Mechanoreceptor distribution in stag beetle jaws corresponds to the material stress in fights

Male stag beetles (Lucanidae) use their extremely elongated jaws to pinch their rivals forcefully in male–male battles. The morphology of these jaws has to be a compromise between robustness (to withstand the bite forces), length and weight. Cyclommatus metallifer stag beetles circumvent this trade-off by reducing their bite force when biting with their slender jaw tips. Here we describe the functional mechanism behind the force modulation behaviour. Scanning Electron Microscopy and micro CT imaging show large numbers of small sensors in the jaw cuticle. We find a strong correlation between the distribution of these sensors and that of the material stress in the same jaw region during biting. The jaw sensors are mechanoreceptors with a small protrusion that barely protrudes above the undulating jaw surface. The sensors stimulate dendrites that extend from the neuronal cell body through the entire thickness of the jaw exoskeleton towards the sensors at the external surface. They form a sensory field that functions in a feedback mechanism to control the bite muscle force. This negative feedback mechanism enabled the stag beetles to evolve massive bite muscles without risking overloading their valuable jaws.     

锹甲的头部形态及常用分类特征

锹甲的外部形态纷繁多样,头部形态尤其复杂并导致种类鉴定混乱,有必要对其深入研究。文章介绍锹甲的头部形态,并以代表性属种为例,比较与讨论上颚、上唇、下颚和下唇、复眼、触角等常用分类特征及其分类学意义。     

Artificial selection on allometry: change in elevation but not slope

To what extent within-species (static) allometries constitute a constraint on evolution is the subject of a long-standing debate in evolutionary biology. A prerequisite for the constraint hypothesis is that static allometries are hard to change. Several studies have attempted to test this hypothesis with artificial-selection experiments, but their results remain inconclusive due to various methodological issues. Here, we present results from an experiment in which we selected independently on the slope and the elevation of the allometric relationship between caudal-fin size and body size in male guppies (Poecilia reticulata). After three episodes of selection, the allometric elevation (i.e. intercept at constant slope) had diverged markedly between the lines selected to increase or decrease it, and showed a realized heritability of 50%. In contrast, the allometric slope remained unaffected by selection. These results suggest that the allometric elevation is more evolvable than the allometric slope, this latter representing a potential constraint on adaptive trait evolution. To our knowledge, this study is the first artificial-selection experiment that directly tests the evolvability of static allometric slopes.     

发育阶段和海拔对岷江源区陇蜀杜鹃小枝功能性状及生物量分配的影响

本研究分析了岷江源区卡卡山典型高山灌丛植物陇蜀杜鹃不同发育阶段(花芽期和开花期)及不同海拔(3600 m低海拔和3800 m高海拔)下功能小枝和叶片性状的差异,以及空间异质性对花芽期和开花期小枝功能性状相关性及其权衡作用的影响.结果表明:低海拔同一生长期陇蜀杜鹃小枝长度显著大于高海拔,高海拔开花期小枝的花数量和花质量显...     

Effects of multiple mating and male eye span on female reproductive output in the stalk-eyed fly, Cyrtodiopsis dalmanni

Females of the stalk-eyed fly, Cyrtodiopsis dalmanni, mate repeatedly during their lifetime and exhibit mating preferencefor males with large eye span. How these mating decisions affectfemale fitness is not fully understood. In this study, we examinedthe effects of multiple mating and male eye span on short-termreproductive output in this species. Experiments that manipulatedthe number of copulations and partners a female received suggested that obtaining a sufficient sperm supply is an important benefitassociated with multiple mating. The average percentage offertile eggs laid by females increased as a function of matingfrequency and ranged from 40% for females mated once, to 80%for females mated continuously. In addition, a high proportionof copulations in this species appeared to be unsuccessful. One-third of all females mated once laid less than 10% fertileeggs. There was no significant difference in reproductive performancebetween females mated to multiple partners and females matedto a single partner. There was also no indication that femalesreceived any short-term reproductive benefits from mating withmales with large eye span. In fact, females mated to males with short eye span laid a higher percentage of fertile eggs thanfemales mated to large eye span males.     

安徽大龙山国家森林公园东亚小金发藓配子体与孢子体个体性状及其相互关系

植物性状是植物对环境变化响应和适应的综合反映。目前对苔藓植物个体水平功能性状的研究较为匮乏。以安徽大龙山国家森林公园分布的东亚小金发藓（Pogonatum inflexum）雌株为例,在其孢子体成熟期测定地上部分孢子体和配子体的形态特征及生物量,系统分析了植株性状变异特征、异速生长关系及协变（整合）格局。结果表明,东亚小金发藓配子体形态性状变异性高于孢子体,且二者生物量变异系数最大。孢子体高度是配子体的2倍,但其生物量仅占地上部分的23%。孢子体和配子体功能性状之间有一定相关性;形态性状（Y）与生物量（X）之间多为指数<1.0异速生长关系,而孢子体和配子体生物量之间为等速生长关系（指数为1.135±0.158）。孢子体生物量分配比例随个体增大而显著减小,体现出显著的负的个体大小依赖。主成分分析表明,东亚小金发藓孢子体和配子体主要个体性状具有不同的协变方向（即两个不同的性状群）,其中孢子体生物量是两类性状群的关键结点。综合来看,东亚小金发藓个体性状间具有与维管植物相似的协变关系。