The function of the wild carrot's dark central floret: attract,guide or deter?

Although Charles Darwin wrote about flower polymorphism in the wild carrot, Daucus carota, the function of the conspicuous central dark floret is still unclear. We used video recordings to evaluate the functional significance of the dark central floret as a short‐distance signal for insects landing on the umbels and analyzed the location of landing points, landing orientation and visit duration. These parameters, as well as insect attraction did not differ on umbels with and without a dark central floret. Hence, we found no evidence for the role of the dark central floret in the pollination of D. carota. Umbels with a dark central floret, however, were parasitized significantly less often by the gall midge Kiefferia pericarpiicola than umbels without a dark central floret. We propose that the dark central floret may play a role in reducing parasite infestation by mimicking an already present gall or deterring oviposition of the gall midge by other means.     

Variable selection patterns on the labellum shape of Geoblasta pennicillata,a sexually deceptive orchid

By mimicking shape and female mating pheromones, flowers of sexually deceptive orchids attract sexually excited males which pollinate them while trying to copulate. Although many studies have demonstrated the crucial importance of odour signals in these systems, most flowers pollinated by pseudocopulation resemble, at least superficially, an insect body and these visual cues may be important to cheat pollinators. In this 2‐year study, we show that the shape of the labellum of Geoblasta pennicillata is a target of pollinator‐mediated natural selection. Contrary to our expectations, plants with a labellum shape more similar to female wasps were not favoured. The strength and pattern of phenotypic selection varied between study years and sexual functions. Although selection through female success was probably associated to the fine‐tuning of the mechanical fit between flower form and male wasp, shape was the target of natural selection through male success in both study years indicating that male wasps use this trait when choosing flowers. The imperfect mimicry and patterns of selection observed indicated that an exact imitation is not needed to attract and deceive the pollinators and they suggested a receiver perceptual bias towards uncommon phenotypes.     

Divergence on floral traits and vertebrate pollinators of two endemic Encholirium bromeliads

Shifts in pollen vectors favour diversification of floral traits, and differences in pollination strategies between congeneric sympatric species can contribute to reproductive isolation. Divergence in flowering phenology and selfing could also reduce interspecific crossing between self‐compatible species. We investigated floral traits and visitation rates of pollinators of two sympatric Encholirium species on rocky outcrops to evaluate whether prior knowledge of floral characters could indicate actual pollinators. Data on flowering phenology, visitation rates and breeding system were used to evaluate reproductive isolation. Flowering phenology overlapped between species, but there were differences in floral characters, nectar volume and concentration. Several hummingbird species visited flowers of both Encholirium spp., but the endemic bat Lonchophylla bokermanni and an unidentified sphingid only visited E. vogelii. Pollination treatments demonstrated that E. heloisae and E. vogelii were partially self‐compatible, with weak pollen limitation to seed set. Herbivores feeding on inflorescences decreased reproductive output of both species, but for E. vogelii the damage was higher. Our results indicate that actual pollinators can be known beforehand through floral traits, in agreement with pollination syndromes stating that a set of floral traits can be associated with the attraction of specific groups of pollinators. Divergence on floral traits and pollinator assemblage indicate that shifts in pollination strategies contribute to reproductive isolation between these Encholirium species, not divergence on flowering phenology or selfing. We suggest that hummingbird pollination might be the ancestral condition in Encholirium and that evolution of bat pollination made a substantial contribution to the diversification of this clade.     

Fenestration: a window of opportunity for carnivorous plants

A long-standing but controversial hypothesis assumes that carnivorous plants employ aggressive mimicry to increase their prey capture success. A possible mechanism is that pitcher plants use aggressive mimicry to deceive prey about the location of the pitcher''s exit. Specifically, species from unrelated families sport fenestration, i.e. transparent windows on the upper surfaces of pitchers which might function to mimic the exit of the pitcher. This hypothesis has not been evaluated against alternative hypotheses predicting that fenestration functions to attract insects from afar. By manipulating fenestration, we show that it does not increase the number of Drosophila flies or of two ant species entering pitchers in Sarracenia minor nor their retention time or a pitcher''s capture success. However, fenestration increased the number of Drosophila flies alighting on the pitcher compared with pitchers of the same plant without fenestration. We thus suggest that fenestration in S. minor is not an example of aggressive mimicry but rather functions in long-range attraction of prey. We highlight the need to evaluate aggressive mimicry relative to alternative concepts of plant–animal communication.     

Flexible pollination system in an unpalatable shrub Daphne miyabeana (Thymelaeaceae)

The stability of plant reproductive success is dependent on the reproductive system of the plant and the surrounding pollinator assemblages. Here we documented the pollination ecology of a shrub, Daphne miyabeana (Thymelaeaceae), that is unpalatable to deer in two different habitats (open and closed canopy) at a site with severe deer browsing. We found that 31.22 ± 3.07% (mean ± SE) and 9.01 ± 1.71% of the total number of D. miyabeana flowers become fruits in open and closed habitats, respectively. Although spontaneous selfing was possible, the fruit set of that was much lower than the fruit set of an artificial outcrossing treatment. In the closed habitat, the fruit set of the natural pollination was lower than that of artificial outcrossing, whereas in the open habitat the fruit set of those two were similar. In the open habitat, small bees were the major flower visitors, whereas in the closed habitat, ants were the major flower visitors, which did not contribute to pollination. Our findings suggest that D. miyabeana is pollinated by occasional visits of small bees, but it is also self‐compatible and spontaneous selfing is possible. Although its pollination is shaped by abiotic environmental factors, D. miyabeana can reproduce in different habitat conditions. These flexible reproductive systems may be an advantage in coping with the recent environmental change in forest habitats.