Short-styled Plants Research Articles

Сравнительная характеристика кариометрических параметров микроспороцитов и клеток тапетума сформированных пыльников длинно- и короткостолбчатых растений Jasminum fruticans L. (Oleaceae)

In connection with the study of the functional activity of generative structures in heterostylous plants, a comparative karyometric analysis of tapetum cells, as well as microsporocytes of the formed anthers of long-styled and short-styled plants Jasminum fruticans L. (Oleaceae) was carried out. Based on the measurement of the nucleus areas, nucleolus, counting the number of nuclei and nucleoli in cells, the total values of the areas of nuclear structures were calculated. Since the processes of transcription and transformation of ribosomal RNA (r-RNA) are associated with nucleoli, the state of nucleolar structures in a cell reflects the level of its functional activity, therefore, the value of the nuclear-nucleolar ratio (NNR) was used as a characteristic of the functional activity of cells. It was found that in both floral forms, binuclear tapetal cells predominate. The number of nucleoli per cell varies from 1 to 14. The number of tapetal cells with 6-8 nucleoli is greater in short-styled plants than in long-styled plants. However, the cells of tapetum of long-styled and short-styled plants do not have a statistically significant difference of the value of NNR. Comparison of karyometric parameters of microsporocytes showed that the areas of their nuclear structures are larger in long-styled plants, while they are characterized by a higher value of NNR (17.61±0.36) compared with short-styled plants (15.59±0.27). A decrease in the value of NNR in short-styled plants is a sign of an increase in the intensity of protein metabolism of their microsporocytes, and, consequently, the level of functional activity of their genomes. Differences in the functional activity of microsporocytes of long-styled and short-styled plants can be considered as a sign of sex manifestation of sex depending on the floral type of the plant.

Fruit formation of the distylous species <i>Jasminum fruticans</i> L. (Oleaceae)

The article presents the results of a comparative analysis of the fruit formation of long-styled and short-styled plants Jasminum fruticans L. (Oleaceae). The long-styled flowers have larger ovaries and ovules than short-styled ones. Visual signs of degeneration and reduction of the structures of the ovules were not detected. At the same time, the morphs of J. fruticans differ in fruit formation. The proportion of dimeric fruits with two seeds is greater in long-styled plants. Three periods of abortion of fruits/seeds were identified: (1) 1-7 days after flowering correspond to the stage of pollination and fertilization; (2) 8-14 days are the proembryonic stage of embryogenesis; (3) 15-35 days are the stage of globular embryo. The periods of fruits abortion are the same for long- and short-styled plants. Statically significant difference between morph was revealed in the first period of abortion. Differences in morphs of fruits formation indicate less effective pollination and fertilization in short-styled plans. The fruits of J. fruticans mature three months after flowering.

Variation in pollen sterility and gender specialization: an investigation with distylous species of Erythroxylum (Erythroxylaceae)

Differences in pollen sterility between morphs in distylous populations may represent the first step in the evolution of gender specialization. Theoretically, for partially or completely male sterile individuals to persist they must have some fitness advantage that compensates for the loss of male function. Gender specialization is considered a widespread process in Erythroxylum, but male sterility and the resource reallocation to female function have been investigated in few species and populations. In 18 populations of four distylous species of Erythroxylum, we quantified the levels of male sterility, estimated through pollen sterility, in short- and long-styled flowers to test if sterility is morph-biased. In one population per species, we also described the frequency of floral visitors, the production of flowers and fruits, and the quality of fruits and seeds of short- and long-styled plants to evaluate the expression of trade-offs in allocation to male and female function. In some populations of E. campestre and E. deciduum, short-styled flowers possessed higher levels of pollen sterility than long-styled flowers. Although most flowers of E. suberosum and E. tortuosum also expressed pollen sterility, the frequency of sterility was similar between morphs in all populations. Differences in reproductive output between morphs occurred only in populations of species with morph-biased sterility, but none of the variations reflect resource allocation to female fitness of short-styled plants. Differences in the level of sterility between morphs indicates the potential for gender specialization in populations of E. campestre and E. deciduum, despite the apparent lack of a trade-off in allocation.

Flowering and fruiting of Sarcotheca macrophylla Bl, an endemic species of Borneo and implication for conservation

Sarcotheca macrophylla (Oxalidaceae) is an endemic species of Borneo. Little is known about the flowering and fruiting of this endemic species. The present study aimed to investigate the flowering and fruiting of S. macrophylla in terms of the first-time flowering, and morphology of the flowers, fruits, and seeds. Morphology of flowers, fruits, and seeds was also recorded and documented. The results showed that the first-time flowering of S. macrophylla occurred at 5 months to 16 months after seed germination with the plant height ranged from 13 to 23cm. These results showed that the first-time flowering of S. macrophylla occured at seedling stage, indicating early reproduction of the species. Two morphs of S. macrophylla (short-styled plants and long-styled plants) confirmed the heterostylous syndrome (different styly length) which is common in Oxalidaceae. Heterostylous is often associated with self-incompatibility which is commonly linked to the low seed set in this plant family. The present study has implication in the conservation of this endemic species, as the species produced low seed set associated with heterostylous syndrome of the flowers. Efforts to increase the seed set to support regeneration and survival of this endemic species are required.

Asymmetries of reproductive isolation are reflected in directionalities of hybridization: integrative evidence on the complexity of species boundaries.

The complex nature of species boundaries has been a central topic in evolutionary biology ever since Darwin. Despite numerous separate studies on reproductive isolation and hybridization, their relationship remains underinvestigated. Are the strengths and asymmetries of reproductive barriers reflected in the extent and directionalities of interspecific genetic exchange? We combined field, experimental, and molecular data to quantify strengths and asymmetries of sympatric reproductive barriers and hybridization between florally heteromorphic primroses. We also assessed whether generalist pollinators discriminate between different floral cues and contribute to reproductive isolation, a long-debated topic. Sympatric reproductive isolation is high but incomplete, and most phenotypic intermediates are genetic F1 hybrids, whereas backcrosses are rare, revealing low interspecific gene flow. Species integrity rests on multiple barriers, but ethological isolation is among the strongest, demonstrating that even generalist pollinators crucially contribute to the maintenance of species boundaries. Furthermore, reproductive barriers are weaker for Primula veris and short-styled plants, results corroborated by molecular data. Thus, in florally heteromorphic systems, both species- and morph-dependent asymmetries affect permeability of species boundaries. Our study illustrates how the interactions between complex floral syndromes and pollinators shape species boundaries in unique, previously undescribed ways.

Avoiding sexual interference: herkogamy and dichogamy in style dimorphic flowers of Narcissus broussonetii (Amaryllidaceae).

Spatial (herkogamy) or temporal (dichogamy) separation of sex organs are mechanisms considered to restrict self-pollination and promote outcrossing. Additionally, avoidance of self-interference is proposed to be the driving force for the evolution of these mechanisms, particularly in self-incompatible species. However, species with anthers and stigmas at different levels may increase the rate of imprecise pollen transfer, resulting in pollen discounting. Non-reciprocal stylar dimorphism has been considered a transitional, unstable stage towards the evolution of reciprocal style dimorphism (distyly), to simultaneously avoid interference and lack of precision. In this study we investigate the spatial and temporal separation of sex organs in a population of the style dimorphic and self-incompatible Narcissus broussonetii and their consequences in the reciprocity between the sex organs of morphs and their fecundity. First, we evaluated the relative growth of sex organs after anthesis. Then, we studied the stigma receptivity along the flower lifespan including its effect on seed production in both morphs. Finally, given the weak reciprocity between the sex organs of morphs of this species, we estimated population genetic diversity parameters in Long- and Short-styled plants to explore differences between them as a result of rates of inbreeding due to different mating strategies. We observed that Long-styled plants and Short-styled plants present different strategies to avoid sexual interference and both of them had negative consequences in the reciprocity between the sex organs of morphs. Long-styled plants exhibited a delay in stigma receptivity and a higher growth rate of the style after anthesis, while Short-styled plants presented higher herkogamy and no delay in stigma receptivity. These findings suggest that the avoidance of self-interference, in stylar dimorphic Narcissus species, seems to be more critical than improving of reciprocity between the sex organs of morphs. This might explain why reciprocal herkogamy (distyly) is rare in the genus.

Elevation-related variation in the population characteristics of distylous Primula nivalis affects female fitness and inbreeding depression

The population characteristics of distylous species are highly sensitive to stochastic natural selection pressure. Therefore, populations growing under different environmental conditions may vary in floral morph ratios, potentially affecting female fitness and leading to inbreeding depression. However, the variation in offspring quality among populations as a result of inbreeding depression is poorly understood in distylous species. This study investigates variations in plant density, seed mass, seed viability, female fitness, and post-dispersal inbreeding depression in both sexual morphs (long-styled and short-styled plants) of the distylous Primula nivalis that were subjected to different pollination treatments along an elevational gradient from 1657 to 2704 m a.s.l. Population characteristics (morph plant density and ratio) and fruit set were significantly affected by sexual morph and elevation. Plant density and fruit set frequencies were lower for short-styled than for long-styled plants at 2704 m a.s.l. The seeds from the cross-pollinated flowers of both morphs were higher in quality than those of self-pollinated flowers. The female fitness of seeds from cross-pollinated flowers of both morphs was higher than that of seeds from open-pollinated and self-pollinated flowers. The female fitness of seeds from long-styled flowers was higher than that of seeds from short-styled flowers at all elevations. Inbreeding depression increased with elevation among plants with short-styled flowers but not among those with long-styled flowers. Variation in the elevation-dependent mating system might influence female fitness and affect inbreeding depression in both floral morphs. In conclusion, the low quality of seeds from short-styled flowers at high elevations might decrease short-styled flower frequency, affecting population characteristics.

History vs. legend: Retracing invasion and spread of Oxalis pes-caprae L. in Europe and the Mediterranean area.

Oxalis pes-caprae L. is a South African geophyte that behaves as an invasive in the eurimediterranean area. According to a long-established hypothesis, O. pes-caprae may have invaded Europe and the Mediterranean area starting from a single plant introduced in the Botanical Garden of Malta at the beginning of the 19th century. The aim of this work was to test this hypothesis, to track the arrival of O. pes-caprae in different countries of the Euro-Mediterranean area and to understand the pathways of spreading and particularly its starting point(s). Historical data attesting the presence of the plant in the whole Euro-Mediterranean region were collected from different sources: herbarium specimens, Floras and other botanical papers, plant lists of gardens, catalogs of plant nurseries and plant dealers. First records of the plant (both cultivated and wild) for each Territorial Unit (3rd level of NUTS) were selected and used to draw up a diachronic map and an animated graphic. Both documents clearly show that oldest records are scattered throughout the whole area, proving that the plant arrived in Europe and in the Mediterranean region more times independently and that its spreading started in different times from several different centers of invasion. Botanical gardens and other public or private gardens, nurseries and plant dealers, and above all seaside towns and harbors seemingly played a strategic role as a source of either intentional and unintentional introduction or spread. A geographic profiling analysis was performed to analyse the data. We used also techniques (Silhouette, Kmeans and Voronoi tessellation) capable of verifying the presence of more than one independent clusters of data on the basis of their geographical distribution. Microsatellites were employed for a preliminary analysis of genetic variation in the Mediterranean. Even if the sampling was insufficient, particularly among the populations of the original area, our data supported three main groups of populations, one of them corresponding to the central group of populations identified by GP analysis, and the other two corresponding, respectively, to the western and the eastern cluster of data. The most probable areas of origin of the invasion in the three clusters of observations are characterized by the presence of localities where the invasive plant was cultivated, with the exception of the Iberian cluster of observation where the observations in the field predate the data about known cultivation localities. Alternative possible reasons are also suggested, to explain the current prevalence of pentaploid short-styled plants in the Euro-Mediterranean area.

Breeding System Evolution in Oxalis alpina: Asymmetrical Expression of Tristylous Incompatibility

Premise of research. Tristylous populations of Oxalis alpina have three floral morphs (short-, mid-, and long-styled), and populations appear to be at different stages in the evolution of distyly via loss of the mid-styled morph. In tristylous populations transitioning to distyly, asymmetrical incompatibility reactions could affect style-morph frequencies and slow the evolution of distyly. We hypothesized that greater success of pollen from long-styled relative to short-styled morphs leads to an excess of mid-styled progeny from mid-styled morphs and favors retention of tristyly despite other forms of selection acting against the mid-styled morph. Methodology. We quantified morph ratios of progeny from naturally pollinated plants. We also compared pollen tube and seed production of mid-styled plants following single-source pollinations using pollen from long- versus short-styled pollen parents, and we investigated the proportion of short-styled progeny following pollinations of mid-styled plants with mixtures of pollen from short- and long-styled plants. Pivotal results. Three lines of evidence generally support the hypothesis that reduced performance of short-styled pollen donors may favor retention of mid-styled plants. (1) Naturally pollinated mid-styled plants exhibited reduced numbers of short-styled progeny for two years in one of two tristylous populations with modified tristylous incompatibility. (2) In populations transitioning toward distyly, mid-styled plants pollinated by short-styled plants had fewer pollen tubes and lower seed production than crosses using long-styled plants as pollen parents. (3) Hand-pollinations of mid-styled plants using mixtures of pollen from short- and long-styled plants resulted in reductions in the proportion of short-styled progeny, consistent with the differences in pollen tube numbers produced by the paternal morphs. Conclusions. Asymmetry in paternity among different pollen donors via pollen tube performance influences the evolution of the breeding system of O. alpina, by affecting the relative proportions of different floral morphs and potentially counteracting selection through inbreeding depression and differential fitness of alleles controlling floral morphs.

The role of short-tongued insects in floral variation across the range of a style-dimorphic plant.

Heterostyly and related style polymorphisms are suitable model systems to evaluate the importance of functional pollinators in the maintenance of population variability. In Narcissus papyraceus different functional pollinators, incompatibility system and flower morphology have been proposed to influence the maintenance of polymorphism through their effect on disassortative mating. Here a test is done to find out if the visitation rate of long- versus short-tongued pollinators correlates with the morph ratio and if the latter is related to other flower traits of the species across its main geographic range. Floral traits from 34 populations in the south-west of the Iberian Peninsula and in north-west Africa were measured, perianth variation was described and a comparison was made of allometric relationships between sex organs and floral tube. Correlations between pollinator guilds, stigma-anther separation of reciprocal morphs (our proxy for disassortative mating) and morph-ratio variation were analysed. Finally, the incompatibility system of the species in the northern and southern borders of its distribution are described. Flowers from southern populations were significantly larger than flowers from centre and northern populations. The abundance of short-styled plants decreased gradually with increasing distance from the core region (the Strait of Gibraltar), with these disappearing only in the northern range. Although there was a significant difference in stigma-anther separation among populations, morph ratio was not associated with reciprocity or floral tube length. Long-style morph frequency increased with short-tongued pollinator visitation rate. Populations from both edges of the distribution range were self-incompatible and within- and between-morph compatible. The style morph ratio changed gradually, whereas perianth trait variation showed abrupt changes with two morphotypes across the range. The positive relationship between the visitation rate of short-tongued pollinators and the decrease of the short-style morph supports our initial hypothesis. The results highlight the importance of different pollinators in determining the presence of style polymorphism.

English

Heterostyly is the occurrence of flowers with different sexual organ arrangements in different plants of the same species. This floral polymorphism occurs in four sections of genus Linum. The present study compares the morphological, palynologycal and genome size (C-value content) characteristics in the long-styled and short-styled plants in three Linum species, that is, Linum austriacum L., Linum album Ky.ex Boiss.and L. glaucum Boiss. & Nöe . 15 qualitative and quantitative morphologicalcharacters from both vegetative and reproductive organs of these plants were studied.A higher mean value of the plant height, size of the basal leaves width, flower leaves width, calyx length, sepal length and petal length occurred in the long-styled plants, while the mean value of branch number, basal leaves length, flower leaves length, calyx width, pedicel length and sepal length was higher in the short-styled plant populations. T-test analysis of morphological characters showed significant difference (p<0.05) for some of the characters studied. Principal coordinate analysis (PCoA) plot of long-styled and short-styled plant populations based on all morphological characters also separated these two kinds of plants in the three species studied. The pollen obtained from the mature buds was prepared for light microscopy (LM) and scanning electron microscopy (SEM). The polar and equatorial views of the pollen grains were similar in the long-styled (Ls) and short-styled (Ss) plants but the aperture shape differed in these populations. C-values obtained by flow cytometry, differed in the long-styled and short- styled plants of the species studied. The analysis of variance (ANOVA) test performed among the three Linum species showed a significant difference in 2C-value content. Positive significant correlation was observed between 2C-value and northern distribution of the Linum species studied, while a negative significant correlation occurred with eastern distribution.   Key words: Heterostyly, Linum, morphology, palynology, genome size

Gender specialization in Palicourea demissa (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.

S-LOCUS EARLY FLOWERING 3 is exclusively present in the genomes of short-styled buckwheat plants that exhibit heteromorphic self-incompatibility.

The different forms of flowers in a species have attracted the attention of many evolutionary biologists, including Charles Darwin. In Fagopyrum esculentum (common buckwheat), the occurrence of dimorphic flowers, namely short-styled and long-styled flowers, is associated with a type of self-incompatibility (SI) called heteromorphic SI. The floral morphology and intra-morph incompatibility are both determined by a single genetic locus named the S-locus. Plants with short-styled flowers are heterozygous (S/s) and plants with long-styled flowers are homozygous recessive (s/s) at the S-locus. Despite recent progress in our understanding of the molecular basis of flower development and plant SI systems, the molecular mechanisms underlying heteromorphic SI remain unresolved. By examining differentially expressed genes from the styles of the two floral morphs, we identified a gene that is expressed only in short-styled plants. The novel gene identified was completely linked to the S-locus in a linkage analysis of 1,373 plants and had homology to EARLY FLOWERING 3. We named this gene S-LOCUS EARLY FLOWERING 3 (S-ELF3). In an ion-beam-induced mutant that harbored a deletion in the genomic region spanning S-ELF3, a phenotype shift from short-styled flowers to long-styled flowers was observed. Furthermore, S-ELF3 was present in the genome of short-styled plants and absent from that of long-styled plants both in world-wide landraces of buckwheat and in two distantly related Fagopyrum species that exhibit heteromorphic SI. Moreover, independent disruptions of S-ELF3 were detected in a recently emerged self-compatible Fagopyrum species and a self-compatible line of buckwheat. The nonessential role of S-ELF3 in the survival of individuals and the prolonged evolutionary presence only in the genomes of short-styled plants exhibiting heteromorphic SI suggests that S-ELF3 is a suitable candidate gene for the control of the short-styled phenotype of buckwheat plants.

Seasonal change in a pollinator community and the maintenance of style length variation in Mertensia fusiformis (Boraginaceae)

In sub-alpine habitats, patchiness in snowpack produces marked, small-scale variation in flowering phenology. Plants in early- and late-melting patches are therefore likely to experience very different conditions during their flowering periods. Mertensia fusiformis is an early-flowering perennial that varies conspicuously in style length within and among populations. The hypothesis that style length represents an adaptation to local flowering time was tested. Specifically, it was hypothesized that lower air temperatures and higher frost risk would favour short-styled plants (with stigmas more shielded by corollas) in early-flowering patches, but that the pollen-collecting behaviour of flower visitors in late-flowering patches would favour long-styled plants. Floral morphology was measured, temperatures were monitored and pollinators were observed in several matched pairs of early and late populations. To evaluate effects of cold temperatures on plants of different style lengths, experimental pollinations were conducted during mornings (warm) and evenings (cool), and on flowers that either had or had not experienced a prior frost. The effectiveness of different pollinators was quantified as seed set following single visits to plants with relatively short or long styles. Late-flowering populations experienced warmer temperatures than early-flowering populations and a different suite of pollinators. Nectar-foraging bumble-bee queens and male solitary bees predominated in early populations, whereas pollen-collecting female solitary bees were more numerous in later sites. Pollinators differed significantly in their abilities to transfer pollen to stigmas at different heights, in accordance with our prediction. However, temperature and frost sensitivity did not differ between long- and short-styled plants. Although plants in late-flowering patches tended to have longer styles than those in early patches, this difference was not consistent. Seasonal change in pollinator-mediated selection on style length may help maintain variation in this trait in M. fusiformis, but adaptation to local flowering time is not apparent. The prevalence of short styles in these populations requires further explanation.

Dimorphisms and self-incompatibility in the distylous species Palicourea demissa (Rubiaceae): possible implications for its reproductive output

Distyly has been interpreted as a mechanism that favors cross-fertilization. In this research we describe floral attributes and ancillary floral polymorphisms typically associated to heterostylous plants in Palicourea demissa (Rubiaceae), a distylous shrub of the Venezuelan Andes cloud forests. A hand-pollination experiment was done to evaluate self- and intramorph incompatibility and female reproductive output in both floral morphs. The studied population was morphologically distylous but morph differences in most ancillary floral polymorphisms and reciprocity of the sexual organ heights were found. The floral morphs were self-incompatible and did not differ in fruit set under controlled cross-pollination conditions, but at the population level they exhibited imperfect reciprocal herkogamy. Fruits and seeds of short-styled plants were larger than those of long-styled plants and fruit set was higher in short-styled plants under natural conditions, suggesting a higher reproductive potential among short-styled plants. Given the 1:1 morph ratio within the studied population, further evidence is needed to determine the influence of floral visitors and seed dispersers in the expression of heterostyly in P. demissa under natural conditions.

Breeding system variation, genetics and evolution in the Turneraceae

We review the genetics and evolution of breeding systems in the Turneraceae. Distyly occurs in seven of 10 genera and 81% of species. The remaining species are homostylous. Polyploid evolution has been significant in Turnera. Approximately 60% of species are polyploid ranging from diploid through decaploid. No relationship between breeding system and polyploidy is evident. The genetics of distyly involves a one-locus two-allele system (S and s). Evidence from crosses with homostylous species and mutants is consistent with the possibility that a "Primula-type" supergene underlies distyly but does not prove this to be the case. A polygalacturonase, and an alpha-dioxygenase specific to the transmitting tissue of short-styled plants both exhibit morph-limited expression in concert with predictions from an evolutionary model. The function of the proteins in distyly, if any, is unknown. We have begun constructing a fine-scale genetic map of Turnera. Two genetic markers lie within 0.2 cm of the distyly locus. This should provide a starting point for positional cloning of the distyly locus and reveal the genetic architecture and molecular basis of distyly.

Heteromorphic Incompatibility and Efficiency of Pollination in Two Distylous Pentanisia Species (Rubiaceae)

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. 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. 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. 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.

Between-year Changes in Functional Gender Expression of Palicourea padifolia (Rubiaceae), a Distylous, Hummingbird-pollinated Shrub

Because distylous species have two hermaphroditic style-length floral morphs, they face two sex allocation problems: the equilibrium morph ratio and the optimal allocation to pollen and seed production in each floral morph. Gender specialization is expected among distylous species when floral morphs differ in reproductive output. However, spatio-temporal variability in female reproductive output between morphs needs to be investigated to fully understand patterns of sexual expression and gender specialization in distylous plants. Between-year variation in flower and fruit production of hummingbird-pollinated Palicourea padifolia (Rubiaceae) was examined, focusing on functional gender expression of long- and short-styled morphs and comparing their reproductive performance in five consecutive years (1998-2002). Between-year variation in inflorescence, floral bud and fruit production was monitored and quantified. These traits were then used as parameters to determine functional gender differences between floral morphs through time. Inflorescence production varied among years but no significant differences were found between floral morphs. Long-styled plants initiated more floral buds per inflorescence every year than short-styled plants, suggesting higher allocation to pollinator attraction and, potentially, an increase in male fitness through pollen donation. Although fruit production was similar between morphs, their functional gender shifted across years. The gender expression inconsistency across years is surprising because a number of floral characters and attributes that contribute to differently attracting and rewarding effective pollinators in P. padifolia suggest gender specialization. The evidence that morphs of distylous species might specialize in functional gender mostly comes from differences among populations in seed production and non-equilibrium morph ratios based on 1-year field population surveys. The results suggest that more sampling through time is needed to detect gender specialization among distylous species with a perennial habit.

Reproductive ecology of distylous Palicourea padifolia (Rubiaceae) in a tropical montane cloud forest. II. Attracting and rewarding mutualistic and antagonistic visitors

By definition, the floral morphs of distylous plants differ in floral architecture. Yet, because cross-pollination is necessary for reproductive success in both morphs, they should not differ in attributes that contribute to attracting and rewarding floral visitors. Floral and vegetative attributes that function in distylous polymorphism in hummingbird-pollinated Palicourea padifolia (Rubiaceae) and the responses of pollinators and insect herbivores to the resources offered by both morphs were investigated. The performance of each morph along multiple stages of the reproductive cycle, from inflorescence and nectar production to fruit production, was surveyed, and pollinator behavior and nectar standing crops were then observed. Costs associated with such attractiveness were also evaluated in terms of herbivore attack and of plant reproductive fitness (female function) as a function of leaf herbivory. The number of inflorescences, floral buds, open flowers, and ripe fruits offered by either floral morph were similar, but short-styled plants almost doubled the number of developing fruits of long-styled plants. Long-styled flowers produced higher nectar volumes and accumulated more nectar over time than short-styled flowers. Measures of nectar standing crop and data on pollinator behavior suggest that hummingbirds respond to this morph-specific scheduling of nectar production. Lastly, long-styled plants suffered a higher herbivore attack and lost more leaf area over time than those with short-styled flowers. Herbivory was negatively correlated with fruit number and fruit mass, and long-styled plants set significantly less fruit mass than short-styled plants. The results suggest that pollinators and herbivores may exert selective pressures on floral and vegetative traits that could also influence gender function.

Distribution of style and pollen polygalacturonases among distylous and homostylous Turnera and Piriqueta spp. (Turneraceae).

We explore the distribution of a style and pollen polygalacturonase in a number of distylous and homostylous species of Turnera, and two species of Piriqueta (Turneraceae). We show, using immunoblotting with antibodies made against these proteins, that the style polygalacturonase is specific to styles of short-styled plants of all the six distylous species of Turnera we have investigated. Styles of a somatic homostylous mutant derived from a short-styled plant do not possess the style polygalacturonase. Distylous P. caroliniana did not appear to possess this protein. We show that the pollen polygalacturonase, while associated with the short-styled morph in three species, is polymorphic among short-styled plants of T. krapovickasii, and absent from T. joelii, T. grandiflora and P. caroliniana. These data support a role for the style polygalacturonase in distyly, possibly in the incompatibility system, but cast doubt on any role for the pollen polygalacturonase. In concert with the predictions for the mode of origin, and the response of styles of homostylous species to pollen from long- and short-styled plants, we find that none of the homostylous species possess the style polygalacturonase. The pollen polygalacturonase does occur in some homostylous species, but not in others. It is not clear that the pollen polygalacturonase, however, provides a marker for the mode of origin of homostyly.