The flower perianth has various, non‐mutually exclusive functions, such as visual signalling to pollinators and protecting the reproductive organs from the elements and from florivores, but how ...different perianth structures and their different sides play a role in these functions is unclear. Intriguingly, in many species there is a clear colour difference between the different sides of the perianth, with colour patterns or pigmentation present on only one side. Any adaptive benefit from such colour asymmetry is unclear, as is how the asymmetry evolved. In this viewpoint paper, we address the phenomenon of flowers with differently coloured inner and outer perianth sides, focusing on petals of erect flowers. Guided by existing literature and our own observations, we delineate three non‐mutually exclusive evolutionary hypotheses that may explain the factors underlying differently coloured perianth sides. The pollen‐protection hypothesis predicts that the outer side of petals contributes to protect pollen against UV radiation, especially during the bud stage. The herbivore‐avoidance hypothesis predicts that the outer side of petals reduces the flower's visibility to herbivores. The signalling‐to‐pollinators hypothesis predicts that flower colours evolve to increase conspicuousness to pollinators. The pollen‐protection hypothesis, the herbivore‐avoidance hypothesis, and the signalling‐to‐pollinators hypothesis generate largely but not entirely overlapping predictions about the colour of the inner and outer side of the petals. Field and laboratory research is necessary to disentangle the main drivers and adaptive significance of inner–outer petal side colour asymmetry.
Evolutionary hypotheses aimed at explaining why inner and outer sides of petals are often differently coloured.
Evidence of pollen and/or resource limitation of seed production in the herbaceous perennial plant Polemonium foliosissimum was investigated. Large numbers of open flowers on selected individuals ...were hand-pollinated at regular intervals, and seed set was compared with that of control blossoms on those same plants as well as with that of control flowers on control individuals. Experimental and control individuals were monitored and reproductive output measured during the following flowering season as well. Although hand-pollinated flowers set significantly more seeds than did either set of control blossoms, the results suggest that individual reproduction (i.e., the total number of seeds produced by a plant) was limited by resources other than pollen. Pollen availability may also have limited seed production, but to a lesser extent. A proper protocol for examining the limitation of seed set is developed, and the biases inherent in most of the simplified procedures currently in use are discussed.
We tested the following two predictions of the hypotheses that predation rate may select for nest spacing and winter breeding in New Holland honeyeaters: (a) the level of nest predation should be ...lower during the breeding season than outside it, and (b) clumped nests should show a higher predation rate than more dispersed nests. Artificial nests, containing budgerigar and artificial eggs, were set out in four different seasons and in two different configurations: clumped and spaced. Clumped nests suffered higher predation than spaced nests but there was no seasonal difference in total predation rates. Birds accounted for 67% of predation events for which the predator was identified. Among nests that were preyed on by birds, there was a highly significant effect of spacing, indicating that birds were responsible for the higher predation on clumped nests. Hence, these results support one prediction of the predator-avoidance hypothesis for territoriality, but do not support the notion that winter breeding may have evolved as a strategy to avoid predation by snakes.
Many species from the family Poeciliidae have been transported around the world by the aquarium trade, often establishing populations in areas far outside their natural range. The one-spot ...livebearer, Phalloceros caudimaculatus is one such poeciliid species. In March 2002, a nonindigenous population of P. caudimaculatus was discovered at Collaroy, in the Sydney metropolitan area, the first record of this species in eastern Australia. Following this discovery, electrofishing and light-trap surveys were conducted at the site, and dip-netting and visual surveys were conducted in surrounding water bodies. P. caudimaculatus was widespread and abundant at the Collaroy site, but no further populations were discovered. Another pest poeciliid species, Gambusia holbrooki, originally present at the site, was absent and, although the mechanism remains unclear, may have been displaced by P. caudimaculatus. Both P. caudimaculatus and G. holbrooki share the characteristics of successful invasive species, with extremely broad physical tolerances and high reproductive outputs. Given the well-documented negative ecological effects of poeciliids, especially G. holbrooki, we recommend that a precautionary approach should be adopted for the management of P. caudimaculatus and its eradication from the site be attempted.
The Green and Golden Bell Frog Litoria aurea is an unusual endangered frog species. It has a high public profile as many populations occur in areas affected by human activities. As a result, there ...has been considerable recent scientific and popular interest in the species. Despite the interest and large volume of documented information there has been no general review of the biology of the species. Litoria aurea is not typical of other endangered species. It has many attributes of a âweedyâ or âcolonizingâ species. Like other such species, it is characterised by occurrence in disturbed or newly created sites, high fecundity and high dispersal ability. However, unlike many âcolonizingâ species that are very common, L. aurea is considered to be endangered. Though the decline of L. aurea is continuing as a result of ongoing threats, it should be possible to promote some recovery of the species through such strategies as increased legislative protection, conservation agreements, habitat manipulation, and control of the impacts of the introduced Plague Minnow Gambusia holbrooki. As in many similar situations, further research will be essential to provide the necessary information-base for the threats to be arrested and the opportunities to be pursued. In this paper we review all available published information with regard to the biology of L. aurea, and include some previously unpublished field observations. We consider the implications of this review in terms of recovery and/or management of the species and the extent of further research on L. aurea that could benefit the recovery process.
Porphyromonas gingivalis and Treponema denticola are strongly associated with chronic periodontitis. These bacteria have been co-localized in subgingival plaque and demonstrated to exhibit symbiosis ...in growth in vitro and synergistic virulence upon co-infection in animal models of disease. Here we show that during continuous co-culture a P. gingivalis:T. denticola cell ratio of 6∶1 was maintained with a respective increase of 54% and 30% in cell numbers when compared with mono-culture. Co-culture caused significant changes in global gene expression in both species with altered expression of 184 T. denticola and 134 P. gingivalis genes. P. gingivalis genes encoding a predicted thiamine biosynthesis pathway were up-regulated whilst genes involved in fatty acid biosynthesis were down-regulated. T. denticola genes encoding virulence factors including dentilisin and glycine catabolic pathways were significantly up-regulated during co-culture. Metabolic labeling using 13C-glycine showed that T. denticola rapidly metabolized this amino acid resulting in the production of acetate and lactate. P. gingivalis may be an important source of free glycine for T. denticola as mono-cultures of P. gingivalis and T. denticola were found to produce and consume free glycine, respectively; free glycine production by P. gingivalis was stimulated by T. denticola conditioned medium and glycine supplementation of T. denticola medium increased final cell density 1.7-fold. Collectively these data show P. gingivalis and T. denticola respond metabolically to the presence of each other with T. denticola displaying responses that help explain enhanced virulence of co-infections.
It was hypothesized that the local geographic distributions of bumblebees near Crested Butte, Colorado and the community patterns exhibited by these bumblebees are the products of competition for ...plants. To evaluate this hypothesis several transects were established and at regular intervals throughout a summer growing season, data were collected along each transect on how many bumblebees of each species and caste were visiting the various plant species. The distributions and abundances of the plant species involved were recorded qualitatively. Seven species of bumblebees accounted for 97% of all bumblebees observed and in this paper attention is restricted to these species. Five other species were observed in very low numbers. Each bumblebee species had a different distributional pattern. The seven bumblebee species form four groups in terms of both their proboscis lengths and the corolla lengths of the plants they preferentially visit. Long-, medium-, and short-tongued groups were most often observed foraging at flowers with long, medium, and short corollas, respectively. Furthermore proboscis lengths of bumblebees tended to be very similar within each group but quite dissimilar between groups. The fourth group consisted of a single short-tongued species which has well-developed mandibles which enable it to rob nectar from many plants with long corollas. It also feeds legitimately on short-corolla flowers. Some anomalies in the above groupings are mentioned and discussed. When the data on bumblebees and plant distributions are combined with data on flower preferences, a pattern consistent with the competition hypothesis emerges. Within each proboscis-length group, bumblebee species tend to replace one another altitudinally in a manner consistent with the hypothesis. The nectar-robbing species is most abundant in areas where a plant that is usually visited by hummingbirds is most common. Other species of bumblebees are unable to gain access to the nectar of this plant. In any uniform well-isolated area, similar floristically to the present study area, only three or four species of bumblebees appear to be able to coexist. Furthermore, a bumblebee community in such an area will apparently consist of a short-, a medium-, and a long-tongued species and in some cases a short-tongued nectar-robber. These patterns are also consistent with the competition hypothesis, as similarity in proboscis length reflects similarity in diet and the intensity of competition should, for these bumblebees, be closely related to diet similarity. It is possible that the observed distributional patterns could also be explained on the basis of different distributions of suitable nest sites for each bumblebee species or different responses to local variations in climatic conditions. Neither alternative seems able, however, to explain the observed patterns.
(1) The carbon budgets of Polemonium foliosissimum individuals were experimentally manipulated. The amount of available carbon was decreased by defoliating 50% of each plant, while available carbon ...was enhanced by daily watering and by removing either 50% or 100% of the flower buds. (2) Rates of nectar production per flower were constant across all treatments except for a significant increase observed in the watered individuals. (3) There were no consistent changes in average seed set per flower or per plant across treatment groups. (4) Defoliated and control individuals did not differ significantly from one another with respect to average seed weight, but end-of-season underground biomass was significantly less for defoliated plants relative to controls. (5) In the year following treatment, no differences were observed in nectar production per flower, seed production per flower or seed production per plant, although a significant difference in rate of growth was observed. Defoliated plants grew least during the 2-year period, followed by control individuals. The debudded plants increased in size by the greatest margin. (6) The trade-offs between resources allocated to nectar, flowers, seeds and vegetative growth can apparently be expressed in terms of biomass.
Pollinators usually maintain directionality while moving through a flower patch, presumably to increase foraging success by minimizing revisitation of previously-emptied flowers. Two alternative ...directionality-generating mechanisms have been proposed: foragers may keep track of their arrival direction at a flower or cluster of flowers and prefer to depart in the same direction (the arrival hypothesis), or they may show little change in orientation while foraging at a flower or flower cluster and prefer to depart in the direction they are last facing (the last-faced hypothesis). Rotation of a flower or inflorescence while the forager is feeding on it will unequivocally distinguish the two hypotheses. We observed worker bumblebees (Bombus melanopygus and B. flavifrons) from captive colonies foraging on a square grid of 25 artificial flowers. Bumblebees were able to keep track of their orientations on a flower relative to their arrival direction, and they choose to leave a flower in about the same direction as their arrival. Whether or not individual flowers or the whole flower patch was rotated 90° clockwise, departure directions were usually the same as arrival directions. In unrotated bees that changed direction between arrival and departure, relatively late changes in orientation during a flower visit tended to compensate for earlier ones. Last-facing directions were better predictors of subsequent movements than were arrival direction, indicating that most compensation for experimentally- or self-imposed rotation while on a flower occurred before a bee left the flower. We conclude that directionality in foraging bumblebees is based on memory of arrival direction.
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