Pollination biology of Harrisia portoricensis (Cactaceae), an endangered Caribbean species

Traits associated with self-pollination are common features of island plant communities. In this work, we studied the pollination biology and the breeding system of Harrisia portoricensis, an island columnar cactus, to test for the presence of inbreeding and inbreeding depression. For H. portoricensis, which bears flowers with typical outcrossing morphology, the results from 322 h of direct observations and videotaping showed that visits to flowers by animals were uncommon. Controlled pollinations demonstrated that H. portoricensis has a partially self-compatible breeding system that it is not autogamous and thus requires an external mechanism for the movement of pollen to set fruit. We detected differences in seed size, seed mass, germination success, and multiplicative fitness estimates between self- and cross-pollination treatments. We found that progeny resulting from natural and self-pollination treatments showed signs of inbreeding depression compared with progeny resulting from cross-pollination; however, the magnitude of the inbreeding depression was less than 50%. Our combined results suggest that for this species an endogamous breeding system should be favored by natural selection.     

Autogamy in Boronia falcifolia: consequences for inbreeding and persistence in fragmented coastal heaths

Coastal heath is becoming increasingly fragmented, resulting in reduced pollinator abundance affecting species viability. The reproductive ecology and inbreeding of a common coastal heath species, Boronia falcifolia (Rutaceae), was investigated. Pollination observations and experiments were carried out at one site, and inbreeding was assessed using genetic markers at eight populations. Four pollination treatments were assessed: cross-pollination, self-pollination, autogamous pollination and open (insect) pollination. Boronia falcifolia was found to be highly self-compatible, frequently setting seeds from autogamous pollination. There were no significant differences between the autogamous, self and cross pollen treatments for any measures of reproductive success (pollen tube growth, fruit set, swollen locules and seed production). Insect activity resulted in fewer seeds per fruit than hand cross pollination, although pollinator visits were few. All populations studied were highly inbred. Autogamous self-pollination is widespread in B. falcifolia and this combined with its ability to vegetatively regenerate enhances its potential for survival when pollinators are few.     

Tibouchina pulchra (Melastomataceae): reproductive biology of a tree species at two sites of an elevational gradient in the Atlantic rainforest in Brazil

Low-temperature environments interfere with plant reproduction by reducing the frequency of pollinators, and this may favour reproductive strategies such as self-pollination and apomixis. Tibouchina pulchra is a common tree species that occurs at high and low sites of the Brazilian Atlantic rainforest. This study focussed on the pollination biology and breeding system of this species, describing the pollinators and the reproductive success at the two sites of an elevational gradient. Observations were made to determine extent of flowering and fruiting, to identify the richness and abundance of pollinators, and to record data on the floral and reproductive biology at these two sites. Despite more dense flowering at the high site, five visits of bees (two species) were recorded during the observation time (60?h), whereas at the low site there were 948 visits (seven species) during the same period. In contrast with the low site, the flowers of the high site released and received few pollen grains on the stigma. At the high site less fruit was set with fewer seeds as a result of open pollination than at the low site; at that site, however, more seeds were obtained from cross-pollination than at the low site. Tibouchina pulchra is self-compatible; however it is not apomictic and needs pollinators for seed set at both sites. Life-history traits other than the breeding system, for example more dense flowering, advantage of greater fertility in cross-pollination, and multiple reproductive events during the lifetime of the tree may reduce inbreeding depression, increase the hybrid vigour, and balance the lack of pollinators at the high site.     

Reproductive Biology of <Emphasis Type="Italic">Asarum sieboldii Miq</Emphasis>.

The seasonal developmental rhythm, floral and fruit morphology, anthesis, and fructification of Asarum sieboldii were studied in a natural plant community in the southern part of the Russian Far East. The flower structure was investigated in ditails. It was found that the flower does not have a gynostemium. The flowers are protogynous. At the first anthesis stage, the anthers are closed and cross-pollination may be realized by ants (Hymenoptera) or flies (Dolichopodidae, Diptera). At the second stage of anthesis, there is direct contact of anthers with the pistil stigma and self-pollination occurs. The perianth is involved in the formation of fruit. The fruit is a six-locular, fleshy, half-inferior capsule. Asarum sieboldii has a high productivity of fruits and seeds. The fruit set is 89% after self-pollination. Viable seeds per fruit is 29 ± 2, the seed set is 69 ± 5%. The agents of seed dissemination are ants: Leptothorax acervorum and Myrmica ruginodis (Formicidae, Hymenoptera).     

Pollination and self-interference in Nothofagus

Interference between male and female functions within a monoecious plant may hinder crossing and decrease seed set. We assessed the probability of self-pollination and the effect of self-pollination on cross-pollination for two self-incompatible species: Nothofagus obliqua and N. nervosa. The probability of self-pollination was studied by tracking the phenologies of staminate and pistillate flowers, including an analysis of stigmatic receptivity. Pure and mixed pollinations were performed in order to evaluate the effect of self-pollination upon cross-pollination. Phenological observations suggest that self-pollination is highly likely in both species. Compared to pure cross-pollination, the application of self-pollination prior to cross-pollination resulted in lower numbers of germinated pollen grains for both species, and also in a lower production of viable seeds in N. nervosa. The low proportion of viable seeds often observed in natural populations of N. obliqua and N. nervosa may be related to self-pollination.     

Floral and reproductive biology of Drosophyllum lusitanicum (L.) Link (Droseraceae)

We studied the floral and reproductive biology of Drosophyllym lusitanicum (Droseraceae), a species endemic to the western Iberian Peninsula and northwest Morocco. Flowering lasted from March to August, peaking in April. The species is clearly homogamous, with pollen germination and stigma receptivity occurring even in preanthesis. This was reflected in the high rates of fruit set and seed set in bagged inflorescences. Fructification did not differ significantly between different pollination treatments, although we did find differences between some treatments in the numbers of viable seeds per flower and fruit. However, seed weight did not differ significantly. The importance of self-pollination over cross-pollination was also supported by the low percentages of fructification (24.67%) after emasculation and open pollination. Metameric deviations were seen in flowers, although this abnormality was not translated as any reproductive benefit or disadvantage (fructification, number or weight of seeds) in comparison with normal flowers.     

Effects of pollen shortage and self-pollination on seed production of an endangered tree, Magnolia stellata

BACKGROUND AND AIMS: Pollen limitation is a significant determinant of seed production, and can result from both insufficient pollen quantity (pollen shortage) and quality (mainly relating to self-pollination). For animal-pollinated tree species with large floral displays, pollen limitation may be determined by a balance between increased pollen quantity due to increased attractiveness for pollinators, countered by increased self-pollination due to increased geitonogamy. The contributions of pollen shortage and self-pollination on seed production were quantitatively examined in the natural pollination of an insect-pollinated, dichogamous, endangered tree, Magnolia stellata, which has a large, showy floral display. METHODS: Manual self- and cross-pollinations were conducted to determine the effects of selfing on seed production. The outcrossing rate was measured using microsatellite analyses of open-pollinated seeds, and the embryo mortality rate caused by self-pollination was indirectly estimated. The frequency of ovule mortality due to pollen shortage was also inferred using the embryo mortality and ovule survival rates from natural pollination. KEY RESULTS: The average fruit set, seed set per fruit, and ovule survival rate per tree from hand cross-pollination were 1.37, 3.15, and 3.34 times higher than those from hand self-pollination, respectively, indicating that self-pollination causes inbreeding depression for fruit and seed set. The multilocus-outcrossing rate (t(m)) was intermediate, 0.632, and the primary selfing rate was 0.657. This indicates that frequent geitonogamous selfing occurs. The ovule mortality rate due to pollen shortage and the embryo mortality rate due to self-pollination were estimated to be 80.8 % and 45.9 %, respectively. CONCLUSIONS: It is concluded that seed production of M. stellata is strongly limited by both pollen shortage and self-pollination. Inefficient beetle-pollination and the automimicry system via asynchronous flowering might be responsible for the high level of pollen shortage and frequent geitonogamy. This is despite a large, showy floral display and the dichogamous system of the species.     

Reproductive biology of the epiphytic bromeliad Werauhia gladioliflora in a premontane tropical forest

The floral phenology, fruit and seed production, and self-compatibility of Werauhia gladioliflora, an epiphytic bromeliad with a wide distribution, were studied in a premontane forest in the Monteverde area in Costa Rica. The species presents the pollination syndrome of chiropterophily, and it is visited by the small bats Hylonycteris underwoodi and Glossophaga commissarisi (Glossophaginae). The population flowering period extended from October to early December (end of rainy season) and seed dispersal occurred from February to April (dry season). Most plants opened a single flower per night, either every day or at one-day intervals during the flowering period. In natural conditions, the average fruit set amounted to almost half of the potential output, but individual fecundity (number of seeds) remained high. Seed number per fruit and germination capacity after artificial selfing and out-crossing treatments did not differ from natural pollination conditions. Werauhia gladioliflora exhibited high levels of autonomous self-pollination and self-compatibility at the individual and population level, characters associated with the epiphytic habitat. These reproductive traits are also associated with early colonizer species, yet life history traits, such as seed dispersal, seedling establishment success, and growth, are likely to have a major role in determining the presence of this species in the successional vegetation patches scattered over the studied premontane area.     

Polyploidy and polyembryony in Anemopaegma (Bignonieae, Bignoniaceae)

Polyploidy is a key process in plant evolution, with the asexual formation of embryos representing a way through which polyploids can escape sterility. The association between polyploidy and polyembryony is known to occur in Bignoniaceae. In this study, we investigate polyembryony in four polyploid species of Anemopaegma: A. acutifolium, A. arvense, A. glaucum and A. scabriusculum as well as in one diploid species, A. album. Polyembryony was observed only in polyploid species. We used seed dissection and germination tests to compare the number of polyembryonic seeds. We tested how the pollen source influences the number of polyembryonic seeds and the number of embryos per seed and tested the correlation between the number of viable seeds per fruit and mean number of embryos per seed. The number of polyembryonic seeds observed by seed dissection was higher than the number of polyembryonic seeds determined by the germination test, with the number of embryos produced per seed being higher than the number of seedlings. The dissection of seeds of A. glaucum indicated that a higher number of polyembryonic seeds and a higher number of embryos were present in seeds from cross-pollination than in seeds from self-pollination. On the other hand, germination tests indicated that a higher number of polyembryonic seeds were present in fruits from self-pollination than from cross-pollination. The mean number of embryos per seed was not influenced by the number of viable seeds per fruit in fruits from open pollination. These results indicate a positive relationship between polyembryony and polyploidy in Anemopaegma.     

Reproductive ecology of <Emphasis Type="Italic">Agave colorata</Emphasis>: the importance of nectar-feeding bats and the germination consequences of self-pollination

Agave colorata is a paniculate agave distributed along the migratory route of the nectar-feeding bat Leptonycteris yerbabuenae. In this paper, we evaluate the importance of nectar-feeding bats in the reproduction of A. colorata in a population in Sonora, Mexico, and describe the germination consequences of self-pollination. We estimated abundance using five plots and set pollination treatments to evaluate the importance of bats. We recorded 14.8?±?6.8 plants/400 m², with a bimodal size distribution. Flowers are protandrous and visited mainly (>?20 visits/plant/30 min) by L. yerbabuenae. Pollination exclusion experiments showed that flowers excluded from diurnal visitors had maximum fruit set values (0.49?±?0.42), while the autonomous self-pollination treatment had the lowest value (0.03?±?0.06). Similarly, the greatest number of viable seeds per fruit was recorded in the diurnal exclusion treatment, while the greatest number of empty seeds was observed in the self-pollination treatment. Fruit set values among untreated plants varied from 32 to 54%, with a mean value of 41.8%. Seeds derived from self-pollination had a narrower window of opportunity for germination compared to seeds derived from nocturnal pollination. Self-pollinated seeds had lower germination, rate of germination or lag time in response to light, osmotic potential and heat shock treatments, compared to other pollination treatments, revealing an inbreeding cost. Overall, our results show that L. yerbabuenae is the likely major pollinator of the studied A. colorata population. However, under pollinator limitation A. colorata may produce seeds by autonomous self-pollination, at a cost expressed as lower germination.     

Reproductive strategies of diploid and polyploid populations of arcticDraba (Brassicaceae)

132 cultivated populations (2x–16x) of 15 arctic-alpine species ofDraba were investigated to clarify a possible relationship between reproductive strategies and polyploid evolution in the genus. The populations were exclusively sexual and produced viable seed after spontaneous self-pollination, but showed large variation both in traits promoting cross-pollination and in autogamous fruit and seed set. Traits promoting cross-pollination, e.g., floral display, protogyny, and delayed selfing, were positively correlated, and these traits were negatively correlated with autogamous fruit and seed set. All diploid and many polyploid populations had high autogamous seed set and small, unscented, non-protogynous, and rapidly selfing flowers. In contrast, all populations with low autogamous seed set and large, scented, and strongly protogynous flowers with distinctly delayed selfing were polyploid. These results are consistent with those previously obtained from enzyme electrophoresis, suggesting that the genetically depauperate diploids are extreme inbreeders and that the highly fixed-heterozygous polyploids vary from extreme inbreeders to mixed maters. The reproductive data lend additional support to the hypothesis that allopolyploidy in arcticDraba serves as an escape from genetic depauperation caused by uniparental inbreeding at the diploid level.     

Pollination biology in an endangered rocky mountain toadflax (Linaria cavanillesii)

Knowledge about the reproductive system of species inhabiting rocky habitats is scarce. The reproductive biology (floral biology, experimental pollination, insect visits, inbreeding depression, and seed predation) of the rupicolous Linaria cavanillesii was analyzed under field and experimental conditions. Self-compatibility was revealed by the high fruit set, seed set, and seed mass in the pollination experiment. Furthermore, results disclose that this species does not need insect visitors for seed production since fruit set after autonomous self-pollination was similar to that by hand cross-pollination. Self-offsprings were not affected by a strong degree of inbreeding depression in early life-cycle stages. Seed predation by Cucurlionidae is the main limiting factor of fruit and seed production in this species. Contrary to other perennial species of Linaria previously studied, L. cavanillesii represents the first clear report of self-fertility.     

Formation of Multiple or Adventive Embryos in Epidendrum nocturnum Jacq (Orchidaceae)

Under greenhouse conditions, Epidendrum nocturnum Jacq. plantsproduce fruits by both self-fertilization and cleistogamy. Althoughadapted to these reproductive processes the species respondalso to cross-pollination. Seeds without embryos and with oneembryo are usual but occasionally seeds with two, three or fourembryos are produced. Multiple embryos are formed by polyembryonyand apomixis. Epidendrum nocturnum, self-pollination, cleistogamy, apomixis, polyembryony, supernumerary embryos     

Movement herkogamy in Kosteletzkya virginica: Effect on reproductive success and contribution to pollen receipt and reproductive assurance

Herkogamy may act as a mechanism to reduce interference between the reproductive functions of female and male organs, but too great a distance between stigmas and anthers may also decrease the outcross pollen transfer and male and female fitness. Our goal was to quantify the effect of movement herkogamy in Kosteletzkya virginica on reproductive success and its contribution to pollen receipt and reproductive assurance. Field investigations and hand-pollination experiments were performed to test: (1) the relationship between herkogamy before curvature of un-pollinated lobes and reproductive success under pollinator exclusion; (2) the contribution of movement herkogamy to pollen receipt; and (3) the relationship between pollen load and seed set. We noted that variation in herkogamy before curvature of un-pollinated lobes did not affect the outcome of autogamous self-pollination measured by fruit set and mean number of seeds per fruit. Under natural conditions, 39% of pollen grains deposited per flower were from autogamous self-pollination via movement herkogamy resulting in contact between anthers and stigmas. The relationship between the amount of pollen grains and the number of seeds per capsule was highly significant. Flowers producing four or five seeds received more pollen grains than those producing only one seed. Our data provides experimental evidence that movement herkogamy, which decreases the separation between anthers and stigmas and results in delayed self-pollination, contributes to pollen receipt and further enhances seed set when pollinators are scarce or absent.     

Movement herkogamy in Kosteletzkya virginica: Effect on reproductive success and contribution to pollen receipt and reproductive assurance

Herkogamy may act as a mechanism to reduce interference between the reproductive functions of female and male organs, but too great a distance between stigmas and anthers may also decrease the outcross pollen transfer and male and female fitness. Our goal was to quantify the effect of movement herkogamy in Kosteletzkya virginica on reproductive success and its contribution to pollen receipt and reproductive assurance. Field investigations and hand-pollination experiments were performed to test: (1) the relationship between herkogamy before curvature of un-pollinated lobes and reproductive success under pollinator exclusion; (2) the contribution of movement herkogamy to pollen receipt; and (3) the relationship between pollen load and seed set. We noted that variation in herkogamy before curvature of un-pollinated lobes did not affect the outcome of autogamous self-pollination measured by fruit set and mean number of seeds per fruit. Under natural conditions, 39% of pollen grains deposited per flower were from autogamous self-pollination via movement herkogamy resulting in contact between anthers and stigmas. The relationship between the amount of pollen grains and the number of seeds per capsule was highly significant. Flowers producing four or five seeds received more pollen grains than those producing only one seed. Our data provides experimental evidence that movement herkogamy, which decreases the separation between anthers and stigmas and results in delayed self-pollination, contributes to pollen receipt and further enhances seed set when pollinators are scarce or absent.     

Role of antioxidant defense system and biochemical adaptation on stress tolerance of high mountain and steppe plants

Plants growing in small fragmented populations under stressful environmental conditions may have reduced sexual reproduction. This can cause low gene flow between populations and eventually extinction. Here we report on a pollination experiment with Sorbus torminalis, a rare fleshy-fruited tree with a submediterranean distribution in Europe. At the northern limit of its range in SE-Denmark two relatively small and isolated populations were studied for effects of seven pollination treatments on fruit production and on the timing of fruit abortion. There was evidence that lack of pollination and spontaneous self-pollination caused particularly high fruit abortion, which indicates that apomixis is unlikely and spontaneous self-pollination not efficient. Fruit abortion was delayed after hand pollination, which suggests limitation by pollen quantity. Self-pollination caused earlier abortion than experimental cross-pollination within or between populations indicating inbreeding depression. There was no evidence for outbreeding depression as measured by fruit abortion. We conclude that generative reproduction of S. torminalis is reduced on its northern distribution limit and that it might be negatively affected by pollen limitation and inbreeding effects, which have not been compensated for by increased self-compatibility or apomixis.     

Reproductive versatility in legumes: the case of amphicarpy in Trifolium polymorphum

Amphicarpy is a fascinating reproductive strategy, defined as fruit produced both below the soil surface and as aerial fruit on the same plant. Trifolium polymorphum is a grassland species subject to herbivory that combines amphicarpy with vegetative reproduction through stolons. Underground flowers have been described as obligate autogamous and aerial ones as self‐compatible allogamous, with aerial floral traits favouring cross‐pollination. In the present work we performed different pollination treatments on aerial flowers to analyse rates of pollen tube development and offspring fitness, measured as fruit set, seed production and germination percentage. This last variable was compared to that of seeds produced underground. No significant differences were found between fruit set in self‐ and cross‐pollinations. Seed production was higher in self‐pollinations, which is consistent with the higher rate of pollen tube development observed in self‐crosses. Spontaneous self‐pollination is limited in aerial flowers; thus pollen transfer by means of a vector is required even within the same flower. Germination tests showed that aerial seeds produced after self‐ and cross‐pollination did not differ in fitness, but underground seeds had higher germination percentage than aerial ones. Thus, we conclude that T. polymorphum has a mixed mating system. In grasslands with heavy grazing pressure, clonal propagation and underground seed production ensure persistence in the field. An intermediate level of selfing in aerial flowers ensures offspring, but morphological (herkogamy) and functional (dicogamy) floral traits maintain a window to incorporate genetic variability, allowing the species to tolerate temporal and spatial pressures.     

濒危植物焕镛木的兼性无融合生殖

2001～2002年连续两年在广西环江木论和广西罗城大黄泥的2个焕镛木(Woonyoungia septentrionalis(Dandy)Law)自然种群中,对单性异株的濒危植物焕镛木进行繁育系统测定,对即将开花的雌花花蕾分别进行套袋、套网、人工授粉处理,并用自然授粉雌花作对照,其座果率和结实率统计结果表明:自然授粉、人工授粉、套袋和套网处理的花均能结实,但它们的座果率和结实率存在较大的差异.在两个种群中,人工授粉和自然授粉的总结实率(PERS)均比套袋和套网处理的高,其中人工授粉的最高,套网处理的最低.由此可见,焕镛木既能通过有性生殖方式结实,又能通过无融合生殖方式结实,而且这两种生殖方式获得的种子均能萌发成幼苗,由此断定,焕镛木的繁育系统为兼性无融合生殖.这是首次报道木兰科植物存在无融合生殖现象.     

濒危植物焕镛木的兼性无融合生殖

2001—2002年连续两年在广西环江木论和广西罗城大黄泥的2个焕镛木(Woonyoungia septentrionalis (Dandy) Law)自然种群中,对单性异株的濒危植物焕镛木进行繁育系统测定,对即将开花的雌花花蕾分别进行套袋、套网、人工授粉处理,并用自然授粉雌花作对照,其座果率和结实率统计结果表明：自然授粉、人工授粉、套袋和套网处理的花均能结实,但它们的座果率和结实率存在较大的差异。在两个种群中,人工授粉和自然授粉的总结实率(PERS)均比套袋和套网处理的高,其中人工授粉的最高,套网处理的最低。由此可见,焕镛木既能通过有性生殖方式结实,又能通过无融合生殖方式结实,而且这两种生殖方式获得的种子均能萌发成幼苗,由此断定,焕镛木的繁育系统为兼性无融合生殖。这是首次报道木兰科植物存在无融合生殖现象。     

Inbreeding effects on fitness traits in the heterocarpic herb Leontodon autumnalis L. (Asteraceae)

Heterocarpic plants are characterized by the production of distinct types of fruits that usually differ in their ecological behavior. In the Asteraceae, differences are mainly found between peripheral non-dispersal and central dispersal achenes (single-seeded fruits). Inbreeding depression is considered as an evolutionary force as it may reduce several fitness traits, and in the case of heterocarpic plants, it could influence fitness traits (e.g., seed set, germination rate, growth rate) of each fruit morph, which may have important ecological and evolutionary consequences. In particular, differential effects on fitness traits and dispersal of selfed and outcrossed progeny can strongly determine the viability of extant populations and the potential to colonize new habitats. We conducted a hand-pollination experiment in greenhouse conditions to test whether inbreeding affects the fitness of achene morphs in the heterocarpic herb Leontodon autumnalis (Asteraceae). Results show that achene morphs significantly differ in their ecological behavior, peripheral achenes germinating more and faster than central achenes. The significant interaction between pollination treatment and achene morph for germination probability might indicate a link between dormancy and mating system in L. autumnalis: germination was higher for outcrossed achenes in central achenes whereas the opposite pattern was exhibited by peripheral achenes. Selfing dramatically reduced seed set, probably as a consequence of strong self-incompatibility mechanisms rather than inbreeding effects. Inbreeding depression significantly affected late life-cycle traits, such as growth rate and biomass at flowering. Overall, results suggest that inbreeding depression seems to be an important selective force maintaining outcrossing in L. autumnalis.