Is increased male flower production a strategy for avoidance of predispersal seed predation in andromonoecious plants?

Floral gender in angiosperms often varies within and among populations. We conducted a field survey to test how predispersal seed predation affects sex allocation in an andromonoecious alpine herb Peucedanum multivittatum. We compared plant size, male and perfect flower production, fruit set, and seed predation rate over three years among nine populations inhabiting diverse snowmelt conditions in alpine meadows. Flowering period of individual populations varied from mid‐July to late August reflecting the snowmelt time. Although perfect flower and fruit productions increased with plant size, size dependency of male flower production was less clear. The number of male flowers was larger in the early‐flowering populations, while the number of perfect flowers increased in the late‐flowering populations. Thus, male‐biased sex allocation was common in the early‐flowering populations. Fruit‐set rates varied among populations and between years, irrespective of flowering period. Fruit‐set success of individual plants increased with perfect flower number, but independent of male flower number. Seed predation by lepidopteran larvae was intense in the early‐flowering populations, whereas predation damage was absent in the late‐flowering populations, reflecting the extent of phenological matching between flowering time of host plants and oviposition period of predator moths. Seed predation rate was independent of male and perfect flower numbers of individual plants. Thus, seed predation is a stochastic event in each population. There was a clear correlation between the proportion of male flowers and the intensity of seed predation among populations. These results suggest that male‐biased sex allocation could be a strategy to reduce seed predation damage but maintain the effort as a pollen donor under intensive seed predation.     

Factors affecting fruit and seed production of Paeonia ostii “Feng Dan”, an economically important oil tree

Many factors may affect reproduction of animal-pollinated species. In this study, the effects of pollen limitation, attractive traits (flower number, plant height and flower width) and flowering phenological traits (flowering onset, duration and synchrony) on female reproduction, as well as the patterns of variation in fruit and seed production within plants, were investigated in Paeonia ostii “Feng Dan” over two flowering seasons (2018 and 2019). Fruit set was very high (90%), and pollen supplementation did not increase fruit and seed production in either year, indicating no pollen limitation. Fruit set, ovule number per fruit and mean individual seed weight per fruit were not affected by any of the six attractive and phenological traits in either year, whereas seed number per fruit was related to the three attractive traits in one or both years. Seed number per plant was positively affected by the three attractive traits and best explained by flower number in both years, but the effect of each of the three phenological traits on seed number per plant differed between years. Within plants, the fruit set, ovule number, seed set and seed number per fruit declined from early- to late-opening flowers, presumably because of resource preemption, but the mean individual seed weight did not vary across the flowering sequence. Our study shows that attractive traits of Paeonia ostii “Feng Dan” are more important than flowering phenological traits in the prediction of total seed production per plant.     

Relationships between flowering phenology,plant size and reproductive success in shape Lotus corniculatus (Fabaceae)

Over three years the flowering phenology of individuals of Lotus corniculatus has been studied in relation to fruit set and seed predation to determine the relationships between four components of flowering time, plant size and reproductive success. Timings of first and peak flowering, and duration and synchrony of flowering differed between individuals in the same years. Between years, timing of first flowering was highly correlated for the same individuals, and was closely correlated with plant size and duration of flowering–larger plants flowered earlier and for a longer period. Peak flowering and synchrony were not correlated between-years for individuals.Fruit production and seed predation were correlated with some of the components of flowering phenology in some years, but not in others. The inconstancy of these relationships suggests that directional or stabilising selection is not acting consistently on the aspects of reproductive success studied in this work. The inconstancy of selection may result in the rather asynchronous flowering phenologies of individuals of L. corniculatus observed.We emphasize the importance of studying different components of flowering phenology in relation to individual plant size over several seasons. This work has shown that plant size not only has a direct effect on individual plant fecundity but also can influence flowering time and hence indirectly affect reproductive output.     

Landscape change alters reproductive phenology and sex expression in <Emphasis Type="Italic">Attalea</Emphasis> palms (Arecaceae) of southwestern Amazonia

As deforestation and land-use/land-cover change advance in tropical forest regions, an understanding of how plants adjust phenology and reproductive dynamics to altered landscapes can provide insights into plasticity, productivity, and population persistence. We compared the reproductive phenology, sex expression, and flower and fruit production of two monoecious Amazonian palms, Attalea phalerata and Attalea speciosa, in old-growth forest and as remnant trees growing in actively grazed pastures. Using 2 years of phenology data collected from natural populations near Vila Extrema, Rondônia, and eastern Acre, Brazil, we compared flowering and fruiting in the two habitats and tested for effects of palm height, crown size, and light availability on inflorescence and sex expression. Forest conversion to pasture stimulated greater overall flowering and fruiting in individual Attalea palms. As a population, remnant pasture palms continuously bore flowers and fruits year-round, while forest palms flowered seasonally in isolated peaks with consecutive months of inactivity. Crown size and greater light exposure affected flowering and fruiting dynamics in A. phalerata and A. speciosa, respectively, and increased light availability shifted A. speciosa sex expression towards greater female investment, primarily through regulation of sex determination and bud abortion. Removal of tropical forest does not always lead to the downfall of remnant tree populations, and under favorable conditions, such as abandonment of cropland and pasture, higher levels of reproduction can facilitate recovery of future generations. Tree species with flexible sex expression may be particularly resilient in the face of land-use and land-cover change.     

Edge effects decrease ant-derived benefits to seedlings in a neotropical savanna

Edge effects may lead to changes in mutualistic plant–animal interactions, such as seed dispersal, that are critical to plant regeneration. However, research into edge effects is neglected in the Brazilian cerrado, the largest neotropical savanna. We evaluated the consequences of edge effects in the cerrado for the regeneration of Erythroxylum pelleterianum (Erythroxylaceae), a shrub that benefits from seed dispersal by ants. We compared air temperature, relative humidity, and vapor pressure deficit, as well as the frequency and outcome of ant–diaspore interactions between cerrado edges and interiors. The inner portion of cerrado was likely to be moister than its borders, but seed production and germination did not differ between edge and interior of cerrado. Ants removed more seeds near fragment edges than at the interior. However, Myrmicinae ants dominated ant–fruit interactions at edges. These ants are likely to provide few benefits to the seeds. Seedlings of E. pelleterianum growing close to Ponerinae ant nests showed higher survival than seedlings growing away from nests in the interior of cerrado, but such effect disappeared near edges. Widespread seedling mortality due to a higher evaporative demand at edges may partially account for this effect. Furthermore, Ponerinae’s nests also showed a lower residence time near edges, decreasing possible benefits derived from ant colony activity such as nutrient enrichment and protection against insect herbivores. Edge effects could change the structure and dynamics of vegetation in cerrado fragments, due in part to the collapse of the mutualistic interactions demonstrated here.     

Reproduction of invasive Amur honeysuckle (Lonicera maackii) and the arithmetic of an extermination strategy

Ecological restorations often require removal of invasive species. The abundance of invasives has tended to catalyze research emphasizing removal, not broader understandings, of species mechanisms for persistence in the landscape (e.g. reproductive output and seed dispersal). Asiatic shrub honeysuckles (Lonicera spp.) are pernicious invaders throughout eastern North America. Heavy tree canopy cover apparently reduces growth and reproductive output in Lonicera maackii, which is widespread through the lower Midwestern United States. To help focus control efforts more effectively, we quantified the effect of tree canopy cover on vegetative growth, flowering, and fruit production under three canopy densities. Mean vegetative growth of flowering shoots was not affected by canopy cover. All aspects of sexual reproduction (flower production, fruit set, fruit number, fruit mass, seed number, and seed size) were strongly reduced by moderate shade. Although all individuals modify community and ecosystem properties, a limited number of high light individuals might also provide the greatest proportion of the seeds. Through model simulation of honeysuckle population structure in relation to canopy cover, we argue that it can sometimes be more efficient to initially target reproductive individuals in the high light edge and interior gap environments than to immediately focus on all individuals in the forest interior.     

Butterfly seed predation: effects of landscape characteristics,plant ploidy level and population structure

Polyploidization has been suggested as one of the most common mechanisms for plant diversification. It is often associated with changes in several morphological, phenological and ecological plant traits, and therefore has the potential to alter insect–plant interactions. Nevertheless, studies evaluating the effect of plant polyploidy on interspecific interactions are still few. We investigated pre-dispersal seed predation by the butterfly Anthocharis cardamines in 195 populations of two ploidy levels of the herb Cardamine pratensis (tetraploid ssp. pratensis, 2n = 30 vs. octoploid ssp. paludosa, 2n = 56–64). We asked if differences in incidence and intensity of predation among populations were related to landscape characteristics, plant ploidy level and population structure. The incidence of the seed predator increased with increasing plant population size and decreasing distance to nearest population occupied by A. cardamines. The intensity of predation decreased with increasing plant population size and was not affected by isolation. Probability of attack decreased with increasing shading, and intensity of predation was higher in grazed than in non-grazed habitats. The attack intensity increased with increasing mean flower number of plant population, but was not affected by flowering phenology. Individuals in tetraploid populations suffered on average from higher levels of seed predation, had higher mean flower number, were less shaded and occurred more often in grazed habitats than octoploid populations. When accounting for differences in habitat preferences between ploidy levels there was no longer a difference in intensity of predation, suggesting that the observed differences in attack rates among populations of the two ploidy levels are mediated by the habitat. Overall, our results suggest that polyploidization is associated with differentiation in habitat preferences and phenotypic traits leading to differences in interspecific interaction among plant populations. This, in turn, may facilitate further divergence of ploidy levels.     

Flowering phenology and reproduction of a forest understorey plant species in response to the local environment

Temperate forest understorey plants are subjected to a strong seasonality in their optimal growing conditions. In winter and early spring, low temperatures are suboptimal for plant growth while light becomes limited later in spring season. We can thus expect that differences in plant phenology in relation to spatiotemporal environmental variation will lead to differences in reproductive output, and hence selection. We specifically studied whether early flowering, a paradoxical pattern that is observed in many plant species, is an adaptive strategy, and whether selection for early flowering was confounded with selection for flower duration or was attributable to environmental variables. We used Geum urbanum as a study species to investigate the effect of relevant environmental factors on the species’ flowering phenology and the consequences for plant reproductive output. We monitored the phenology of four to six plants in each of ten locations in a temperate deciduous forest (Belgium). We first quantified variation in flowering time within individuals and related this temporal variation to individual flower reproductive output. Then, we studied inter-individual variation here-in and linked this to reproduction at the plant level, hence studying the selection differential. We found that flowering within individual plants of Geum urbanum was spread over a long period from June to October. Reproductive output of individual flowers, measured as total seed mass per flower, declined during the season. We found no indication for selection for early flowering but rather for longer flower duration. Larger plants had an earlier flowering onset and a higher seed mass, which suggests that these factors covary and are condition dependent. None of the studied environmental variables could explain plant size, although soil pH and to a lesser extent light availability had a positive direct effect on seed mass per plant. Finally, we suggest that the high intra-individual variation in flowering time, which might be a risk spreading strategy of the plant in the presence of seed predation, limits the potential for selection on flowering phenology.

     

Plant size,flowering synchrony and edge effects: What,how and where they affect the reproductive success of a Neotropical tree species

Plant reproductive success is supposedly influenced by phenology and individual size, which may be modified under edge effects. We tested if reproductive success, estimated by fruit set, in Senefeldera verticillata (Euphorbiaceae) is related to flowering synchrony and tree size, including plant height and circumference at breast height. The study was carried out in the interior and in edges of clearings for gas pipelines and electric lines of a lowland rainforest in south‐eastern Brazil. Monthly observations were performed during one reproductive season, of 19 individuals that grew at edges of electric lines and gas pipelines and at forest interior. Reproductive success was significantly higher at forest interior than at gas pipeline area; there was no significant difference between gas pipeline and electric line areas or between forest interior and electric line area. In the forest edges, only plant height was positively related to plant reproductive success. This is probably related to crown exposure to sunlight, which enhances flower production. At forest interior, reproductive success was positively influenced by the synchrony of flowering activity among neighbouring individuals. In contrast, flowering synchrony based on phenophase intensity negatively impacted reproductive success. Senefeldera verticillata shows temporal dioecy and is mainly pollinated by small social bees, and the high degree of flowering synchrony at low intensity may increase the number of mating partners and therefore enhance its reproductive success. Inside the forest fragments, individuals with thicker trunks showed lower reproductive success, which may be related to a loss of reproductive capacity of older individuals. Our results evidenced the complexity of responses experienced by tropical plants subjected to forest fragmentation because of linear clearings.     

FLOWERING,SEX RATIOS,POLLEN-OVULE RATIOS,FRUIT SET,AND REPRODUCTIVE EFFORT OF A DIOECIOUS TREE,MYRISTICA INSIPIDA (MYRISTICACEAE), IN TWO DIFFERENT RAIN FOREST COMMUNITIES

The flowering of Myristica insipida R. Br. was studied in two rain forest communities in northern Queensland. This dioecious, subcanopy tree had a male-biased sex ratio at both study sites. In the lowland population the male-bias could be attributed to males (trees producing staminate flowers) starting to flower at a smaller average size than females (trees producing pistillate flowers). There were no intersexual differences in spacing or distribution within the study sites. Males trees flowered earlier, flowered longer, and produced over twice as many flowers as females during the study season. Although the onset of flowering was rather variable, 18–22 days following heavy rains, most trees had a synchronous period of maximum flowering. Pollination manipulations determined that there was no fruit development without pollination, and that increasing pollen loads resulted in increased fruit set with diminishing effect. Taking into account the sex-ratios and intersexual differences in flower production, the pollen-ovule ratio was calculated to be 16,000–19,000. Male trees were found to expend more energy on flowering than female trees. Open-pollination resulted in 1.0% of female flowers setting fruit. The much greater cost of fruit production resulted in females expending 421% more energy on reproduction than males. Fruit and seed production were judged to be pollination-limited. Nonetheless, this species exhibited several characteristics that are predicted if dioecy evolved by means of sexual selection.     

Fecundity limits in Frangula alnus (Rhamnaceae) relict populations at the species’ southern range margin

The geographic range of many temperate plant species is constrained by climate, but it remains little known how climate affects population performance at low-latitude range margins. This study investigated the reproduction of the Eurasian tree Frangula alnus in relict populations near its southwestern range limit in southern Spain. The aim was to identify the principal stages and causes of ovule loss experienced by these marginal populations. More than 6,800 flowers were monitored over 2 years, insect observations and different experiments were carried out to assess levels of pollen and resource limitation, as well as the influence of flowering phenology on seed production. Most ovule losses occurred during flower anthesis and were due to strong cross-pollen limitation. Fruit set was affected by tree size, light regime and flowering phenology, probably through their effects on pollinator behaviour. Fruit set was almost zero throughout the first half of the flowering season. Then it increased paralleling changes in pollinator abundance but was soon overridden by increasing ovule desiccation due to summer drought. Successful seed production was mostly confined to a brief period near the end of the flowering season. Adverse weather during this period in the second study year resulted in a threefold bud and flower mortality and a 50% decrease of fruit production. Spring rainfalls in southwestern Spain have diminished more than 30% through past decades leading to an earlier onset of summer drought. This trend and its adverse effects on seed production may contribute to explaining the recent decline of F. alnus at its southwestern range limit.Electronic Supplementary Material Supplementary material is available in the online version of this article at     

VARIATION IN INDIVIDUAL FLOWERING TIME AND REPRODUCTIVE SUCCESS OF AGALINIS STRICTIFOLIA (SCROPHULARIACEAE)

Field studies on two populations of Agalinis strictifolia were conducted over a 3-year period to investigate the relationship between flowering time of individuals and plant size, flowering duration, flower and fruit production, fruit predation, and growth rate. Seasonal patterns of pollinator visitation were compared with those of individual flowering time, flower density, percent fruit production, and mean seeds/fruit. In general, early and middle flowering individuals (as determined by either first flowering date or peak flowering) were larger, flowered longer, and produced more flowers and fruits than late flowering individuals. Early and middle flowering individuals (based on first flowering date) also grew faster than late flowering individuals. Although early and middle flowering individuals produced more fruits, fruit predators did not damage a disproportionate number of fruits compared to late flowering individuals. Patterns of bee visitation showed no association with seasonal patterns of flower density, percent fruit production, mean seed/fruit, or individual flowering time. In populations of A. strictifolia, it would seem that biotic or environmental determinants of growth rate (hence size and reproductive success) may be more important in generating variation in individual flowering time than patterns of pollinator visitation or fruit predation.     

31种木本植物开花物候与系统发育的关系

植物物候通常被认为是由环境因素,如降水、温度和日照长度所决定,然而环境因素是否是物候唯一的决定因素仍然存在很大争议。谱系结构表征了植物在进化上的顺序,该发育时序是否对物候产生影响,当前仍然未知。在调查2016年春季新疆乌鲁木齐市最常见的31种木本植物的初始开花时间、败花时间和开花持续时间的基础上,通过分析植物开花物候的分布特征、开花物候在乔灌木间的差别、以及植物谱系距离与开花物候距离间的关系,试图揭示植物的开花物候和物种谱系(进化)顺序间的关系。结果表明:(1)新疆乌鲁木齐市31种木本植物的初始开花时间为4月18日±9d、败花时间为5月5日±12d、开花持续时间为(16±8)d;(2)乔木的初始开花时间和败花时间的标准差分别均低于灌木,乔木开花物候相对灌木更稳定;(3)乔木的初始开花和败花时间均显著早于灌木(P0.05),但开花持续时间在两者间未有显著性差异(P0.05);(3)31种木本植物间的初始开花时间距离、败花时间距离和开花持续时间距离均与物种谱系距离存在显著线性回归关系(P0.05)。综上可知:乔灌木在垂直空间上的分化使得木本植物的开花物候在植物生活型间存在不同。对植物的开花物候,除已被证明的降水、温度和日照长度等环境因素的影响外,物种进化顺序也可能造成了它在植物种间、时间和空间上的变异。     

Phenological variation in fruit characteristics in vertebrate-dispersed plants

Summary We investigated inter-specific variation in fruit characteristics — fruit size, seed number per fruit, seed weight, nutritional content, fruit persistence, and fruit synchronization — in relation to flowering and fruiting phenology in 34 species of fleshy fruited plants. Except for aspects of fruit synchrony and persistence, the results in general were inconsistent with previous suggestions about adaptive variation in phenologically related fruit traits. The main results were as follows: (1) Late flowering, late fruiting, lengthy development time from flower to fruit, and highly persistent fruits constitute a complex of correlated characteristics among the species. (2) Synchronization of fruiting within individuals increased from early ripening fruits to late ripening fruits. Fruiting synchrony was more pronounced in species with a small crop size than in species with a large fruit crop, whereas synchrony was not significantly related to flowering synchronization, nor to life form. (3) Nitrogen and carbohydrate content of fruit pulp did not vary in relation to phenology, whereas lipid content decreased from early to late ripening fruits. (4) No seasonal trends were found for variation in seed size or seed number per fruit. (5) Interactions with flowering phenology and developmental constraints are important in phenological fruiting patterns. Temporal variation in start of fruiting was partly (36%) explained by variation in flowering time. Seed weight variation explained 17% of variation in development time from flower to fruit. (6) Despite constraints from flowering and seed development, some adaptive adjustment in fruiting phenology is likely to be allowed for among the investigated species. Such an adaptive variation in fruiting phenology was suggested by intra-generic comparisons of Prunus and Vaccinium species.     

COMPARATIVE REPRODUCTIVE BIOLOGY OF ALPINE BIENNIAL AND PERENNIAL GENTIANS (GENTIANA: GENTIANACEAE) IN CALIFORNIA

Reproductive characteristics of three sympatric species of Gentiana exhibiting perennial and non-perennial life histories were studied in alpine meadows of the White Mountains of California during three consecutive years. High fruit and seed set and the production of a relatively large number of seeds characterized the alpine biennials, Gentiana tenella and G. prostrata. In contrast, fruit and seed set were considerably reduced and yearly seed production was relatively low in the alpine perennial, G. newberryi. Successful seed production in the biennial species was a result of low rates of flower predation, self-pollination, and the allocation of a comparatively high proportion of biomass to reproductive structures. Seed production in the perennial species was limited by high rates of flower predation, insufficient amounts of pollen reaching stigmas, an unusually late flowering period, and by the relatively small proportion of biomass allocated to reproduction.     

Factors affecting pollinator movement and plant fitness in a specialized pollination system

The rate of pollen exchange within and among flowers may depend on pollinator attraction traits such as floral display size and flowering plant density. Variations in these traits may influence pollinator movements, pollen receipt, and seed number. To assess how floral display size and flowering plant density affect parameters of pollinator visitation rate, pollen receipt per flower, seed number per fruit and the between-plant pollinator movements, we studied the self-incompatible plant, Nierembergia linariifolia. Per-flower pollinator visitation rate and bout length increased linearly with increasing floral display size. Pollen receipt per flower increased linearly with increasing flowering plant density. For seed number per fruit, a polynomial model describing an increased seed number per fruit at low density and a decreased seed number per fruit at high density provided a significant fit. Per-flower pollinator visitation rate was not associated with pollen receipt per flower and seed number per fruit. Bees visited plants located near to the center of the population more frequently than plants located at the periphery. Increases in both floral display size and flowering plant density led to an increased chance of a plant being chosen as the center of the pollinator foraging area. These results suggest that even though large floral displays and high flowering plant density are traits that attract more pollinators, they may also reduce potential mate diversity by restricting pollen movement to conspecific mates that are closely located.     

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.     

Oviposition pattern and within-season spatial and temporal variation of pre-dispersal seed predation in a population of Mimosa bimucronata trees

Spatial and temporal variation of pre-dispersal seed predation was investigated in a population of Mimosa bimucronata trees located in the south-east region of Brazil. Three main hypotheses were addressed: (1) that the life stages of the seed predator Acanthoscelides schrankiae are synchronised with the reproductive stages of its host plant; (2) that seed predation levels vary spatially as a result of differences in fruiting phenology synchrony and fruit production among trees; and (3) that predation levels should be affected by the proximity of trees, showing a spatial structure. Also investigated was the oviposition pattern of A. schrankiae among seeds and fruits. Twenty spatially referenced trees were monitored throughout a year to examine tree phenology and egg laying and adult emergence. The bruchine’s life stages were synchronised with the reproductive stages of M. bimucronata trees. Egg distribution among seeds and fruits was aggregated. Infestation rates of adult bruchines were not spatially related to fruiting phenology and there is evidence that seed predation is a spatially density-independent process, because the relationship between infestation rates and fruit production was not significant. Finally, it was observed that the distribution of adult bruchines was spatially structured, because similar levels of infestation were found among nearby trees.