Clonal and genetic structure of two Mexican oaks: Quercus eduardii and Quercus potosina (Fagaceae)

Quercus eduardii and Q. potosina are dominant oak species in Sierra Fría, Aguascalientes, Mexico. These species have been exploited for multiple purposes since the 16th century. Both species produce clonal offspring through root suckering and acorns through sexual reproduction. To understand clonality for the implementation of the most adequate actions for the conservation of these species, we addressed the following questions: (a) what is the spatial clonal structure of both species? (b) How much clonal and genetic diversity is maintained in these species? Random Amplified Polymorphic DNAs (RAPDs) were used as molecular markers for these analyses. Genets of both species have few ramets and these grow close the parent tree. Autocorrelation analyses at the ramet level showed an aggregated distribution at short distances and a random spatial distribution at larger distances. Also, at the genet level the autocorrelation analyses showed a random distribution. Clonal diversity was high in both species (Q. eduardii: D=0.963, G/N=0.60; Q. potosina: D=0.985, G/N=0.65). Genetic diversity was high within populations (Q. eduardii: H _e =0.33±0.11; Q. potosina: H _e =0.35±0.11). Low levels of genetic differentiation among populations were observed (Q. eduardii ? _st =0.19, P < 0.002; Q. potosina ? _st =0.13, P < 0.002). Both species maintain high levels of clonal and genetic diversity, probably due to successful sexual reproduction, which allows gene flow among populations. Conservation and/or reforestation programs must include seed collections and germplasm banks. Due to the small genet size and the high clonal diversity of these species, seeds can be collected in any place in Sierra Fría, Aguascalientes.     

Heavy metals modify costs of reproduction and clonal growth in the stoloniferous herb Potentilla anserina

We examined costs of sexual reproduction and clonal propagation, and their consequences for resource allocation in the clonal stoloniferous herb, Potentilla anserina, a typical pioneer species in disturbed areas. We used heavy-metal treatment in soil to create unfavourable growing conditions, because costs of reproduction are more likely to be expressed when resources are limited. We also studied whether heavy metals affect the plasticity of clonal growth form that enables the plants to avoid poor growing conditions. Ramets collected from field were grown in a greenhouse under the heavy-metal treatment consisting of a control and two levels of heavy-metals added in soil. Clonal propagation was costly in terms of total biomass of flowering ramets. Also the costs of sexual reproduction were detected in flowering ramets. Contrary to our predictions, the costs of flower production were visible in the control but not in the heavy-metal contaminated plants. Only the flowering ramets were able to produce longer stolons under heavy-metal stress, but the stolon biomass was not affected by heavy metals. Results indicate that clonal propagation and sexual reproduction may be costly for P. anserina. However, the costs are modified by heavy-metal contamination.Co-ordinating editor: J. Tuomi     

Drosophila do not skew offspring sex ratio as predicted by trivers and willard (Diptera: Drosophilidae)

Based on both previously published literature and results reported here, it appears thatDrosophila melanogaster meet the explicit assumptions of the Trivers and Willard offspring sex allocation model. However, contrary to the model's predictions, offspring sex ratio was not significantly affected when we manipulated factors that influence offspring quality. We suggest that contrary to implicit predictions of offspring sex ratio models,Drosophila may lack the genetic plasticity to readily alter sex ratio.     

Food supplementation affects colony-level life history traits in the annual social wasp <Emphasis Type="Italic">Polistes metricus</Emphasis> (Hymenoptera,Vespidae)

Summary A field population of Polistes metricus Say near St. Louis, Missouri was supplemented with dilute Apis mellifera honey and Trichoplusia ni caterpillars during the entire colony development period. Offspring were collected at two times to coincide with emergence of worker and reproductive broods. Food supplementation had no effect on nest size, the number of worker offspring, or the size of workers. Supplemented colonies did produce more females in August but female size was unaffected by supplementation. Supplementation had no effect on the number of males produced, but males were slightly larger on supplemented nests. We interpret these findings in the context of social insect life history theory.Received 30 June 2003; revised 9 December 2003; accepted 18 December 2003.     

夜光藻有性繁殖研究进展

夜光藻是全球最主要的赤潮生物之一,也是我国近海常见的浮游甲藻。根据营养方式分为异养的红色夜光藻和混合营养的绿色夜光藻,前者广泛分布于温带和亚热带近岸水域,后者仅分布于热带西太平洋、阿拉伯海、阿曼湾和红海。夜光藻的生活史包括无性繁殖和有性繁殖过程。少部分营养细胞自发转变为配子母细胞,启动了有性繁殖。每个配子母细胞可形成大量配子,具有横沟、纵沟和2根鞭毛,形态与裸甲藻接近。配子两两融合形成合子,合子不经过休眠孢囊阶段直接发育成新的营养细胞。目前,对配子母细胞形成的调控机制、合子发育的影响因素的认识还存在分歧。研究发现,营养细胞经过一定次数的二分裂后都会转变为配子母细胞,而配子的存在能够中止此过程,使营养细胞继续进行二分裂。因此,有性繁殖可能通过产生新个体对种群增长做出贡献,还可能通过释放配子维持无性繁殖,进而促进种群增长。配子在相模湾水域全年都有分布,其丰度峰值与营养细胞丰度峰值同步或提前出现,配子的大量出现可能是赤潮形成的必要条件。对有性繁殖的研究佐证了夜光藻在甲藻的系统进化中处于较为古老的地位。此外,还简单介绍了研究夜光藻有性繁殖的主要方法,回顾了国内的夜光藻研究,并对相关研究进行了展望。     

Phenotypic Variations in the Life History of Two Clones of Macrobiotus richtersi (Eutardigrada, Macrobiotidae)

A comparative study of life history traits of two clones (CDMr01 and CDMr02) of a triploid thelytokous apomictic population of the eutardigrade Macrobiotus richtersi has been carried out. Both clones were reared under the same lab conditions: temperature of 14 °C, photoperiod of 12 h/12 h (L/D), and nematodes ad libitum as food. Statistical analysis of the life history traits considered has indicated interclonal variability. The two clones were significantly different in the number of eggs per clutch (fertility), number of eggs laid per female per life span (fecundity), hatching percentage of eggs and hatching time. Similarities between clones have been observed with regard to life span, total number of ovipositions per life span, and age at first oviposition. In addition, significant differences in hatching time, with eggs hatched over a long period, were found within each clone. Interclonal variability in life history traits indicated the effects of genetic factors, whereas intraclonal variability reflected the effects of environmental factors. The evolutionary and adaptive significance of the life history phenotypic variations is discussed.     

No long-term costs of meristem allocation to flowering in stoloniferous Trifolium species

Clonal plants propagate by means of clonal growth and sexual reproduction. The commitment of meristems to branching and flowering govern the expression of these two mutually exclusive life-history functions. We used a modelling and an experimental approach to examine the consequences of a structural trade-off between flowering and clonal growth on future growth and fitness in stoloniferous species with a determinate module architecture. The model revealed negative effects of flowering on vegetative growth due to a structural trade-off at the meristem level. Total fecundity was maximized at intermediate flowering frequencies. In addition, optimal meristem commitment to flowering depended strongly on the time available for growth and reproduction. This indicates an interaction between optimal flowering frequency, the length of the growing period and the rate of ontogenetic development. The greenhouse study made use of 15 genotypes of two closely related, stoloniferous Trifolium species. Despite the existence of a structural trade-off at the meristem level, we found no evidence for costs of flowering on the whole-plant level. High allocation to flowering did not result in reduced plant performance (biomass and module production) and total fecundity, indicating that there were no demographic costs of meristem investment to different life-history functions. Flowering frequencies never exceeded the model prediction for optimal commitment of meristems to sexual reproduction, suggesting strong past selection to eliminate high levels of meristem allocation to flowering. Hence, clonal growth seems to have evolutionary priority over sexual reproduction in our species. This revised version was published online in November 2006 with corrections to the Cover Date.     

Life history, aspects of reproductive biology and production of Corophium orientale (Crustacea: Amphipoda) in Monolimni lagoon (Evros Delta, North Aegean Sea)

Monthly samples of Corophium orientale were collected during February 1998–February 1999 in both parts of Monolimni lagoon (0.3 < Sal. < 6 psu, 2 < Temp. < 28.5 °C). Corophium orientaleshowed a semiannual life cycle. In the southern part, breeding occurred from early spring to mid autumn having three peaks, in early spring, early summer and early autumn, and three cohorts were produced, a spring cohort, a summer cohort and an overwintering one. In the shallower innermost northern part of Monolimni lagoon, breeding peaked in mid-spring and, also, in early autumn, and two discrete cohorts, a spring and an overwintering one, were produced. A lack of large individuals, attributed to a temporary size – selective predation by migrating shorebirds, was observed during summer. That lack possibly contributed to the hiatus in reproduction. Photoperiod seemed to be a more important cue than temperature in the initiation of the reproductive cycle, while extremely low salinities (<1 psu) did not deter breeding. Females attained maturity at a smaller size in late spring and, especially, in summer than in early spring at lower temperatures. Brood size was a function of females body size. Females, matured during summer at high temperatures, showed the lowest brood size, body length ratio. Mean brood size was small (12–13 early embryos) and embryo loss during development high (54%), possibly due to a negative effect of low salinities. A 1:1 sex ratio existed in the small body length classes, but females preponderated in the large ones. The spring cohort in the southern part, which developed at moderate temperatures, showed the highest growth rate (40 m day^–1). Secondary production of C. orientalecalculated by Hyness method gave a mean annual density of 4562.5 and 9327.6 ind. m^–2, a mean annual crop (B) of 1.03 and 2.67 g DW m^–2, an annual production (P) of 6.91 and 22.54 g DW m^–2 and a P/B ratio of 6.7 and 8.4 in the northern and southern part of the lagoon, respectively.     

Sexual reproduction and life cycle of Ceratium furcoides (Dinophyceae) in situ in the lake Plußsee (F.R.)

The life cycle of Ceratium furcoides (Levander) Langhans which features sexual reproduction is described for the first time in situ from the lake Plußsee (northern West Germany). Anisogamic copulation occurs during the bloom period in July–August by incorporation of the male gamete by the female gamete, resulting in an overwintering planozygote. The planozygote develops into a benthic hypnozygote which germinates in spring to establish a planomeiocyte. The morphology and structure of the stages of the life cycle are described using light and scanning electron microscopy.     

Differences in demographic parameters among electrophoretic clones of Daphnia obtusa Kurz (Crustacea: Cladocera)

In an 18-month electrophoretic study, a Daphnia obtusa population that recently colonized Lake Orta (a large, severely polluted lake in Northern Italy) showed no genetic variation.Populations from other localities were sampled. From clones established by single females, genotype differences were determined by two life table experiments (using Lake Orta and Lake Maggiore water as a culture medium).As expected, in the Lake Orta water the colonizing clone (LO) had longer survival, produced more newborns and had a larger rate of increase than the other clones. In the Lake Maggiore water the LO clone still fared better than the other clones.     

Causes and consequences of extreme variation in reproductive strategy and vegetative growth among invasive populations of a clonal aquatic plant, <Emphasis Type="Italic">Butomus umbellatus</Emphasis> L. (Butomaceae)

The mode of reproduction may influence the spread of invasive species by affecting evolutionary potential and dispersal ability. We sampled 51 introduced North American populations of the clonal aquatic plant Butomus umbellatus L. (flowering rush) and found extreme variation in sexual fertility caused by polyploidy. Populations consisted of diploids that produced thousands of viable seeds or of sexually sterile triploids. Although a trade-off between sexual and clonal reproduction predicts that the sexual sterility of triploids would be compensated for by greater clonal reproduction, a greenhouse experiment involving eight diploid and 10 triploid populations showed that diploid plants not only invest substantially in sexual structures but also make hundreds of tiny clonal bulbils on both rhizomes and inflorescences. In contrast, triploids do not make bulbils and have very limited scope for clonal multiplication and dispersal. Diploid populations were more frequent than triploid populations, especially in the Great Lakes region. This is probably because of the difference between cytotypes in clonal rather than sexual reproduction, as genetic analyses indicate a general lack of sexual recruitment in North America. Although triploids were less common, they have a wider geographical distribution. This could be due to a greater ecological tolerance resulting from polyploidy. However, genetic evidence suggests that triploids have become widespread via their use in and escape from horticulture. North America is being colonized by two distinct forms of B. umbellatus that differ strongly in reproductive strategy as well as the vectors and pathways of invasion.     

不同年龄巴山木竹种群克隆结构

很多竹类植物是典型的克隆植物,也是大熊猫的食物。研究典型竹子种群克隆结构的形成和发展对竹林的生产和抚育具有理论和实践意义,可为预测该竹林群落的演替趋势和大熊猫保护提供科学依据。利用SSR标记研究不同年龄A(7龄)、B(30龄)和C(60龄)巴山木竹种群的克隆结构和多样性,探讨小尺度范围内不同年龄巴山木竹种群的克隆结构及斑块的建立和发展。8对SSR引物共扩增出了118个位点,3个种群样地的256个样本共检测到了49个克隆(基因型),A、B和C种群分别检测出31、10个和8个克隆。随着种群年龄的增长,巴山木竹克隆面积增加,克隆数量减少;A和B样地各克隆分布格局为团块状,而C样地克隆既有团块状又有离散状。这一结果显示出在幼苗定居的初期,基株可能以短距离的克隆延伸为主从而呈现出团块状;而随着年龄的增长,克隆面积不断扩大,当复轴混生型的巴山木竹克隆受到强大的压迫时,基株可能会进行较多的单轴和长距离克隆延伸,呈现出离散状。Mantel检测和空间自相关分析都支持3个样地在小尺度范围内存在明显的克隆空间遗传结构。3个样地在10 m等级下显著的正相关空间遗传结构距离为3.1、28、48 m,X-轴截距为9.051、30.698和50.536,空间自相关系数的范围分别为0.1—0.167、0.008—0.703和0.006—0.735。由此可推断,随着年龄的增长,巴山木竹克隆斑块的规模在不断地扩大,同一克隆的分株数量增加,在均匀取样情况下,正相关空间遗传结构距离范围内取到具有相同基因型的可能性越大。A、B和C 3样地的基因型比率(G/N)为1、0.14和0.055,Simpson多样性指数(D)分别为1、0.876和0.744。这说明巴山木竹幼苗期基因型比例远远高于成年的竹林,随着年龄的增长巴山木竹克隆多样性虽有所降低,但由于有性繁殖的作用仍然保持了较高的多样性。聚类和主坐标分析均表明总体上各样地的克隆被聚为一类,但不同样地少数克隆的基因型有重叠和聚集,可推断出不同巴山木竹种群之间可能存在着基因流动和近似的克隆起源。     

ÜberHydrianum viride (Characiaceae,Chlorophyceae), seine fortpflanzung und taxonomie

The little known epiphytic algaHydrianum viride was studied and pictured. The morphology and the variability of the vegetative cells are described in detail and compared with the observations of other authors. For the first time typical biflagellate zoospores of the chlorophycean-type have been recognized and the course of the asexual reproduction is studied. The residual protoplasm, that is the proximal half of the zoosporangium protoplast, growth up to the original size, typical for the genusHydrianum. The life cycle, especially the settling down of the zoospores, is described.Hydrianum viride belongs to the characteristic inhabitants of peaty waters; it belongs together with the host alga,Microspora loefgrenii, to the dominants of algal association of peat-springs. At last the taxonomic position and the synonyma of this organism are discussed.

     

Induction of sexual forms in the rose aphid Macrosiphum rosae

The rose aphid, Macrosiphum rosae (L.), was tested for its ability to produce sexual forms on rose leaves, after induction by environmental conditions in the field and in the laboratory. Clones were collected in Tübingen, Federal Republic of Germany, and in south-eastern New South Wales, Australia. The German clones all produced sexual forms, while the response of the Australian clones was weak. There appeared to be a bias in the sex ratio towards females: This is discussed in developmental terms. The environmental and genetic factors influencing the response are considered.     

Life history,resting egg formation,and hatching may explain the temporal-geographical distribution ofArtemia strains in the Mediterranean basin

Life history traits are presented for the sexual species (Artemia tunisiana) and for parthenogenetic diploid and tetraploid strainsA. parthenogenetica reared at 15 °, 24 ° and 29.5 °C.In laboratory cultures, we present evidence that the seasonal appearance of the sexualArtemia tunisiana (the dominant winter-spring population), and of two parthenogenetic populations ofArtemia (the dominant spring-summer populations) in certain Spanish saltworks is controlled by temperature through its effect on reproductive and survival traits. Minimum and maximum reproductive output and survival for the sexual and parthenogenetic populations, respectively, occurred at a typical temperature (24 °C) of the late-spring season when the sexual population is replaced by parthenogenetic forms. Furthermore, the high production and hatchability of cysts from the sexual population at low temperatures (15 °C), and of the parthenogenetic populations at middle temperature (24 °C), indicate the role of dormancy as an adaptation regulating seasonal occurrence.     

What makes a species vulnerable to extinction? Comparative life-history traits of two sympatric snakes

Although it is well known that species vary in their vulnerability to extinction, the reasons are poorly understood. Theory predicts that long-lived species with slow life histories (small litters, slow growth, late maturation) should be at greater risk than short-lived species with high potential rates of increase. This hypothesis was tested by comparing life-history traits of two species of sympatric, elapid snakes: the endangered broad-headed snake, Hoplocephalus bungaroides, and common small-eyed snake, Cryptophis nigrescens. From 1992 to 2000 a mark–recapture study of both species was undertaken in Morton National Park, south-eastern Australia, and this information was used to construct transition matrices for each species. The endangered H. bungaroides was found to mature late (6 years of age), had a high juvenile (54.7%) and adult (81.6%) survival rate, and a long generation length (10.4 years). In striking contrast, the common C. nigrescens matured early (within 3 years), had a lower juvenile (30.4%) and adult (74.4%) survival rate (but higher recruitment rate), and a substantially shorter generation length (5.9 years). Elasticity analyses revealed that H. bungaroides was considerably more sensitive to survival past the age of 2 years (68.6%) than C. nigrescens (37.4%). These results provide support for the hypothesis that species with slow life histories are more vulnerable to extinction.