Phylogenetic evidence for a flower size and number trade-off

The size and number of flowers displayed together on an inflorescence (floral display) influences pollinator attraction and pollen transfer and receipt, and is integral to plant reproductive success and fitness. Life history theory predicts that the evolution of floral display is constrained by trade-offs between the size and number of flowers and inflorescences. Indeed, a trade-off between flower size and flower number is a key assumption of models of inflorescence architecture and the evolution of floral display. Surprisingly, however, empirical evidence for the trade-off is limited. In particular, there is a lack of phylogenetic evidence for a trade-off between flower size and number. Analyses of phylogenetic independent contrasts (PICs) of 251 angiosperm species spanning 63 families yielded a significant negative correlation between flower size and flower number. At smaller phylogenetic scales, analyses of individual genera did not always find evidence of a trade-off, a result consistent with previous studies that have examined the trade-off for a single species or genus. Ours is the first study to support an angiosperm-wide trade-off between flower size and number and supports the theory that life history constraints have influenced the evolution of floral display.     

No evidence of sperm selection by female common shrews.

There is currently much interest in the suggestion that females are capable of post-copulatory (or cryptic) choice for male genetic compatibility. Here, I investigate this idea using data from mixed-paternity litters of the common shrew (Sorex araneus). Females of this species are highly promiscuous and, in natural populations, regularly incur costs of inbreeding by mating with close relatives. Selection should therefore favour female ability for sperm selection on the basis of male relatedness. No evidence was found in support of this idea. Relative number of offspring sired within mixed paternity litters was not significantly correlated with genetic similarity of males to the female mated. Relative fertilization success was, however, significantly related to male epididymal sperm counts. I conclude that most variation in relative fertilization success of male common shrews can be explained in terms of sperm competition, and that females of this species may not be capable of sperm selection.     

American Kestrel reproduction: evidence for the selection hypothesis and the role of dispersal

Many hypotheses attempt to explain why younger, less experienced birds have a relatively low reproductive output. We evaluated reproductive patterns of marked American Kestrels Falco sparverius nesting in boxes in southwestern Idaho from 1992 to 2006 to test predictions of these hypotheses. Results were consistent with the selection (differential mortality) hypothesis and did not support the constraint, restraint or recruitment hypotheses. Most known-age Kestrels nested in their first year of life, and there was no apparent short-term or long-term reproductive advantage to delayed breeding. The number of years that Kestrels nested in study area boxes ranged from 1 to 6 years, with most Kestrels nesting in only 1 year. Reproductive rates were higher for birds with at least 1 year of nesting experience than for birds nesting in boxes for the first time. After 2 years of nesting, reproductive rates levelled off; there was no evidence for additional improvement or for senescence. Differences in reproductive output with experience/age were due to variation among and not within individuals. Individuals that nested in more than 1 year had similar reproductive rates in their first and second years. Poor producers either died or dispersed after 1 year of nesting in study area boxes. Successful females that nested early in the season and successful males that had been produced locally had the highest probability of returning to nest in a subsequent year.     

Rapid response to artificial selection on flower size in Phlox

Quantitative characters are often said to evolve rather slowly, taking many generations to exhibit appreciable differences among populations. We tested this notion experimentally by performing bi-directional selection on corolla diameter of plants from a wild population of Phlox drummondii for three generations. By monitoring flower size, tube length and stigma-anther proximity of flowers, we obtained the direct and indirect responses to selection, and calculated genetic correlations, realized and narrow sense heritabilities using offspring-mother regression. Realized heritability of flower size was high (0.83), whereas genetic correlations among traits were weak or not significant. The per-generation average of the response in corolla diameter was about 5%. We found that P. drummondii has a great capacity to respond rapidly to selection, and this capacity may be in part responsible for the observed high degree of differentiation within the species. We also concluded that rapid evolution of morphological floral traits is possible.     

Effects of flower size and number on pollinator visitation to wild radish,Raphanus raphanistrum

Plant traits that increase pollinator visitation should be under strong selection. However, few studies have demonstrated a causal link between natural variation in attractive traits and natural variation in visitation to whole plants. Here we examine the effects of flower number and size on visitation to wild radish by two taxa of pollinators over 3 years, using a combination of multiple regression and experimental reductions in both traits. We found strong, consistent evidence that increases in both flower number and size cause increased visitation by syrphid flies. The results for small bees were harder to interpret, because the multiple regression and experimental manipulation results did not agree. It is likely that increased flower size causes a weak increase in small-bee visitation, but strong relationships between flower number and small-bee visitation seen in 2 years of observational studies were not corroborated by experimental manipulation of this trait. Small bees may actually have responded to an unmeasured trait correlated with flower number, or lower small-bee abundances when the flower number manipulation was conducted may have reduced our ability to detect a causal relationship. We conclude that studies using only 1 year, one method, or measuring only one trait may not provide an adequate understanding of the effects of plant traits on pollinator attraction.     

No evidence for pre-copulatory sexual selection on sperm length in a passerine bird

There is growing evidence that post-copulatory sexual selection, mediated by sperm competition, influences the evolution of sperm phenotypes. Evidence for pre-copulatory sexual selection effects on sperm traits, on the other hand, is rather scarce. A recent paper on the pied flycatcher, Ficedula hypoleuca, reported phenotypic associations between sperm length and two sexually selected male traits, i.e. plumage colour and arrival date, thus invoking pre-copulatory sexual selection for longer sperm. We were unable to replicate these associations with a larger data set from the same and two additional study populations; sperm length was not significantly related to either male plumage colour or arrival date. Furthermore, there was no significant difference in sperm length between populations despite marked differences in male plumage colour. We also found some evidence against the previously held assumption of longer sperm being qualitatively superior; longer sperm swam at the same speed as shorter sperm, but were less able to maintain speed over time. We argue that both empirical evidence and theoretical considerations suggest that the evolution of sperm morphology is not primarily associated with pre-copulatory sexual selection on male secondary sexual traits in this or other passerine bird species. The relatively large between-male variation in sperm length in this species is probably due to relaxed post-copulatory sexual selection.     

Effect of selection for spot size on reproduction and body weight in mice

Summary Spot size in descendants from the Goodale white-spotted stock of mice responded to selection for increased spot size. The realized heritability estimate was 0.52. However, no correlated response of reproduction to spot size selection was found in the present study, nor was there any correlated response among body weight variables.Joint project of Purdue University and USDA-SEA-ARS, North Central Region. Journal paper number 8279 from the Purdue Agricultural Experiment Station     

No evidence for learned mating discrimination in male Drosophila pseudoobscura

Background  

Since females often pay a higher cost for heterospecific matings, mate discrimination and species recognition are driven primarily by female choice. In contrast, frequent indiscriminate matings are hypothesized to maximize male fitness. However, recent studies show that previously indiscriminate males (e.g., Drosophila melanogaster and Poecilia reticulata) can learn to avoid heterospecific courtship. This ability of males to discriminate against heterospecific courtship may be advantageous in populations where two species co-occur if courtship or mating is costly.     

Differential gender selection on flower size in two Neotropical savanna congeneric species

Larger flowers greatly increase among-individual pollen exchange within populations. However, water costs associated to transpirational cooling also increase with increasing flower size. Overall, the interplay between pollen and resource limitation determines the intensity of selection on flower size and this process is mostly dependent on gender and ecological context. To examine how pollinators and water use affect flower size, we determined corolla transpiration, pollen limitation, and selection through male and female fitness in two Kielmeyera species from the Brazilian cerrado flowering at different seasons. Hand-pollination experiments suggested pollen limitation through female fitness in both species, but K. coriacea showed lower limitation levels than K. regalis. For male fitness, the percentage of pollen removal was 1.5-times higher in K. coriacea. Higher air temperature and water deficit during flowering season of K. coriacea resulted in 4-fold higher corolla transpiration rates compared to K. regalis. Selection on flower size through male function was positive and significantly higher than selection through female components in both species. We also detected stabilizing selection in K. coriacea and positive selection in K. regalis on flower size through seed number. Our results suggest that selection on flower size in K. coriacea was mainly limited by water, whereas in K. regalis it was more limited by pollen. We demonstrate that differences in pollen and abiotic resource limitation determine gender-specific selection on flower size.     

Strong evidence for selection for larger brood size in a great tit population

We measured the selection pressure on brood size in a recentlyestablished population of great tits (Parus major L.) in thenorthern Netherlands by manipulating brood size in three years(1995: n = 51, 1997: n = 66, 1998: n = 51), and we estimatedfitness consequences in terms of local survival of both offspringand parents. Enlarged broods had highest fitness; the offspringfitness component was positively affected by manipulation andthe parental fitness component was unaffected. Parental survivaland the probability that parents produced a second clutch werenot affected by the treatment. However, parents that had raisedenlarged broods produced their second clutch later in the season.Clutch size, brood size, and laying date of birds recapturedin the next breeding season were largely independent of thetreatment. We conclude that there is strong evidence for selectionfor larger brood size and reject the individual optimizationhypothesis for this population because the number of young inthe nest predicts fitness independently of the manipulationhistory.     

Floral symmetry: pollinator-mediated stabilizing selection on flower size in bilateral species

Pollinator-mediated stabilizing selection (PMSS) has been proposed as the driver of the evolutionary shift from radial to bilateral symmetry of flowers. Studies have shown that variation in flower size is lower in bilateral than in radial species, but whether bilateral flowers experience more stabilizing selection pressures by employing fewer, more specialized pollinators than radial flowers remains unclear. To test the PMSS hypothesis, we investigate plant–pollinator interactions from a whole community in an alpine meadow in Hengduan Mountains, China, to examine: (i) variance in flower size and level of ecological generalization (pollinator diversity calculated using functional groups) in 14 bilateral and 13 radial species and (ii) the role pollinator diversity played in explaining the difference of variance in flower size between bilateral and radial species. Our data showed that bilateral species had less variance in flower size and were visited by fewer pollinator groups. Pollinator diversity accounted for up to 40 per cent of the difference in variance in flower size between bilateral and radial species. The mediator effect of pollinator diversity on the relationship between floral symmetry and variance in flower size in the community is consistent with the PMSS hypothesis.     

Effect of flower number on the pollinator attractiveness and the threshold plant size for flowering in Pertya triloba (Asteraceae)

Pertya triloba (Asteraceae) is a perennial herb growing in the understory of deciduous broad-leaved forests in central Japan. Its capitulum consists of a single floret that differs from those of most other Asteraceae species. A bagging experiment clearly showed that breeding of P. triloba required cross-pollination. By using female fertility as a measure of pollination success, the effect of an attractive floral display on the threshold plant size for flowering in P. triloba was surveyed. The number of florets per plant in a P. triloba population was artificially adjusted between one and 30. In both control plants and experimental plants with adjusted floret number, the seed set increased with an increase in the number of florets per plant and became constant (60%) when the floret number per plant was more than 10. Thus, the number of florets per plant has an important role in attracting pollinators, and more than 10 florets per plant must be the effective floral display size. In the P. triloba population, 98.5% of the flowering plants had 10 or more flowers. The effective floral display size might be determined through the mutual relationship between plants and pollinators. The number of florets per plant increased with an increase in the plant leaf area. Therefore, the threshold plant size for flowering might be determined by the productivity needed to support an attractive floral display.     

Genetic differentiation for size at first reproduction through male versus female functions in the widespread Mediterranean tree Pinus pinaster

Background and Aims

The study of local adaptation in plant reproductive traits has received substantial attention in short-lived species, but studies conducted on forest trees are scarce. This lack of research on long-lived species represents an important gap in our knowledge, because inferences about selection on the reproduction and life history of short-lived species cannot necessarily be extrapolated to trees. This study considers whether the size for first reproduction is locally adapted across a broad geographical range of the Mediterranean conifer species Pinus pinaster. In particular, the study investigates whether this monoecious species varies genetically among populations in terms of whether individuals start to reproduce through their male function, their female function or both sexual functions simultaneously. Whether differences among populations could be attributed to local adaptation across a climatic gradient is then considered.

Methods

Male and female reproduction and growth were measured during early stages of sexual maturity of a P. pinaster common garden comprising 23 populations sampled across the species range. Generalized linear mixed models were used to assess genetic variability of early reproductive life-history traits. Environmental correlations with reproductive life-history traits were tested after controlling for neutral genetic structure provided by 12 nuclear simple sequence repeat markers.

Key Results

Trees tended to reproduce first through their male function, at a size (height) that varied little among source populations. The transition to female reproduction was slower, showed higher levels of variability and was negatively correlated with vegetative growth traits. Several female reproductive traits were correlated with a gradient of growth conditions, even after accounting for neutral genetic structure, with populations from more unfavourable sites tending to commence female reproduction at a lower individual size.

Conclusions

The study represents the first report of genetic variability among populations for differences in the threshold size for first reproduction between male and female sexual functions in a tree species. The relatively uniform size at which individuals begin reproducing through their male function probably represents the fact that pollen dispersal is also relatively invariant among sites. However, the genetic variability in the timing of female reproduction probably reflects environment-dependent costs of cone production. The results also suggest that early sex allocation in this species might evolve under constraints that do not apply to other conifers.     

Natural selection on flower size in invasive Cytisus scoparius along an elevation gradient

已建群的入侵植物物种在其本地生长范围内比单一种群具有更多样化的基因库。这种遗传和表型变异可以使入侵植物与群落的其他成员相互作用,从而进行自然选择,并形成快速适应机制。对于入侵的开花植物,与传粉者的相互作用可能使其适应异质性的传粉者群落。入侵地内传粉昆虫群落的变化与本地范围内的变化相似,这表明适应性可能反映了在本地范围内看到的模式。在本论文中,我们研究了在华盛顿州的国会国家森林公园内的一种入侵豆科灌木金雀儿(Cytisus scoparius)花的大小沿海拔梯度的变化。我们在每个样地中测量了10株植物花的宽度和传粉花的比例。我们对沿海拔梯度分布样地的金雀儿在单株水平下的物候变化进行三次测定。研究发现,尽管没有呈现出明显的高海拔具有高选择性的规律,但对于花的大小呈现正选择效应。从授粉昆虫的造访率和种子产量两方面,可以看出自然选择的模式。我们还发现,造成种子产量变化的最大因素不是海拔高度或花的大小,而是管理措施。     

Energetics of reproduction: consequences of divergent selection on egg size, food limitation, and female age for egg composition and reproductive effort in a butterfly

Using lines artificially selected on egg size and being subjected to a restricted and an unrestricted feeding treatment, we examined the relationships between egg size, egg number, egg composition, and reproductive investment in the butterfly Bicyclus anynana . Despite a successful manipulation of egg size, correlated responses to selection in larval time, pupal mass, pupal time, longevity, fecundity, or the amount of energy allocated to reproduction were virtually absent. Thus, there was no indication for an evolutionary link between offspring size and reproductive investment. Egg composition, in contrast, was affected by selection, with larger eggs containing relatively more lipid and water, but less protein and energy compared to smaller eggs. Hence, females producing large eggs did not have to sacrifice fecundity due to adjustments in egg composition. Food limitation per se caused only minor changes in egg composition, and there was no general reduction in egg provisioning with female age. The latter was restricted to food-limited females, whereas egg quality remained remarkably similar throughout the females' life in control groups. We conclude that neglecting changes in biochemical egg composition, depending on genetic background, food availability, and female age, may introduce substantial error when estimating reproductive effort, and may ultimately lead to invalid conclusions.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 403–418.     

No evidence for a major role of polymorphisms during bupropion treatment

This study evaluated the ability of polymorphisms in five candidate genes to predict weight gain among patients taking bupropion or placebo in a smoking cessation trial. Five hundred fifty-three smokers were enrolled into a randomized double-blind, placebo-controlled trial and followed for 12 months. Five candidate genes [DRD2 Taq1 (rs1800497), DRD2-141 (rs1799732), C957T (rs6277), COMT (rs4818), and SLC6A3] were genotyped. Weights at baseline, at end of treatment, and after 6 and 12 months of follow-up were self-reported. Smoking abstinence at each endpoint was self-reported and confirmed biochemically. A self-reported average weight gain after 12 months of 1.1 +/- 6.0 kg (mean +/- standard deviation) in the bupropion group and 1.8 +/- 4.8 kg in the placebo group was noted. For subjects with biochemically confirmed abstinence from smoking, the HL genotype (alleles coding Val at codon 108 are denoted as H, and those coding Met are denoted as L) at the COMT locus and A1A1 genotype at the DRD2 Taq1 locus were associated with less weight gain at the end of treatment. The TC genotype at the C957T locus was associated with increased weight gain at 6 months of follow-up. However, no polymorphisms or their interactions with bupropion consistently and significantly predicted baseline BMI or weight change during treatment for all study subjects. Overall, our results do not support a major role for these five candidate genes in weight gain after smoking cessation.     

Sexual selection in a hermaphroditic plant through female reproductive success

Sexual selection is well accepted as a mechanism of shaping traits in animals. However, whether and how floral traits are sexually selected in hermaphroditic plants remains less clear. Here, we use Passiflora incarnata to address how floral traits that affect pollination success are selected via female function. We manipulated the ecological context by limiting pollination and adding resources to expand the phenotypic distribution and alter the intensity of sexual selection. Total sexual selection favoured lower style deflexion because of its impact on pollen receipt and subsequent seed number. However, total selection on style deflexion was not significant, indicating additional selection on style deflexion through routes other than mating. Limited pollination and enhanced resources were expected to alter the distribution of pollen deposition and seed production and therefore intensify the Bateman gradient – the relationship between pollen receipt and seed production. Indeed, the Bateman gradient was strongest when pollination was limited, suggesting potential for sexual selection to influence floral trait evolution under these conditions. Overall, we found floral traits may be shaped by sexual selection through female reproductive success in this hermaphroditic plant. These results support manipulations to enhance the variance in mating as a mechanism to understand patterns of sexual selection.     

Altitudinal flower size variation correlates with local pollinator size in a bumblebee‐pollinated herb,Prunella vulgaris L. (Lamiaceae)

The influence of locally different species interactions on trait evolution is a focus of recent evolutionary studies. However, few studies have demonstrated that geographically different pollinator‐mediated selection influences geographic variation in floral traits, especially across a narrow geographic range. Here, we hypothesized that floral size variation in the Japanese herb Prunella vulgaris L. (Lamiaceae) is affected by geographically different pollinator sizes reflecting different pollinator assemblages. To evaluate this hypothesis, we posed two questions. (1) Is there a positive correlation between floral length and the proboscis length of pollinators (bumblebees) across altitude in a mountain range? (2) Does the flower–pollinator size match influence female and male plant fitness? We found geographic variation in the assemblage of pollinators of P. vulgaris along an altitudinal gradient, and, as a consequence, the mean pollinator proboscis length also changed altitudinally. The floral corolla length of P. vulgaris also varied along an altitudinal gradient, and this variation strongly correlated with the local pollinator size but did not correlate with altitude itself. Furthermore, we found that the size match between the floral corolla length and bee proboscis length affected female and male plant fitness and the optimal size match (associated with peak fitness) was similar for the female and male fitness. Collectively, these results suggest that pollinator‐mediated selection influences spatial variation in the size of P. vulgaris flowers at a fine spatial scale.