Age changes in the vegetative vs. reproductive allocation by module demographic strategies in a perennial plant

Retama sphaerocarpa (L.) Boiss. is aMediterranean shrub with a remarkably simplified metameric structure. Terminalyoungest shoots act as units of modular growth, being able to produce newshootsby basal axillary buds (at the base of the shoot) and inflorescencesby lateral axillary buds. In this study, we have analysed the structural andgrowth potential features of these modules, as well as theirdemographic proportions, regarding the allocation of newvegetative and reproductive growth in plants of different age. Reproductiveeffort is proportionally higher in older plants. This shift in the allocationstrategy with plant ontogeny is not attained with changes in the shoot modules(which maintain a constant size, nutrient composition and show a similarnew growth investment per module) but through a differentdemographic composition of the population ofmodulesaccording to their developmental fate (vegetative or reproductive).This indicates a high level of iterativity and a purely modular growth, sincethe attributes of the individual (age of the plants) do not seem toaffect those of the integrating modular units (growth performance of theshoots).     

Functional features and ontogenetic changes in reproductive allocation and partitioning strategies of plant modules

In the concept of modularity, plant modules are considered as iterative units and their changes are analyzed in terms of number or size. This paper, however, analyses changes with respect to the reproductive functional performance of modules and individual plant age. Patterns of resource allocation and partitioning in reproductive modules (fruits) are compared between two different age groups of a bushy perennial plant, Cistus ladanifer.Although modules do not differ in their allocation strategies (young plant modules produce the same seed and packing/protective structure biomass as old plant modules), their partitioning strategies change with plant age: young plant modules produce a larger number of lighter seeds than old plants. These differences have a direct consequence on the plant pre-dispersal fitness, which is not counteracted by insect predation on reproductive modules. These results are empirical evidence of a differentiation in the performance of reproductive modules with the ontogenetic development of this plant species. We think that the consideration of such kind of changes in module features is essential in the analysis of the iterative construction of plants.     

荒漠植物白刺属4个物种的生殖分配比较

选定乌兰布和沙漠地区白刺属4种植物为研究对象,通过对其样株在花期的各生殖构件的数量特征及生物量调查,系统研究了唐古特白刺(Nitraria tangutorum Bobr.)、西伯利亚白刺(Nitraria sibirica Pall.)、大白刺(Nitraria roborowskii Kom.)和泡泡刺(Nitraria sphaerocarpa Maxim.)4种白刺属植物在生殖枝水平上的生殖分配。结果表明:不同白刺属植物在分株高度、生殖枝长、生殖枝基径、单枝花数、花序干重、枝叶干重等生殖构件的数量性状方面均有显著差异,其中泡泡刺的各生殖构件的数量均最小;除了西伯利亚白刺的生殖分配值达到44.51%外,其余3种白刺的生殖分配值均没有超过20%。经统计分析,4种白刺种群的生殖枝长分别与分株高度呈显著(P<0.05)的直线性正相关关系;生殖枝花序干重与分株高显著正相关;4种白刺的生殖分配随着分株生殖枝生物量的增加而减少,即白刺的个体大小与生殖分配之间呈现负相关关系。这种生殖分配特点反映了不同白刺植物对生长环境的资源利用、与克隆繁殖的权衡及对生态适应的策略。     

Structural cost of shoot modules and its implications on plant potential fitness in a Mediterranean perennial shrub, Retama sphaerocarpa (L.) Boiss

This paper introduces a methodology to analyse the structural costs on plant potential fitness, empirically exemplified in the hierarchical shoot system of a Mediterranean perennial plant, Retama sphaerocarpa (L.) Boiss. During growing season every year (March-August), the terminal shoot (which is the basic unit of growth) develops inflorescences, flowers and fruits, as well as new shoots (first-, second- and third-order branching shoots) which have the potential to "behave" as terminal shoots in the following year. Different morphological and demographical aspects of the modules within the terminal shoot were measured in 100 terminal shoots selected from different plants of a natural population of R. sphaerocarpa. Complementary samples of 100 shoots of different branching orders were collected to obtain biomass estimations of the terminal shoots. We propose a simple procedure to estimate structural cost (biomass investment) on plant potential fitness (flowering buds) as a methodology for interpreting and comparing the consequences on fitness of different plant growth patterns. The results of this study exemplify how differential allocation patterns among plant structural modules, depending on their position within the shoot system, can be quantified to estimate their influence upon plant potential fitness.     

Roles of nectar robbers in reproduction of the tropical treelet Quassia amara (Simaroubaceae)

Summary Different subsets of mainland nectarivores visited Quassia amara (Simaroubaceae), a self-compatible, predominately bird-pollinated treelet, at three islands and the mainland in Panamá. Factors correlated with reproductive success, defined as seed to ovule ratio, included the species pollinating and robbing flowers, visitor activity, pollinator response to nectar robbing, and internal regulation of fruit production. The absence of robbers and former pollinators on an island separated from the mainland during the holocene was associated with shifts in flower size, nectar production, and 3–4fold increases in population reproductive success and pollinator efficiency (=seeds produced per visit). Exclusion of robbers at three sites resulted in seed production 4–12 times greater than control flowers, at which robbers accounted for 52–98% of all visits. Although 36% of buds and over 83% of all flowers were robbed, this had no direct influence on the recorded 36–61% respective abortion rates of buds and flowers. Opportunistic avian robbers appeared where normal robbers were absent; three avian robbers extensively used floral perforations made by Trigona bees, and all ancillary pollinators also robbed. Selection pressures from nectar robbers are discussed that may relate to plant reproductive fitness.     

What does the male function hypothesis claim?

Paternal, rather than maternal, fitness consequences of reproductive traits are the lynchpin in many hypotheses about reproductive evolution in hermaphroditic angiosperms. These hypotheses often differ in their predictions, so that supporting or contradictory evidence for one hypothesis may not reflect similarly on another, even though both may be referred to as ‘the male function hypothesis’. We provide graphical representations of four male function hypotheses from the recent literature in order to highlight their differences. We offer and explain two recommendations to reduce ambiguity in terminology: (1) male function hypotheses should address the evolution of excess flowers per se, rather than total flower number, which is usually highly plastic in modular organisms with open growth form; and (2) attention must be given to whole plant fitness, rather than fitness per flower or per inflorescence. In empirical studies, we recommend the use of path analysis to dissect the multiple pathways (through both male and female function) by which selection may act on excess flower number.     

Consequences of nectar robbing for the fitness of a threatened plant species

The effect of nectar robbing on plant fitness is poorly understood and restricted to a few plant species. Furthermore, the available studies generally evaluate the effects of nectar robbing on female fitness, disregarding the male component. Here we measured the effects of the nectar-robbing bumblebees on male (measured as pollen analogue flow distance) and female (measured as seed production) reproductive success in the insect-dependent Polygala vayredae, a narrow endemic species from the pre-Pyrenees (Spain). Intense nectar robbing by bumblebees significantly reduced the nectar available to legitimate pollinators in the studied population, and this reduction affected both male and female fitness. Significant differences were observed in fluorescent dye dispersion between robbed and non-robbed flowers within the population. Fluorescent dyes from non-robbed flowers were dispersed to larger distances and over a larger number of flowers when compared with robbed ones. Moreover, significant differences were observed in both fruit set and seed ovule ratios between the two groups, with non-robbed flowers presenting higher reproductive outcomes. However, no effect on seed weight was detected among treatments. The data obtained suggest that in this species, nectar robbing has important indirect and negative effects on plant fecundity, through both male and female functions, due to a modification in the foraging behaviour of legitimate visitors.     

Individual heterogeneity in fitness in a long‐lived herbivore

Heterogeneity in the intrinsic quality and nutritional condition of individuals affects reproductive success and consequently fitness. Black brant (Branta bernicla nigricans) are long‐lived, migratory, specialist herbivores. Long migratory pathways and short summer breeding seasons constrain the time and energy available for reproduction, thus magnifying life‐history trade‐offs. These constraints, combined with long lifespans and trade‐offs between current and future reproductive value, provide a model system to examine the role of individual heterogeneity in driving life‐history strategies and individual heterogeneity in fitness. We used hierarchical Bayesian models to examine reproductive trade‐offs, modeling the relationships between within‐year measures of reproductive energy allocation and among‐year demographic rates of individual females breeding on the Yukon‐Kuskokwim Delta, Alaska, using capture–recapture and reproductive data from 1988 to 2014. We generally found that annual survival tended to be buffered against variation in reproductive investment, while breeding probability varied considerably over the range of clutch size‐laying date combinations. We provide evidence for relationships between breeding probability and clutch size, breeding probability and nest initiation date, and an interaction between clutch size and initiation date. Average lifetime clutch size also had a weak positive relationship with apparent survival probability. Our results support the use of demographic buffering strategies for black brant. These results also indirectly suggest associations among environmental conditions during growth, fitness, and energy allocation, highlighting the effects of early growth conditions on individual heterogeneity, and subsequently, lifetime reproductive investment.     

崇明东滩湿地芦苇种群内功能性状及生态对策变异分析

植物种群功能性状及生态对策变异对其自身环境适应能力及群落结构具有重要影响。该文基于崇明东滩湿地芦苇(Phragmites australis)种群内3个小种群不同发育时期分株集合的多项性状指标,分析了其性状及生态对策变异,并基于CSR、LHS生态对策体系,对各小种群的生态对策进行了排序。结果表明, 3个芦苇小种群的21项性状指标及C、R对策得分均存在显著差异。在LHS体系中,以比叶面积(11.5 mm2/mg)、株高(175 cm)和花序干质量(4 g)为分界线,可对3个小种群进行区分。处于生殖生长期的芦苇分株具有更大的植株大小、更高的叶片干物质含量及S对策得分,而处于营养生长期的分株则具有较小的植株大小、较大的比叶面积及R对策得分。总体而言,崇明东滩湿地3个芦苇小种群间及各小种群内处于不同生长发育阶段的分株集合间,都存在显著的性状差异及生态对策差异,且二者的差异模式基本吻合。芦苇种内性状及生态对策变异特征,可为该区芦苇种群的生态保育和恢复实践提供重要的理论参考和技术支撑。     

Effects of two types of herbivores on the population dynamics of a perennial herb

The joint effects of multiple herbivores on their shared host plant have received increasing interest recently. The influence of herbivores on population dynamics of their host plants, especially the relative roles of different types of damage, is, however, still poorly understood. Here, we present a modelling approach, including both deterministic and stochastic matrix modelling, to be used in estimating fitness effects of multiple herbivores on perennial plants. We examined the effects and relative roles of two specialist herbivores, a pre-dispersal seed predator, Euphranta connexa, and a leaf-feeding moth, Abrostola asclepiadis, on the population dynamics and long-term fitness of their shared host plant, a long-lived perennial herb Vincetoxicum hirundinaria (Asclepiadaceae). We collected demographic data during 3 years and combined these data with the effects of natural levels of herbivory measured from the same individuals. We found that both seed predation and leaf herbivory reduced population growth of V. hirundinaria, but only very high damage levels changed the growth trend of the vigorously growing study populations from positive to negative. Demographic modelling indicated that seed predation had a greater impact on plant population growth than leaf herbivory. The effect of leaf herbivory was weaker and diminished with increasing level of seed predation. Evaluation of individual fitness components, however, suggested that leaf herbivory contributed more strongly to host plant fitness than seed predation. Our results emphasize that understanding the effects of a particular herbivore on plant population dynamics requires also knowledge on other herbivores present in the system, because the effect of a particular type of herbivory on plant population dynamics is likely to vary according to the intensity of other types of herbivory. Furthermore, evaluating herbivore impact from using individual fitness components does not necessarily reflect the long-term effects on total plant fitness.     

Activation of the <Emphasis Type="Italic">WUS</Emphasis> gene induces ectopic initiation of floral meristems on mature stem surface in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

A gain-of-function Arabidopsis mutant was identified via activation tagging genetic screening. The mutant exhibited clustered ectopic floral buds on the surface of inflorescence stems. The mutant was designated as sef for stem ectopic flowers. Our detailed studies indicate that the ectopic flower meristems are initiated from the differentiated cortex cells. Inverse PCR and sequence analysis indicated that the enhancer-containing T-DNA from the activation tagging construct, SKI015, was inserted upstream of the previously cloned WUS gene encoding a homeodomain protein. Studies from RT-PCR, RNA in situ hybridization and transgenic plant analysis further confirmed that the phenotypes of sef are caused by the overexpression of WUS. Our results suggest that overexpression of WUS could trigger the cell pluripotence and reestablish a new meristem in cortex. The type of new meristems caused by WUS overexpression was dependent upon the developmental and physiological stages of a plant. With the help of some undefined factors in the reproductive organs the new meristems differentiated into floral buds. In a vegetative growth plant, however, only the new vegetative buds can be initiated upon the overexpression of WUS. These studies provide new insights of WUS on flower development.     

Temporally changing male reproductive success and resource allocation strategy in protandrousHeracleum lanatum (Apiaceae)

Few observations have been made on temporal changes in the siring success of flowers in the male stage. In this study, we estimated both male and female contributions to fitness for 21 plants of protandrous andromonoeciosHeracleum lanatum with differing dates of first flowering. The results of multiple regression analysis showed that total male fitness significantly increases with the advance of the first-flowering date but does not depend upon plant size, whereas female fitness increases with plant size but does not depend upon the first-flowering date. We also showed that the earlier-flowering plants have more late-blooming male flowers in their secondary umbels. Based on these results, we suggest that polymorphism of the early- and late-bloomers may be maintained by frequency-dependent selection through temporally changing male reproductive success.     

毛状副冠对高山植物喉毛花的适应意义

高山地区生境极端,却拥有许多形态特化的植物,非生物因素在塑造花部性状及其进化过程中发挥着重要作用。该研究选取龙胆科典型高山植物喉毛花(Comastoma pulmonarium)为对象,探究其毛状副冠在多雨、强辐射的极端高山环境中的适应意义及其对植物雌雄繁殖适合度的影响。结果表明:通过比较自然状态和人工去除副冠的花,毛状副冠有效减少了雨水对花粉的冲刷(t=2.61,P0.05),提高了受精比率(t=2.05,P0.05),但是对种子的质量,即种子重量和种子萌发率的影响不显著。另外,花粉浸泡在蒸馏水中后,其萌发率显著低于蔗糖溶液中(t=30.67,P0.001),表明毛状副冠能够有效减小雨水浸泡对花粉活力的影响;同时,与自然状态相比,去除毛状副冠后的花,经太阳暴晒后,其花粉萌发率同样极显著地降低(t=9.89,P0.001),表明毛状副冠有效地避免了太阳辐射对花粉质量产生的不利影响。该研究结果表明喉毛花的毛状副冠结构是应对高山恶劣环境的一种适应策略,对植株的雌性和雄性繁殖成功都具有重要意义,从而进一步证实了非生物因素在植物花部特征演化中的重要作用。     

High propagule production and reproductive fitness homeostasis contribute to the invasiveness of Lespedeza cuneata (Fabaceae)

Comparative studies of congeneric native and exotic species have proved fruitful in understanding plant traits that foster invasion. Using this approach, we investigate the complex reproductive system of the invasive Lespedeza cuneata (Dum.-Cours.) G. Don in relation to three native congeners in the variable environment of the North American tallgrass prairie. Lespedeza species produce both chasmogamous (CH) and cleistogamous (CL) flowers, and propagate clonally via vegetative buds. Utilizing multiple natural populations over 2 years, we investigated reproductive modes of individuals from bagged and unbagged treatments of each species. We found that L. cuneata produced a mean of five times as many seeds and a significantly greater number of vegetative buds than any native studied, and over twenty times as many CH flowers. Insect visitation significantly affected seed set in CH flowers, though some autonomous CH selfing occurred in all species. The invasive relied relatively less on selfing than the natives and exhibited less variation in reproductive output from both modes of reproduction. We conclude that the diverse reproductive biology and wide regeneration niche of L. cuneata in relation to its native congeners confer a fitness homeostasis that facilitates the successful spread of this invasive under a wide range of conditions.     

Are mismatches the norm? Timing of flowering,fruiting, dispersal and germination and their fitness effects in Frangula alnus (Rhamnaceae)

The close morphological and temporal links between phases of plant growth and reproduction call for integrated studies incorporating several reproductive phases from flowering to recruitment, and associated plant‐animal interactions. Phenological strategies, as well as plastic phenological response to climate change, incorporate complex interactions between developmental constraints, pollination and seed dispersal. Relationships between reproductive phenology and components of fitness were studied for two years in the north‐temperate, self‐incompatible, insect‐pollinated, and bird‐dispersed shrub Frangula alnus (Rhamnaceae). Fruit set, dispersal, germination and juvenile survival, as well as seed mass and juvenile size were measured in relation to flowering, fruiting and germination time. The results suggest that effects of flowering and fruiting time prevailed in subsequent phases, to some extent as far as to the juvenile phase, but effects of timing were complex and had partly opposing effects on different fitness components. Early flowers had higher fruit‐set and experiments indicated that synchronous peak flowering increased fruit‐set, but later flowers had higher seed mass. Peak fruiting was not associated with peak dispersal. Late fruits derived from late flowers promoted dispersal. Juvenile recruitment was enhanced by increasing seed size. We conclude that the phenology of flowering and fruiting in F. alnus comprises several features, each with different and sometimes counteracting effects on fitness components. From a general perspective, this result implies that we should not expect to find finely tuned matches in timing specifically between flowering and pollinators, and fruiting and seed dispersing birds.     

Multiple herbivores and coevolutionary interactions in an Ipomopsis hybrid swarm

Studies focusing on pairwise interactions between plants and herbivores may not give an accurate picture of the overall selective effect of herbivory, given that plants are often eaten by a diverse array of herbivore species. The outcome of such interactions may be further complicated by the effects of plant hybridization. Hybridization can lead to changes in morphological, phenological and chemical traits that could in turn alter plant–herbivore interactions. Here we present results from manipulative field experiments investigating the interactive effects of multiple herbivores and plant hybridization on the reproductive success of Ipomopsis aggregata formosissima X I. tenuituba. Results showed that ungulate herbivores alone had a net positive effect on plant relative fitness, increasing seed production approximately 2-fold. Caterpillars had no effect on plant relative fitness when acting alone, with caterpillar-attacked plants producing the same number of flowers, fruits and seeds as the uneaten controls. Caterpillars, however, significantly reduced flower production of ungulate browsed plants. Flower production in these plants, however, was still significantly greater (approximately 1.7-fold greater) than uneaten controls, likely leading to an increase in reproductive success through the paternal component of fitness given that fruit and seed production was not significantly different from that of herbivore-free controls. Although results suggest that herbivore imposed selection is pairwise, ungulates likely have a large influence on the abundance of, and hence the amount of damage caused by, caterpillar herbivores. Thus, because of the ecological interactions between ungulates and caterpillars, selection on Ipomopsis may be diffuse rather than pairwise, assuming such interactions translate into differential effects on plant fitness as herbivore densities vary. Plant hybridization had no significant effect on patterns of ungulate or caterpillar herbivory; i.e., no significant interactions were detected between herbivory and plant hybridization for any of the fitness traits measured in this study nor did plant hybridization have any significant effect on host preference. These results may be due to patterns of introgression or the lack of species-specific differences between I. aggregate formosissima and I. tenuituba. Plant hybridization per se resulted in lowered reproductive success of white colored morphs due in part to the effects of pollination. Although it appears that there would be strong directional selection favoring darker flower colors due to the lower reproductive success of the white colored morphs in the short run, the natural distribution of hybrids suggest that over the long run selection either tends to average out or there are no fitness differences among morphs in most years due to the additive fitness effects of hawkmoth and hummingbird pollinators.     

Modification of flower sex and acid phosphatase activity by phthalimides in female plants of Morus nigra L.

Phthalimide treatments at 125, 250 and 500 mg 1^–1 to female plants of dioecious Morus nigra L. induced intersex and male flowers. Qualitative and quantitative analyses of acid phosphatase in male and female flower buds showed that the male flower had significantly higher levels of the enzyme activity than the female flower buds. The level of acid phosphatase activity significantly increased in intersex and male flowers induced on female plants after phthalimide treatments.     

Compensation and Plasticity in an Invasive Plant Species

Plant plasticity under varying resources is one character that contributes to competitiveness and invasibility. The plasticity of plant modules of the invasive Japanese stilt grass (Microstegium vimineum) was examined under different light and nutrient levels using a balanced field and greenhouse study. Ample light and nutrients resulted in the greatest biomass accumulation in all plant modules. However, M. vimineum showed extreme plasticity, producing stolons and flowers (reproductive structures) under a wide range of environmental conditions except infertile, low light. The addition of nutrients under various shading regimes compensated for lower light levels, rendering little change in the allocation of carbon to reproductive structures. Data from the field study corroborate the greenhouse results, but also suggest plasticity in response to competition.     

Inter- and intra-generic differences in growth,reproduction, and fitness of nine herbaceous annual species grown in elevated CO2 environments

In assessing the capacity of plants to adapt to rapidly changing global climate, we must elucidate the impacts of elevated carbon dioxide on reproduction, fitness and evolution. We investigated how elevated CO₂ influenced reproduction and growth of plants exhibiting a range of floral morphologies, the implications of shifts in allocation for fitness in these species, and whether related taxa would show similar patterns of response. Three herbaceous, annual species each of the genera Polygonum, Ipomoea, and Cassia were grown under 350 or 700 ppm CO₂. Vegetative growth and reproductive output were measured non-destructively throughout the full life span, and vegetative biomass was quantified for a subsample of plants in a harvest at first flowering. Viability and germination studies of seed progeny were conducted to characterize fitness precisely. Early vegetative growth was often enhanced in high-CO₂ grown plants of Polygonum and Cassia (but not Ipomoea). However, early vegetative growth was not a strong predictor of subsequent reproduction. Phenology and production of floral buds, flowers, unripe and abscised fruits differed between CO₂ treatments, and genera differed in their reproductive and fitness responses to elevated CO₂. Polygonum and Cassia species showed accelerated, enhanced reproduction, while Ipomoea species generally declined in reproductive output in elevated CO₂. Seed quality and fitness (in terms of viability and percentage germination) were not always directly correlated with quantity produced, indicating that output alone may not reliably indicate fitness or evolutionary potential. Species within genera typically responded more consistently to CO₂ than unrelated species. Cluster analyses were performed separately on suites of vegetative and reproductive characters. Some species assorted within genera when these reproductive responses were considered, but vegetative responses did not reflect taxonomic affinity in these plants. Congeners may respond similarly in terms of reproductive output under global change, but fitness and prognoses of population persistence and evolutionary performance can be inferred only rarely from examination of vegetative characters alone.     

Florivory affects pollinator visitation and female fitness in <Emphasis Type="Italic">Nemophila menziesii</Emphasis>

While herbivory has traditionally been studied as damage to leaves, florivory – herbivory to flowers prior to seed set – can also have large effects on plant fitness. Florivory can decrease fitness directly, either through the destruction of gametes or through alterations to plant physiology during fruit set, and can also change the appearance of a flower, deterring pollinators and reducing seed set. In order to distinguish between these hypotheses, it is necessary to both damage flowers and add pollen in excess to study the effects of damage on pollen limitation. Very few studies have used this technique over the lifetime of a plant. Here I describe a series of experiments showing the effects of natural and artificial damage on reproductive success in the annual plant Nemophila menziesii (Hydrophyllaceae, sensu lato). I show that natural and artificial petal damage decreased radial symmetry relative to controls and that both types of damage deterred pollinator activity. Both naturally damaged flowers and artificially damaged flowers in the field set fewer fruit or seed relative to undamaged control flowers. Finally, in an experiment crossing artificial petal damage with pollen addition, petal damage alone over the lifetime of this plant decreased female fitness, but only after a threshold of damage was reached. The fitness effect appeared to be direct because there was no detectable effect of pollen addition on the relationship between florivory and fitness. This result implies that both damaged and undamaged plants show similar amounts of pollen limitation and suggests that pollinator-mediated effects contributed little to the negative effects of florivory on female fitness. Florivores may thus be an under-appreciated agent of selection in certain plants, although more experimental manipulation of florivory is needed to determine if it is important over a range of taxa.