SEX ALLOCATION IN THE MONOECIOUS HERB BEGONIA SEMIOVATA

Sex-allocation models predict that the evolution of self-fertilization should result in a reduced allocation to male function and pollinator attraction in plants. The evolution of sex allocation may be constrained by both functional and genetic factors, however. We studied sex allocation and genetic variation for floral sex ratio and other reproductive traits in a Costa Rica population of the monoecious, highly selfing annual Begonia semiovata. Data on biomass of floral structures, flower sex ratios, and fruit set in the source population were used to calculate the average proportion of reproductive allocation invested in male function. Genetic variation and genetic correlations for floral sex ratio and for floral traits related to male and female function were estimated from the greenhouse-grown progeny of field-collected maternal families. The proportion of reproductive biomass invested in male function was low (0.34 at flowering, and 0.07 for total reproductive allocation). Significant among-family variation was detected in the size (mass) of individual male and female flowers, in the proportion of male flowers produced, and in the proportion of total flower mass invested in male flowers. Significant among-family variation was also found in flower number per inflorescence, petal length of male and female flowers, and petal number of female flowers. Except for female petal length, we found no difference in the mean value of these characters between selfed and outcrossed progeny, indicating that, with the possible exception of female petal length, the among-family variation detected was not the result of variation among families in the level of inbreeding. Significant positive phenotypic and broad-sense genetic correlations were detected between the mass of individual male and female flowers, between male and female petal length, and between number of male and number of female flowers per inflorescence. The ratio of stamen-to-pistil mass (0.33) was low compared to published data for autogamous species with hermaphroditic flowers, suggesting that highly efficient selfing mechanisms may evolve in monoecious species. Our results indicate that the study population harbors substantial genetic variation for reproductive characters. The positive genetic correlation between investment in male and female flowers may reflect selection for maximum pollination efficiency, because in this self-pollinating species, each female flower requires a neighboring male flower to provide pollen.     

Size-dependent sex allocation within flowers of the annual herb Clarkia unguiculata (Onagraceae): ontogenetic and among-plant variation

The relative allocation of resources to male and female functions may vary among flowers within and among individual plants for many reasons. Several theoretical models of sex allocation in plants predict a positive correlation between the resource status of a flower or individual and the proportion of reproductive resources allocated to female function. These models assume that, independent of resource status, a negative correlation exists between male and female investment. Focusing on the allocation of resources within flowers, we tested these theoretical predictions and this assumption using the annual Clarkia unguiculata (Onagraceae). We also sought preliminary evidence for a genetic component to these relationships. From 116 greenhouse-cultivated plants representing 30 field-collected maternal families, multiple flowers and fruits per plant were sampled for gamete production, pollen?:?ovule ratio, seed number, ovule abortion, seed biomass/fruit, mean individual seed mass, and petal area. If sex allocation changes as predicted, then (1) assuming that flowers produced early have access to more resources than those produced later, basal flowers should exhibit a higher absolute and proportional investment in female function than distal flowers and (2) plants of high resource status (large plants) should produce flowers with a higher proportional investment in female function than those of low resource status. Within plants, variation in floral traits conformed to the first prediction. Among plants and families, no significant effects of plant size (dry stem biomass) on intrafloral proportional sex allocation were observed. We detected no evidence for a negative genetic correlation between male and female investment per flower, even when controlling for plant size.     

苔藓植物生殖生态学研究

近年来苔藓植物生殖生态学研究主要集中于繁育系统、生殖代价与对策,以及不同生殖方式对种群遗传变异的影响等方面。生殖结构的原始性及其对水分的独特需求,以及雌雄异株比例较高等导致苔藓植物中有性生殖比例偏低;雌配子体很少完成整个有性生殖过程,其“真实的生殖代价”主要指雌性性表达(雌配子发生)的能耗,并且显著低于雄性性表达;基于对资源有效分配的生殖对策而导致雌性偏向及部分孢子体败育。无性生殖有利于不同生境条件下有效种群的发展与维持,其多样化的繁殖方式导致复杂的种群动态。苔藓植物具有较高的种群遗传多样性,生殖方式与种群遗传变异无直接因果关系,孢子与无性繁殖体不同的散布能力对于种群间遗传分化具有一定的影响。     

Action of the Tunicate locus on maize floral development

The co-dominant Tunicate (Tu) mutation in maize causes nonreproductive structures in both the male and female inflorescences to be enlarged. This mutation also affects sex determination, permitting the development of pistils in the normally staminate tassel. In order to characterize the role of the normal tu gene product, we have analysed genetic interaction between Tu and other mutations that perturb specific stages of floral development. Synergistic interactions observed suggested that the tu product functions in at least three stages of floral development–determination of spikelet primordia, differentiation of non-reproductive organs and pistil abortion in the tassel. © 1994 Wiley-Liss, Inc.     

Reproductive correlates of mating system variation in Eichhornia paniculata (Spreng.) Solms (Pontederiaceae)

Comparative studies of related plant species indicate that evolutionary shifts in mating systems are accompanied by changes in reproductive attributes such as flower size, floral morphology, and pollen/ovule ratio. Recent theoretical work suggests that patterns of investment in reproduction should also change with the mating system. In a glasshouse study, we investigated the extent to which mating system differences among populations of Eichhornia paniculata (Pontederiaceae) were correlated with changes in allocation to male and female function, floral display, and the regulation of investment in reproduction through fruit and ovule abortion. Significant differences in the amount of biomass allocated to reproductive structures were evident among six populations of E. paniculata. As predicted by sex allocation theory, the proportion of dry weight allocated to male function decreased with the outcrossing rate of populations. Six of the eight attributes used to characterize floral display also differed significantly among populations. However, with the exception of two attributes describing the number of flowers produced by inflorescences, these were not correlated with outcrossing rate. Levels of fruit and ovule abortion were determined in two populations with contrasting mating systems under different nutrient and pollination treatments. Virtually all fruits initiated by plants from a self-fertilizing population were matured, while the amount of fruit abortion in an outcrossing population increased with flower production. Ovule abortion was low in both populations. Our results demonstrate that the evolution of self-fertilization in E. paniculata is associated with changes in investment to reproduction that normally distinguish selfing and outcrossing species.     

Sex determination in the monoecious species cucumber is confined to specific floral whorls

In unisexual flowers, sex is determined by the selective repression of growth or the abortion of either male or female reproductive organs. The mechanism by which this process is controlled in plants is still poorly understood. Because it is known that the identity of reproductive organs in plants is controlled by homeotic genes belonging to the MADS box gene family, we analyzed floral homeotic mutants from cucumber, a species that bears both male and female flowers on the same individual. To study the characteristics of sex determination in more detail, we produced mutants similar to class A and C homeotic mutants from well-characterized hermaphrodite species such as Arabidopsis by ectopically expressing and suppressing the cucumber gene CUCUMBER MADS1 (CUM1). The cucumber mutant green petals (gp) corresponds to the previously characterized B mutants from several species and appeared to be caused by a deletion of 15 amino acid residues in the coding region of the class B MADS box gene CUM26. These homeotic mutants reveal two important concepts that govern sex determination in cucumber. First, the arrest of either male or female organ development is dependent on their positions in the flower and is not associated with their sexual identity. Second, the data presented here strongly suggest that the class C homeotic function is required for the position-dependent arrest of reproductive organs.     

Floral herbivore effect on the sex expression of an andromonoecious plant,Isomeris arborea (Capparaceae)

Flower-feeding insects may influence the reproductive behavior of their host plant. In plants with labile sex expression, the ratio of maternal to paternal investment may change in response to damage, an effect that goes beyond the direct reduction of plant gametes. We examined the effects of floral herbivory by the beetle Meligethes rufimanus (Nitidulidae) on the ratio of hermaphroditic flowers to male flowers in an andromonoecious shrub, Isomeris arborea (Capparaceae) in southern California. Plants exposed to herbivory had a greater rate of flower bud abortion than those protected from herbivory. Exposed plants produced a greater proportion of hermaphroditic flowers to male flowers, although damaged inflorescences still produced fewer fruit. An additional manipulative experiment showed that the removal of pistils on inflorescences led to an increase in the proportion of hermaphroditic flowers. This suggests that the presence of fruit may lead to pistil suppression in developing flowers. Adaptive responses to herbivory which favor andromonoecy thus include the continued production of hermaphroditic flowers when floral damage is high (and hence low fruit set), and a switch to male flower production when floral damage is low (and fruit production increases). The consequences of an altered six ratio induced by insect herbivores may lead to indirect effects on both the male and female reproductive success of this plant.     

Floral sex allocation at individual and branch levels in Betula platyphylla var. japonica (Betulaceae), a tall, wind-pollinated monoecious tree species

Floral sex allocation at the individual and first-order branch levels and the relation between these levels were examined in Betula platyphylla var. japonica, a wind-pollinated monoecious tree. Floral sex allocation at the individual level varied with resource availability in a pattern similar to that predicted by the Masaka and Takada model (Journal of Theoretical Biology 240: 114-125). Thus, individual trees with few reproductive resources produced only female or male inflorescences, whereas individuals with many resources rarely had a high male ratio (i.e., number of male inflorescences/total number of inflorescences). Furthermore, the number of male inflorescences tended to reach an upper limit, whereas the number of female inflorescences increased monotonically with increasing reproductive investment. The patterns of floral sex allocation at the first-order branch level were analogous to those at the individual level. Thus, each first-order branch of B. platyphylla var. japonica behaves like an individual, and the floral sex allocation of a given branch does not necessarily represent the individual tree. The effect of the individual-level floral sex ratio on branch-level floral sex allocation indicates that branch behavior is controlled by the individual.     

Sexual differentiation in higher plants

As in all organogenetic studies, sex differentiation implies three fields of research: the identification of macsomalecular markers specific for stamens or carpels }expression program); the analysis of the signals (such as phytohormones{ inducing them: and finally the knowledge of the regulator genes (sex detsrmination genes).
In dioecious plants, sex determination (male and female genes or combinations of heterochromosomes) occurs at the fertilization stage. These regulators probably act early by means of inducers; their action is perceptible mainly when reproductive organs develop, and the existence of target cells able to respond to the inductive message is obvious. Experimental control of sex expression by phytohormones leads to the repression of the normal organogenetic program (induced by the presence of the sex genes) arrd to the induction of the opposite program (normally incompatible with these genes).
Analogous mechanisms occur in monoecious plants, but here the male program is always expressed before the female one. Experimental control of sex expression suggests that the successive induction of first male and then the female program results from inverse gradients of male and female signals. Sex differentiation studies of monaeciousness are more difficult than studies on dioeciousness since, in all the cells. not only male and female programs co-exist as in dioeciousness, but also male and female sex penes and signals.
The present model has been tested in the dioecious Mercurialisannua (2n = 16) and some other species, and the results that have been established are described.     

Sex-Biased Temporal Gene Expression in Male and Female Floral Buds of Seabuckthorn (Hippophae rhamnoides)

Seabuckthorn is an economically important dioecious plant in which mechanism of sex determination is unknown. The study was conducted to identify seabuckthorn homologous genes involved in floral development which may have role in sex determination. Forty four putative Genes involved in sex determination (GISD) reported in model plants were shortlisted from literature survey, and twenty nine seabuckthorn homologous sequences were identified from available seabuckthorn genomic resources. Of these, 21 genes were found to differentially express in either male or female flower bud stages. HrCRY2 was significantly expressed in female flower buds only while HrCO had significant expression in male flowers only. Among the three male and female floral development stages (FDS), male stage II had significant expression of most of the GISD. Information on these sex-specific expressed genes will help in elucidating sex determination mechanism in seabuckthorn.     

雌雄异熟植物露蕊乌头开花时间对雌雄功能期及表型性别的影响

开花时间决定了植物雌雄功能的交配机会, 最终影响繁殖成功。交配环境假说认为雌雄异熟植物开花时间的差异能引起植物表型性别的变异, 改变种群内的交配环境, 影响植物对雌雄功能的最佳性分配。为了研究开花时间对雌雄异熟植物的雌雄性别时期及表型性别的影响, 本文以毛茛科雄性先熟植物露蕊乌头(Aconitum gymnandrum)为实验材料, 记录了雄性和雌性功能期, 分析了植株开花时间、花的雌雄功能期和表型性别的关系。结果表明: 在植物同一花序内, 较晚开放的花有更长的雄性期和更短的雌性期, 性分配在时间上偏雄。雌雄功能期在时间上的相对分配随植物开花时间的变化表现出相似的趋势： 较晚开的花或较晚开花的个体, 花的雄性功能期相对于雌性功能期更长, 在时间上更偏向雄性功能。而且, 开花时间的差异影响种群内花的性比和植物个体的表型性别动态。随着开花时间由早到晚的变化, 种群内早期以雄花为主,末期以雌花为主, 种群内性别环境由偏雄向偏雌变化, 因此植株个体的平均表型性别则从偏雌转向偏雄。本文结果支持交配环境假说, 雄性先熟的露蕊乌头开花早期, 种群内花的性别比偏雄, 种群表型性别环境偏雄, 因而植物个体平均表型性别偏雌, 性别分配(即时间分配)偏向雌性功能, 而晚开花个体的平均性别偏雄, 更偏向雄性功能的分配。     

Selection on floral characters in natural Spanish populations of Silene latifolia

In insect-pollinated plants, floral characters are expected to play an important role in paternal and maternal reproductive success. Bateman's principle states that male reproductive success increases with more mating opportunities, while female reproductive success is limited by the amount of resources available to produce progeny, thus there should be greater selection on male floral characters than on female. In the case of the dioecious plant Silene latifolia, floral characters are likely to be influenced by its association within its native European range with moths of the genus Hadena, which serve as both pollinators and seed predators. The present study addresses relationships between male and female reproductive success, spatial location and floral characters (corolla, calyx and claw) over a 2-year period in two Spanish populations of S. latifolia in the presence of Hadena moths. A maximum likelihood paternity analysis using genetic variation at six allozyme markers showed heterogeneity in male reproductive success. There was much less variation in female reproductive success. When this analysis was extended to include interplant distance as a causal factor underlying variation in male success, we found that successful pollination tended to be limited to nearby females, in accordance with exponential decay of pollen dispersal with increasing distance. When the paternity analysis included floral characters as a causal factor underlying variation in male success, our data showed little evidence for directional selection, but there was stabilizing selection in one of the two years for calyx diameter. Selection on female characters varied widely between sites and years, in most of the site/year combinations there was little selection on female floral characters; however, in one site/year there was evidence for selection on all three floral characters. We conclude that pollinators visit flowers that are close together, and that while floral characters are important for the attraction of pollinators, larger flowers do not necessarily attract more pollinators at all sites and that variation among sites and years makes difficult any conclusions about the long-term importance of the predictions suggested by Bateman's principle.     

用模式生物青鳉概观硬骨鱼性别决定及性分化研究进展

鱼类性别决定和性分化呈多元性,既有雌雄同体也有雌雄异体。性腺的雌雄性分化过程受遗传和环境因素(如温度、光照、激素和pH值等)影响,具有可逆可塑性。随着生物技术和基因组学的迅速发展,近年来脊椎动物性别决定和性分化的研究有了重大进展和显著突破。本文通过聚焦青鳉及其他硬骨鱼纲保守存在的dmrt1、gsdf、amh等雄性因子,探讨硬骨鱼普遍存在的雌雄性别可塑可逆信号通路,并介绍了新的基因组编辑和性控育种技术,为单性选育等水产养殖技术的研发提供参考。     

Hormonal Control of Sex Differentiation of Potentially Female Floral Buds of Lagenaria siceraria var. hispida In Vitro

In the present study, several kinds of phytohormones were used for the control of sex differentiation of the potentially female floral buds of Lagenaria siceraria var. hispida in vitro. It was shown that both GA3 and STS (silver thiosulphate) could effectively change the direction of sex differentiation of the potentially female floral buds in vitro. In the MS medium, supplemented with IAA, BA and ACC(1-aminocyclopropane-l-carboxylic acid) at l nmol/L, male flowers would be induced from the potentially female floral buds by the addition of GA3 (1–500μmol/L). Herein the male flowers were induced more effectively by GA3 within 5–-20 μmol/L but it was not as effective as STS. In the MS medium supplemented with IAA, BA and ACC at 1 nmol/L and with GA3 at 20 nmol/L more male flowers were differentiated from the potentially female floral buds with the addition of STS within 100–500 μmol/L. On the contrary, when the MS medium were supplemented with IAA and ACC at 1 nmol/L and with BA increased to 100 nmol/L more female flowers were differentiated from the potentially female floral buds, even with addition of 10–50 nmol/L of GA3.     

Intraspecific variation in sex allocation in hermaphroditic Plantago coronopus (L.)

Models for sex allocation assume that increased expenditure of resources on male function decreases the resources available for female function. Under some circumstances, a negative genetic correlation between investment in stamens and investment in ovules or seeds is expected. Moreover, if fitness returns for investment in male and female function are different with respect to size, sex allocation theory predicts size‐specific gender changes. We studied sex allocation and genetic variation for investment in stamens, ovules and seeds at both the flower and the plant level in a Dutch population of the wind‐pollinated and predominantly outcrossing Plantago coronopus. Data on biomass of floral structures, stamens, ovules, seedset and seedweight were used to calculate the average proportion of reproductive allocation invested in male function. Genetic variation and (genetic) correlations were estimated from the greenhouse‐grown progeny of maternal families, raised at two nutrient levels. The proportion of reproductive biomass invested in male function was high at flowering (0.86 at both nutrient levels) and much lower at fruiting (0.30 and 0.40 for the high and low nutrient treatment, respectively). Androecium and gynoecium mass exhibited moderately high levels of genetic variance, with broad‐sense heritabilities varying from 0.35 to 0.56. For seedweight no genetic variation was detected. Significant among‐family variation was also detected for the proportion of resources invested in male function at flowering, but not at fruiting. Phenotypic and broad‐sense genetic correlations between androecium and gynoecium mass were positive. Even after adjusting for plant size, as a measure of resource acquisition, maternal families that invested more biomass in the androecium also invested more in the gynoecium. This is consistent with the hypothesis that genetic variation for resource acquisition may in part be responsible for the overall lack of a negative correlation between male and female function. Larger plants had a more female‐biased allocation pattern, brought about by an increase in seedset and seedweight, whereas stamen biomass did not differ between small and large plants. These results are discussed in relation to size‐dependent sex allocation theory (SDS). Our results indicate that the studied population harboured substantial genetic variation for reproductive characters.     

Sexual differentiation of brain and behavior in quail and zebra finches: Studies with a new aromatase inhibitor, R76713

In many species of vertebrates, major sex differences affect reproductive behavior and endocrinology. Most of these differences do not result from a direct genomic action but develop following early exposure to a sexually differentiated endocrine milieu. In rodents, the female reproductive phenotype mostly develops in the absence of early steroid influence and male differentiation is imposed by the early action of testosterone, acting at least in part through its central conversion into estrogens or aromatization. This pattern of differentiation does not seem to be applicable to avian species. In Japanese quail (Coturnix japonica), injection of estrogens into male embryos causes a permanent loss of the capacity to display male-type copulatory behavior when exposed to testosterone in adulthood. Based on this experimental result, it was proposed that the male reproductive phenotype is “neutral” in birds (i.e. develops in the absence of endocrine influence) and that endogenous estradiol secreted by the ovary of the female embryo is responsible for the physiological demasculinization of females. This model could be recently confirmed. Females indeed display a higher level of circulating estrogens that males during the second part of their embryonic life. In addition, treatment of female embryos with the potent aromatase inhibitor, R76713 or racemic vorozole™ which suppresses the endogenous secretion of estrogens maintains in females the capacity to display the full range of male copulatory behaviors. The brain mechanisms that control this sexually differentiated behavior have not been identified so far but recent data suggest that they should primarily concern a sub-population of aromatase-immunoreactive neurons located in the lateral parts of the sexually dimorphic preoptic nucleus. The zebra finch (Taeniopygia guttata) exhibits a more complex, still partly unexplained, differentiation pattern. In this species, early treatment with exogenous estrogens produces a masculinization of singing behavior in females and a demasculinization of copulatory behavior in males. Since normal untreated males sing and copulate, while females never show these behaviors even when treated with testosterone, it is difficult to understand under which endocrine conditions these behaviors differentiate. In an attempt to resolve this paradox, we recently treated young zebra finches with R76713 in order to inhibit their endogenous estrogens secretion during ontogeny and we subsequently tested their behavior in adulthood. As expected, the aromatase inhibitor decreased the singing frequency in treated males but it did not affect the male-type copulatory behavior in females nor in males. In addition, the sexuality differentiated brain song control nuclei which are also masculinized in females by early treatment with estrogens, were not affected in either sex by the aromatase inhibitor. In conclusion, available data clearly show that sexual differentiation of reproductive behaviors in birds follows a pattern that is almost opposite to that of mammals. This difference may be related to the different mechanisms of sex determination in the two taxa. In quail, the ontogeny of behavioral differentiation is now well understood but we only have a very crude notion of the brain structures that are concerned. By contrast, in zebra finches, the brain mechanisms controlling the sexually differentiated singing behavior in adulthood have been well identified but we do not understand how these structures become sexually dimorphic during ontogeny.     

Male-biased sex allocation in late-blooming flowers driven by resource limitation in the clonal perennial Aconitum kusnezoffii (Ranunculaceae)

Flowering phenology and clonal growth are known to affect resource and pollen availability, and therefore select for adaptive or constrained sex allocation strategies to some degree. However, the consequences of temporal sex allocation patterns for reproductive fitness across the flower, inflorescence, and genet levels have rarely been examined. Moreover, experimental tests of the underlying regulatory mechanisms are scarce. We examined the association of flowering phenology and inflorescence position with temporal sex allocation and reproductive success in the protandrous perennial clonal herb, Aconitum kusnezoffii, over four consecutive growing seasons by examining more than 39 000 flowers. We also conducted controlled experiments to test the effects of resource and pollen limitation on the female reproductive success of lateral inflorescences. We found that some male functions were positively correlated with flowering phenology, whereas female reproductive success was negatively correlated with flowering phenology and inflorescence position. Lateral inflorescences invested more in male function than terminal inflorescences and therefore yielded fewer and smaller seeds. Resource limitation may serve as the key mechanism underlying this differentiated pattern. Decreased female reproductive success was consistently observed at the flower and inflorescence levels as flowering occurred later in the growth season. Late-blooming lateral inflorescences specialized in the male function, and their female reproductive success was constrained by early-blooming terminal inflorescences. This might be the first attempt to systematically demonstrate sex allocation strategy differentiation in a protandrous plant species at the inflorescence level. In addition, our study provides empirical evidence of dichogamy selecting for specialized sex allocation strategies among inflorescences.