Evolution of floral scent in relation to self-incompatibility and capacity for autonomous self-pollination in the perennial herb Arabis alpina

Background and AimsThe transition from outcrossing to selfing is a frequent evolutionary shift in flowering plants and is predicted to result in reduced allocation to pollinator attraction if plants can self-pollinate autonomously. The evolution of selfing is associated with reduced visual floral signalling in many systems, but effects on floral scent have received less attention. We compared multiple populations of the arctic–alpine herb Arabis alpina (Brassicaceae), and asked whether the transition from self-incompatibility to self-compatibility has been associated with reduced visual and chemical floral signalling. We further examined whether floral signalling differ between self-compatible populations with low and high capacity for autonomous self-pollination, as would be expected if benefits of signalling decrease with reduced dependence on pollinators for pollen transfer.MethodsIn a common garden we documented flower size and floral scent emission rate and composition in eight self-compatible and nine self-incompatible A. alpina populations. These included self-compatible Scandinavian populations with high capacity for autonomous self-pollination, self-compatible populations with low capacity for autonomous self-pollination from France and Spain, and self-incompatible populations from Italy and Greece.Key ResultsThe self-compatible populations produced smaller and less scented flowers than the self-incompatible populations. However, flower size and scent emission rate did not differ between self-compatible populations with high and low capacity for autonomous self-pollination. Floral scent composition differed between self-compatible and self-incompatible populations, but also varied substantially among populations within the two categories.ConclusionsOur study demonstrates extensive variation in floral scent among populations of a geographically widespread species. Contrary to expectation, floral signalling did not differ between self-compatible populations with high and low capacity for autonomous self-pollination, indicating that dependence on pollinator attraction can only partly explain variation in floral signalling. Additional variation may reflect adaptation to other aspects of local environments, genetic drift, or a combination of these processes.     

Outcrossing rates in an experimentally admixed population of self-compatible and self-incompatible Arabidopsis lyrata

The transition to self-compatibility from self-incompatibility is often associated with high rates of self-fertilization, which can restrict gene flow among populations and cause reproductive isolation of self-compatible (SC) lineages. Secondary contact between SC and self-incompatible (SI) lineages might re-establish gene flow if SC lineages remain capable of outcrossing. By contrast, intrinsic features of SC plants that reinforce high rates of self-fertilization could maintain evolutionary divergence between lineages. Arabidopsis lyrata subsp. lyrata is characterized by multiple origins of self-compatibility and high rates of self-fertilization in SC-dominated populations. It is unclear whether these high rates of selfing by SC plants have intrinsic or extrinsic causes. We estimated outcrossing rates and examined patterns of pollinator movement for 38 SC and 40 SI maternal parents sampled from an admixed array of 1509 plants sourced from six SC and six SI populations grown under uniform density. Although plants from SI populations had higher outcrossing rates (mean t_m = 0.78 ± 0.05 SE) than plants from SC populations (mean t_m = 0.56 ± 0.06 SE), outcrossing rates among SC plants were substantially higher than previous estimates from natural populations. Patterns of pollinator movement appeared to contribute to lower outcrossing rates for SC plants; we estimated that 40% of floral visits were geitonogamous (between flowers of the same plant). The relatively high rates of outcrossing for SC plants under standardized conditions indicate that selfing rates in natural SC populations of A. lyrata are facultative and driven by extrinsic features of A. lyrata, including patterns of pollinator movement.Subject terms: Plant evolution, Self incompatability, Ecological genetics, Population genetics     

Effects of pollination by bats on the mating system of Ceiba pentandra (Bombacaceae) populations in two tropical life zones in Costa Rica

The identity and behavior of pollinators are among the main factors that determine the reproductive success and mating system of plants; however, few studies have directly evaluated the relationship between pollinators and the breeding system of the plants they pollinate. It is important to document this relationship because the global decline in pollinators may significantly affect the breeding systems of many animal-pollinated plants, particularly specialized systems. Ceiba pentandra is a tropical tree that has chiropterophilic flowers and a variable breeding system throughout its distribution, ranging from fully self-incompatible, to a mixed system with different degrees of selfing. To determine if regional differences in pollinators may result in regional differences in the outcrossing rate of this species, we used systematic observations of pollinator behavior in two tropical life zones and high-resolution genetic analysis of the breeding system of populations from these two regions using microsatellites. We found a predominantly self-incompatible system in regions with high pollinator visitation, while in environments with low pollinator visitation rates, C. pentandra changed to a mixed mating system with high levels of self-pollination.     

The evolution of self-fertility in apomictic plants

Self-fertilization and apomixis have often been seen as alternative evolutionary strategies of flowering plants that are advantageous for colonization scenarios and in bottleneck situations. Both traits have multiple origins, but different genetic control mechanisms; possible connections between the two phenomena have long been overlooked. Most apomictic plants, however, need a fertilization of polar nuclei for normal seed development (pseudogamy). If self-pollen is used for this purpose, self-compatibility is a requirement for successful pollen tube growth. Apomictic lineages usually evolve from sexual self-incompatible outcrossing plants, but pseudogamous apomicts frequently show a breakdown of self-incompatibility. Two possible pathways may explain the evolution of SC: (1) Polyploidy not only may trigger gametophytic apomixis, but also may result in a partial breakdown of SI systems. (2) Alternatively, frequent pseudo self-compatibility (PSC) via aborted pollen may induce selfing of pseudogamous apomicts (mentor effects). Self-fertile pseudogamous genotypes will be selected for within mixed sexual–apomictic populations because of avoidance of interploidal crosses; in founder situations, SC provides reproductive assurance independent from pollinators and mating partners. SI pseudogamous genotypes will be selected against in mixed populations because of minority cytotype problems and high pollen discounting; in founder populations, SI reactions among clone mates will reduce seed set. Selection for SC genotypes will eliminate SI unless the apomict maintains a high genotypic diversity and thus a diversity of S-alleles within a population, or shifts to pollen-independent autonomous apomixis. The implications of a breakdown of SI in apomictic plants for evolutionary questions and for agricultural sciences are being discussed.     

Adaptive significance of self-fertilization in a hermaphroditic perennial, Trillium camschatcense (Melanthiaceae)

The evolution of self-fertilization from primarily outcrossing ancestors is one of the most common evolutionary transitions in plants; however, the ecological mechanisms that maintain self-fertilization have remained controversial. Theoretical studies suggest that selfing is advantageous over outcrossing in terms of genetic transmission and assurance of seed production under pollen-limited circumstances. Trillium camschatcense is a herbaceous perennial distributed in Hokkaido and northern Honshu, Japan. Geographical variation in the breeding system (self-compatible, SC; or self-incompatible, SI) has been reported in populations in Hokkaido. Here, we used several SC and SI populations of T. camschatcense to investigate the adaptive significance and the evolutionary basis of self-fertilization. Pollination experiments and genetic analyses demonstrated that the potential availability of outcross pollen in SC populations was sufficient and that the number of pollen donors was equal to that of SI populations. However, despite the high availability of outcross pollen, the SC populations produced seeds predominantly by selfing and so underwent severe inbreeding depression. Although none of the suggested advantages for self-fertilization were supported by our analyses, we propose two possible scenarios for the evolution of self-fertilization in T. camschatcense.     

How rapidly do self‐compatible populations evolve selfing? Mating system estimation within recently evolved self‐compatible populations of Azorean Tolpis succulenta (Asteraceae)

Genome‐wide genotyping and Bayesian inference method (BORICE) were employed to estimate outcrossing rates and paternity in two small plant populations of Tolpis succulenta (Asteraceae) on Graciosa island in the Azores. These two known extant populations of T. succulenta on Graciosa have recently evolved self‐compatibility. Despite the expectation that selfing would occur at an appreciable rate (self‐incompatible populations of the same species show low but nonzero selfing), high outcrossing was found in progeny arrays from maternal plants in both populations. This is inconsistent with an immediate transition to high selfing following the breakdown of a genetic incompatibility system. This finding is surprising given the small population sizes and the recent colonization of an island from self‐incompatible colonists of T. succulenta from another island in the Azores, and a potential paucity of pollinators, all factors selecting for selfing through reproductive assurance. The self‐compatible lineage(s) likely have high inbreeding depression (ID) that effectively halts the evolution of increased selfing, but this remains to be determined. Like their progeny, all maternal plants in both populations are fully outbred, which is consistent with but not proof of high ID. High multiple paternity was found in both populations, which may be due in part to the abundant pollinators observed during the flowering season.     

Inbreeding depression in self-incompatible North-American Arabidopsis lyrata: disentangling genomic and S-locus-specific genetic load

Newly formed selfing lineages may express recessive genetic load and suffer inbreeding depression. This can have a genome-wide genetic basis, or be due to loci linked to genes under balancing selection. Understanding the genetic architecture of inbreeding depression is important in the context of the maintenance of self-incompatibility and understanding the evolutionary dynamics of S-alleles. We addressed this using North-American subspecies of Arabidopsis lyrata. This species is normally self-incompatible and outcrossing, but some populations have undergone a transition to selfing. The goals of this study were to: (1) quantify the strength of inbreeding depression in North-American populations of A. lyrata; and (2) disentangle the relative contribution of S-linked genetic load compared with overall inbreeding depression. We enforced selfing in self-incompatible plants with known S-locus genotype by treatment with CO₂, and compared the performance of selfed vs outcrossed progeny. We found significant inbreeding depression for germination rate (δ=0.33), survival rate to 4 weeks (δ=0.45) and early growth (δ=0.07), but not for flowering rate. For two out of four S-alleles in our design, we detected significant S-linked load reflected by an under-representation of S-locus homozygotes in selfed progeny. The presence or absence of S-linked load could not be explained by the dominance level of S-alleles. Instead, the random nature of the mutation process may explain differences in the recessive deleterious load among lineages.     

Spatiotemporal variation in the reproductive ecology of two parapatric subspecies of Oenothera cespitosa (Onagraceae)

?Premise of the study: Flowering plants that rely on pollinators for most of their reproduction may experience unpredictable and inconsistent availability of effective pollinators throughout their reproductive lifetime. We investigated the reproductive ecology of two subspecies of the tufted evening primrose, Oenothera cespitosa, which occupy geographically and edaphically distinct habitats in western North America: O. cespitosa subsp. navajoensis inhabits sandstone soils on open sites or rocky slopes in the Colorado Plateau and O. cespitosa subsp. cespitosa grows in clay soils on talus slopes and exposed rocky ridges in the western Great Plains and northern Rocky Mountains of the United States. ?Methods: Pollen augmentation and selfing experiments, floral visitor observations, and single-visit effectiveness experiments were conducted over 4 years to examine the breeding system and spatiotemporal variation in pollinator behavior, assemblage, and abundance at different populations for each subspecies. ?Key results: Both subspecies of O. cespitosa were self-incompatible and pollen-limited, suggesting that the relative abundance, effectiveness, and movement patterns of different insects as pollinators influenced the quality and quantity of seed production in these plants. Medium-sized vespertine hawkmoths (Hyles lineata, Sphinx vashti) were effective pollinators when present, as were large matinal bees (Anthophora affabilis, A. dammersi, Xylocopa tabaniformis androleuca), whereas small oligolectic Lasioglossum bees primarily functioned as pollen thieves in the evening and morning. ?Conclusions: These findings highlight the importance of variability of pollinator composition and abundance in the evolution of plant breeding systems and reproductive success at varying spatial and temporal scales.     

Does gall midge larvae cause pre-dispersal seed mortality and limit cornflower population growth?

Many kinds of pests can reduce seed production. Some directly attack seeds before they are released, and some are hosted by the fruit and impact seed ripening and viability indirectly. Pre-dispersal seed mortality may have strong effects on plant population dynamics and evolution. Our goals were to determine to what extent insect-mediated pre-dispersal seed mortality contributes to population-level declines of cornflower, Centaurea cyanus L. We recorded occurrence and abundance of seed-feeding insects on flower heads in twelve cornflower populations. We measured flower head size, number of disc florets, seed production, and seed viability and germination. Larger flower heads had proportionally fewer healthy seeds. Although we observed no visible damage to the C. cyanus seed, the presence of gall midge (Cecidomyiidae) larvae inside the flower head correlated with four times fewer viable seeds. It seems that gall midges could have a significant impact on ovule fertilization, seed abortion and viability of fully developed cornflower seeds. The higher rate of aborted seeds in the presence of gall midge larvae could have been because the larvae extracted resources from the seeds, or because the larvae repelled pollinators. The viability of apparently healthy seeds was 40% lower in flower heads that contained larvae and/or aborted seed. Insect-mediated pre-dispersal mortality could select against evolution toward larger flower head, and have detrimental consequences on seed number, viability and germination, all of which could limit the spread of C. cyanus populations.     

The evolution of self-compatible and self-incompatible populations in a hermaphroditic perennial, <Emphasis Type="Italic">Trillium camschatcense</Emphasis> (Melanthiaceae)

The evolution of selfing from outcrossing ancestors is known to have occurred repeatedly in angiosperms. Theoretical studies have argued that the transition from outcrossing to selfing is accomplished more easily than the reverse case, and phylogenetic analyses involving self-compatible (SC) and self-incompatible (SI) species has basically supported this assumption. The evolutionary direction of self-compatibility and self-incompatibility was examined in Trillium camschatcense, which contains geographically widespread SC populations, and restricted SI populations. Ecological surveys have revealed that the SC populations were suitable for outcrossing, and selfing in these populations did not confer any fitness advantage. Since reproductive fitness indicates the possibility of an evolutionary shift from self-compatibility to self-incompatibility, the phylogenetic relationships of SI and SC populations of T. camschatcense were investigated based on cpDNA variations and nuclear DNA microsatellite polymorphisms. Although phylogenetic analyses did not provide credible evidence to determine evolutionary direction, the SI populations turned out to be monophyletic with extremely low genetic differentiation. Based on these results, we proposed two possible scenarios for the evolutionary backgrounds of SI and SC populations in T. camschatcense. The plausibility of each scenario was evaluated based on the reproductive and geographical features of the mating systems. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A rare case of self-incompatibility in arctic plants: Draba palanderiana (Brassicaceae)

During the last decades, it has been shown that arctic plants show larger variation in reproductive strategies than traditionally assumed. Obligate outcrossing based on a self-incompatibility system is, however, very rare in the typically harsh, insect-poor arctic environment. Here we present the second, to our knowledge, documented example of a fully self-incompatible arctic species, Draba palanderiana Kjellm. Because of its large, scented flowers and frequently aborted fruits it has been suggested that this species is strictly outcrossing. To test this hypothesis, we conducted a pollination experiment with two populations from arctic North America. Pollen stainabilities were above 80% in most plants. Full female and male fertility was demonstrated by crosses resulting in fertile F₁ offspring. In contrast, no viable seeds were obtained after spontaneous or hand-facilitated selfing, demonstrating that these D. palanderiana populations are fully self-incompatible and thus obligately outcrossing.     

Genetic variability of plant characters in the partial inbreeder Collinsia heterophylla (Scrophulariaceae)

Quantitative genetic variability for six characters was estimated in four populations of the annual plant, Collinsia heterophylla, with estimated selling rates ranging from 0.36 to 0.68. Based on large samples of parental plants, all four populations showed significant genetic variation for two or more characters, and there was no sign that the more selfing populations had lower amounts of genetic variance or lower heritability values. Autogamous fruit set rates in the absence of pollinators also showed significant heritability in one population.     

Does cleistogamy variation translate into outcrossing variation in the annual species Lamium amplexicaule (Lamiaceae)?

The maintenance of cleistogamy, the ability to produce closed, obligately selfing flowers (CL), and open, potentially outcrossed flowers (CH), in different proportions, is classically explained through different morphological/physiological properties of the two floral types, but rarely as a mechanism of adjusting the outcrossing rate. We explore the link between CH proportion and overall outcrossing rate in natural populations of Lamium amplexicaule. We assessed number of calices, CH proportion, CH and overall outcrossing rate in four natural populations in two distant areas in France. In each region, we had one favorable and one unfavorable habitat population. Unfavorable habitats produce smaller plants (with fewer calices) with higher CH proportions compared to favorable habitats, regardless of the geographic origin of the populations. CH outcrossing rate did not change significantly among populations. Thus, the overall outcrossing rate in L. amplexicaule is mainly determined by the CH proportion. Contrary to the classical view, unfavorable environments in our study are associated with higher rate of chasmogamous flowers, supposedly more costly to produce. We propose that cleistogamy variation can be considered as a variation of the outcrossing rate and could be explained by classic forces driving the evolution of mating systems (inbreeding depression, pollinators’ abundance).     

TRANSMISSION ADVANTAGE FAVORS SELFING ALLELE IN EXPERIMENTAL POPULATIONS OF SELF‐INCOMPATIBLE WITHERINGIA SOLANACEA (SOLANACEAE)

The evolution of self‐fertilization is one of the most commonly traversed transitions in flowering plants, with profound implications for population genetic structure and evolutionary potential. We investigated factors influencing this transition using Witheringia solanacea, a predominantly self‐incompatible (SI) species within which self‐compatible (SC) genotypes have been identified. We showed that self‐compatibility in this species segregates with variation at the S‐locus as inherited by plants in F1 and F2 generations. To examine reproductive assurance and the transmission advantage of selfing, we placed SC and SI genotypes in genetically replicated gardens and monitored male and female reproductive success, as well as selfing rates of SC plants. Self‐compatibility did not lead to increased fruit or seed set, even under conditions of pollinator scarcity, and the realized selfing rate of SC plants was less than 10%. SC plants had higher fruit abortion rates, consistent with previous evidence showing strong inbreeding depression at the embryonic stage. Although the selfing allele did not provide reproductive assurance under observed conditions, it also did not cause pollen discounting, so the transmission advantage of selfing should promote its spread. Given observed numbers of S‐alleles and selfing rates, self‐compatibility should spread even under conditions of exceedingly high initial inbreeding depression.     

Dichogamy correlates with outcrossing rate and defines the selfing syndrome in the mixed-mating genus Collinsia

Background and Aims

How and why plants evolve to become selfing is a long-standing evolutionary puzzle. The transition from outcrossing to highly selfing is less well understood in self-compatible (SC) mixed-mating (MM) species where potentially subtle interactions between floral phenotypes and the environment are at play. We examined floral morphological and developmental traits across an entire SC MM genus, Collinsia, to determine which, if any, predict potential autonomous selfing ability when pollinators are absent (AS) and actual selfing rates in the wild, s_m, and to best define the selfing syndrome for this clade.

Methods

Using polymorphic microsatellite markers, we obtained 30 population-level estimates of s_m across 19 Collinsia taxa. Species grand means for the timing of herkogamy (stigma–anther contact) and dichogamy (stigmatic receptivity, SR), AS, floral size, longevity and their genetic correlations were quantified for 22 taxa.

Key Results

Species fell into discrete selfing and outcrossing groups based on floral traits. Loss of dichogamy defines Collinsia''s selfing syndrome. Floral size, longevity and herkogamy also differ significantly between these groups. Most taxa have high AS rates (>80 %), but AS is uncorrelated with any measured trait. In contrast, s_m is significantly correlated only with SR. High variance in s_m was observed in the two groups.

Conclusions

Collinsia species exhibit clear morphological and developmental traits diagnostic of ‘selfing’ or ‘outcrossing’ groups. However, many species in both the ‘selfing’ and the ‘outcrossing’ groups were MM, pointing to the critical influence of the pollination environment, the timing of AS and outcross pollen prepotency on s_m. Flower size is a poor predictor of Collinsia species'' field selfing rates and this result may apply to many SC species. Assessment of the variation in the pollination environment, which can increase selfing rates in more ‘outcrossing’ species but can also decrease selfing rates in more ‘selfing’ species, is critical to understanding mating system evolution of SC MM taxa.     

Limited phenological and pollinator-mediated isolation among selfing and outcrossing Arabidopsis lyrata populations

Transitions from outcrossing to selfing have been a frequent evolutionary shift in plants and clearly play a role in species divergence. However, many questions remain about the initial mechanistic basis of reproductive isolation during the evolution of selfing. For instance, how important are pre-zygotic pre-pollination mechanisms (e.g. changes in phenology and pollinator visitation) in maintaining reproductive isolation between newly arisen selfing populations and their outcrossing ancestors? To test whether changes in phenology and pollinator visitation isolate selfing populations of Arabidopsis lyrata from outcrossing populations, we conducted a common garden experiment with plants from selfing and outcrossing populations as well as their between-population hybrids. Specifically, we asked whether there was isolation between outcrossing and selfing plants and their between-population hybrids through differences in (1) the timing or intensity of flowering; and/or (2) pollinator visitation. We found that phenology largely overlapped between plants from outcrossing and selfing populations. There were also no differences in pollinator preference related to mating system. Additionally, pollinators preferred to visit flowers on the same plant rather than exploring nearby plants, creating a large opportunity for self-fertilization. Overall, this suggests that pre-zygotic pre-pollination mechanisms do not strongly reproductively isolate plants from selfing and outcrossing populations of Arabidopsis lyrata.     

Ecological context of the evolution of self-pollination in Clarkia xantiana: population size, plant communities, and reproductive assurance

The repeated evolutionary transition from outcrossing to self-pollination in flowering plants has been suggested to occur because selfing provides reproductive assurance. Reports from biogeographical and ecological surveys indicate that selfing taxa are often associated with stressful and ephemeral environments, situations in which plant abundance is low (e.g., Baker's law) and with novel plant communities, however experimental tests of ecological hypotheses are few. In this study, we examined the ecological context of selection on mating system traits (herkogamy and protandry) in a California annual, Clarkia xantiana, where natural selfing populations differ from outcrossing populations in that they are often of small size or low density and occur mainly outside the range of pollinator-sharing congeners. We constructed artificial populations of plants with broad genetic variation in floral traits and manipulated two ecological factors, plant population size, and the presence versus absence of pollinator-sharing congeners, in the center of the geographic range of outcrossing populations. We found evidence for context-dependent selection on herkogamy and protandry via female fitness in which reduced traits, which promote autonomous selfing, were favored in small populations isolated from congeners whereas selection was comparatively weak in large populations or when congeners were present. In small, isolated populations, the fertility of plants with low herkogamy or protandry was elevated by 66% and 58%, respectively, compared to those with high herkogamy or protandry. The presence of pollinator-sharing congeners augmented bee visitation rates to C. xantiana flowers by 47% for all bees and by 93% for pollen specialists. By facilitating pollinator visitation, congeners mitigated selection on mating system traits in small populations, where outcross mating success is often low (the Allee effect). We also found support for the hypothesis that pollinator availability directly influenced variation in the strength of selection on herkogamy among populations. The striking parallels between our experimental results and patterns of variation in ecological factors across the geographic range of outcrossing and selfing populations suggest that reproductive assurance may play a central role in directing mating system evolution in C. xantiana.     

Small reductions in corolla size and pollen: ovule ratio,but no changes in flower shape in selfing populations of the North American <Emphasis Type="Italic">Arabidopsis lyrata</Emphasis>

The shift from outcrossing to selfing is often accompanied by striking changes in floral morphology towards a “selfing syndrome”, which is characterized by flowers with reduction in size, pollen: ovule (P/O) ratio, and herkogamy. This study aims to test whether such changes have occurred in the North American Arabidopsis lyrata, which is of particular interest because of the relatively recent transitions to selfing in this system. Flower size, flower shape, herkogamy levels, P/O ratio, and floral integration of six self-incompatible (outcrossing) and six self-compatible (selfing) populations of A. lyrata were measured in a common environment using conventional and geometric morphometrics methods. Although selfers had on average 9.2% smaller corollas, 8.4% longer pistils, and 21.5% lower P/O ratios than outcrossers, there were no differences in shape, floral integration, and herkogamy between outcrossing and selfing populations. Moreover, most variation in floral traits was explained by population genetic background rather than by mating system. We conclude that selfing populations in A. lyrata have not evolved a selfing syndrome.     

How variable is delayed selfing in a fluctuating pollinator environment? A comparison between a delayed selfing and a pollinator-dependent Schizanthus species of the high Andes

Delayed selfing has been considered the best-of-both-worlds response to pollinator unpredictability because it can provide reproductive assurance without decreasing outcrossing potential. According to this hypothesis, selfing rates in delayed selfing species should be highly variable in fluctuating pollinator environments. To test this prediction, as well to explore the consequences of delayed selfing on genetic patterns, we compared two sister species that grow in the high Andes of Chile: Schizanthus grahamii that exhibits delayed selfing and Schizanthus hookeri, which is self-compatible but requires pollinators for seed set. We estimated genetic diversity within and among five populations of each species using six shared microsatellites. Our results indicated that selfing rates in S. grahamii (range 0.07–0.81) were significantly more variable than in S. hookeri (range 0–0.26). The highest levels of selfing were found in the populations of S. grahamii located at highest altitudes (r = 0.78) and at northern margin range, where pollinators are probably more scarce. These populations also showed the lowest allelic richness and heterozygosity values. Southern populations of S. grahamii had mixed mating, and showed heterozygosity and diversity values close to those detected for S. hookeri along all the sampled range. Selfing in this species results from geitonogamy, and did not covary with altitude. Schizanthus grahamii showed greater population differentiation than S. hookeri. Overall, our results indicated that selfing rates were widely variable in S. grahamii, with some populations predominantly selfing and others showing mixed mating. This pattern may be associated with the strong fluctuations in pollinator service that typically occur in the high Andes of Chile.     

Floral colour variation of Nicotiana glauca in native and non-native ranges: Testing the role of pollinators' perception and abiotic factors

• Invasive plants displaying disparate pollination environments and abiotic conditions in native and non-native ranges provide ideal systems to test the role of different ecological factors driving flower colour variation.
• We quantified corolla reflectance of the ornithophilous South American Nicotiana glauca in native populations, where plants are pollinated by hummingbirds, and in populations from two invaded regions: South Africa, where plants are pollinated by sunbirds, and the Balearic island of Mallorca, where plants reproduce by selfing. Using visual modelling we examined how corolla reflectance could be perceived by floral visitors present in each region. Through Mantel tests we assessed a possible association between flower colour and different abiotic factors.
• Corolla reflectance variation (mainly along medium to long wavelengths, i.e. human green-yellow to red colours) was greater among studied regions than within them. Flower colour was more similar between South America and South Africa, which share birds as pollinators. Within invaded regions, corolla reflectance variation was lower in South Africa, where populations could not be distinguished from each other by sunbirds, than in Spain, where populations could be distinguished from each other by their occasional visitors. Differences in corolla colour among populations were partially associated with differences in temperature.
• Our findings suggest that shifts in flower colour of N. glauca across native and invaded ranges could be shaped by changes in both pollination environment and climatic factors. This is the first study on plant invasions considering visual perception of different pollinators and abiotic drivers of flower colour variation.