Seed fitness of hermaphrodites in areas with females and anther smut disease: Silene acaulis and Microbotryum violaceum

Sex-dependent infection rates could change the effective sex ratio of a population. Here, I tested whether females and hermaphrodites of Silene acaulis were equally likely to be infected by Microbotryum violaceum, a fungus that sterilizes the host, and whether sex allocation in hermaphrodites differed between low and high disease plots. Sex ratios of healthy and diseased plants were estimated in five natural plots. Fitness gained through seed production was estimated by measuring seed quantity and quality for each sex morph in eight plots for 2 yr; four plots had 1-5% disease frequency and four plots had 18-25% disease frequency. Sex ratios of healthy and diseased plants did not differ in five plots. The proportion of fitness hermaphrodites gained through ovules varied from 25 to 48%, indicating that this population is near the cosexual end of gynodioecy. Variation in functional gender of hermaphrodites was not explained by sex-dependent infection rates. Spatial heterogeneity in resources and microclimate seems to be important in explaining both disease frequency and variation in seed production by females and hermaphrodites.     

Nursery pollination by a moth in Silene latifolia: the role of odours in eliciting antennal and behavioural responses

Since the 1970s it has been known that the nursery pollinator Hadena bicruris is attracted to the flowers of its most important host plant, Silene latifolia, by their scent. Here we identified important compounds for attraction of this noctuid moth. Gas chromatographic and electroantennographic methods were used to detect compounds eliciting signals in the antennae of the moth. Electrophysiologically active compounds were tested in wind-tunnel bioassays to foraging na?ve moths, and the attractivity of these compounds was compared with that to the natural scent of whole S. latifolia flowers. The antennae of moths detected substances of several classes. Phenylacetaldehyde elicited the strongest signals in the antennae, but lilac aldehydes were the most attractive compounds in wind-tunnel bioassays and attracted 90% of the moths tested, as did the scent of single flowers. Our results show that the most common and abundant floral scent compounds in S. latifolia, lilac aldehydes, attracted most of the moths tested, indicating a specific adaptation of H. bicruris to its host plant.     

Natural selection on floral traits of female Silene dioica by a sexually transmitted disease

Floral traits endowing high reproductive fitness can also affect the probability of plants contracting sexually transmitted diseases. We explore how variations in floral traits influence the fitness of Silene dioica females in their interactions with pollinators carrying pollen or spores of the sterilizing anther-smut fungus Microbotryum violaceum. We collected healthy and infected plants in a highly diseased population and grew them under conditions that 'cure' infected individuals, and used standard regression methods to detect natural selection on floral traits. Narrow-sense heritabilities, coefficients of additive genetic variation (CV(A)) and genetic correlations among traits were estimated from paternal half-sib groups. Pollinator preferences imposed strong direct and directional selection on traits affecting female attractiveness and pollen-/spore-capturing abilities. Levels of additive genetic variance were high in these traits, suggesting that rapid responses to selection are possible. By considering our results in the light of spatial and temporal heterogeneity resulting from the colonization dynamics typical for this species, we suggest that the conflicting selective effects of pollen/spore loads lead to the maintenance of genetic variation in these traits.     

Floral development in the tribe Cedreleae (Meliaceae, sub-family Swietenioideae): Cedrela and Toona

BACKGROUND AND AIMS: Floral development of Cedrela and Toona, the genera comprising the basal tribe Cedreleae of the sub-family Swietenioideae of Meliaceae, is described. The focus was on three endangered, ecologically and economically important species: Cedrela fissilis, Cedrela odorata and Toona ciliata. The aims of the study were to characterize the patterns of floral development in the tribe and to establish apomorphic and plesiomorphic floral characters in relation to other taxa within the family based on the current molecular phylogeny of Meliaceae. METHODS: A detailed floral structural and developmental study was completed using both scanning electron microscopy and visualization of microtome sections with a light microscope. KEY RESULTS: Twelve floral developmental stages were identified. The initial development of the pentamerous flowers of both Toona and Cedrela is strikingly similar. The morphological differences observed between them are due to differential patterns of organ elongation and adnation/connation occurring late in development. Additionally, the formation of functionally male and female flowers was found to occur at specific positions within the inflorescence. CONCLUSIONS: Due to the basal position of the tribe Cedreleae in the phylogeny of Meliaceae, functionally either male or female pentamerous flowers and the presence of (at least partially) free stamens may be considered plesiomorphic traits within the family. In contrast, sympetaly and the absence of nectaries in Cedrela species are synapomorphies.     

Effects of inbred/outbred crosses on progeny sex ratio in Silene latifolia (Caryophyllaceae)

Sex ratio polymorphism has been extensively studied in Silene latifolia, but it is neither known whether inbreeding (which is likely to occur under field conditions) affects it, nor which of the proposed mechanisms (Y degeneration, X-linked drive) is more important. Both mechanisms predict reduced pollen performance. In this study, females were crossed with pollen from related and unrelated males in single-donor and two-donor crosses, and the sex ratio of offspring (n = 866, 60 crosses), sons'in vitro pollen germination and sex ratios in parental families were scored. Flowers receiving only unrelated pollen produced a significant excess of sons. Sex ratios were not significantly correlated between generations. Sons'in vitro pollen germination was significantly negatively correlated with the 'sex-ratio phenotype' of maternal grandfathers, but not of fathers. This generation leap may be consistent with X-linked determinants because Y-linked determinants alone cannot explain it (grandfathers, fathers and sons share the same Y chromosome). Further work is required, but inbreeding and limited dispersal may lead to local accumulation of biasing factors, a process potentially countered by conditional shifts to produce more sons in pure outbred crosses.     

Characterization of microsatellite loci in Lychnis flos‐cuculi (Caryophyllaceae)

We cloned microsatellite repeats from ragged robin Lychnis flos‐cuculi (Caryophyllaceae) and developed 20 primer pairs for microsatellite marker analysis. We used 18 individuals of a large Swiss population to screen microsatellites. Seven loci were polymorphic. Between seven and 11 alleles were found per locus and the observed heterozygosity was between 0.308 and 0.813. Observed heterozygote deficits were significant in five of the seven loci, in line with the mixed mating system of L. flos‐cuculi.     

Consequences of inbreeding for offspring fitness and gender in Silene vulgaris,a gynodioecious plant

Abstract In gynodioecious plants, hermaphrodite and female plants co‐occur in the same population. In these systems gender typically depends on whether a maternally inherited cytoplasmic male sterility factor (CMS) is counteracted by nuclear restorer alleles. These restorer alleles are often genetically dominant. Although plants of the female morph are obligatorily outcrossing, hermaphrodites may self. This selfing increases homozygosity and may thus have two effects: (1) it may decrease fitness (i.e. result in inbreeding depression) and (ii) it may increase homozygosity of the nuclear restorer alleles and therefore increase the production of females. This, in turn, enhances outcrossing in the following generation. In order to test the latter hypothesis, experimental crosses were conducted using individuals derived from four natural populations of Silene vulgaris, a gynodioecious plant. Treatments included self‐fertilization of hermaphrodites, outcrossing of hermaphrodites and females using pollen derived from the same source population as the pollen recipients, and outcrossing hermaphrodites and females using pollen derived from different source populations. Offspring were scored for seed germination, survivorship to flowering and gender. The products of self‐fertilization had reduced survivorship at both life stages when compared with the offspring of outcrossed hermaphrodites or females. In one population the fitness of offspring produced by within‐population outcrossing of females was significantly less than the fitness of offspring produced by crossing females with hermaphrodites from other populations. Self‐fertilization of hermaphrodites produced a smaller proportion of hermaphroditic offspring than did outcrossing hermaphrodites. Outcrossing females within populations produced a smaller proportion of hermaphrodite offspring than did crossing females with hermaphrodites from other populations. These results are consistent with a cytonuclear system of sex determination with dominant nuclear restorers, and are discussed with regard to how the mating system and the genetics of sex determination interact to influence the evolution of inbreeding depression.     

Within‐ and among‐population variation in infectivity,latency and spore production in a host–pathogen system

In spatially structured populations, host–parasite coevolutionary potential depends on the distribution of genetic variation within and among populations. Inoculation experiments using the plant, Silene latifolia, and its fungal pathogen, Microbotryum violaceum, revealed little overall differentiation in infectivity/resistance, latency or spore production among host or pathogen populations. Within populations, fungal strains had similar means, but varied in performance across plant populations. Variation in resistance among seed families indicates the potential for parasite‐mediated selection, whereas there was little evidence for local pathogen genotype × plant genotype interactions assumed by most theoretical coevolution models. Lower spore production on sympatric than allopatric hosts confirmed local fungal maladaptation already observed for infectivity. Correlations between infectivity and latency or spore production suggest a common mechanism for variation in these traits. Our results suggest low variation available to this pathogen for tracking its coevolving host. This may be caused by random drift, breeding system or migration characteristic of metapopulation dynamics.     

米瓦罐的光合特性研究

采用美国LI-COR生产的LI-6400便携式光合系统研究了米瓦罐的光合特性。结果表明,米瓦罐光 合速率的日变化呈单峰曲线,上午10:00时光合速率达到最大值;在大气CO2浓度下,米瓦罐的光饱和点为 1 800μmol·m-2·s-1,光补偿点为30μmol·m-2·s-1;在光饱和点的光强下,米瓦罐的CO2饱和点为1 200 μmolCO2·mol-1,CO2补偿点为40μmolCO2·mol-1。