Statistical differentiation between self incompatibility and pseudo-self compatibility in Petunia hybrida Hort,using female and male coefficient of crossability

Discriminating styles (DS), pollen-mediated pseudo-self compatibility (PMPSC), and general pseudo-self compatibility (PSC) phenomena were investigated by re-analyzing data from Petunia hybrida where known S genotypes were used. This demonstrated how female coefficient of crossability (FCC)/male coefficient of crossability (MCC) scatter diagrams and regression analyses aid in identifying and quantifying PSC within an self incompatible (SI) population. One of the female testers was identified by statistics to be SI, not DS, in contrast to what was reported in the original report, where all the plants were assumed to have operating DS. In addition, none of the females expressed PMPSC. Based on regression analysis and chi-square tests, a threshold between 27% and 31% PSC was estimated to be necessary for expression of DS. The presence of DS was also required to test for the existence of PMPSC as reported previously. The upper left-hand quadrant of the FCC/MCC scatter diagram which contains all the deviants from the theoretical SI model, is the location expression of DS has been identified. Placement for PMPSC deviants is not possible, due to the interrelationship with DS. Percent PSC did not directly equate with the different types of PSC phenomena but was useful for identifying and ranking DS in female parents. The compatible tester used in this experiment did not always produce the highest outcross seed set with the females as expected. Therefore, due to the confounding effects of the different types of PSC, it is important to choose the compatible testers with care. Regression analyses of FCC/MCC values indicated that S2.2 and S1.2 male testers did not behave in a similar fashion to S1.1 testers. It is hypothesized that this disparity could be the result of the expression of a general PSC gene, different from the DS or PMPSC genes, which is linked to the S2 allele. Since these general PSC effects associated with the S2 allele are minor in comparison to DS and PMPSC, it was necessary to distinguish the difference using statistical analysis.     

Peculiarities in PMC Meiosis of Pisum sativum

Summary Nemesia strumosa plants were discovered which had styles capable of discriminating among incompatible pollen tubes from different pollinators, allowing growth of some but not others. All but 3 of 26 families tested had at least some members with discriminating styles (DS). Presence and level of DS was independent of S genotype. Plants with pseudo-self-compatiblity (PSC) levels greater than 10% had the trait, though many plants with strong DS had PSC levels less than 10%. Self pollination of highly DS plants produced mostly DS offspring, but of differing sensitivities. Some progenies from crosses between a family of highly DS plants and unrelated, probably low DS plants segregated half DS and half non-DS, while others consisted of mostly DS or mostly non-DS. The DS phenomenon is probably caused by PSC genes.Scientific Journal Series Paper No. 11,677 of the Minnesota Agricultural Experiment Station     

Sporophytic recognition of pollen S alleles in the gametophytic self-incompatibility system of Nemesia strumosa benth

Summary Several seedlings of Nemesia strumosa with various levels of pseudo-self-compatibility (PSC) often produced more seed after self pollination than when pollinated using pollen from incompatible plants bearing the same S alleles. Sporophytic recognition of self pollen apparently increases PSC levels above those attributable to modifying genes which interfere with normal stylar activity.Scientific Journal Series Paper Number 9546 of the Minnesota Agricultural Experiment Station.     

Pollen tube expression of pseudo-self-compatibility (PSC) inPetunia hybrida

Summary AnS _1.1 self-incompatible (SI) petunia plant which showed atypical seed set was found in an I₇ population. This plant showed a strong SI reaction when selfed but produced varying amounts of seed when used as the seed parent in crosses with unrelated individuals homozygous for the sameS allele. Reciprocal crosses yielded no seed indicating that the reaction was a stylar response. Self seed obtained by high temperature treatments produced 18 plants, all of which exhibited the parental characteristics, the ability to reject self pollen but accept, to varying degrees, pollen bearing the sameS allele from unrelated plants. Several petunias homozygous forS ₁, and exhibiting various levels of PSC as determined by self seed set, progeny tests and temperature treatments, were used as pollen parents. The mean seed set of these crosses produced a ranking of the pollen parents which reflected the PSC levels obtained by other methods. The behavior of the F₁ and F₂ populations suggests that the pollen discriminating ability may be a simply inherited, dominant character in these plants. The styles of these unusual petunias illustrate the participation of the pollen tube in determining PSC.Scientific Journal Series Paper Number 10.479 of the Minnesota Agricultural Experiment Station     

The inheritance of pseudo-self-compatibility (PSC) in Nemesia strumosa Benth

Summary Pseudo-self-compatibility (PSC) in Nemesia strumosa was determined by recessive modifying genes which interferred with the normal stylar incompatibility reaction. The PSC levels ranged from none or low to amounts resembling full self-compatibility. PSC within a progeny could be maintained at low or high levels by selecting parents either high or low in PSC. Pollen from plants of any PSC level failed to produce seed when placed on other incompatible styles bearing the same S alleles.Scientific Journal Series Paper Number 9420 of the Minnesota Agricultural Experiment Station.     

Reproductive biology of the invasive exotic shrub, Rhododendron ponticum L. (Ericaceae)

The reproductive biology of an exotic species will affect its ability to become naturalized and invasive in non-native habitats. Rhododendron ponticum is an ecologically damaging exotic weed in the British Isles, which spreads predominantly by seed. I investigated how inbreeding and outcrossing affect seed production and germination in a wild population of this species in Ireland. Experimental manipulations revealed low fruit and seed set when insects were excluded from flowers, suggesting that this species has limited capability for spontaneous autogamy. Hand-pollination treatments showed that, although flowers are self-compatible (with self and same plant pollen), higher levels of seed set occur following outcrossing (xenogamy). There was no significant difference in rate of germination of seeds from inbred or outcrossed treatments. The addition of xenogamous pollen to open flowers did not increase fruit or seed set, suggesting that flowers in this population are not pollen limited: native generalist pollinators, mainly bumblebees ( Bombus spp.), are providing an adequate pollinator service. This work demonstrates that outcrossing increases seed set and pollinators are required to facilitate this. Hence, generalist native pollinators can promote invasion by exotic plants. Native pollinators can clearly play an important part in alien species invasion.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 373–381.     

Pollination ecology of the pre-Pyrenean endemic Petrocoptis montsicciana (Caryophyllaceae): effects of population size

Petrocoptis montsicciana (Caryophyllaceae) is a threatened pre‐Pyrenean endemic that grows exclusively on caves and walls of limestone. We studied its pollination ecology by monitoring phenology and by evaluating pollen and nectar production, pollinator activity (frequency and behaviour of visitors), quantity and quality of pollination services, pollen/ovule ratio, and seed set in response to insect exclusion and self‐compatibility tests. We also analysed the effect of population size on reproductive mechanisms by comparing a large and a small population. Flowers of P. montsicciana produced nectar and were visited by Hymenoptera (79.7%), Diptera (11.5%), and Lepidoptera (8.8%). The most frequent pollinators (60.6% of total visits) were long‐tongued bees of the genus Anthophora. Both populations had a similar range of pollinators. We found a correlation between the number of visited flowers and the number of open flowers per census; 88.7% of pollen grains deposited on the stigmas were conspecific and the main competitor was another chasmophyte plant, Antirrhinum molle. Bagged flowers set seeds but significantly less so than hand‐self‐pollinated and control flowers. Thus, although self‐compatible and self‐pollinated, entomophilous pollination of P. montsicciana is required in order to explain c. 10–40% of total seed set, in accordance with P/O ratio estimations. Bagged flowers from the small population set significantly more seeds than the large one. Visitation rates were lower in the small population, but, unexpectedly, showed higher stigmatic pollen loads and similar or higher seed set. These results suggest an increase of spontaneous selfing rates in the small population, probably favoured by a smaller flower size, which can not only assure reproductive success when pollinators are scarce, but also provide additional potential to adapt to climatic changes. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 76 , 79–90.     

Pollen limitation and pollinator preferences in Scorzonera hispanica

The plant life cycle is often affected by animal–plant interactions. In insect‐pollinated plants, interaction with pollinators is very important. When pollen transfer due to a lower abundance of pollinators limits seed production, selection pressures on plant traits related to plant attraction to pollinators might occur, e.g. on flowering phenology, height or number of flowerheads. Landscape changes (e.g. habitat fragmentation or changed habitat conditions) may cause plant–pollinator systems to lose balance and consequently affect population dynamics of many plant species. We studied the relationship between measured plant traits, environmental variables and pollinator preferences in Scorzonera hispanica (Asteraceae), a rare perennial, allogamous herb of open grasslands. We estimated the pollen limitation by comparing seed set of supplemental‐pollinated plants with that of open‐pollinated ones. Pollinators selected plants based on position within the locality (isolated plants close to trees) rather than on their traits. In spite of a high proportion of undeveloped seeds on the plants, we demonstrated that they are not pollen limited. Instead, seed set and weight of seeds was correlated with plant size traits (height and flowerhead number), with larger plants producing more and larger seeds. This suggests that the studied plants are likely resource limited. Overall, the results suggest that pollinators are not a selection factor in this system, in contrast to studies on various plant species, including self‐compatible species of the Asteraceae. The lack of any effect of pollinators in the system may be caused by a strong negative effect of ungulate herbivores, which could play a decisive role in functioning of the system.     

Pollination Biology of the Exotic Rattleweed Crotalaria retusa L. (Fabaceae) in NE Brazil1

The rattleweed Crotalaria retusa was introduced in Brazil from Africa, and combines a series of characters that have ensured its establishment in NE Brazil. We focused on its reproductive biology and pollinator behavior to explain its reproductive success. We performed manual pollination and germination experiments, and monitored the behavior of C. retusa's main pollinators in monospecific plots, and in mixed plots where C. retusa occurred together with two congeners, Crotalaria pallida and Crotalaria lanceolata. Crotalaria retusa is self‐compatible and capable of automatic selfing. Inbreeding depression was expressed at the level of percent seed germination, but not seed set. Few insects visited the inflorescences. Legitimate pollinators were two large carpenter bees, Xylocopa frontalis and Xylocopa grisescens which, together, accounted for more than 90 percent of the visits. The former foraged on C. retusa exclusively and has low pollen spread potential. The latter flew longer distances between plants and visited fewer flowers per inflorescence, potentially increasing the extent of pollen carryover, but at the risk of increasing heterospecific pollen transfer, because it visits other Crotalaria species during the same foraging bout. The different foraging strategies, allied to morphological disadvantages represented by pollen overlap on X. grisescens' body, may partially explain the much lower seed germination observed in C. pallida and C. lanceolata. These results are consistent with the hypothesis that a reduction in flower constancy may significantly depress viable seed set by increasing the chances of self‐pollination.     

Reproductive conflicts ofPalicourea padifolia (Rubiaceae) a distylous shrub of a tropical cloud forest in Mexico

We studied a population of the distylousPalicourea padifolia (Rubiaceae) in a cloud forest remnant near Xalapa City, Veracruz, México to explore possible asymmetries between floral morphs in the attractiveness to pollinators, seed dispersers, nectar robbers, floral parasites, and herbivores. We first assessed heterostyly and reciprocal herkogamy by measuring floral attributes such as corolla length (buds and open flowers), style and anther heights, stigma and stamen lengths and the distance between the anther tip to the stigma lobe. We then estimated floral and fruit attributes such as flower size, anther height, number and size of pollen grains, fruit size, seed size, nectar production, and flower and fruit standing crops to assess differences between floral morphs in attracting and effectively using mutualistic pollinators and seed dispersers. Also, floral parasitism and nectar robbing were assessed in this study as a measure of flower attractiveness to antagonists. The system seems to conform well to classical heterostyly (e.g. reciprocal stamen/style lengths, pollen and anther dimorphism, intramorph incompatibility) yet, there were several tantalizing differences observed between pin and thrum morphs. Thrum flowers have longer corollas and larger but fewer pollen grains than pin flowers. Both morphs produced the same total number of inflorescences, developed the same number of buds, and opened the same number of flowers per inflorescence during the flowering season. Nectar production and sugar concentration were similar between floral morphs but the reward was not offered symmetrically to floral visitors throughout the day. Nectar concentration was higher in pin flowers in the afternoon. The numbers of developing, fully developed, and ripe fruits were the same between floral morphs, however, fruits and seeds were larger than those of thrums. The incidence of fly larvae was higher among thrum flowers and damage by nectar robbing was the same between floral morphs. Fruit abortion patterns of flowers manually pollinated suggest intra-morph sterility (self and intramorph incompatibility). There were no differences between morphs in fruit and seed set per flower following legitimate pollination although thrums were more leaky than the pins (intramorph compatibility).     

CONTRIBUTION OF CRYPTIC INCOMPATIBILITY TO THE MATING SYSTEM OF EICHHORNIA PANICULA TA (PONTEDERIACEAE)

Tristylous populations of the annual aquatic Eichhornia paniculata have high levels of outcrossing and intermorph mating despite being fully self- and intramorph compatible. Experimental studies of pollen germination, ???pollen-tube growth, and pollinations with mixtures of genetically marked pollen were used to determine whether postpollination processes contribute to the observed mating patterns. Differences in pollen germination were small and did not contribute to differences in pollen siring ability. The fraction of pollen tubes first entering the ovary, however, was greater for legitimate outcross pollen than for either of the other two pollen types (self or outcross illegitimate pollen) in all recipient morphs. Moreover, legitimate pollen had higher siring success when in competition with illegitimate pollen types (self or outcross) in each recipient style morph. The ranking of pollen performance for different pollen-style combinations was the same for both the pollen-tube growth and marker-gene experiments indicating that differences in pollen-tube growth rate are the principal cause of differences in pollen siring ability. Cryptic incompatibility in E. paniculata may represent a weak heteromorphic incompatibility system because the observed patterns of pollen-tube growth parallel pollen-tube growth and seed-set patterns that occur in related species with strong trimorphic incompatibility. The ability to produce mostly outcrossed progeny when pollinators are abundant, but to reliably produce seed under a variety of environmental and demographic conditions may be favored in E. paniculata because of its colonizing life history and occurrence in ephemeral habitats. Cryptic incompatibility may be more likely to occur in species subject to wide fluctuations in population size and levels of pollinator service.     

Reproductive system and fitness of Vriesea friburgensis,a self‐sterile bromeliad species

Reproductive biology and plant fertility are directly related to many aspects of plant evolution and conservation biology. Vriesea friburgensis is an epiphytic and terrestrial bromeliad endemic to the Brazilian Atlantic rainforest. Hand‐pollination experiments were used to examine the reproductive system in a wild population of V. friburgensis. Plant fertility was assigned considering flower production, fruit and seed set, seed germination, and pollen viability. Self‐sterility observed from spontaneous selfing and manual self‐pollination treatments may be the consequence of late‐acting self‐incompatibility. Hand‐pollination results indicated no pollen limitation in the population studied. Floral biology features such as a few daily open flowers, nectar production, and sugar concentration corroborate hummingbirds as effective pollinators, although bees were also documented as pollinators. Components of fitness such as high flower, fruit, and seed production together with high seed and pollen viability indicate that this wild population is viable. From a conservation point of view, we highlight that this self‐sterile species depends on pollinator services to maintain its population fitness and viability through cross‐pollination. Currently, pollinators are not limited in this population of V. friburgensis. Conversely, the maintenance and continuous conservation of this community is essential for preserving this plant–pollinator mutualism.     

Ovule pre-emption and pollen limitation in a self-fertile perennial herb (Blandfordia grandiflora,Liliaceae)

The extent, frequency and causes of pollenlimited seed production were examined in partially selffertile populations of Blandfordia grandiflora for 2 years. Percentage seed set of open-pollinated plants (50–57%) did not differ within or between years, and was about 19% less than experimentally cross-pollinated plants (70–75%). Floral visits by honeybees did not differ through the flowering season and the number of pollen grains deposited on stigmas within 12 h of flowers opening exceeded the number of ovules per flower, indicating that the quality rather than the quantity of pollination limited seed set. Pollen limitation was caused by concurrent self- and cross-pollination and the subsequent abortion of some selfed ovules due to inbreeding depression. Natural seed set (55%) was intermediate between selfed (43%) and crossed (75%) flowers and was not increased when flowers that had been available to pollinators for 24 h were hand cross-pollinated, suggesting that ovules were already fertilized. Similarly, experimental pollination with both cross and self pollen within 24 h of flowers opening did not increase seed set relative to natural seed set, indicating that both cross- and self-fertilizations had occurred. In contrast, when selfing followed crossing by 48 h, or vice versa, seed set did not differ from crossed-only or selfed-only flowers, respectively, indicating that ovules were pre-empted by the first pollination. Collectively, these results indicate that under natural conditions self pollen pre-empts ovules, rendering them unavailable for cross-fertilization. This selfing reduces fecundity by 50%, as estimated from the natural production of cross seeds when selfing was prevented. Consequently, selection should favour floral traits, such as increased stigma-anther separation or protandry, that reduce interference between male and female functions that leads to selfing.     

Entomophily of the cloudberry (Rubus chamaemorus)

Cloudberry (Rubus chamaemorus L.), a dioecious perennial plant of boreal circumpolar distribution, is greatly prized for its berries. We crossed two treatments, pollinator exclusion and supplementary hand-pollination, to determine i) the relative importance of insects as pollinators, ii) if pollinator activity was a limiting factor for the sexual reproduction of the plant, and iii) the relative contribution of diurnal vs. nocturnal visitors to pollination. The activity of natural pollinators resulted in 97.5 and 88.5% fruit set, along with 76.7 and 62.5% seed set in 1998 and 1999, respectively. When insects were excluded, fruit-set dropped significantly to 18.4 (1998) and 12.8% (1999) and seed-set to 5.4 (1998) and 5.0% (1999) showing the importance of mid- and large-sized insects as pollinators. Natural levels of insect activity were sufficient to ensure complete pollination in both years as supplementary hand-pollination did not significantly increase either parameter in plots where pollinators had free access. Nocturnal insects may serve as pollinators (fruit-set = 41%), although they were less effective than diurnal pollinators (fruit-set = 93%).     

Pollination biology of the hexaploid self‐compatible species Turnera velutina (Passifloraceae)

• The evolution of monomorphisms from heterostylous ancestors has been related to the presence of homostyly and the loss of self‐incompatibility, allowing the occurrence of selfing, which could be advantageous under pollinator limitation. However, flowers of some monomorphic species show herkogamy, attraction and rewarding traits that presumably favour cross‐pollination and/or a mixed mating system. This study evaluated the contributions of pollinators, breeding system and floral traits to the reproduction of Turnera velutina, a herkogamous monomorphic species.
• Floral visitors and frequency of visits were recorded, controlled hand cross‐pollinations were conducted under greenhouse and natural conditions, and individual variation in floral traits was characterised to determine their contribution to seed production.
• Apis mellifera was the most frequent floral visitor. Flowers presented approach herkogamy, high variation in nectar features, and a positive correlation of floral length with nectar volume and sugar concentration. Seed production did not differ between manual self‐ and cross‐pollinations, controls or open cross‐pollinations, but autonomous self‐pollination produced, on average, 82.74% fewer seeds than the other forms, irrespective of the level of herkogamy.
• Differences in seed production among autonomous self‐pollination and other treatments showed that T. velutina flowers depend on insect pollination for reproduction, and that approach herkogamy drastically reduced seed production in the absence of pollen vectors. The lack of differences in seed production from manual cross‐ and self‐pollinations suggests the possible presence of a mixed mating system in the studied population. Overall, this species was possibly derived from a distylous ancestor but appears fully capable of outcrossing despite being monomorphic.

     

Visitation, effectiveness, and efficiency of 15 genera of visitors to wild radish, Raphanus raphanistrum (Brassicaceae)

Plant-pollinator interactions are one of the most important and variable mutualisms in nature. Multiple pollinators often visit plants and can vary in visitation rates, pollen removal and deposition, and spatial and temporal distribution, altering plant reproduction and patterns of pollinator-mediated selection. Although some visitors may not be effective pollinators, pollinator effectiveness is rarely estimated directly as seed set resulting from a single visit by each taxon visiting generalist plants. For two years, effectiveness of visitors to wild radish, Raphanus raphanistrum, was quantified by counting seeds set and pollen grains removed as a result of a single visit. We calculated a pollinator's importance to plant reproduction as the product of visitation rate and single-visit seed set, and regressed pollinator body size on pollen-removal and on seed set effectiveness. Although pollinators differed in effectiveness and visitation rates, pollinator importance was primarily determined by visitation rates. In contrast to similar 2-yr studies, pollinator assemblage composition varied little, suggesting pollinator-mediated selection can be consistent across years for this generalist. Larger pollinators were more effective than smaller at effecting seed set, but body size was a poor predictor of pollen removal ability. Instead, pollen-removal effectiveness may be more influenced by foraging behavior than size.     

Secondary pollen presentation and the temporal dynamics of stylar hair retraction and style elongation in Campanula trachelium (Campanulaceae)

To increase the accuracy of pollen capture and transfer by pollinators some plant species have developed secondary pollen presentation structures. Because the presence of secondary pollen presentation structures at the pistil may reduce the spatial separation between the sexual functions and increase the risk of self‐interference and selfing, temporal segregation of the sexual organs, triggered by visiting insects, can be expected to occur. We investigated secondary pollen presentation and the temporal dynamics of the sexual phases in combination with the physiological self‐incompatibility system in Campanula trachelium, a protandrous insect‐pollinated herb. Stylar hair retraction (male function) and curling of the stigmatic lobes (female function) were modelled using Gompertz growth functions. Finally, we performed pollination experiments in the lab and field to assess seed set and pollen limitation under natural conditions. About 68% of the total pollen load was captured by stylar hairs. Manual manipulation of the stylar hairs, mimicking pollinator visitation, significantly shortened the male phase and accelerated the female phase, resulting in a significant decline in temporal overlap between the two sexual functions. Conversely, when pollinators and/or manual manipulations were lacking, the male phase was substantially prolonged and sexual overlap was maximal. This suggests that spreading of the sexual phases and thus the risk of sexual interference are largely determined by the interaction between stylar hairs and visiting pollinators. Natural seed set was high and not pollinator limited. Overall, these results indicate that secondary pollen presentation and partial protandry resulted in efficient pollen capture, transfer and deposition.     

Floral display and habitat fragmentation: Effects on the reproductive success of the threatened mass‐flowering Conospermum undulatum (Proteaceae)

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Noncorrelated evolution between herbivore- and pollinator-linked features in Aristolochia chilensis (Aristolochiaceae)

The effect of mutualists (i.e. pollinators) and antagonists (i.e. herbivores) can have non-additive effects on plant fitness. This is often interpreted as evidence for correlated evolution on a suite of traits leading to an increase and decrease of the interaction of plants with mutualists and antagonists, respectively. This situation has been found to prevail in plants that have large floral and fruit displays but are not limited by pollinators for seed set. We suggest the alternative hypothesis, where plants limited by pollinators for seed set (e.g. deceit-pollinated plants) exhibit additive effects of pollinators and herbivores on fitness (i.e. noncorrelated evolution). Using a 2 × 2 factorial design, we tested this hypothesis by solely and simultaneously evaluating the effects of pollinators and the single herbivore, Battus polydamas archidamas , on female reproductive success of Aristolochia chilensis . Plants exposed to herbivores presented 2.6-fold greater herbivory than plants that excluded them. In addition, plants exposed to pollinators showed strong limitation by pollinators for seed set compared with other plants of the genus Aristolochia. However, only pollinators had a significant effect on fruit and seed set because plants that excluded them did not set fruits or seeds. Furthermore, herbivores and pollinators exerted additive effects on fruit and seed production. Collectively, these results indicate that herbivore- and pollinator-linked traits in A. chilensis exhibit noncorrelated evolution.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 239–245.     

BREEDING SYSTEM AND POLLINATION ECOLOGY OF TRIENTALIS BOREALIS (PRIMULACEAE)

Selfing in Trientalis borealis is reduced by spatial separation of stigma and anthers during anther dehiscence and by internal self-incompatibility. Artificial self-pollination resulted in low levels of fruit set (2.0%). Crosses made within patches of plants yielded variable (0–72.7%), but generally low fruit set (x̄ = 21.4%). This may be caused by patches often consisting of a single genet. In contrast crosses made among patches resulted in uniformly high levels of fruit set (x̄ = 84.3%). Pollinator activity was higher at open sites than at heavily shaded sites and was correlated with fruit set. Pollinator activity, however, showed no correlation with seed set. We conclude that the primary pollinators, Halictid and Andrenid bees, play an important role in the breeding system of the plant by promoting outcrossing but that availability or efficiency of pollinators may limit seed set.