雌全同株植物三脉紫菀花期偏雄的个体大小依赖的性别分配

经典的虫媒传粉植物个体大小依赖的性别分配模型通常预期:分配给雌性功能的资源比例将随着个体大小的增大而增加;但一些研究表明,花期个体大小依赖的性别分配模式表现出随个体大小增大而偏雄的趋势.我们以植株高度衡量个体大小,从花和花序两个水平上研究了雌花、两性花同株植物三脉紫菀(Aster ageratoides)花期个体大小依赖的性别分配策略.随着植株高度的增大,植株产生的头状花序数量增加,表明三脉紫菀投入到繁殖的资源不是固定不变的,而是随个体大小增大而增加的.在花和花序水平上,繁殖资源在雌雄性别功能之间的分配均表现为随个体大小的增大而更偏雄的模式,即花粉/胚珠比增加,产生花粉的两性花占两性花和雌花总花数的比例升高.这些结果与花期个体越大、性别分配越偏雄的预期一致.花期更偏雄的性别分配可能有助于植物在花期通过输出花粉提高雄性适合度,从而实现个体适合度的最大化.     

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。     

Patterns of resource allocation in the dioecious alpine herb Aciphylla simplicifolia (Apiaceae)

Abstract Patterns of reproductive and vegetative biomass allocation were compared in male and female plants of the alpine herb Aciphylla simplicifolia. Male and female plants had similar vegetative biomass but differed in the pattern of resource allocation. Inflorescences of males and females were similar in weight at the time of flowering, but differed in biomass allocation to some structures within the inflorescences, particularly those associated with ovule production and pollinator attraction (number and size of flowers). At the time of fruit production, female inflorescences were 2.6 times heavier than at flowering with developing fruit six times heavier than flowers. In addition to the increase in biomass allocated to structures associated with the provisioning and dissemination of seed, support structures (main and side stalks) were also heavier. As a result of this additional investment of resources at the time of fruit production, the reproductive effort (RE) of female plants was much higher than that of males: 37% of above ground biomass compared with 21% for males. Differences in RE did not change with plant size; however, allocation to reproduction appeared to be a constant proportion of biomass over nearly all plant sizes sampled. These results show that sex‐specific resource allocation can be a complex of temporal and morphological patterns.     

Facultative sex allocation in snow skink lizards (Niveoscincus microlepidotus)

Mathematical models suggest that reproducing females may benefit by facultatively adjusting their relative investment into sons vs. daughters, in response to population‐wide shifts in operational sex ratio (OSR). Our field studies on viviparous alpine skinks (Niveoscincus microlepidotus) document such a case, whereby among‐ and within‐year shifts in OSR were followed by shifts in sex allocation. When adult males were relatively scarce, females produced male‐biased litters and larger sons than daughters. The reverse was true when adult males were relatively more common. That is, females that were courted and mated by few males produced mainly sons (and these were larger than daughters), whereas females that were courted and mated by many males produced mainly daughters (and these were larger than sons). Maternal body size and condition also covaried with sex allocation, and the shifting pattern of sexual size dimorphism at birth may reflect these correlated effects rather than a discrete component of an evolved sex‐allocation strategy.     

Observations on the sexual system and the natural history of the semi-terrestrial shrimp Merguia rhizophorae (Rathbun, 1900)

Abstract. The sexual system of the semi-terrestrial shrimp Merguia rhizophorae is described, along with natural history observations on this unusual caridean. Individuals of M. rhizophorae in the Bocas del Toro Archipelago, Panama, were found occupying fossilized coral terraces in the upper and mid-intertidal zones, inhabiting caves and crevices, in and out of water. These fossilized coral terraces represent a new habitat for this species, which was previously reported only from mangrove swamps. Males, which made up 65% of the studied population, were smaller than females on average. No small juvenile females were observed, but transitional individuals having the characteristics of both males (gonopores) and females (ovaries) were observed in the population. These data suggest that individuals of M. rhizophorae are protandric hermaphrodites. Logistic regression indicated that the carapace length at which 50% of the individuals change sex is 4.89 mm. The abundance of shrimps at the study site was low. Shrimps were usually solitary, but occasionally observed in groups of ≤5 individuals. Shrimps were commonly observed walking while out of water, and in some cases, emerged shrimps jumped vigorously, presumably to avoid capture by the researcher or by predatory crabs. Additional studies on the reproductive biology and the behavioral ecology of members of this genus and of members of the closely related families Barbouridae and Lysmatidae will aid in understanding the evolutionary origin and the adaptive value of gender expression patterns in shrimps.     

Spiderling sex ratio and maternal investment in the bolas spider Mastophora cornigera (Araneae,Araneidae)

Male Mastophora cornigera exit egg sacs as adults, which allowed us to determine spiderling sex ratios and patterns of maternal investment in this species. We collected 15 egg sacs produced by seven mothers, which yielded 1945 emergent spiderlings which were sexed, 1850 of which were weighed. Two emergent broods were significantly male and female biased and were unaffected by pre-emergence mortality. The weights of male and female spiderlings differed in eight broods, with males and females being heavier in four cases each. Five of these broods were derived from multiple egg sac sets produced by one mother, and in each case, the total mean male and female spiderling weights for all broods in a set were biased in the same direction as the biased brood(s) within that set. Mean emergent spiderling weight was independent of brood size and sex ratio for both males and females. Despite such independence, sex allocation in M. cornigera can favor sons, daughters, or both equally, and by numbers, by weight, or both at once. The proximate mechanisms and adaptive significance of such variability is unknown. We also review evidence for gender-biased allocations in arachnid offspring and suggested mechanisms for their applicability to M. cornigera.     

Genetic variation in sex allocation in a parasitic wasp: variation in sex pattern within sequences of oviposition

In order to maximize their fitness under Local Mate Competition (LMC), arrhenotokous female wasps have to produce a precise sex ratio when encountering hosts. Recent progress in the theory of hymenopterous parasitoid reproduction suggest that they manage to do it by laying male and female eggs in a particular order and that such reproductive strategies are adaptive. Therefore, the determinism of such sequential patterns would be regulated by genetic control on which natural selection could act. To test this hypothesis, sequences of oviposition were recorded in a set ofTrichogramma brassicae Bezdenko (Hymenoptera; Trichogrammatidae) females and in their daughters by providing themEphestia kuehniella Zeller (Lepidoptera; Pyralidae) eggs. In order to describe accurately sex pattern within these oviposition sequences, I present a joined non-parametric and multivariate statistical method. It is shown thatT. brassicae females do not produce male and female eggs in random sequences. Moreover, the way they organize the sequence of the sexes in their progeny seems to be under a strong genetic control. The evolutionary consequences of such results are discussed.     

Complex sex allocation in the laughing kookaburra

In groups of the cooperatively breeding laughing kookaburra(Dacelo novaeguineae), offspring sex varied with the type ofsocial group and with hatch rank. Groups with female helpers,especially if all helpers were female, had male-biased clutchand fledging sex ratios. Groups without female helpers (unassistedpairs or male-only helpers) had female-biased clutch and fledgingsex ratios. Breeding females responded facultatively to increasesin the number of female helpers in their group by producingmore male eggs. These biases may occur if breeding femalestry to limit the number of daughters recruited into their groupbecause unlike male helpers, female helpers depress the breedingsuccess of their parents. Across all nests, two-thirds of first-hatchedyoung were male, two-thirds of second-hatched young were female, and the sex ratio of third-hatched young was even. Hatch ranksex ratios also varied dramatically between different typesof social groups, from 16.7% for second-hatched nestlings ofunassisted pairs to 100% for first-hatched nestlings of groupswith only female helpers. A corollary of the relationship betweenhatch rank and sex was that hatching sex sequences were distributed nonrandomly: all groups avoided hatching a daughter first followedby a son (FM). Sibling competition is aggressive and sometimesfatal. Since females grow to be 15% larger than males the hatchingsequence of sexes could affect nestling growth and mortality.However, an exhaustive analysis found little evidence thatgrowth or survival of males was compromised if hatched aftera sister. The small number of FM sequences may only have occurredin nests that were able to ameliorate any negative consequences.Alternatively, when clutch size is small and fledging successunpredictable because of brood reduction, the preferred broodsex ratio may be contingent on the number of fledged young,making it advantageous to order the sexes in the brood.     

Selectable components of sex allocation in colonies of the honeybee (Apis mellifera L.)

Colonies of social insects that undergo fission as a componentof reproduction produce large excesses of males. Hypothesesto explain this phenomenon have assumed that the workers thatconstitute the entourage for the new queen (or queens) representinvestment in female reproductives. Selection for optimal colonysex allocation then leads to an increase in production of malesthat balances the investment in females based on their relativereproductive values. We show that the construction of comb dedicatedto the production of males (drone comb) versus workers (workercomb) is a component of sex investment under the control ofcolony workers. Relative comb construction was highly correlatedwith the relative investment in male and worker brood. Coloniesthat invested relatively more in their total numbers of malesinvested less in the dry weight of individual workers. Coloniesthat had more adult workers produced a greater number of malesand workers, but colony size did not affect the proportionalinvestment in drone comb or brood. Genetic variability was foundfor the number of adult workers in colonies, the amount of dronecomb produced, the amount of worker comb produced, and the dryweight of adult workers, suggesting that sex allocation is aselectable trait in honeybees.     

Floral sex ratios and gynomonoecy in Solidago (Asteraceae)

Gynomonoecy is the sexual system in which individual plants bear both female and bisexual flowers. Little attention has been paid to the adaptive significance of this sexual system, which is particularly prevalent in the Asteraceae. We investigated one hypothesized advantage of having two flower types, namely that this arrangement permits flexibility in allocation of resources to male and female reproductive functions. We examined six species of goldenrod ( Solidago ), a genus of gynomonoecious, perennial herbs. In greenhouse experiments, we varied one or more of three environmental variables – light, nutrients and water – and/or examined heads in different positions on the plants. Most variables had little or no effect on the proportion of ray flowers. Significant effects were found for light in 0 of 5 experiments, for nutrients in 4 of 9 experiments and for water in 0 of 3 experiments. Heads in different positions in the inflorescence differed in the proportion of ray flowers in half of the experiments, though the differences were small. We also monitored temporal patterns in four species and found that the proportion of ray flowers increased significantly over the blooming period and the number of flowers per head declined. Because of the small number of significant effects and their modest magnitude, we conclude that the presence of two flower types in goldenrods is probably not advantageous in allowing flexibility in sex expression. It seems likely that this sexual system has been more important either in increasing pollinator attraction or in reducing pollen–pistil interference. The small observed changes in floral ratios were generally accompanied by changes in disc size in a manner consistent with an explanation based on allometry.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 413–422.