不同生境下珠芽蓼（蓼科）的繁殖策略比较

在青藏高原横断山区以海拔相同的高山流石滩和高寒草甸中的珠芽蓼（Polygonum viviparum）居群为研究对象,探讨该物种在不同生境条件下的繁殖策略以及无性繁殖和有性繁殖间的关系。结果发现,流石滩居群的珠芽蓼植株高度和珠芽数量显著低于高寒草甸居群,而珠芽和花总数量、花数量和每个花序上的花比例却显著高于高寒草甸居群。研究结果表明珠芽蓼在环境更为恶劣的高山流石滩生境中增加了对繁殖器官和花资源的投资,说明在高山植物中繁殖优先于营养生长,且有性繁殖比无性繁殖具有更为重要的作用。而对每个植株上花数量和珠芽数量的统计结果表明,两者呈显著的负相关关系,进一步证明了同一植株内无性繁殖和有性繁殖的权衡关系。     

Vivipary in Polygonum viviparum: an adaptation to cold climate?

Populations of Polygonurn viviparurn were investigated in the Swiss Alps at 14 sites, ranging from 450 m to 2530 m above sea level. The average length of stems and the mean number of reproductive organs (flowers + bulbils) decreased significantly with increasing altitude. On average, the ratio of flowers to bulbils per inflorescence also declined so that at high altitudes, bulbil production was more pronounced. Increased allocation to vegetative reproduction is discussed as an adaptation to cold climate. It is suggested that enhanced vegetative reproduction might be controlled by incornplete floral induction in high altitudes. In addition variability within and between populations was investigated by isozyme electrophoresis and the examination of bulbil colours. A considerable amount of variability was found in alpine populations. The demonstrated genetic variability showed that in P. viviparum it is likely that minor sexual reproduction is maintained even under alpine conditions. This is reflected in different enzyme phenotypes and different bulbil colours.     

Genetic variation and evolutionary trade-offs for sexual and asexual reproductive modes in Allium vineale (Liliaceae)

Populations of Allium vineale commonly include individuals with very different allocation patterns to three modes of reproduction: sexual flowers, aerially produced asexual bulbils, and belowground asexual offsets. If selection is currently acting to maintain these different allocation patterns there must be a genetic basis for variation in allocation to these three reproductive modes. In addition, negative genetic correlations between reproductive traits would imply evolutionary trade-offs among reproductive strategies. We evaluated the heritability of these allocation patterns by growing 16 clones from a single population in the greenhouse at two levels of fertilization. Bulb mass and the mass and number of bulbils, offsets, and flowers were used as response variables, in addition to the proportion allocated to each reproductive mode. We found evidence of substantial heritable variation in allocation to sexual reproduction and in allocation within the two modes of asexual reproduction, indicating high sensitivity of these allocation patterns to natural selection. We also found evidence of strong negative genetic correlations between bulbil and flower traits, as well as between bulbil and offset traits, with one group of genotypes allocating greater resources to aerial asexual bulbils and the second group allocating more resources to belowground asexual offsets and aerial flowers. Phenotypic plasticity in allocation to above- vs. belowground asexual reproduction and sexual vs. asexual aerial reproduction was limited, indicating that plants are unlikely to change reproductive mode in response to nutrient availability. Together, then, we have demonstrated strong heritability for, and trade-offs in, the reproductive allocation patterns within this plant population.     

The ecology of flower and bulbil production in Polygonum viviparum

Polygonum viviparum produces inflorescences which bear both sexual flowers and asexual bulbils in highly variable proportions. This paper investigates the proportion of flowers and bulbils per inflorescence at 12 sites in central Norway. It is shown that there is a 'trade—off between flowers and bulbils so that one cannot be increased without reducing the other'. On average, the balance is tilted in favour of bulbils, but there are significant differences in the proportion of bulbils per inflorescence among sites and among quadrats within 11 of the sites. Of these 11 sites there are 6 in which the proportion of bulbils per inflorescence is correlated with factors of the biotic environment. The factors include: (1) the amount of vascular plant cover, which is negatively correlated with the proportion of bulbils at 2 sites; (2) the cover of P. viviparum , which is positively correlated at 1 site; (3) the number of P. viviparum inflorescences, which is negatively correlated at 3 sites. The results suggest that both intra– and inter–specific factors of the biotic environment play a role in the control of bulbil and flower production in P. viviparum.     

Extremely reduced sexual reproduction in the clonal cactus Echinopsis thelegona

Sexual and asexual reproduction may occur simultaneously in some plant species. Under certain environmental conditions asexual reproduction is predominant, which generates ecological consequences on sexual fecundity. In this context, we studied the reproductive ecology of the creeping clonal cactus Echinopsis thelegona in La Bodega (Salta, Argentina), where low fruit and seed production was preliminarily observed. Specifically, we studied the flower availability, fruit and seed production, reproductive system, floral visitors and effects of neighbor ramets on reproductive success. The number of available flowers per day was low, and fruit production was low or null as well. Echinopsis thelegona is self-incompatible. Although its flowers have sphingophilous traits, we did not find evidence of moths visiting them. Only native and exotic bees visited the flowers of this species, though with a low number of visits. Therefore, nocturnal visitors were not registered as pollinators of E. thelegona, perhaps because of their low local abundances. On the other hand, bees behaved as inefficient pollinators of E. thelegona due to their foraging behavior, which moves pollen within individuals. A pollen-addition experiment revealed that there is no fruit production at short distances among ramets. Therefore, the combination of self-incompatibility, low flower production and low local abundance of pollinators could account for the low fruit production observed in this species. This finding suggests that populations of E. thelegona persist by clonality and that they tend toward the loss of sexuality.     

青藏高原露蕊乌头不同海拔居群的开花持续期与繁殖分配

对青藏高原东部3个不同海拔居群的露蕊乌头(Aconitum gymnandrum)(毛茛科)开花持续期和繁殖分配进行了野外观察和检测试验。结果表明:(1)随着海拔的升高,露蕊乌头的开花持续期时间延长,且不同居群间存在显著差异。(2)露蕊乌头的植株个体越大,繁殖投入越高。(3)露蕊乌头的繁殖分配在地上总生物量中所占的比例随海拔升高而增加。研究认为,露蕊乌头在高海拔地区较高的繁殖分配比例强调了有性繁殖在高山恶劣环境中的重要性,而高海拔地区开花持续期的延长补偿了传粉昆虫的减少并增加了对传粉昆虫的吸引能力。     

外来杂草薇甘菊在不同群落中的种子生产特征

对3个群落花甘菊种群种子生产的3个特征即花序特征、种子产量和种子干粒重进行了分析。结果表明：不同种群中小花数、结实率、种子产量和种子干粒重存在显著差异,小花数变异范围为93281．6-154698．0朵／0．25m^2;平均结实率为25．75％一34．58％;平均种子产量的变异范围为23673．40—52616．71粒／0．25m^2;干粒重为0．0880—0．10208。在以有性生殖为主的种群和以无性生殖为主的种群中,前者的种子较大。结合薇甘菊种群对环境的适应对结果进行了讨论。     

Barriers to sexual reproduction in Polygonum viviparum: a comparative developmental analysis of P. viviparum and P. bistortoides

Polygonum viviparum is widely distributed in arctic and alpine regions of the northern hemisphere. Fruit set has never been observed in North American populations and has been reported only very rarely in Europe. Although this species is extremely well studied, the impediments to successful fruit production are unknown. We investigated the sexual reproductive process in P. viviparum growing in the southern Colorado Rocky Mountains. For comparison, we also examined this process in the sympatric congener P. bistortoides, in which reproduction is exclusively sexual. Lack of viable fruit production in P. viviparum has no single developmental explanation; defects occur in each of the processes and structures associated with sexual reproduction studied, yet, these processes and structures also appear to function normally in at least some flowers or individuals. Development is abnormal in many ovules of P. viviparum, however, comparison with P. bistortoides shows that these abnormalities do not contribute to differences in seed production between the two species. The virtual absence of sexual reproduction in P. viviparum appears to be due largely to a low rate of fertilization and to embryo/fruit abortion.     

养分供应对3种舞花姜属植物繁殖方式的影响

该研究选用的3种舞花姜属植物中,毛舞花姜(Globba barthei)和双翅舞花姜(G. schomburgkii)自然条件下开花不结实,以珠芽进行繁殖;异果舞花姜(G. racemosa)则同时以种子和珠芽进行繁殖。在人工栽培条件下,高养分处理显著增加毛舞花姜的珠芽干重((1.11±0.10) g vs. (3.08±0.69) g,p=0.010 7)、珠芽数量((30.58±2.92) vs. (74.74±9.73),p=0.000 4)、珠芽大小((10.5±1.48) mg vs. (53.50±11.42) mg,p=0.001 5)、植株营养体重((3.99±0.23) g vs. (9.67±1.17) g,p=0.000 2)和双翅舞花姜的珠芽数量((51.74±3.64) vs. (108.71±21.52),p=0.018 1)。不同养分条件下两种舞花姜的开花数量无显著差异。人工去除珠芽、花对两种舞花姜植株当年生花和珠芽的数量无显著影响(p<0.05)。自然条件下异果舞花姜不同居群间珠芽大小、珠芽数、珠芽重、果实重、种子数和营养体重等均存在极显著差异(p<0.001)。异果舞花姜各居群植株珠芽数和营养体重(r=0.901,p<0.05)、珠芽重和珠芽大小 (r=0.849,p<0.05) 呈显著正相关;果实重和种子数(r=0.998,p<0.05) 呈显著正相关。土壤因子主成分分析表明前3个主成分提供的信息量分别为50.575%、18.204% 和11.883%,其中第一主成分中的全氮(0.959)、速效氮(0.885)和有机质(0.821)负荷量最大,第二主成分中土壤速效磷(0.824)负荷量最大。植株营养体重和土壤速效磷极显著正相关(r=0.906,p<0.01),珠芽大小与全氮(r=0.798)、速效氮(r=0.780)和有机质(r=0.821)均呈显著正相关(p<0.05)。果实重和种子数与土壤因子相关性不显著(p<0.05)。3种舞花姜的无性繁殖器官更易受到养分供应的影响,有性繁殖器官对养分供应变化响应不显著,有性和无性繁殖之间似不存在补偿关系。     

Causes of variation in sexual and asexual reproduction in diploid and triploid populations of <Emphasis Type="Italic">Allium scorodoprasum</Emphasis>

Allium scorodoprasum is a bulbous geophyte that reproduces by seeds, aerial bulbils, and subterranean daughter bulbs. This research represents the analysis of intraspecific variations in sexual and asexual reproduction in relation to ploidy levels and the environmental conditions from 11 diploid and 24 triploid populations in Lithuania. The results showed that the seed production was extremely rare and occurred only in diploid populations. The numbers of flowers and aerial bulbils per plant as well as mean mass of one bulbil were the characteristics in which differences between ploidy levels were the biggest. The diploids on average produced more (61.9), but smaller (mean mass = 29.6 mg) bulbils and more flowers (16.7), while triploids produced less (41.7), but larger (mean mass = 45.9 mg) bulbils and fewer (5.2) flowers. The study revealed that the main determinant of intracytotypic variation in quantity of both sexual and asexual structures was light availability.     

Aspects of sexual failure in the reproductive processes of a rare bulbiliferous plant,<Emphasis Type="Italic"> Titanotrichum oldhamii</Emphasis> (Gesneriaceae), in subtropical Asia

Titanotrichum oldhamii produces both flowers and asexual bulbils on its inflorescences. However, field observations and herbarium collections indicate that seed set is infrequent and that most reproduction is from vegetative bulbils. We have investigated the failure of sexual reproduction and identified four major causes: (1) in the wild, the seed:ovule ratio for open pollination was only 1.9%, in contrast to 10.1% for artificial cross-pollination, implying poor pollinator services. (2) The overall reproductive success was 5–10 times greater in glasshouse pollination treatments compared to field treatments. This suggests suboptimal environmental conditions for seed set in natural habitats, which may eliminate natural seed set completely. (3) Pollination experiments showed that outcrossed populations set significantly more seed and had higher germination rates than intra-populational and self crosses, in both field and glasshouse experiments. T. oldhamii thus appears to benefit from wide outcrossing. Pollen transfer between populations, however, seems to be infrequent because of the rarity and scattered distribution of Titanotrichum populations. (4) Flowers near the apex of the inflorescence are less likely to set seed, especially late in the season when inflorescences convert to bulbil production. In these late flowers, pollen tubes showed poor guidance as they approach the micropyle of the ovules. Even under optimal glasshouse conditions, the average outcrossing success was only 0.229. Almost one-half of the ovules remained undeveloped and 13.5% of ovules aborted after pollination, indicating a strong shift of resource allocation toward vegetative bulbils and rhizome development. Efficient reproduction from asexual bulbils may thus have released Titanotrichum from strong selection for efficient sexual reproduction. However, occasional seed set observed in the wild may be very important for maintaining some genetic diversity in populations, and promoting overall fitness.     

海拔对青藏高原东缘弯齿风毛菊繁殖特征的影响

研究了海拔对青藏高原东缘不同海拔12个居群弯齿风毛菊繁殖特征的影响.结果表明: 弯齿风毛菊的个体大小、繁殖器官和营养器官生物量、每株头状花序数量及种子总数量均随海拔的升高而减小,而每个头状花序质量和种子百粒重随海拔的升高而增加,表明弯齿风毛菊可以通过减小个体大小来降低资源消耗,把获取的有限资源分配到繁殖部分以达到繁殖成功.为了保证顺利完成有性繁殖,繁殖分配随海拔升高而增大.弯齿风毛菊头状花序的数量与大小、种子数量与百粒重之间均存在资源分配上的权衡,以此来适应环境胁迫,提高自身的适合度.     

Variations in sexual and asexual reproduction of Scirpus mariqueter along an elevational gradient

In order to assess the importance of sexual and asexual reproduction during the life history of Scirpus mariqueter, its reproductive and growth characters were concurrently examined along an elevational gradient (from low elevation to high elevation). The proportions of flowering shoot and inflorescence mass, seed : flower ratio and seed weight were used to quantify the investment in sexual reproduction. The proportions of current-year shoot and rhizome mass were used to quantify the investment in asexual reproduction, and the proportion of corm mass was used for growth, respectively. It was found that vegetative propagation predominated at low elevation, whereas sexual reproduction predominated at high elevation; and that sexual reproduction increased with declining asexual reproduction along the gradient. The results suggest that asexual reproduction is relatively favored in the early life stage, whereas sexual reproduction is favored when the population becomes mature and aged, probably because of the functional differentiation between the two reproductive types. Sexual productive characters (i.e. the proportions of flowering shoot and inflorescence mass) were negatively correlated to both growth and asexual reproductive characters along the gradient, indicating there might exist some trade-offs among growth, sexual and asexual reproduction during the life history. However, no obvious pattern was found between asexual reproductive characters and growth characters along the elevational gradient, possibly because of the varied relationships between them at different life stages. The variations in sexual and asexual reproduction in the species and the relationship between them are thought to be of great significance for local population growth, species persistence and evolution.     

新疆郁金香营养生长、个体大小和开花次序对繁殖分配的影响

植物有性繁殖与资源分配的关系研究对于揭示植物生活史特征及繁育系统进化具有重要意义。新疆郁金香(Tulipa sinkiangensis)是新疆天山北坡荒漠带特有的一种多年生早春短命植物。在自然生境中,该物种仅以有性繁殖产生后代,每株能产生1-8朵花,且不同植株上的花数及果实数以及花序不同位置上的花与果实大小明显不同。本文通过对新疆郁金香有性繁殖与营养生长及植株大小的关系以及花序中不同位置花及果实间的资源分配研究,旨在揭示营养生长、个体大小及开花次序对其繁殖分配的影响。结果表明:在开花和果实成熟阶段,新疆郁金香植株分配给营养器官(鳞茎和地上营养器官)与繁殖器官的资源间均存在极显著的负相关关系(P<0.01),说明其植株的营养生长与生殖生长间存在权衡关系。多花是新疆郁金香的一个稳定性状,其植株上花数目、花生物量、果实生物量和种子数量与植株生物量间均呈极显著的正相关关系(P<0.01),说明新疆郁金香植株的繁殖分配存在大小依赖性。在具2-5朵花的新疆郁金香植株中,花序内各花的生物量、花粉数和胚珠数、结实率、果实生物量、结籽数、结籽率及种子百粒重按其开花顺序依次递减,说明花序内各花和果实的资源分配符合资源竞争假说。植株通过减少晚发育的花或果实获得的资源来保障早发育的花或果实获得较多的资源,从而达到繁殖成功。     

Pollen and Resource Limitation in Veratrum nigrum L. （Liliaceae）, an Andromonoecious Herb

Pollen limitation and resource limitation were invoked to account for the pattern that flowering plants produce more flowers and ovules than fruits and seeds. This study aimed to determine their relative importance in Veratrum nigrum, a self-compatible, perennial, andromonoecious herb. In order to determine whether female production was limited by pollen grains on stigmas or by available resources, we performed supplemental hand pollination in three populations, male-flower-bud removal in three other populations, and emasculation of hermaphroditic flowers in still another population, resulting in a total of seven populations experimentally manipulated. Across the three populations, supplemental hand pollination did not significantly increase fruit set, seed number per fruit, and total seed production per individual, nor did emasculation of hermaphroditic flowers. Taken together, our results suggest that pollen grains deposited on stigmas were abundant enough to fertilize all the ovules. Male-flower-bud removal significantly increased the mean size of hermaphroditic flowers in all three populations. Female reproductive success was increased in one population, but not in the other two populations possibly due to heavy flower/seed predation. We concluded that the female reproductive success of V. nigrum was not limited by pollen grains but by available resources, which is consistent with Bateman＇s principle. Furthermore, the female reproduction increase of male-flower-bud removal individuals might suggest a trade-off between male and female sexual functions.     

Trade-offs between sexual and clonal reproduction in an aquatic plant: experimental manipulations vs. phenotypic correlations

That trade-offs result from the allocation of limited resources is a central concept of life history evolution. We quantified trade-offs between sexual and clonal reproduction in the aquatic plant, Butomus umbellatus, by experimentally manipulating sexual investment in two distinct nutrient environments. Increasing seed production caused a significant but nonlinear trade-off. Pollinating half of all flowers strongly reduced clonal bulbil production, but pollinating the remaining flowers did not cause any further trade-off. Trade-offs were not stronger under low nutrient conditions that clearly limited plant growth. Experimentally induced trade-offs were not reflected in negative phenotypic correlations between sexual and clonal allocation among plants within eight populations grown in a uniform greenhouse environment. Diminishing effects of increased sexual allocation plus a lack of accord between experimental manipulations and phenotypic correlations suggest that trade-offs between sexual and clonal reproduction are unlikely to constrain the evolution of reproductive strategy in this species.     

Genetic Control of Contagious Asexuality in the Pea Aphid

Although evolutionary transitions from sexual to asexual reproduction are frequent in eukaryotes, the genetic bases of such shifts toward asexuality remain largely unknown. We addressed this issue in an aphid species where both sexual and obligate asexual lineages coexist in natural populations. These sexual and asexual lineages may occasionally interbreed because some asexual lineages maintain a residual production of males potentially able to mate with the females produced by sexual lineages. Hence, this species is an ideal model to study the genetic basis of the loss of sexual reproduction with quantitative genetic and population genomic approaches. Our analysis of the co-segregation of ∼300 molecular markers and reproductive phenotype in experimental crosses pinpointed an X-linked region controlling obligate asexuality, this state of character being recessive. A population genetic analysis (>400-marker genome scan) on wild sexual and asexual genotypes from geographically distant populations under divergent selection for reproductive strategies detected a strong signature of divergent selection in the genomic region identified by the experimental crosses. These population genetic data confirm the implication of the candidate region in the control of reproductive mode in wild populations originating from 700 km apart. Patterns of genetic differentiation along chromosomes suggest bidirectional gene flow between populations with distinct reproductive modes, supporting contagious asexuality as a prevailing route to permanent parthenogenesis in pea aphids. This genetic system provides new insights into the mechanisms of coexistence of sexual and asexual aphid lineages.     

Meristem fate and bulbil formation in Titanotrichum (Gesneriaceae)

Titanotrichum oldhamii (a monotypic genus from Taiwan, Okinawa, and adjacent regions of China) has inflorescences bearing either showy yellow flowers or asexual bulbils. Asexual reproduction by bulbils is important in natural populations, and bulbil production increases in August and September at the end of the flowering season (which runs from June to the end of September). The bulbils are small (～1-2.5 mm long) and numerous. They consist of a small portion of stem (bract-stem) topped by opposite storage bracts that enclose a minute apical meristem. A secondary root develops from the side of the bract-stem. The floral meristem of T. oldhamii has three possible fates: (1) bulbil formation, (2) flower formation, or (3) bracteose proliferation. Bracteose proliferation rarely occurs and appears to be a developmental transition between the bulbiliferous and racemose inflorescence forms. It is strongly reminiscent of the floricaula and squamosa mutants of Antirrhinum. In the bulbiliferous form a single floral primordium, which would normally produce one flower, gives rise to ～50-70 bulbils by repeated subdivision of the meristem. This form of bulbil production appears to be unique to Titanotrichum. Occasionally a floral meristem divides, but the subdivision forms multiflowered units of up to four flowers rather than bulbils, suggesting that meristem fate is reversible up to the first or second meristem subdivision. In Titanotrichum, therefore, primordium fate is apparently not determined at inception but becomes irreversibly determined shortly after the appearance of developmental characteristics of the floral or bulbil pathway.     

SPATIAL AND TEMPORAL VARIATION IN CHASMOGAMY AND CLEISTOGAMY IN OXALIS MONTANA (OXALIDACEAE)

Chasmogamous (CH) and cleistogamous (CL) flower production was investigated in natural populations of the perennial herb Oxalis montana in southern Quebec, Canada. Every 10–12 days during two flowering seasons, we recorded the reproductive output of approximately 2,000 plants distributed among five forest sites. The percentage of plants flowering, proportion of flowering plants producing CH and CL flowers, CH and CL flower number per flowering plant, and the proportion of flowers that are CL differed significantly among sites and corresponded to site differences in forest type and habitat quality. Unlike patterns in most CL species, however, reproduction by cleistogamy increased in sites with habitat conditions favorable to plant growth and sexual reproduction, and decreased in less productive sites. Chasmogamous and CL flower production increased with increasing plant size but plant size explained a significantly greater proportion of the variation in CL flower numbers. The percentage of flowering plants producing CH flowers decreased between years while the proportion of CL flowers increased at all sites during the second flowering season. The somewhat unusual aspects of reproduction in Oxalis may stem from its perennial habit which allows use of stored resources in adjusting the balance of cleistogamy versus chasmogamy in different environmental regimes.     

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。