THE GEOGRAPHICAL MOSAIC OF COEVOLUTION IN A PLANT–POLLINATOR MUTUALISM

Although coevolution is widely accepted as a concept, its importance as a driving factor in biological diversification is still being debated. Because coevolution operates mainly at the population level, reciprocal coadaptations should result in trait covariation among populations of strongly interacting species. A long-tongued fly ( Prosoeca ganglbaueri ) and its primary floral food plant ( Zaluzianskya microsiphon ) were studied across both of their geographical ranges. The dimensions of the fly's proboscis and the flower's corolla tube length varied significantly among sites and were strongly correlated with each other. In addition, the match between tube length of flowers and tongue length of flies was found to affect plant fitness. The relationship between flower tube length and fly proboscis length remained significant in models that included various alternative environmental (altitude, longitude, latitude) and allometric (fly body size, flower diameter) predictor variables. We conclude that coevolution is a compelling explanation for the geographical covariation in flower depth and fly proboscis length.     

The geographical mosaic of coevolution in a plant-pollinator mutualism.

Although coevolution is widely accepted as a concept, its importance as a driving factor in biological diversification is still being debated. Because coevolution operates mainly at the population level, reciprocal coadaptations should result in trait covariation among populations of strongly interacting species. A long-tongued fly (Prosoeca ganglbaueri) and its primary floral food plant (Zaluzianskya microsiphon) were studied across both of their geographical ranges. The dimensions of the fly's proboscis and the flower's corolla tube length varied significantly among sites and were strongly correlated with each other. In addition, the match between tube length of flowers and tongue length of flies was found to affect plant fitness. The relationship between flower tube length and fly proboscis length remained significant in models that included various alternative environmental (altitude, longitude, latitude) and allometric (fly body size, flower diameter) predictor variables. We conclude that coevolution is a compelling explanation for the geographical covariation in flower depth and fly proboscis length.     

Indirect costs counteract the effects of pollinator-mediated phenotypic selection on corolla size in the Mediterranean shrub Halimium atriplicifolium

Aims Larger corollas receive more pollinator visits but involve higher production and maintenance costs, especially under hot and dry conditions. This can result in indirect costs on reproductive output, which may counteract the effects of pollinator-mediated phenotypic selection on corolla size. In this study, I explored the relationship between corolla size and indirect costs and whether these costs counteract the effects of pollinator-mediated phenotypic selection on this trait in the Mediterranean shrub Halimium atriplicifolium. I hypothesized that (i) corolla production entails direct costs in dry mass, N and P, (ii) corollas entail significant indirect costs in terms of fruit and seed production, (iii) indirect costs increase with corolla size, (iv) this species may suffer pollen limitation to a certain degree and (v) indirect costs counteract the effects of pollinator-mediated selection on corolla size.Methods I compared fruit set and seed production of petal-removed flowers (R flowers) and unmanipulated control flowers (C flowers) and evaluated the influence of individual mean corolla size on relative fruit and seed gain of R compared to C flowers. I also estimated phenotypic selection on corolla size mediated by indirect costs and the combined effect of costs and pollinators (i.e. total selection).Important findings Corollas allocated sizeable amount of resources in terms of dry mass relative to the other floral structures. Fruit set and seed per fruit were significantly higher in R flowers, while individual mean corolla size showed a positive relationship with relative fruit gain. Phenotypic selection analysis revealed cost-mediated negative directional selection and absence of positive directional total selection on corolla size through fruit set. This translated into stabilizing total selection. These results suggest that Mediterranean environments can impose constraints on corolla size, counteracting advantages of larger corollas from the pollination point of view with increased indirect costs of such flowers.     

Flower-fruit size allometry at three taxonomic levels in Crepis (Asteraceae)

The present investigation utilizes the major axis technique to examine the allometric relationship between flower and fruit size, two developmentally related characters. Regression of log (corolla length) on log (fruit length) using data from 188 species of Crepis , 52 populations of C. tectorum and 40 sibships from a population of C. tectorum demonstrated that flower size shows a decelerating increase with increasing fruit size at all taxonomic levels, with the allometric slope varying from 0.53 to 0.69. The null hypothesis of isometry was rejected in analyses using species or sibships as observations, while the comparison of populations revealed a slope significantly different from 1 only if two outliers were excluded from the analysis. Numerous species and populations have escaped the constraint linking flower and fruit size, including C. tectorum (which has a high ratio of flower to fruit size within the genus) and C. tectorum subsp. pumila (which has a high ratio of flower to fruit size within the species).     

Colour, design and reward: phenotypic integration of fleshy fruit displays

The functional or structural linkage among traits [phenotypic integration (PI)] within complex structures can constrain the evolutionary response of individual traits. To analyse whether frugivores with distinct sensory ecology have shaped the patterns of fruit diversification differently, we compared PI values of fleshy fruits that are consumed by birds and mammals. We used phylogenetic comparative analyses of PI among 13 morphological, nutritional and visual fruit traits from 111 Mediterranean plant species. Results showed that morphological traits had higher PI values than nutritional and colour traits. Visual and nutritional traits show positive phylogenetic covariance, while negative covariation occurs between fruits size and nutrients. Importantly, fruits consumed by birds were relatively more integrated than fruits consumed partly or solely by mammals. Hence, we show that major groups of mutualistic frugivores can shape the covariance among some fruit traits differently and thereby influence fruit diversification.     

Patterns of contemporary phenotypic selection and flower integration in the hummingbird‐pollinated Nicotiana glauca between populations with different flower–pollinator combinations

We studied six populations of the hummingbird‐pollinated Nicotiana glauca to determine if the marked differences in the degree of floral‐pollinator mismatch between populations promote divergences in the pattern of pollinator‐mediated phenotypic selection on single traits and on the evolution of complexes of many interacting floral traits. We found evidence that flower phenotype is being shaped by pollinator‐mediated phenotypic selection, since corolla length was consistently under contemporary directional or stabilizing selection. Weak directional selection for longer corollas was found in two populations with low flower–pollinator mismatch; much stronger directional selection was detected for shorter corollas in two populations with high flower–pollinator mismatch; finally, the remaining two populations with intermediate flower–pollinator mismatch showed stabilizing selection for corolla length. N. glauca populations differed in every flower character measured but variations in pollinator‐mediated selection among populations were only observed for corolla length. Multiple covariation among traits was favoured, as suggested by the predominately functional patterns of integration and selection of complexes of many interacting floral traits. This was consistent with the patterns of correlational selection exhibited by four of the six populations, where corolla length was under significant selection in combination with corolla width, style length or stamen length. Overall floral integration was relatively high in all populations but phenotypic integration patterns were not clearly accounted by the degree of flower–pollinator mismatch or type of phenotypic selection, suggesting that trait covariation at the entire flower level is not explained by the current scenario of pollinator‐mediated selection.     

中国夹竹桃目的形态演化趋势及其进化系统

本文探讨了中国夹竹桃目主要器官分类性状的进化趋势,发现了中国夹竹桃目有关花萼、花冠、副花冠、雄蕊、花粉、子房和果实等分类性状密切关系和演化的规律性(图1),从而在作者参考蒋英教授工作成就的基础上,提出了中国夹竹桃目各分类群的进化系统(图2)。     

The influence of insects and hummingbirds on the geographical variation of the flower phenotype in Mimulus luteus

We describe the geographical variation of corolla and nectar guide size in seven populations of Mimulus luteus (Phrymaceae) in central Chile, and examine whether flower phenotypes associate with taxonomic composition and flower visit patterns of pollinators across populations. Flowers showed higher variation in nectar guide size than corolla size. Mean corolla size increased with the proportion of bees and decreased with the proportion of lepidopterans in the pollinator assemblages. Nectar guide size increased with the proportion of hummingbirds in the pollinator assemblages. When the frequency of flower visits rather than taxonomic composition was considered, the results revealed similar patterns. Because these traits previously have been described as targets of bee- and hummingbird-mediated selection in M. luteus , our results have implications for understanding the processes that determine flower diversification in Chilean Mimulus . Although we cannot rule out ecological sorting as an explanation for the geographical association between pollinators and flower phenotypes, changes in the prevalence and importance of bees and hummingbirds across populations appear to account, at least in part, for the flower phenotypic variation across populations. The extent to which insect and hummingbird pollination in M. luteus produces pollinator-mediated divergence among populations needs to be examined in future studies.     

Exploring the limiting causes of fruit production in the tropical tree Ipomoea wolcottiana Rose (Convolvulaceae)

Path analysis was used to evaluate a group of variables related to fruit production in the tropical tree Ipomoea wolcottiana (Convolvulaceae). The variables were tree size (trunk diameter), available phosphorus in the soil, floral phenotypic sex expression (i.e. gynoecium biomass allocation), flower production, fruits initiated, and length of the corolla and diameter of its opening. The path model explained 79.9% of the total variation, and the production of mature fruits was related in large part by the number of fruits initiated and by phenotypic sex expression. In turn, fruits initiated were related to corolla tube diameter and to a lesser extent to corolla tube length. The model could explain a low percentage of the variation (18.5%) of the number of fruits initiated, but once a fruit was initiated it had a high probability of maturing. Phenotypic sex expression related negatively to the number of flowers produced and positively, to almost the same degree, to available phosphorus in the soil. Tree size had a positive effect on flower production but a negligible effect on fruits initiated and matured. Soil phosphorus affected positively, although weakly all variables. The relationships between tree size, number of flowers and phenotypic sex expression suggested that abundant flowering in this species functions more for pollen donation than its reception.     

Genetic and environmental correlation and path coefficient analysis of fruit yield per bush and other traits in black currants (Ribes nigrum L.)

Twenty-five F1 hybrid families of black currants (Ribes nigrum L.) originating from diallel crosses of five cultivars were assessed. Phenotypic correlation coefficient between full-sib family means (rFS), genetic correlation coefficient between full-sib family expected values (rG) and the environmental correlation were estimated on the basis of two years of observations for 12 quantitative characteristics studied. Evident repeatability of correlations in both years was proved. A considerable consistency between the values of genetic and phenotypic correlation coefficients was also observed. Coefficients of phenotypic and environmental correlation were significant for many pairs of traits. Most of the significant environmental correlation coefficients were found for the same pairs of characteristics for which phenotypic correlation coefficients were significant. This shows that genetic and environmental factors affected similar traits. Fruit yield expressed the largest number of significant correlations with other traits. Path coefficient analysis indicated that plant and berry size were the main factors influencing directly fruit yield in both years. It was proved that the number and length of one-year-old shoots via bush size had very large indirect effects on fruit yield per plant.     

Floral stability,pollination efficiency,and experimental manipulation of the corolla phenotype in Nemophila menziesii (Hydrophyllaceae)

The present study examines the degree of phenotypic stability in vegetative and floral traits in a population of the annual, self-compatible, and protandrous Nemophila menziesii (Hydrophyllaceae) and examines whether local pollinators select for a uniform floral phenotype in this population. I found a strong positive association between flower number, leaf size, shoot length, and pedicel length, implying a general effect of overall plant vigor on this suite of traits, while characters reflecting corolla shape were phenotypically stable across a broad range of plant sizes. However, results of a manipulative experiment indicate that individual flowers maintain high pollination success despite drastic changes in the size and shape of the corolla. This suggests that pollinator-mediated selection does not directly favor floral stability in N. menziesii or that selection was weak during the course of this study. Seed number per flower was positively correlated with plant size, which varied greatly from one patch to another.     

QUANTITATIVE GENETICS OF SIZE AND PHENOLOGY OF LIFE-HISTORY TRAITS IN CHAMAECRISTA FASCICULATA

Despite numerous adaptive scenarios concerning the evolution of plant life-history phenologies few studies have examined the heritable basis for and genetic correlations among these phenologies. Documentation of genetic variation for and covariation among reproductive phenologies is important because it is this variation/covariation that will determine the potential for response to evolutionary forces. To address this problem, I conducted a breeding experiment to determine narrow-sense heritabilities for and genetic correlations among the phenologies of life-history events and plant size in Chamaecristafasciculata, a temperate summer annual plant species. Paternal families showed no evidence of heritable variation for two estimates of plant size, six measures of reproductive phenology or two fitness components. Similarly, paternal estimates of genetic correlations among these traits were low or zero. In contrast, maternal estimates of heritability suggested the influence of maternal parent on one estimate of plant size and four phenological traits. Likewise, maternal effects influenced maternal estimates of genetic correlations. These maternal effects can arise from three sources: endosperm nuclear, cytoplasmic genetic and/or maternal phenotypic. The degree to which the phenology of one life-history trait acts as a constraint on the evolution of other phenological traits depends on the source of the maternal influence in this species.     

ECOLOGICAL CONSEQUENCES AND PHENOTYPIC CORRELATES OF PETAL SIZE VARIATION IN WILD RADISH,RAPHANUS SATIVUS (BRASSICACEAE)

In this paper we examine some ecological consequences and phenotypic correlates of flower size variation in wild radish, Raphanus sativus. Mean corolla diameter varied significantly among individuals within natural populations of R. sativus in California. On the average, almost 40% of flower biomass was allocated to corolla tissue. In field experiments, pollinator visitation increased significantly with corolla size. Large flowers also accumulated more nectar when pollinators were excluded from plants. In three populations, corolla size was positively correlated with allocation to pollen per flower (either anther weight or pollen grain number), but there was usually no phenotypic relationship between corolla size and several measures of female allocation (ovule number per flower, proportion fruit set, and total seed mass per fruit). Plants growing in the field produced fewer large flowers per unit of stem, and stem biomass was negatively related to corolla size for plants grown under controlled greenhouse conditions. Male and female fitness may covary differently with allocation to attractive floral features in species such as R. sativus, where seed production is often limited by resources rather than by pollen.     

金钟连翘与东北连翘种间杂交F1代表型性状遗传分析

为了阐明连翘属植物主要观赏性状和抗寒性的遗传特点,以金钟连翘品种‘Lynwood’(Forsythia intermedia‘Lynwood’)和东北连翘(F.mandschurica)杂交获得的F1代群体为研究对象,对杂交群体的花冠口直径、花裂片长度、抗寒性等12个表型性状进行测定,并对这些性状进行相关性分析和混合遗传模型分析。结果表明:金钟连翘与东北连翘杂交群体的表型性状变异丰富,各表型性状均出现大于高亲或小于低亲的超亲个体。除花裂片长度、花裂片宽度、叶片长度外,其他性状的变异度均超过15%,达到中等水平以上。各性状之间存在一定的相关性,其中抗寒性与着花密度呈极显著正相关,与花冠口直径、植株冠幅呈极显著负相关关系。混合遗传模型分析显示,花裂片长度、花裂片宽度、花裂片长宽比、叶片长度、叶片宽度、叶片长宽比、当年生枝条长度、抗寒性由微效多基因控制,花冠口直径和植株冠幅由一对加性—显性主基因控制,着花密度由两对加性—显性主基因控制,株高由两对等加性—显性主基因控制。花冠口直径、冠幅、着花密度和株高的主基因遗传力分别为76.05%、60.3%、72.22%和64.75%。研究结果为定向培育综合性状优良的连翘新品种提供了依据。     

Floral ontogeny in Sophoreae (Leguminosae: Papilionoideae): II. Sophora sensu lato (Sophora group)

Floral ontogeny is described in eight species of Sophora sensu lato, representing the Sophora group, as part of a comparative ontogenetic analysis of Polhill's eight groups of tribe Sophoreae, subfamily Papilionoideae. This tribe includes taxa having relatively unspecialized floral structure. Flowers have a five-lobed calyx, a corolla of five free petals, ten mostly unfused, identical stamens, and a carpel. Order of initiation is predominantly acropetal (except for the carpel): sepals, petals, outer stamens plus carpel, inner stamens. Order of initiation within each whorl is unidirectional from the abaxial side. Overlapping initiation among whorls occurs only in S. chrysophylla. Keel petals are slightly fused in six species, and wing petals are fused in 5. tomentosa. Two bird-pollinated species (S. chrysophylla, S. microphylla) lack the papilionaceous corolla of other species, and their petals are unusually long and lack wing sculpturing found in the others. Other floral differences among species mostly involve flower color, differing absolute or relative sizes among organs, and degree of reflexing of vexillum. All but S. davidii have a hypanthium, which develops very late, starting when the bud is about 5 mm long. The distinctions among species (petal size, degree of reflexed position of vexillum, petal sculpturing, color, anther shape, filament hairs, hypanthium presence, calyx lobing) tend to be expressed late in ontogeny.     

Phenetic analysis of Datura section Dutra (Solanaceae) in Mexico

Phenetic analysis of morphological characters of taxa in the section Dutra of the genus Datura from native populations on mainland Mexico supported the recognition of seven species: D. discolor, D. inoxia, D. kymatocarpa, D. lanosa, D. metel, D. pruinosa , and D. reburra . These taxa aggregated into three large groups which shared similar anther length, seed surface texture, fruit dehiscence, corolla length, calyx lobe length, stamen length and leaf length. Based on the similarity of morphological characters, it is probable that the domesticated D. metel was derived from wild D. inoxia in southern Mexico.     

Investigating the independent evolution of the size of floral organs via G-matrix estimation and artificial selection

The attractiveness of a plant to pollinators is dependent on both the number of flowers produced and the size of the petals. However, limiting resources often result in a size/number trade-off, whereby the plant can make either more flowers or larger flowers, but not both. If developmental genes underlying sepal and petal identity (some of which overlap) also influence size, then this shared genetic basis could constrain the independent evolution of floral size and attractiveness. Here, we determined whether the size of sepals and petals in the dioecious perennial, Silene latifolia, are developmentally independent by performing two experiments: a genetic variance-covariance experiment to estimate genetic correlations between calyx width, petal-limb length, flower mass, and number and a four-bout artificial-selection experiment to alter calyx width and estimate the correlated response in petal-limb length. In addition, we determined whether variation in petal-limb length is the result of cell expansion or cell proliferation. The first experiment revealed that petal-limb length is not genetically correlated with calyx width, and the second experiment confirmed this; selection on calyx width did not result in a predictable or significant change in petal-limb length. Flower number was negatively correlated with all the floral traits measured, indicating a flower size/number trade-off. Cell number, but not size, explained a significant amount of the variation in petal-limb length. We conclude that the size of the two outer floral organs can evolve independently. This species can therefore increase the number of flowers produced by decreasing investment in the calyx without simultaneously decreasing petal size and the attractiveness of each individual flower to pollinators.     

Ecological diversification associated with the benthic‐to‐pelagic transition by North American minnows

Ecological opportunity is often regarded as a key factor that explains why diversity is unevenly distributed across life. Colonization of novel environments or adaptive zones may promote diversification. North American minnows exhibit an ancestral benthic‐to‐pelagic habitat shift that coincided with a burst in diversification. Here, we evaluate the phenotypic and ecological implications of this habitat shift by assessing craniofacial and dietary traits among 34 species and testing for morphology–diet covariation, convergence and adaptive optima. There were several instances of morphology–diet covariation such as correlations between mouth angle and the consumption of terrestrial insects and between relative gut length and the consumption of algae. After accounting for size and phylogenetic nonindependence, benthic species had longer heads, longer snouts, eyes positioned higher on their head, smaller mouth angles and longer digestive tracts than pelagic minnows. Benthic minnows also consumed more algae but less terrestrial insects, by volume, than pelagic minnows. Lastly, there were three distinct evolutionary regimes and more convergence in morphology and dietary characteristics than expected under a Brownian motion model of evolution. These findings indicate that colonization of the pelagic zone by minnows involved myriad phenotypic and dietary changes associated with exploitation of terrestrial subsidies. Thus, minnows exhibit phenotype–dietary covariation, an expansion of ecological roles and a burst in diversification rates in response to the ecological opportunity afforded by the colonization of a novel habitat.     

Competition for pollination influences selection on floral traits of Ipomopsis aggregata

Although rarely tested, it is often assumed that interspecific competition results in the divergence of traits related to resource use. Using a plant-pollinator system as a model, I tested the prediction the presence of a competitor for pollination influences the strength and/or direction of pollinator-mediated selection on floral traits. I measured phenotypic selection via female fitness on five floral traits of Ipomopsis aggregata in seven populations. Four contained only conspecifics (I only) and three also contained the competitor Castilleja linariaefolia (C + I). Directional selection via fruits/plant and conspecific pollen deposited/flower on corolla length was positive and significantly stronger in C + I populations. This difference in selection was apparently driven by interpopulation variation in the degree to which reproduction of I. aggregata was pollen limited. Consistent with expectations of interspecific competition, I. aggregata plants in C + I populations received less conspecific pollen per flower and set fewer seeds per fruit and fruits per plant than those in I only populations. Ipomopsis aggregata's corollas were also significantly longer in C + I populations, suggesting that there had been a response to a similar selective regime in past generations. Phenotypic correlations between corolla length and width, which determine the variation in I. aggregata's flower shape, were significantly weaker in C + I populations. These data suggest that competition for pollination can influence the strength of selection on and patterns of correlations among floral traits of I. aggregata. If I. aggregata populations with and without competitors for pollination are linked by gene flow, then measuring selection in competitive and noncompetitive environments maybe necessary to accurately predict how floral traits will evolve.     

HERITABILITY AND GENETIC CORRELATION OF COROLLA SHAPE AND SIZE IN ERYSIMUM MEDIOHISPANICUM

Flower shape has evolved in most plants as a consequence of pollinator-mediated selection. Unfortunately, no study has explored the genetic variation of flower shape, despite that this information is crucial to understand its adaptive evolution. Our main goal here is to determine heritability of corolla shape in Erysimum mediohispanicum (Brassicaceae). Also, we explore heritability of other pollinator-selected traits in this plant species, such as plant size, flower display, and corolla size. In addition, we investigate genetic correlations between all these traits. We found significant heritability for one plant-size trait (stalk height), for number of flowers, for all corolla-size traits (corolla diameter, corolla tube length and corolla tube width), and for corolla shape. Consequently, this species retains a high ability to respond to the selection exerted by its pollinators. Genetic correlation was strong between all functionally related traits and between flower number and plant size, weak between corolla size and plant size and no correlation between corolla shape and any other trait. Thus, selection affecting some E. mediohispanicum traits would also indirectly affect other functionally related and unrelated traits. More importantly, the observed genetic correlation seems to be at least partially adaptive because positive correlational selection currently acts on the covariance between some of these traits ( Gómez 2003 ; Gómez et al. 2006 ).