Effects of embryonic exposure to conspecific chemical cues on hatching and larval traits in the common frog <Emphasis Type="Italic">(Rana temporaria)</Emphasis>

Summary. Recent studies indicate that amphibian eggs are capable of hatching plasticity in response to chemical cues released by predators feeding on conspecific eggs or larvae. However, information is scarce on the relative importance of predator and conspecific cues in such a process. In particular, no attempt has been made to compare the effects of embryonic exposures to chemical cues indicative of a predation risk for eggs and larvae, although both life stages can co-occur in natural habitats. In this context, common frog embryos (Rana temporaria) were raised until hatching in the presence of crushed conspecific extracts from eggs and tadpoles to assess their respective influences on some hatching and larval traits. While a significant delay in hatching time was observed in embryos exposed to chemical cues from tadpole extract, this life-history shift appeared unaffected by embryonic exposure to egg extract. Hatchlings derived from eggs incubated in the presence of both conspecific extracts showed a significantly greater weight than unexposed controls. However, such an effect was no longer apparent 15, 30 and 50 days after hatching, suggesting that embryonic exposure to chemical cues from damaged conspecific eggs and tadpoles has no influence on larval growth. Lastly, morphological measurements performed on hatchlings and older tadpoles (15, 30 and 50 days old) revealed no significant effect of embryonic treatments on the shape of body and tail.     

松嫩草地羊草克隆构型特征在不同种群密度下的可塑性

对不同密度羊草(Leymuschinensis)种群的克隆构型特征进行了调查,比较在资源水平相对一致时,羊草克隆构型特征,如根茎节间长度、间隔子长度、分枝距离和分枝角度,对种群密度变化的可塑性.结果表明:随着种群密度增加,羊草根茎节间长度和间隔子长度逐渐减小,分枝角度增大,且分枝角度在不同密度间差异显著.分枝角度的频率分布格局在不同密度间也存在显著差异,种群密度高时,羊草根茎具有更多的大分枝角.此外,羊草根茎节间长度、间隔子长度和分枝角度与其种群密度具有较强的冥函数关系.羊草根茎克隆特征在不同密度间具有较强的可塑性,当种群密度低时,羊草克隆特征更趋于“游击型”;随着种群密度的增加,其“游击型”特征减弱. 图2表2参19     

高光和低光下木本植物形态和生理可塑性响应

光资源的时空异质性普遍存在.为了提高光利用效率或有效避免强光的伤害,植物通常采取多种调节措施.植物适应林下异质、多变的环境过程中,表型的可塑性是非常关键的.植物表型可塑性与其环境异质性密不可分.植物通过生长变化、生物量分配、光合器官结构调整、叶氮分配、抗氧化防御系统、热耗散机制,以及长期的表型可塑性来增大截取光资源的潜力和实际光资源利用效率,同时也为自身提供了一种有效的保护机制.大量实验证明,阳生植物比阴生植物表现出较大的表型可塑性,且其可塑性方式存在差异.本文主要阐述了植物对高光和低光条件的形态和生理可塑性适应,为了解植物在极端光照条件下生存与繁殖提供参考.大量的人工模拟与自然光照实验有待进行来阐明植物对自然光照条件的适应,为植被恢复和重建提供参考和依据.参96     

Social,environmental and genetic factors in the ontogeny of phenotypic differentiation in a lizard with alternative male reproductive strategies

Summary Adult male tree lizards, Urosaurus ornatus, practise alternative (territorial or sneaker/satellite) reproductive strategies that are correlated with differences in throat color and body size. In this study we raised tree lizards from hatching in the laboratory to examine the question of whether the phenotypic expression of secondary sex coloration and body size can be facultatively influenced by social or abiotic environmental factors. We compared males reared in the laboratory under different social and environmental conditions to males in the field and found no effect of different conditions on phenotypic differentiation (Figs. 2–4). Thus, phenotypic differences between morphs probably result largely from nonfacultative expression of different genotypes. This suggests that alternative male morphs practise a mixed evolutionary stable strategy (ESS) rather than one morph making the best of a bad situation. However, in the context of ESS theory it is difficult to explain our further result that the nonterritorial morph in this species grows faster and reaches a larger adult body size than the territorial morph (Fig. 5).     

单位挤压力的主应力求法

以正挤压为例 ,利用塑性变形问题的主应力解法 ,推导了单位挤压力的理论计算公式。并就影响挤压力的主要因素进行了分析。     

Behavioral diversification in a young species flock of pupfish (<Emphasis Type="Italic">Cyprionodon</Emphasis> spp.): shoaling and aggressive behavior

Increasing empirical and theoretical evidence supports the idea that sympatric speciation is operating, for example, in species flocks comprising several closely related fish species within one lake. Divergent natural selection (promoting spatial and food niche partitioning) and sexual selection (assortative mating) have been identified as key selection factors in intralacustric adaptive radiations. However, the evolution of social behaviors accompanying such adaptive radiations is less well understood. Using a phylogenetically young species flock of pupfish (Cyprinodon spp.) as a model, we examined differences among six sympatric species and compared their shoaling, aggressive, and territorial behaviors with that of a sister species (C. artifrons). Despite an estimated age of the species flock of less than 8,000 years, pronounced behavioral differentiation was found. C. simus, the smallest species in the flock, shoaled more than the other species and was less aggressive and less territorial than C. beltrani. F₁-hybrids between C. simus males and C. beltrani females showed an intermediate expression of shoaling and aggressive behavior. Niche partitioning among the members of this species flock appears to be accompanied by rapid divergent evolution of social behaviors. We discuss the potential role of phenotypic plasticity and within-species variation of social behaviors for such rapid behavioral diversifications in sympatric speciation processes.     

Patchiness and bistability in the comprehensive cyanobacterial model (CCM)

We analyzed spatiotemporal dynamics of cyanobacteria using a four-component mathematical model with nutrients, unicellular algae, colonial algae and herbivorous zooplankton. One of the astonishing abilities of cyanobacteria is the morphological change from the unicellular type to the colonial or filamentous type in response to grazing activities of zooplankton, the phenomenon known as phenotypic plasticity. Our model, referred to as comprehensive cyanobacterial model (CCM), includes the effects of phenotypic plasticity. Depending on parameter values, CCM exhibits not only bistability but also limit cycle oscillations without showing the paradox of enrichment, which has been a controversy among mathematical ecologists. Further, CCM is modified to reaction–advection–diffusion equations, the simulation results of which indicate that the ratio of the lateral diffusivity to the turbulent velocity significantly affects the appearance of patchiness patterns.     

地质体材料剪切带内部的常剪切应变点及速度分布分析

对于峰后线性应变软化的地质体材料,剪切带内部的总剪切应变等于弹性剪切应变(由经典弹性理论描述)及由微结构效应而引起的局部塑性剪切应变(由非局部理论或梯度塑性理论描述)之和。若剪切应力—塑性剪切应变曲线的斜率的绝对值(称之为软化模量)小于剪切弹性模量的两倍,则在剪切带的任一剖面内存在两个总剪切应变不依赖于剪切应力的点,称之为常剪切应变点。在这两个点上,弹性剪切应变的降低和局部塑性剪切应变的增加处于平衡状态,总剪切速度达到它的最大值或最小值。在两个常剪切应变点之间,局部总速度随剪切应力率的降低而增加。剪切带内部的局部总速度分布是非线性的,这与通常采用的剪切带内部速度的线性分布假定(忽略微结构效应)不同。     

Effects of colony food shortage on behavioral development in honey bees

Three experiments were conducted to explore the effects of severe food shortage on the control of two important and interrelated aspects of temporal division of labor in colonies of the honey bee (Apis mellifera): the size and age distribution of a colony's foraging force. The experiments were conducted with single-cohort colonies, composed entirely of young bees, allowing us to quickly distinguish the development of new (precocious) foragers from increases in activity of bees already competent to forage. In experiment 1, colony food shortage caused an acceleration of behavioral development; a significantly greater proportion of bees from starved colonies than from fed colonies became precocious foragers, and at significantly younger ages. Temporal aspects of this starvation effect were further explored in experiment 2 by feeding colonies that we initially starved, and starving colonies that we initially fed. There was a significant decrease in the number of new foragers in starved colonies that were fed, detected 1 day after feeding. There also was a significant increase in the number of new foragers in fed colonies that were starved, but only after a 2-day lag. These results suggest that colony nutritional status does affect long-term behavioral development, rather than only modulate the activity of bees already competent to forage. In experiment 3, we uncoupled the nutritional status of a colony from that of the individual colony members. The behavior of fed individuals in starved colonies was indistinguishable from that of bees in fed colonies, but significantly different from that of bees in starved colonies, in terms of both the number and age distribution of foragers. These results demonstrate that effects of starvation on temporal polyethism are not mediated by the most obvious possible worker-nest interaction: a direct interaction with colony food stores. This is consistent with previous findings suggesting the importance of worker-worker interactions in the regulation of temporal polyethism in honey bees as well as other social insects. Received: 17 April 1997 / Accepted after revision: 26 December 1997     

Effect of scale on trait predictors of species responses to agriculture

Species persistence in human‐altered landscapes can depend on factors operating at multiple spatial scales. To understand anthropogenic impacts on biodiversity, it is useful to examine relationships between species traits and their responses to land‐use change. A key knowledge gap concerns whether these relationships vary depending on the scale of response under consideration. We examined how local‐ and large‐scale habitat variables influence the occupancy dynamics of a bird community in cloud forest zones in the Colombian Chocó‐Andes. Using data collected across a continuum of forest and agriculture, we examined which traits best predict species responses to local variation in farmland and which traits best predict species responses to isolation from contiguous forest. Global range size was a strong predictor of species responses to agriculture at both scales; widespread species were less likely to decline as local habitat cover decreased and as distance from forest increased. Habitat specialization was a strong predictor of species responses only at the local scale. Open‐habitat species were particularly likely to increase as pasture increased, but they were relatively insensitive to variation in distance to forest. Foraging plasticity and flocking behavior were strong predictors of species responses to distance from forest, but not their responses to local habitat. Species with lower plasticity in foraging behaviors and obligate flock‐following species were more likely to decline as distance from contiguous forest increased. For species exhibiting these latter traits, persistence in tropical landscapes may depend on the protection of larger contiguous blocks of forest, rather than the integration of smaller‐scale woodland areas within farmland. Species listed as threatened or near threatened on the International Union for Conservation of Nature Red List were also more likely to decline in response to both local habitat quality and isolation from forest relative to least‐concern species, underlining the importance of contiguous forests for threatened taxa.