Breeding systems in Clivia (Amaryllidaceae): late‐acting self‐incompatibility and its functional consequences

Late‐acting (ovarian) self‐incompatibility, characterized by minimal or zero seed production following self‐pollen tube growth to the ovules, is expected to show phylogenetic clustering, but can otherwise be difficult to distinguish from early‐acting inbreeding depression. In Amaryllidaceae, late‐acting self‐incompatibility has been proposed for Narcissus (Narcisseae) and Cyrtanthus (Cyrtantheae). Here, we investigate whether it occurs in the horticulturally important genus Clivia (Haemantheae) and test whether species in this genus experience ovule discounting in wild populations. Seed‐set results following controlled hand pollinations revealed that Clivia miniata and C. gardenii are largely self‐sterile. Self‐ and cross‐pollinated flowers of both species had similar proportions of pollen tubes entering the ovary, and those of C. gardenii also did not differ in the proportions of pollen tubes that penetrated ovules, thus ruling out classical gametophytic self‐incompatibility acting in the style, but not early inbreeding depression. Flowers that received equal mixtures of self‐ and cross‐pollen set fewer seeds than those that received cross‐pollen only, but it was unclear whether this effect was a result of ovule discounting or interactions on the stigma. The prevention of self‐pollination by the emasculation of either single flowers or whole inflorescences in wild populations did not affect seed set, suggesting that ovule discounting is not a major natural limitation on seed production. Flowers typically produce one to three large fleshy seeds from approximately 16 available ovules, even when supplementally hand pollinated, suggesting that fecundity is mostly resource limited. The results of this study suggest that Clivia spp. are largely self‐sterile as a result of either a late‐acting self‐incompatibility system or severe early inbreeding depression, but ovule discounting caused by self‐pollination is not a major constraint on fecundity. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175 , 155–168.     

Staminal hairs enhance fecundity in the pollen‐rewarding self‐incompatible lily Bulbine abyssinica

Flowering plants typically use floral rewards to attract animal pollinators. Unlike nectar, pollen rewards are usually visible and may thus function as a signal that influences landing decisions by pollen‐seeking insects. Here we artificially manipulate the presence of both pollen and staminal hairs (a putative false signal of pollen reward availability) in the hermaphroditic lily Bulbine abyssinica (Xanthorrhoeaceae) to investigate their effects on bee visitation and fecundity, and also test for trade‐offs between pollen production and seed production. Honeybees, the primary floral visitors, are probably not able to distinguish between colours of petals, staminal hairs and pollen of B. abyssinica, according to analysis of reflectance spectra in a bee vision model. Flowers with both pollen and hairs removed had the lowest levels of bee visitation, seed set and seed abortions. Flowers containing hairs had an ～50% increase in visitation rate and seed set compared with emasculated flowers, while intact controls had the highest seed abortion rate. Ovule discounting in intact flowers is probably due to ovarian self‐incompatibility (or strong early inbreeding depression) as ovules penetrated by tubes from self‐pollen uniformly failed to develop into seeds. These results show that staminal hairs can enhance plant fecundity by increasing attraction of pollen‐seeking insects to flowers without increasing the risk of ovule discounting through pollinator‐mediated self‐pollination. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 481–490.     

Breeding systems in Cyrtanthus (Amaryllidaceae): variation in self‐sterility and potential for ovule discounting

• Breeding systems of plants determine their reliance on pollinators and ability to produce seeds following self‐pollination. Self‐sterility, where ovules that are penetrated by self‐pollen tubes that do not develop into seeds, is usually considered to represent either a system of late‐acting self‐incompatibility or strong early inbreeding depression. Importantly, it can lead to impaired female function through ovule or seed discounting when stigmas receive mixtures of self and cross pollen, unless cross pollen is able to reach the ovary ahead of self pollen (‘prepotency’). Self‐sterility associated with ovule penetration by self‐pollen tubes appears to be widespread among the Amaryllidaceae.
• We tested for self‐sterility in three Cyrtanthus species – C. contractus, C. ventricosus and C. mackenii – by means of controlled hand‐pollination experiments. To determine the growth rates and frequency of ovule penetration by self‐ versus cross‐pollen tubes, we used fluorescence microscopy to examine flowers of C. contractus harvested 24, 48 and 72 h after pollination, in conjunction with a novel method of processing these images digitally. To test the potential for ovule discounting (loss of cross‐fertilisation opportunities when ovules are disabled by self‐pollination), we pollinated flowers of C. contractus and C. mackenii with mixtures of self‐ and cross pollen.
• We recorded full self‐sterility for C. contractus and C. ventricosus, and partial self‐sterility for C. mackenii. In C. contractus, we found no differences in the growth rates of self‐ and cross‐pollen tubes, nor in the proportions of ovules penetrated by self‐ and cross‐pollen tubes. In this species, seed set was depressed (relative to cross‐pollinated controls) when flowers received a mixture of self and cross pollen, but this was not the case for C. mackenii.
• These results reveal variation in breeding systems among Cyrtanthus species and highlight the potential for gender conflict in self‐sterile species in which ovules are penetrated and disabled by pollen tubes from self pollen.

     

Cryptic self‐incompatibility and distyly in Hedyotis acutangula Champ. (Rubiaceae)

Distyly, floral polymorphism frequently associated with reciprocal herkogamy, self‐ and intramorph incompatibility and secondary dimorphism, constitutes an important sexual system in the Rubiaceae. Here we report an unusual kind of distyly associated with self‐ and/or intramorph compatibility in a perennial herb, Hedyotis acutangula. Floral morphology, ancillary dimorphisms and compatibility of the two morphs were studied. H. acutangula did not exhibit precise reciprocal herkogamy, but this did not affect the equality of floral morphs in the population, as usually found in distylous plants. Both pin and thrum pollen retained relatively high viability for 8 h. The pollen to ovule ratio was 72.5 in pin flowers and 54.4 in thrum flowers. Pistils of pin flowers remained receptive for longer than those of thrum flowers. No apparent difference in the germination rate of pin and thrum pollen grains was observed when cultured in vitro, although growth of thrum pollen tubes was much faster than that of pin pollen tubes. Artificial pollination revealed that pollen tube growth in legitimate intermorph crosses was faster than in either intramorph crosses or self‐pollination, suggesting the occurrence of cryptic self‐incompatibility in this species. Cryptic self‐incompatibility functioned differently in the two morphs, with pollen tube growth rates after legitimate and illegitimate pollination much more highly differentiated in pin flowers than in thrum flowers. No fruit was produced in emasculated netted flowers, suggesting the absence of apomixis. Our results indicate that H. acutangula is distylous, with a cryptic self‐incompatibility breeding system.     

Pollination biology of a night‐flowering Galápagos endemic,Ipomoea habeliana (Convolvulaceae)

Ipomoea habeliana is an endemic, night‐flowering member of the Galápagos flora. Pollination experiments, flower‐visitor observations, nectar sampling, pollen transfer, and pollen to ovule ratio and pollen size studies were included in this project. The large, white flowers of this species set fruit via open pollination (55%), autonomous autogamy (51%), facilitated autogamy (91%), cross‐pollination (80%), diurnal open pollination (60%) and nocturnal open pollination (60%). Fruit set is pollen‐limited. Ants, beetles, crickets and hawk moths regularly visit the flowers. Ants are the most frequent visitors, but hawk moths are the only effective pollinators. Nectar is available throughout the night, but is most abundant early in the evening when hawk moth visits are most frequent. Experiments with fluorescent dust demonstrate intra‐ and inter‐plant pollen movement by hawk moths. Although this species is adapted for hawk moth pollination, it readily sets fruit via autonomous autogamy when no visits are made. Thus, it is concluded that it is facultatively xenogamous. Additional support for this conclusion is provided by the pollen to ovule ratio of 1407 and by the fact that the plants grow in a region that has few or no faithful pollinators. Conservation efforts for I. habeliana should include hand pollinations, which could significantly increase seed set. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 11–20.     

A ballistic pollen dispersal system influences pollination success and fruit‐set pattern in pollinator‐excluded environments for the endangered species Synaphea stenoloba (Proteaceae)

The critically endangered Synaphea stenoloba (Proteaceae) has numerous scentless flowers clustered in dense inflorescences and deploys a ballistic pollen ejection mechanism to release pollen. We examined the hypothesis that active pollen ejection and flowering patterns within an inflorescence influence the reproductive success (i.e. fruit formation) of individual flowers within or among inflorescences of S. stenoloba in a pollinator‐excluded environment. Our results showed that: (1) no pollen grains were observed deposited on the stigma of their own flower after the pollen ejection system was manually activated, indicating self‐pollination within an individual flower is improbable in S. stenoloba; (2) fruit set in the indoor open pollination treatment and the inflorescence‐closed pollination treatment indicated that S. stenoloba is self‐compatible and pollen ejection can potentially result in inter‐floral pollination success; (3) fruit set in the inflorescence‐closed pollination treatment was significantly lower than that of indoor open pollination, indicating within‐ and between‐flower pollination events in an inflorescence are most likely limited, with pollination between inflorescences providing the highest reproductive opportunity; and (4) analysis of the spatial distribution of cumulative fruit set on inflorescences showed that pollen could reach any flower within an inflorescence and there was no functional limitation on seed set among flowers located at various positions within the inflorescence. These data suggest that the pollen ejection mechanism in S. stenoloba can enhance inter‐plant pollination in pollinator‐excluded environments and may suggest adaptation to pollinator scarcity attributable to habitat disturbance or competition for pollinators in a diverse flora. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170 , 59–68.     

Ovarian self‐incompatibility in Narcissus papyraceus (Amaryllidaceae) is the result of a pre‐zygotic response

Ovarian self‐incompatibility, including pre‐ and post‐zygotic reactions, is a complex mechanism for which we still lack many details relating to its function and significance. The joint presence of ovarian self‐incompatibility with style polymorphism is a rare combination that is found in the genus Narcissus. Usually, style polymorphic species have heteromorphic (diallelic and linked to style length locus) incompatibility, which prevents fertilization between individuals of the same morph, thereby helping to maintain equal proportions of floral morphs in populations. However, when present, self‐incompatibility in Narcissus is not linked to style polymorphism and cross‐fertilization within each morph is possible. Hence, self‐incompatibility in Narcissus is of particular interest when attempting to unravel the nature of the rejection reaction and aiming to assess possible cryptic differences in the fertilization process in intra‐ and inter‐morph crosses, which might ultimately explain the wide variation of morph‐ratio in the field. We examined the breeding system of Narcissus papyraceus, a style‐dimorphic species that has biased morph ratios in most of its populations. We studied pollen‐tube growth in the pistil and ovule fate after experimentally controlled hand pollinations. The growth of pollen tubes in self‐ and intra‐ and inter‐morph crosses was similar up to the point of micropyle penetration in both morphs but, subsequently, a pre‐zygotic failure appeared to affect male and female gametophytes in selfed pistils. A high proportion of ovules from self‐pollinated flowers showed signs of collapse and self‐pollen tubes were blocked or behaved abnormally before entering the embryo sac. Self‐incompatibility was stronger in the long‐styled morph than in the short‐styled morph. We did not find any conclusive sign of differential functioning between intra‐ and inter‐morph cross‐pollinations in any morph. These results enable us to rule out the possible effects of pollen–pistil interactions in N. papyraceus as a cause of morph‐ratio biases and confirm the exceptional nature of the self‐incompatibility mechanism in this polymorphic species. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 629–643.     

Evidence for autonomous selfing in grassland Protea species (Proteaceae)

It has been assumed that species of the large African genus Protea have strong self‐incompatibility systems. However, this assumption was based largely on studies conducted on a clade of bird‐pollinated species that occur in the shrubby fynbos vegetation of the Cape region of southern Africa. To test whether self‐incompatibility occurs in a grassland/savanna Protea clade, which is largely insect‐pollinated, we performed controlled pollination experiments on four species, P. caffra, P. dracomontana, P. simplex and P. welwitschii. Although pollen–ovule ratios of all four species fall within the range for outcrossers, all four species are self‐compatible and capable of autonomous seed production. Using fluorescence microscopy, we found that self‐pollen tubes had the same probability of reaching ovules as cross‐pollen tubes. In the small tree P. caffra, selfed progeny had rates of germination and survivorship that were identical to those of crossed progeny. The grassland Protea spp. studied are likely to have mixed mating systems on account of being both visited by insects and capable of autonomous selfing. If one assumes previous reports of self‐incompatibility in Protea to be reliable, there have been at least five losses of self‐incompatibility and two gains of autonomous selfing in this genus. However, earlier studies in the genus were often methodologically flawed and a thorough re‐analysis of breeding systems in Protea is required. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 169 , 433–446.     

Pollination and fruit‐set of Grevillea robusta in western Kenya

The floral visitors of silky oak, Grevillea robusta A. Cunn. ex R.Br., their foraging behaviour and their effects on fruit‐set were studied at Malava, western Kenya. Grevillea robusta is a popular tree for farm plantings in the eastern and central African highlands. Yield of seed has been disappointingly low in some areas and a lack of appropriate pollinators has been suggested as a possible cause. Investigations involved the monitoring of visitors on active inflorescences, assessment of the rewards available to potential pollinators, and exclusion experiments to establish the effects of various visitors on fruit‐set. The flowers are visited mainly by birds and insects. The likely pollinators of G. robusta are sunbirds (Nectarinia amethystina, N. cyanolaema, N. olivacea, N. superba and N. venusta) and white‐eyes (Zosterops kikuyuensis and Z. senegalensis). Very little aggressive behaviour between birds was recorded. No nocturnal pollinators were observed. Nectar was the major floral reward for pollinators, but is likely depleted by ants and honey bees, the foraging behaviour of which confirmed them to be nectar‐robbers. These insects hardly ever touched stigmas during their visits. Eighty‐nine per cent of bird visits were in the morning (07.00–10.00 hours) when nectar volume was highest. Inflorescences bagged to exclude birds set no fruits, and unmanipulated flowers and flowers bagged with self‐pollen set no fruits, indicating a self‐incompatibility mechanism. Control cross‐pollinated flowers displayed greatly increased fruit‐set (25.1%) compared with natural open‐pollination (0.9%). All these findings confirm the importance of cross‐pollen transfer to flowers and the necessity of pollinators for fruit‐set. Effective seed production requires activity of pollinators for self‐pollen removal and cross‐pollen deposition. Seed production stands for G. robusta should be established where flowering is prolific and bird pollinators are abundant.     

Microgametophytes in flowers with and without fruits ofPhlox drummondii (Polemoniaceae)

Relationships between microgametophyte numbers per flower and fruit-set were sought inPhlox drummondii Hook. This was accomplished by counting fluorescentstained pollen tubes in flowers with and without fruits in 21 populations, and in flowers subject to either supplemental or sparse pollination, and then determining whether the flowers initiate fruits. There was a conspicuous variation in mean pollen tubes per flower (3–38) and in percent fruit-set (17%–92%) among populations. Neighboring populations often differed strikingly in these respects. Flowers with fruits had an average of 15.2 pollen tubes per stigma whereas those without had an average of 3 7 tubes. Over all flowers, there was a mean of 3.7 tubes per ovule. There was a strong correlation between mean tube number within populations and their percent fruit-set (r = 0.86). Supplemental pollination significantly enhanced fruit-set, thereby supporting the notion that fruit-set was pollen-limited in most populations. In both natural and artificial pollinations a portion of flowers without fruits still had several pollen tubes. The occurrence of fruitless flowers containing tubes is explained by attrition factors, like late-acting pollen-pistil incompatibility, and resource limitation. Fruit-set could be initiated with one pollen tube, but this rarely occurred in nature. Higher pollen loads were accompanied by higher percents of fruit-set and number of seeds per flower.     

Nectarless flowers with deep corolla tubes in Pedicularis: does long pistil length provide an arena for male competition?

Pollinator‐mediated selection does not seem to have a direct influence on the evolution of a long corolla tube in a nectarless flower. We hypothesized that the long pistil length of the nectarless flower with a deep corolla tube provided an opportunity for male competition. Pedicularis siphonantha, a nectarless and partially self‐incompatible lousewort with substantial variation in corolla tube length, was used to test the hypothesis. We tested whether and how corolla tube length affected seed production per capsule and seed germination rate with different pollination treatments. Flowers were hand‐pollinated with pollen from one self donor and one outcross donor and mixed pollen grains consisting of equal amounts from the two donor types, respectively. Additionally, seeds from open‐pollinated flowers with different corolla tube lengths were collected separately for measurement of germination rate. Pollination treatment and corolla tube length significantly affected number of seeds per capsule. Moreover, a significant positive relationship between seeds per capsule and corolla tube length was found when mixed hand pollination was conducted. Seeds of self hand‐pollinated flowers had a lower germination rate than those from outcross‐pollinated flowers. Under open pollination, seeds from flowers with longer corolla tubes tended to have higher germination rate. In P. siphonantha, outcross pollen may have a higher probability of contributing to the next generation when transferred to flowers with longer corolla tubes. The pistil length, therefore, should be seen as a female choice mechanism, which provides an arena for male‐to‐male competition. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 526–532.     

Self‐pollination and parthenocarpic ability in developing ovaries of self‐incompatible Clementine mandarins (Citrus clementina)

This study aimed to determine if self‐pollination is needed to trigger facultative parthenocarpy in self‐incompatible Clementine mandarins (Citrus clementina Hort. ex Tan.). ‘Marisol’ and ‘Clemenules’ mandarins were selected, and self‐pollinated and un‐pollinated flowers from both cultivars were used for comparison. These mandarins are always seedless after self‐pollination and show high and low ability to develop substantial parthenocarpic fruits, respectively. The time‐course for pollen grain germination, tube growth and ovule abortion was analyzed as well as that for carbohydrates, active gibberellins (GA₁ and GA₄), auxin (IAA) and abscisic acid (ABA) content in the ovary. ‘Clemenules’ showed higher pollen grain germination, but pollen tube development was arrested in the upper style 9 days after pollination in both cultivars. Self‐pollination did not stimulate parthenocarpy, whereas both un‐pollinated and self‐pollinated ovaries set fruit regardless of the cultivar. On the other hand, ‘Marisol’ un‐pollinated flowers showed greater parthenocarpic ovary growth than ‘Clemenules’ un‐pollinated flowers, i.e. higher ovule abortion rate (+21%), higher fruit set (+44%) and higher fruit weight (+50%). Further, the greater parthenocarpic ability of ‘Marisol’ paralleled higher levels of GA₁ in the ovary (+34% at anthesis). ‘Marisol’ ovary also showed higher hexoses and starch mobilization, but lower ABA levels (?64% at anthesis). Self‐pollination did not modify carbohydrates or GA content in the ovary compared to un‐pollination. Results indicate that parthenocarpy in the Clementine mandarin is pollination‐independent with its ability to set depending on the ovary hormone levels. These findings suggest that parthenocarpy in fertile self‐incompatible mandarins is constitutively regulated.     

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.     

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.     

Pollen tube growth and early ovule development following self- and cross-pollination in<Emphasis Type="Italic"> Eucalyptus nitens</Emphasis>

Controlled self- and cross-pollinations were conducted on flowers of five mature Eucalyptus nitens trees. Levels of self-sterility of the trees ranged from 25.8 to 93.6%. Pollen tube numbers in styles and ovule penetration by pollen tubes was investigated 2 weeks after pollination by fluorescence microscopy. There were no significant differences between treatments in the number of pollen tubes present in styles or in the percentage of ovules penetrated by pollen tubes. Embryology of material harvested 2 and 4 weeks after pollination was investigated by bright-field microscopy. Fertilisation had taken place by 2 weeks after pollination with nearly every ovule showing evidence of fertilisation. Cross-pollination resulted in a greater proportion of healthy, developing ovules, at both 2 and 4 weeks after pollination, compared with self-pollination. The proportion of degenerating ovules increased from 2 to 4 weeks after pollination. The reduced ability of E. nitens to set self-pollinated seed compared with cross-pollinated seed appears to be controlled by a post-zygotic mechanism. Differences in ovule size may potentially assist in the identification of trees incapable of setting self-pollinated seed.     

Reproductive systems and low outbreeding barriers between Jacaranda cuspidifolia and J. mimosifolia (Jacarandeae,Bignoniaceae)

The genus Jacaranda shows notable karyotype stability and a prevailing self‐sterile breeding system with evidence of late‐acting self‐incompatibility in several species. However, some studies have indicated self‐compatibility in J. mimosifolia, a species cultivated worldwide in tropical and subtropical areas. Jacaranda cuspidifolia is a closely related species with natural distribution broadly overlapping with that of J. mimosifolia, and manual heterospecific pollination studies have indicated that these species are interfertile, but there is no report on the breeding system of the former. In this study, we used hand‐pollination experiments, pistil longevity, epi‐fluorescence and histological analysis of post‐pollination events to determine the breeding system of J. cuspidifolia. We also employed intra and interspecific crosses and seed germination tests to reevaluate the breeding system of J. mimosifolia and the inter‐fertility between the two species. Some fruits were initiated from self‐pollinated pistils in J. mimosifolia, but none of them reached maturity. On the other hand, complete absence of fruit development by self‐pollination was verified in J. cuspidifolia, while in situ pollen tube growth and histological analysis of post‐pollination events in selfed pistils revealed the characteristic ovule penetration, fertilization and endosperm initiation also observed in other bignoniaceous species with late‐acting self‐incompatibility. Low outbreeding barriers seem to operate between these species because reciprocal interspecific crosses and hybrid seed germination tests indicated they are bilaterally interfertile. However, fruit/seed production and seed germinability were significantly lower when pistils of J. cuspidifolia were pollinated with pollen of J. mimosifolia, compared with crosses in the opposite direction, which indicates a partial unilateral incompatibility. This result is discussed in the context of the possible occurrence of self‐compatibility in J. mimosifolia. The low level of incongruity operating between the two species also points to their recent evolutionary divergence.     

Obligate association of an oligolectic bee and a seasonal aquatic herb in semi‐arid north‐eastern Brazil

Hydrocleys martii (Limnocharitaceae) is an annual aquatic herb common in ephemeral isolated ponds in semi‐arid northe‐astern Brazil. We studied pollination of H. martii, emphasizing reproductive success and association with oligolectic pollinators. The yellow flowers bear a central cone of staminodes that encloses the fertile stamens and four free carpels. The self‐incompatible species depends on pollinators to set fruits. In 25 temporary water bodies in five Brazilian states, Protodiscelis palpalis bees (Colletidae, Paracolletinae) were the unique effective pollinators of H. martii and, in 18 of these, the sole flower visitors. Females of this narrowly oligolectic species show adapted behaviour to access the pollen chamber in the flower centre. Females removed more than 80% of the 480 000 pollen grains in only 2 h from the flowers but maintained a high visitation frequency almost until flower senescence. In this highly specialized plant‐pollinator system, on average, 1.6% of the pollen grains reached the stigmatic surface and 9.6% remained uncollectible in the flowers. In the absence of P. palpalis, flowers set almost no seeds, indicating reproductive dependence on the oligolectic species. This pioneer pollination study of a species of Limnocharitaceae provides evidence of a close relationship of the family to species of Protodiscelis, their specific pollinators. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 355–368.     

Mixed pollen load and late‐acting self‐incompatibility flexibility in Adenocalymma peregrinum (Miers) L.G. Lohmann (Bignonieae: Bignoniaceae)

• Mixed cross and self‐pollen load on the stigma (mixed pollination) of species with late‐acting self‐incompatibility system (LSI) can lead to self‐fertilized seed production. This “cryptic self‐fertility” may allow selfed seedling development in species otherwise largely self‐sterile. Our aims were to check if mixed pollinations would lead to fruit set in LSI Adenocalymma peregrinum, and test for evidence of early‐acting inbreeding depression in putative selfed seeds from mixed pollinations.
• Experimental pollinations were carried out in a natural population. Fruit and seed set from self‐, cross and mixed pollinations were analysed. Further germination tests were carried out for the seeds obtained from treatments.
• Our results confirm self‐incompatibility, and fruit set from cross‐pollinations was three‐fold that from mixed pollinations. This low fruit set in mixed pollinations is most likely due to a greater number of self‐ than cross‐fertilized ovules, which promotes LSI action and pistil abortion. Likewise, higher percentage of empty seeds in surviving fruits from mixed pollinations compared with cross‐pollinations is probably due to ovule discounting caused by self‐fertilization. Moreover, germinability of seeds with developed embryos was lower in fruits from mixed than from cross‐pollinations, and the non‐viable seeds from mixed pollinations showed one‐third of the mass of those from cross‐pollinations.
• The great number of empty seeds, lower germinability, lower mass of non‐viable seeds, and higher variation in seed mass distribution in mixed pollinations, strongly suggests early‐acing inbreeding depression in putative selfed seeds. In this sense, LSI and inbreeding depression acting together probably constrain self‐fertilized seedling establishment in A. peregrinum.

     

Resource limitation and pollen source (self and outcross) affecting seed production in two louseworts, Pedicularis siphonantha and P. longiflora (Orobanchaceae)

Two animal-pollinated hermaphrodite plants, Pedicularis siphonantha and P. longiflora , have been used to investigate factors limiting seed production in natural populations. To evaluate the potential seed abortion due to resources limitation, seed development has been observed and seed count conducted twice. Seed production per capsule has been compared when flowers have been removed and in a control group. Open pollination has been investigated and pollen supplementation undertaken to estimate the possibility of pollen limitation. Results show that seed abortion is frequent. Stigmatic pollen load is significantly higher than ovule number per ovary under open pollination for both species. Additional self and outcross pollen did not affect seed production. Flower removal significantly increases seed production per capsule, which indicates that seed production of the studied species is limited by available resources. To detect differences in seed production between flowers pollinated by self and outcross pollen, hand pollination of bagged flowers has also been conducted in natural populations of the two Pedicularis species. Compared with open pollination, hand-pollinating self-pollen decreases, while outcross pollen increases seed production per capsule. Such results suggest that inbreeding depression in the two self-compatible species may also result in partial seed abortion under open pollination if mixed pollen is deposited on the stigma. Our results also suggest that pollen interference plays an important role in low female fertility in the two Pedicularis species.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 83–89.     

Mating in the pseudogamic apomictic Anemopaegma acutifolium DC: another case of pseudo‐self‐compatibility in Bignoniaceae?

Self‐compatibility in apomictic pseudogamic species is considered fundamental to assure reproduction by seeds in extreme situations, making apomictic species more advantageous than sexual ones in these scenarios. Anemopaegma acutifolium is a polyploidy, apomictic sporophytic species with no endosperm development in ovules of unpollinated pistils, which indicates obligate pseudogamy. Thus, the aim of the present work is to study the breeding system and post‐pollination events to test if there is similar pseudogamous development irrespective of pollination treatment. We analysed fruit and seed set obtained in controlled experimental pollinations, as well as embryo number per seed, and the progress of ovule penetration, fertilisation and early endosperm development between self‐ and cross‐pollinated pistils. We found that the species is self‐fertile and that spontaneous selfing fruit set is also possible, although emasculated flowers never form fruits. Selfed pistils were as efficient as crossed ones for all parameters analysed, except for a delay in endosperm development observed in the former that may be an effect of the late‐acting self‐incompatibility. Therefore, the avoidance of selfed pistil abortion seems to be promoted by the presence of adventitious embryos and a normal endosperm. We conclude that A. acutifolium shows apomixis‐related pseudo‐self‐compatibility, as in other self‐fertile apomictic species of Bignoniaceae, which confer reproductive assurance and increases fruit‐set and persistence ability in fast‐changing tropical habitats.