Autonomous Selfing Research Articles

Multiple reproductive modes of Myrcianthes coquimbensis (Myrtaceae), an endangered shrub endemic to the Atacama Desert

Many plants can produce seeds via multiple reproductive modes, such as selfing and outcrossing. Having multiple reproductive modes can be advantageous if it assures seed production when outcrossing fails, which is important for species inhabiting environments where pollinators are scarce or variable. However, it can also be disadvantageous due to the fitness costs associated to selfing. Consequently, plants have mechanisms to reduce the incidence of selfing. Here we examined the breeding system of Myrcianthes coquimbensis; this threatened Atacama Desert shrub is the last species to bloom in the community and exhibits low visitation rates per flower because pollinators are less abundant. Our aim was to determine whether this plant can produce fruits by modes other than outcrossing, and whether it possesses floral traits to prevent sexual interference. We conducted experimental flower treatments in two localities to determine whether fruits were produced by outcrossing, selfing, autonomous selfing and agamospermy. We also evaluated stigma receptivity and pollen viability during a flower’s lifespan. M. coquimbensis developed fruits and seeds by all the reproductive modes assessed, including selfing and agamospermy. Flowers presented partial segregation of sexual functions, with the peak of pollen viability occurring before the peak of stigma receptivity. Selfing is unavoidable in M. coquimbensis and likely interferes with outcrossing. Coupled with possible early inbreeding depression, it probably results in a cost for seed production. Our results suggest that this species may be vulnerable in scenarios where pollinators are scarce; however, agamospermy may provide an alternative route of seed production in these scenarios.

Do floral traits and the selfing capacity of Mimulus guttatus plastically respond to experimental temperature changes?

Climate change can negatively impact plant-pollinator interactions, and reduce outcross pollination. For reproductive assurance, an increased capacity for autonomous selfing should benefit the persistence of plants under new temperature conditions. Plastic responses of the autonomous selfing capacity to climate change may occur indirectly due to changes in floral traits associated with this capacity. We tested whether the mixed mating plant Mimulus guttatus is capable of plastic changes in floral traits favoring autonomous selfing in response to temperature changes. In seven growth chambers, we grew M. guttatus originating from a large range of latitudes (from 37.89° N to 49.95° N) and thus home temperatures in North America, and experimentally assessed the (autonomous) selfing and outcrossing capacities of the plants. With an increase in the difference between the overall mean daytime and nighttime experimental test temperature and home temperature, flower length and width decreased. The plastic response in flower size suggests that plants may be more successful at autonomous selfing. However, we did not find direct evidence that M. guttatus responded to increased temperature by an increased autonomous selfing capacity. With an increase in temperature difference, the odds of seed production, number of seeds, and individual seed mass decreased. Our results indicate that global warming and the associated increase in extreme temperature events may be detrimental to the reproduction and thus persistence of some plants.

Geographic isolation, pollination syndromes, and pollinator generalization in HimalayanRoscoeaspp. (Zingiberaceae)

AbstractThe pollination syndromes have been widely used to predict effective pollinators of plant species and provide the mechanistic explanation of floral diversity. However, in recent years, the predictive applicability of pollination syndromes has been frequently questioned. The accuracy of the syndromes among the closely related plant species may vary temporally and spatially. This suggests the need for the standardized, comprehensive evaluation of factors influencing the matching of a pollination syndrome of a plant species to the predominant pollinator community. We studied the pollination biology of three geographically/phenologically isolated alpine gingers (Roscoea auriculata,Roscoea capitata, andRoscoea tumjensis) exhibiting the correlated suites of floral traits that suggest long‐tongued insects as major pollinators, to test for the predictive power of the respective pollination syndrome. We also tested if geographical and temporal isolation affects interspecies breeding system and extent of pollinator generalization. We demonstrate that the threeRoscoeaspecies are self‐compatible but lack autonomous selfing, and thus completely rely on pollinators for pollination success. Five years of observations demonstrate that only diurnal insect visitors foraged on the flowers of the threeRoscoeaspecies. Estimates of the pollinator importance (pollen deposition) of the observed floral visitors indicate that morphologically mismatched bumblebees contribute more than 90% of pollination service in all the threeRoscoeaspecies, while long‐tongued butterflies and moths function as nectar robbers. We found that geographical isolation and temporal variation in flowering period does not affect the breeding system and pollinator generalization in the threeRoscoeaspecies. The three geographically and phenologically isolated HimalayanRoscoeaspp., with long‐tongued insect pollination syndrome, exhibit generalized pollination system and primarily rely on the morphologically mismatchedBombusspecies for pollination success. While, for threeRoscoeaspp., our result suggests that pollination syndromes are a weak predictor of efficient contemporary pollinator community, it also substantiates the role of non‐pollinator agents for the evolution of floral traits. The evolution ofBombuspollination in these alpine gingers suggests how the mismatch between plant and pollinator phenology can lead to the emergence of novel reproductive strategies among the congeners, which ultimately seems to play a key role for the speciation and diversification of the genusRoscoeain the Himalayas.

Self-compatibility and autonomous selfing of plants in meadow communities.

One of the most fundamental, although controversial, questions related to the evolution of plant mating systems is the distribution of outcrossing rates. Self-compatibility, and especially autonomous self-pollination, can become particularly beneficial in anthropogenically degraded habitats with impoverished pollinator assemblages and increased pollen limitation. In a hand-pollination experiment with 46 meadow plants from the Železné hory Mts., Czech Republic, we evaluated the species' ability to adopt different mating systems. For a subset of the species, we also tested seed germination for inbreeding depression. Subsequently, we analysed relationships between the species' mating systems and 12 floral and life-history traits. We found a relatively discrete distribution of the studied species into four groups. Fully and partially self-incompatible species formed the largest group, followed by self-compatible non-selfers and mixed mating species. The germination experiment showed an absence of inbreeding depression in 19 out of 22 examined species. Nectar sugar per flower, nectar sugar per shoot and dichogamy were significant associated with the mating system. Spontaneous selfing ability and self-incompatibility in species of the meadow communities had a discrete distribution, conforming to the general distribution of mating and breeding systems in angiosperms. The low frequency of spontaneous selfers and the lack of inbreeding depression at germination suggest the existence of a selection against selfing at the later ontogenetic stages. Some floral traits, such as the level of dichogamy and amount of nectar reward, may strongly impact the balance between selfing and outcrossing rates in the self-compatible species and thus shape the evolution of mating systems.

Fitness costs of delayed pollination in a mixed-mating plant.

To predict the evolutionary consequences of pollinator declines, we need to understand the evolution of delayed autonomous self-pollination, which is expected to evolve as a mechanism of reproductive assurance when cross-pollination becomes unreliable. This involves estimating the costs of increased levels of selfing as well as those associated with floral senescence. We studied the mechanisms and costs of delayed self-pollination in the mixed-mating vine Dalechampia scandens (Euphorbiaceae) by first assessing among-population variation in herkogamy and dichogamy, which together determine the rate and timing of autonomous self-pollination. We then tested whether floral longevity responds plastically to delayed pollination. Finally, we assessed the costs of delayed self-pollination in terms of seed number and size, explicitly separating inbreeding depression from effects of floral senescence. Herkogamy varied extensively, while variation in dichogamy was more limited. Unpollinated blossoms increased their longevity, but seed quantity and quality decreased with increasing delays in pollination, independently of inbreeding depression. In D. scandens, earlier autonomous selfing is facilitated by reduced herkogamy rather than reduced protogyny, providing reproductive assurance while maintaining the possibility for outcrossing events. Effective early autonomous self-pollination may evolve under reduced cross-pollination reliability in response to costs associated with floral senescence.

Pollen limitation and autonomous selfing ability interact to shape variation in outcrossing rate across a species range.

Hermaphroditic plants commonly reproduce through a mixture of selfing and outcrossing. The degree to which outcrossing rates reflect the availability of outcross pollen, genetic differentiation in the ability to autonomously self-fertilize, or both is often unclear. Despite the potential for autonomy and the pollination environment to jointly influence outcrossing, this interaction is rarely studied. We reviewed studies from the literature that tested whether the pollination environment or floral traits that cause autonomous selfing predict variation in outcrossing rate among populations. We also measured outcrossing rates in 23 populations of Campanula americana and examined associations with the pollination environment, autonomy, and their interaction. Our review revealed that traits that facilitate selfing were often negatively associated with outcrossing rates whereas most aspects of the pollination environment poorly predicted outcrossing. Populations of C. americana varied from mixed mating to highly outcrossing, but variation was unrelated to population size, density, pollen limitation, or autonomous selfing ability. Outcrossing rate was significantly influenced by an interaction between autonomous selfing ability and pollen limitation. Across highly autonomous populations, elevated pollen limitation was associated with reduced outcrossing, while there was no relationship for less autonomous populations. Both the ability to self autonomously and pollen limitation interact to shape outcrossing rates in C. americana. This work suggests that autonomy affords mating-system flexibility, though it is not ubiquitous in all populations across the species range. Interactions between traits influencing autonomy and pollen limitation are likely to explain variation in outcrossing rates among populations of flowering plants.

Prior selfing can mitigate the negative effects of mutual reproductive interference between coexisting congeners

Abstract When more than one closely related plant species share the same pollination niche, reproductive interference via interspecific pollen transfer should limit their coexistence. However, some studies have reported the sympatric coexistence of two native close relatives pollinated by the same pollinators under reproductive interference, even without niche partitioning. We examined the frequency dependency of reproductive interference between close relatives in natural conditions and the potential roles of autonomous selfing in mitigating the negative reproductive interference effects between congeneric species. We investigated sympatrically growing Commelina communis (Cc) and C. c. f. ciliata (Ccfc) populations. These species exhibit very large overlaps in habitat preference, flowering phenology and pollination niche, but seldom produce hybrids. First, we conducted a hand‐pollination experiment to examine the negative effects of heterospecific pollen deposition on seed production and the potential of self‐pollination to mitigate the effects in both species. Then, we examined the effects of reproductive interference on reproductive success and the potential for autonomous selfing in the field. We found significant negative effects of heterospecific pollen deposition on seed production and the mitigation effects of prior and competing self‐pollination, in both Cc and Ccfc. For both species in the field, intraspecific pollinator movements and reproductive success significantly decreased with an increase in the relative floral abundance of competing species, although the negative reproductive interference effect on reproductive success was lower in Cc than in Ccfc. We also found greater potential for prior autonomous selfing in Cc than in Ccfc. Our findings suggest that Cc flowers were less affected by reproductive interference from competing species, which was likely due to a higher prior selfing ability compared to Ccfc flowers. The asymmetry in susceptibility to reproductive interference may explain the Cc‐biased distribution in the study area. The study improves our understanding of how prior autonomous selfing can reduce the negative reproductive interference effect from competing species in mixed‐mating species with frequent pollinator visits. A plain language summary is available for this article.

Reproductive system of the critically endangered taxon Gentianella praecox subsp. bohemica

Gentianella praecox subsp. bohemica is a critically endangered taxon endemic to the Bohemian Massif and very dependent on appropriate management. We found that it is also very dependent on pollinator services, as the probability of autonomous selfing is low. Both hand-selfing and outcrossing resulted in similar seed production. Three out of four of the populations studied appeared to be pollen limited. The most frequent visitors and effective pollinators were bumblebees. However, we found that the different species of bumblebee differed greatly in their efficiency as pollinators due to differences in their behaviour. In contrast to other bumblebees, Bombus wurflenii, which nearly always robbed nectar through a hole in the corolla tube and only accidentally touched the reproductive organs, was an inefficient pollinator. Other important pollinators of G. praecox subsp. bohemica were honeybees (in lowland areas) and hoverflies. This study indicates that management for conservation should focus not only on creating gaps to improve the germination of G. praecox subsp. bohemica and reduce competition from other species, but also on improving conditions for pollinators. Hand pollination may be necessary to increase survival in populations that are close to extinction.

Pollination biology and breeding system in five nocturnal species of Oenothera (Onagraceae): reproductive assurance and opportunities for outcrossing

The capacity to produce seed, both by selfing and outcrossing, or mixed mating strategies, is considered a mechanism for overcoming unpredictable pollinator availability. In the present study, we investigate breeding system, insect visitations and the role of insect visitors in the pollination of five species of Oenothera subsect. Oenothera. Field experiments showed that autonomous selfing occurs at bud stage, prior to the opening of the flower. Control flowers showed similar seed set to hand-pollinated flowers, whereas emasculated flowers and those subject to open pollination set fewer seed. These results are consistent with the hypothesis that the investigated Oenothera exhibit a great capacity for autonomous selfing and that selfing is selected in order to provide reproductive assurance. Although flowers were visited mostly by nocturnal lepidopterans, these insects did not precipitate pollination and are thus considered nectar thieves. Conversely, analysis of pollen loads and behavior during foraging by diurnal insect visitors revealed that honeybees and bumblebees are the probable pollinators. We conclude that production of flowers capable of autonomous selfing at bud stage, followed by anthesis and opportunities for outcrossing, probably improves the invasive potential of these Oenothera in Europe, together with a rapid increase in their populations, even when pollinators are scarce.

The role of phenotypic plasticity and pollination environment in the cleistogamous, mixed mating breeding system of Triodanis perfoliata.

The role of variable pollination environments in maintaining mixed mating systems is an active area of research. Dimorphic cleistogamy, in which a plant reproduces by both open, facultative outcrossing chasmogamous (CH) flowers and closed, cleistogamous (CL) flowers presents an excellent opportunity to study mixed mating. For example, plastic responses in allocation to an optimal floral type could serve as an adaptive strategy that maintains mixed mating under variable pollination environments. We tested for pollen limitation and plastic responses in allocation to different floral types under manipulated pollination conditions in the dimorphic cleistogamous, mixed mating annual, Triodanis perfoliata. Using a field population, we quantified pollen limitation, auto-fertility and plastic responses in the breeding system by measuring allocation to flower number and seed set of floral types. We found no evidence for pollen limitation for CH flowers, and CH flowers had low efficacy of autonomous selfing. Importantly, we found that T. perfoliata alters floral number following changes in pollination conditions, with pollen-supplemented plants having lower relative CH flower number than non-supplemented plants. Breeding system plasticity may allow for benefits from outcrossing through CH flowers, but also increased overall fitness through relatively cheap CL reproduction. After CH flowers receive pollen, subsequent production of CH flowers was reduced, which may be due to resource limitation. Our findings did not support a theoretical model predicting increased CH flowers with high pollination levels. These results increase our understanding of the role of pollination services and resource allocation in the maintenance of mixed mating systems, which also warrants further investigation.

Shifts to earlier selfing in sympatry may reduce costs of pollinator sharing.

Coexisting plant congeners often experience strong competition for resources. Competition for pollinators can result in direct fitness costs via reduced seed set or indirect costs via heterospecific pollen transfer (HPT), causing subsequent gamete loss and unfit hybrid offspring production. Autonomous selfing may alleviate these costs, but to preempt HPT, selfing should occur early, before opportunities for HPT occur (i.e., "preemptive selfing hypothesis"). We evaluated conditions for this hypothesis in Collinsia sister species, C. linearis and C. rattanii. In field studies, we found virtually identical flowering times and pollinator sharing between congeners in sympatric populations. Compared to allopatric populations, sympatric C. linearis populations enjoyed higher pollinator visitation rates, whereas visitation to C. rattanii did not differ in sympatry. Importantly, the risk of HPT to each species in sympatry was strongly asymmetrical; interspecies visits comprised 40% of all flower-to-flower visits involving C. rattanii compared to just 4% involving C. linearis. Additionally, our greenhouse experiment demonstrated a strong cost of hybridization when C. rattanii was the pollen donor. Together, these results suggest that C. rattanii pays the greatest cost of pollinator sharing. Matching predictions of the preemptive selfing hypothesis, C. rattanii exhibit significantly earlier selfing in sympatric relative to allopatric populations.

Equipped for Migrations Across High Latitude Regions? Reduced Spur Length and Outcrossing Rate in a Biennial Halenia elliptica (Gentianaceae) With Mixed Mating System Along a Latitude Gradient.

Halenia (Gentianaceae) originated from the mountain regions of East Asia, and diversified in America following long migrations via Beringia. While Halenia elliptica, one species of the genus in China, migrated toward high latitudes in China. Spur length of H. elliptica is highly variable. We examined the relationship between spur length and mating pattern along a latitude gradient. Field experiments were performed in two populations of H. elliptica, and we found that this species could produce seeds via both autonomous selfing and the aid of pollinators, suggesting a mixed mating system. In seven populations of H. elliptica along a latitudinal gradient, we found a trend of decrease in spur length with the increase of latitude. Based on molecular data from 11 microsatellite loci, we found that multilocus outcrossing rate decreased with the increase of latitude while the estimated inbreeding depression increased significantly, indicating that a high degree of inbreeding depression might have prevented evolution toward complete selfing in the high latitude populations with short spur length, and thus maintained mixed mating system of H. elliptica. Our results suggest that the mixed mating system of this species might be helpful in overcoming pollinator scarcity in newly colonized populations toward high latitudes after its origination in the mountain regions of China, and the decrease of spur length in the high latitude populations could result from reduced resource allocation to pollinator associated traits.

Populations with greater flexibility in floral traits modify mating system in response to the pollinator environment

Abstract Mixed mating and variation in outcrossing rate among populations of the same species are common. Outcrossing can be affected by pollinator activity and floral traits that facilitate or impede autonomous self‐fertilization. However, the relative contribution of pollen limitation and evolved differences in the ability to self‐fertilize to variation in the mating system is poorly understood and can only be disentangled using an experimental approach. We placed arrays of plants from eight Campanula americana populations that varied in autonomous selfing ability (hereafter “autonomy”) in sun and shade habitats to create high‐ and low‐pollination environments. Floral visitors were observed and pollen limitation, dichogamy, herkogamy and pollen persistence within the flower were measured. Outcrossing rate was estimated for a subset of the arrays. Pollen limitation was over three times higher in the shade than the sun due to differences in pollinator visitation. Populations with high levels of autonomy displayed greater pollen persistence and dichogamy in the more pollen‐limited environments than in the high‐pollination environments. In these high‐autonomy populations, outcrossing rates were tightly associated with pollen limitation, with reduced outcrossing under strong pollen limitation. In contrast, populations with intermediate autonomy levels had less plastic floral traits and their outcrossing rates changed little with pollen limitation. Mating system was shaped by both the pollination environment and the magnitude of plasticity in floral traits. The experimental approach used here revealed that plasticity in floral traits provides the ability to adjust mating system in response to limited potential for outcrossing. The lack of plasticity in some populations could explain mismatches between pollinator activity and mating system in natural populations. Finally, flexibility in the mating system may help explain the prevalence of mixed mating. A plain language summary is available for this article.

Disentangling the role of herkogamy, dichogamy and pollinators in plant reproductive assurance

ABSTRACTBackground: Autonomous selfing can be favoured by reduced floral herkogamy, dichogamy and pollinator visitation. Autonomous selfing diminishes as pollinator abundance increases; however, the ways pollinators contribute to such result have not been tested. Pollinators can reduce the occurrence of autonomous selfing by two not mutually exclusive mechanisms: successful pollen deposition on stigmas and pollen removal from anthers.Aims: We tested the role of herkogamy and protandry on autonomous selfing and the role of pollinators to reduce it via pollen removal.Methods: We studied Lepechinia floribunda (Lamiaceae) in two natural populations in the Chaco Serrano forest, Argentina. Pollination treatments were conducted to test if floral herkogamy and pollen removal by one pollinator visitation decreased seed set by autonomous selfing.Results: Seed set in pollinator exclusion and emasculation treatments were higher in flowers with lack of herkogamy and selfing increased seed set only in these flowers. Pollen removal during the male phase decreased by 72% the probability of autonomous self-pollination.Conclusions: Flowers with lack of herkogamy are reproductively more advantageous than flowers with approach herkogamy independently of pollinator abundance. We demonstrated for the first time that only one pollinator visitation during the male phase can strongly decrease autonomous selfing by pollen removal.

Secondary pollen presentation on anther hairs enhances reproductive fitness in Brandisia hancei, a protogynous perennial with autonomous selfing

ABSTRACTBackground: Secondary pollen presentation (SPP) is a phenomenon where pollen is relocated from within the anthers to other floral structures for presentation.Aims: We report a new mechanism of androecial SPP on anther hairs, which is involved in increasing reproductive fitness in Brandisia hancei.Methods: The morphological change of anther hairs during floral ageing was recorded, and pollen grains were quantified after anther hair removal to clarify the roles played by hairs in pollen retention. Additionally, fruit set and seed set were assessed to investigate the efficiency of anther hairs to reproductive success.Results: Young flowers of B. hancei showed approach herkogamy, while autonomous selfing was achieved by changes in relative positions of the stigma and anthers during floral ageing. In B. hancei, anthers developed characteristic hairs of epidermal origin, and hairs originated along the furrow between the paired pollen sacs and were used for SPP after anther dehiscence. Anther hairs increased pollen retention by over 70% in later floral-age stages, and seed set decreased by about 30% after anther hairs had been removed.Conclusions: In the process of autonomous selfing, SPP on anther hairs enhances both the male and female functions of the flowers of B. hancei.

The best of both worlds? A review of delayed selfing in flowering plants.

In a seminal body of theory, Lloyd showed that the fitness consequences of selfing will depend on its timing in anthesis. Selfing that occurs after opportunities for outcrossing or pollen dispersal can provide reproductive assurance when pollinators are limited and is expected to incur little cost, even when inbreeding depression is high. As a result, delayed selfing is often interpreted as a "best-of-both-worlds" mating system that combines the advantages of selfing and outcrossing. We surveyed 65 empirical studies of delayed selfing, recording floral mechanisms and examining information on inbreeding depression, autofertility, and other parameters to test the support for delayed selfing as a best-of-both-worlds strategy. Phylogenetic distribution of the diverse floral mechanisms suggests that some basic floral structures may predispose plant taxa to evolve delayed selfing. Delayed selfing appears to serve as a best-of-both-worlds strategy in some but not all species. While the capacity for autonomous selfing is often high, it is lower, in some cases, than in related species with earlier modes of selfing. In other delayed-selfers, low inbreeding depression and reduced investment in corollas and pollen suggest limited benefits from outcrossing. Despite a growing literature on the subject, experimental evidence for delayed selfing is limited and major gaps in knowledge remain, particularly with respect to the stability of delayed selfing and the conditions that may favor transitions between delayed and earlier selfing. Finally, we suggest a potential role of delayed selfing in facilitating transitions from self-incompatibility to selfing.

Breeding system and pollination of Gesneria pauciflora (Gesneriaceae), a threatened Caribbean species

Knowledge of plant breeding systems may be critical to facilitate recovery of species considered at risk. Gesneria pauciflora is a threatened, rupiculous, and riverine species with floral-traits that suggest a hummingbird-pollination system. Because these habitat-pollinator conditions have been linked to pollinator-independent reproductive systems, we expected a breeding system that provides reproductive assurance. We assessed the breeding system and potential vulnerabilities during pollination phase using field observations and pollination experiments, to determine pollinator dependency and the existence of strategies for reproductive assurance. Gesneria pauciflora was pollinated by two hummingbird species but visitation rates were low, probably due to low nectar rewards. Fruit set and seed production were significantly higher in flowers when pollen was artificially delivered (self- and cross-pollination) compared to when it was not (control and autogamy), suggesting that reproduction is pollen-limited. Gesneria pauciflora is self-compatible, with some seeds produced via autonomous selfing without any effects of pollination mechanism on seed germination rates. Florivory by the native plume-moth Postplatyptilia caribica was observed, but its incidence was low (12%). Our findings are consistent with theory on the evolution of plant breeding systems on islands, and contribute to the understanding of the evolution of breeding systems in Caribbean gesneriads. Overall, data do not show immediate vulnerabilities to this listed species at the pollination phase, and autogamy may represent reproductive assurance counteracting unpredictable environmental factors that influence its reproduction. However, its capacity for selfing is small relative to other tubular Puerto Rican Gesneria which may explain its rare status.

Correlation between the timing of autonomous selfing and floral traits: a comparative study from three selfing Gentianopsis species (Gentianaceae)

About 20% of angiosperms employ self-fertilization as their main mating strategy. In this study, we aimed to examine how the selfing timing correlated with floral traits in three Gentianopsis species in which autonomous selfing is achieved through filament elongation. Although the three Gentianopsis species exhibit no significant variation in their capacity for autonomous selfing, flowers of G. grandis last longer, are larger and have a higher corolla biomass, P/O ratios and male biomass allocation than those of G. paludosa, and especially those of G. contorta. Autonomous selfing occurs in the early floral life of G. paludosa and G. contorta and in the later floral life of G. grandis. Seed production mainly results from autonomous selfing in G. paludosa and G. contorta; however, G. grandis could be more described as having a mixed mating system. We suggest that autonomous selfing in later floral life increases the chance of cross-pollination prior to this, while autonomous selfing in early floral life offers a selective advantage to plants by reducing the resource investment in traits that may increase pollinator attraction and visitation.

Delayed selfing ensures reproductive assurance in Utricularia praeterita and Utricularia babui in Western Ghats.

Numerous bladderwort (Utricularia) species are distributed worldwide, but their reproductive biology is rarely investigated. Bladderworts are known to depend on tiny organisms to meet a significant proportion of their energy requirement by trapping them in bladders. However, information on the extent of their reliance on insects for pollination success is limited. We examined the reproductive strategy of two Utricularia species viz. Utricularia praeterita and U. babui, endemic to Western Ghats, India. The main aspects of the investigation involved floral biology, breeding system, pollination mechanism, and reproductive success. Flowers of both the species are structured for outbreeding through entomophilous floral suites, herkogamy, protandrous dichogamy and sensitive lobes of the stigma. With nearly 65% natural fruit-set, both the species appeared to be sufficiently open-pollinated. However, pollinators failed to show in plants of U. praeterita while in U. babui there was an apparent mismatch between the extent of fruit-set and pollinator visits. The study demonstrated that in the absence/insufficient visits of pollinators, the two species resort to autonomous selfing. In U. babui, denser patches of plants appeared to be crucial for attracting the pollinators. Both species are self-compatible, and reproductive success is predominantly achieved by delayed autonomous selfing. The sensitive stigma in the species fails to prevent selfing due to diminished herkogamy during the late anthetic stages. It is inferred that in the pollinator-limited environment, delayed selfing contributes to absolute natural fecundity in U. praeterita, while it produces a mixed progeny in U. babui.

Timing is everything: Dichogamy and pollen germinability underlie variation in autonomous selfing among populations.

The evolution of multiple floral traits often underlies the transition from outcrossing to selfing. Such traits can influence the ability to self, and the timing at which selfing occurs, which in turn affects the costs of selfing. Species that display variation in autonomous selfing provide an opportunity to dissect the phenotypic changes that contribute to variability in the mating system. In a common garden, we measured dichogamy and herkogamy in 24 populations of the protandrous mixed-mating herb Campanula americana, and related these to autonomous fruit set (autonomy). We then measured the timing of self-pollen deposition and fruit production in populations with high and low autonomy, and determined whether pollen germinability across floral development contributes to variation in autonomy. Populations that transitioned more rapidly to female phase displayed elevated autonomous selfing, but herkogamy was unassociated with autonomous selfing. Selfing occurred more rapidly in highly autonomous populations because of greater self-pollen deposition early in female phase. Pollen germinability in low-autonomy populations remained constant across floral development, but in high-autonomy populations it increased after floral anthesis and was highest near the onset of female phase. Reduced dichogamy, elevated self-pollen deposition, and higher pollen germination late in male phase contribute to both earlier selfing and greater selfing. These traits vary among populations, likely reflecting past selection on the mating system. While delayed selfing bears fewer fitness costs, the evolution of earlier selfing may be favored if self-pollen availability decreases over floral development.