Floral traits and isolation of three sympatric Aquilegia species in the Qinling Mountains, China

Floral isolation has been considered to be an important reproductive mechanism governing the species diversification in many genera. In a classic example Aquilegia, sympatric species from North America with diverse floral traits are generally associated with specialized pollinators that prohibit interspecific hybridization. It remains unclear whether species diversification in the genus from Eurasia is also maintained by floral isolation. We investigated floral phenology, floral characteristics and pollinators in three sympatric Aquilegia species (A. ecalcarata, A. incurvata and A. yabeana) in the Qinling Mountains, Shanxi Province, China from 2001 to 2005. The spurless A. ecalcarata flowers earlier than the other two species with nectar spurs but their floral phenology overlaps. Major pollinators of A. ecalcarata are syrphid flies while bumblebees are major for A. incurvata and A. yabeana. Therefore our observations confirm that mechanical isolation through differential pollinators could contribute reproductive isolation between spurless and spurred species, as demonstrated by studies from North America. Whether floral isolation plays a major role in the reproductive isolation between two spurred species (A. incurvata and A. yabeana), however, remains to be seen. Further studies are required to quantify the potential role of geographical isolation because they occupy different habitats.     

Comparative floral and vegetative differentiation between two European Aquilegia taxa along a narrow contact zone

As a first step in determining the identity and relative importance of the evolutionary forces promoting the speciation process in two closely related European taxa of Aquilegia, we investigated the levels of morphological variation in floral and vegetative characters over the narrow region where their ranges enter into contact, and evaluate the relative importance of both types of traits in their differentiation. A total of 12 floral and ten vegetative characters were measured on 375 plants belonging to seven A. vulgaris populations and six A. pyrenaica subsp. cazorlensis populations located in southeastern Spain. Floral and vegetative morphological differentiation occur between taxa and among populations within taxa, but only vegetative characters (particularly plant height and leaf petiolule length) contribute significantly to the discrimination between taxa. Differentiation among populations within taxa is mostly explained by variation in floral traits. Consequently, morphological divergence between the two taxa cannot be interpreted as an extension of among-population differences occurring within taxa. Multivariate vegetative, but not floral, similarity between populations could be predicted from geographical distance. Moreover, the key role of certain vegetative traits in the differentiation of A. vulgaris and A. p. cazorlensis could possibly be attributable to the contrasting habitat requirements and stress tolerance strategies of the two taxa. These preliminary findings seem to disagree with the currently established view of the radiation process in the genus Aquilegia in North America, where the differentiation of floral traits seems to have played a more important role.     

The diversity of elaborate petals in Isopyreae (Ranunculaceae): a special focus on nectary structure

Elaborate petals are highly diverse in morphology, structure, and epidermal differentiation and play a key role in attracting pollinators. There have been few studies on the elaborate structure of petals in the tribe Isopyreae (Ranunculaceae). Seven genera in Isopyreae (Aquilegia, Semiaquilegia, Urophysa, Isopyrum, Paraquilegia, Dichocarpum, and Leptopyrum) have petals that vary in morphology, and two genera (Enemion and Thalictrum) have no petals. The petals of nine species belonged to 7 genera in the tribe were studied to reveal their nectary structure, epidermal micromorphology and ancestral traits. The petal nectaries of Isopyreae examined in this study were located at the tip of spurs (Aquilegia yabeana and A. rockii), or the bottom of shallow sacs (Semiaquilegia adoxoides, Urophysa henryi, Isopyrum manshuricum, and Paraquilegia microphylla), a cup-shaped structure (Dichocarpum fargesii) and a bilabiate structure (Leptopyrum fumarioides). The petal nectary of eight species in Isopyreae (except A. ecalcarata) was composed of secretory epidermis, nectary parenchyma, and vascular tissues, and some sieve tubes reached the secretory parenchyma cells. Among the eight species with nectaries examined in the present study, A. yabeana had the most developed nectaries, with 10–15 layers of secretory parenchyma cells. The epidermal cells of mature petals of the nine species were divided into 11 types. Among these 11 types, there were two types of secretory cells and two types of trichomes. Aquilegia yabeana and A. rockii had the highest number of cell types (eight types), and I. manshuricum and L. fumarioides had the lowest number of cell types (three types). Aquilegia ecalcarata had no secretory cells, and the papillose conical polygonal secretory cells of D. fargesii were different from those of the other seven species with nectaries. Trichomes were found only in Aquilegia, Semiaquilegia, Urophysa, and Paraquilegia. The ancestral mode of nectar presentation in Isopyreae was petals with hidden nectar (70.58%). The different modes of nectar presentation in petals may reflect adaptations to different pollinators in Isopyreae.

     

Loss of innovative traits underlies multiple origins of Aquilegia ecalcarata

Traits are basic attributes of organisms that form the basis for speciation and diversity. The floral nectar spur is a classic example of a key innovative trait. Differences in nectar spur morphology can lead to pollinator specialization and thereby promote reproductive isolation between species. Despite its importance, the nectar spur has been lost in some members of the columbine genus (Aquilegia), resulting in a new spurless trait, and the evolutionary influence of this trait has become a topic of scientific interest. Aquilegia ecalcarata is an important representative columbine species that lacks spurs. Here, we resequenced the genomes of 324 individuals from A. ecalcarata and four related species. We found that A. ecalcarata was divided into three groups based on the phylogenetic relationships and population genetic structures. Topology weighting analysis revealed that A. ecalcarata has multiple origins, and Patterson′s D statistic showed that the spurless trait may have one origin. Floral morphological analysis revealed significant differences between A. ecalcarata and its spurred sister groups, and the floral phenotypes of the three A. ecalcarata groups have identical or similar floral phenotypes. Our results confirmed that the spurless trait not only produced the phenotype of A. ecalcarata but also contributed to the emergence of the A. rockii phenotype. Moreover, the spurless trait promoted the divergence between A. ecalcarata and its close, spurred relatives. Our research shows that the loss of key innovative traits can play a very important role in speciation and species diversity.     

The role of genetic constraints on the diversification of Iberian taxa of the genus Aquilegia (Ranunculaceae)

The microevolutionary process of adaptive phenotypic differentiation of quantitative traits between populations or closely‐related taxa depends on the response of populations to the action of natural selection. However, this response can be constrained by the structure of the matrix of additive genetic variance and covariance between traits in each population ( G matrix). In the present study, we obtained additive genetic variance and narrow sense heritability for 25 floral and vegetative traits of three subspecies of Aquilegia vulgaris, and one subspecies of Aquilegia pyrenaica through a common garden crossing experiment. For two vegetative and one floral trait, we also obtained the G matrix and genetic correlations between traits in each subspecies. The amount of genetic variation available in wild populations is not responsible for the larger differentiation of vegetative than floral traits found in this group of columbines. However, the low heritability of some traits constrained their evolution because phenotypic variability among taxa was larger for traits with larger heritability. We confirmed that the process of diversification of the studied taxa involved shifts in the G matrix, mainly determined by changes in the genetic covariance between floral and vegetative traits, probably caused by linkage disequilibrium in narrow endemic taxa. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 252–261.     

Evidence of incipient speciation in the Neotropical mangrove Pelliciera rhizophorae (Tetrameristaceae) as revealed by molecular,morphological, physiological and climatic characteristics

Two variants of the Neotropical mangrove species Pelliciera rhizophorae distributed along both sides of the Isthmus of Panama were detected by different colouration of the floral bracts and the size of the floral and vegetative structures. These findings raised questions concerning a possible speciation event in P. rhizophorae, for which a series of macro‐ and microscopic morphological traits (reproductive and vegetative structures), molecular markers from plastid DNA and climatic profiles were analyzed. Samples of P. rhizophorae were collected in three localities from the Panamanian Caribbean and Pacific coasts. The data obtained from molecular markers and morphological traits showed significant differences between the variants. The climatic profiles showed contrasting characteristics of rainfall and temperature in their habitats: variant A is found in wetter zones and variant B occupies drier zones. Evidence suggesting that a process of incipient speciation has occurred in P. rhizophorae in response to ecogeographical isolation due to climatic factors is presented. The presence of two geographically separate genetic‐morphological groups, adapted to contrasting climatic conditions, will be the basis for suggesting the existence of incipient lineages in Pelliciera. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 499–510.     

贵州特有药用植物毕节小檗的形态变异

为探讨贵州特有药用植物毕节小檗(Berberis guizhouensis)形态多样性的变异式样及其适应机制,对其野外居群营养器官和花部形态进行研究。对毕节小檗一直空缺的花部性状进行了描述。结果表明,毕节小檗的性状在同一居群或同一性状在不同居群中都存在较丰富的变异,变异系数为0.03~0.57。从总体来看,营养器官性状的变异程度要高于花部性状。单因素方差分析表明居群间部分花部性状存在显著差异(P0.05)。聚类分析表明小白岩居群形成1个独立的分支,这种分化很可能是环境压力选择的结果。主成分分析表明花部性状与营养性状在维持形态结构的稳定性具有协调一致的生态适应。     

Population differentiation in floral and life history traits ofOxalis corniculata L. (Oxalidaceae) with style length polymorphism

A quantitative genetic analysis was conducted on the amounts and distribution of variation of 20 floral, reproductive and life history traits of a self-compatible perennial,Oxalis cornlculata L. (Oxalidaceae). This species comprises two floral morphs, homostyled and long-styled, with different breeding systems. The hierarchical design of the experiments on three homostyled and three long-styled populations allowed partitioning of variation into four levels of organization using nested ANOVAs. Seven of the 20 traits examined were differentiated between homostyled and long-styled populations. Significant genetic variance components were detected in the major traits (114 of the 120 traits) examined for six populations. Average values of variance components among families within a population across 20 traits for homostyled populations were higher than those of long-styled populations. These responses likely reflect the consequences of different levels of selfing and/or mixed mating on genetic variation in the two floral morphs ofO. corniculata. Pearson product-moment correlations for family means of seven traits selected were also calculated. Two groups of trait combinations (i.e., between floral traits, and between reproductive and life history traits) showed significant family mean correlation coefficients. The origins of these varlation patterns found in different populations ofO. corniculata are discussed in terms of the underlying selective regimes operating in each population.     

VEGETATIVE AND FLORAL RELATIONSHIPS AMONG WESTERN NORTH AMERICAN POPULATIONS OF COLLOMIA LINEARIS NUTTALL (POLEMONIACEAE)

Thirty-seven characters were measured on greenhouse grown progenies of twenty-three populations representing, for Collomia linearis, a broad geographical and ecological distribution in western North America. Twelve vegetative and seventeen floral characters showed significant among-population/within-population variance ratios (F-statistics). Overall, floral characters showed higher F-statistics than did vegetative characters. The F-statistics and character means were used to construct phenograms based on weighted similarity measures and single-linkage clustering. With the exception of a homogeneous cluster comprising northern Rocky Mountain OTUs, relationships based on floral characters were geographically random. No clearly defined morphological trends toward increased autogamy were observed in association with geographical or ecological distribution. Several clustering relationships, based on vegetative characters, were interpreted as representing geographically unrelated genotypes convergent with respect to ecotypic differentiation. The most distinctive clusters of OTUs in the vegetative phenogram were associated with subalpine and wet meadow sites, habitats considered as ecologically marginal for the species. Comparison of the two phenograms revealed considerable disparity between relationships based on floral characters and those based on vegetative characters. This disparity lends support to the hypothesis that floral and vegetative character combinations are subject to independent selective processes. The absence of polyploidy or mitotically detectable chromosomal rearrangements indicates that the observed variation among widely separated populations represents either divergence or convergence via genetic differentiation at the diploid level.     

Covariance and decoupling of floral and vegetative traits in nine Neotropical plants: a re-evaluation of Berg's correlation-pleiades concept

Nearly forty years ago R. L. Berg proposed that plants with specialized pollination ecology evolve genetic and developmental systems that decouple floral morphology from phenotypic variation in vegetative traits. These species evolve separate floral and vegetative trait clusters, or as she termed them, "correlation pleiades." The predictions of this hypothesis have been generally supported, but only a small sample of temperate-zone herb and grass species has been tested. To further evaluate this hypothesis, especially its applicability to plants of other growth forms, we examined the patterns of phenotypic variation and covariation of floral and vegetative traits in nine species of Neotropical plants. We recognized seven specific predictions of Berg's hypothesis. Our results supported some predictions but not others. Species with specialized pollination systems usually had floral traits decoupled (weak correlation; Canna and Eichornia) or buffered (relationship with shallow proportional slope; Calathea and Canna) from variation in vegetative traits. However, the same trend was also observed in three species with unspecialized pollination systems (Echinodorus, Muntingia, and Wedelia). One species with unspecialized pollination (Croton) and one wind-pollinated species (Cyperus) showed no decoupling or buffering, as predicted. While species with specialized pollination usually showed lower coefficients of variation for floral traits than vegetative traits (as predicted), the same was also true of species with unspecialized or wind pollination (unlike our prediction). Species with specialized pollination showed less variation in floral traits than did species with unspecialized or wind pollination, as predicted. However, the same was true of the corresponding vegetative traits, which was unexpected. Also in contrast to our prediction, plants with specialized pollination systems did not exhibit tighter phenotypic integration of floral characters than did species with generalized pollination systems. We conclude that the patterns of morphological integration among floral traits and between floral and vegetative traits tend to be species specific, not easily predicted from pollination ecology, and generally more complicated than R. L. Berg envisaged.     

Evolutionary potential in the wild: more than meets the eye

The genus Aquilegia consists of 60–70 perennial plant species widely distributed throughout the northern hemisphere. Its flowers have a delicate and ornamental appearance that makes them a favourite of gardeners. In this genus, adaptive radiations for both floral and vegetative traits have occurred. These adaptive radiations, and the key phylogenetic placement of Aquilegia between Arabidopsis and rice, make this genus a ‘model system’ for plant evolution ( Kramer 2009 ). In this issue, Castellanos et al. (2011) use a marker‐based method to infer heritability for floral and vegetative traits in two Aquilegia species. Layered on top of this are estimates of the strength of natural selection. This novel joint estimation of heritability and selection in the wild showed that vegetative traits, compared to floral traits, have the highest evolutionarily potential. Evolutionary potential is the most important quantity to measure in wild populations. It combines inheritance and strength of selection and predicts the potential for populations to adapt to changing environments. The combination of molecular techniques with species in natural environments makes this work a model for molecular ecological investigations.     

Floral integration,phenotypic covariance structure and pollinator variation in bumblebee‐pollinated Helleborus foetidus

By analysing patterns of phenotypic integration and multivariate covariance structure of five metric floral traits in nine Iberian populations of bumblebee‐pollinated Helleborus foetidus (Ranunculaceae), this paper attempts to test the general hypothesis that pollinators enhance floral integration and selectively modify phenotypic correlations between functionally linked floral traits. The five floral traits examined exhibited significant phenotypic integration at all populations, and both the magnitude and the pattern of integration differed widely among populations. Variation in extent and pattern of integration was neither distance‐dependent nor significantly related to between‐population variation in taxonomical composition and morphological diversity of the pollinator assemblage. Patterns of floral integration were closer to expectations derived from consideration of developmental affinities between floral whorls than to expectations based on a pollinator‐mediated adaptive hypothesis. Taken together, results of this study suggest that between‐population differences in magnitude and pattern of floral integration in H. foetidus are probably best explained as a consequence of random genetic sampling in the characteristically small and ephemeral populations of this species, rather than reflecting the selective action of current pollinators.     

Adaptive genetic differentiation in life-history traits between populations of <Emphasis Type="Italic">Mimulus guttatus</Emphasis> with annual and perennial life-cycles

The optimal allocation to sexual and vegetative reproduction as well as the optimal values of other life-history characteristics such as phenology, growth and mating system are likely to depend on the life-cycle of the organism. I tested whether plants of Mimulus guttatus originating from temporarily wet populations where the species has an enforced annual life-cycle have higher allocation to sexual reproduction, lower allocation to vegetative reproduction, more rapid phenology, faster growth, and floral traits associated with a self-fertilizing mating system than plants from permanently wet populations where the species has a perennial life-cycle. I grew a total of 1377 plants originating from three populations with an annual life-cycle and 11 populations with a perennial life-cycle in a greenhouse under permanently and temporarily wet conditions. Plants of M. guttatus in permanently wet conditions had significantly more vegetative reproduction and tended to have a faster growth than plants in the temporarily wet conditions, indicating plasticity in these life-history traits. Plants from populations with an annual life-cycle invested significantly more in sexual reproduction and significantly less in vegetative reproduction than the ones from populations with a perennial life-cycle. Moreover, this study showed that plants originating from populations with an annual life-cycle have a significantly faster development and floral traits associated with autonomous self-fertilization. In conclusion, this study suggests that there has been adaptive evolution of life history traits of M. guttatus in response to natural watering conditions that determine the life span of the species.     

Historical and ecological divergence among populations of Monttea chilensis (Plantaginaceae), an endemic endangered shrub bordering the Atacama Desert,Chile

The coastal deserts of northern Chile show an important latitudinal gradient of aridity with more arid areas to the north of the Atacama Desert than to the south. Several plant species have disjunct distributions that correspond with the extremes of this latitudinal gradient. In this study, using genetic (chloroplast and nuclear DNA), morphological (vegetative and floral traits of various kinds) and climatic and topographic information, we explored ecological and historical events that have putatively shaped patterns of variation among Monttea chilensis populations—a species that shows this disjunct distribution. Through phylogeographic and phylogenetic analyses, two divergent lineages were identified located at the latitudinal extremes. The lineage located northern lineage (NG) of the Atacama Desert showed more genetic diversity and better-resolved phylogeographic structure than the southern lineage (SG). Considerable morphological variation across the geographical range corresponds with these genetic groups. We observed contrasting relationships between floral and vegetative traits: populations from the most arid region NG possessed larger flowers, but smaller vegetative values, and vice versa. Niche modelling and multivariate analyses, including environmental data, revealed different environmental requirements for each lineage. NG plants occur in regions with warmer and drier climatic conditions and at higher altitudes, while SG populations inhabit colder and more humid environments and lower altitudes. The evolutionary history of M. chilensis exhibits a phylogeographical footprint consistent with past fragmentation and allopatric differentiation, where the hyper-arid zone formed by the Atacama Desert clearly acted as an important gene flow barrier. This barrier has led to considerable differentiation in morphology and ecology, resulting in two ecotypes or geographical races, suggesting incipient speciation promoted by local adaptation and geographical isolation.     

Floral specialization for different pollinators and divergent use of the same pollinator among co‐occurring Impatiens species (Balsaminaceae) from Southeast Asia

Floral variation among closely related species is thought to often reflect differences in pollination systems. Flowers of the large genus Impatiens are characterized by extensive variation in colour, shape and size and in anther and stigma positioning, but studies of their pollination ecology are scarce and most lack a comparative context. Consequently, the function of floral diversity in Impatiens remains enigmatic. This study documents floral variation and pollination of seven co‐occurring Impatiens spp. in the Southeast Asian diversity hotspot. To assess whether floral trait variation reflects specialization for different pollination systems, we tested whether species depend on pollinators for reproduction, identified animals that visit flowers, determined whether these visitors play a role in pollination and quantified and compared key floral traits, including floral dimensions and nectar characteristics. Experimental exclusion of insects decreased fruit and seed set significantly for all species except I. muscicola, which also received almost no visits from animals. Most species received visits from several animals, including bees, birds, butterflies and hawkmoths, only a subset of which were effective pollinators. Impatiens psittacina, I. kerriae, I. racemosa and I. daraneenae were pollinated by bees, primarily Bombus haemorrhoidalis. Impatiens chiangdaoensis and I. santisukii had bimodal pollination systems which combined bee and lepidopteran pollination. Floral traits differed significantly among species with different pollination systems. Autogamous flowers were small and spurless, and did not produce nectar; bee‐pollinated flowers had short spurs and large floral chambers with a wide entrance; and bimodally bee‐ and lepidopteran‐pollinated species had long spurs and a small floral chamber with a narrow entrance. Nectar‐producing species with different pollination systems did not differ in nectar volume and sugar concentration. Despite the high frequency of bee pollination in co‐occurring species, individuals with a morphology suggestive of hybrid origin were rare. Variation in floral architecture, including various forms of corolla asymmetry, facilitates distinct, species‐specific pollen‐placement on visiting bees. Our results show that floral morphological diversity among Impatiens spp. is associated with both differences in functional pollinator groups and divergent use of the same pollinator. Non‐homologous mechanisms of floral asymmetry are consistent with repeated independent evolution, suggesting that competitive interactions among species with the same pollination system have been an important driver of floral variation among Impatiens spp.     

Pleiotropic quantitative trait loci contribute to population divergence in traits associated with life-history variation in Mimulus guttatus

Evolutionary biologists seek to understand the genetic basis for multivariate phenotypic divergence. We constructed an F2 mapping population (N = 539) between two distinct populations of Mimulus guttatus. We measured 20 floral, vegetative, and life-history characters on parents and F1 and F2 hybrids in a common garden experiment. We employed multitrait composite interval mapping to determine the number, effect, and degree of pleiotropy in quantitative trait loci (QTL) affecting divergence in floral, vegetative, and life-history characters. We detected 16 QTL affecting floral traits; 7 affecting vegetative traits; and 5 affecting selected floral, vegetative, and life-history traits. Floral and vegetative traits are clearly polygenic. We detected a few major QTL, with all remaining QTL of small effect. Most detected QTL are pleiotropic, implying that the evolutionary shift between these annual and perennial populations is constrained. We also compared the genetic architecture controlling floral trait divergence both within (our intraspecific study) and between species, on the basis of a previously published analysis of M. guttatus and M. nasutus. Eleven of our 16 floral QTL map to approximately the same location in the interspecific map based on shared, collinear markers, implying that there may be a shared genetic basis for floral divergence within and among species of Mimulus.     

Floral and vegetative morphometrics of five Pleurothallis (Orchidaceae) species: correlation with taxonomy,phylogeny, genetic variability and pollination systems

Morphometric analyses of vegetative and floral characters were conducted in 21 populations of five Pleurothallis (Orchidaceae) species occurring in Brazilian 'campo rupestre' vegetation. A phylogenetic analysis of this species group was also carried out using nuclear ribosomal DNA internal transcribed spacers (ITS1 and ITS2). Results of the ordination and cluster analyses agree with species' delimitation revealed by taxonomic and allozyme studies. The groups formed in ordination analysis correspond to the pollinator groups determined in a previous pollination study. Relationships among the species in the cluster analysis using only vegetative characters are similar to those found in a previous allozyme study, but those indicated by cluster analysis using only floral characters differ. These results support the hypothesis that floral similarities are due to convergence driven by similar pollination mechanisms, and therefore floral traits may not be good indicators of phylogenetic relationships in this group. The results of the phylogenetic analysis support this conclusion to some extent. There is no correlation between genetic (allozyme) and morphological variability in the populations nor in the way this variability is distributed among conspecific populations. We describe a new subspecies of Pleurothallis ochreata based on differences in vegetative and chemical characters as well as geographic distribution. Absence of differentiation in floral characters, attraction of the same pollinator species, interfertility and genetic similarity support the argument for subspecific rather than specific status.     

Multidisciplinary approaches for species delimitation in Sisyrinchium (Iridaceae)

A remarkable morphological similarity in natural populations of different groups of Sisyrinchium spp. (Iridaceae) makes classification of some species difficult. The present paper focused on two morphological categories of S. sellowianum (MC‐I and MC‐II) with distinct morphological traits. Morphological, cytogenetic, reproductive biology and genetic studies were performed, aiming to elucidate and better characterize such variation. The basic chromosome number established for the species was x = 9 and diploid and tetraploid populations were observed for MC‐I, whereas MC‐II showed only diploid populations. Different pollen morphologies were recognized in each morphological category. Based on pollination experiments, MC‐I is out‐crossing, whereas MC‐II is selfing. The populations were highly differentiated (F_ST = 0.46, θ^B = 0.62). In MC‐I, observed variation was greater within populations (69%) than among populations (31%), whereas in MC‐II, 61% of the variation was among populations and 39% within populations. This study evidenced that the two morphological categories correspond to distinct and reproductively isolated species and that floral traits reflect their breeding system, with allogamous plants in MC‐I and autogamous in MC‐II. Furthermore, MC‐II is unveiled as S. platycaule, a neglected taxon of Sisyrinchium in Brazil. The tools applied in this study were substantially able to check the identity of the two morphological categories as two different species and present the variation encountered in the taxa.     

Unravelling plant diversification: Intraspecific genetic differentiation in hybridizing Anacyclus species in the western Mediterranean Basin

Premise

The interfertile species Anacyclus clavatus, A. homogamos, and A. valentinus represent a plant complex coexisting in large anthropic areas of the western Mediterranean Basin with phenotypically mixed populations exhibiting a great floral variation. The goal of this study was to estimate the genetic identity of each species, to infer the role of hybridization in the observed phenotypic diversity, and to explore the effect of climate on the geographic distribution of species and genetic clusters.

Methods

We used eight nuclear microsatellites to genotype 585 individuals from 31 populations of three Anacyclus species for population genetic analyses by using clustering algorithms based on Bayesian models and ordination methods. In addition, we used ecological niche models and niche overlap analyses for both the species and genetic clusters. We used an expanded data set, including 721 individuals from 129 populations for ecological niche models of the genetic clusters.

Results

We found a clear correspondence between species and genetic clusters, except for A. clavatus that included up to three genetic clusters. We detected individuals with admixed genetic ancestry in A. clavatus and in mixed populations. Ecological niche models predicted similar distributions for species and genetic clusters. For the two specific genetic clusters of A. clavatus, ecological niche models predicted remarkably different areas.

Conclusions

Gene flow between Anacyclus species likely explains phenotypic diversity in contact areas. In addition, we suggest that introgression could be involved in the origin of one of the two A. clavatus genetic clusters, which also showed ecological differentiation.     

Can indirect selection and genetic context contribute to trait diversification? A transition‐probability study of blossom‐colour evolution in two genera

Darwin recognized that biological diversity has accumulated as a result of both adaptive and nonadaptive processes. Very few studies, however, have addressed explicitly the contribution of nonadaptive processes to evolutionary diversification, and no general procedures have been established for distinguishing between adaptive and nonadaptive processes as sources of trait diversity. I use the diversification of flower colour as a model system for attempting to identify adaptive and nonadaptive causes of trait diversification. It is widely accepted that variation in flower colour reflects direct, adaptive response to divergent selective pressures generated by different pollinators. However, diversification of flower colour may also result from the effects of nonadaptive, pleiotropic relationships with vegetative traits. Floral pigments that have pleiotropic relationships to vegetative pigments may evolve and diversify in at least two nonadaptive ways. (1) Indirect response to selection on the pleiotropically related nonfloral traits may occur (indirect selection). (2) Divergent evolution in response to parallel selective pressures (e.g. selection by pollinators for visually obvious flowers) may occur because populations are at different genetic starting points, and each population follows its own genetic `line of least resistance.' A survey of literature suggests that pleiotropic relationships between flower colour and vegetative traits are common. Phylogenetically informed analyses of comparative data from Dalechampia (Euphorbiaceae) and Acer (Aceraceae), based on trait‐transition probabilities and maximum likelihood, indicated that floral and vegetative pigments are probably pleiotropically related in these genera, and this relationship better explains the diversification of floral colour than does direct selection by pollinators. In Dalechampia pink/purple floral bract colour may have originated by indirect response to selection on stem and leaf pigments. In Acer selection by pollinators for visually obvious flowers may to have led to the evolution of red or purple flowers in lineages synthesizing and deploying red anthocyanins in leaves, and pale‐green or yellow flowers in species not deploying red anthocyanins in vegetative structures. This study illustrates the broader potential of indirect selection and parallel selection on different genetic starting points to contribute to biological diversity, and the value of testing directly for the operation of these nonadaptive diversifying processes.