Ecological factors associated with pre-dispersal predation of fig seeds and wasps by fig-specialist lepidopteran larvae

In brood pollination mutualisms, predation of developing fruit can have large negative repercussions for both plant and pollinator population dynamics. The Sonoran Desert rock fig Ficus petiolaris and its highly-coevolved wasp pollinator are subject to frequent attack by lepidopteran larvae that consume fig fruit and the developing seeds and larval pollinators they contain. We used generalized linear mixed models to investigate how the phenology, quantity, and spatial distribution of fig fruits is associated with variation in lepidopteran damage intensity on individual trees at nine geographic locations spanning a 741 km latitudinal transect along Mexico's Baja California Peninsula. We found lepidopteran damage to be strongly positively associated with more synchronous fig crops and larger trees, and only weakly associated with lower local host tree density. These results imply that fruit production that is asynchronous within trees and spread out over time, as observed in several fig species, benefits female and male components of fitness (pollen disperser and seed production, respectively) by reducing pre-dispersal predation by frugivores.     

Effects of soil properties and clonal growth on the apparent sex ratio of the flowering stems of the dioecious clonal shrub Aucuba japonica var. borealis growing in an evergreen coniferous secondary forest

In dioecious plants, the frequencies of flowering stems in each sex produced through clonal growth provide important information on the potential for reproductive success in the populations. However, apart from the light environment in their habitat, the factors affecting the flowering of each sex have not been well documented in shrub species that can maintain their populations in shady environments. In this research, we investigated seven soil variables and the flowering of stems of Aucuba japonica var. borealis in patches of this dioecious clonal shrub with different apparent stem sex ratios in an evergreen coniferous secondary forest with a shady forest floor. Of the 53 patches examined, 52 contained stems with flowers. Flowering stem ratios exhibited a positive relationship with available soil phosphate but a marginal negative relationship with exchangeable magnesium, whereas soil water content was associated with a female-biased flowering sex ratio. Stem density tended to be negatively related to flowering stem ratios in patches containing stems with female flowers but not males. While the results demonstrate that abundant amounts of certain nutrients and moisture in soils promote the production of flowers and/or a bias toward femaleness in patches, it is suggested that antagonistic effects of cations in the soil can inhibit the flowering of both sexes. In addition, the trade-off between sexual reproduction and clonal propagation in the females may amplify the variations in flowering in the population.     

Vegetative and reproductive phenological traits of Rhizophora mucronata Lamk. and Sonneratia alba Sm.

Mangrove phenology is important in understanding the past, present and future response of mangrove species to impacts of climate change. Our study is the first long term direct observation of the phenology of Rhizophora mucronata and Sonneratia alba in Kenya. Objective of the study was to determine, interpret and document the timing of the various phenoevents and phenophases, and to establish relationships between phenology and the climatic variables. Phenological traits were investigated in six monospecific mangrove stands in Gazi Bay, south of Mombasa, for 2 years. Leaf emergence, leaf fall, flower bud, flower and fruit initiation data were recorded every fortnight in 54 shoots of 9 trees at each site. Continuous leaf emergence and loss characterized by multimodal peaks was observed for the two species. Leaf emergence and leaf fall peaked in the wet months and was reduced in the dry months. There was a relationship between the leaf emergence and drop with the reproductive phenology in the two species. Mean leaf longevity for R. mucronata and S. alba was 12.8 ± 1.2 and 4.9 ± 0.5 months respectively. The reproductive cycle took approximately 16–20 months in R. mucronata and 4–5 months in S. alba. Bud initiation in R. mucronata was seasonal and occurred in October and September. Buds were observed for 8–11 months developing slowly on the shoots. Shifts were observed in the timing of flower initiation, and the flowering period lasted in total for 4–5 months. The time period from flower appearance to the developmental start of immature propagules lasted about 1 month at reforested sites and up to 5 months in stands of natural vegetation. In R. mucronata initiation of immature propagules was not seasonal and varied among the sites. Fruiting in S. alba was short and seasonal without overlap, and shifts were observed in the timing of flowering, flowering and fruiting peaks. Abscission of reproductive parts started in July and in June, respectively, in the years 2005 and 2006. Fruiting was observed starting in August in both years, and fruiting peak was reached in October in 2005 and one month earlier in 2006. In R. mucronata vegetative and reproductive phenophases significantly correlated with climatic variables, whereas in S. alba only leaf emergence and leaf fall correlated with temperature. The flowering plasticity in the reproductive phenology of the two species indicates possible sensitivity to certain climatic and environmental triggers. Our results also indicate that R. mucronata trees have a distinctly higher investment in the reproductive cycle than S. alba.     

Mapping a floral trait in Shepherds purse – ‘Stamenoid petals’ in natural populations of Capsella bursa-pastoris (L.) Medik

Striking feature of angiosperm diversity is the huge number of variations in corolla morphology including complex innovations like variations in symmetry or the identity and number of floral organs. Throughout the Brassicaceae, the disymmetric flower structure is highly conserved. Still, quite a few floral alterations occur like a variant of Common Shepherds purse (Capsella bursa-pastoris), in which all petals have been transformed into additional stamens. This “decandric” phenotype has been reported for the first time about 200 years ago. In some of the original locations the variant has been recovered recently. The long term persistence indicates the establishment of an evolutionary novelty in wild populations in sympatric occurrence with wild-type plants. Due to this fact the floral variant has become an interesting model for evolutionary studies. The phenotype is heritable and just a single locus, termed “Stamenoid petals” (Spe), is assumed to be involved in the molecular origin. To unravel the chromosomal localization of this locus, a linkage map analysis was carried out using molecular markers (AFLPs, RAPDs). The final map includes 15 linkage groups and the floral trait was integrated on linkage group 12 (CBP12) including six AFLP markers. Out of these, five markers were successfully sequenced and revealed sequence identities with chromosome IV of the A. thaliana genome. Interestingly, AGAMOUS is located on this chromosome, the only class C floral organ identity gene in the A. thaliana genome, which is compatible with the assumption that Spe is an allele of AGAMOUS rather than a regulator of that gene.     

An analysis of age-and size-dependent flowering: A critical-production model

Three critical phenomena of flowering can be recognized in nature: critical age, critical initial size and critical switchover size. In order to understand the ecological significance of these flowering phenomena from the viewpoint of matter production, a simple model of flowering phenomean (critical-production model) was studied, assuming that plant flowering is controlled by the productive capacity of the plant (critical-production model, under the condition that plants forecast environmental conditions affecting matter production. Thus, we concluded that all three critical phenomena are various manifestation of the same critical-production principle. Then, using the model simulation, the reliability of each critical phenomenon for securing a given critical production was investigated in relation to the photosynthetic productivity of the habitat. The main predictions obtained from the simulation were as follows: 1) Only annual and biennial plants will show critical age phenomena, and most biennials will be facultative. 2) Among perennials, the critical initial size phenomenon will appear in low productive habitats, whereas in high productive habitats the critical switchover size phenomenon will be observed.     

Phytochrome and photoperiodic induction

The photoreceptor phytochrome has been extensively characterized at the chromophore, protein and gene level. It consists of a family of red/far-red reversible molecules and the genes for three members have been sequenced. Phytochromes are chromoproteins, which probably exist as dimers in vivo. Photoperiodism in higher plants involves the interaction of phytochrome with an endogenous timekeeping system. The interaction is complex, and several distinct actions of light can be distinguished. The possible involvement of different phytochromes in different actions of light in both long-day plants and short-day plants is discussed. Potential roles for different members of the phytochrome family and homo-and hetero-dimers of phytochrome are proposed.     

Effects of solar UV-B radiation on growth,flowering and yield of central and southern European bush bean cultivars (Phaseolus vulgaris L.)

Different cultivars of bush beans (Phaseolus vulgaris L.) originating from Central and Southern Europe were grown from July to August/September 1993 up to 7 and 8 weeks, respectively, in two greenhouses covered by different UV-B-absorbing (280-320nm) plastic foils. By using the ambient UV-B radiation of the southern location (Portugal, 38.7°N, 9.1°W) in one of the greenhouses as intense UV-B radiation compared to the reduced radiation in the second greenhouse at the same place, a difference in UV-B of about 8–10% was simulated. All cultivars examined showed significant reductions in height of up to 31,8% in most growth phases under intense UV-B. Also fresh and dry weight as well as leaf area were reduced under intense UV-B in the cultivars Purple Teepee, Cropper Teepee and Goldstrahl, and in early growth phases also in Coco bianco, but with ongoing development this cultivar caught up. Cultivars Hilds Maja, Primel, Manata and Cannellino exhibited no UV-B effects on weight and leaf area. A flowering delay of up to 1 day was observed under intense UV-B in several cultivars. Probably due to this delay the yield (fresh weight of fruits) decreased in all cultivars up to 55% under intense UV-B at harvest time, while the potential yield (sum of buds, opened flowers and fruits) was reduced only in the cultivars Cropper Teepee, Purple Teepee, Cannellino and Goldstrahl. The UV-sensitivity index (UVSI) calculated according to the UV induced changes in growth, dry weight and yield at the second harvest date has shown that all cultivars are UV-sensitive, however the index was numerically higher for Southern European cultivars (average = 2.5) than for Central European ones (average = 2.3) which means that the first group was slightly less UV-sensitive than the second.     

Inhibition of growth and synchronised cell division in the shoot apex in relation to flowering in Silene

When plants of Silene coeli-rosa (L.) Godron were induced by seven long days, then exposed to darkness for 48 h before being returned to short days, they went on to initiate flowers with a delay of about 2 d. The synchronisation of cell division which normally occurs before flower initiation was suppressed, showing that it is not essential for flowering. Periods of darkness of up to 240 h inhibited apical growth and leaf initiation but did not prevent eventual flowering in short days. The commitment of the apex to flower was therefore maintained while apical growth was inhibited.Abbreviations SD short day(s) - LD long day(s)     

Megagametogenesis in Halophila johnsonii, a threatened seagrass with no known seeds,and the seed-producing Halophila decipiens (Hydrocharitaceae)

Megagametogenesis, the development of a megaspore into an embryo sac, has been identified in the seagrass Halophila johnsonii, a threatened species with no known sexual reproduction or seeds. Megagametogenesis in H. johnsonii was compared with megagametophyte development in Halophila decipiens, a related species known to readily produce viable seeds. In both species, ovules were structurally similar, megaspore mother cells were seen in premeiotic ovules, and linear tetrads and megagametophytes with two to eight nuclei were present in postmeiotic ovules. However, H. decipiens postmeiotic ovules had a chalazal pouch that was absent in the postmeiotic ovules of H. johnsonii. Late-stage H. decipiens ovules also contained embryos, indicating that they had been fertilized, whereas all late-stage H. johnsonii ovules were degrading and showed no signs of fertilization. These observations suggest that meiosis does occur in H. johnsonii megasporocytes, leading to the formation of viable megagametophytes and egg cells that could be fertilized if pollination occurred. Thus, the lack of seed set is due to a lack of pollination rather than any loss of capacity to produce seeds in this species.