不同沙地生境下黄柳(Salix gordejevii)种群若干数量特征的比较研究

对分布于３种不同沙地生境（半固定沙丘、固定沙丘、丘间低地）黄柳灌丛的个体形态、生长和群体数量特征进行了比较研究,同时测定了灌丛下草本层植物种类组成及频率。结果显示：分布于丘间低地的黄柳灌丛当年枝平均长度增加缓慢,短枝条的比例较高,枝长频度分布（当年枝）峰值偏左,分枝也较多,叶片短而狭,长宽比大;与之相比,分布于半固定沙丘上的灌丛当年枝平均长度增加较快,长枝条比例较高,枝长频度分布趋于正态分布,分枝     

中国安徽省祁门县大鲵属一新种（两栖纲：隐鳃鲵科）

中国大鲵(Andrias davidianus)是世界上最大的两栖动物,曾在中国广泛分布。前期的3项分子遗传学研究表明：黄山的中国大鲵种群存在独特的遗传分化,是一个未被描述的物种。这3项研究中的分子数据均基于本文通讯作者1995年之前采自中国安徽省黄山市祁门县的原生大鲵标本。本文基于形态学比较,将1995年以前本文通讯作者在祁门县采集的11个大鲵标本描述为大鲵属一新种：祁门大鲵(Andrias cheni sp. nov.)。我们测量了11个标本的25个形态特征,并与大鲵属的其他物种进行比较。祁门大鲵与大鲵属其他物种可通过以下特征进行区分：(1)头躯扁平,头长略大于头宽,头宽/头长(HW/HL)比为0.80 ~ 0.98;(2)头部和下颌相对光滑,有不规则排列的小结节;(3)颈部侧褶与体褶不连续;(4)第三指比第一指长,指式Ⅰ< Ⅳ < Ⅲ < Ⅱ;(5)四肢粗而短,后肢比前肢长,前肢长/后肢长(FLL/PLL)比为0.78 ~ 0.96;(6)尾部肌肉发达,基部粗大,后部和上部逐渐变平,尾长约为总长度的1/3。经形态比较,本研究将祁门大鲵描述为新种,大鲵属物种增加到5个。本文提供了相对完备的形态数据,可为后续大鲵野生谱系的资源保护、人工种群遗传管理和增殖放流等提供参考。     

Metamorphosis in the paired species of lampreys, Lampetra fluviatilis (L.) and Lampetra planeri (Bloch): 2. Quantitative data for body proportions, weights, lengths and sex ratios

Representatives of the various Stages (1–9) in the metamorphosis and short adult life of the brook lamprey, Lampetra planeri , were used to provide quantitative data to describe the pattern of changes that take place during this period of the life cycle. During the transformation of the oral hood into an oral disc, this ventral region of the snout first declines in length before increasing markedly. The branchial region declines in length and remains relatively smaller than in the ammocoete, a feature probably correlated with the concomitant internal changes in the pharynx which permit a change from a unidirectional to a tidal respiratory flow. The eye increases in size only through the initial Stages (1–5). The main period of fin enlargement occurs rather later in metamorphosis than the above changes.
During maturation the two initially separate dorsal fins increase further in height and eventually become separated only by a notch. Differences between the two sexes are found in the relative size of the disc and fins, the larger structures of the male probably being related to their greater activity in spawning behaviour. Measurements on metamorphosed L. fluviatilis confirm that in this species the eye and disc are relatively larger than in L. planeri. Data are presented which illustrate that in collections taken during the metamorphosis of both species the males are smaller and slightly more numerous than the females and that transformation is initiated at a longer length in L. planeri than in L. fluviatilis .     

Individual variation in the growth of captive infant gorillas

Serial anthropometric data were obtained during the first year of life of six nursery-reared infant gorillas in the Columbus (Ohio) Zoo. Two of the infants are likely to be monozygotic twins as determined by DNA analysis. Growth curves were fitted to serial measures of cephalo-thoracic-abdominal length, arm length, leg length, head circumference, upper arm circumference, and weight from each gorilla, to describe individual patterns of variation in skeletal growth and body composition. Growth in skeletal measures tended to be curvilinear to varying degrees over the first year of life. Body composition varied more than skeletal measures throughout the first year as a consequence of individual health status. Individual growth and body composition variations appear to reflect both genetic and environmental influences in this small sample of captive infant gorillas.     

MicroRNAs Cause Accelerated Decay of Short-Tailed Target mRNAs

1. Download : Download high-res image (118KB)
2. Download : Download full-size image

     

Long bone lengths and gestational age distributions of post-contact period Arikara Indian perinatal infant skeletons

Prenatal growth is adversely affected by poor socioeconomic conditions where disease and chronic undernutrition prevail. Premature and small-for-gestational-age births occur at higher frequency. Post-contact Arikara Indian populations of South Dakota experienced a rapidly changing and disruptive environment that included deterioration of the subsistence base and increased morbidity. This research tests resulting fetal growth effects through comparative analysis of two perinatal infant samples of the early (A.D. 1600-1733) and the late (A.D. 1760-1835) post-contact period. Perinatal infants recovered from late cemeteries include a higher percentage of smaller skeletons, as determined using long bone diaphyseal lengths, than is documented for the earlier time period. This contrast shows that it is possible to detect fetal growth differences in samples of archaeological context.     

Morphological correlates of locomotor performance in hatchling Amblyrhynchus cristatus

Previous studies of locomotor performance from a variety of perspectives often assumed that speed and limb length were strongly correlated. Despite support of this assumption from biomechanical models, few empirical studies have demonstrated a significant relationship between measures of locomotor capacity, such as maximum velocity, and length of the hindlimb at either the inter- or intra-specific level. We examined whether one measure of locomotor performance, maximum velocity, correlates with body size and elements of the hindlimb in hatchling marine iguanas (Amblyrhynchus cristatus). Larger hatchlings ran faster. Removing the effects of body size revealed that relative lengths of the tibia and hindfoot correlated with size-adjusted maximum velocity. Individuals with relatively long tibia and short pes were relatively faster than individuals with short tibia and long pes. Functional morphological analyses predict that femur length should correlate with maximum velocity. However, our analyses failed to support this prediction. Because hatchling marine iguanas exploit relatively open habitats, the relationship between maximum velocity and limb morphology may be interpreted as an adaptation enhancing escape from predators.     

Eastern gamagrass (Tripsacum dactyloides) root penetration into and chemical properties of claypan soils

Claypans restrict rooting depth and availability of moisture and nutrients to plants during periods of drought. Eastern gamagrass (Tripsacum dactyloides var. dactyloides [L.] L.) often remains green during summer droughts, while other plants turn brown. Questions arose whether eastern gamagrass roots had or could penetrate claypans to obtain needed moisture. Pits were dug (2 m deep) under eastern gamagrass plants that had been growing 50+ and 5+ years at two sites in Missouri. Clay contents were 30 to 50% in soil layers below 30 cm, and moisture was not limiting in these deep soil layers. Soil pH_Ca in the lower soil layers, except at 180 cm, was below 5.0, and in some cases near 4.0. Extractable Al was especially high in the 90 and 120 cm deep soil layers where pH was low. Extractable Ca, Mg, and K increased with soil depth. The eastern gamagrass roots effectively penetrated claypan soils. Root lengths and root weights were extensive to 180 cm depth, and decreased from the surface with soil depth. Roots of eastern gamagrass were aerenchymous (having cellular compartments which allow air movement) at all depths, were mycorrhizal to at least 150 cm depth, and had relatively high tolerance to acidic Al toxic Tatum subsoil (Typic Hapludult) and toxic levels of Al in nutrient solution. The eastern gamagrass roots also provided root channels through claypans, which could enable new eastern gamagrass or other plant roots to grow into deeper soil layers.     

The evolution of proteins from random amino acid sequences: II. Evidence from the statistical distributions of the lengths of modern protein sequences

This paper continues an examination of the hypothesis that modern proteins evolved from random heteropeptide sequences. In support of the hypothesis, White and Jacobs (1993, J Mol Evol 36:79–95) have shown that any sequence chosen randomly from a large collection of nonhomologous proteins has a 90% or better chance of having a lengthwise distribution of amino acids that is indistinguishable from the random expectation regardless of amino acid type. The goal of the present study was to investigate the possibility that the random-origin hypothesis could explain the lengths of modern protein sequences without invoking specific mechanisms such as gene duplication or exon splicing. The sets of sequences examined were taken from the 1989 PIR database and consisted of 1,792 super-family proteins selected to have little sequence identity, 623 E. coli sequences, and 398 human sequences. The length distributions of the proteins could be described with high significance by either of two closely related probability density functions: The gamma distribution with parameter 2 or the distribution for the sum of two exponential random independent variables. A simple theory for the distributions was developed which assumes that (1) protoprotein sequences had exponentially distributed random independent lengths, (2) the length dependence of protein stability determined which of these protoproteins could fold into compact primitive proteins and thereby attain the potential for biochemical activity, (3) the useful protein sequences were preserved by the primitive genome, and (4) the resulting distribution of sequence lengths is reflected by modern proteins. The theory successfully predicts the two observed distributions which can be distinguished by the functional form of the dependence of protein stability on length.The theory leads to three interesting conclusions. First, it predicts that a tetra-nucleotide was the signal for primitive translation termination. This prediction is entirely consistent with the observations of Brown et al. (1990a,b, Nucleic Acids Res 18:2079–2086 and 18: 6339-6345) which show that tetra-nucleotides (stop codon plus following nucleotide) are the actual signals for termination of translation in both prokaryotes and eukaryotes. Second, the strong dependence of statistical length distributions on sequence-termination signaling codes implies that the evolution of stop codons and translation-termination processes was as important as gene splicing in early evolution. Third, because the theory is based upon a simple no-exon stochastic model, it provides a plausible alternative to a limited universe of exons from which all proteins evolved by gene duplication and exon splicing (Dorit et al. 1990, Science 250:1377–1382).     

Cladistic analysis of molecular and morphological data

Considerable progress has been made recently in phylogenetic reconstruction in a number of groups of organisms. This progress coincides with two major advances in systematics: new sources have been found for potentially informative characters (i. e., molecular data) and (more importantly) new approaches have been developed for extracting historical information from old or new characters (i. e., Hennigian phylogenetic systematics or cladistics). The basic assumptions of cladistics (the existence and splitting of lineages marked by discrete, heritable, and independent characters, transformation of which occurs at a rate slower than divergence of lineages) are discussed and defended. Molecular characters are potentially greater in quantity than (and usually independent of) more traditional morphological characters, yet their great simplicity (i. e., fewer potential character states; problems with determining homology), and difficulty of sufficient sampling (particularly from fossils) can lead to special difficulties. Expectations of the phylogenetic behavior of different types of data are investigated from a theoretical standpoint, based primarily on variation in the central parameter λ (branch length in terms of expected number of character changes per segment of a tree), which also leads to possibilities for character and character state weighting. Also considered are prospects for representing diverse yet clearly monophyletic clades in larger-scale cladistic analyses, e. g., the exemplar method vs. “compartmentalization” (a new approach involving substituting an inferred “archetype” for a large clade accepted as monophyletic based on previous analyses). It is concluded that parsimony is to be preferred for synthetic, “total evidence” analyses because it appears to be a robust method, is applicable to all types of data, and has an explicit and interpretable evolutionary basis. © 1994 Wiley-Liss, Inc.