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To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2745.2010.01688.x Byline: Hui Guo (1), Susan J. Mazer (2), Guozhen Du (1) Keywords: elevation; geographic variation; Pedicularis; population differentiation; reproductive ecology; seed mass; size-number trade-off Abstract: Summary 1. We examined geographic variation in mean individual seed mass (MISM) among 38 populations within and across nine Pedicularis species in the eastern Tibetan Plateau, measuring the effects of one extrinsic factor (elevation) and two intrinsic factors (plant size and mean seed number per fruit). 2. Across all populations, elevation is negatively correlated with MISM; within eight of nine species, this pattern is also observed among populations. This relationship, however, is not significant when controlling for variation in plant size or seeds per fruit. High-elevation populations produce smaller plants with more seeds per fruit than low-elevation populations; controlling for these variables eliminates the negative correlation between elevation and MISM. 3. Across all populations, the predicted trade-off between MISM and seeds per fruit is consistently strong, with or without controlling for the effects of plant size. By contrast, the trade-off between MISM and total seasonal fecundity can be detected only when controlling for plant size. 4. Independent of plant size, populations that produce small seeds do not support individuals with particularly low reproductive yield (fecundity x MISM). Accordingly, high-elevation populations exhibit neither lower reproductive yield nor smaller seeds than expected given their lower biomass. 5. Synthesis. In Pedicularis, elevation, plant size and seeds per fruit are all correlated with MISM among populations across species. Elevation is less important, however, than intrinsic factors in determining the MISM of a population; the effect of elevation on MISM disappears when the effects of intrinsic factors are controlled statistically. The observed decline in MISM with increasing elevation is therefore partly mediated by the decline in plant size and partly by an increase in mean seed number per fruit with elevation. Altitudinal variation in MISM across populations or species has been described before, but this is the first study to control for the effect of intrinsic factors simultaneously. This result calls into question the conclusions of studies that have detected geographic variation in MISM without controlling for variation in intrinsic factors. Author Affiliation: (1)Key Laboratory of Arid and Grassland Ecology Under Ministry of Education, Lanzhou University, Lanzhou 730000, China (2)Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA 93105, USA Article History: Received 24 September 2009; accepted 2 June 2010 Handling Editor: Hans Jacquemyn Article note: (*) Correspondence author. E-mail: guozdu@lzu.edu.cn

Premise of the study: The study of geographic variation in ecologically important traits within and among taxa is a first step toward understanding the environmental factors that contribute to population differentiation and species divergence. This study examines variation in mean sex allocation per flower (androecium mass/gynoecium mass) among 49 wild populations representing 12 Pedicularis species across an elevation gradient on the eastern Tibetan Plateau. Methods: We used population means to evaluate sources of variation in per-flower sex allocation within and across species. In particular, we evaluate the relative influence of intrinsic (i.e., plant size, estimated as aboveground stem biomass) vs. extrinsic factors affecting mean sex allocation among populations. Key results: Mean sex allocation per flower (the relative investment in male floral organs) is negatively correlated with mean plant size; populations of large plants produce relatively female-biased flowers. This relationship between mean plant size and mean sex allocation is not statistically significant, however, when the effect of elevation is controlled statistically. Among populations within and across species, mean sex allocation increases with elevation. This relationship persists even when the effect of mean plant size is controlled statistically. Factors associated with increasing elevation appear to favor genotypes and/ or taxa with male-biased flowers. Conclusion: Extrinsic environmental conditions may be more important than intrinsic resource status in determining patterns of geographic variation in mean sex allocation among populations or species of Pedicularis. We cannot conclude whether the effect of elevation on mean sex allocation is the result of environmentally induced plasticity, genetically based adaptation, or species sorting, but it is only partly mediated by mean plant size. Key words: elevation; geographic variation; Orobanchaceae; Pedicularis; population differentiation; sex allocation. doi: 10.3732/ajb.0900301

The study of plant responses to touch, particularly the responses of leaves, stems, and roots, has a long history. By contrast, floral responses are relatively unexplored. Stigma closure is common in the Bignoniaceae, but the factors influencing it are not well understood. We investigated factors influencing stigma closure and reopening and its effects on pollen receipt in seven Oroxylum indicum trees near Hat Yai, Thailand. The effects of pressure, conspecific and heterospecific pollen, and pollen load (the amount of pollen deposited) on stigma behavior were examined in 270 flowers (of the total 430 flowers evaluated in the entire study). Pressure alone resulted in faster closure than did conspecific pollination and faster reopening than did heterospecific pollination. Stigmas never reopened after conspecific pollination. Pollen load had no effect on stigma behavior. Stigmas discriminated between conspecific and foreign pollen; they reopened only after pollination with the latter. A manipulative experiment revealed that stigma closure did not affect the number of conspecific pollen grains received. We also counted pollen tubes in styles that were either hand-supplemented with outcross conspecific pollen or open-pollinated. Pollen tube numbers were highest after light pollination (~900 grains), indicating that interference among pollen grains may occur after pollination with very heavy loads (>6000 grains). Possible fitness consequences of these responses are discussed. Key words: bat pollination: Bignoniaceae floral movement: Oroxylum indicum; stigma closure. doi: 10.3732/ajb.0900100

The number of ovules per flower varies over several orders of magnitude among angiosperms. Here we consider evidence that stochastic uncertainty in pollen receipt and ovule fertilization has been a selective factor in the evolution of ovule number per flower. We hypothesize that stochastic variation in floral mating success creates an advantage to producing many ovules per flower because a plant will often gain more fitness from occasional abundant seed production in randomly successful flowers than it loses in resource commitment to less successful flowers. Greater statistical dispersion in pollination and fertilization among flowers increases the frequency of windfall success, which should increase the strength of selection for greater ovule number per flower. We therefore looked for evidence of a positive relationship between ovule number per flower and the statistical dispersion of pollen receipt or seed number per flower in a comparative analysis involving 187 angiosperm species. We found strong evidence of such a relationship. Our results support the hypothesis that unpredictable variation in mating success at the floral level has been a factor in the evolution of ovule packaging in angiosperms. Key words: bet hedging; ovule; pollination; reproductive evolution; seed set; stigmatic pollen load. doi: 10.3732/ajb.0800183

Multiple field populations of two pairs of diploid sister taxa with contrasting mating systems in the genus Clarkia (Onagraceae) were surveyed to test predictions concerning the effects of resource status, estimated as plant size, on pollen and ovule production and on the pollen:ovule (P:O) ratio of flowers. Most theoretical models of size-dependent sex allocation predict that, in outcrossing populations, larger plants should allocate more resources to female function. Lower P:O ratios in larger plants compared to smaller plants have been interpreted as supporting this prediction. In contrast, we predicted that P:O ratio should not vary with plant size in predominantly selfing plants, in which each flower contributes to reproductive success equally through male and female function. We found that, in all four taxa, both ovule and pollen production per flower usually increased significantly with plant size and that the shape of this relationship was decelerating. However, ovule production either decelerated more rapidly than or at the same rate as pollen production with plant size. Consequently,the P:O ratio increased or had no relationship with plant size. This relationship was population-specifc (not taxon-specific) and independent of the mating system. Possible explanations for the increasing maleness with plant size are discussed. Key words: Clarkia: gametophyte production; mating system; Onagraceae; pollen to ovule ratio; size-dependent sex allocation.

To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2745.2009.01485.x Byline: Simon A. Queenborough (1), Susan J. Mazer (2), Steven M. Vamosi (3), Nancy C. Garwood (4), Renato Valencia (5), Rob P. Freckleton (1) Keywords: Amazonia; breeding system; dioecy; hermaphrodite; reproductive biology; seed size Abstract: Summary Dioecious species may suffer a reproductive handicap compared to sympatric cosexual (hermaphroditic or monoecious) species of equal abundance simply because populations of dioecious species contain fewer seed-producing individuals. To compensate for this population-level disadvantage, natural selection in dioecious populations should favour females that reallocate those reproductive resources, that in cosexual individuals are invested in male function, towards the production of higher quality or more seeds, potentially leading to a higher density of established individuals. We tested for two compensatory fitness advantages (heavier seeds and higher population densities) in dioecious species in the flora of a high-diversity tropical forest in Western Amazonia. Using a phylogenetically corrected generalized linear modelling approach, we examined the phylogenetic dependence (Pagel's [lambda]) of seed mass, abundance, growth form and wood-specific gravity for 641 species from Yasuni National Park, Ecuador. Seed mass was highly correlated with phylogeny, but abundance was not. We then used AIC values to test for models (including breeding system) that best explained seed mass and species abundance, using the maximum likelihood values of [lambda]. Contrary to expectations, dioecious species exhibited no advantage with respect to either seed mass or population density; there was no difference in mean seed mass or abundance between dioecious species and their most closely related cosexual species. We compared our results with those from a similar forest in the Tambopata Wildlife Reserve, Peru. There, dioecious shrubs had larger seeds than hermaphroditic shrubs, but (as for Yasuni) there was no difference between breeding systems in seed size among trees. Differences in the composition of species sampled may have contributed to differences in the results between the two sites. We suggest that other individual fitness advantages, such as reduced inbreeding, increased dispersal, superior seed quality (e.g. better defences) or increased seed number contribute to the persistence of dioecious populations at Yasuni. Synthesis. Similarities in the statistical models of seed mass and abundance for plant species in a Western Amazonian rain forest indicate that selective pressures on the seed-producing individuals are similar, despite variation in sexual system. Therefore, breeding system may play a more limited role in community assembly of tropical forests than was previously considered. Author Affiliation: (1)Department of Animal and Plant Science, University of Sheffield, Western Bank, Sheffield S10 2TN, UK (2)Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA 93106, USA (3)Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4 (4)Department of Plant Biology, Southern Illinois University, Carbondale, IL 62901-6509, USA (5)Department of Biological Sciences, Pontificia Universidad Catolica del Ecuador, Quito, Ecuador Article History: Received 16 June 2008; accepted 19 January 2009 Handling Editor: Bettina Engelbrecht Article note: *Correspondence author. E-mail: s.a.queenborough@sheffield.ac.uk

In rare circumstances, scientists have been able to revive dormant propagules from ancestral populations and rear them with their descendants to make inferences about evolutionary responses to environmental change. Although [...]

A well-known, but largely untested, prediction in plant reproductive ecology is that dioecious taxa should produce larger, more, higher-quality, or better-defended seeds than cosexual taxa. Using a data set composed of 972 species in 104 families, representing the flora of the Tambopata Wildlife Reserve (Madre de Dios, Peru), we evaluated the first component of this prediction, examining ecological and evolutionary relationships between breeding system and mean seed size with two kinds of tests. First, we conducted cross-species analyses to determine whether species with different breeding systems differed significantly with respect to mean individual seed size. Second, we used a hypothesized phylogeny to identify pairs of the most closely related taxa or clades within the Tambopata community that differed with respect to breeding system. Comparing pair members allowed us to determine whether evolutionary divergence in breeding system (between taxa with unisexual vs. cosexual individuals) was consistently associated with evolutionary change in seed size. In both analyses, we controlled for potentially confounding effects of growth form by examining these relationships within woody and nonwoody taxa. Cross-species analyses revealed that dioecious species produced larger seeds than cosexual species among woody species, shrubs, lianas (each growth form analyzed separately), and all species pooled, but not among trees. Phylogenetically independent contrasts upheld the significant association between breeding system and seed size among woody taxa, lianas, and all taxa pooled, but not among shrubs. We discuss the implications of our findings for evolutionary hypotheses regarding associations between dioecy and seed size. Key words: angiosperms, breeding system, dioecy; monoecy; plant growth forms; rain forest; seed size.

The assumption of a ubiquitous trade-off between male and female investment is challenged by arguing that in highly self-fertilizing species, stabilizing natural selection should favor highly efficient ratios of male to female gametes. Further, an artificial selection on pollen and ovule production per flower in two sister species with contrasting mating systems is conducted.

As pollinators decline globally, competition for their services is expected to intensify, and this antagonism may be most severe where the number of plant species is the greatest. Using meta-analysis and comparative phylogenetic analysis, we provide a global-scale test of whether reproduction becomes more limited by pollen receipt (pollen limitation) as the number of coexisting plant species increases. As predicted, we find a significant positive relationship between pollen limitation and species richness. In addition, this pattern is particularly strong for species that are obligately outcrossing and for trees relative to herbs or shrubs. We suggest that plants occurring in species-rich communities may be more prone to pollen limitation because of interspecific competition for pollinators. As a consequence, plants in biodiversity hotspots may have a higher risk of extinction and/or experience increased selection pressure to specialize on certain pollinators or diversify into different phenological niches. The combination of higher pollen limitation and habitat destruction represents a dual risk to tropical plant species that has not been previously identified. extinction | latitudinal gradients | speciation | competition | pollen delivery

Autogamously self-fertilizing taxa have evolved from outcrossing progenitors at least 12 times in the annual wildflower genus, Clarkia (Onagraceae). In C. xantiana, individuals of the selfing subspecies (ssp. parviflora) flower at an earlier age, produce successive flowers more rapidly, and produce flowers that complete their development more rapidly than their outcrossing counterparts (ssp. xantiana). Two hypotheses have been proposed to explain the joint evolution of these whole-plant and individual floral traits. The accelerated life cycle hypothesis proposes that selection favoring a short life cycle in environments with short growing seasons (such as those typically occupied by parviflora) has independently favored genotypes with early reproduction, synchronous flower production, and rapidly developing, self-fertilizing flowers. The correlated response to selection hypothesis similarly proposes that selection in environments with short growing seasons favors early reproduction, but that rapid floral development and increased selfing evolve as correlated responses to selection due to genetic linkage (or pleiotropy) affecting both whole-plant and floral development. We conducted a greenhouse experiment using maternal families from two field populations of each subspecies to examine covariation between floral and whole-plant traits within and among populations to seek support for either of these hypotheses. Our results are consistent with the accelerated life cycle hypothesis but not with the correlated response to selection hypothesis. Key words: Clarkia; development rate; life history; mating systems; Onagraceae; protandry; self-fertilization.

Determining whether seed production is pollen limited has been an area of intensive empirical study over the last two decades. Yet current evidence does not allow satisfactory assessment of the causes or consequences of pollen limitation. Here, we critically evaluate existing theory and issues concerning pollen limitation. Our main conclusion is that a change in approach is needed to determine whether pollen limitation reflects random fluctuations around a pollen-resource equilibrium, an adaptation to stochastic pollination environments, or a chronic syndrome caused by an environmental perturbation. We formalize and extend D. Haig and M. Westoby's conceptual model, and illustrate its use in guiding research on the evolutionary consequences of pollen limitation, i.e., whether plants evolve or have evolved to ameliorate pollen limitation. This synthesis also reveals that we are only beginning to understand when and how pollen limitation at the plant level translates into effects on plant population dynamics. We highlight the need for both theoretical and empirical approaches to gain a deeper understanding of the importance of life-history characters, Allee effects, and environmental perturbations in population declines mediated by pollen limitation. Lastly, our synthesis identities a critical need for research on potential effects of pollen limitation at the community and ecosystem levels. Key words: elasticities; hand pollination; plant demography, pollen; pollen limitation, causes and consequences; pollinators; seed set; supplemental pollination.

Research has been conducted on the genotype fitness of the individual for such allozymes as phosphoglucoisomerase. The effect of allelic variation at the phosphoglucoisomerase C1 locus in Clarkia unguiculata on the male and female function components has been investigated and the results indicate the existence of differences between pollen donors for different phosphoglucoisomerase alleles.

Many species exhibit reduced siring success of self-relative to outcross-pollen donors. This can be attributed either to postfertilization abortion of selfed ovules or to cryptic self-incompatibility (CSI). CSI is a form of self-incompatibility whereby the advantage to outcross pollen is expressed only following pollinations where there is gametophytic competition between self and outcross pollen. Under the definition of CSI, this differential success is due to the superior prefertilization performance (pollen germination rate and pollen tube growth rate) of outcross pollen relative to self pollen. Although CSI has been demonstrated in several plant species, no studies have assessed among-population variation in the expression of CSI. We conducted a greenhouse study on Clarkia unguiculata (an annual species with a mixed-mating system) to detect CSI, and we compare our observations to previous reports of CSI in C. gracilis and another population of C. unguiculata. In contrast to these previous studies of CSI in Clarkia, we used genetic rather than phenotypic markers to measure the relative performance of selfed vs. outcross pollen. In this study, we measured the intensity of CSI in C. unguiculata from a large population in southern California and we determined whether the magnitude of pollen competition (manipulated by controlling the number of pollen grains deposited on a stigma) influenced the outcome of competition between self and outcross pollen. In contrast to previous investigations of Clarkia, we found no evidence for CSI. The mean number of seeds sired per fruit did not differ between self and outcross pollen following either single-donor or mixed pollinations. In addition, the relative success of selfed vs. outcross pollen was independent of the magnitude of pollen competition. These results suggest that: (1) one of the few nonheterostylous species previously thought to be cryptically self-incompatible is completely self-compatible (at least in the population studied here) or (2) phenotypic markers may be problematic for the detection of CSI. Key words: Clarkia; cryptic self-incompatibility; gametophytic competition; mating system; Onagraceae; outcrossing; pollen performance; selfing; siring success.

Modular organs present a special problem for evolutionary geneticists aiming to measure the genetic component of their variation. If the phenotype of traits expressed by newly produced leaves, flowers, or [...]

Evolutionary ecologists typically assess the degree of genetic variation in fitness-related traits in order to evaluate the potential for natural selection, genetic drift, and gene flow to drive genetic change. [...]

We sampled four wild populations of the highly autogamous Spergularia marina (Caryophyllaceae) in California to detect and to measure the magnitude of within- and among-population sources of phenotypic variation in gender and floral traits. From flowers and fruits collected from field and greenhouse-raised plants, we measured ovule number, seed number, mean seed mass, pollen production (greenhouse families only), mean pollen grain volume (greenhouse families only), anther number, anther/ovule ratio, pollen/ovule ratio (estimated using different flowers for pollen than for ovules; greenhouse families only), petal number, and petal size. Using greenhouse-raised genotypes, variation among maternal families nested within populations was evaluated for each trait to determine whether populations differ in the degree of maternally transmitted phenotypic variation. For each population, we used 15 greenhouse-raised maternal families to estimate the broad-sense heritability and genetic coefficient of variation of each floral trait. The magnitude and statistical significance of broad-sense heritability estimates were trait- and population-specific. Each population was characterized by a different combination of floral traits that expressed significant maternally transmitted (presumably genetic) variation under greenhouse conditions. Flowers representing two populations expressed low levels of maternally transmitted variation (three or fewer of nine measured traits exhibited significant maternal family effects on phenotype), while flowers representing the other two populations exhibited significant maternal family effects on phenotype for five or more traits. Our ability to detect statistically significant differences among the four populations depended upon the conditions under which plants were grown (field vs. greenhouse) and on the floral trait observed. Field-collected flowers exhibited significant differences among population means for all traits except anther number. Flowers sampled from greenhouse-raised maternal families differed among populations for all traits except ovule number, seed number, and petal size. We detected negligible evidence that genetic correlations constrain selection on floral traits in Spergularia marina.

Phenotypic and genetic variation and correlations among floral traits within and among four Primula species were measured to seek evidence for potential constraints on the independent evolution of floral characters, to examine the relationship between mating system, ploidy level, and sex allocation, and to determine whether some traits are more conservative than others within and across these congeners. We measured mean flower diameter, corolla depth, pollen production, modal pollen grain volume, ovule number per flower, and pollen: ovule ratios for 64 field-collected genotypes from northern Europe. These represented one heterostylous (P. farinosa: 2n = 18) and three homostylous (P. scotica: 2n = 54, P. scandinavica: 2n = 74, and P. stricta: 2n is similar to 126) species. All traits differed significantly among species and among the six taxon/morph categories identified (including three morphs of P. farinosa: pin, thrum, and homostylous). Pollen production per flower was significantly higher (and individual pollen grain volume lower) in the outcrossing P. farinosa than in any of the homostylous species; also, pin morphs produced significantly more pollen per flower than thrums in P. farinosa. Among the homostylous species, there were significant differences in all traits except modal pollen grain volume. Ovule number per flower and flower size were less variable among taxa than pollen production and pollen volume. Within species, there were several strong negative correlations among genets between pairs of traits, but each species exhibited a unique set of inverse relationships. We detected only one significant positive genetic correlation; in P. stricta, ovule number and pollen production per flower were positively correlated among genets. Among species means, two pairs of traits were negatively correlated: mean ovule number per flower vs. flower diameter (but P = 0.0587), and mean pollen production per flower vs. modal pollen grain volume. These negative correlations within and among taxa suggest that there may be intrinsic genetic constraints on the independent evolution of these floral characters, but that these constraints differ among species.

To determine the effects of density, genotype, and their interaction on individual seed mass in Raphanus sativus L., we replicated maternal and paternal families of seed across two planting densities in an experimental garden. Seeds were produced by a nested breeding design performed in the greenhouse. Among garden-raised plants, density had a strong negative effect on the mass of seeds produced. At low density, the identity of the greenhouse-grown maternal plants had a strong effect on F(sub 2) seed mass, while in high-density plots, there were no significant parental effects on mean seed mass. Significant parental genotype times density interactions contributed to variation in F(sub 2) seed mass. Norms of reaction for each of the 15 paternal sibships illustrate paternal family times density interactions. Three sibships exhibited significant declines in mean seed mass with increasing density; 12 sibships showed no change. Maternal family times density interaction effects on seed mass were also detected; among maternal sibships, mean seed mass at low density was negatively correlated with mean seed mass at high density. These results demonstrate: a) planting density has a strong effect on mean individual seed mass produced by adults; b) density influences the magnitude of maternal effects on progeny phenotype; and c) genotype times density interactions influence seed mass, potentially contributing to the maintenance of maternal genetic variation in seed mass in natural populations of wild radish.

To determine the effect of growing conditions on population parameters in wild radish, (Raphanus sativus L.: Brassicaceae), we replciated maternal and paternal half-sib families of seed across three planting densities in an experimental garden. A nested breeding design performed in the greenhouse produced 1,800 [F.sub.1] seeds sown in the garden. We recorded survivorship, measured phenotypic correlations among and estimated narrow-sense and broad-sense heritabilities ([h.sup.2]) of: days to germination, days to flowering, petal area, ovule number/flower, pollen production/flower, and modal pollen grain volume. Survivorship declined with increasing density, but the relative abundances of surviving families did not differ significantly among densities. Seeds in high-density plots germinated significantly faster than seeds sown in medium- or low-density plots, but they flowered significantly later. Plants in high-density plots had fewer ovules per flower than those in the other treatments. Petal area and pollen characters did not differ significantly among densities. Densities differed with respect to the number and sign of significant pheonotypic correlations. Analyses of variance were conducted to detect additive genetic variance ([V.sub.a]) of each trait in each density. At low density, there were significant paternal effects on flowering time and modal pollen grain volume; in medium-density plots, germination time, flowering time and ovule number exhibited significant paternal effects; in high-density plots, only pollen grain volume differed among paternal sibships. The ability to detect maternal effects on progeny phenotype also depended on density. Narrow-sense [h.sup.2] estimates differed markedly among density treatments for germination time, flowering time, ovule number and pollen grain volume. Maternal, paternal and error variance components were estimated for each trait and density to examine the sources of variation in narrow-sense [h.sup.2] across densities. Variance components did not change consistently across densities; each trait behaved differently. To provide qualitative estimates of genetic correlations between characters, correlation coefficients were estimated using paternal family means; these correlations also differed among densities. These results demonstrate that: a) planting density influences the magnitude of maternal and paternal effects on progeny phenotype, and of [h.sup.2] estimates, b) traits differ with respect to the density in which heritability is greatest, c) density affects the variance components that comprise heritability, but each trait behaves differently, and d) the response to selection on any target trait should result in different correlated responses of other traits, depending on density. Floral traits, heritability estimates, life history, phenotype, planting density, population parameters, Raphanus sativus.

A study to examine the correlates of pollen limitation in an effort to understand its occurrence and importance in plant evolutionary ecology is presented. The magnitude of pollen limitation observed in natural populations depends on both historical constraints and contemporary ecological factors.

Research has been conducted on selfing annual Spergularia marina (Caryophyllaceae). The role of genetic attributes of the individual's local environment in floral trait expression in Caryophyllaceae has been investigated via the greenhouse experiment, and the results are described.

Research has been conducted on phenotypic selection. Results suggest that selection coefficients estimated by path analysis via the use of phenotypic data are correlated with those based on genotypic data, and that the use of path analysis can reduce environmental biases in selection coefficient estimation.

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

Author(s): Susan J. Mazer [1] by The Committee on the Status of Pollinators in North America, National Research Council of the National Academies The National Academies Press: 2007. 307 pp. [...]

Status of Pollinators in North America by The Committee on the Status of Pollinators in North America, National Research Council of the National Academies The National Academies Press: 2007. 307 [...]

This study evaluated the ecological and taxonomic correlates of seed mass variation among 648 angiosperm species of the Indiana Dunes region (113 families, 507 genera in the original flora). The sample represented 50% of the species, 60% of the genera, and 67% of the families reported from the area. Species were chosen at random from the published flora. Each species was characterized by family membership, habitat, life history, phenological characters, and native vs. alien status, in order to determine the relationship among species between these variables and mean seed mass. Unique to this study are measurements of the effects of phenology and taxonomic family on seed mass. Each species occurred in [is greater than or equal to] 1 of 13 habitat types described in the Indiana Dunes flora. To determine the effect of apparent water and light availability on seed mass, each habitat was assigned to one of four categories representing combinations of inferred water and light availability. Life histories or life forms represented were: annuals, biennials, herbaceous vines, parasites, perennials, short-lived perennials, shrubs, small trees, trees, and woody vines. Two phenological variables were available for most species: the time at which flowering begins (early, middle, or late), and the duration of flowering (short: 3 mo). The mean seed mass of each species was established by weighing samples from herbarium specimens in the United States National Herbarium. The frequency distribution of raw seed mass is highly skewed among species, so mean seed mass for each species was assigned to 1 of 14 seed mass classes based on a log scale (cf. Baker 1972). This transformation achieved a nearly normal distribution and made the data presentation comparable to that of Baker. One-way ANOVAs measured the effects of each factor across all other variables: two-way ANOVAs were conducted to detect significant interactions and strong associations between characters; multi-factorial ANOVAs were performed to measure the effect of each class variable independent of the others and to corroborate associations between characters suggested by the two-way ANOVAs. One-way ANOVAs revealed a statistically significant effect of all ecological and taxonomic factors on seed mass, with the exception of native vs. alien status. Seed mass variance was accounted for as follows: family, 30%; life history, 22%; habitat, 8%; water/light category, 5%; onset of flowering, 5%; and duration of flowering, 4%. The smallest seeds were produced by the Scrophulariaceae and the largest by the Fabaceae, Liliaceae, and Rosaceae. The largest seeded species lived in closed habitats: wooded dunes, thickets, and wet dunes. Small-seeded species were associated with open habitats: wet dunes, aquatic habitats, marshes, and streamsides. Light availability was a better predictor of relative seed mass than was inferred water availability. The strong effect of life history on seed mass was due primarily to the extremely large seeds produced by trees. Significant differences in seed mass were not detected among life forms producing seeds of intermediate mass (seeds produced by annuals, biennials, perennials, shrubs, small trees, and vines were statistically indistinguishable). Early flowering and flowering of short duration were associated with the production of large seeds. Two-way ANOVAs detected eight significant two-way interactions: family x native vs. alien status, family x life history, family x onset of flowering, habitat x life history, water/light category x life history, water/light category x native vs. alien status, life history x duration of flowering, and onset of flowering x duration of flowering. These were further evaluated to determine the source of the interaction. Multi-factorial ANOVAs provided measurements of the effects of one class variable on seed mass while all other variables were controlled statistically. The statistical effect on seed mass of each variable independent of the others was much lower than in the one-way ANOVAs. Seed mass variance was explained independently by each variable as follows: family, 13%; life history, 13%; habitat, 4%; water/light category, 3%; onset of flowering, 1%; and duration of flowering, 1%. Two strong associations were detected in these ANOVAs: an association between family and habitat, and between life history and onset of flowering. Although the effects of ecological and life history characters on seed mass evaluated in this study were highly statistically significant, the [R.sup.2] values associated with these effects were quite low. For example, habitat accounted for only 4% of the variance in seed mass independent of the other effects measured. This suggests that at the geographic scale investigated in this study, there is no primary habitat-specific ecological attribute that determines the seed mass of a habitat's component species. Seed mass of a species is determined by a combination of its phylogeny, life history, phenology, and ecological attributes, including variables not measured in this study. Even the most complete ANOVAs (including effects due to all variables measured) accounted for no >44% of the total variance in seed mass among species. The results of this study parallel previous comparative works that have demonstrated associations between seed mass and life form or habitat type. Seed mass does segregate among species occupying distinct habitats, but this relationship is due largely to associations among taxonomic family, life form, and habitat.

Hermaphroditic plants gain fitness through both female and male reproductive success (RS). We present an equation for estimating male RS in panmictic populations of self-incompatible plants with perfect flowers. The results of the simulations conducted using this model demonstrate that male RS and plant gender are sensitive to the frequency distribution of mate size and to the number of mates. When the frequency distribution of flower number per plant is changed from normal to L-shaped, the male fitness function decelerates with increasing flower number. Compared to large populations, in small populations small individuals will reproduce relatively more through pollen, while large individuals will be relatively more female.

We examined the effects of seed mass on performance between the time of seed dispersal and emergence within seven sympatric rain forest woody species of Psychotria in two contrasting natural habitats: gaps and shaded forest. We determined the effects of seed mass on emergence (the total proportion of emerged seedlings) and on the speed of emergence (the time necessary to reach 50% total emerged seedlings) in both greenhouse and field conditions, and we observed the effects of seed mass on the risk of removal by animals in the field. The effects of seed mass on performance were specific to species and habitat. For example, in two species, seed mass had a positive effect on emergence, while another showed a negative effect; for most of the species, effects on performance restricted to only one habitat (shaded forest or gap). Similarly, the results for effects of seed mass on the risk of removal were species- and habitat-specific. In the greenhouse, seed mass did not affect either emergence or the speed of emergence under either high or low light conditions. Our results suggest that: (i) seed mass did not have a general effect on emergence success and (ii) the effects of seed mass on seedling emergence are driven by external ecological factors more than by intrinsic effects of seed mass. Seed-removing animals appear to be an important ecological agent operating on intraspecific seed mass variation. Key words: germination; neotropical rain forest; Psychotria; Rubiaceae; seed mass; seed mass variation; seed size; seed size variation; seedling emergence., INTRODUCTION Offspring size plays a key role in the establishment of the juvenile phase of an organism's life cycle. In plants, seed mass can influence the probability of seedling establishment [...]

Two widespread assumptions that underlie models of the evolution of sex allocation in hermaphroditic systems are tested using Spergularia marina. These assumptions, that resource allocations to male and female function are heritable and that a genetically-based correlation between male and female reproductive function exists, are shown to be justified. Results show that a negative relationship between male versus female primary investment exists, although the asymmetrical correlated responses to selection suggest that this relationship is not always expressed.

Ecology, Biogeography, and Evolution of Dormancy and Germination by Carol C. Baskin and Jerry M. Baskin Academic, San Diego, 1998. 680 pp. $99.95. ISBN 0-12-080260-0. We often regard the life [...]