Evolution of wind pollination in Leucadendron (Proteaceae) : experimental evidence and floral trait shifts.

M. Sc. University of KwaZulu-Natal, Pietermaritzburg 2014.Evolutionary transitions from insect to wind pollination are thought to have occurred many times during the angiosperm radiation. This transition is commonly associated with a suite of distinctive floral traits such as reduction of flower size and a transition to dry pollen. In the dioecious genus, Leucadendron (Proteaceae), evolutionary shifts from insect to wind pollination have been postulated based on floral morphology features. In this study, I aimed to experimentally test the potential for wind versus insect pollination in several Leucadendron species and document a variety of floral traits (pollen size, inflorescence size, scent, colour, etc.) in order to determine their functional significance whilst utilizing phylogenetic comparative methods to test the statistical significance of evolutionary associations between particular floral traits and pollination systems. Fifteen representative Leucadendron species were investigated to verify insect and wind pollination in as many clades as possible. Insect exclusion experiments confirmed that five Leucadendron species, L. rubrum, L. salicifolium, L. dubium, L. coniferum and L. teretifolium are indeed wind-pollinated. Pria cinerascens (Nititulidae) was found to be the main pollinator of the insect-pollinated Leucadendron species due to their abundance, high stigmatic contact and relatively pure Leucadendron pollen loads. Overall, however, the abundance of insects visiting inflorescences was not significantly different between insectand wind-pollinated species, which highlights the importance of conducting insect exclusion experiments to evaluate whether a species is wind- or insect-pollinated. From the previously determined pollination systems of 17 Leucadendron species, floral traits associated with the shift to wind pollination were investigated to determine whether transitions from insect to wind pollination were accompanied by modifications of pollination-relevant floral traits. In a wind tunnel, pollen grains of wind-pollinated species were found to be more motile than those of insect-pollinated species. Phylogenetic analyses suggest that transitions from insect to wind pollination occurred at least four times during the diversification of Leucadendron and that, compared to insect-pollinated cogeners, wind-pollinated Leucadendron species are characterized by increased production of smaller pollen grains, higher inflorescence density, less attractive visual and olfactory cues, and a greater degree of sexual dimorphism for these visual and olfactory cues. In conclusion, this study experimentally confirms that there were several shifts from insect to wind pollination in Leucadendron and identifies floral traits that were evolutionarily modified during these shifts

Nectar palatability can selectively filter bird and insect visitors to coral tree flowers

Secondary compounds in nectar may play a decisive role in determining the spectrum of floral visitors on plants. Flowers of the African coral tree Erythrina caffra are visited mainly by generalist passerine nectarivores, such as weavers and bulbuls. As the nectar of this species tastes very bitter to humans, it was hypothesized that secondary compounds may repel sunbirds and honeybees which are common in the same habitats yet seldom consume the nectar. We conducted choice tests using fresh nectar and both sucrose and hexose (glucose/fructose) solutions of the same concentration as the nectar. Whitebellied Sunbirds (Cinnyris talatala) were repelled by nectar of both E. caffra and a related species Erythrina lysistemon, but Dark-capped Bulbuls (Pycnonotus tricolor) did not discriminate between the Erythrina nectar and control sugar solution in terms of amounts consumed. Honeybees (Apis mellifera scutellata) probed exposed droplets of E. caffra nectar and a control sugar solution at the same rate, suggesting that there is no volatile deterrent, but they immediately withdrew their proboscis far more often from the droplets of Erythrina nectar than they did from the sugar solution, suggesting that they find Erythrina nectar distasteful. These results contribute to a growing awareness that non-sugar components of nectar can play important functional roles in plant pollination systems.South African National Research Foundation (NRF)http://link.springer.com/journal/106822016-03-31hb201

Data from: Floral trait evolution associated with shifts between insect and wind pollination in the dioecious genus Leucadendron (Proteaceae)

Transitions between animal and wind pollination have occurred in many lineages and have been linked to various floral modifications, but these have seldom been assessed in a phylogenetic framework. In the dioecious genus Leucadendron (Proteaceae), transitions from insect to wind pollination have occurred at least four times. Using analyses that controlled for relatedness among Leucadendron species, we investigated how these transitions shaped the evolution of floral structural and signaling traits, including the degree of sexual dimorphism in these traits. Pollen grains of wind-pollinated species were found to be smaller, more numerous, and dispersed more efficiently in wind than were those of insect-pollinated species. Wind-pollinated species also exhibited a reduction in spectral contrast between showy subtending leaves and background foliage, reduced volatile emissions, and a greater degree of sexual dimorphism in color and scent. Uniovulate flowers and inflorescence condensation are conserved ancestral features in Leucadendron and likely served as exaptations in shifts to wind pollination. These results offer insights into the key modifications of male and female floral traits involved in transitions between insect and wind pollination

PGEE table

The table use to conduct PGEE analysis for several floral traits in Leucadendron

Pollen production in Leucadendron species

The number of pollen grains in one pre-dehiscent male flower. Pollen grains are counted in five subsamples of 2 μl from each sample and extrapolated total pollen production per flower from the initial sample volume of 1 ml

Measurements of pollen grain size

Vertical height (h) and base (b) of pollen grains were measured by imaging pollen grains with a Scanning Electron Microscope (Zeiss Evo LS 15) and using AnalySis ® (version 3.2) on the SEM photographs with the scale bar as reference

Inflorescence measurements

Measurements of flowers per inflorescence, size of inflorescence and inflorescences per branch

Wind tunnel data

Pollen dispersal capability in a wind tunnel at different speeds and distances

Derivation and validation of a clinical decision rule to risk‐stratify COVID‐19 patients discharged from the emergency department: The CCEDRRN COVID discharge score

Abstract Objective To risk‐stratify COVID‐19 patients being considered for discharge from the emergency department (ED). Methods We conducted an observational study to derive and validate a clinical decision rule to identify COVID‐19 patients at risk for hospital admission or death within 72 hours of ED discharge. We used data from 49 sites in the Canadian COVID‐19 Emergency Department Rapid Response Network (CCEDRRN) between March 1, 2020, and September 8, 2021. We randomly assigned hospitals to derivation or validation and prespecified clinical variables as candidate predictors. We used logistic regression to develop the score in a derivation cohort and examined its performance in predicting short‐term adverse outcomes in a validation cohort. Results Of 15,305 eligible patient visits, 535 (3.6%) experienced the outcome. The score included age, sex, pregnancy status, temperature, arrival mode, respiratory rate, and respiratory distress. The area under the curve was 0.70 (95% confidence interval [CI] 0.68–0.73) in derivation and 0.71 (95% CI 0.68–0.73) in combined derivation and validation cohorts. Among those with a score of 3 or less, the risk for the primary outcome was 1.9% or less, and the sensitivity of using 3 as a rule‐out score was 89.3% (95% CI 82.7–94.0). Among those with a score of ≥9, the risk for the primary outcome was as high as 12.2% and the specificity of using 9 as a rule‐in score was 95.6% (95% CI 94.9–96.2). Conclusion The CCEDRRN COVID discharge score can identify patients at risk of short‐term adverse outcomes after ED discharge with variables that are readily available on patient arrival