Floral Morph Ratios Research Articles

Floral and reproductive biology of Commelina erecta L. (Commelinaceae) in a coastal dune system on the Gulf of Mexico

The most common sexual systems found in Commelinaceae species are hermaphroditic and andromonoecious, and although enantiostyly is also recognized in the family, it has only been recorded in a few species. The presence of different sexual systems (v.gr., andromonoecious and enantiostyly) in the same species is still unnoted. Commelina erecta is a common andromonoecious-enantiostylous species (i.e., it bears male, left-styled and right-styled flowers) of the coastal dunes of La Mancha in Veracruz, Mexico. Our aims were to determine: (1) the type of enantiostyly, (2) the floral morph-ratios in a population, (3) the differences in size of flowers structures among floral morphs, to (4) characterize the floral visitor community in the different floral morphs, and (5) evaluate differences in fruit set in the hermaphroditic flowers. We found that C. erecta in La Mancha is characterized by non-reciprocal monomorphic enantiostyly. The proportion of floral morphs varied among sampling months. Discriminant analysis and a Wilcoxon test using canonical scores indicated that the anther area and filament length of male flowers are larger in size than those in hermaphroditic flowers. In total, we recorded 220 visits to the flowers of C. erecta by 18 species of insects belonging to five orders. Our study shows that the main floral visitor was the halictid bee Augoclorella sp. Left- and right-styled flowers were equally successful in terms of producing fruits and seeds of the same weight and size, but overall reproductive success was low, with fruit set of only 29%.

Genetic and reproductive characterization of distylous Primula reinii in the Hakone volcano, Japan: implications for conservation of the rare and endangered plant

Genetic and ecological evaluation are crucial in effective management of rare and endangered species, including those exhibiting complex breeding systems such as distyly. We studied a threatened distylous herb Primula reinii in the Hakone volcano, central Japan, to obtain baseline information of reproductive and genetic status towards conservation. In two representative populations inhabiting a central cone and somma of the volcano, population size, floral morph ratio, stigmatic pollen deposition, and fruit-set were measured. Using microsatellite markers, we evaluated genetic diversity, structure and differentiation of populations. Population bottlenecks and historical changes in population size were also estimated from genotype data. We found significant deviation from equal morph ratios in the central cone population, which also exhibited skewed mating success together with a high frequency of pollination within the same morph. These trends were not detected in the somma population. From genetic insights, the central cone population showed slightly lower genetic diversity, whereas no significant deviation from Hardy-Weinberg equilibrium was found in either population. The estimated moderate genetic differentiation and admixed genetic structure suggest recent lineage divergence and/or gene flow between populations. While robust evidence for a recent bottleneck was not obtained in our analyses, a clear signature of historical population contraction was detected in the central cone population. Our findings suggest that the skewed morph ratio strongly influenced the reproduction of small and isolated populations in the short-term, highlighting the vulnerability of distylous plant populations under ongoing anthropogenic pressure.

Global patterns of reproductive and cytotype diversity in an invasive clonal plant

The reproductive systems of invasive species play a key role in determining their geographical distributions. Oxalis pes-caprae is a clonal, polyploid, heterostylous, plant native to South Africa, but now invasive in all major Mediterranean climatic regions. Here, we extend earlier surveys in the Western Mediterranean basin of floral morph ratios, reproductive traits and ploidy level to include populations from South Africa and introduced regions of Australia, California and Chile. We sampled a total of 104 populations, 33 in South Africa, 29 in Australia, 27 in California and 15 in Chile and collected data on floral morph representation (trimorphic, dimorphic, monomorphic), flower size, fruit set, and ploidy level using flow cytometry. There were significant differences among regions in floral morph structure of populations, reproductive traits and ploidy level. Populations in South Africa were exclusively tristylous and largely tetraploid (4x); Australian populations were mostly pentaploid (5x, 65.5%), comprised exclusively of the short-styled morph, with the remaining populations either dimorphic or trimorphic. Populations in California and Chile were comprised exclusively of the 5x short-styled morph. Fruit set varied dramatically among populations with no fruit produced in 5x populations. Our study demonstrates striking geographical variation among regions in reproductive systems ranging from a mixture of sexual and clonal reproduction in the native range to exclusively clonal propagation in some introduced regions. This variation is likely to have important consequences for local adaptation and should be considered in future management decisions of invasive populations.

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.

Architectural constraints, male fertility variation and biased floral morph ratios in tristylous populations.

Tristyly is a genetic polymorphism in which populations are comprised of three floral morphs (mating types) differing reciprocally in sex-organ height. Intermorph (disassortative) mating governed by a trimorphic incompatibility system should result in 1:1:1 morph ratios at equilibrium, but both deterministic and stochastic processes can cause skewed morph ratios in tristylous populations. Here, we investigate mechanisms causing morph-ratio bias in Pontederia parviflora, an emergent aquatic native to tropical America. We compared reproductive traits among morphs and surveyed 71 populations to determine patterns of morph-ratio bias. We then used simulation models of morph-frequency dynamics to test the hypothesis that morph-specific differences in pollen production and their influence on male fertility can explain patterns of morph-ratio bias. Ninety-seven percent of populations that we sampled were tristylous, but with a significant excess of the short-styled morph and a deficiency of the long-styled morph. Atypically for a tristylous species, mid-level anthers of the short-styled morph produced over twice as much pollen compared with the corresponding anthers of the long-styled morph. Our computer models incorporating this difference in male fertility resulted in morph ratios not significantly different from the average frequencies from our survey suggesting that the short-styled morph is more successful than the long-styled morph in siring ovules of the mid-styled morph. We propose that the difference in male fertility between morphs may be a non-adaptive consequence of a developmental constraint caused by the architecture of tristyly in Pontederiaceae.

Intraspecific variation of self-incompatibility in the distylous plant Primula merrilliana.

Heteromorphic self-incompatibility can prevent self- and intramorph fertilization while favouring intermorph mating and the maintenance of morph-ratio stability in heterostylous populations. However, variation in the expression of self-incompatibility intraspecies has seldom been assessed. Through hand pollinations and microsatellite markers, the variation in the expression of self-incompatibility and genetic diversity were studied in distylous plant Primula merrilliana. We discovered that the strength of self-incompatibility varied extensively among individuals and populations, from pronounced to weaker self-incompatibility in distylous populations, all the way to strong self-compatibility in homostylous populations. Each distylous population included self-incompatible (SI), partly self-compatible (PSC) and self-compatible (SC) individuals, with the index of self-compatibility (ISC) ranging from 0.07 to 0.68 across populations. Self-compatible populations (ISC > 0.25) were not genetically clustered but were more closely related to populations with high SI and SC individuals were mixed with SI individuals within populations. The ISC and the proportions of SC and PSC individuals were higher in peripheral than in central populations, but no decrease of genetic diversity and no deviations of floral morph ratio from isoplethy were detected in peripheral populations. Additionally, the expression of self-incompatibility was stronger in long-styled flowers than in short-styled flowers. The variation in the strength of self-incompatibility documented in P. merrilliana cautions against the estimation of ISC from a few individuals or populations in distylous species and provides a more complex and nuanced understanding of the role of self-incompatibility in heterostyly.

The influence of floral morph ratios and low plant density on mating and fertility in a tristylous colonizing species

Sexual reproduction in heterostylous populations may be vulnerable to demographic conditions because of the small number of mating types in populations. Here, we investigate mating and fertility under natural and experimental conditions in tristylous Lythrum salicaria L., an invasive species that exhibits a wide range of floral morph ratios and demographic contexts. We grew 147 open-pollinated seed families from six populations with different morph structures to estimate intermorph mating (d). In a field experiment, we used progeny ratios from 47 spatially isolated individuals to estimate d, and measured the intensity of pollen limitation experienced by the morphs. The M- and S-morphs experienced high rates of d, regardless of population size or morph ratio. Estimates for the L-morph revealed low levels of intramorph mating in three dimorphic and two trimorphic populations, but near complete intramorph mating in a monomorphic population. Despite high levels of intermorph mating in the field experiment, the morphs experienced significant pollen limitation of fruit and seed set, but this did not differ in intensity among the morphs. Our field experiment demonstrates that although plant isolation was associated with pollen limitation of seed set, “long-distance” bee-mediated pollen flow served to maintain intermorph mating. Tristyly in L. salicaria is remarkably robust to the demographic variation associated with colonization.

Range-wide population genetics and variation in morph ratio in style-dimorphic Narcissus papyraceus.

• Theoretical models state that natural selection and mating patterns account for floral morph ratio in style-polymorphic plants. However, the demographic history of populations can also influence variation in morph ratios. If so, we hypothesize an association between the morph ratios and the genetic structure across populations.• We used nuclear microsatellites to assess genetic variation and structure in populations of Narcissus papyraceus, a style-dimorphic plant whose floral morph ratios (L-morph to S-morph) gradually vary throughout its distribution range in the southwestern Mediterranean Basin. We implemented analyses to relate the genetic features of populations with their morph ratios.• We found greater frequencies of the S-morph in central populations and declining frequencies toward the periphery. This geographic pattern was not associated with the genetic structure of populations. Instead, we found two distinct genetic groups, mainly separated by the Strait of Gibraltar, with a mixture of morph ratios within each one. Overall, there was a weak genetic structure. Genetic diversity was greater in central and southern dimorphic populations than in northern L-monomorphic populations.• Altogether, our results do not support the hypothesis that the demographic history of populations can account for the observed geographical pattern of morph ratios in N. papyraceus. We suggest that adaptive processes shown in previous studies in the species are the main determinant of the existing variation in the morph composition of populations.

Distylous traits in Cordia dodecandra and Cordia sebestena (Boraginaceae) from the Yucatan Peninsula

Distyly is a genetically-controlled polymorphism with two floral morphs exhibiting spatial, reciprocal separation between stigmas and anthers; one morph has long styles and short stamens and the other short styles and long stamens. Distyly is linked to a self-incompatibility system that prevents self-pollination and crosses between plants of the same morph, thereby ensuring symmetrical mating and equal morph ratios within populations. This is the first report of distylous traits in the tropical trees species Cordia dodecandra and C. sebestena on the Yucatan Peninsula. Principal components analysis of flower morphological traits identified segregation into two groups with characteristically distylous morphology. Estimation of reciprocal herkogamy using indices showed almost perfect reciprocity in the distance between long and short sexual organs in the two flower morphs of both species. Reciprocity between organs was less exact in C. dodecandra , suggesting less accuracy in pollen transference between morphs. Self-incompatibility was observed for C. dodecandra , but could not be confirmed for C. sebestena . However, a 1:1 floral morph ratio within the sampled C. sebestena populations suggests the existence of a distylous, self-incompatibility system in this species. Morph distribution in C. dodecandra did not follow a typically distylous distribution, suggesting a disruption in population processes such as seed dispersion and seedling establishment in this species. The reported data confirm the existence of the distyly syndrome in the two Cordia species.

Variation in floral morph ratios in tristylous Oxalis squamata (Oxalidaceae): an Andean alpine endemic

Negative frequency-dependent selection resulting from disassortative mating should result in equal morph ratios in tristylous populations at equilibrium. However, surveys of morph-frequency variation in tristylous species commonly report deviations from equality. Here, we report variation in morph ratios in Oxalis squamata Zucc., an endemic of the Andean region of Chile and Argentina. Absence of clonal propagation in this species allows unambiguous estimates of the morph ratio of genets. We sampled floral morph ratios in 20 populations occurring in Central Chile and investigated the relation between morph evenness in populations and their size. All populations of O. squamata were tristylous but with significant heterogeneity among populations in morph ratios. Although small populations exhibited a greater variance in morph evenness, biased ratios were also evident in several large populations. We found no evidence of morph loss or a consistent bias in morph frequencies as reported in some tristylous species. Biased morph frequencies in large populations probably arise from episodic sexual recruitment following disturbance and a slow approach to equilibrium.

Floral and reproductive biology of the Mexican endemic Chamaecrista chamaecristoides (Fabaceae)1

Arceo-Gómez, G. (Department of Biological Sciences, University of Pittsburgh, 4249 Fifth Ave., Pittsburgh, PA, USA), M. L. Martínez (Red de Ecología Funcional, Instituto de Ecología A. C. carretera antigua a Coatepec N° 351 El Haya, Xalapa Veracruz, México C.P. 91070), V. Parra-Tabla (Departamento de Ecología Tropical, Campus de Ciencias Biológicas y Agropecuarias, Universidad Autónoma de Yucatán, Km. 15.5 carretera Mérida-Xmatkuil, Mérida, Yucatán, México), and J. G. García-Franco (Red de Ecología Funcional, Instituto de Ecología A. C. carretera antigua a Coatepec N° 351 El Haya, Xalapa Veracruz, México C.P. 91070). Floral and reproductive biology of the Mexican endemic Chamaecrista chamaecristoides (Fabaceae). J. Torrey Bot. Soc. 139: 260–269. 2012.—Chamaecrista chamaecristoides is an enantiostylous shrub endemic to the coast of Mexico that is being heavily impacted by human activities along the Gulf of Mexico. Chamaecrista chamaecristoides is considered a key species of the sand dune communities, particularly for its role as a nurse species and in dune stabilization. While certain aspects of its population biology have been well studied, others, such as its reproductive biology, have been overlooked. Understanding the factors that contribute to the successful reproduction of this species is crucial for its maintenance in natural populations. In this study, we examine the floral and reproductive biology of C. chamaecristoides. Specifically, we evaluate flower morphology and phenology, the breeding system and the identity and foraging patterns of floral visitors. Our results show that flower morphs are morphologically identical; however, position, size, and pollen production vary between stamens within each flower, suggesting functional differentiation. Furthermore, plants differ in their proportion of right- and left-styled flowers over the flowering season. While this could promote cross-fertilization by favoring pollen transfer among individuals with opposite floral-morph ratios, the presence of a stamen adjacent to the style, its self-compatibility and the absence of inbreeding depression all compromise the role of enantiostyly as an outcrossing strategy in this species. Finally, even though flowers are visited by at least ten different floral visitors, reproduction of C. chamaecristoides depends heavily on only three species that together account for more than 70% of the total number of visits. Overall, our results suggest that C. chamaecristoides is highly dependent on a small subset of the community of floral visitors and that it has evolved floral strategies to reduce pollen loss and enhance the efficiency of pollen transfer. For these reasons, future conservation strategies must also consider the preservation of suitable habitat for the somewhat limited pollinator community of this species.

Distribution of Flower Morphs, Ploidy Level and Sexual Reproduction of the Invasive Weed Oxalis pes-caprae in the Western Area of the Mediterranean Region

Oxalis pes-caprae is a widespread invasive weed in regions with a Mediterranean climate. In its native habitat (southern Africa) this species has been reported as heterostylous with trimorphic flowers and a self- and morph-incompatible reproductive system. In most of the areas invaded, only a pentaploid short-styled morphotype that reproduces mainly asexually by bulbils is reported, but this has only been confirmed empirically. This study aims to analyse the floral morph proportions in a wide distribution area, test the sexual female success, and explain the causes of low sexual reproduction of this species in the western area of the Mediterranean Basin. Fifty-five populations of O. pes-caprae were sampled in the Iberian Peninsula and Morocco to evaluate the floral morph ratio and individual fruit set. In plants from a dimorphic population, hand-pollination experiments were performed to evaluate the effect of the pollen source on pollen tube growth through the style. The ploidy level and genome size of individuals of each floral morph were analysed using flow cytometry. 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 verified but no fruit production was observed in any population. A sterile form was also recorded in several populations. Hand-pollination experiments revealed that pollen grains germinated over recipient stigmas. In intermorph crossings, pollen tubes were able to develop and fruit initiation was observed in some cases, while in intramorph pollinations, pollen tube development was sporadic and no fruit initiation was observed. All individuals within each floral form presented the same DNA ploidy level: SS plants were pentaploid and LS and the sterile form were tetraploid. The low or null sexual reproduction success of this species in the area of invasion studied seems related with the high frequency of monomorphic populations, the unequal proportion of floral morphs in dimorphic populations and the presence of different ploidy levels between SS and LS morphs. The discovery of the occurrence of an LS floral morph and a sterile form, whose invading capacity in these areas is as yet unknown, will be valuable information for management programmes.

Fenologia da floração, morfologia floral e sistema de incompatibilidade em espécies distílicas de Rubiaceae em fragmento florestal do Sudeste brasileiro

This work was carried out at the Estacao de Pesquisa, Treinamento e Educacao Ambiental Mata do Paraiso, Vicosa, Minas Gerais State, a forest fragment in the Atlantic Forest. Its main objective was to analyze the flowering phenology, floral morphology, and incompatibility system of the distylous species of Rubiaceae: Palicourea longepedunculata Gardner, P. marcgravii A. St.-Hil., Psychotria conjugens Mull. Arg., P. hastisepala Mull. Arg., P. hygrophiloides Benth., P. nuda (Cham. & Schltdl.) Wawra, P. sessilis Vell. and Rudgea lanceolata Nutt. It also aimed to verify whether the floral morphs were in balanced equilibrium. The flowering in the species of Psychotria conjugens, P. hastisepala, P. hygrophiloides and P. sessilis were sequential, occurring during the rainy season (September through March). Significant differences were observed in the lengths of the stamens and styles between the thrum and pin flowers, except for P. hygrophiloides, in which only thrum flowers could be observed. Furthermore, dimorphism was observed in the length of stigmatic lobules, corollas, corolla lobules and anthers. Flowers opened in the morning lasting about 24 h, except for P. nuda flowers, that lasted 48 h. In most of the species the floral morph ratio was 1:1, except P. marcgravii, P. conjugens and P. hygrophiloides. Heteromorphic self-incompatibility was observed with growth inhibition of the incompatible pollen tubes occurring in the stigma of most of the species analyzed, except for the pin morphs of P. longepedunculata and P. hastisepala, in which reaction occurred in the style.

Reproductive success and genetic structure of populations of the heterostylous aquatic plant Nymphoides indica (L.) Kuntze (Menyanthaceae)

Differences in the reproductive mode (sexual and vegetative reproduction) between populations of a species may produce diverse patterns of genetic structure within and among populations. We analyzed the clonal diversity of populations of a heterostylous plant ( Nymphoides indica (L.) Kuntze) having different floral morph ratios in the Higashi-harima area of Japan. The number of MLGs (multilocus genotypes) in populations with equal floral morph ratios was significantly higher than that among populations with biased floral morph ratios and among monomorphic populations. Populations with equal floral morph ratios followed the Hardy–Weinberg equilibrium. A dispersal distance of 0–4.2 km was significantly correlated with Nei's genetic distance, supporting a stepping-stone model of dispersal. Four rare MLGs were included in populations with equal floral morph ratios, distributed among neighboring populations. We concluded that clonal diversity of N. indica in the Higashi-harima area is maintained by the success of seed production and establishment of seedlings, and by the proximate occurrence of habitats around the populations where successful sexual reproduction occurs.

CORRELATED EVOLUTION OF FLORAL MORPHOLOGY AND MATING-TYPE FREQUENCIES IN A SEXUALLY POLYMORPHIC PLANT

In sexually polymorphic species, reproductive morphology governs mating patterns and the character of negative frequency-dependent selection. If local environmental conditions cause sexual morphs to differ between populations, then frequency-dependent selection should create corresponding geographic variation in morph frequencies. We investigate this relation with a model of morph-ratio evolution and analysis of geographic variation in the heterostylous plant Narcissus triandrus. Unlike other tristylous species, N. triandrus possesses both imperfect reciprocity among morphs in sex-organ position and a self-incompatibility system that permits outcrossing within and between morphs. We sampled 137 populations throughout the Iberian Peninsula for floral-morph ratios, and measured floral morphology in 31 populations. Morph ratios exhibited three atypical features: (1) predominance of the long-styled (L) morph; (2) absence of the mid-styled (M) morph from 17.5% of populations; and (3) a negative relation between the frequencies of the L and M morphs among populations. Morph ratios varied geographically, with decreasing frequency of the M morph from the southeast to the northwest of the species' range. Much of this variation accompanied allometric change in the positions of sex organs, especially the mid-level organs, with the M morph declining in frequency and ultimately being lost in large-flowered populations. Using multivariate multiple regression, we demonstrate that variation in floral morphology among populations predicts this geographic variation in morph frequencies. Our theoretical analysis illustrates that patterns of pollen transfer governed by imperfect sex-organ reciprocity can select for unequal equilibrium morph ratios like those observed for N. triandrus. We interpret the L-biased morph ratios and the unusual morphology of N. triandrus as a consequence of its atypical intramorph compatibility system.

Floral morph composition and pollen limitation in the seed set of Nymphoides indica populations

We investigated the floral morph composition and seed set of the populations in a heterostylous aquatic plant, Nymphoides indica O. Kuntze (Menyanthaceae). The bias of floral morph ratio in the populations was negatively correlated with the seed set. In the populations with biased floral morph ratio, the pollen on the stigma of the common morphs were dominated by pollen of the same morph, resulting in reduced seed set. The addition of pollen of the opposite morph on the stigmas of the common morph resulted in an increase of fruit and seed set rates. The intermorph pollination rate and the fruit and seed set rates of Nymphoides indica were highest when two floral morphs were close in the populations. Various insect species including Lepidoptera, Diptera and Hymenoptera visited the flowers. However, geitonogamous pollination was common because of the short flying distance of the pollinators. These results indicate that the seed set of Nymphoides indica is limited by the shortage of compatible pollens and that the success of intermorph pollination is influenced by spatial distribution of the two floral morphs. As Nymphoides indica is endangered, conservation of the populations with high fecundity is proposed by us.