Outcross Pollen Research Articles

Plant Mating Systems Often Vary Widely Among Populations

Most flowering plants are hermaphroditic, yet the proportion of seeds fertilized by self and outcross pollen varies widely among species, ranging from predominant self-fertilization to exclusive outcrossing. A population’s rate of outcrossing has important evolutionary outcomes as it influences genetic structure, effective population size, and offspring fitness. Because most mating system studies have quantified outcrossing rates for just one or two populations, past reviews of mating system diversity have not been able to characterize the extent of variation among populations. Here we present a new database of more than 30 years of mating system studies that report outcrossing rates for three or more populations per species. This survey, which includes 741 populations from 105 species, illustrates substantial and prevalent among-population variation in the mating system. Intermediate outcrossing rates (mixed mating) are common; 63% of species had at least one mixed mating population. The variance among populations and within species was not significantly correlated with pollination mode or phylogeny. Our review underscores the need for studies exploring variation in the relative influence of ecological and genetic factors on the mating system, and how this varies among populations. We conclude that estimates of outcrossing rates from single populations are often highly unreliable indicators of the mating system of an entire species.

Intercontinental dispersal and whole-genome duplication contribute to loss of self-incompatibility in a polyploid complex.

Angiosperm species often shift from self-incompatibility to self-compatibility following population bottlenecks. Across the range of a species, population bottlenecks may result from multiple factors, each of which may affect the geographic distribution and magnitude of mating-system shifts. We describe how intercontinental dispersal and genome duplication facilitate loss of self-incompatibility. Self and outcross pollinations were performed on plants from 24 populations of the Campanula rotundifolia polyploid complex. Populations spanned the geographic distribution and three dominant cytotypes of the species (diploid, tetraploid, hexaploid). Loss of self-incompatibility was associated with both intercontinental dispersal and genome duplication. European plants were largely self-incompatible, whereas North American plants were intermediately to fully self-compatible. Within both European and North American populations, loss of self-incompatibility increased as ploidy increased. Ploidy change and intercontinental dispersal both contributed to loss of self-incompatibility in North America, but range expansion did not affect self-incompatibility within Europe or North America. When species are subject to population bottlenecks arising through multiple factors, each factor can contribute to self-incompatibility loss. In a widespread polyploid complex, the loss of self-incompatibility can be predicted by the cumulative effects of whole-genome duplication and intercontinental dispersal.

Could seasonally deteriorating environments favour the evolution of autogamous selfing and a drought escape physiology through indirect selection? A test of the time limitation hypothesis using artificial selection in Clarkia.

The evolution of selfing from outcrossing may be the most common transition in plant reproductive systems and is associated with a variety of ecological circumstances and life history strategies. The most widely discussed explanation for these associations is the reproductive assurance hypothesis - the proposition that selfing is favoured because it increases female fitness when outcross pollen receipt is limited. Here an alternative explanation, the time limitation hypothesis, is addressed, one scenario of which proposes that selfing may evolve as a correlated response to selection for a faster life cycle in seasonally deteriorating environments. Artificial selection for faster maturation (early flowering) or for low herkogamy was performed on Clarkia unguiculata (Onagraceae), a largely outcrossing species whose closest relative, C. exilis, has evolved higher levels of autogamous selfing. Direct responses to selection and correlated evolutionary changes in these traits were measured under greenhouse conditions. Direct responses to selection on early flowering and correlated evolutionary changes in the node of the first flower, herkogamy, dichogamy, gas exchange rates and water use efficiency (WUE) were measured under field conditions. Lines selected for early flowering and for low herkogamy showed consistent, statistically significant responses to direct selection. However, there was little or no evidence of correlated evolutionary changes in flowering date, floral traits, gas exchange rates or WUE. These results suggest that the maturation rate and mating system have evolved independently in Clarkia and that the time limitation hypothesis does not explain the repeated evolution of selfing in this genus, at least through its indirect selection scenario. They also suggest that the life history and physiological components of drought escape are not genetically correlated in Clarkia, and that differences in gas exchange physiology between C. unguiculata and C. exilis have evolved independently of differences in mating system and life history.

Aggregate enantiostyly: Floral visitor interactions with a previously unreported form of floral display

Floral herkogamy, or the spatial separation of reproductive structures, plays an important role in the evolution of plant mating systems. One form of herkogamy is enantiostyly, or the alternate presentation of stigmas to the left and right of the floral axis. Theoretically, enantiostyly increases outcrossing rate by promoting reciprocal pollen deposition and export, but empirical evidence of this is lacking. Understanding how pollinators interact with enantiostylous flowers will illuminate the mechanisms by which enantiostyly encourages outcross pollination. We quantified style deployment within and among plants, of Allionia incarnata L. (Nyctaginaceae), a species with a new kind of enantiostyly we call “aggregate enantiostyly”. A. incarnata is the first species known to have “compound blossoms”, with different flowers each containing a left- or right-handed style. We quantify the autonomous selfing rate and describe floral visitor interactions with this unique floral structure. We found equal frequency of left- and right-handed blossoms within and among plants. Common floral visitors, Hemiargus ceraunus and Halictus sp., interacted with either anthers or stigmas, but not both, indicating effective outcrossing at the flower level. Outcrossing produced more fruits than selfing. The order in which floral visitors interacted with reproductive structures indicates that enantiostyly may increase pollen export. However, we did not find evidence that enantiostyly affected pollen deposition. Our study provides an intriguing first look at the reproductive ecology of a species with a new unique form of herkogamy, and provides evidence on the adaptive significance of enantiostyly.

HIGH OUTCROSSING RATE AND POLLEN DISPERSAL DISTANCE of Diospyros celebica Bakh. (EBENACEAE), AN ENDEMIC TREE SPECIES IN SULAWESI ISLAND, INDONESIA

Diosphyros celebica Bakh., also known as Sulawesi ebony, is an endemic to central and northern Sulawesi. Information about pollen dispersal patterns of D. celebica have not been previously investigated. This study was aimed to determine pollination type, percentage of selfing and outcrossing, as well as distance of pollen dispersal of D. celebica. This study was conducted at experimental forest of Universitas Hasanuddin, Maros District, South Sulawesi Province, Indonesia. One hundred and sixty six individuals of D. celebica consisted of adult trees and seedlings were analyzed in this study. Ninety four adult trees were selected to become parent trees. The trees were mapped with GPS coordinates . All samples were genotyped using four SSR markers loci. Parental analysis and determination of pollen dispersal patterns were carried out using Cervus 3.0.3. Results indicated that the evaluated markers were effective for assigning candidate of male parents to all evaluated seedlings. Donated pollens could come from male parents in any directions relative to female parent positions. Pollen dispersal pattern showed outcrossing pollination among different male parents (pollen donated trees). The results indicated that seeds were produced predominatly by outcrossing. Pollen dispersal reached up to 166 m. Pollen related processes were linked through female parents, pollinators availability and ecological environment. Simultaneous use of progeny genotyping, spatially explicit analysis of environmental variables and outcomes of plant–animal interactions, were the key elements for an expanded approach to gene flow analysis considering dispersal via pollen and seeds. Research on pollen dispersal of D. celebica should be carried out in other forest types, such as mixed forest and highland forest.

The effect of removing numerically dominant, non-native honey bees on seed set of a native plant.

Pollination services are compromised by habitat destruction, land-use intensification, pesticides, and introduced species. How pollination services respond to such stressors depends on the capacity of pollinator assemblages to function in the face of environmental disruption. Here, we quantify how pollination services provided to a native plant change upon removal of the non-native, western honey bee (Apis mellifera)-a numerically dominant floral visitor in the native bee-rich ecosystems of southern California. We focus on services provided to clustered tarweed (Deinandra fasciculata), a native, annual forb that benefits from outcross pollination. Across five different study sites in coastal San Diego County, tarweed flowers attracted 70 insect taxa, approximately half of which were native bees, but non-native honey bees were always the most abundant floral visitor at each site. To test the ability of the native insect fauna to provide pollination services, we performed Apis removals within experimental 0.25m2 plots containing approximately 20 tarweed plants and compared visitation and seed set between plants in removal and paired control plots (n=16 pairs). Even though 92% of observed floral visits to control plots were from honey bees, Apis removal reduced seed production by only 14% relative to plants in control plots. These results indicate that native insect assemblages can contribute important pollination services even in ecosystems numerically dominated by introduced pollinators.

Studies of Pollen Characteristics in Plants of Fruitless Tecomella undulata (Sm.) Seem. (Bignoniaceae) in Golparaki Region of Jiroft City, Iran

Tecomella undulata is valued for beautiful flowers, resistance against extreme temperature and drought, stabilizing shifting sand dunes, medicinal properties and wood production. In spite of massive flowering, the species is seedless. The present study examines the causes of its sterility indicating on pollen characteristics. Flowers were hand pollinated by pollen of either self- or outcross pollen. Some flowers were tagged as open pollination treatment. Pollen structure, in situ and in vitro pollen germination and pollen tube growth were analyzed. Mature pollen grains are heteromorphic, mostly heterogeneous sized as small and large. Both pollen grains types are prolate and tricolpate with rugulate–reticulate sculpture. Flowers are protandrous and have long stylus; a nectariferous tissue secreting abundant nectar exists in the ovary base. No effective pollinator visited flowers during the observation period. No pollen germination and pollen tube growth were observed in self- and cross-pollinated styles and under in vitro condition. It seems that pollen heterogeneity, lack of pollinators and pollen limitation, the failure of autogamy due to protandry or long styli as well as self-incompatibility resulted in pollen sterility and seedlessness. In addition, probably polyploidy and cytomixis affect infertility too that needs to be studied in detail in the future.

A geographic cline in the ability to self-fertilize is unrelated to the pollination environment.

The reproductive assurance (RA) hypothesis predicts that the ability to autonomously self-fertilize should be favored in environments where a lack of mates or pollinators limits outcross reproduction. Because such limits to outcrossing are predicted to be most severe at range edges, elevated autonomy in peripheral populations is often attributed to RA. We test this hypothesis in 24 populations spanning the range of Campanula americana, including sampling at the range interior and three geographic range edges. We scored autonomous fruit set in a pollinator-free environment and detected clinal variation-autonomy increased linearly from the southern to the northern edge, and from the eastern to the western edge. We then address whether the cline reflects the contemporary pollination environment. We measured population size, plant density, pollinator visitation, outcross pollen limitation and RA in natural populations over two years. Most populations were pollen limited, and those that experienced higher visitation rates by bumblebees had reduced pollen limitation. Reproductive assurance, however, was generally low across populations and was unrelated to pollen limitation or autonomy. Neither pollen limitation nor RA displayed geographic clines. Finally, autonomy was not associated with pollinator visitation rates or mate availability. Thus, the data do not support the RA hypothesis; clinal variation in autonomy is unrelated to the current pollination environment. Therefore, geographic patterns of autonomy are likely the result of historical processes rather than contemporary natural selection for RA.

Reproductive Biology of Three Wildflower Species: Implications of Floral Compatibility Systems and Pollen Limitation for Prairie Restoration

abstract We conducted a hand pollination experiment to test the effects of supplemental pollen and pollen identity on subsequent reproductive success in three American wildflower species: Chamaecrista fasciculata, Gaillardia pulchella and Salvia coccinea. These species are commonly used in ecological restoration plantings and vary in pollination syndrome and compatibility system. We hypothesized that for all three species, treatments that supplemented pollen would yield greater fruit and seed set. Plants were germinated in a closed greenhouse until flowering, then divided into three treatments: “control”, with no supplemental pollen added; “self”, with supplemented self-pollen; and “outcross”, with supplemented outcross pollen. Treated flowers were bagged and allowed to develop to mature fruit stage, and any resulting fruits and seeds were counted and weighed. Results varied between species. Outcross C. fasciculata flowers had significantly higher fruit set than self or control treated flowers, whereas S....

Slow stamen movement in a perennial herb decreases male-male and male-female interference.

Approximately 80 % of angiosperm species produce hermaphroditic flowers, which face the problem of male-male sexual interference (one or more anthers gets in the way of disseminating pollen from other anthers) or male-female sexual interference (the pistil interferes with disseminating pollen from the anthers by preventing the anther from touching a pollinator, or the anther prevents pollinator from depositing outcross pollen on the stigma). Slow stamen movement in hermaphrodite flowers has been interpreted as an adaptation for reducing male-male sexual interference. Using slow stamen movement in Lychnis cognata (Caryophyllaceae), this study presents new evidence that this phenomenon can reduce both male-male and male-female sexual interference. Ten stamens in L. cognata flowers vertically elongated their filaments in two batches and displayed similar patterns in pollen dispensing. More importantly, 10 stamens bend out of the floral centre by curving the filament also in 2 batches and pollen grains located at the flower centre displayed the highest viability. Thus, three stages of stamen movement can be identified, comprising two male stages (M1 and M2) and one female stage (F). We found that the main pollinator for L. cognata, Bhutanitis yulongensis (Papilionodae) generally preferred M1 flowers. Manipulation experiments show that vertical stamen movement enabled the anthers to dehisce at different times to prolong the presentation of pollen grains. Horizontal movement of the stamen decreased both male-male and male-female interference. However, vertical stamen movement had a minor role in increasing amount of pollen received by the stigma. This study provides the first direct experimental evidence of concurrent male-male and male-female interference in a flower. We suggest that the selection pressure to reduce such interference might be a strong force in floral evolution. We also propose that other selective pressure, including pollen dispensing mechanisms, pollen longevity, pollinator behaviour and weather, might contribute to floral evolution.

Experimental insights on Darwin's cross‐promotion hypothesis in tristylous purple loosestrife (Lythrum salicaria)

Darwin proposed that the reciprocal arrangement of anthers and stigmas in heterostylous plants promotes cross-pollination through pollen segregation on pollinators' bodies. The floral tube in most heterostylous species constrains the feeding posture of pollinators determining the site of contact with sex organs located at different heights within a flower. Here, we evaluate Darwin's hypothesis in tristylous Lythrum salicaria, a species with a partially tubular corolla, and examine the extent to which the location of sex organs within a flower influence compatible and incompatible pollination. We predicted that the proficiency of cross-pollination would increase for more inserted sex organs due to the restrictions imposed by the floral tube on pollinator positioning. We used experimental trimorphic and monomorphic arrays and emasculated flowers to quantify intermorph pollen transfer and capture among all sex-organ heights, and estimated the contribution of intraflower self-pollination, geitonogamous self-pollination, and intramorph outcross pollination to total intramorph pollination. As predicted, disassortative pollination varied significantly with sex-organ height and was highest for short-level organs and lowest for long-level organs. In monomorphic arrays, most intramorph pollination resulted from outcross pollination followed by intraflower and geitonogamous self-pollination. Our results provide evidence for the Darwinian hypothesis. Reciprocal herkogamy promoted varying degrees of disassortative pollination with the magnitude strongly influenced by sex-organ height within a flower.

Pollen limitation, plasticity in floral traits, and mixed mating system in an alpine plant Pedicularis siphonantha (Orobanchaceae) from different altitudes

AbstractPlant mating systems rapidly respond to pollen limitation in changing environments. However, whether and how floral traits are involved in a mating system shift requires further investigation. A widely distributed and bumblebee‐pollinated lousewort, Pedicularis siphonantha D. Don was studied. We investigated pollination systems, reproductive success, and floral traits in four large populations growing from 3200 m to 4300 m. Pollinator activity in low altitude populations was lower and these populations had a decreased fruit set and seed number per capsule compared to populations at high altitudes. Supplemental hand pollination with outcross pollen significantly increased seed production per capsule for plants from high altitudes but not for those from lower altitudes. We also found that bumblebees visited more flowers within an inflorescence in a single foraging bout in high altitudes compared with low altitudes, which caused a high possibility of geitonogamous mating. These differences may be pollination‐dependent rather than inheritance‐based because hand pollination on bagged flowers did not cause a difference in seed production across populations. Compared to plants from low altitudes, high‐altitude plants had increased flower longevity, larger floral displays, higher pollen production per flower, and shorter corolla tubes, which were found to be well in accordance with changes in both pollination environment and mating system. Plasticity in floral traits might help plants to adjust their resource allocation strategies in response to their habitat, which might be linked with pollination environment. The variability among these populations might be beneficial for this widely distributed species to cope with environmental changes.

A Lévy-flight diffusion model to predict transgenic pollen dispersal.

The containment of genetically modified (GM) pollen is an issue of significant concern for many countries. For crops that are bee-pollinated, model predictions of outcrossing rates depend on the movement hypothesis used for the pollinators. Previous work studying pollen spread by honeybees, the most important pollinator worldwide, was based on the assumption that honeybee movement can be well approximated by Brownian motion. A number of recent studies, however, suggest that pollinating insects such as bees perform Lévy flights in their search for food. Such flight patterns yield much larger rates of spread, and so the Brownian motion assumption might significantly underestimate the risk associated with GM pollen outcrossing in conventional crops. In this work, we propose a mechanistic model for pollen dispersal in which the bees perform truncated Lévy flights. This assumption leads to a fractional-order diffusion model for pollen that can be tuned to model motion ranging from pure Brownian to pure Lévy. We parametrize our new model by taking the same pollen dispersal dataset used in Brownian motion modelling studies. By numerically solving the model equations, we show that the isolation distances required to keep outcrossing levels below a certain threshold are substantially increased by comparison with the original predictions, suggesting that isolation distances may need to be much larger than originally thought.

Reproductive success through high pollinator visitation rates despite self incompatibility in an endangered wallflower.

Self incompatibility (SI) in rare plants presents a unique challenge-SI protects plants from inbreeding depression, but requires a sufficient number of mates and xenogamous pollination. Does SI persist in an endangered polyploid? Is pollinator visitation sufficient to ensure reproductive success? Is there evidence of inbreeding/outbreeding depression? We characterized the mating system, primary pollinators, pollen limitation, and inbreeding/outbreeding depression in Erysimum teretifolium to guide conservation efforts. We compared seed production following self pollination and within- and between-population crosses. Pollen tubes were visualized after self pollinations and between-population pollinations. Pollen limitation was tested in the field. Pollinator observations were quantified using digital video. Inbreeding/outbreeding depression was assessed in progeny from self and outcross pollinations at early and later developmental stages. Self-pollination reduced seed set by 6.5× and quadrupled reproductive failure compared with outcross pollination. Pollen tubes of some self pollinations were arrested at the stigmatic surface. Seed-set data indicated strong SI, and fruit-set data suggested partial SI. Pollinator diversity and visitation rates were high, and there was no evidence of pollen limitation. Inbreeding depression (δ) was weak for early developmental stages and strong for later developmental stages, with no evidence of outbreeding depression. The rare hexaploid E. teretifolium is largely self incompatible and suffers from late-acting inbreeding depression. Reproductive success in natural populations was accomplished through high pollinator visitation rates consistent with a lack of pollen limitation. Future reproductive health for this species will require large population sizes with sufficient mates and a robust pollinator community.

Spatial genetic structure of forest and xerophytic plant species in arid Eastern Central Asia: insights from comparative phylogeography and ecological niche modelling

Central Asia is one of the major arid regions of the world, and the spatial genetic structure of plant species in this area displays broad significance with respect to the understanding of plant evolution and biogeographical patterns of temperate arid lands. Although the genetic structure of some plants has been examined in previous studies, it remains mostly unconfirmed whether different plants in the same habitat have similar genetic structure, and the factors that have influenced structure in plants of the region are also unknown. Accordingly, we employed the approaches of molecular phylogeography and species distribution modelling to compare spatial genetic structure and ecological niches for three montane forest and four lowland xerophytic plants in East Central Asia. The results obtained suggest that the three forest species retreat westward during the Last Glacial Maximum as indicated by higher genetic differentiation in western populations. By contrast, multiple peaks of genetic differentiation were detected from chloroplast DNA datasets among populations in each of the four xerophytic species. Based on nuclear ribosomal internal transcribed spacer datasets, anemophilous pollination had shaped the high dispersal ability for pollen-mediated gene flow and outcrossing pollination had triggered extensive heterozygosity among populations. In conclusion, palaeoclimatic changes and species traits have mainly influenced the spatial genetic structure of forest and xerophytic plants in arid Eastern Central Asia.

Complex pollination of a tropical Asian rainforest canopy tree by flower-feeding thrips and thrips-feeding predators.

In tropical rainforests of Southeast Asia, a highly fecund thrips (Thrips spp.) responds rapidly to the mass flowering at multiple-year intervals characteristic of certain species such as the canopy tree studied here, Shorea acuminata, by feeding on flower resources. However, past DNA analyses of pollen adherent to thrips bodies revealed that the thrips promoted a very high level of self-pollination. Here, we identified the pollinator that contributes to cross-pollination and discuss ways that the pollination system has adapted to mass flowering. By comparing the patterns of floral visitation and levels of genetic diversity in adherent pollen loads among floral visitors, we evaluated the contribution of each flower visitor to pollination. The big-eyed bug, Geocoris sp., a major thrips predator, was an inadvertent pollinator, and importantly contributed to cross-pollination. The total outcross pollen adhering to thrips was approximately 30% that on the big-eyed bugs. Similarly, 63% of alleles examined in S. acuminata seeds and seedlings occurred in pollen adhering to big-eyed bugs; about 30% was shared with pollen from thrips. During mass flowering, big-eyed bugs likely travel among flowering S. acuminata trees, attracted by the abundant thrips. Floral visitation patterns of big-eyed bugs vs. other insects suggest that these bugs can maintain their population size between flowering by preying upon another thrips (Haplothrips sp.) that inhabits stipules of S. acuminata throughout the year and quickly respond to mass flowering. Thus, thrips and big-eyed bugs are essential components in the pollination of S. acuminata.

Effects of pollination and postpollination processes on selfing rate in Mimulus ringens.

Selfing rates vary widely within and among populations of self-compatible flowering plants. This variation is often attributed to differences in the amount and timing of self and outcross pollen deposition on stigmas, as well as to the influence of postpollination mechanisms that control fertilization success. This study explores the relative importance of pollination and postpollination processes in determining selfing rates in monkeyflower, Mimulus ringens. We hand-pollinated flowers on 17 unrelated mothers with pollen from one of three experimental treatments intended to replicate field conditions: (1) simultaneous deposition of 50% self pollen and 50% outcross pollen from 5 unrelated donors; (2) self pollen followed 15 min later by application of an equal amount of outcross pollen from five unrelated donors; and (3) outcross pollen from 5 unrelated donors followed 15 min later by application of an equal amount of self pollen. We genotyped 757 progeny at 8 polymorphic microsatellite loci and used paternity exclusion to determine whether each seedling was selfed or outcrossed. When self and outcross pollen arrived simultaneously, and when self pollen arrived 15 min prior to outcross pollen, the observed proportions of self and outcross progeny did not deviate from the expected 1:1 ratio. However, when outcross pollen was applied 15 min prior to self pollen, there was a significant excess of outcross progeny. Selfing rate in Mimulus ringens is influenced by small differences in the timing of pollen arrival, but not by nonrandom postpollination sorting.

Fruiting Strategies of Perennial Plants: A Resource Budget Model to Couple Mast Seeding to Pollination Efficiency and Resource Allocation Strategies.

Masting, a breeding strategy common in perennial plants, is defined by seed production that is highly variable over years and synchronized at the population level. Resource budget models (RBMs) proposed that masting relies on two processes: (i) the depletion of plant reserves following high fruiting levels, which leads to marked temporal fluctuations in fruiting; and (ii) outcross pollination that synchronizes seed crops among neighboring trees. We revisited the RBM approach to examine the extent to which masting could be impacted by the degree of pollination efficiency, by taking into account various logistic relationships between pollination success and pollen availability. To link masting to other reproductive traits, we split the reserve depletion coefficient into three biological parameters related to resource allocation strategies for flowering and fruiting. While outcross pollination is considered to be the key mechanism that synchronizes fruiting in RBMs, our model counterintuitively showed that intense masting should arise under low-efficiency pollination. When pollination is very efficient, medium-level masting may occur, provided that the costs of female flowering (relative to pollen production) and of fruiting (maximum fruit set and fruit size) are both very high. Our work highlights the powerful framework of RBMs, which include explicit biological parameters, to link fruiting dynamics to various reproductive traits and to provide new insights into the reproductive strategies of perennial plants.

The bees don't know and the flowers don't care: the effect of heterospecific pollen on reproduction in co-occurringThysanotusspecies (Asparagaceae) with similar flowers

Species integrity relies on the maintenance of reproductive isolation, particularly between closely related species. Further, it has been hypothesized that the presence of heterospecific pollen on flower stigmas adversely affects plant reproduction with increasing effect in closely related species. Using two pairs of co-occurring buzz-pollinated Thysanotus spp. in the Mediterranean climate region of Perth, Western Australia, we quantified the effect of heterospecific pollen on fruit and seed set. We first determined the mating systems of the two focal species using self- and outcross pollen, followed by separate treatments with heterospecific pollen within each species pair. Of the two species receiving pollen, Thysanotus triandrus had a mixed mating system, but with significantly lower fruit and seed set from self-pollen relative to outcross pollen. Thysanotus tenellus was autogamous with no difference in fruit or seed set between autogamous, self- or outcross pollinations. Heterospecific pollen had no effect on fruit or seed set of either focal species. These outcomes point to post-pollination reproductive isolation, consistent with a floral morphology that causes low specificity of pollen placement and thus a poor capacity for pre-pollination discrimination. Negative effects of heterospecific pollen, therefore, do not appear to play a role in the reproduction in this group of buzz-pollinated flowers.

Natural land cover drives pollinator abundance and richness, leading to reductions in pollen limitation in cotton agroecosystems

Cotton is the most economically and culturally important fiber crop worldwide. Though cotton may potentially benefit from animal mediated pollination, it is unknown if the species is indeed pollen limited across agroecological landscapes. Our study had three objectives: (1) identify the land use attributes that impact wild pollinator abundance and diversity, (2) investigate the relationship between pollinator community composition and cotton pollen limitation and (3) determine the extent of direct and indirect effects of land use on pollinator community composition and pollination service. To address these objectives, we used a combination of pollinator community surveys, GIS analysis, and pollen limitation experiments across 12 cotton landscapes in South Texas. Overall, we found that pollinator community composition was closely related to the abundance of natural areas (250m radius). We also found evidence of substantial cotton pollen limitation, as significantly larger bolls were produced with the addition of outcross pollen. Further, we reveal that pollen limitation was negatively correlated with pollinator abundance and richness. Path analysis confirmed the two direct effects of land use composition on pollinator community and pollinator community composition on pollen limitation. Overall, our results reveal potential for increased crop yields via wild pollinator-mediated fruit set, equivalent to more than $108/acre with a regional gain of over $1.1 million USD. Further, our research provides insight into the specific land management practices that support pollinator communities within cotton agroecosystems. Cotton landscapes that maintain natural areas promote wild pollinator abundance and diversity, and subsequently experience reduced pollination limitation and increased crop yields.