Effects of fine‐scale genetic structure on male mating success in gynodioecious Beta vulgaris ssp. maritima

Plant mating systems are known to influence population genetic structure because pollen and seed dispersal are often spatially restricted. However, the reciprocal outcomes of population structure on the dynamics of polymorphic mating systems have received little attention. In gynodioecious sea beet (Beta vulgaris ssp. maritima), three sexual types co‐occur: females carrying a cytoplasmic male sterility (CMS) gene, hermaphrodites carrying a non‐CMS cytoplasm and restored hermaphrodites that carry CMS genes and nuclear restorer alleles. This study investigated the effects of fine‐scale genetic structure on male reproductive success of the two hermaphroditic forms. Our study population was strongly structured and characterized by contrasting local sex‐ratios. Pollen flow was constrained over short distances and depended on local plant density. Interestingly, restored hermaphrodites sired significantly more seedlings than non‐CMS hermaphrodites, despite the previous observation that the former produce pollen of lower quality than the latter. This result was explained by the higher frequency of females in the local vicinity of restored (CMS) hermaphrodites as compared to non‐CMS hermaphrodites. Population structure thus strongly influences individual fitness and may locally counteract the expected effects of selection, suggesting that understanding fine scale population processes is central to predicting the evolution of gender polymorphism in angiosperms.     

Effect of light stress from phytoplankton on the relationship between aquatic vegetation and the propagule bank in shallow lakes

1. The way light stress controls the recruitment of aquatic plants (phanerogams and charophytes) is a key process controlling plant biodiversity, although still poorly understood. Our aim was to investigate how light stress induced by phytoplankton, that is, independent from the aquatic plants themselves, determines the recruitment and establishment of plant species from the propagule bank. The hypotheses were that an increase in light stress (i) decreases abundance and species richness both of established aquatic plants and of propagules in the bank and (ii) decreases the recruitment success of plants from this bank. 2. These hypotheses were tested in 25 shallow lakes representing a light stress gradient, by sampling propagule banks before the recruitment phase and when the lakes are devoid of actively growing plants (i.e. at the end of winter), established vegetation at the beginning of the summer and phytoplankton biomass (chlorophyll a) during the recruitment and establishment phase. 3. The phytoplankton biomass was negatively correlated with the richness and abundance of established vegetation but was not correlated with the propagule bank (neither species richness nor propagule abundance). The similarity between the propagule bank and established vegetation decreased significantly with increasing phytoplankton biomass. 4. The contrast in species composition between the vegetation and the propagule bank at the highest light stress suggests poor recruitment from the propagule bank but prompts questions about its origin. It could result from dispersal of propagules from neighbouring systems. Propagules could also originate from a persistent propagule bank formerly produced in the lake, suggesting strong year‐to‐year variation in light stress and, as a consequence, in recruitment and reproductive success of plants.     

Effect of local spatial plant distribution and conspecific density on bumble bee foraging behaviour

1. Size variations in pollinator populations may modify competitive interactions among foragers. Competition among pollinators has been shown to lead to one of two contrasting behaviours: either specialisation to the most profitable plant species or generalisation to several species. When foraging, pollinators are also confronted with heterogeneity in the spatial distribution of plant resources. Because variations in both the forager density and plant spatial distribution can affect pollinator behaviour, focus was on the interactive effect of these two factors. 2. Bumble bee (Bombus terrestris L.) individuals were trained on a focal species (Lotus corniculatus L.) and experimentally tested whether variations in the forager density (two or six bumble bees foraging together), plant community spatial distribution (two plant species: L. corniculatus and Medicago sativa, which were either patchily or randomly distributed), and their interaction modified bumble bee foraging behaviour. 3. It was shown that when confronted with a high forager density, bumble bees focused their visits towards the most familiar species, especially when foraging under a random plant distribution. These modifications affected the fruiting of the focal plant species, with a significantly lower reproductive success under low density/patchy conditions. 4. This study demonstrates that the foraging decisions of bumble bees are influenced by variations in both the conspecific density and plant spatial distribution. Given the increasing impact of human activities on plant‐pollinator communities, this raises the question of the potential implications of these results for plant communities in natural conditions when confronted with variations in the pollinator density and spatial distribution of plants.     

Potassium channels in barley: cloning, functional characterization and expression analyses in relation to leaf growth and development

It is not known how the uptake and retention of the key osmolyte K⁺ in cells are mediated in growing leaf tissue. In the present study on the growing leaf 3 of barley, we have cloned the full-length coding sequence of three genes which encode putative K⁺ channels ( HvAKT1 , HvAKT2 , HvKCO1 / HvTPK1 ), and of one gene which encodes a putative K⁺ transporter ( HvHAK4 ). The functionality of the gene products of HvAKT1 and HvAKT2 was tested through expression in Xenopus laevis oocytes. Both are inward-rectifying K⁺ channels which are inhibited by Cs⁺. Function of HvAKT1 in oocytes requires co-expression of a calcineurin-interacting protein kinase ( At CIPK23) and a calcineurin B-like protein (AtCBL9) from Arabidopsis , showing cross-species complementation of function. In planta , HvAKT1 is expressed primarily in roots, but is also expressed in leaf tissue. HvAKT2 is expressed particularly in leaf tissue, and HvHAK4 is expressed particularly in growing leaf tissue. Within leaves, HvAKT1 and HvAKT2 are expressed predominantly in mesophyll. Expression of genes changes little in response to low external K⁺ or salinity, despite major changes in K⁺ concentrations and osmolality of cells. Possible contributions of HvAKT1 , HvAKT2 , HvKCO1 and HvHAK4 to regulation of K⁺ relations of growing barley leaf cells are discussed.     

Electrophysiological characterization of pathways for K+ uptake into growing and non-growing leaf cells of barley

Potassium is a major osmolyte used by plant cells. The accumulation rates of K⁺ in cells may limit the rate of expansion. In the present study, we investigated the involvement of ion channels in K⁺ uptake using patch clamp technique. Ion currents were quantified in protoplasts of the elongation and emerged blade zone of the developing leaf 3 of barley ( Hordeum vulgare L.). A time-dependent inward-rectifying K⁺-selective current was observed almost exclusively in elongation zone protoplasts. The current showed characteristics typical of Shaker-type channels. Instantaneous inward current was highest in the epidermis of the emerged blade and selective for Na⁺ over K⁺. Selectivity disappeared, and currents decreased or remained the same, depending on tissue, in response to salt treatment. Net accumulation rates of K⁺ in cells calculated from patch clamp current–voltage curves exceeded rates calculated from membrane potential and K⁺ concentrations of cells measured in planta by factor 2.5–2.7 at physiological apoplastic K⁺ concentrations (10–100 m m ). It is concluded that under these conditions, K⁺ accumulation in growing barley leaf cells is not limited by transport properties of cells. Under saline conditions, down-regulation of voltage-independent channels may reduce the capacity for growth-related K⁺ accumulation.     

Flocking behaviour of foraging birds in a neotropical rain forest and the antipredator defence hypothesis

Randomly encountered foraging birds were recorded in a primary rain forest of French Guiana (13,550 records of 216 species), together with their size, diet and habitat use, to assess the relative frequencies of different types of flocking behaviour and some of their ecological correlates. Overall, 42% of birds foraged singly, primarily carnivores (raptors), nectarivores (hummingbirds) and lek-mating frugivores (manakins, some cotingas). For-aging in pairs (26.6%) was widespread, notably among insectivores in the 17–32-g size class. The remaining 31.4% of records were birds in groups of different composition and function, including, in order of decreasing frequency, (1) multispecies upper canopy flocks (83 member species identified)—the largest and most mobile associations of small insectivores, nectarivores and frugivores, mostly tanagers; (2) understorey mixed species flocks of small insectivores, at midlevels of closed forest interior, with 12 core, obligate members and 74 occasional species, mostly active foliage or bark gleaners and probers sharing a unique set of ecological characteristics; (3) monospecific groups (29 species), either gregarious foragers but solitary breeders (large frugivores in canopy) or also breeding colonially or several permanently group living cooperative breeders; (4) opportunistic gatherings of frugivores at fruiting trees (at least 40 species); (5) army ant followers near ground of closed understorey (29 species of mid- to large-sized insectivores); (6) followers of Red-throated Caracaras Daptrius americanus (23 species, usually canopy frugivores entering understorey with caracaras); (7) two raptors following monkeys. Attributes of vulnerability to predators defined by habitat structure (vegetation density or openness) and foraging behaviour (conspicuousness, speed, degree of vigilance) were important determinants of flocking propensity, at least in flocks that were not attracted by a particular food source. The results suggest that the permanent mixed-species flocks in the mature forest under-storey may be an antipredator defence to compensate for the conspicuousness and reduced vigilance resulting from active foraging behaviour in semi-open vegetation, where early detection of predators is difficult.     

MtZR1, a PRAF protein,is involved in the development of roots and symbiotic root nodules in Medicago truncatula

PRAF proteins are present in all plants, but their functions remain unclear. We investigated the role of one member of the PRAF family, MtZR1, on the development of roots and nitrogen‐fixing nodules in Medicago truncatula. We found that MtZR1 was expressed in all M. truncatula organs. Spatiotemporal analysis showed that MtZR1 expression in M. truncatula roots was mostly limited to the root meristem and the vascular bundles of mature nodules. MtZR1 expression in root nodules was down‐regulated in response to various abiotic stresses known to affect nitrogen fixation efficiency. The down‐regulation of MtZR1 expression by RNA interference in transgenic roots decreased root growth and impaired nodule development and function. MtZR1 overexpression resulted in longer roots and significant changes to nodule development. Our data thus indicate that MtZR1 is involved in the development of roots and nodules. To our knowledge, this work provides the first in vivo experimental evidence of a biological role for a typical PRAF protein in plants.