Morph-specific differences in reproductive success in the distylous Primula veris in a context of habitat fragmentation

Heterostylous self-incompatible plant species are particularly sensitive to habitat fragmentation and to disruption of pollination processes because of the need of intermorph cross-pollination for producing seeds. Heterostyly is characterized by sexual polymorphism through the occurrence of two (distyly) or three (tristyly) morph types that differ in floral traits (style length and anther position). We examined whether the long-styled (pin) and short-styled (thrum) morph types show differences in reproductive components and responses to habitat fragmentation in the distylous, self-incompatible perennial herb Primula veris. We documented reproductive components for pin and thrum individuals and their relationships with population size, plant density and morph ratio (pin frequency), in nine populations from Flanders (northern Belgium) located in fragmented habitats of the intensively used agricultural landscape. Seed abortion increased in small populations as a result of inbreeding depression. Fruit set increased with plant density. Seed set was positively related to pin proportion. Seed set was higher for pin than thrum in small populations, but lower in large populations. Two hypotheses can be considered to explain these morph-specific differences: a pollen transfer asymmetry, and a reproductive advantage for the partially self-compatible pin morph. Morph types appear to respond differently to habitat fragmentation constraints. A floral morph type showing partial self-compatibility may be favored in populations under pollination failure, because it can increase reproductive success and mating opportunities through intramorph crosses.     

Effect of plant traits and population structure on the female reproductive success of the endemic Primula elatior subsp. bergidensis (Primulaceae)

This study explores the possible causes of variation in female reproductive success of the subspecific taxon Primula elatior subsp. bergidensis, a distylic endemic to the north-western Iberian Peninsula, by analysing both vegetative and reproductive traits. In three populations, we marked vegetative and reproductive individuals either by mapping the spatial position of every individual (in one population), or by establishing permanent quadrats (in the remainder two populations). We recorded floral morph (pin or thrum), width and length of the largest leaf, scape length, and number of flowers produced; all individuals were monitored to estimate the number of fruits and seeds produced. The results show that the morph ratio did not differ significantly from 1:1 in any of the populations. The number of flowers per plant varied between populations, and longer scape length was associated with higher fruit set in all populations. Plant size, scape length, and population spatial structure all had major effects on reproductive success, but the strength—and in some cases the direction—of the effects varied among populations.     

Sequential variation in the components of reproductive success in the distylousJasminum fruticans (Oleaceae)

A 2-year study of three natural populations of the distylousJasminum fruticans showed that mean fruit and seed production were significantly greater in shortstyled plants (thrums) than in long-styled plants (pins). In this study, we investigated the role of four sequential factors which may differentially influence fruit and seed set in the two floral morphs: (1) differences in flowering phenology, (2) a limitation of pollen transfer towards pins, (3) a differential capacity of the two morphs to act through famale and male function and (4) differential fruit abortion in the two morphs. Fruit set was significantly influenced by differences in flowering phenology although there were no differences in flowering time between the two morphs. supplementary pollinations in a natural population significantly increased fruit set and reduced the difference in fruit set between the two morphs in relation to controls, indicating a limitation on pollen transfer which was most severe towards pin stigmas. In reciprocal crosses, seed set was significantly dependent on the paternal and maternal identity of the pin parent. There was no significant variation among thrums for their performance as male or female parent. Furthermore, individual pin plants with relatively high percentage seed set as female parents gave poor seed set as male parents and vice-versa. Whereas fruit removal had no effect on seed number in thrum plants, a greater proportion of viable seeds were produced on pin plants which were left to naturally mature their fruits than on pins which had fruits artificially removed, suggesting the occurrence of selective fruit abortion in pins but not in thrums. The initially greater maternal fitness of thrums due to their greater success as pollen recipients may thus be opposed by increased viable seed set in the pins due to factors acting after the pollination stage. The relative reproductive success of floral morphs in the distylousJ. fruticans is thus differentially influenced by ecological factors occurring at different stages of the reproductive process.     

Reproductive conflicts ofPalicourea padifolia (Rubiaceae) a distylous shrub of a tropical cloud forest in Mexico

We studied a population of the distylousPalicourea padifolia (Rubiaceae) in a cloud forest remnant near Xalapa City, Veracruz, México to explore possible asymmetries between floral morphs in the attractiveness to pollinators, seed dispersers, nectar robbers, floral parasites, and herbivores. We first assessed heterostyly and reciprocal herkogamy by measuring floral attributes such as corolla length (buds and open flowers), style and anther heights, stigma and stamen lengths and the distance between the anther tip to the stigma lobe. We then estimated floral and fruit attributes such as flower size, anther height, number and size of pollen grains, fruit size, seed size, nectar production, and flower and fruit standing crops to assess differences between floral morphs in attracting and effectively using mutualistic pollinators and seed dispersers. Also, floral parasitism and nectar robbing were assessed in this study as a measure of flower attractiveness to antagonists. The system seems to conform well to classical heterostyly (e.g. reciprocal stamen/style lengths, pollen and anther dimorphism, intramorph incompatibility) yet, there were several tantalizing differences observed between pin and thrum morphs. Thrum flowers have longer corollas and larger but fewer pollen grains than pin flowers. Both morphs produced the same total number of inflorescences, developed the same number of buds, and opened the same number of flowers per inflorescence during the flowering season. Nectar production and sugar concentration were similar between floral morphs but the reward was not offered symmetrically to floral visitors throughout the day. Nectar concentration was higher in pin flowers in the afternoon. The numbers of developing, fully developed, and ripe fruits were the same between floral morphs, however, fruits and seeds were larger than those of thrums. The incidence of fly larvae was higher among thrum flowers and damage by nectar robbing was the same between floral morphs. Fruit abortion patterns of flowers manually pollinated suggest intra-morph sterility (self and intramorph incompatibility). There were no differences between morphs in fruit and seed set per flower following legitimate pollination although thrums were more leaky than the pins (intramorph compatibility).     

新疆郁金香营养生长、个体大小和开花次序对繁殖分配的影响

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

A REEXAMINATION OF THE POLLEN-DONATION HYPOTHESIS IN AN EXPERIMENTAL POPULATION OF ASCLEPIAS EXALTATA

The evolution of large floral displays in hermaphroditic flowering plants has been attributed to natural selection acting to enhance male, rather than female, reproductive success. Proponents of the “pollen-donation hypothesis” have assumed that maternal resources, rather than levels of effective pollination, limit fruit set. We investigated the pollen-donation hypothesis in an experimental population of poke milkweed, Asclepias exaltata, where effective pollination did not limit fruit set. Specifically, we examined the effects of flower number per plant, and flower number per umbel on male reproductive success (number of fruits sired) and female reproductive success (number of fruits matured). In 1990, a paternity analysis was performed on fruits collected from 53 plants whose inflorescences were not manipulated. Flower number per plant was significantly correlated with male success, but not with plant gender. Flower number per plant was also significantly correlated with female success, but umbel number and stem number per plant together explained more than half (58%) the variation in female success. The percentage of fruit set was not significantly correlated with flower number per plant. Plants with large floral displays did not disproportionately increase in male reproductive success, relative to female success, as predicted by the pollen-donation hypothesis. In 1991, the effect of flower number per umbel on male and female reproductive success was investigated. Flower number per umbel was manipulated on four umbels per plant by removing flowers to leave 6, 12, or 18 flowers in each umbel. Plants with the largest umbels effectively pollinated twice as many flowers on other plants, but produced only 1.35 times as many fruits as plants with 6 and 12 flowers per umbel. Relative maleness of plants with large umbels was nearly twice that of small and medium umbels. Although these observations are consistent with the pollen-donation hypothesis at the level of umbels, they are problematic, because much of the variation in flower number per umbel exists within, rather than among, plants in natural populations. Thus, plants consist of both reproductively male (large) and female (small) inflorescences, which act to increase total reproductive success. It is therefore inappropriate to explain the evolution of large floral displays in milkweeds solely in terms of potential male reproductive success.     

Pollination biology and the impact of floral display, pollen donors, and distyly on seed production in Arcytophyllum lavarum (Rubiaceae)

In animal-pollinated plants, two factors affecting pollen flow and seed production are changes in floral display and the availability of compatible mates. Changes in floral display may affect the number of pollinator visits and the availability of compatible mates will affect the probability of legitimate pollination and seed production. Distyly is a floral polymorphism where long-styled (pin) and short-styled (thrum) floral morphs occur among different individuals. Distylous plants frequently exhibit self and intra-morph incompatibility. Therefore changes in morph abundance directly affect the arrival of compatible pollen to the stigmas. Floral morph by itself may also affect female reproductive success because floral morphs may display differences in seed production. We explored the effects of floral display, availability of neighboring compatible mates, and floral morph on seed production in the distylous herb ARCYTOPHYLLUM LAVARUM. We found that floral display does not affect the mean number of seeds produced per flower. There is also no effect of the proportion of neighboring legitimate pollen donors on seed production in pin or thrum flowers. However, floral morphs differed in their female reproductive success and the thrum morph produced more seeds. Hand pollination experiments suggest that differences in seed production between morphs are the result of pollen limitation. Future research will elucidate if the higher seed production in thrum flowers is a consequence of higher availability of pollen donors in the population, or higher efficiency of the pin morph as pollen donor.     

Reproductive phenology in three Genisteae (Fabaceae) shrub species of the W Mediterranean Region

We studied the flower duration, the phenology of flowering and fruiting, and flower, fruit, and seed production in three Genisteae shrub species of the W Mediterranean Region: Cytisus multiflorus, C. striatus , and Retama sphaerocarpa . Flower duration was negatively correlated with temperature, and in the case of C. striatus it was also influenced by pollination. In Cytisus multiflorus , which flowers during winter in the population studied, two floral morphs were recognized differentiated by flower size, phenological pattern, and production of the reproductive organs: morph LF (large flowers) and morph SF (small flowers). The former is earlier in phenology but its reproductive success is less than the second since it not only produces significantly fewer flowers/plant, but also a smaller crop of fruit and seeds. The flowering of the LF morph lasted some three months and of the SF morph 11 weeks. The winter-spring flowering C. striatus , with a four month duration of flowering time, is sympatric with C. multiflorus and their flowering periods overlap, but the former is more successful reproductively. Retama sphaerocarpa is clearly spring flowering, with an extremely short duration of flowering (c. 6.5 weeks), but, unlike the other two species which disperse their seeds in the same season in which they are produced, it staggers the dispersal of its diaspores over more than one year. Despite the great flower per plant production, especially in Retama sphaerocarpa , and of the number of fruit initiated, the final crop of fruit and seed/plant is low in the three species (C. multiflorus : fruit 8.40% and seeds 1.96%; C. striatus : fruit 13.09% and seeds 4.12%; Retama sphaerocarpa : fruit 5.65% and seeds 1.33%).     

Vulnerability and determinants of reproductive success in the narrow endemic Antirrhinum microphyllum (Scrophulariaceae)

The breeding system and flowering phenology of the narrow endemic Antirrhinum microphyllum (Scrophulariaceae) were studied in order to assess the main factors affecting female reproductive success and to identify existing or potential threats to the viability of its populations. Hand-pollination experiments showed that A. microphyllum is an allogamous self-incompatible species. In both populations studied, the flowering season was 4 mo long and mean flowering duration per plant was about 1 mo. Peak flower production took place between mid-April and mid-May and overlapped with the period of activity of the main pollinator, Rhodanthidium sticticum (Megachilidae). Estimated mean number of seeds produced per plant was 9391, showing that population viability is not presently limited by seed output. The study of the direct and indirect effects of plant size, phenological traits (first flowering date, flowering duration, and flowering synchrony), and distance to neighbor plants on reproductive success was performed using structural equation modeling (SEM). In both populations, number of flowers and plant size were the main factors that determined the total number of fruits produced by a plant. First flowering date and flowering synchrony also affected fruit production. Multisample comparison of path coefficients for the two populations rejected the possibility that reproductive patterns could be described by one single model.     

BREEDING SYSTEM EVOLUTION IN LEAVENWORTHIA: BREEDING SYSTEM VARIATION AND REPRODUCTIVE SUCCESS IN NATURAL POPULATIONS OF LEAVENWORTHIA CRASSA (CRUCIFERAE)

Populations of Leavenworthia crassa (Cruciferae) studied for 3 years exhibited among- and within-population genetic variation for a suite of floral and reproductive traits (flower width, petal length, anther position, ability to set seeds in the absence of pollinators, time to first flowering) associated with breeding system. We used electrophoretic markers to show that a population with small, monomorphically colored flowers with introrse anthers had a significantly lower outcrossing rate (t = 0.03) than did a population with larger, polymorphically colored flowers with extrorse anthers (t = 0.33). In the more-outcrossing population the correlation between higher maternal plant outcrossing rate and the suite of six traits approached significance (P < 0.067), with greater petal size, greater flower width, and reduced ability to set seeds in the absence of pollinators contributing significantly. Plants in selfing populations had a generally higher reproductive success, with a higher number of flowers per plant, a smaller proportion of unfertilized ovules, a smaller proportion of fertilized ovules aborted, a higher rate of fruit set, and overall a larger number of seeds matured than did plants from the more outcrossing populations. Pollen limitation did not appear to account for lower reproductive success in outcrossing populations. Resource limitation did not differ substantially between populations. However, within-ovary patterns of fertilization, abortion, and seed weight were significantly less random in outcrossing populations than in selfing populations, suggesting that differential gamete and embryo success may be responsible for lower reproductive success in outcrossing populations.     

Extended flowering in a Mediterranean shrub: Seasonal variability in seed quality and quantity

Fluctuating conditions throughout the year and changes in floral display may promote shifts in pollinator activity and predator pressure, influencing female reproductive output, especially for extended flowering species under seasonal climates. In this regard, flowering and fruit production were tracked in 2 different years in 2 populations of Ononis tridentata in Central Spain. Total fruit production was estimated, and fruits were harvested to obtain primary fruit investment, pollination success, predation incidence, seed production, seed weight and germination rates. Ononis tridentata combined spring mass flowering with a steady long flowering period across the summer and fall. The fewer flowers that are produced in fall were successfully pollinated, and produced fruits that were subject to minimal predation pressure relative to spring fruits. Moreover, fall fruits contained a higher number of heavier seeds and showed higher germination rates than those of spring seeds. Fall reproductive output represent 10% of annual viable seeds and thus may act as an important complement to the main spring reproductive investment. Extended flowering could be interpreted as a “bet-hedging strategy” for enduring Mediterranean unpredictable and changing environmental conditions.     

Genetic structure and AFLP variation of remnant populations in the rare plant Pedicularis palustris (Scrophulariaceae) and its relation to population size and reproductive components

We investigated plant reproduction in relation to genetic structure, population size, and habitat quality in 13 populations of the rare biennial plant Pedicularis palustris with 3-28500 flowering individuals. We used AFLP (amplified fragment length polymorphism) profiles to analyze genetic similarities among 129 individuals (3-15 per population). In a cluster analysis of genetic similarities most individuals (67%) were arranged in population-specific clusters. Analysis of molecular variance indicated significant genetic differentiation among populations and among and within subpopulations (P < 0.001). Gene flow (N(e) m) was low (0.298). On average, plants produced 55 capsules, 17 seeds per fruit, and 42 seedlings in the following growing season. The number of seeds per capsule was independent of population size and of genetic variability. In contrast, the number of capsules per plant (P < 0.05) and the number of seedlings per plant (P < 0.05) were positively correlated with population size. The relation between population size and the number of seeds per plant was not significant (P = 0.075). The number of capsules and of seeds and seedlings per plant (P < 0.01) were positively correlated with genetic variability. Genetic variability was independent of actual population size, suggesting that historical population processes have to be taken into account, too. Stepwise multiple regressions revealed additional significant relationships of habitat parameters (soil pH, C:N ratio), vegetation composition, and standing crop on reproductive components. We conclude that populations of P. palustris are genetically isolated and that reproductive success most likely is influenced by population size, genetic variability, and habitat quality. Management strategies such as moderate grazing, mowing, and artificial gene flow should endeavor to increase population size as well as genetic variation.     

CONSEQUENCES OF FLORAL VARIATION FOR MALE AND FEMALE REPRODUCTION IN EXPERIMENTAL POPULATIONS OF WILD RADISH,RAPHANUS SATIVUS L

We documented effects of floral variation on seed paternity and maternal fecundity in a series of small experimental populations of wild radish, R. sativus. Each population was composed of two competing pollen donor groups with contrasting floral morphologies and several designated maternal plants. Progeny testing with electrophoretic markers allowed us to measure paternal success. Realized fecundity by each maternal plant and the fraction of those seeds attributable to each pollen donor group were used as outcome variables in path analysis to explore relationships between floral characters (petal size, pollen grain number per flower, and modal pollen grain size), pollinator visitation patterns, and reproductive success. A wide range of pollinator taxa visited the experimental populations, and patterns of discrimination appeared to vary among them. The impact of visitation on male and female reproduction also varied among taxa; visits of small native bees significantly increased paternal success, while those of honey bees reduced male fitness. Only visits by large native bees had discernible effects on recipient fecundity, and, overall, fecundity was not limited by visitation. Maternal plants bearing large-petalled flowers produced fewer flowers during the experiment, reducing their total seed production. In these small populations, postpollination processes (at least in part, compatibility) significantly influenced male and female reproductive success. Variation in pollinator pools occurring on both spatial and temporal scales may act to preserve genetic variation for floral traits in this species.     

Patterns of pollinator-generated fruit set inOrchis morio (Orchidaceae)

Reproductive success of a deceptive species,Orchis morio, was investigated in relation to floral display, vertical position of fruits and dispersion pattern. A caging experiment confirmed the necessity of the presence of insect vectors for fruit development. In two Czech populations studied in 1997, insect-pollinated plants had on average 27.3 and 38% fruit set, compared to 96.7% for flowers pollinated by hand. Floral display (number of flowers per spike) was expected to positively affect the probability of pollinator visit. However, fruit set (number of fruits per spike) did not increase linearly with increasing floral display, but rose sigmoidally and approached an asymptotic value. Floral display enhanced reproductive success (fruit/flower ratio) up to a certain number of flowers (11–14), above which the relationship started to decrease and only increased the probability of production of at least one fruit. We also studied the effect of flower position within an inflorescence on the probability of being pollinated and we counted the number of seeds per capsule. A rapid decline in fruit set from the bottom to the top of the inflorescence observed probably reflects the behaviour of pollinators. The number of seeds per one capsule varied from 550 to 12 270. In addition, individuals growing in large clumps or isolated had lower reproductive success than those growing in small clumps. This result implies the existence of an intraspecific competition for pollinators and on the other hand inability of isolated individuals to attract a large number of pollinators.     

Effects of floral display size on male and female reproductive success in Mimulus ringens

Background and Aims

The number of flowers blooming simultaneously on a plant may have profound consequences for reproductive success. Large floral displays often attract more pollinator visits, increasing outcross pollen receipt. However, pollinators frequently probe more flowers in sequence on large displays, potentially increasing self-pollination and reducing pollen export per flower. To better understand how floral display size influences male and female fitness, we manipulated display phenotypes and then used paternity analysis to quantify siring success and selfing rates.

Methods

To facilitate unambiguous assignment of paternity, we established four replicate (cloned) arrays of Mimulus ringens, each consisting of genets with unique combinations of homozygous marker genotypes. In each array, we trimmed displays to two, four, eight or 16 flowers. When fruits ripened, we counted the number of seeds per fruit and assigned paternity to 1935 progeny.

Key Results

Siring success per flower declined sharply with increasing display size, while female success per flower did not vary with display. The rate of self-fertilization increased for large floral displays, but siring losses due to geitonogamous pollen discounting were much greater than siring gains through increased self-fertilization. As display size increased, each additional seed sired through geitonogamous self-pollination was associated with a loss of 9·7 seeds sired through outcrossing.

Conclusions

Although total fitness increased with floral display size, the marginal return on each additional flower declined steadily as display size increased. Therefore, a plant could maximize fitness by producing small displays over a long flowering period, rather than large displays over a brief flowering period.     

Effects of floral display and plant abundance on fruit production of Ryncholaelia glauca (Orchidaceae)

Flowering plant density can increase number of visits and fruit set in multi-flowering plants, however this aspect has not been studied on few flower species. We studied the effects of individual floral display and plant density on the fruit production of the epiphytic, moth-pollinated orchid, Ryncholaelia glauca, in an oak forest of Chavarrillo, Veracruz, Mexico. Species is non-autogamous, and produced one flower per flowering shoot each flowering season. We hypothesized that orchids with more flowering shoots and those on trees with clumps of conspecific should develop more fruits than isolated ones. R. glauca population flowers synchronouly, and individual flowers last up to 18 days, with flowers closing rapidly after pollination. Individuals produced few flowers per year, although some plants developed flowers in both seasons and fewer of them developed fruits both years. There was no relationship between flower number per orchid, or per host tree, with the number of fruits developed per plant. Host trees with flowering and fruiting orchids were randomly dispersed and the pattern of distribution of flowering and fruiting plants was not related. Apparently, pollinators visit the flowers randomly, with no evidence of density dependence. The fruit set of R. glauca was as low as fruit set of multi-flowered orchids moth pollinated, suggesting that fruit set on moth pollinated orchids could be independent of the number of flowers displayed.     

濒危植物安徽羽叶报春两种花型的繁育特性及其适应进化

二型花柱的维持机制和自然选择压力多年来一直是生态学和进化学研究领域的热点之一。通过实验室栽培和野外观察统计相结合的方法,对安徽羽叶报春两种花型(长柱花和短柱花)的形态特征、花粉活力、柱头可授性、花粉/胚珠比、自然授粉及结籽能力、自交亲和性等繁育特性进行了比较研究。结果表明:长、短柱花的花冠直径和裂片宽无明显差异,而花冠筒、雌蕊和雄蕊高、花粉数目及大小、P/O比均有显著差异。在自然条件下,长柱花所接受的总花粉数要明显高于短柱花的总花粉数,但所接受的异型花花粉数和平均每果结籽数两者无显著差异。长柱花和短柱花的花粉和柱头活力相似,均能在较长时间内维持较高活力,仅在开花末期显著下降。两种花型的花在自花授粉、同型异花授粉、异型花授粉条件下均能结籽,但异型花授粉的结籽数均明显高于自花授粉和同型异花授粉结籽数。在长柱花各种授粉方式中,花粉萌发率无明显差异,但异型花花粉管的生长速度明显比同型异花花粉和自花花粉的快,而在短柱花柱头上表现为异型花授粉的萌发率最高,但只要萌发后在花柱中的生长速度无显明差异。此外,综合上述结果,对二种花型花部综合征的维持机制及自然选择压力进行了探讨。     

Relationship between population size, allozyme variation, and plant performance in the narrow endemic Cochlearia bavarica

We studied population viability in relation topopulation size and allelic variation in thenarrowly-endemic, monocarpic perennial plantCochlearia bavarica in Bavaria. In 1996,we analysed allelic variation by allozymeelectrophoresis in 24 populations ranging from8–2000 flowering individuals. Fitness-relatedcharacters were investigated in 22 of the 24populations in the field in 1996 (reproductiveand vegetative traits) and 1998 (reproductivetraits only). Differences in allozyme patternwere large between a south-eastern and awestern population group. Genetic diversity,assessed by the Shannon-Wiener diversity index,was low within but high among populations.Small populations had fewer alleles per locus,fewer polymorphic loci, lower observedheterozygosity, and lower genetic diversitythan large populations. Environmentalvariables were not significantly correlatedwith population size or fitness with theexception of light availability, indicatingthat habitat quality was similar for large andsmall populations. Population size showedpositive correlations with number of flowers,fruit set per plant, number of seeds per fruit,and total seed output per plant. Fruit set andnumber of seeds per fruit were positivelycorrelated with the observed heterozygosity andthe proportion of polymorphic loci. We usedpath analyses to study the possible causalrelationships among population size, allelicvariation, and reproductive characters. Thesemodels showed that allelic variation had nodirect influence on reproductive characters,whereas population size did. We conclude thatat present population size reduces viabilityand also reduces allelic variation; but thereduced allelic variation may in the longerterm have negative feed-backs on bothpopulation size and viability.     

Pollinators and Reproductive Success of the Wild Cucurbit Cucurbita maxima ssp. andreana (Cucurbitaceae)

Abstract: We studied the reproductive success and pollinators of Cucurbita maxima ssp. andreana in different disturbed habitats where it grows naturally. Data were obtained from three populations. One grew within a soybean crop, the other within a corn crop, and the third in an abandoned crop field. Cucurbita maxima ssp. andreana is an annual vine with a flowering period from December to April. Male flowers appear first, thereafter female and male flowers appear together. Flower lifetime (9 h) was similar in male and female flowers. The pollinator guild was comparable for the three populations but some differences in the frequency of the insect species were observed. Native bees were the main pollinators in the population in the abandoned field, while beetles pollinated the populations in crop fields. These differences were not linked with the pre-emergent reproductive success, fruit and seed set, or fruit quality. This is a self-compatible plant. Fruit and seed set and fruit traits (total mass, width and length of fruits, number of seeds per fruit, and seed mass) did not show significant differences between hand-cross and hand-self pollinated flowers. This wild cucurbit is a generalist with respect to pollinator guild, and flower visitors seem to be highly efficient in pollen transference. Cucurbita maxima ssp. andreana is well adapted to disturbed habitats because plants ripened fruits successfully, regardless of the group of insects visiting flowers.     

Flowering phenology and female fitness: impact of a pre-dispersal seed predator on a sexually polymorphic species

In order to produce seeds, animal-pollinated plants must flower synchronously with and be attractive to their pollinators while avoiding antagonists. Here, we explore temporal and inter-individual patterns in pollination and pre-dispersal seed predation of Dianthus sylvestris by Hadena moths, within and among three sex morphs. We scored plants that started flowering at different periods in 2001 and 2003 and found that fruit set decreased and predation rates increased over one season, and most of the other season, granting a female reproductive advantage to early flowering plants, though, we found no morph-specific temporal patterns. Female plants set more fruits, and more of their fruits escaped predation in one year, but this did not grant them a reproductive advantage since they produce fewer flowers per plant than the other morphs. Instead, mixed plants showed a clear female reproductive advantage. We also examined predation types by Hadena and seed production in attacked and intact fruits of individually marked flowers. Though female Hadena moths laid eggs preferentially into perfect flowers, flower sexes suffered similar predation by itinerant caterpillars. Attacked fruits contained fewer and lighter seeds than un-attacked ones. We conclude that pre-dispersal seed predation by Hadena may select on flowering onset of this sexually polymorphic species.