共查询到20条相似文献，搜索用时 562 毫秒
1.
Experimental evidence is presented supporting a developmental model that explains the genetic basis for brain and body size associations. Evolutionary change in body size causes correlated change in brain size because some genes affect both traits. The commonly observed correlation between brain and body size results from genetic variation in growth determinants affecting both traits simultaneously during fetal and early postnatal growth. Later growth reduces brain-body correlation because of changes in the underlying causal components of growth in each trait. Brain-body size evolution shows a different pattern at higher taxonomic levels from that seen within and between closely related species because body-size evolution among higher taxa occurs primarily by change in early portions of growth, which share more genetic growth determinants with brain size. 相似文献
2.
Many hypotheses have been postulated regarding the early evolution of the mammalian brain. Here, x-ray tomography of the Early Jurassic mammaliaforms Morganucodon and Hadrocodium sheds light on this history. We found that relative brain size expanded to mammalian levels, with enlarged olfactory bulbs, neocortex, olfactory (pyriform) cortex, and cerebellum, in two evolutionary pulses. The initial pulse was probably driven by increased resolution in olfaction and improvements in tactile sensitivity (from body hair) and neuromuscular coordination. A second pulse of olfactory enhancement then enlarged the brain to mammalian levels. The origin of crown Mammalia saw a third pulse of olfactory enhancement, with ossified ethmoid turbinals supporting an expansive olfactory epithelium in the nasal cavity, allowing full expression of a huge odorant receptor genome. 相似文献
3.
Relative brain size: a new measure 总被引：2，自引：0，他引：2
L Radinsky 《Science (New York, N.Y.)》1967,155(764):836-838
The relation of the volume of the endocranial cavity to the area of the foramen magnum is a measure of relative brain size in mammals. The outstanding advantage of this method is that only a skull is required for a set of measurements. 相似文献
4.
庄伟建 《福建农林大学学报(自然科学版)》1990,(2)
甘蔗不同种茎的贮藏细胞体积、维管束大小及其密度都有很大差别.原始栽培种的细胞体积大于野生种的;维管束密度以野生种和春尼为高,竹蔗、黑车里本和拔地拉较低;维管束大小顺序则为伊利安>黑车里本>拔地拉>竹蔗>春尼>割手密.从野生种、原始栽培种到这些种远缘杂交和回交培育的生产品种的系统发育中,生产品种的茎贮藏细胞体积居野生种和原始栽培种之间,而维管束则呈增粗且密度变稀的趋势.细胞体积、维管束密度与糖分的相关是有一定范围的.在生产品种和原始栽培种中,细胞体积大于2000000μm~3时,与糖分呈显著负相关;生产品种的维管束密度在小于300条/cm~2时,与糖分呈正相关. 相似文献
5.
May RM 《Science (New York, N.Y.)》1988,241(4872):1441-1449
This article surveys current answers to the factual question posed in the title and reviews the kinds of information that are needed to make these answers more precise. Various factors affecting diversity are also reviewed. These include the structure of food webs, the relative abundance of species, the number of species and of individuals in different categories of body size, along with other determinants of the commonness and rarity of organisms. 相似文献
6.
Geographic patterns in species richness are mainly based on wide-ranging species because their larger number of distribution records has a disproportionate contribution to the species richness counts. Here we demonstrate how this effect strongly influences our understanding of what determines species richness. Using both conventional and spatial regression models, we show that for sub-Saharan African birds, the apparent role of productivity diminishes with decreasing range size, whereas the significance of topographic heterogeneity increases. The relative importance of geometric constraints from the continental edge is moderate. Our findings highlight the failure of traditional species richness models to account for narrow-ranging species that frequently are also threatened. 相似文献
7.
中国薏苡属植物染色体核型的研究 总被引：3，自引：0，他引：3
本文以根尖为材料,通过压片法制片和核型分析,研究了中国薏苡属植物川谷和薏苡的染色体核型。结果表明：川谷和薏苡具有统一的染色体核型公式２ｎ＝２０＝１８ｍ（２ＳＡＴ）＋２ｓｍ,但二者在某些染色体编排顺序、随体大小上有差异。根据这一结果,从染色体水平上讨论了川谷和薏苡的亲缘关系。 相似文献
8.
Radinsky L 《Science (New York, N.Y.)》1983,221(4616):1189-1191
Allometric analysis of skull proportions in 25 species of fossil equids indicates that both scaling effects (allometry) and reorganization were factors in the evolutionary transformation of horse skulls. A relatively longer preorbital portion of the skull resulted from the ventral and forward displacement of the tooth row relative to the jaw joint and the orbit when high-crowned teeth evolved. Correlated with the increased distance between jaw joint and tooth row is an increase in the relative size of the attachment areas of masseter and internal pterygoid muscles. 相似文献
9.
Microtubules in brain homogenates 总被引：2，自引：0，他引：2
J B Kirkpatrick 《Science (New York, N.Y.)》1969,163(863):187-188
Microtubules from neurons are preserved in homogenates of mammalian brain by medium containing organic solvents at acidic pH. By means of negative staining and electron microscopy, the relative concentration of microtubules in suspensions can be assayed. Microtubules from brain have a filamentous and substructure. 相似文献
10.
Högstedt G 《Science (New York, N.Y.)》1980,210(4474):1148-1150
Reproductive output from enlarged or reduced magpie broods showed that each female generally lays a clutch of optimal size. This size varies considerably between females. Approximately 85 percent of the within-years variation in clutch size was associated with differences between territories. Colonial bird species, lacking individual foraging territories, have a smaller clutch size variation than territorial species. 相似文献
11.
Khaitovich P Hellmann I Enard W Nowick K Leinweber M Franz H Weiss G Lachmann M Pääbo S 《Science (New York, N.Y.)》2005,309(5742):1850-1854
The determination of the chimpanzee genome sequence provides a means to study both structural and functional aspects of the evolution of the human genome. Here we compare humans and chimpanzees with respect to differences in expression levels and protein-coding sequences for genes active in brain, heart, liver, kidney, and testis. We find that the patterns of differences in gene expression and gene sequences are markedly similar. In particular, there is a gradation of selective constraints among the tissues so that the brain shows the least differences between the species whereas liver shows the most. Furthermore, expression levels as well as amino acid sequences of genes active in more tissues have diverged less between the species than have genes active in fewer tissues. In general, these patterns are consistent with a model of neutral evolution with negative selection. However, for X-chromosomal genes expressed in testis, patterns suggestive of positive selection on sequence changes as well as expression changes are seen. Furthermore, although genes expressed in the brain have changed less than have genes expressed in other tissues, in agreement with previous work we find that genes active in brain have accumulated more changes on the human than on the chimpanzee lineage. 相似文献
12.
淀山湖鱼类调查样本量优化设计 总被引：1，自引：0，他引：1
渔业资源的独立调查是获得高质量数据的重要手段,可以为渔业资源评估与管理提供科学依据,而样本量(站位数量)直接影响调查数据的质量。以淀山湖鱼类资源调查为例,利用重采样方法,研究样本量对调查结果精确度和准确性的影响。结果表明:在减少样本量的情况下同样可获得较高精确度和准确性的结果。不同指数的相对估计误差(REE)随着样本量的增加而降低,当样本量大于等于8时大部分指数的REE均趋于稳定;REE与指数的空间变异性呈正相关关系,REE存在指数间差异和季节差异。为保持相同精确度,不同指数在同一季节所需样本量不同,分析鱼类多样性指数所需样本量最少,其次是鱼类群体资源量指数,分析单个物种资源量指数所需样本量最多;同一指数不同季节所需样本量也不相同,分析资源量丰度指数冬季所需样本量最多,分析鱼类多样性指数夏季所需样本量最多。适当调整样本量可以在保证调查结果精确度和准确性的情况下降低调查对资源量较小的鱼类的负面影响。 相似文献
13.
Sallet J Mars RB Noonan MP Andersson JL O'Reilly JX Jbabdi S Croxson PL Jenkinson M Miller KL Rushworth MF 《Science (New York, N.Y.)》2011,334(6056):697-700
It has been suggested that variation in brain structure correlates with the sizes of individuals' social networks. Whether variation in social network size causes variation in brain structure, however, is unknown. To address this question, we neuroimaged 23 monkeys that had been living in social groups set to different sizes. Subject comparison revealed that living in larger groups caused increases in gray matter in mid-superior temporal sulcus and rostral prefrontal cortex and increased coupling of activity in frontal and temporal cortex. Social network size, therefore, contributes to changes both in brain structure and function. The changes have potential implications for an animal's success in a social context; gray matter differences in similar areas were also correlated with each animal's dominance within its social network. 相似文献
14.
To investigate whether the temporal cortex of a nonprimate species contains cells responsive to the sight of faces, a study was made in conscious sheep of the responses of neurons in this brain region to the sight of faces. Of 561 cells from which responses were recorded, 40 responded preferentially to faces. Different categories of these cells were influenced by dominance (presumably indicated by the presence and size of horns), breed and familiarity, and threatening faces such as those of humans and dogs. These results demonstrate that cells that respond preferentially to faces are present in the temporal cortex of a nonprimate species, and that the responses of these cells are influenced by factors relevant to social interaction. 相似文献
15.
为了减少葡萄霜霉病在经济上造成不必要的损失,采集湖南、福建、江西三省的不同地区、不同葡萄品种的19份葡萄霜霉病菌,检测了它们的孢子囊大小和在户太八号、夏黑、醉金香、紫秋葡萄、维多利亚5个不同葡萄品种的致病力差异。结果表明,采自不同葡萄品种的霜霉病菌孢子囊大小存在一定的差异,来源于刺葡萄的病原菌孢子囊明显大于来源于巨峰、红地球上的霜霉病菌孢子囊;来源于江西的菌株致病性普遍较强,而来源于湖南的菌株致病性普遍较弱。欧美杂交种葡萄,如户太8号、夏黑、醉金香,其病情指数相对较低;欧亚杂交种和东亚种葡萄,如维多利亚,紫秋葡萄,其病情指数相对偏高。上述结果表明,采自不同寄主的葡萄霜霉病菌的致病力及孢子囊大小均存在一定程度的分化。 相似文献
16.
Sensory events and the representation of past experience cause distinctive changes in the electrical activity of widespread regions of the brain. These regions have similar roles in the engram in the sense that they all seem to participate in responses to external events and in subsequent representations of these events. However, the relative contribution of these processes to the activity of different brain regions is quantitatively different, in that some regions are much more strongly affected than others. These results may constitute the basis for reconciliation of localizationist and antilocalizationist views of brain function. 相似文献
17.
傅杰才 《湖南农业大学学报(自然科学版)》1990,17(4)
在某些特殊条件下,如作相对运动的一对尺寸完全相同但不按规律分布的表面,只有在相对运动一个周期后才能再重合一次.此运动特性应用于某些情况下随行夹具运送机构的设计,可以简化机构,提高可靠性.这种原理已在某项设计中被采用.本文并介绍了实际进行设计时应注意的一些具体事项. 相似文献
18.
Multiple causes of high extinction risk in large mammal species 总被引：2，自引：0，他引：2
Cardillo M Mace GM Jones KE Bielby J Bininda-Emonds OR Sechrest W Orme CD Purvis A 《Science (New York, N.Y.)》2005,309(5738):1239-1241
Many large animal species have a high risk of extinction. This is usually thought to result simply from the way that species traits associated with vulnerability, such as low reproductive rates, scale with body size. In a broad-scale analysis of extinction risk in mammals, we find two additional patterns in the size selectivity of extinction risk. First, impacts of both intrinsic and environmental factors increase sharply above a threshold body mass around 3 kilograms. Second, whereas extinction risk in smaller species is driven by environmental factors, in larger species it is driven by a combination of environmental factors and intrinsic traits. Thus, the disadvantages of large size are greater than generally recognized, and future loss of large mammal biodiversity could be far more rapid than expected. 相似文献
19.
20.
几种杨树对光肩星天牛的抗性研究 总被引：6，自引：0，他引：6
该文对宁夏新引进和原有的１４ 种杨树的生长及抗虫性进行了研究,发现欧洲山杨三倍体、截叶毛白杨等数种杨树,在一定的环境条件下,具有较好的相对抗虫性．并对其抗虫强度进行了排序．其抗虫性都优于新疆杨． 相似文献