Morph-ratio variation, population size and female reproductive success in distylous Pulmonaria officinalis (Boraginaceae)

Theory predicts that morph ratios in heterostylous populations are governed by negative frequency-dependent selection typically resulting in equal morph ratios at equilibrium. Previous work on the distylous perennial herb Pulmonaria officinalis, however, showed asymmetric mating between floral morphs and a weak self-incompatibility system, with the long-styled morph (L-morph) producing significantly higher seed set following intramorph crosses and even selfing than the short-styled morph (S-morph), two aspects thought to affect female fecundity and morph-ratio variation. Here, we evaluated morph ratios and population size of all known P. officinalis populations in the northern part of Belgium. Morph ratios deviated significantly from 1:1 (range 0.09-1 L-morph frequency, mean = 0.58). Relative fecundity of the S-morph (i.e. mean seed set of the S-morph/mean seed set of the L-morph) was on average 0.73, was positively related to the frequency of the L-morph, and reached 1 (similar levels of female fecundity) at an average L-morph frequency of 0.66 in the population. As some small populations had the S-morph in majority, our results suggest that local morph ratios are influenced both by the relative fecundity of L- and S-morph individuals and by stochastic processes in small populations.     

Floral display size and spatial distribution of potential mates affect pollen deposition and female reproductive success in distylous Pulmonaria officinalis (Boraginaceae)

In animal‐pollinated plants, both the spatial distribution of flowering individuals and the number of flowers that an individual displays affect pollen deposition rates and female reproductive success. Heterostylous species are likely to be particularly sensitive to the contingencies of spatial distribution, as they are reproductively subdivided into distinct mating groups, which usually exhibit self‐ and intra‐morph incompatibility and differ in floral morphology. In this paper, we explore the joint effects of both spatial distribution of potential mates and floral display size on morph‐specific pollen deposition rates and seed set patterns in two natural populations of Pulmonaria officinalis, a distylous species with a weak self‐incompatibility system. Both total stigmatic pollen load and the proportion of legitimate pollen decreased with increasing spatial isolation. Legitimate (intermorph) pollen transfer was, however, asymmetric and decreased more rapidly with decreasing proximity to a compatible legitimate mating partner in the S‐morph than in the L‐morph. Total stigmatic pollen loads per flower increased with increasing floral display size, indicating that large plants are disproportionately more visited than smaller individuals. However, because legitimate pollen deposition decreased with increasing floral display size, these results also suggest that larger numbers of flowers increase the degree of geitonogamous pollination. In both the L‐ and S‐morph, seed set significantly decreased with increasing isolation from a legitimate mating partner, but in the L‐morph seed set was less dependent on the spatial distribution of the S‐morph. In addition, seed set significantly increased with floral display size in the L‐morph, but not in the S‐morph. These findings indicate that the spatial distribution of potential mates and variation in floral display size may cause morph‐specific differences in pollen deposition rates and female reproductive success.     

The control of incompatibility in distylous Pulmonaria affinis Jordan (Boraginaceae)

In P. affinis, pin pollen is shorter on average than thrum pollen. Pins have more coronal hooks on stigmatic papillae than thrums, but gaps between papillae are relatively smaller for thrums. Pin stigmas receive more pollen than thrum stigmas. Thrum stigmas receive more (dissortive) pin pollen, but pin stigmas are assortively pollinated. Pollen only germinates when trapped below papilla coronas. On thrum stigmas, most trapped pollen is pin. Pollen germination is better on thrum stigmas than pin stigmas, and thrum stigmas show a close relationship between numbers of legitimate pollen grains, numbers of germinating grains, and numbers of pollen tubes in the style. There is no inhibition of illegitimate pollen germination. Illegitimate pollen tubes are inhibited in the style. Incompatibility operates by a combination of dissortive pollination, dissortive pollen trapping, and stylar pollen tube inhibition. All heteromorphic features differing between pins and thrums are implicated in the inhibition of within-morph fertilization in thrums.     

Cleistogamy in the rare high Andean perennial herb Cryptantha capituliflora (Boraginaceae)

 Axial and apical flowers of Cryptantha capituliflora were analyzed with regard to morphology and pollen tube growth to assess the occurrence of cleistogamy. Although intermediate floral forms do occur, cleistogamous flowers were significantly smaller than chasmogamous flowers, had fewer anthers, and showed a distinctive stigmatic surface. Chasmogamous flowers can be cross-pollinated. Nevertheless, the growth of self-pollen tubes in few chasmogamous buds jointly with flower characters suggests that these flowers can probably produce fruits through autonomous selfing. The mean seed number per fruit did not differ between fruits from chasmogamous and cleistogamous flowers. Cleistogamous flowers were only observed in axial inflorescences, which are completely covered by the leaf. Other species of section Cryptantha also show the same trend, with cleistogamous flowers located in the lower half of the stems. This pattern is discussed in relation to dissimilarities in the outcrossing opportunities between flower types within the plant. Received May 22, 2002; accepted November 14, 2002 Published online: March 20, 2003     

Size-dependent pollination efficiency in Anchusa officinalis (Boraginaceae): causes and consequences

Summary Bumblebees foraging on the self-incompatible Anchusa officinalis fly between near neighbour plants and between near neighbour inflorescences within plants. Although many-flowered plants attracted most bumblebees these plants received fewer visits on a per flower basis than smaller plants, and each bumblebee visited a smaller proportion of the flowers. The calculated effective visitation rate per flower was highest on plants of an intermediate size. If pollen-carryover was assumed to be limited the most efficient plant was predicted to be smaller since the proportion of fertilized flowers per bumblebee visit is expected to decrease further on the largest plants in relation to the total flower number. These predictions were tested by measuring fruit-set in the field. The percentage fruit-set decreased with plant size at all sizes that were investigated. That the most efficient plant was small indicates that pollen-carryover was indeed limited. However, the low percentage fruit-set associated with large size did not present a serious problem since the total estimated seed production per plant still increased with size. Selection favoring smaller plants may be low or absent in Anchusa.     

Pollen morphology in theBoragineae (Boraginaceae) in relation to the taxonomy of the tribe

The results of a comparative survey on pollen morphology in theBoragineae by means of light, scanning and transmission electron microscopy are presented and discussed in relation to the taxonomy of the tribe. Multivariate analyses lead to the recognition of 15 pollen morphotypes for which a discriminant key is proposed. The discriminatory characters concern mainly the stereostructural and ultrastructural features of the grains, such as tectum sculpture and aperture morphology, while the number of apertures appears variable within genera and even single species. Seven out of the 12 investigated genera, as currently circumscribed, are matched by palynological data:Anchusella, Borago, Brunnera, Elizaldia, Lithodora, Symphytum andTrachystemon. On account of aperture shape,Lithodora is however closer to theLithospermeae than to theBoragineae. Other genera, and in particularNonea, show a wide variation in tectum ornamentation, shape of grains and number of apertures. Palynological data do not support a broad concept of the genusAnchusa, and point to the autonomy of the satellite generaHormuzakia, Gastrocotyle, Phyllocara, Pentaglottis andCynoglottis.     

Pollen morphology of the tribes Eritrichieae and Cynoglosseae (Boraginaceae) in the Iberian Peninsula and its taxonomic significance

DÍEZ, M. J. & VALDÉS, B., 1991. Pollen morphology of the tribes Eritrichieae and Cynoglosseae (Boraginaceae) in the Iberian Peninsula and its taxonomic significance.
The pollen morphology of 33 species of Boraginaceae from the Iberian Peninsula belonging to the tribes Eritrichieae and Cynoglosseae has been studied by light and scanning electron microscopy. The results confirm the eurypalinous character of this family, in which a large number of species can be recognized by their pollen characters.
The pollen of these two tribes is basically heterocolpate, a type which is very uncommon in the angiosperms, with 6, 8 or 10 apertures, sometimes with ectoapertures anastomosed at the equator (ectocingulum), or diorate, minute or small in size, outline elliptic or rectangular-elliptic in equatorial view, with or without a constriction at the equator, exine 0.5-1.0 urn thick and the tectum psilate with granules around the colpi. The similarity in shape and apertural system found in several genera such as Asperugo, Gyrocarion and Omphalodes, and some species of Myosotis, does not permit the two tribes to be distinguished on pollen characters. The generic limits of Cynoglossum and the infrageneric classification of Myosotis are discussed.     

The influence of enhanced UV-B radiation on the spring geophyte Pulmonaria officinalis

Pulmonaria officinalis is an understorey spring geophyte, which starts its vegetative period before full foliation of the tree storey. During its early growth phase it is exposed to full solar radiation, therefore the enhanced UV-B radiation could present a threat to this species. An outdoor experiment in which potted plants were exposed to below ambient, ambient, and above ambient (corresponding to 17% ozone reduction) UV-B radiation, was conducted in order to evaluate the radiation effects. The amount of photosynthetic pigments and photochemical efficiency of PSII were not affected, but the amount of UV-B absorbing compounds was lower in plants grown under reduced UV-B. This change was measurable after only fourteen days in reproductive shoots, while in the vegetative shoots, it was not detectable until after three months. The leaves of P. officinalis are variegated and the light green spots became less transparent to PAR under enhanced UV-B. The results reveal that under simulated 17% ozone depletion the harmful effects of UV-B on the measured parameters were negligible.     

中国紫草科破布木属花粉形态和外壁超微结构

为了深入探讨紫草科（Boraginaceae）的分类问题,用光学显微镜和扫描电子显微镜观察了该科破布木属（CordiaL.) 10种植物的花粉形态和外壁超微结构。发现该属花粉具三孔、三孔沟、三拟孔沟和三合沟4种萌发孔类型。外壁表面具微刺状纹饰、刺状纹饰、网状纹饰和不规则的条纹网状纹状。破布木属的花粉特征表明,该属花粉在紫草科中既是独特的分类群,又是比较原始的属种。     

Pollen deposition in country villages of Eastern Liguria (Northern Italy)

Summary Recent pollen rain in 14 country villages of Ligurian hinterland was examined, in the framework of pollen deposition studies based upon moss polsters analysis, now in progress. The above mentioned localities are prevailingly situated in the Trebbia, Aveto and Vara valleys, within 300 and 1000 m a.s.l. For each locality a moss sample was examined (two for Torriglia: north and south) consisting of several sub-samples from various zones of the built-up area. All the samples have proved rich in pollen and provided spectra in accordance with qualitative and quantitative features of the urbanized areas vegetation and the spontaneous one of the neighbourhood. Sticking to general considerations, an attempt was made to compare the present results with those of the city area of Genova, previously obtained with the same methods.     

Anatomy and evolution in MacaronesianEchium (Boraginaceae)

The endemic Macaronesian members of the genusEchium (Boraginaceae) were examined anatomically to elucidate their relationships. Vessel length to breadth ratio was used as the initial guide to the relative primitive or derived nature of each taxon. Together with other features (e.g. trichome structure) it was possible to establish the phylogenetic pathways within this recently evolved relict group (Fig. 1).     

Bourreria (Boraginaceae) in tropical Africa

Five species of Ehretia in eastern Africa are shown to be better placed in the currently entirely American genus Bourreria . The new species B. lyciacea from S Somalia and E Kenya is described and illustrated. New combinations are B. petiolaris, B. nemoralis, B. orbicularis and B. teitensis .     

中国紫草科天芥菜亚科花粉形态及其系统学意义

为了深入研究紫草科Boraginaceae的分类问题,用光学显微镜和扫描电子显微镜观察了中国紫草科天芥菜亚科Heliotropioideae天芥菜属Heliotropium 6种,砂引草属Messerschmidia 2种和紫丹属Tournefortia 1种植物的花粉形态.它们的花粉为长球形,赤道面观为椭圆形,极面观为六裂圆形或八裂圆形,少数为三角形.萌发孔有三种类型:(1)三孔沟与三假沟交替排列;(2)四孔沟和四假沟交替排列;(3)三孔沟.外壁表面具微弱的小穿孔,皱波状纹饰或表面近光滑.上述结果表明天芥菜亚科三个属之间有密切的亲缘关系.花粉特征表明紫丹属在天芥菜亚科中可能是比较原始的,天芥菜属的演化水平比紫丹属和砂引草属要高,而砂引草属介于其他两个属之间.花粉形态特征显示天芥菜亚科是厚壳树亚科Ehretioideae到紫草亚科Boraginaceae的过渡类型.紫丹属的花粉具三孔沟的萌发孔类型表明天芥菜亚科与破布木亚科Cordioideae有一定的亲缘关系.     

Biased morph ratios and skewed mating success contribute to loss of genetic diversity in the distylous Pulmonaria officinalis

Background and Aims

In heterostylous plant species, skewed morph ratios are not uncommon and may arise from a range of factors. Despite the recognized importance of skewed morph ratios on overall reproductive success within populations, little is known about the impact of skewed morph ratios on population genetic diversity and differentiation in heterostylous species. This study specifically aimed to clarify the effect of population size and morph bias on population genetic diversity and differentiation in the temperate forest herb Pulmonaria officinalis. This species is characterized by a distylous breeding system and shows morph-specific differences in reproductive success.

Methods

Genetic diversity was determined for 27 P. officinalis populations in northern Belgium by using eight recently developed microsatellite markers. Multiple regressions were used to assess the relationship between genetic diversity, morph bias and population size, and F_ST-values were calculated for short- and long-styled morphs separately to study genetic differentiation as a function of morph type.

Key Results

For all genetic measures used, morph bias was more important in explaining patterns of genetic diversity than population size, and in all cases patterns of population genetic diversity followed a quadratic function, which showed a symmetrical decrease in genetic diversity with increasing morph bias. However, probably due to the reproductive advantage of L-morphs relative to S-morphs, maximum genetic diversity was found in populations showing an excess of L-morphs (60·7 % L-morph). On the other hand, no significant difference in pairwise genetic distances between populations was observed between L- (0·107) and S-morphs (0·106).

Conclusions

Our results indicate that significant deviations from equal morph ratios not only affect plant reproductive success but also population genetic diversity of heterostylous plant species. Hence, when defining conservation measures for populations of heterostylous plant species, morph ratios should be considered as an important trait affecting their long-term population viability.     

Among-Population Variation in Microbial Community Structure in the Floral Nectar of the Bee-Pollinated Forest Herb Pulmonaria officinalis L

Background

Microbial communities in floral nectar have been shown to be characterized by low levels of species diversity, yet little is known about among-plant population variation in microbial community composition.

Methodology/Principal Findings

We investigated the microbial community structure (yeasts and bacteria) in floral nectar of ten fragmented populations of the bee-pollinated forest herb Pulmonaria officinalis. We also explored possible relationships between plant population size and microbial diversity in nectar, and related microbial community composition to the distance separating plant populations. Culturable bacteria and yeasts occurring in the floral nectar of a total of 100 plant individuals were isolated and identified by partially sequencing the 16S rRNA gene and D1/D2 domains of the 26S rRNA gene, respectively. A total of 9 and 11 yeast and 28 and 39 bacterial OTUs was found, taking into account a 3% (OTU_0.03) and 1% sequence dissimilarity cut-off (OTU_0.01). OTU richness at the plant population level (i.e. the number of OTUs per population) was low for yeasts (mean: 1.7, range: 0–4 OTUs_0.01/0.03 per population), whereas on average 6.9 (range: 2–13) OTUs_0.03 and 7.9 (range 2–16) OTUs_0.01 per population were found for bacteria. Both for yeasts and bacteria, OTU richness was not significantly related to plant population size. Similarity in community composition among populations was low (average Jaccard index: 0.14), and did not decline with increasing distance between populations.

Conclusions/Significance

We found low similarity in microbial community structure among populations, suggesting that the assembly of nectar microbiota is to a large extent context-dependent. Although the precise factors that affect variation in microbial community structure in floral nectar require further study, our results indicate that both local and regional processes may contribute to among-population variation in microbial community structure in nectar.     

Correlation between distyly and ploidy level in Damnacanthus (Rubiaceae)

Somatic chromosomes were observed in 661 individuals of 14 taxa, nine species and five varieties, of Damnacanthus (Rubiaceae). Chromosome numbers are reported for the first time for 13 taxa. Diploid (2n = 22) and tetraploid (2n = 44) counts were obtained. Distyly is reported for the first time for four species, D. angustifolius, D. henryi, D. labordei, and D. officinarum. A strong correlation exists between chromosome number and occurrence of distyly. Regardless of taxa in Damnacanthus, distylous populations are diploid, and monomorphic populations are tetraploid. Flowers of the monomorphic populations observed have a long style and short stamens with few exceptions. Polyploidization may have caused the breakdown of distylous to monomorphic flowers. In D. indicus, leaves from the tetraploid populations tend to be larger than those from the diploid populations. Populations of tetraploid D. indicus were distributed in more northern areas than those of the diploid. Three types of sympatric distribution were found for the varieties of D. indicus in Japan: diploid and tetraploid, two diploids, and two tetraploids. Based on the present chromosome number study, the taxonomy of the varieties of D. indicus should be revised.     

The evolutionary breakdown of distyly inLinum tenuifolium (Linaceae)

Distyly inLinum tenuifolium L. is associated with a high degree of self-incompatibility. Breakdown in this system has occurred without the morphological rearrangement expected as the result of cross-over within the distyly supergene. Pollen-flow in both distylous and monomorphic populations is leptokurtic. A high proportion of intra-flower pollination occurs. Pollen production per ovule is reduced in the self-compatible race. Mean seed-set is increased. Individuals of the self-compatible race produce less vegetative growth and require a shorter time to reach reproductive maturity under cultivation. Increased fecundity appears to provide the selective advantage promoting the breakdown of self-incompatibility in this species. This is achieved through a massive shift of resources toward female reproductive function in plants of the monomorphic race. Subsequent colonization by this race has led to its increased distribution in C. & S. Europe.