individuals were sampled semi-monthly from June to November (10 sampling intervals over 178 days) across temperature changes of more than 18 degrees C. On 5 September, which represented the peak of inactivity and lack of feeding, A. japonicus decreased its body mass, gut mass and gut length by 50%, 85%, and 70%, respectively, in comparison to values for these parameters preceding the inactive period. The activities of amylase, cellulase and lipase decreased by 77%, 98%, and 35% respectively, in comparison to mean values for these enzymes in June, whereas pepsin activity increased two-fold during the inactive phase. Alginase and trypsin activities were variable and did not change significantly across the 178-day experiment. With the exception of amylase and cellulase, all body size indices and digestive enzyme activities recovered and even surpassed the mean values preceding the inactive phase during the latter part of the experiment (October-November). Principal Component Analysis (PCA) utilizing the digestive enzyme activity and body size index data divided the physiological state of this cucumber into four phases: an active stage, prophase of inactivity, peak inactivity, and a reversion phase. These phases are all consistent with previously suggested life stages for this species, but our data provide more defined characteristics of each phase. A. japonicus clearly exhibits phenotypic plasticity (or life-cycle staging) of the digestive tract during its annual inactive period.     

Small-scale elevational variation in the abundance of Eufriesea violacea (Blanchard) (Hymenoptera: Apidae)

Eufriesea violacea (Blanchard) males were sampled in a small-scale elevational gradient in Southeastern Brazil and showed sequential peaks of abundance from lowest (700 m) to highest (1,100 m) altitudes during the sampling period. The influence of the temperature on the length of the egg-to-adult period and flowering dates of plants producing food (nectar) suggests that it may be one of the factors determining the distribution of male abundance along the altitudinal gradient. The results emphasize the importance of obtaining altitudinal stratified samples when studying Euglossini populations, especially when the studies are done at sites with marked topographical variation.     

Ecological correlates and determinants in the geographical variation of deer morphology

Previous studies on patterns in ungulate size variations have emphasized the effect of a particular environmental factor such as Bergmann's rule and the island rule. However, although multiple environmental factors may influence the body size, these studies focused on a single factor, and various measurements that may be influenced by different environmental factors (at least partly) were used as indices of body size. In this study, we used several skull and limb measurements to examine size variations among island populations of sika deer (Cervus nippon) in southern Japan considering the effects of multiple environmental factors. We found that all measurements differed markedly between populations. We focused on the skull and limb condylobasal length (CBL) and metacarpal length because they had the most important variations among the populations and the largest sample sizes. The common environmental factors influencing CBL and metacarpal length were island area and precipitation. Since these environmental factors reflect the availability of food resources, the causal factor of body size variation may be food resources. Interpopulation variation in metacarpal length was greater than that of CBL, indicating that metacarpal length may be affected by additional factors besides the common factors shared with CBL. Specific environmental factors influencing relative (CBL adjusted) metacarpal length were precipitation and slope. A common direct cause of those environmental factors was discussed in relation to topography. Analyses of phenotypic variation using multiple measurements with multiple environmental factors are useful to gain insight into underlying causes and can lead to identification of a measurement-specific variation with a specific driving force.     

ALTITUDINAL CLINAL VARIATION IN WING SIZE AND SHAPE IN AFRICAN DROSOPHILA MELANOGASTER: ONE CLINE OR MANY?

Geographical patterns of morphological variation have been useful in addressing hypotheses about environmental adaptation. In particular, latitudinal clines in phenotypes have been studied in a number of Drosophila species. Some environmental conditions along latitudinal clines—for example, temperature—also vary along altitudinal clines, but these have been studied infrequently and it remains unclear whether these environmental factors are similar enough for convergence or parallel evolution. Most clinal studies in Drosophila have dealt exclusively with univariate phenotypes, allowing for the detection of clinal relationships, but not for estimating the directions of covariation between them. We measured variation in wing shape and size in D. melanogaster derived from populations at varying altitudes and latitudes across sub‐Saharan Africa. Geometric morphometrics allows us to compare shape changes associated with latitude and altitude, and manipulating rearing temperature allows us to quantify the extent to which thermal plasticity recapitulates clinal effects. Comparing effect vectors demonstrates that altitude, latitude, and temperature are only partly associated, and that the altitudinal shape effect may differ between Eastern and Western Africa. Our results suggest that selection responsible for these phenotypic clines may be more complex than just thermal adaptation.     

东太平洋赤道海域茎柔鱼的营养生态位和肠道微生物组成

掌握海洋生物的营养生态位特征及其应对环境变化的响应机制,对于评估渔业和气候变化对海洋生态系统功能的影响至关重要。茎柔鱼(Dosidicus gigas)是东太平洋重要的渔业经济物种,在生态系统中具有承上启下的重要生态作用。在气候变化的大背景下,掌握茎柔鱼应对气候变化的响应过程将有利于合理把控其资源状况。本研究采用稳定同位素和高通量技术手段,分别从宏观和微观角度量化比较分析了正常时期和厄尔尼诺时期赤道海域的茎柔鱼营养生态位、肠道长度及肠道微生物组成。结果表明: 不同气候时期茎柔鱼的δ¹³C值存在显著差异,说明食物来源具有差异性;其肠道微生物主要由放线菌门、拟杆菌门、蓝细菌门、厚壁菌门、变形菌门和软壁菌门组成,不同时期微生物群落组成无显著差异,但多样性和相对丰度差异显著。在厄尔尼诺时期,茎柔鱼个体具有较小的营养生态位、较长的肠道、更高的肠道微生物群落多样性及丰富度;肠道微生物的差异主要体现在厚壁菌门、拟杆菌门、螺旋体门、WPS-2和Kiritimatiellaeota,样本距离更为集中。这表明由厄尔尼诺事件导致的栖息地环境及食物变化可能限制茎柔鱼的活动,改变其肠道微生物的结构和功能,有利于其适应环境及食性的变化。