Neither Biased Sex Ratio nor Spatial Segregation of the Sexes in the Subtropical Dioecious Tree Eurycorymbus cavaleriei (Sapindaceae)

Knowledge of sex ratio and spatial distribution of males and females of dioecious species is both of evolutionary interest and of crucial importance for biological conservation. Eurycorymbus cavaleriei, the only species in the genus Eurycorymbus (Saplndaceae), is a dioecious tree endemic to subtropical montane forest in South China. Sex ratios were investigated in 15 natural populations for the two defined ages (young and old). Spatial distribution of males and females was further studied in six large populations occurring in different habitats (fragmented and continuous). The study revealed a slight trend of malebiased sex ratio in both ages of E. cavaleriei, but sex ratio of most populations (13 out of 15) did not display statistically significant deviation from equality. All of the four significantly male-biased populations in the young class shifted to equality or even female-biased. The Ripley's K analysis of the distribution of males with respect to females suggested that individuals of the opposite sexes were more randomly distributed rather than spatially structured. These results suggest that the male-biased sex ratio in E. cavaleriei may result from the precocity of males and habitat heterogeneity. The sex ratio and the sex spatial distribution pattern are unlikely to constitute a serious threat to the survival of the species.     

Mating System in a Low-density Natural Population of the Dioecious Wind-pollinated Patagonian Cypress

The mating system of a species is an essential factor that determines the genotypic frequencies of its populations in each generation. Thus, knowledge in this regard is important in the application of practical measures in conservation and forest tree breeding. Austrocedrus chilensis (D.DON) PIC. SER. ET BIZZARRI is a member of the Cupressaceae native to the Andean–Patagonian Forest of Argentina and Chile with regional economic importance. It is a dioecious tree with pollen and seeds distributed by wind. Isozyme markers were utilized to study the mating system of this species through the survey of individual effective pollen clouds in a natural low-density population. If random mating occurs, effective pollen clouds that pollinate single seed trees are expected to be genetically homogeneous. The classical HardyWeinberg test of panmixia was also performed. Although it failed to reject random mating, the analysis of the pollen clouds showed that this mating pattern does not occur. Evidence of locally distributed heterogeneous pollen clouds is presented. The two methods are critically compared.     

Sex ratio and spatial pattern of males and females in the dioecious sandhill shrub, Ceratiola ericoides ericoides (Empetraceae) Michx

Sex ratio, size, age, and spatial pattern were investigated for males and females of the dioecious shrub Ceratiola ericoides ericoides (Empetraceae) Michx. within seven mapped populations in Georgia and South Carolina, USA. Among the sites studied, two are regularly burned and one site long-unburned. Age was estimated from node counts of individual shrubs. Only one (fire-suppressed) population showed a female-biased sex ratio, while all others did not differ significantly from 1:1. Mean age estimates did not differ between sexes at any site nor did mean shrub canopy diameter. Bivariate Ripley’s K analysis with a null hypothesis of random labeling was used to investigate whether any of the mapped populations exhibited spatial segregation of the sexes (SSS). No population showed strong evidence of SSS. Rather all sites but one showed males and females to be associated (though not significantly) at a scale of 1–10 m. At a scale of 10–35 m male and female shrubs were located randomly with respect to one another at all sites.     

山西稀有濒危植物脱皮榆群落的种间分离

通过对山西太岳山脱皮榆群落1 hm²样地内出现的14种乔木进行调查,在应用ArcGIS软件分析每个个体的最近邻体植株的基础上,采用N×N最近邻体列联表及其2×2列联表截表的方法和Pielou分离指数计算分析了脱皮榆群落的种间分离规律,并根据种间分离情况以及物种对环境的适应方式,利用PCA排序将样地中14个物种进行了生态种组的划分。结果表明:（1）该群落中出现的14种乔木构成的91个种对中,随机毗邻种对占绝大多数（74.73%）,正分离种对较少（23.07%）,负分离种对极少（2.20%）,群落趋于稳定。（2）群落的种间分离在不同种之间存在着一定的差异,脱皮榆仅与其他树种随机毗邻;正分离常发生在群落中的优势种之间,而负分离常发生在群落中的伴生种之间。（3）种间分离与群落的生境异质性和物种的生态需求具有密切的关系,即两个具有不同生境要求的物种之间常常发生正分离,而具有相同或相似生境要求的物种之间常常发生负分离。（4）脱皮榆群落中14种乔木可划分为3个生态种组。研究认为,脱皮榆群落内物种的总体分离规律为全面不分离。由生境异质性、物种间不同的生物学特性和生态需求为基础的种间关系可能是维持太岳山脱皮榆群落稳定共存的机制之一。     

雌雄异株植物长梗柳传粉系统和生殖策略研究

为探讨长梗柳(Salix dunnii)的传粉系统和不同性别的生殖投资策略,对居群性别比例、花部特征和访花昆虫进行了调查和观察,采用气相色谱-质谱联用技术(GC-MS)检测了花序的挥发性成分。结果表明,东边村居群的性别比例显著偏雄性(♂∶♀=1.28∶1, P < 0.05), 郭墩村和高地村的居群的性别比偏离不显著; 长梗柳雄株枝条的花序数显著多于雌株, 单花序的雄花数显著多于雌花, 雌花序平均长度显著大于雄花序; 长梗柳传粉系统是虫媒和风媒混合传粉系统, 主要访花昆虫为中华蜜蜂(Apis cerana)且显著偏好访问雌花; 吸引中华蜜蜂的挥发成分β-石竹烯的相对含量在雌花序中显著高于雄花序, 雌花序还具有β-榄香烯和芳香醇等吸引中华蜜蜂的特有挥发成分。因此, 长梗柳雄株在开花阶段投入了较多的资源产生雄花, 可能利于风媒传粉; 而雌株通过增加吸引传粉者的挥发成分来抵抗“传粉者限制”的效应, 可能利于虫媒传粉, 通过风媒和虫媒有效组合提升其繁殖效率。     

Male gametophyte development and two different DNA classes of pollen grains in <Emphasis Type="Italic">Rumex acetosa</Emphasis> L., a plant with an XX/XY<Subscript>1</Subscript>Y<Subscript>2</Subscript> sex chromosome system and a female-biased sex ratio

Female-biased sex ratio is an interesting phenomenon observed in Rumex acetosa, a dioecious plant with an XX/XY₁Y₂ sex chromosome system. Previous authors have suggested that the biased sex ratio in this species is conditioned not only postzygotically (sex-differential sporophytic mortality) but also prezygotically, because the sex ratio of seeds is also female-biased, although to a lesser extent than the sex ratio of flowering plants. The mechanisms underlying female bias in Rumex seeds are only poorly understood. To gain more knowledge of them, we analysed male gametophyte development and used flow cytometry to determine the frequency of female-determining (n = 7, A + X) and male-determining (n = 8, A + Y₁Y₂) pollen grains in anthers. Embryological studies showed a regular course of male gametophyte development in R. acetosa. There were no signs of degeneration of microspores or disturbances in pollen divisions (irregular nuclei, micronuclei, delayed chromosomes and anaphase bridges). The Alexander test revealed only 1.6% nonviable pollen grains within anthers. All mature pollen grains were uniformly equipped with starch granules. The two sexes were shown to substantially differ in nuclear 2C DNA amount in somatic tissues (7.00 pg in 2A + XX females and 7.50 pg in 2A + XY₁Y₂ males), and two clearly different DNA classes of mature pollen grains, with lower and with higher DNA amounts (16.8% difference) were found. Most probably the grains with the lower DNA amount possess seven chromosomes, and grains with the higher DNA amount eight of them. The quantitative ratio of these grains in anthers at anthesis was 1:1.2, very close to the sex ratio of seeds observed by the majority of previous authors. All these observations support the opinion that the sex-ratio bias in Rumex is determined prezygotically to some extent.     

Large-Scale Temporal Changes in Spatial Pattern During Declines of Abundance and Occupancy in a Common Moth

We examined the changes in spatial pattern that accompanied the population decline of the garden tiger moth, Arctia caja (L.) in Britain between 1968 and 1999 using Spatial Analysis by Distance Indices (SADIE) techniques. A principal co-ordinate analysis of all pair-wise spatial associations between years indicated three groupings of years: 1969–1978,1979–1990,1991–1999, which revealed three phases during the population decline: an early period with highly structured spatial pattern; a middle period with nearly random distribution overall; and a recent period with highly structured spatial pattern but small abundance overall. The change in spatial structure in the early 1980’s accompanied rapid changes in abundance but preceded a sharp decline in occupancy and confirms that the sharp decline in abundance included decreases from widespread high-density sites. Perhaps unusually, A. caja varied from spatially aggregated to randomly distributed and back to spatially aggregated, all while its abundance declined sharply. Present distribution pattern may reflect past abundance changes poorly in this species. Areas showing the greatest variation in abundance displayed the greatest range in spatial structure, but also the greatest stability of spatial pattern, indicating changes between extremes of spatial pattern occurred slowly. SADIE techniques are a powerful method to quantify temporal changes in spatial pattern and relate them to temporal changes in abundance.     

Spatial Segregation of Congeneric Invaders in Central Pennsylvania, USA

Carduus acanthoides and Carduus nutans (plumeless and musk thistles) are among the most noxious weeds in the United States of America, presenting a serious challenge in cropping and pasture systems. Unfortunately, a lack of detailed spatial distribution information hampers both our ability to understand the factors affecting their invasive success, and the effectiveness of monitoring and management efforts. To examine patterns of distribution and co-occurrence at a local level, we sampled a 5000 km² area of central Pennsylvania that cut a transect across known areas of C. acanthoides and C. nutans infestation. A number of potential environmental explanatory variables were recorded and analyzed to examine whether they correlated with observed species distribution patterns. Patterns of forest density and spatial aggregation of the thistles were the primary covariates that significantly impacted both species’ distributions. The survey established that the frequency of sightings for each species diminished as the ranges converged, with only brief overlap: the two species are strongly negatively correlated in space. Understanding environmental correlates of infestation and the pattern of spatial dissociation of these two invasive species is an important step towards an improved understanding of the mechanisms underlying their invasive potential, and hence towards effective weed control.     

Within-population spatial variation in pollinator visitation rates, pollen limitation on seed set, and flower longevity in an alpine species

Pollen limitation through insufficient pollen deposition on stigmas caused by too infrequent pollinator visitation may influence the reproductive outcome of plants. In this study we investigated how pollinator visitation rate, the degree of pollen limitation, and flower longevity varied spatially among three sites at different altitudes within a population of the dwarf shrub Dryas octopetala L. in alpine southern Norway. Significant pollen limitation on seed set only occurred at the mid-elevation site, while seed set at the other sites appeared to be mainly resource limited, thus indicating a spatial variation in pollen limitation. There was no association between the spatial variation in the extent of pollen limitation and pollinator visitation rate to flowers. However, pollinator visitation rates were related to flower longevity of Dryas; sites with low visitation rates had long-lived flowers and vice versa. Thus, our results suggest within-population spatial co-variation between pollinator visitation rates, pollen limitation, and a developmental response to these factors, flower longevity.     

Flower morphology of the resurrection plant Chamaegigas intrepidus Dinter and some of its potential pollinators

The resurrection plant Chamaegigas intrepidus Dinter (Scrophulariaceae) is a rare endemic species growing in ephemeral rock pools on isolated granite outcrops in Central Namibia. Previous studies suggested a high degree of gene flow within individual pools. Therefore, floral morphology, pollination and potential pollinators of the plant species were studied while the plants were at full flower set.The zygomorphous, intensively scenting flowers carry dense layers of trichomes (400–1600 mm⁻²) on the lower lip, similar to well-known oil-flowers. Four species of potential pollinators could be found. Two of them the Hymenoptera, Apis mellifera and Liotrigona bottegoi, were found to be rare, whereas beetles of the genus Condylops spec. (Condylops erongoensis and a new species) showed up with numbers up to 50 individuals m⁻² in some pools, visiting the flowers most frequently. Individuals of Liotrigona and Condylops were proven to carry pollen of Chamaegigas after their flower visits. The results are discussed in relation to the genetic variability of the plant and the phenomenon of pollen limitation in rare plant species.     

Sex ratio variation and spatial segregation of the sexes in populations ofRumex acetosa andR. acetosella (Polygonaceae)

Populations ofRumex acetosa andR. acetosella were studied during two growth seasons. The ramet sex ratios ofR. acetosa were always female-biased. InR. acetosella the sex ratios expressed more variation but were mostly female-biased. In both species the sex ratios commonly varied between subpopulations reflecting a partial spatial segregation of the sexes. No marked differences between sexes in vegetative vigour were detected in either species. Interactions between sex ratios, various soil characteristics and population densities were determined. Possible mechanisms for causing biased sex ratios and partial spatial segregation of the sexes are discussed.     

Reproductive consequences of mate quantity versus mate diversity in a wind-pollinated plant

Since most pollen travels limited distances in wind-pollinated plants, both the local quantity and diversity of mates may limit female reproductive success. Yet little evidence exists on their relative contribution, despite the importance of viable seed production to population dynamics.To study how variation in female reproductive success is affected by the quantity versus the diversity of surrounding mates contributing pollen, we integrated pollination experiments, data on natural seed set and seed viability, and AFLP genetic marker data in the wind-pollinated dioecious clonal forest herb Mercurialis perennis.Pollination experiments indicated weak quantitative pollen limitation effects on seed set. Among-population crosses showed reduced seed viability, suggesting outbreeding depression due to genetic divergence. Pollination with pollen from a single source did not negatively affect reproductive success. These findings were consistent with results of the survey of natural female reproductive success. Seed set decreased with the distance to males in a female plants’ local neighborhood, suggesting a shortage of pollen in isolated female plants, and increased with the degree of local genetic diversity. Spatial isolation to other populations and population size did not affect seed set. None of these variables were related to seed viability.We conclude that pollen movement in M. perennis is likely very limited. Both male proximity and the local degree of genetic diversity influenced female reproductive success.     

珍稀濒危植物黄杉种群结构与空间分布格局北大核心CSCD

为了解珍稀濒危植物黄杉种群的生存现状和更新机制,对贵州省威宁县黄杉自然保护区内天然分布的黄杉(Pseudotsuga sinensis)群落的结构特征和空间分布格局进行了研究。结果表明,黄杉种群的中龄级个体数较多,幼龄级和老龄级个体相对较少,呈典型的“∩”型结构。种群结构动态指数V_(pi)(13.49%)和V′_(pi)(0.05%)均大于0,种群属于增长型,但增长幅度逐渐降低,对外界干扰敏感度较高。种群存活曲线趋于Deevey-II型,生命期望值单调下降,死亡率呈“V”型,有2个死亡高峰,第1个出现在I龄级,第2个出现在IX龄级。黄杉种群除部分样地(Q2和Q7)呈均匀分布外,大部分样地呈集群分布;随龄级的增加,空间分布格局由集群分布逐渐趋向于均匀分布。因此,黄杉种群濒危的主要因素是幼树个体无法及时补充种群,建议加强对幼苗的抚育和通过适度干扰,促进黄杉种群的更新。     

Ecological Segregation and Population Structuring of the Cormorant Phalacrocorax carbo in Europe, in Relation to the Recent Introgression of Continental and Marine Subspecies

Populations of the “continental” Great Cormorant P. c. sinensis have expanded from north-eastern Europe towards the western part of the range of the “marine” P. c. carbo breeding in the United Kingdom and France. The aim of the study was to test the hypothesis of ecological segregation between subspecies by analysing the structuring of the European populations. Sequencing the mtDNA of 231 birds belonging to 20 colonies revealed 38 haplotypes based on 25 polymorphic sites (5.76% sequence divergence). P. c. sinensis (“S”) was well confirmed, but usual P. c. carbo formed two coastal populations, the real P. c. carbo “C” mainly in the western part of the range (United Kingdom, coastal France), and also in Norway and Sardinia, and “N”, branched to the Japanese Cormorant P. capillatus and probably isolated by glaciations, mainly present in the Nordic range (Norway, but also on the coasts from Sweden to Brittany), we named P. c. norvegicus. In a variable position in the trees but close to C is a group of undetermined origin haplotypes, named U, also present in both traditional ranges. The new tree-nesting colonies in Brittany are clearly a mixture of S and the two clades C and N previously described as P. c. carbo, with a decreasing proportion of C + N between 1993 (67%), 1996 (60%) and 2002 (33%) for the pioneering Grand-Lieu colony. These results confirmed the current introgression of continental populations in the western range, with probable hybridization. Although the subspecies can switch habitats locally due to social behaviour and migrations, the ecological segregation between the two usual subspecies appears to be largely confirmed in Europe.     

The effect of host size on the sex ratio of Syngaster lepidus, a parasitoid of Eucalyptus longhorned borers (Phoracantha spp.)

The solitary larval ectoparasitoid, Syngaster lepidus Brullé, parasitizes the cryptic larvae of two wood-boring beetles, Phoracantha recurva Newman and Phoracantha semipunctata F. The objective of this study was to determine how the female parasitoids allocated the sex of progeny when presented with larval hosts of uniform size classes. Host size was directly correlated with age of the Phoracantha larval hosts. Groups of Phoracantha larvae of a single age class (2-, 3-, 4-, or 5-week-old) were exposed to parasitoids, and sex ratios of the resulting parasitoid progeny from each host age class were determined. A significant relationship was observed among the sizes of P. recurva and P. semipunctata hosts and the sex ratio of emerging parasitoids. Parasitized 2-week-old beetle larvae of both Phoracantha spp. produced only male S. lepidus progeny, whereas older larval hosts produced increasing proportions of female parasitoids (up to 80% females from 5-week-old hosts). Two-week-old Phoracantha larvae of both species produced fewer parasitoids than host larvae 3–5-week-old. The size of parasitoid progeny consistently increased with host larval age (size), and female parasitoids were larger than males across all host size classes. Male S. lepidus developed in approximately 25 days from 2-week-old hosts, and 19–21 days in 3–5-week-old hosts. Female S. lepidus developed in 22–25 days, with developmental time increasing with host size.     

Environmental conditions affect sex expression in monoecious, but not in male and female plants of Urtica dioica

Urtica dioica is a sub-dioecious plant species, i.e. males and females coexist with monoecious individuals. Under standard conditions, seed sex ratio (SSR, fraction of males) was found to vary significantly among seed samples collected from female plants originating from the same population (0.05–0.76). As a first step, we investigated the extent to which SSR and sex expression of male, female, and monoecious individuals is influenced by external factors. We performed experiments to analyse: (1) whether the environment of a parental plant affects the sex ratio (SR) of its offspring, (2) whether SSR can be affected by environmental conditions before flowering, and (3) whether sex expression of male, female and monoecious plants that have already flowered can be modified by environmental conditions or by application of phyto-hormones. Within the range of our experimental design, SSR was not influenced by external factors, and gender in male and female plants was stable. However, sex expression in monoecious plants was found to be labile: flower sex ratio (FSR, fraction of male flowers) differed considerably between clones from the same individual within treatments, and increased toward 100% maleness under benign conditions. These results provide strong evidence that monoecious individuals are inconstant males, which alter FSR according to environmental circumstances. In contrast, we consider sex expression in male and female individuals to be solely genetically based. The observed variation in SSR between maternal parents cannot be explained by sex-by-environment interactions.     

榕树高度专性共生体系内影响传粉蜂子代繁殖的因素

为探讨影响传粉蜂子代数量及性比的因素,以广州地区分布的粗叶榕(Ficus hirta Vahl)及其传粉小蜂爪哇榕小蜂(Valasia javana Mayr)为材料,采用自然收蜂与控制放蜂试验进行研究。结果表明,果内的榕小蜂群落随季节更替发生显著变化,非传粉蜂的介入、季节差异使雌蜂间的干扰强度不同,导致传粉蜂子代数量发生变化,其中雌蜂间的干扰会使传粉蜂性比显著升高,而非传粉蜂的介入对传粉蜂性比的影响不大,传粉蜂仍能正常地进行繁殖。另外,传粉蜂在雌花期雄花序内的产卵和存活时间一般较短,约为15 h;传粉蜂子代在干、湿季的雄花序内的发育时间差异显著,干季时间长,湿季时间短。这表明传粉榕小蜂进化出了适应广州地区季节变化的繁殖策略。     

Planting densities and bird and rodent absence affect size distributions of four dicots in synthetic tallgrass communities

Variability in the size distributions of populations is usually studied in monocultures or in mixed plantings of two species. Variability of size distributions of populations in more complex communities has been neglected. The effects of seeding density (35 or 350 seeds/species/m²) and presence of small vertebrates on the variability of size distributions were studied for a total of 1,920 individuals of 4 species in replicated synthetic communities of 18 species in northern Illinois. End-of season height and above-ground biomass were measured for prairie perennials Dalea purpurea (purple prairie clover), Echinacea purpurea (purple coneflower), Desmanthus illinoensis (Illinois bundleflower) and Heliopsis helianthoides (early sunflower). Variability in biomass distribution of the four target species was twice as great at low than at high densities when small vertebrates were excluded. Our results suggest that inter- and intraspecific competition may affect all individuals more under high-density conditions, thereby reducing the variability in their biomass distributions within this community. This result, a consequence of plant-plant interaction, is obscured when small birds or mammals are present, presumably because either or both add variance that overwhelms the pattern.     

Male Dominance Rank,Female Mate Choice and Male Mating and Reproductive Success in Captive Chimpanzees

Mating and consequently reproductive success in male vertebrates are predominantly determined by intermale competition and female mate choice. Their relative importance however, is still poorly understood. We investigated the interrelationship between male dominance rank — a formal indicator of male competitive ability — female mate choice, and male mating success in a multimale-multifemale group of captive chimpanzees. In addition, we examined the relationship between male dominance rank and reproductive success determined by genetic paternity analysis over a 13-yr period in the same captive population. We related the frequencies of sociosexual behaviors to the female anogenital swelling stage and female fertile phase as determined by urinary and fecal progestogen analysis. Rates of behaviors in both sexes increased with increasing intensity of female swelling, but they were not influenced by the timing of the fertile phase. Male mating success was clearly related to male dominance rank, with high-ranking males performing the overwhelming majority of copulations. This was mainly due to both rank-related rates of male soliciting behavior and intermale aggressiveness during the period of well-developed female anogenital swelling. Although females solicited copulations mainly from the high-ranking males and thus expressed a mate choice based on rank, their overall contribution in initiating copulations and thus influencing male mating success was low. The data on paternity from the population, which always contained 4 adult males, revealed that -males sired the majority (65%) of offspring. We conclude, that male dominance rank is an important determinant of male mating and reproductive success in captive (and presumably wild) chimpanzees and that female mate choice is of minor importance in modulating male reproductive outcome.     

Effect of population spatial structure on pollination and seed set of a clonal distylous plant,Persicaria japonica (Polygonaceae)

In order to assess the mechanisms through which the spatial structure of the population influences female reproductive success, spatial distribution of clones, degrees of limitation of legitimate (inter-morph) pollination, type and abundance of pollen loaded on the stigmas, and seed set were measured for many clones of two natural populations of the distylous clonal plant,Persicaria japonica. Within the populations, according to the spatial relation to the nearest opposite morph clone, individual clones were assorted into two spatial types,i.e., clones that congregated with clones of the opposite morph (congregating clones), and clones that occurred singly at a considerable distance from the nearest opposite-morph clone (single clones). The pollination success,i.e., the proportion of legitimately pollinated flowers, and seed set were severely limited in the single clones compared to the congregating clones. Since artificial legitimate pollination improved the seed set in single clones, at least to some degree pollination failure was responsible for the reduced seed set in the single clones.