Distribution of flower morphs, ploidy level and sexual reproduction of the invasive weed Oxalis pes-caprae in the western area of the Mediterranean region

Background and Aims: Oxalis pes-caprae is a widespread invasive weed in regions witha Mediterranean climate. In its native habitat (southern Africa)this species has been reported as heterostylous with trimorphicflowers and a self- and morph-incompatible reproductive system.In most of the areas invaded, only a pentaploid short-styledmorphotype that reproduces mainly asexually by bulbils is reported,but this has only been confirmed empirically. This study aimsto analyse the floral morph proportions in a wide distributionarea, test the sexual female success, and explain the causesof low sexual reproduction of this species in the western areaof the Mediterranean Basin. Methods: Fifty-five populations of O. pes-caprae were sampled in theIberian Peninsula and Morocco to evaluate the floral morph ratioand individual fruit set. In plants from a dimorphic population,hand-pollination experiments were performed to evaluate theeffect of the pollen source on pollen tube growth through thestyle. The ploidy level and genome size of individuals of eachfloral morph were analysed using flow cytometry. Key Results: From the populations studied 89·1 % were monomorphic,with most of them containing the short-styled (SS) floral morph,and 10·9 % were dimorphic containing long-styled(LS) and SS morphs. In some of these, isoplethy was verifiedbut no fruit production was observed in any population. A sterileform was also recorded in several populations. Hand-pollinationexperiments revealed that pollen grains germinated over recipientstigmas. In intermorph crossings, pollen tubes were able todevelop and fruit initiation was observed in some cases, whilein intramorph pollinations, pollen tube development was sporadicand no fruit initiation was observed. All individuals withineach floral form presented the same DNA ploidy level: SS plantswere pentaploid and LS and the sterile form were tetraploid. Conclusions: The low or null sexual reproduction success of this speciesin the area of invasion studied seems related with the highfrequency of monomorphic populations, the unequal proportionof floral morphs in dimorphic populations and the presence ofdifferent ploidy levels between SS and LS morphs. The discoveryof the occurrence of an LS floral morph and a sterile form,whose invading capacity in these areas is as yet unknown, willbe valuable information for management programmes.     

THE BREEDING SYSTEM OF OXALIS SUKSDORFII

The Pacific Coast species Oxalis suksdorfii (section Corniculatae) is morphologically tristylous. Flowers of the 3 kinds of plants present in natural populations differ in style length, stamen length, pollen size, stigma size and orientation, and stylar pubescence. Experimental studies and field observations indicate that plants with long-styled flowers are weakly self-compatible and show little differentiation in size or compatibility relationships of pollen from the 2 sets of stamens. Plants with mid-styled flowers have strongly differentiated pollen, but produce few capsules or seed after any artificial or natural pollinations. Plants with short-styled flowers are self-incompatible and show slight pollen differentiation. The data presented suggest that O. suksdorfii approaches functional dimorphism since the mid-styled form contributes little pollen and few seeds in sexual reproduction. The species may be in the process of losing the mid-styled form completely and provides a model of certain physiological and morphological changes which may have accompanied elimination of the mid-styled form in other Oxalis species. The abundance of plants with mid-styled flowers in natural populations suggests, however, that this form may be retained because it contributes to general population fitness, or because the genetic control of heterostyly in this species prevents its elimination.     

Flexible mating system in distylous populations of <Emphasis Type="Italic">Psychotria carthagenensis</Emphasis> Jacq. (Rubiaceae) in Brazilian Cerrado

In family Rubiaceae distyly is very common, and large variation in heterostyly characteristics has been previously documented. Analysis of these variations, even within a species, is very useful to our understanding of the evolutionary process that caused this polymorphism. For this reason, the goal of this study is to investigate the floral morphology and diallelic incompatibility system of three populations of Psychotria carthagenensis. The three studied populations of P. carthagenensis occur in forest fragments in protected areas in an urban matrix in the Municipality of Campo Grande, Mato Grosso do Sul State, Brazil. Reciprocal position of style length and stamen height was found in populations, and in general short-styled flowers were larger than long-styled flowers. All populations presented 1:1 morph ratio between short-styled and long-styled flowers. Regarding breeding system, flowers of P. carthagenensis were self-compatible and compatible within plants of the same morph, and there was no pollen limitation in the populations in any case. In only one of the populations were there differences in the extent of compatibility between morphs, with the long-styled morph being more self-compatible than the short-styled morph. The reproductive strategy of these populations can be advantageous in case of fluctuation of pollinator activity.     

Sexual reproduction of the pentaploid,short‐styled Oxalis pes‐caprae allows the production of viable offspring

Reproduction is a key factor for the successful establishment and spread of introduced species. Oxalis pes‐caprae is a tristylous species with a self‐ and morph‐incompatibility sexual system that, in the invaded range of the western Mediterranean Basin, has been found to reproduce asexually because only the pentaploid, short‐styled morph (5x S‐morph) was introduced. The objective of this study was to test the ability of the 5x S‐morph of O. pes‐caprae to produce viable offspring in the absence of compatible mates, exploring the hypothesis that new morphs could have emerged by sexual reproduction events of the initially introduced morph. Pollen germination, pollen tube development, fruit and seed production, seed germination and offspring ploidy levels were analysed after controlled hand‐pollinations to assess self‐ and morph‐incompatibility and production of viable gametes by the 5x S‐morph. The self‐incompatibility system is still operating, but a partial breakdown in the morph‐incompatibility system combined with the production of viable gametes was observed, allowing sexual reproduction of the 5x S‐morph in the invaded range. The ability of the 5x S‐morph to reproduce sexually may have major consequences for the dynamics of invasive populations of O. pes‐caprae and could be one of the factors involved in the occurrence of new floral morphs in this invaded range.     

Reproductive ecology in the endemic Primula apennina Widmer (Primulaceae)

Abstract

Disassortative mating in distylous self-incompatible species should result in the equilibrium of morph types in natural populations. Deviation from isoplethy may affect pollen transfer, and in isolated populations it could lead to Allee effect and genetic drift. Pollen limitation has been found to occur in several distylous species, for which mating opportunities are actually reduced to half population. In this study, we investigated the reproductive features and pollination ecology of the narrow endemic Primula apennina. We recorded equilibrium of morph frequencies in the studied population, reflecting the comparable fecundity found in the two morphs. Long-styled flowers produce more pollen grains of smaller size than short-styled ones: we hypothesize that in thrum flowers, pollen is more easily removed by the insect pollinator Macroglossum stellatarum, resulting in equal pollen amounts carried to both short styles and long styles. This lower pollen transfer efficiency from long-styled to short-styled flowers is also reflected in legitimate pollen–ovule ratio values. Despite results show no evidence of imminent threats to population persistence at study site, the strict dependence on one or very few pollinator species, and ecological traits, may increase extinction risks in the long-term period.     

Reproductive strategy of the invasive Oxalis pes-caprae: distribution patterns of floral morphs, ploidy levels and sexual reproduction

Oxalis pes-caprae, a tristylous flowering plant native to South Africa, is described in the western Mediterranean basin as an asexual—only 5x short-styled morph (5x S-morph) invasive weed losing all mating partners after introduction. The objective of this study was to reassess the patterns of floral morph and cytotype distribution and the sexual reproduction ability in this invaded range. For that, floral morph and cytotype composition were evaluated in 39 populations of O. pes-caprae in a methodical sampling. The reproductive success of natural populations was assessed as fruit and seed production and seed germination for all floral morphs and cytotypes detected. Self- and morph-incompatibility were also studied with controlled hand pollinations. A remarkable diversity in floral morph and cytotype composition was observed. Furthermore, we observed successful sexual reproduction in several localities across the surveyed area. The S-morph is still dominant in this invaded area, and although it was mostly 5x, an additional cytotype (4x) was also recorded. Records of both a mid-styled morph (M-morph) and an area with trimorphic populations of this species are reported here for the first time in the invasive range of the Mediterranean basin. The long-styled morph appears to occur randomly across the surveyed area, while the M-morph is concentrated mainly in Estremadura province (Portugal), where a breakdown in the incompatibility system was observed. These distribution patterns may result from events of sexual reproduction after incompatibility breakdown and/or from multiple introduction events from the native area. The ability to reproduce sexually, undetected so far, may have important impacts in the population dynamics and major consequences for the adaptation and selection potential of O. pes-caprae in this invaded area.     

Gender specialization in <Emphasis Type="Italic">Palicourea demissa</Emphasis> (Rubiaceae), a distylous,hummingbird-pollinated treelet

Distyly has been interpreted as a mechanism that promotes cross-pollination among conspecific plants and as one of the routes leading to the evolution of dioecy. In one of the possible evolutionary pathways, pollinators may disrupt intermorph pollen flow, and, as a consequence, floral morphs may gradually specialize as either male or female (functional dioecy). Natural patterns of pollen deposition and fruit and seed production were estimated in Palicourea demissa (Rubiaceae) and used as parameters to assess functional gender differences between floral morphs. Pollen flow was asymmetrical in P. demissa. Long-styled flowers were more effective than short-styled flowers in pollen deposition towards compatible stigmas, whereas short-styled flowers were more effective in legitimate pollen receipt. Accordingly, short-styled plants produced more fruits and viable seeds than long-styled plants. The contributions of male and female function to the potential functional gender were equivalent in both morphs. However, the realized functional gender deviated significantly from the potential functional gender in both morphs, in which short-styled plants were more successful through their female function, but long-styled plants through their male function. If pollinators disrupt the complementarities of pollen transfer between the two morphs (asymmetric pollen flow), the expression of a more profitable gender is expected in each morph. Thus, our results support the hypothesis that dioecy may evolve in distylous populations through the gradual specialization of each morph as either male or female.     

Heterostylous morph differences in pollen transfer and deposition patterns in Primula sieboldii on a visitation by a queen bumblebee, measured with a semi-natural experimental system

Abstract Under a semi-natural setting the between-morph pollen exchange patterns were studied in distylous Primula sieboldii flowers by measuring pollen removal from the anthers on a single visit by a Bombus diversus tersatus queen, and stigmatic pollen deposition along the sequence of the visitation of the opposite-morph flowers by the bee. Despite the twofold larger number of pollen grains produced in a single flower of the long-styled morph compared to that of the short-styled morph, no significant difference in pollen removal from a flower was found between the morphs. The stigmas of the long-styled morph received significantly more opposite-morph pollen grains than those of the short-styled morph on a single visit by the bee. Sufficient legitimate pollen grains, surpassing the ovule number, were loaded on the stigmas of 27% and 17% of visited flowers of the long- and short-styled morphs, respectively. The short-styled morph could more efficiently donate pollen to the opposite morph stigmas than the long-styled morph.     

Stigma and style anatomy and ultrastructure in Italian Oxalis pes-caprae L. and their possible connection with self-incompatibility

The South-African Oxalis pes-caprae with trimorphic flowers is naturalised in many Mediterranean countries. In Italy only short-styled (S) populations are known for certain and the plant is believed to reproduce only asexually, due to self- and intramorph-incompatibility. This study aims to clarify anatomical, biochemical and ultrastructural features of the stigma and style of an Italian S population, also to define their possible role in incompatibility. Additional observations were also carried out on other Italian population and on short-, long- (L) and mid-styled (M) flowers from plants of South African origin. Morphological and biochemical features of flowers collected in different phenological stages during the whole flowering season were observed both under LM and TEM. In S flowers, three different zones could be distinguished in each stigma-style complex: zone I (stigmatic), zone II (substigmatic), zone III (stylar). The main differences concern the transmitting tissue: in zones I and III this is composed of loosely arranged cells with thick walls, with an abundant soft matrix which at anthesis is rich in mucopolysaccharides and lacks pectins. In zone II, it is more compact, with a less abundant wall matrix, at anthesis containing both mucopolysaccharides and pectins. In S flowers, subjected to illegitimate pollination, many pollen tubes penetrate the stigmatic papillae but apparently are arrested in zone II; only few—and mostly at the end of flowering period—succeed reaching zone III, where they encounter no further resistance to growth. Differently, after legitimate pollinations, pollen tubes succeed in crossing transmitting tissue of zone II, where cell walls of cells lying close to pollen tubes show a considerably reduced pectin content. In L and M flowers of South African origin, no peculiar transmitting tissue could be noticed in the substigmatic zone. In such flowers, pollen tubes seemingly grow easily from stigma to style both after legitimate and illegitimate pollinations. Results suggest that in S flowers the rigid transmitting tissue in zone II acts as a mechanical barrier for illegitimate pollen tubes, as the spaces between cells are narrower than the tube diameter and pectins maintain the rigidity of the cell walls, preventing cells from separating from one another. This obstacle can be overcome by legitimate pollen tubes, which make their way between cells, possibly releasing or activating specific pectinases. However, the blocking of illegitimate tubes is not absolute: a few of such tubes grow beyond zone II and reach the ovules, so that occasional fertilisation and embryo formation can be observed. In M and L flowers, different self-incompatibility mechanisms can be hypothesised.     

Shading by invasive shrub reduces seed production and pollinator services in a native herb

Plant invasions disrupt native plant reproduction directly via competition for light and other resources and indirectly via competition for pollination. Furthermore, shading by an invasive plant may reduce pollinator visitation and therefore reproduction in native plants. Our study quantifies and identifies mechanisms of these direct and indirect effects of an invasive shrub on pollination and reproductive success of a native herb. We measured pollinator visitation rate, pollen deposition, and female reproductive success in potted arrays of native Geranium maculatum in deciduous forest plots invaded by the non-native shrub Lonicera maackii and in two removal treatments: removal of aboveground L. maackii biomass and removal of flowers. We compared fruit and seed production between open-pollinated and pollen-supplemented plants to test for pollen and light limitation of reproduction. Plots with L. maackii had significantly lower light, pollinator visitation rate, and conspecific pollen deposition to G. maculatum than biomass removal plots. Lonicera maackii flower removal did not increase pollinator visitation or pollen deposition compared to unmanipulated invaded plots, refuting the hypothesis of competition for pollinators. Thus, pollinator-mediated impacts of invasive plants are not limited to periods of co-flowering or pollinator sharing between potential competitors. Geranium maculatum plants produced significantly fewer seeds in plots containing L. maackii than in plant removal plots. Seed set was similar between pollen-supplemented and open-pollinated plants, but pollen-supplemented plants exhibited higher seed set in plant removal plots compared to invaded plots. Therefore, we conclude that the mechanism of impact of L. maackii on G. maculatum reproduction was increased understory shade.     

Heteromorphic incompatibility and efficiency of pollination in two distylous Pentanisia species (Rubiaceae)

BACKGROUND AND AIMS: Distyly has been hypothesized to promote cross-pollination by reducing intrafloral and geitonogamous self-pollination, and enhancing intermorph pollination. Distylous plants typically display both reciprocal herkogamy and a heteromorphic incompatibility system, which allows mating only between morphs. Distyly and its pollination consequences were examined in two Pentanisia species with long-tubed flowers which are pollinated almost exclusively by butterflies. METHODS: Anther and stigma heights were measured to quantify reciprocal herkogamy. The type of incompatibility system was determined by observing pollen tubes and seed production following controlled hand pollination. Pollen loads on pollinators and stigmas were also examined to assess the efficiency of intermorph pollen flow. KEY RESULTS: Pentanisia prunelloides and P. angustifolia exhibit reciprocal herkogamy and a host of ancillary dimorphisms, including pollen colour, exine sculpturing, stigmatic papilla shape and floral-tube pubescence. Controlled hand-pollinations revealed the presence of a strong heteromorphic incompatibility system in both species. The site of incompatibility differed between the morphs; intramorph pollen tubes were blocked in the style of the short-styled morph and on the stigmatic surface of the long-styled morph. Butterflies carried pollen from the short- and long-styled morphs primarily on their head and proboscis, respectively. Natural pollination resulted in a higher proportion of pollen transfer from long- to short-styled plants than vice versa. Nevertheless, fruit set did not differ between morphs. CONCLUSIONS: Both Pentanisia species are fully distylous. Reciprocal herkogamy results in pollen from the two morphs being carried on different locations on pollinators' bodies, which in turn promotes intermorph pollination. Intramorph pollination does not result in fertilization, because of an effective heteromorphic incompatibility system.     

Dioecism of the genusCallicarpa (Verbenaceae) in the Bonin (Ogasawara) Islands

The morphology and function of the flowers of three species of the genusCallicarpa, C. glabra, C. nisnimurae andC. subpubescens, endemic to the Bonin Islands, revealed that all three species were dioecious. Male plants had short-styled flowers with sterile ovaries, while female plants had long-styled flowers with non-germinating inaperturate pollen grains. Such dioecism has never been reported from the family Verbenaceae. This curious sexual system with non-germinating pollen grains may have been maintained as a reward to insect pollinators.     

The influence of an invasive plant species on the pollination success and reproductive output of three riparian plant species

Besides competition for abiotic resources, an increasing number of studies show evidence of the effects of invasive species on the pollination success and reproductive output of indigenous species. We studied the effect of the invasive Impatiens glandulifera Royle on the process of reproduction in the indigenous Lythrum salicaria L. and Alisma plantago-aquatica L. and the naturalized Oenothera biennis L. The latter three species (target species) were transplanted into pots and placed in invaded and non-invaded areas. During flowering season of each of these species, we measured species composition and abundance of pollinators, pollinator behaviour, pollen deposition and female reproductive output of the target species. Competitive effects were found for L. salicaria, in which fewer pollinator species and number of foraging individuals were observed, and also, lower pollen deposition and seed set were measured in these invaded populations. In contrast, the reproductive success of A. plantago-aquatica and O. biennis was not affected by the presence of I. glandulifera. Our data indicate that when invasive and indigenous species show a large overlap in pollinator community, which is the case for I. glandulifera and L. salicaria, competition between these species can occur. When both species have a different pollinator community, pollination success and reproductive output is not affected, even when the indigenous populations are densely and abundantly invaded.     

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.     

Pollen transfer patterns in a distylous plant with overlapping pollen-size distributions

In this study we quantify the relative rates and amounts of between-morph (legitimate) cross-pollination, within-morph (illegitimate) cross-pollination and self-pollination in a natural population of distylous Gaertnera vaginata (Rubiaceae) endemic to the oceanic island of La Réunion in the Indian Ocean. Since pollen size distributions of each morph overlap we develop a method, based on chi-squared comparisons of observed to expected pollen size distributions, to quantify pollen transfer proficiencies. This method, unlike previous methods, does not assume an equal chance of pollen transfer for pollen grains in the region of overlap. The probability that a single pollen grain from a short-styled plant undergoes legitimate pollen transfer to long-styled flowers (4.19×10⁻²) was more than twice that for illegitimate transfer to other short-styled plants (1.56×10⁻²). In contrast, the probability that a single pollen grain from a long-styled flower undergoes legitimate pollen transfer to short-styled flowers (1.65×10⁻²) was no greater than that of illegitimate pollen transfer to other long-styled plants (2.15×10⁻²). The transfer proficiencies of individual pollen grains are thus highly asymmetric. However, because long-styled flowers produce significantly more pollen, the ratio of legitimate to illegitimate pollen on the stigmas of short-styled flowers (1.85) markedly exceeded that for long-styled flowers (1.11). Short-styled flowers incurred significantly higher levels of self-pollination than long-styled plants, emphasizing the importance for self-pollination to be removed before comparing stigmatic pollen loads. The method we propose could be applied to other distylous species with pollen size overlap between morphs and thus allow for a more widespread study of the pollination ecology of heterostylous species.     

Morph-specific patterns of variation in stigma height in natural populations of distylous Jasminum fruticans

The purpose of this study was to describe morph-specific patterns of stigma–anther separation and style curling in the distylous Jasminum fruticans . We also examined whether variation in floral traits is correlated with variation in seed production. Stigma–anther separation is more variable in short-styled plants than in long-styled plants. In all populations studied, some plants bear flowers that lack any stigma–anther separation. These plants have the pollen characteristics (size and number) and compatibility relations of short-styled plants. Comparison with other distylous species illustrates that the variability of stigma–anther separation in short-styled plants is a novel finding for a distylous species. Long-styled plants have greater stigma–anther separation than short-styled plants, styles are often curled and protrude from the corolla, and anthers are placed well within the corolla tube. The frequency of long-styled plants with curled styles and the mean degree of style curling were significantly correlated with style length. Short-styled plants have larger corollas than long-styled plants and never have curled styles. Morph ratios are always 50:50 in natural populations. Mean values of each floral trait in the two morphs were significantly correlated among populations. There were no consistent differences in fecundity of the two morphs nor any correlation between floral traits and seed set for each morph in natural populations. We discuss the potential causes and significance of the two morph-specific patterns we describe; reduced stigma–anther separation in short-styled plants and the presence of curled styles in long-styled plants.     

Patterns and sources of variation in pollen deposition and pollen tube formation in flowers of the endemic monoecious shrub Cnidoscolus souzae (Euphorbiaceae)

Pollen deposition and pollen tube formation are key components of angiosperm reproduction but intraspecific variation in these has rarely been quantified. Documenting and partitioning (populations, plants and flowers) natural variation in these two aspects of plant reproduction can help uncover spatial mosaics of reproductive success and underlying causes. In this study, we assess variation in pollen deposition and pollen tube formation for the endemic monoecious shrub Cnidoscolus souzae throughout its distribution range in Mexico, and determine how this variation is structured among populations, plants and flowers. We also infer the relative importance of pollen quantity and quality in determining pollination success in this species. While we found no evidence suggesting that pollen receipt limits C. souzae reproduction across 19 populations, we did find extensive variation in pollen load size and pollen tube number per flower. Total variation in pollen receipt and pollen tube number was mostly explained by intra‐individual and among‐population variance. Furthermore, pollen load size had a stronger effect on the number of pollen tubes at the base of the style than pollen germination rate, suggesting that pollen quantity may be more important than quality for pollen tube success in C. souzae. Our results suggest that both small within‐plant flower differences and broad‐scale differences in community attributes can play an important role in determining pollination success. We emphasise the need to evaluate patterns and sources of variation in pollen deposition and pollen tube formation as a first step in understanding the causes of variation in pollination success over broad spatial scales.     

Extremely high proportions of male flowers and geographic variation in floral ratios within male figs of Ficus tikoua despite pollinators displaying active pollen collection

Most plants are pollinated passively, but active pollination has evolved among insects that depend on ovule fertilization for larval development. Anther‐to‐ovule ratios (A/O ratios, a coarse indicator of pollen‐to‐ovule ratios) are strong indicators of pollination mode in fig trees and are consistent within most species. However, unusually high values and high variation of A/O ratios (0.096–10.0) were detected among male plants from 41 natural populations of Ficus tikoua in China. Higher proportions of male (staminate) flowers were associated with a change in their distribution within the figs, from circum‐ostiolar to scattered. Plants bearing figs with ostiolar or scattered male flowers were geographically separated, with scattered male flowers found mainly on the Yungui Plateau in the southwest of our sample area. The A/O ratios of most F. tikoua figs were indicative of passive pollination, but its Ceratosolen fig wasp pollinator actively loads pollen into its pollen pockets. Additional pollen was also carried on their body surface and pollinators emerging from scattered‐flower figs had more surface pollen. Large amounts of pollen grains on the insects' body surface are usually indicative of a passive pollinator. This is the first recorded case of an actively pollinated Ficus species producing large amounts of pollen. Overall high A/O ratios, particularly in some populations, in combination with actively pollinating pollinators, may reflect a response by the plant to insufficient quantities of pollen transported in the wasps’ pollen pockets, together with geographic variation in this pollen limitation. This suggests an unstable scenario that could lead to eventual loss of wasp active pollination behavior.     

Effects of pollen quantity and quality on reproduction and offspring vigor in the rare plant Scorzonera humilis (Asteraceae)

We studied the effects of pollinator exclusion, interparental distance, and supplementary hand pollination on reproduction and progeny vigor in Scorzonera humilis (Asteraceae), a rare plant of fragmented, nutrient-poor grasslands. Caged flowers produced no seeds and selfed flowers only very rarely, indicating that S. humilis is mainly self-incompatible. Seed production, seed mass, and seed germination following between-population crosses were consistently, but not significantly, higher than after within-population crosses. Seed set increased with local density of conspecifics, indicating that the reduced plant density in fragmented populations may reduce plant reproductive success. Seed set was pollen limited in all four populations studied. Supplementary hand-pollination strongly increased the survival of offspring, indicating that either pollinators transferred pollen from related individuals resulting in inbreeding depression in spite of the incompatibility system or that higher pollen loads increased pollen competition and the selectivity among gametes. In one of the populations, adding pollen from a different population strongly increased progeny fitness compared with both natural pollination and pollen supplementation from the same population. The results indicate that S. humilis is sensitive to inbreeding and that pollen limitation can reduce both the number and quality of offspring.     

绣球茜的二型花柱及其传粉生物学初步研究

首次对绣球茜(Dunnia sinensis Tutch)的花药和柱头高度、花粉和柱头形态,以及人工辅助授粉的结实情况等进行了研究.结果表明:绣球茜在同一居群中同时具有长花柱(Pin 型)和短花柱(Thrum)两种花型,长花柱植株的柱头和雄蕊高分别为9.61±0.36 mm和6.79±0.38 mm,短花柱则为6.11±0.56 mm和8.96±0.59 mm,表现出互补式雌雄异位的花部特征.通过人工辅助授粉,两种花型植株的自交和同型植株间异交都不结实,仅在型间异交方能正常结实,说明绣球茜中存在极强的自交不亲和和型内不亲和现象.在花粉与柱头形态方面:长柱型花的单花花粉量(38555.6±6258.4)显著地小于短柱型花(52145.45±8924.5)(t=4.009,P＜0.01),长柱花和短柱型花的胚珠数分别为38.73±1.85和39.1±2.25(t=-4.13,P＞0.01);长柱型花花粉粒的大小(极径21.27±0.70 μm)显著地小于短柱花(21.92±0.79μm)类型(t=3.890,P＜0.01),而柱头乳突大小长柱类型要大于短柱类型,表现出明显的二型性.研究结果表明绣球茜是一种典型的二型花柱植物.此外,对其传粉昆虫及昆虫访花行为的观察表明,蝶类(青风蝶属Graphium)和蜂类(熊蜂Bombus sp.和木蜂Xylocopa magnifica Smith)为绣球茜的主要访花昆虫和传粉昆虫,它们能够在两种不同花型植株之间有效地传粉.