EVOLUTION OF LEAF FORM IN MARSILEACEOUS FERNS: EVIDENCE FOR HETEROCHRONY

Using an explicit phylogenetic framework, ontogenetic patterns of leaf form are compared among the three genera of marsileaceous ferns ( Marsilea , Regnellidium , and Pilularia ) with the outgroup Asplenium to address the hypothesis that heterochrony played a role in their evolution. We performed a Fourier analysis on a developmental sequence of leaves from individuals of these genera. Principal components analysis of the harmonic coefficients was used to characterize the ontogenetic trajectories of leaf form in a smaller dimensional space. Results of this study suggest that the evolutionary juvenilization observed in these leaf sequences is best described using a mixed model of heterochrony (accelerated growth rate and early termination at a simplified leaf form). The later stages of the ancestral, more complex, ontogenetic pattern were lost in Marsileaceae, giving rise to the simplified adult leaves of Marsilea , Regnellidium , and Pilularia . Life-history traits such as ephemeral and uncertain habitats, high reproductive rates, and accelerated maturation, which are typical for marsileaceous ferns, suggest that they may be r strategists. The evidence for heterochrony presented here illustrates that it has resulted in profound ecological and morphological consequences for the entire life history of Marsileaceae.     

四棱草属比较形态及其分类系统位置的研究Ⅱ．四棱草属及其近缘属叶片宏观结构

采用“外类群对比准则（ＯｕｔｇｒｏｕｐＣｏｍｐａｒｉｓｏｎＣｒｉｔｅｒｉａ,Ｃｒａｃｒａｆｔ,１９８３）”的性状分析方法,对我国特有植物四棱草属Ｓｏｈｎａｂｅｌｉａ及其近缘属筋骨草属Ａｊｕｇａ,香科科属Ｔｅｕｃｒｉｕｍ（唇形科Ｌａｂｉａｔａｅ）和获属Ｃａｒｙｏｐｌｅｒｉｓ,大青属Ｃｌｅｒｏｄｅｎｄｒｕｎ（马鞭草科Ｖｅｒｂｅｎａｃｅａｅ）等５属６种主要植物叶片进行比较研究,结果表明;叶形卵圆形（Ｏｖａｔｅ一ｓｈａｐｅｄ）或椭圆形（Ｅｌｌｉｐｓｅ一ｓｈａｐｅｄ）;叶缘均具齿,叶脉同为羽状脉（Ｅｕｃａｍｐｔｅｄｒｏｍｏｕｓ）;三级脉为分枝型（Ｒａｍｉｆｉｅｄ）和贯串型（Ｐｅｒｃｕｒｅｎｔｏｉｄ）;边缘未级脉（Ｍａｒｇｉｎａｌｕｌｔｉｍａｔｅｖｅｎａｔｉｏｎ）均为不完全型（Ｉｎｃｏｍｐｌｅｔｅｏｉｄ）：齿型（Ｔｏｏｔｈ－ｔｙｐｅ）为金粟兰型齿（Ｃｈｌｏ－ｒａｎｔｈｏｉｄ）;费特吉型齿（Ｆｏｔｈｅｒｇｉｌｌｏｉｄ）;和非费特吉型齿（ＮｏｎｔｙｐｉｃａｌＦｏｔｈｅｒｇｉｌｌｏｉｄ）;网隙（Ａｒｅｏｌｅ）属不完全型（Ｉｎｃｏｍｐｌｅｔｅ）或不完善型（Ｉｍｐｅｒｆｅｃｔ）;齿腺体（Ｇｌａｎｄｕｌａｒ一Ｂｏｄｙ）宿存或脱落等     

Heterochrony and allometry: the analysis of evolutionary change in ontogeny

The connection between development and evolution has become the focus of an increasing amount of research in recent years, and heterochrony has long been a key concept in this relation. Heterochrony is defined as evolutionary change in rates and timing of developmental processes; the dimension of time is therefore an essential part in studies of heterochrony. Over the past two decades, evolutionary biologists have used several methodological frameworks to analyse heterochrony, which differ substantially in the way they characterize evolutionary changes in ontogenies and in the resulting classification, although they mostly use the same terms. This review examines how these methods compare ancestral and descendant ontogenies, emphasizing their differences and the potential for contradictory results from analyses using different frameworks. One of the two principal methods uses a clock as a graphical display for comparisons of size, shape and age at a particular ontogenic stage, whereas the other characterizes a developmental process by its time of onset, rate, and time of cessation. The literature on human heterochrony provides particularly clear examples of how these differences produce apparent contradictions when applied to the same problem. Developmental biologists recently have extended the concept of heterochrony to the earliest stages of development and have applied it at the cellular and molecular scale. This extension brought considerations of developmental mechanisms and genetics into the study of heterochrony, which previously was based primarily on phenomenological characterizations of morphological change in ontogeny. Allometry is the pattern of covariation among several morphological traits or between measures of size and shape; unlike heterochrony, allometry does not deal with time explicitly. Two main approaches to the study of allometry are distinguished, which differ in the way they characterize organismal form. One approach defines shape as proportions among measurements, based on considerations of geometric similarity, whereas the other focuses on the covariation among measurements in ontogeny and evolution. Both are related conceptually and through the use of similar algebra. In addition, there are close connections between heterochrony and changes in allometric growth trajectories, although there is no one-to-one correspondence. These relationships and outline links between different analytical frameworks are discussed.     

INDIVIDUAL VARIATION OF ONTOGENIES: A LONGITUDINAL STUDY OF GROWTH AND TIMING

This study of growth and developmental time in the water strider Limnoporus canaliculatus (Heteroptera: Gerridae) is based on longitudinal data from specimens reared individually in the laboratory. I analyzed multivariate allometry using a common principal components approach. This technique identified patterns of variation that were uncorrelated both within and among instars and which remained fairly constant throughout the growth period; in contrast, the overall amount of variation increased from young to older instars. Negative correlations between size and subsequent growth increments indicated convergent growth in the first three instars, but there was a transition to positive correlations (divergent growth) in later instars. Analysis of covariation among measurements made in different instars showed strong ontogenetic autocorrelation and revealed patterns remarkably similar to those found in mammals and birds; yet corresponding analyses of growth increments showed mainly independent variation in different instars. Therefore, I conclude that the strong correlations among stage-specific measurements result from the part-whole relationships inherent to these cumulative size data, but do not reflect specific properties of the organisms studied. In contrast to size increments, instar durations of water striders were highly correlated throughout the larval period, indicating that individuals tended to develop at either relatively fast or relatively slow rates in all instars. The correlations between growth increments and instar durations were nil or negative, contrary to expectations from life-history theory. The results of these analyses of individual variation match the findings from other water striders and from interspecific comparisons in the genus Limnoporus, but information about physiological mechanisms of molting and growth in insects cannot completely explain the patterns observed.     

贵州寒武纪杷榔组Changaspis elongata Chien,1961个体发育研究及意义

根据采自贵州剑河辣子寨杷榔组的张氏虫Changaspis 296块标本,采用传统形态测量方法,对头部及躯干特征进行度量;结合散点图、简化主轴回归分析及线性拟合对比分析后,确认这些标本均为长形张氏虫Chang-aspis elongata的标本,厘定出从分节6期至成虫期共计12个连续个体发育序列,揭示其形态变化特点。从分节6期至10期,背壳长、头鞍长、头盖长和宽的增长幅度相对小;随着体节的增多,头盖长度与背壳长度的比值从50%减少至34%;随着头鞍长度的增长,头鞍前部及后部宽均呈线性关系的连续增长趋势;个体发育序列确认该种成虫期有17节胸节,不同以往认为的16节胸节。对比分析及线性拟合的数据比较论证,确认原为C.micropyge和C.placenta 2个种的特征应为C.elongata在个体发育变化中的种内差异,确认先前命名的这2种应为C.elongata的晚出同义名。     

A COMPARISON OF COVARIANCE STRUCTURE IN WILD AND LABORATORY MUROID CRANIA

Mutations have the ability to produce dramatic changes to covariance structure by altering the variance of covariance-generating developmental processes. Several evolutionary mechanisms exist that may be acting interdependently to stabilize covariance structure, despite this developmental potential for variation within species. We explore covariance structure in the crania of laboratory mouse mutants exhibiting mild-to-significant developmental perturbations of the cranium, and contrast it with covariance structure in related wild muroid taxa. Phenotypic covariance structure is conserved among wild muroidea, but highly variable and mutation-dependent within the laboratory group. We show that covariance structures in natural populations of related species occupy a more restricted portion of covariance structure space than do the covariance structures resulting from single mutations of significant effect or the almost nonexistent genetic differences that separate inbred mouse strains. Our results suggest that developmental constraint is not the primary mechanism acting to stabilize covariance structure, and imply a more important role for other mechanisms.     

DISENTANGLING GENETIC AND PRENATAL SOURCES OF FAMILIAL RESEMBLANCE ACROSS ONTOGENY IN A WILD PASSERINE

Cross‐fostering experiments are widely used by quantitative geneticists to study genetics and by behavioral ecologists to study the effects of prenatal investment. Generally, the effects of genes and prenatal investment are confounded and the interpretation given to such experiments is largely dependent on the interests of the researcher. Using a large‐scale well‐controlled experiment on a wild population of blue tits (Cyanistes caeruleus), we are able to partition variation in body mass across ontogeny into the effects of genes and the effects of between‐clutch variation in egg characteristics. We show that although egg effects are important early in ontogeny they quickly dissipate, suggesting that the genetic interpretation of cross‐fostering experiments may be preferable for many types of trait. However, the heritability of body mass is smaller than has previously been reported. Our results suggest that this is due to a combination of controlling postnatal environmental effects more carefully and accounting for viability selection operating early in ontogeny.     

HETEROCHRONY AND DEVELOPMENTAL INNOVATION: EVOLUTION OF FEMALE GAMETOPHYTE ONTOGENY IN GNETUM,A HIGHLY APOMORPHIC SEED PLANT

Seed plant female gametophytes are focal points for the evolutionary modification of development. From a structural perspective, the most divergent female gametophytes among all seed plants are found in Gnetum, a clade within Gnetales. Coenocytic organization at sexual maturity, absence of defined egg cells (free nuclei are fertilized), lack of centripetal cellularization, and postfertilization development of embryo-nourishing tissues are features of the female gametophytes of Gnetum unparalleled among seed plants. Although the female gametophyte of Gnetum retains the three basic phases of somatic development common to female gametophytes of plesiomorphic seed plants (free nuclear development, cellularization, cellular growth), the timing of fertilization has been accelerated relative to the rate of somatic development. As a consequence, the female gametophyte of Gnetum matures sexually (is fertilized) at a juvenile (compared with the ancestral somatic ontogeny) and free nuclear stage of somatic development, thereby precluding differentiation of egg cells. Unlike progenetic animals, where truncation of somatic ontogeny evolves in tandem with acceleration in the timing of sexual maturation, the female gametophyte of Gnetum completes the entire ancestral somatic ontogeny after precocious sexual maturation. This results in the evolution of postfertilization development of embryo-nourishing female gametophyte tissues, a phenomenon unique among seed plants. Nonheterochronic developmental innovations have also played important roles in the evolution of the female gametophyte of Gnetum. Centripetal cellularization, which is always associated with the phase change from coenocytic to cellular organization among plesiomorphic seed plant female gametophytes, is lacking in Gnetum. Instead, during early phases of development, apomorphic free nuclear organization is coupled with a highly anomalous pattern of cellularization. Stage-specific innovations during early development in the female gametophyte of Gnetum do not affect plesiomorphic aspects of later phases of development. Thus, a complex array of heterochronic and nonheterochronic developmental innovations have played critical roles in the ontogenetic evolution of the highly apomorphic female gametophyte of Gnetum.     

玉米类囊体膜的超分子结构及LHCP在个体发育中的变化

对玉米(Zea mays)营养生长期中的下位叶(第5叶)和生殖生长时期的中位叶(果穗叶)和上位叶(顶生叶)的成熟叶片的冰冻撕裂电镜观察,发现叶绿体类囊体膜所有撕裂面上各种功能蛋白颗粒的密度均以果穗叶中的最大,依次是顶生叶和第5叶的。以果穗叶与顶生叶相比,其类囊体膜中包含有绝大多数 LHCP 的 EFs 颗粒增加28%;包含有 PSI 反应中心与LHCP 相结合的 PFu 颗粒增加20%;包含有 PSII 反应中心与 LHCP 相结合的 EFs 颗粒增加19%。这一超分子结构的电镜观察结果与其 SDS-聚丙烯酰胺梯度凝胶板电泳解析的结果相一致。即 SDS-聚丙烯酰胺梯度凝胶板电泳解析的色素带上,同样是果穗叶类囊体膜上呈现的21kD(LHCP Ⅰ)和25 kD(LHCPⅡ)多肽的色素带相应地也比顶生叶的加宽,表明果穗叶叶绿体类囊体膜上镶嵌的叶绿素 a/b 蛋白复合体等比顶生叶的显著地增多,这有利于果穗叶光合作用中光能的吸收、传递、分配和转化。     

新疆昭苏野生油菜与黑芥品种尤嫩斯染色体组型和带型比较研究

大量的细胞学观察表明,昭苏野生油菜与黑芥之间,不论是在染色体数上,还是在染色体组型、带型以及染色体大小、总长上都有较大的差异。昭苏野生油菜的染色体数为2n=18,芥黑则为2n=16;染色体组型,前者为14m+4m(SAT),后者为8m+4sm+4sm(SAT);染色体带型,前者为12C/C+2CN/C+2WN~O/O+2W/O,后者为12C/C+2WN/C+2WN~O/C;染色体长度前者为2.00—4.00μ,后者为6.48—3.75μ,虽然黑芥染色体条数少于野生油菜,但总长度却长于昭苏野生油菜。通过观察测量和分析比较,我们认为,昭苏野生油菜与黑芥在亲缘关系上有着较大的距离,二者为不同的物种。     

广西栽培与野生岩黄连的质量比较研究

通过对广西栽培与野生岩黄连(Corydalis saxicola Bunting)全草的性状、组织构造、化学反应、薄层层析、紫外吸收的比较,表明栽培岩黄连与当地野生品质量基本一致,为广西发展岩黄连资源提供科学依据。     

洞庭湖区三个湖泊水生植物多样性的比较研究

比较研究了洞庭湖区华容县东湖、益阳市大通湖和岳阳市郊南湖水生植物多样性的现状,讨论了30年来3个湖泊水生植物多样性丧失的情况及与其所受人为干扰的关系,探讨了野菱、密齿苦草和菹草对人为干扰的适应机制、大通湖和南湖水生植物多样性及其退化水生态系统恢复的途径。主要结论如下：（1）199－2000年东湖、大通湖与南湖各分布有水生植物61种、56种和32种,其分别隶属于29科43属、26科39属和20科27属;各有水生植物群丛8个、6个和4个;水生植被覆盖率分别为26．17％、10．60％和9．99％。（2）30年来三个湖泊分别有3种、9种和13种水生植物消失,2个、5个和5个水生植物群丛类型消失。（3）水生植物多样性的现状是：东湖＞大通湖＞南湖,多样性下降的程度与其所受干扰强度成正相关。     

裂叶沙参和泡沙参种群有性生殖和无性繁殖的比较

通过对裂叶沙参(Adenophora lobophylla Hong)和泡沙参(A.potaninii Korsh.)种群有性生殖和无性繁殖特性的对比,揭示濒危植物裂叶沙参的种群内部致濒机制。结果表明:裂叶沙参种群幼苗抢占草本层上层空间能力弱于泡沙参种群;裂叶沙参种群是以相对长的生殖期和高产籽量来适应环境;裂叶沙参种群开花结实量虽高于泡沙参种群,但其中成熟种子少,种子质量差,致使其种群由种子到一年生幼苗的转化率极低,并且幼苗生活力弱,是导致其种群濒危的重要内部原因。裂叶沙参种群除有性生殖外还兼有较弱的无性繁殖,是对其有性生殖的一个重要补充。     

乙肝表面抗原a表位粘膜疫苗的构建及免疫原性检测

利用DNA重组技术 ,构建霍乱毒素B亚单位与乙肝病毒表面抗原a表位的融合基因 ,并在大肠杆菌表达体系pET 30a BL2 1 (DE3)中获得以包涵体形式的高效表达。免疫印迹表明表达产物具有免疫学活性 ,包涵体复性后 ,表达产物能够象CTB那样形成五体 ,以腹腔注射、灌胃、鼻饲形式免疫小鼠均能产生抗HBsAg抗体     

西藏和北极巴罗地区菊科植物几个属的花粉

对西藏和北极巴罗地区菊科4个属(蒿属、飞蓬属、风毛菊属和千里光属)17个种的花粉形态进行了光学和扫描电子显微镜的观察、比较。结果表明这两个地区菊科4个属的花粉粒大多为球形或近球形,少数是扁球形或长球形。萌发孔的类型均为三孔沟。但在花粉大小、萌发孔形状、外壁厚度以及表面纹饰等方面存在差异。通过对这两个地区菊科植物花粉形态的观察有可能为菊科分化、迁移,以及化石孢粉的研究提供参考资料。     

岗柴与刹柴(茅柴)的茎秆与纤维的比较解剖观察

荻(Miscanthus sacchariflorus)属禾本科多年生草本植物,在长江流域以南分布很广。它不仅是草类纤维中主要的造纸原料植物,而且也有防沙固堤,净化污水等作用。目前湖北省主要是采用荻的茎秆作造纸原料。但湖北省的老苇田里,常有与岗柴形     

THE GEOGRAPHY OF COEVOLUTION: COMPARATIVE POPULATION STRUCTURES FOR A SNAIL AND ITS TREMATODE PARASITE

Gene flow and the genetic structure of host and parasite populations are critical to the coevolutionary process, including the conditions under which antagonistic coevolution favors sexual reproduction. Here we compare the genetic structures of different populations of a freshwater New Zealand snail (Potamopyrgus antipodarum) with its trematode parasite (Microphallus sp.) using allozyme frequency data. Allozyme variation among snail populations was found to be highly structured among lakes; but for the parasite there was little allozyme structure among lake populations, suggesting much higher levels of parasite gene flow. The overall pattern of variation was confirmed with principal component analysis, which also showed that the organization of genetic differentiation for the snail (but not the parasite) was strongly related to the geographic arrangement of lakes. Some snail populations from different sides of the Alps near mountain passes were more similar to each other than to other snail populations on the same side of the Alps. Furthermore, genetic distances among parasite populations were correlated with the genetic distances among host populations, and genetic distances among both host and parasite populations were correlated with “stepping-stone” distances among lakes. Hence, the host snail and its trematode parasite seem to be dispersing to adjacent lakes in a stepping-stone fashion, although parasite dispersal among lakes is clearly greater. High parasite gene flow should help to continuously reintroduce genetic diversity within local populations where strong selection might otherwise isolate “host races.” Parasite gene flow can thereby facilitate the coevolutionary (Red Queen) dynamics that confer an advantage to sexual reproduction by restoring lost genetic variation.     

COMPARATIVE POPULATION GENETIC STRUCTURE OF A PARASITE (FASCIOLOIDES MAGNA) AND ITS DEFINITIVE HOST

The population genetic structure of the American liver fluke, Fascioloides magna, and its definitive host the white-tailed deer, Odocoileus virginianus, was examined in South Carolina. Flukes were significantly more common in deer from river-swamp habitat than upland areas and prevalence increased with host age. The distribution of flukes among deer occurred as a negative binomial with the mean dispersion parameter, k, equal to 0.17 and the range from 0.10 to 1.11 within local areas. Significant spatial genetic differentiation was observed for flukes and deer. Patterns of genetic distance in flukes were not concordant with those of the definitive host nor were they related to geographic distance between sample locations. Spatial genetic differentiation among flukes reflected the tendency for individual hosts to harbor multiple individuals from a limited number of parasite clones. The large population size of the parasite and movements of the definitive host tend to counteract factors that lead to spatial differentiation.