Mixed Mating System Research Articles

The effects of selfing on multi-step adaptation.

Macroevolutionary studies have estimated higher extinction rates of self-compatible lineages than self-incompatible ones. A leading explanation is that selfing may prevent adaptation, since models show that selfing can inhibit the fixation of adaptive alleles at a single locus (1-step adaptation). However, adaptation often involves changes at multiple loci (multi-step adaption), but the effects of selfing remain unclear because selfing increases homozygosity, which affects selection intensity, the effective population size, and the effective recombination rate. By modeling using population genetic models, I investigate the effects of selfing on adaption requiring fixation of 2 adaptive alleles, I show that intermediate selfing rates generally promote adaption, by increasing the fixation probability of the double-mutant haplotype once it is generated. In constant-sized populations, selfing increases the rate of adaptation through the fixation of new mutations even when both alleles are dominant. In demographically declining populations, the rescue probability rises sharply as the selfing rate increases from zero, but quickly drops to be low when it approaches 1.0. These findings are at odds with the hypothesis that higher extinction rates of self-compatible lineages result from reduced adaptive potential but may help explain why some studies have failed to detect relaxation of selection in selfers and also the prevalence of mixed-mating systems.

Waiting for love but not forever: Modeling the evolution of waiting time to selfing in hermaphrodites

Although mixed mating systems involving both selfing and outcrossing are fairly common in hermaphrodites, the mechanisms maintaining mixed mating are still unknown in many cases. In some species, individuals that have not yet found a mating partner delay self-fertilization for some time. This “waiting time” to selfing (WT) can exhibit heritable variation between individuals and is subject to two opposing selection pressures: waiting longer increases the density-dependent probability to encounter a mate within that time and thereby the chance to avoid inbreeding depression (ID) in offspring, but also increases the risk of dying before reproduction. It has long been hypothesized that fluctuations in population density and thus mate availability can lead to stable intermediate WTs, but to our knowledge there are so far no quantitative models that also take into account the joint evolutionary dynamics of ID. We use an individual-based model and a mathematical approximation to explore how delayed selfing evolves in response to density and density fluctuations. We find that at high density, when individuals meet often, WT evolution is dominated by genetic drift; at intermediate densities, strong ID causes WT to increase; and at low densities, ID is purged and WT approaches zero. Positive feedback loops drive the system to either complete selfing or complete outcrossing. Fluctuating density can slow down convergence to these alternative stable states. However, mixed mating, in the sense of either a stable polymorphism in WT, or stable intermediate waiting times, was never observed. Thus, additional factors need to be explored to explain the persistence of delayed selfing.

Transposable elements maintain genome-wide heterozygosity in inbred populations

Elevated levels of inbreeding increase the risk of inbreeding depression and extinction, yet many inbred species are widespread, suggesting that inbreeding has little impact on evolutionary potential. Here, we explore the potential for transposable elements (TEs) to maintain genetic variation in functional genomic regions under extreme inbreeding. Capitalizing on the mixed mating system of Arabidopsis lyrata, we assess genome-wide heterozygosity and signatures of selection at single nucleotide polymorphisms near transposable elements across an inbreeding gradient. Under intense inbreeding, we find systematically elevated heterozygosity downstream of several TE superfamilies, associated with signatures of balancing selection. In addition, we demonstrate increased heterozygosity in stress-responsive genes that consistently occur downstream of TEs. We finally reveal that TE superfamilies are associated with specific signatures of selection that are reproducible across independent evolutionary lineages of A. lyrata. Together, our study provides an important hypothesis for the success of self-fertilizing species.

Mating system of a Mammillaria magnimamma (Cactaceae) population of the semi-arid central Mexican region

Knowledge on the reproductive biology of globose cacti in the genus Mammillaria is incipient, despite being one of the most diverse and threatened groups in Cactaceae. We studied a clonal population of Mammillaria magnimamma (Hawort) located in the Valle del Mezquital, Mexico in which sexual reproduction occurs, although neither seedlings nor juveniles were observed. Based on their short life cycle, globose life form, and melittophilous pollination syndrome, this species was expected to exhibit a mixed mating system and null seed recruitment. We examined the population structure, reproductive phenology, and the mating system by means of controlled-pollination experiments (autonomous self-pollination, manual self-pollination, manual outcross pollination and open pollination). We tested for differences between treatments in the number of seeds per fruit and estimated outcrossing rates. Most (88%) of the M. magnimamma population consisted of clones (10.6 stems/ind) and no juvenile plants or seedlings were recorded. Seed were produced in all the experimental treatments. The average number of seeds per fruit was significantly higher (χ2 = 29.52; d.f. = 3; P < 0.0001) in the outcross than the self-pollination treatments. Outcrossing rates estimated from fruits, te, fruits = 0.829, and seeds, te, seeds = 0.8774, showed that M. magnimamma exhibits a mixed mating system. Despite the large number of seed produced, the persistence of these populations likely depends on clonal reproduction. The null recruitment and elevated anthropogenic pressure that this species undergoes across its distribution range threaten its populations.

Weak population differentiation and high diversity in Salsola tragus in the inland Pacific Northwest, USA

Salsola tragus is a widespread and problematic weed of semi-arid wheat production globally, and in the inland Pacific Northwest region of the USA. The species exhibits high levels of phenotypic diversity across its range and, at least in California USA, previous work has described cryptic diversity comprising a multi-species complex. Such cryptic diversity could suggest the potential for a differential response to management inputs between groups, and have important implications for the spread of herbicide resistance or other adaptive traits within populations. We used a genotyping-by-sequencing approach to characterize the population structure of S. tragus in the inland Pacific Northwest. Our results indicated that the population in this region is comprised of a single, tetraploid species (S. tragus sensu latu) with weak population structure on a regional scale. Isolation-by-distance appears to be the primary pattern of structure, but an independent set of weakly differentiated clusters of unknown origin were also apparent, along with a mixed mating system and high levels of largely unstructured genetic diversity. Despite considerable phenotypic variability within S. tragus in the region, agronomic weed managers can likely consider it as a single entity across the region, rather than a collection of cryptic subgroups with possible differential responses to management inputs or agroecosystem conditions. A lack of strong barriers to migration and gene flow mean that adaptive traits, such as herbicide resistance, can be expected to spread rapidly through populations across the region. © 2022 Society of Chemical Industry.

Rapid evolution of selfing syndrome traits in Viola arvensis revealed by resurrection ecology.

As part of global change, climate warming and pollinator decline are expected to affect plant phenology and plant-pollinator interactions. This paper aims at characterizing rapid evolution of life history traits and floral traits over two decades in the wild pansy (Viola arvensis), a common weed in agrosystems. We used a resurrection ecology approach with genotypes sampled in 1991 and 2012 from a population in Burgundy (France). The species has a mixed mating system (hereafter: mixed selfer) and presents a floral polymorphism. To correct for maternal effects, we measured plant traits in the second generation in a common garden (after a refreshing generation) to characterize plant evolution during the two decades. In addition, historical population selfing rates in 1991 and 2012 were inferred from microsatellites markers through heterozygote deficiency and identity disequilibrium. Phenotypic data revealed a significant advance in flowering date, reduced flower sizes and a higher propensity of plants to set seed by autonomous selfing. Moreover, we detected a change in color morph frequency with an increase of the pale morph frequency. In accordance with phenotypic data, the neutral genetic data revealed an increase in historical selfing rates from 0.68 in 1991 to 0.86 in 2012. Taken together, such data suggest that the wild pansy, a mixed selfer, is evolving a selfing syndrome that may be the consequence of reduced pollinator activity in agrosystems.

Climate change is associated with increased allocation to potential outcrossing in a common mixed mating species.

PremiseAlthough the balance between cross‐ and self‐fertilization is driven by the environment, no long‐term study has documented whether anthropogenic climate change is affecting reproductive strategy allocation in species with mixed mating systems. Here, we test whether the common blue violet (Viola sororia; Violaceae) has altered relative allocation to the production of potentially outcrossing flowers as the climate has changed throughout the 20th century.MethodsUsing herbarium records spanning from 1875 to 2015 from the central United States, we quantified production of obligately selfing cleistogamous (CL) flowers and potentially outcrossing chasmogamous (CH) flowers by V. sororia, coupled these records with historic temperature and precipitation data, and tested whether changes to the proportion of CL flowers correlate with temporal climate trends.ResultsWe find that V. sororia progressively produced lower proportions of CL flowers across the past century and in environments with lower mean annual temperature and higher total annual precipitation. We also find that both CL and CH flower phenology has advanced across this time period.ConclusionsOur results suggest that V. sororia has responded to lower temperatures and greater water availability by shifting reproductive strategy allocation away from selfing and toward potential outcrossing. This provides the first long‐term study of how climate change may affect relative allocation to potential outcrossing in species with mixed mating systems. By revealing that CL flowering is associated with low water availability and high temperature, our results suggest the production of obligately selfing flowers is favored in water limited environments.

The mixed mating system of a widespread weed: the case of Argemone ochroleuca Sweet (Papaveraceae)

Background: Argemone ochroleuca is a worldwide invasive weed but is also highly valuable for their chemical compounds. Knowledge about its reproduction will help create plans for its control or its propagation.&#x0D; Questions: Does A. ochroleuca has an incompatibility system like other Papaveraceae species? Which are the reproductive strategies that favor the seed formation in A. ochroleuca ?&#x0D; Studied species: A. ochroleuca is an annual species with bisexual flowers.&#x0D; Study site and dates: Mexico City, Mexico. The fieldwork was performed from February to May in 2013, 2014, and 2017.&#x0D; Methods: Direct observations were made to describe the flower cycle of A. ochroleuca . We used self-pollinated flowers to analyze if this species is self-incompatible by following the pollen tube growth through gynoecium. Controlled pollinations were made to quantify and compare the number of seeds produced per treatment to know the mating system and explore if the species presents a mechanism of reproductive assurance through autogamy, or exhibits inbreeding depression.&#x0D; Results: A. ochroleuca is self-compatible and exhibits a mixed mating system. Although outcrossing is how more seeds are produced, both autogamy and pseudocleistogamy are present as reproductive assurance mechanisms. Naturally pollinated flowers produce the maximum number of seeds, but inbreeding depression is present in the population. Thus, the number of seeds will be affected by continuous selfing.&#x0D; Conclusions: This study highlights the mixed mating system and reproductive assurance mechanisms as successful strategies for A. ochroleuca , a common pattern in invasive weeds.

Phenotypic Selection in Halenia elliptica D. Don (Gentianaceae), an Alpine Biennial with Mixed Mating System.

The transition from outcrossing to selfing is a common evolutionary trend in flowering plants, and floral traits change significantly with the evolution of selfing. Whether or not plant traits are subjected to selection remains an open question in species with mixed mating systems. We examined phenotypic selection in two populations of Halenia elliptica with different selfing rates. We found that the pollen–ovule ratio, seed size, plant height, spur length, and pollinator visitation rate in the population with the higher selfing rate were lower than those in the population with the lower selfing rate. Selfing provides reproductive assurance for populations when pollinator service is low, and the floral traits that are associated with selfing syndrome are evident in populations with a higher selfing rate but are subjected to weak selection in each of the two populations with different selfing rates. Directional selection for an early flowering time indicated that late blooming flowers could experience a risk of seed development in alpine environments, and for large plants, selection indicated that seed production could be limited by the available resources. The floral traits that are associated with pollinator attraction and specialization could be subjected to weak selection at the plant level as selfing evolves, and the selective pressures that are independent of pollinators might not change significantly; highlighting the selective biotic and abiotic pressures that shape the morphological traits of plant species and their independence from the mating system.

Pollination ecology and breeding system of Ecbolium Ligustrinum (Acanthaceae): a transition from autogamy to xenogamy through specialised plant-pollinator interactions

In view of the ongoing rarity ofEcbolium ligustrinumthere is an urgent need for conservation of the species. For this, a detailed work was carried out regarding the untold story of its reproductive ecology. The work was done for three consecutive years (2015–2017) at Midnapore, West Bengal over three different populations collected from three different areas of West Bengal. Field data were also recorded from these three wild populations. The species produces gullet flowers with bi-labiate corolla having long slender tubes. The flowers exhibit one day of longevity. The flowers are visited by 10 species of insects. Among those, four species viz.Eristalis tenax, a Dipteran member and three ant species of Hymenoptera such asCamponotussp.,Formicasp. andMonomoriumsp. are the effective pollinators. As per pollination efficiency,Eristalis tenax(PEi= 0.76) is the most successful one. The flowers are shortly protandrous (dichogamous) and passed by three distinct reproductive (male, bisexual and female) phases. The breeding system clearly depicts that the species is facultatively xenogamous supported by myophilous mode of pollination. However, geitonogamous type of pollination is also observed through myrmecophily, an atypical instance found in plants. Lastly, the plant retained some sort of autogamy through ‘fail-safe’ mechanism of pollination, an adaptation which might be developed in absence of pollinators. Therefore, undoubtedly it can be concluded thatE. ligustrinumis a partially self-incompatible (ISI = 0.27) species having a mixed mating system, adapted for xenogamy through specialised mode of plant-pollinator interactions.

Reproductive biology of Myrtillocactus geometrizans (Cactaceae) flowers with contrasting orientation

AbstractIn columnar cacti, a higher production of reproductive structures on branches oriented towards the Equator has been explained by their higher interception of photosynthetic active radiation (PAR) as well as resource availability. The goal of this study was to evaluate the effect of orientation on diverse aspects of the reproductive biology of Myrtillocactus geometrizans. Phenology was studied in north‐ and south‐facing branches. Floral cycle events, floral visitors, reproductive traits associated with sexual and attraction functions, and reproductive success were estimated from reproductive structures with contrasting orientation. Pollination experiments were conducted to evaluate the effect of orientation on mating system. Our results showed that south‐facing branches had a longer duration of the mature fruit phenophase. Moreover, flower synchrony, production of reproductive structures, and floral traits associated with the male (number of anthers and pollen grains per floral bud), female (number and size of ovules and dimensions of both ovary and ovary cavity), and attraction (petal size) functions had higher values in south‐facing flowers. The beginning and ending of the male function and the end of flower anthesis occurred earlier in south‐facing flowers. Diversity of floral visitors was similar between orientations, except for beetles whose abundance was greater in flowers oriented towards the south. North‐ and south‐facing flowers had a mixed mating system, with similar reproductive success. Our results showed strong differences in the reproductive biology of an intertropical columnar cactus, probably in response to the uneven PAR interception and resource availability in branches and flowers with contrasting orientation.

Reproductive biology of an endangered lithophytic shrub and implications for its conservation

BackgroundPlants in cliff habitats may evolve specific reproductive strategies to cope with harsh environments, and unraveling these reproductive characteristics can improve our understanding of survival strategies and lithophyte evolution. This understanding is especially important for efforts to protect rare and endemic plants. Here, we investigated the reproductive biology of Lonicera oblata, an endangered lithophytic shrub that is scattered in highly fragmented and isolated cliff habitats of the Taihang and Yan mountains in North China.ResultsFlowers of L. oblata are herkogamous and protandrous, characteristics that can prevent autogamy at the single-flower level, and insects are necessary for pollination. The outcrossing index, pollen/ovule ratio, and the results of hand pollination were measured and all revealed a mixed mating system for L. oblata, that combines cross-fertilization and partial self-fertilization. The floral traits of L. oblata of zygomorphic and brightly yellowish corolla, heavy fragrance, and rich nectar, suggest an entomophilous pollination system. Sweat bees were observed as the most effective pollinators but their visiting frequencies were not high. Pollen limitation may limit the reproductive success of L. oblata.ConclusionsWe determined the reproductive characteristics of L. oblata, a critically endangered species endemic to cliffs in North China, providing insight into its endangerment and suggesting conservation strategies. L. oblata has highly pollinator-dependent self-fertilization as part of a mixed mating system. Floral features such as low-flowering synchrony, asynchronous anthers dehiscence, and high duration of stigma receptivity, improve pollination efficiency in the case of low pollinator service. Our work provides reference information to understand the survival strategies and conservation of L. oblata and other lithophytes.

Reproductive biology of green-stemmed and red-stemmed Basella alba

Basella alba is an important, underutilised vegetable rich in vitamins and consumed in many parts of the world. However, the reproductive biology of this species is insufficiently known; therefore, this study was performed aiming to fill this knowledge gap. Although green-stemmed and red-stemmed Basella alba share a lot of reproductive attributes in common, the obtained results showed differences in their flower bud apex colour, anther colour, spike colour, days to 50% flowering, plant height at flower bud initiation and the mean number of flowers per spike. In both forms, the floral attributes favoured self-pollination. However, the possibility of cross-pollination among them due to the activities of pollinators such as ants, moths, butterflies and bees suggests a mixed mating system. Furthermore, both forms attained sexual maturity at varying periods, thus indicating the existence of a temporal prezygotic barrier between them and limiting the chances of their hybridisation. They could also be responsible for the ability to remain in their distinct forms even when they exist together in the same habitat.

The explosive flowers of Marsypianthes chamaedrys (Lamiaceae) resort to self-pollination and improve reproduction

Explosive pollination includes a rapid release of floral sexual elements that are enclosed in modified petals, and a subsequent contact with pollinators’ body. It requires specific groups of visitors in order to assure plant reproduction, thus reproductive success is threatened in species with explosive pollination mechanisms, especially when pollinator activity is uncertain. Autogamy can alleviate such a problem by improving plant reproductive output. Here we investigated the mating strategies of Marsypianthes chamaedrys, a species with an explosive pollen release mechanism and whose medicinal properties are broadly investigated, but no data is available regarding its reproduction. We studied its floral morphology, anthesis, floral visitors and breeding system. Flowers have a bilabiate organization with the reproductive structures housed within a lower, keel-like petal lobe. The species is protandrous and flowers have short life span. Only bees were able to activate the explosive mechanism, while butterflies acted as nectar thieves. Marsypianthes chamaedrys is self-compatible and able to autonomously self-pollinate, likely due to the elongation of the pistil within the keel of unvisited flowers. Marsypianthes chamaedrys likely has a mixed mating system, in which bee pollination and autogamy interplay to improve its reproductive output.

Biological Flora of the British Isles: Salvia pratensis

Abstract This account presents information on all aspects of the biology of Salvia pratensis L. (Meadow Clary) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history and conservation. Salvia pratensis is an erect, rosette‐forming, perennial herb with a broad native distribution covering much of Europe—from the British Isles, Spain and Morocco in the west, across Europe into Asia, as far east as the Urals. In the British Isles, the species is nationally scarce, confined to a few south‐ to west‐facing sites with calcareous soils in Southern England and one site in Wales. It is predominately found in unimproved pasture, hay meadows and grassy verges, but can occur on the fringes of scrub or woodland. Although the species is abundant in central Europe, changes to land management since the mid‐20th century have resulted in fragmented and threatened populations in several European countries. It is cultivated as an ornamental, as is S. × sylvestris, the hybrid with S. nemorosa. Populations are typically gynodioecious, having both female (male‐sterile) and hermaphrodite individuals at variable proportions. The species has a mixed mating system and is self‐compatible via insect pollination, but predominantly outcrosses. Honeybees and bumblebees are abundant pollinators, but a diverse range of bee species and other insect species visit S. pratensis flowers. Inbreeding depression has been documented, presenting a conservation concern for small, fragmented populations. The species is the focus of conservation efforts and has been reintroduced to sites where it had become locally extinct in Britain. To sustain favourable habitat, site management should maintain low soil nutrient levels, and prevent scrub encroachment and the dominance of coarse grasses. The removal of sward by hay cutting or grazing after plants have flowered and set seed is advised, in addition to maintaining a degree of disturbance to provide bare patches of soil for seedling recruitment.

Long‐term progression of inbreeding depression in a Mediterranean ornithophilous shrub

AbstractThe ornithophilous species Anagyris foetida L. is a Mediterranean shrub with highly fragmented populations and a mixed mating system. In a previous study, we analyzed the first 3 years of the life cycle of two progenies (selfed and outcrossed) grown from seed obtained by hand pollination and planted in an experimental garden in 2005. In that study, we found that inbreeding depression (ID) was manifested both reproductively and vegetatively throughout the life cycle, with male reproductive function being the most affected trait. In the present study, our main aim was to check the progression of the two progenies 12 years after transplantation. For this we analyzed their survival and their vegetative and reproductive traits. According to our results, levels of ID were similar to those obtained in the previous study, with some factors decreased and thus varying with the age of the studied individuals. Vegetative parameters were found to have a greater influence than reproductive ones (δ = 0.56 vs. δ = 0.36) on overall ID. As indicated by the global ID (δ = 0.72) the populations have a mating system that is intermediate between outcrossing and a mixed system. Furthermore, the lower male reproductive capacity of the selfed individuals has been maintained over time. Our study also demonstrates the importance of studying the ID value throughout the life cycle of plants.

Evolutionary disruption in the pollination system of Vanilla (Orchidaceae).

Pollination of the pantropical Vanilla has been linked to melittophily and food deception. Here we investigated the role of flower traits on the reproduction of Neotropical Vanilla. We also studied the evolution of pollination systems in order to understand the origin of production of flower resources and the diversification of pollinators in this orchid genus. Our study was founded on data of adaptations in flower morphology, production of resources, scent release, pollinators and breeding systems of Vanilla and presenting new data on reproductive biology of V. palmarum. Data on reproductive biology of Vanilla were mapped onto a phylogeny to address our queries on the evolution of pollination systems in this genus. Vanilla palmarum shows a mixed mating system, with its facultative autogamous flowers being pollinated by hummingbirds. Its yellow flowers are scentless and produces nectar. Mapping of the pollination system onto trees resulted in one origin for bird pollination and at least two origins for autogamy in Vanilla. Nectar secretion has a single origin in the Neotropical thick-leafed lineage. Bird pollination of Vanilla is shown for the first time. The origin of ornithophily within a bee-pollinated clade is supported by flower morphology. Floral transitions to ornithophily have been favoured by the occupation of a distinct niche from that of the other thick-leafed Vanilla species. Despite its specialized pollination, V. palmarum is autogamous. A mixed mating system can promote reproductive assurance in the case of a decline in pollinator populations, or in areas where pollinator services are irregular or absent.

Understanding how an amphicarpic species with a mixed mating system responds to fire: a population genetic approach.

Amphicarpic plants produce both above-ground and below-ground seeds. Because below-ground seeds are protected in the soil and may maintain viability when above-ground conditions are stressful, they were proposed as an adaptation to recolonize a site after disturbance. However, whether below-ground seeds are the main colonizers after a disturbance remains unknown. Our goal was to understand whether recolonization by an amphicarpic species after fire was accomplished primarily through germination of seeds produced above-ground or below-ground. We investigated Polygala lewtonii, an amphicarpic, perennial species endemic to fire-prone Florida sandhill and scrub, where fire kills plants but subsequently increases recruitment and population sizes. Polygala lewtonii produces three flower types: above-ground chasmogamous flowers and above-ground and below-ground cleistogamous flowers, with previous research demonstrating chasmogamous flowers produce a much greater proportion of seeds than cleistogamous flowers. We quantified outcrossing in seeds produced by chasmogamous flowers to determine whether it differed from the 100 % self-fertilized below-ground seeds. Approximately 25 % of seeds from chasmogamous flowers showed evidence of cross-pollination. Assuming that chasmogamous flowers produce the majority of the above-ground seeds, as was shown previously, this indicates it is possible to differentiate between germination by above-ground versus below-ground seeds in post-fire colonization. We next compared genetic diversity, admixture, inbreeding and population genetic structure pre- and post-fire. If fire promoted germination of chasmogamous seeds, heterozygosity and admixture would increase, and genetic structure and inbreeding would decrease. Instead, inbreeding and genetic structure increased and admixture decreased, suggesting that the below-ground selfed seeds (with limited dispersal ability) increased their contribution to the population after fire, possibly because fire reduced above-ground seed viability. Additionally, new alleles not found previously in range-wide analyses emerged from the seed bank post-fire. These results suggest that amphicarpy is a powerful adaptation to preserve genetic variation, maintain adaptive potential and promote rapid post-fire colonization.

So close, so far: spatial genetic structure and mating system inPetunia exserta, an endemic from a peculiar landscape in the Brazilian Pampa grasslands

AbstractGene flow via seed or pollen dispersal is fundamental for establishing population diversity and structure of plants, especially in naturally fragmented environments. Petunia exserta (Solanaceae) is endemic to small shelters in rocky towers in the Brazilian Pampa grassland, an ancient and isolated region. The landscape is a long-term fragmented habitat, and ecological conditions inside the shelters constitute an inhospitable environment for other Petunia spp., which usually inhabit open and sunny grasslands. We aimed to evaluate the mating system and gene flow impact on genetic diversity and population structure in P. exserta throughout its geographical range. We used eight microsatellite markers to employ fine-scale genetic structure and paternity analyses in 15 populations, including 361 adults and 244 progeny. Our results showed that P. exserta has low genetic diversity and a homozygous excess compared with its congeners. We identified four genetic clusters that did not reflect the spatial population distribution and a strong genetic structure at the first spatial distance. Pollen and seed dispersal mainly occurred at short distances, and the species has a mixed mating system with high selfing levels. We did not observe recent population reduction, and most population clusters showed a small effective population size. The landscape micro-habitat features contribute to pollen flow that occurs mainly inside shelters through geitonogamy or biparental inbreeding. The self-compatible status of P. exserta and related lineages could be important in the colonization of a new environment for the genus.

The eco‐evolutionary dynamics of prior selfing rates promote coexistence without niche partitioning under conditions of reproductive interference

Abstract Pollinator‐mediated reproductive interference can occur when two or more plant species share the same pollinators. Recent studies have suggested that prior autonomous selfing mitigates reproductive interference, potentially facilitating coexistence even in the absence of pollination niche partitioning (i.e. the pre‐emptive selfing hypothesis). However, whether the evolution of prior selfing promotes coexistence, in the context of the eco‐evolutionary dynamics of population size, selfing rates and inbreeding depression, remains poorly understood. We constructed an individual‐based model to examine the conditions under which the evolution of prior selfing promotes coexistence in the context of mutual reproductive interference. In the model, two plant species compete by way of mutual reproductive interference, and both have the potential to evolve the capacity for prior autonomous selfing. We expected that purging of deleterious mutations might result in evolutionary rescue, assuming that the strength of inbreeding depression declines as the population selfing rate increases; this would enable inferior competitors to maintain population density through the evolution of prior selfing. Our simulation demonstrated that evolution of prior selfing may promote coexistence, whereas reproductive interference in the absence of such evolution results in competitive exclusion. We found that lower pollinator availability is likely to favour rapid evolutionary shifts to higher prior selfing rates, thereby neutralising the negative effects of reproductive interference in both species. When the strength of inbreeding depression decreased with an increase in the population‐level selfing rate, moderate pollinator availability resulted in long‐term coexistence in which relative abundance‐dependent selection on the prior selfing rate served to intermittently maintain the population density of the inferior competitor. Synthesis. We demonstrate that the evolution of prior selfing may increase population growth rates of inferior competitors and may consequently promote long‐term coexistence via an evolutionary rescue. This constitutes a novel mechanism explaining the co‐evolutionary coexistence of closely related plant species without niche partitioning, and is consistent with recent studies reporting that closely related species with mixed mating systems can co‐occur sympatrically, even under conditions of mutual reproductive interference.