First record of troglobitic Hemiptera (Fulgoromorpha: Cixiidae) from La Réunion Island

A new species of troglobitic Cixiidae (Hemiptera: Fulgoromorpha), Brixia briali n. sp. is described from a lava tube on La Réunion Island. Information on its ecology, distribution, and comments on its tentative systematic placement into the genus Brixia is provided. The new discovery from La Réunion is placed into the context of cavernicolous Fulgoromorpha of the world, their zoogeography, ecology and biology.     

Self-incompatibility and pollen limitation in the rare tristylous endemic Hugonia serrata on La R��union Island

Surveys of the incompatibility status of island floras have shown a deficit in taxa possessing homomorphic or heteromorphic incompatibility. This observation provides strong evidence for Baker??s Rule (1967) in that self-incompatibility can impede these taxa of colonizing and establishing on islands. The woody liana Hugonia serrata Lam. (Linaceae) is an extremely rare plant species endemic to the Mascarene Islands of La Réunion and Mauritius in the southern Indian Ocean. Previous research has documented the existence of tristyly in this species, thereby raising the number of known tristylous families to six. However, data were based on a very small sampling size and currently no data on the self-incompatibility system of the species are available. In this study, we investigated in detail the breeding system of H. serrata. Calculation of reciprocity and precision indices based on measurements of reproductive organs in a much larger sample size confirmed tristyly in this species. This style?Cstamen polymorphism was accompanied by several ancillary polymorphisms in stigma size, stigma color, anther size and pollen size. The rigidity of the heteromorphic incompatibility system was tested using experimental hand-pollinations. Significantly fewer pollen tubes arrived at the ovary after self- and illegitimate pollination (7%) than after legitimate pollination (12%). Seed set after self-pollination (3.6%) was also much lower than after legitimate pollination (66.7%). Comparison of seed set after legitimate pollination with natural seed set showed evidence for outcross pollen limitation. Our results indicate that despite severe pollen limitation and limited mate availability the heteromorphic incompatibility system in H. serrata is still strict after colonization of La Réunion Island. Because H. serrata is extremely long-lived, these results suggest that establishment of heterostylous species on islands may have been favored by their long life span.     

Pollen and stigma size changes during the transition from tristyly to distyly in Oxalis alpina (Oxalidaceae)

• Pollen and stigma size have the potential to influence male fitness of hermaphroditic plants, particularly in species presenting floral polymorphisms characterised by marked differences in these traits among floral morphs. In this study, we take advantage of the evolutionary transition from tristyly to distyly experienced by Oxalis alpina (Oxalidaceae), and examined whether modifications in the ancillary traits (pollen and stigma size) respond to allometric changes in other floral traits. Also, we tested whether these modifications are in accordance with what would be expected under the hypothesis that novel competitive scenarios (as in distylous‐derived reproductive system) exert morph‐ and whorl‐specific selective pressures to match the available stigmas.
• We measure pollen and stigma size in five populations of O. alpina representing the tristyly–distyly transition.
• A general reduction in pollen and stigma size occurred along the tristyly–distyly transition, and pollen size from the two anther levels within each morph converged to a similar size that was characterised by whorl‐specific changes (increases or decreases) in pollen size of different anthers in each floral type.
• Overall, results from this study show that the evolution of distyly in this species is characterised not only by changes in sexual organ position and flower size, but also by morph‐specific changes in pollen and stigma size. This evidence supports the importance of selection on pollen and stigma size, which increase fitness of remaining morphs following the evolution of distyly, and raises questions to explore on the functional value of pollen size in heterostylous systems under pollen competition.

     

Tristyly, self-compatibility and floral variation in Decodon verticillatus (Lythraceae)

Heterostyly typically involves reciprocal polymorphism in stamen and style lengths, physiological self- and intramorph-incompatibility, and a set of associated polymorphisms of pollen and stigma characters. This study examined floral morphology and compatibility relationships in the monotypic, herbaceous perennial Decodon verticillatus (Lythraceae). There have been conflicting reports on the occurrence of tristyly in the species, probably because of frequent loss of style morphsm from populations in parts of the species' range. Floral morphology was examined using material collected from natural populations throughout the range. Detailed floral measurements revealed discrete trimorphism in style length and anther positioning in three populations. Data from two dimorphic populations showed similar patterns of floral polymorphism, except that both were missing the mid-styled morph. In one dimorphic population, there was evidence for modification in the length of mid-level stamens. Measurements in three populations indicated pronounced floral variability, including high frequencies of modified phenotypes with reduced stigma-anther separation. Pollen size was only weakly differentiated among anther levels, and there were no differences in pollen production among anther levels or morphs. In contrast, stigma size and papilla length showed a strong negative correlation with style length; a pattern opposite to most heterostylous species. Experimental crosses performed under glasshouse conditions on plants from two populations showed a high degree of both self- and intramorph-compatibility. A comparative analysis of floral morphology showed that D. verticillatus is not unusual in terms of the precision and reciprocity of organ positioning compared with 13 other tristylous species.     

Sexual and asexual reproduction of the holothurian Stichopus chloronotus (Echinodermata): a comparison between La Réunion (Indian Ocean) and east Australia (Pacific Ocean)

Summary

Stichopus chloronotus (Brandt, 1835) is one among nine aspidochirotide holothurian species known to reproduce both sexually by broadcast spawning and asexually by transverse fission. New data on the sexual cycle of this species in La Réunion are presented here and information available on sexual and asexual reproduction in this species is summarised. Sexual reproduction on La Réunion shows a distinct seasonality with a main spawning period in the warm season (November-February). The spawning period the Great Barrier Reef appears to be at the same time. Some intriguing deviations from unity in sex-ratio, usually biased towards more male individuals, have been observed in both geographic regions (sex ratio at La Reunion 31:1). New data on the asexual reproduction of this species in La Réunion confirm the high rates of fission. The peak of asexual reproduction in both the Indian and Pacific Ocean was observed in winter (June-July). Thus, asexual reproduction in this species occurs outside the season for sexual reproduction. The rate of asexual reproduction appears to vary between sample locations. However, results of population genetic studies on S. chloronotus (Uthicke et al., 1999; Uthicke et al., 2001) indicated that in most populations investigated a maximum of about 60% of all individuals may be derived from sexual recruitment. Cluster analyses on genetic distances between populations grouped populations within Oceans together, with the exception of one sample from a nearshore reef of the GBR. Although genetic differences between the two regions exist, these are relatively small regarding the large geographic distance. We conclude that asexual reproduction in S. chloronotus is important to maintain local population sizes, but that larval exchange between populations mediated by sexual reproduction is important for colonisation of new areas and to provide connectivity between populations. Here, we present the first synthesis of these phenomena for a holothurian species.     

Haplotype diversity of the nematode Pristionchus pacificus on Réunion in the Indian Ocean suggests multiple independent invasions

Pristionchus pacificus has been established as a nematode model system in evolutionary developmental biology and evolutionary ecology. Field studies in North and South America, Asia, Africa and Europe indicated that nematodes of the genus Pristionchus live in association with scarab beetles. Here, we describe the first account of soil‐ and beetle‐associated nematodes on an island setting by investigating the island of Réunion in the Indian Ocean. Réunion has high numbers of endemic insects and is one among several attractive islands for biodiversity studies. Being of volcanic origin, Réunion is 2–3 million years old, making it the youngest of the Mascareigne islands. We show that beetle‐ and soil‐derived nematodes on Réunion are nearly exclusively hermaphroditic, suggesting that selfing is favoured over gonochorism (outcrossing) during island colonization. Among members of four nematode genera observed on Réunion, Pristionchus pacificus was the most prevalent species. A total of 76 isolates, in association with five different scarab beetles, has been obtained for this cosmopolitan nematode. A detailed mitochondrial haplotype analysis indicates that the Réunion isolates of P. pacificus cover all four worldwide clades of the species. This extraordinary haplotype diversity suggests multiple independent invasions, most likely in association with different scarab beetles. Together, we establish Réunion as a case study for nematode island biogeography, in which the analysis of nematode population genetics and population dynamics can provide insight into evolutionary and ecological processes. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 170–179.     

Increasing distribution and damage to palms by the Neotropical whitefly,Aleurotrachelus atratus (Hemiptera: Aleyrodidae)

In recent years, the coconut whitefly, Aleurotrachelus atratus Hempel, has been recorded from various islands in the southwestern Indian Ocean. Field surveys in La Réunion, the Seychelles, the Comoros and glasshouses in Paris have allowed us to record this whitefly on 56 palm species, some of which are endemic and/or threatened species. Most of trees showed low infestation levels, except for the coconut palm that is its main host plant. Such a wide host range has facilitated the rapid geographical dissemination of this whitefly. A field study was conducted in 2006 in La Réunion, to gain a better understanding of the bioecology of A. atratus in a tropical insular ecosystem. The whitefly was found throughout the island, from sea level to 800‐m altitude. Five parasitoid species (Hymenoptera: Aphelinidae) were found associated with the populations of this pest, with Eretmocerus cocois Delvare being the dominant one. A laboratory study showed that the pre‐imaginal development of A. atratus is around 48 days at 25–27°C, which is relatively long compared to other whitefly species. With a sex ratio of one male per 1022 females collected in La Réunion, it appears that the whitefly reproduces by thelytoky. It represents a threat to ornamental and agricultural palms as well as to natural palm ecosystems in the absence of effective parasitoids.     

Evolutionary consequences of extensive morph loss in tristylous decodon verticillatus (Lythraceae): a shift from tristyly to distyly?

The evolution of distyly from tristyly has occurred repeatedly, especially in the Lythraceae. However, the evolutionary forces involved remain unclear since species exhibiting transitional stages between tristyly and distyly have rarely been studied. The self-compatible, wetland perennial Decodon verticillatus (Lythraceae) may provide this transitional variation since populations commonly lack style morphs, particularly the mid-styled (M) morph. In dimorphic populations lacking the M morph, anthers positioned at the mid level in both the long- (L) and short-styled (S) morphs have lost their target stigma, setting the stage for either evolutionary repositioning of mid-level anthers to increase pollen export to L and S stigmas, or increased variability in mid-level anther position resulting from relaxed selection. We examined these two hypotheses by comparing floral morphology in eight dimorphic and ten trimorphic populations from throughout the species’ range. We found no evidence that loss of the M morph has led to evolutionary modification of mid-level stamens. While mid-level stamens of the S morph were 11.0 ± 4.0% (mean ± 1 SE) longer than those of the L morph in dimorphic populations, divergence in stamen length between morphs occurred to the same extent (10.4 ± 2.0%) in trimorphic populations and cannot be attributed to the absence of the M morph. Analyses of variability using median ratio tests revealed no difference in the variability of mid-level stamen length between dimorphic and trimorphic populations. Mid-level stamens were not more variable than long- and short-level stamens within dimorphic populations. The consistent divergence in mid-level stamens between the L and S morphs may reflect morph-specific differences in the optimal position of mid-level anthers for maximizing cross-pollination and avoiding self-fertilization.     

Evidence for a Founder Effect After Introduction of <Emphasis Type="Italic">Tomato Yellow Leaf Curl Virus</Emphasis>–Mild in an Insular Environment

Evolution of Tomato yellow leaf curl virus–Mild (TYLCV-Mld[RE]) (family Geminiviridae, genus Begomovirus) was monitored in La Réunion island from its first upsurge in 1997 until 2004. Two genome fragments, one comprising partial C4 and C1 open reading frames (ORFs), and the other comprising part of the V1 and V2 ORFs and part of the intergenic region were sequenced in 111 isolates. The very low initial diversity of TYLCV-Mld[RE] in La Réunion was followed by a quasi-linear increase in genetic diversity across years. In addition, the population effective size of TYLCV-Mld[RE] has undergone a sudden increase from 2001 to 2004, which is consistent with a founder effect due to the introduction of a small number of virus individuals in an insular environment. Surprisingly, one nucleotide substitution introducing a premature stop codon in the C4 ORF was observed in an increasing number of isolates in the population of TYLCV-Mld[RE] over time, contrasting with the other substitutions which were observed at low frequencies. This substitution which shortens the C4 protein by four amino acids may therefore have been selected during TYLCV-Mld[RE] evolution. [Reviewing Editor: Dr. Nicolas Galtier]     

Population-level variation in the expression of heterostyly in three species of Rubiaceae: does reciprocal placement of anthers and stigmas characterize heterostyly?

Heterostyly (i.e., reciprocal placement of anthers and stigmas between two or three floral morphs) is hypothesized to enhance outcrossing and reduce selfing. However, few studies have documented reciprocity among individual plants; instead, mean anther and stigma heights for floral morphs are usually reported, masking interindividual variation. We measured eight floral dimensions for individuals in five populations of three heterostylous Rubiaceae. The three methods used to quantify reciprocity yielded different conclusions regarding the degree to which populations conformed to expectations for heterostylous plants. Only Psychotria poeppigiana had stigma and, to a lesser degree, anther heights in discrete classes. Variation among plants of Bouvardia ternifolia and Psychotria chiapensis yielded a continuum of anther and stigma heights across populations. Comparison of distances between stigma and anthers indicated that only flowers of B. ternifolia had, as expected, a constant value for this distance. Finally, regression relationships between anther and stigma heights and corolla length showed that only in one population each of B. ternifolia and P. poeppigiana, and in P. chiapensis, was distance between anthers and stigmas the same across the range of corolla sizes for both floral morphs. Variation among these species in expression of heterostyly was not clearly linked to phylogenetic relationship or pollinator syndromes. Two approach herkogamous (AH) species were studied for comparison. Flowers of Psychotria brachiata were consistently AH, but flowers of P. pittieri were highly variable. Determining fitness consequences of population-level variation in sexual systems requires studies linking floral morphology to pollinator behavior and pollen transfer.     

Environmental contribution to floral trait variation in Chamaecrista fasciculata (Fabaceae: Caesalpinoideae)

Although intraspecific variation in plant floral traits has been documented for a number of plant species, the causes of such variation are largely unknown. We first quantified floral trait variation in an Illinois prairie population of Chamaecrista fasciculata Michx. We then used a field experiment to determine the contribution of leaf herbivory to this variation and a greenhouse experiment to determine the contribution of leaf herbivory, and variable soil nutrient and water content to floral trait variation. Variation in environmental factors explained a significant portion of the naturally occurring variation in corolla width, ovule number, ovule size, and anther length. In the field, manual removal of 25% or more leaf area reduced ovule size and anther length (and by inference, pollen production), and delayed flowering. In the greenhouse, plants from which we removed 25% or more of their leaf area or which were given limited water produced fewer ovules than control plants. Addition of nutrients interacted with soil moisture to affect corolla diameter and ovule number. Despite our demonstration of significant environmental impacts on reproductive traits, these impacts were relatively much smaller than those on plant size, suggesting that floral traits are buffered against variable resource availability.     

Geographic origin and taxonomic status of the invasive Privet, Ligustrum robustum (Oleaceae), in the Mascarene Islands, determined by chloroplast DNA and RAPDs

Information concerning the area of origin, genetic diversity and possible acquisition of germplasm through hybridisation is fundamental to understanding the evolution, ecology and possible control measures for an introduced invasive plant species. Among the most damaging of alien plants that are invading and degrading native vegetation in the Mascarene Islands of the Indian Ocean is the Tree Privet, Ligustrum robustum. Exact information about the geographic source of introduced material of this species is lacking, in part because Ligustrum is a taxonomically difficult genus. Native material of L. robustum ssp. walkeri from Sri Lanka, L. robustum ssp. robustum from northeastern India, and the closely related L. perrottetii from southern India was compared with introduced material from La Réunion and Mauritius using chloroplast DNA RFLP markers and random amplified polymorphic DNA (RAPDs). Sri Lankan and introduced material was monomorphic for the same cpDNA haplotype that was absent from south and northeast Indian Ligustrum. Sri Lankan and introduced material was also clearly distinguished from Indian Ligustrum by RAPDs. It was concluded that material introduced and established in the Mascarene Islands is derived from the Sri Lankan subspecies L. robustum ssp. walkeri. No geographic structuring of genetic variation within Sri Lanka was detected for this taxon, so the location(s) within Sri Lanka from which introduced material is derived could not be pinpointed. RAPDs indicate that L. robustum ssp. walkeri in Sri Lanka is more similar to south Indian L. perrottetii than to northeast Indian L. robustum ssp. robustum. Moreover, RAPDs showed that introduced material in La Réunion has undergone little or no loss of genetic diversity since introduction. However, there was no evidence that it is introgressed with germplasm from two other alien Ligustrum species present on La Réunion.     

Reproductive compatibility and genetic and morphometric variability among populations of the predatory mite,Amblyseius largoensis (Acari: Phytoseiidae), from Indian Ocean Islands and the Americas

The red palm mite (RPM), Raoiella indica Hirst (Acari: Tenuipalpidae), is an invasive phytophagous mite that was recently introduced into The Americas. The predatory mite Amblyseius largoensis Muma (Acari: Phytoseiidae) has been the only natural enemy consistently found in association with RPM. This study aimed to determine if A. largoensis populations from the Indian Ocean Islands (La Réunion and Mauritius) and the Americas (Brazil, Trinidad and Tobago and the USA) consist a taxonomic unit or a group of cryptic species. First, the morphological variability among the A. largoensis populations from these areas was evaluated through morphometric analyses of 36 morphological traits. Then, their genetic variability and phylogenetic relationships were assessed based on two target DNA fragments: the nuclear Internal Transcribed Spacer and the mithochondrial 12S rRNA. Finally, reproductive compatibility of the populations from La Réunion and Roraima, Brazil was evaluated. Morphometric differences between the A. largoensis specimens from La Réunion Island and the Americas were observed, most of them on the length of the setae. Molecular analysis indicated that the A. largoensis populations from the Indian Ocean Islands and the Americas belong to the same taxonomic entity, although to two well defined genetic groups. Crossings involving the A. largoensis populations from La Réunion Island and Roraima, Brazil revealed complete reproductive compatibility between these populations. Information on the morphometric and genetic variability among studied A. largoensis populations can be further exploited in future studies to follow colonization of Indian Ocean Islands populations in the Americas, in the case of field releases.     

茜草科二型花柱植物滇丁香传粉精确性研究

异型花柱是一种受遗传因素控制的花型多态性现象,其适应意义在于提高不同花型间传粉精确性,从而促进异交。为检验二型花柱植物滇丁香（Luculia pinceana）是如何促进异交并确定有效传粉者的类型,实验统计自然种群中长、短柱型的植株数量,测量花部特征,统计自然种群植株柱头上的型间花粉落置的数量和比例,比较型内、型间花粉的萌发率以及花粉管长度,比较不同人工授粉处理结实情况,观察传粉昆虫类型并测量虫体特征。结果表明（1）滇丁香自然居群中长、短柱型植株的数量没有显著性差异。长柱型的筒深、筒直径、开口直径、雄蕊长和柱头长均显著小于短柱型,而长柱型的叶片长和宽、雌蕊长、花药体积、花粉粒体积、柱头厚均显著大于短柱型。（2）自然种群植株柱头上型间花粉所占比例显著低于型内花粉的比例。（3）型间授粉的花粉萌发率以及花粉管长度均大于型内授粉和混合授粉。（4）型间授粉的结实率显著高于型内授粉的结实率,型内授粉具有一定的结实。（5）夜行性长喙条背天蛾（Cechenena lineosa）是滇丁香的有效传粉者,其吻长和滇丁香的花筒深相适应。本研究表明二型花柱植物滇丁香主要是通过与其花部特征相匹配的长喙天蛾实现有效的传粉,通过促进型间花粉的萌发和花粉管的伸长而有利于型间授粉结实,提高传粉精确性。     

Casuarina Invasion Alters Primary Succession on Lava Flows on La Réunion Island

Invasive plants can alter community dynamics and the successional trajectories of ecosystems they colonize. We explore how interactions between disturbance and invasion govern successional trajectories in the case of Casuarina equisetifolia invading lava flows on La Réunion Island. Surveys from 1972 and 1990 were compared with results of a survey in 2012 to detail progression of the invasion over time. General additive models were used to estimate the influence of altitude, distance to putative source of introduction, and lava flow age on the abundance of C. equisetifolia. Based on the predictions, we estimated the likely rate and eventual extent of spread of the species in the area through time. We placed our findings in the context of a conceptual model of successional processes in the area to highlight how the invasion of C. equisetifolia and natural and human‐mediated disturbances are changing natural vegetation dynamics. The extent of invasion by C. equisetifolia has increased twentyfold over the past 40 yr from 110 ha in 1972 to 2373 ha in 2012. Lava flows have facilitated this spread, and in turn C. equisetifolia has started to radically change successional trajectories, increasing the rate of succession sevenfold. The continued spread of this species poses a major threat to the small area of remaining native lowland rain forests on La Réunion Island, which cover <2 percent of their original extent.     

Variation in expression of trimorphic incompatibility in Pontederia cordata L. (Pontederiaceae)

Summary Pontederia cordata L. (Pontederiaceae), a perennial diploid, possesses the rare genetic polymorphism tristyly. A controlled pollination programme was conducted over a three year period, under glasshouse conditions, on 36 clones of P. cordata var. cordata to examine the nature of the self-incompatibility system. The three major findings of the pollination study were: (1) the three floral morphs display different levels of self-incompatibility, (2) pollen from the two anther levels within a flower exhibits different compatibility behaviour in self-pollinations, (3) considerable individual genetic variation in the expression of self-incompatibility is evident among clones within floral morphs. Similar results were also obtained from a smaller study on 15 clones of P. cordata var. lancifolia conducted over a 6 month period. In common with other Pontederia species the mid-styled morph (M) of P. cordata produces large amounts of seed when self-pollinated with pollen from long-level anthers. A developmental model is proposed to explain the high level of self-compatibility of the M morph in Pontederia species. Self-pollination of segregating progenies from M and S morphs of known incompatibility status demonstrated that the expression of incompatibility is closely associated with style length. It is suggested that overall differences in incompatibility behaviour among the floral morphs may be due to the pleiotropic effects of major genes controlling sub-characters of the tristylous syndrome, rather than linked modifier genes. However, the variable expression of trimorphic incompatibility within floral morphs suggests that this variation may be polygenic in origin.     

Reproductive trait variation in the functionally dioecious and morphologically heterostylous island endemic Chassalia corallioides (Rubiaceae)

Documenting the floral biology and breeding system of species throughout the Rubiaceae family provides data on the number of times heterostyly and dioecy may have evolved in this large family. The objectives of this paper are to quantify (a) whether Chassalia corallioides , a small tree endemic to La Reunion Island in the Indian Ocean, is another example of the evolution of dioecy from distyly and (b) whether reproductive traits linked to male and female function vary over the ecological distribution of this species. Quantification of pollen production and fruit set following controlled and natural pollinations demonstrate that this species is dioecious. Male flowers have longer corolla tubes than female flowers. Female flowers have long styles with stigmas placed above the anthers whereas males have short styles with stigmas placed below the anthers. Stigmas and anthers are reciprocally placed in each morph, illustrating that the species is morphologically heterostylous. Both fecundity and flower size are negatively correlated with altitude. In male plants, corollas are shorter and wider and anthers are placed closer to the mouth of the corolla tube with increasing altitude. Male plants flowered more often than female plants, the likely cause of the male biased sex ratio in each of the two years studied. The evolution of dioecy in relation to the island biogeography of the region and the diversification of the genus Chassalia is discussed.     

FEATURES OF POLLEN FLOW IN DIMORPHIC SPECIES OF LYTHRUM SECTION EUHYSSOPIFOLIA

The North American Lythrum lineare L., L. alatum Pursh, L. curtissii Fernald, and L. californicum T. & G. have distylous flowers that differ in a number of traits. In the two species examined, pins have a stronger incompatibility system than thrums. Pins outnumber thrums in natural populations, but the ratio of the two may change radically during the course of a year, probably as a result of sexual reproduction. Exotic honeybees visiting L. californicum exhibited preferential collection of pin pollen over thrum pollen. The relative proportion of pin and thrum pollen grains transferred to stigmas is not dependent upon the proportion in which these pollen grains are produced in a population. Analyses of stigmatic pollen loads of L. lineare and L. californicum indicate very high levels of intramorph pollen flow. Although distyly is likely derived from tristyly in Lythrum, pollen flow patterns in trimorphic species seem to operate more “efficiently” than in dimorphic ones. It is probable that distyly has evolved from tristyly several times in the Lythraceae, but comparisons between pollen flow patterns in distylous species and those in a tristylous species provide no clear insights into the selective pressures that have led to this fundamental change in floral morphology and reproductive system.     

Specificity and seasonal prevalence of anther smut disease Microbotryum on sympatric Himalayan Silene species

Host sympatry provides opportunities for cross‐species disease transmission and compounded disease effects on host population and community structure. Using the Silene–Microbotryum interaction (the castrating anther smut disease), eleven Himalayan Silene species were assessed in regions of high host diversity to ascertain levels of pathogen specificity. We also investigated disease prevalence, seasonal dynamics of infection and flowering patterns in five co‐blooming Silene species. We identified several new Microbotryum lineages with varying degrees of specialization that is likely influenced by degrees of host divergence and ecological similarities (i.e. shared pollinator guilds). Affected species had 15%–40% of plants infected by anther smut. Flowering was seasonally overlapping among host species (except for the species pair S. asclepiadea and S. atrocastanea), but diseased flowering onset was earlier than healthy plants, leading to dramatic seasonal shifts in observed disease prevalence. Overlapping distributions and flowering provides opportunities for floral pathogen movement between host species, but host specialization may be constrained by the plant phylogenetic relatedness, adaptation to micro‐habitats and difference in pollinator/vector guilds.     

Genetic control of floral morph in tristylous Pickerelweed (Pontederia cordata L.)

Pickerelweed (Pontederia cordata L.) is a diploid (2n = 2x = 16) tristylous aquatic perennial. Populations usually contain 3 floral morphs that differ reciprocally in style length and anther height (referred to as the long-, mid-, and short-styled morphs, hereafter L-, M-, and S-morphs). The floral polymorphism promotes disassortative mating among the 3 floral morphs and is maintained in populations by negative frequency-dependent selection. The objective of this study was to determine the number of loci, number of alleles, and gene action controlling floral morph in pickerelweed. Three parental lines (one each of the L-, M-, and S-morph) were used to create S1 and F1 populations. F2 populations were produced through self-pollination of F1 plants. Progeny ratios of S1, F1, and F2 generations revealed that tristyly is controlled by 2 diallelic loci (S and M) with dominant gene action. The S locus is epistatic to the M locus, with the S-morph produced by plants with the dominant S allele (genotype S _ _ _). Plants with recessive alleles at the S locus were either L-morph (ssmm) or M-morph (ssM_). The results of this experiment demonstrate that the inheritance of tristyly in pickerelweed is the same as previously reported for several tristylous species in the Lythraceae and Oxalidaceae.