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Data from: Divergent selection on the biomechanical properties of stamens under wind and insect pollination
Timerman, David; Barrett, Spencer C.H.; Barrett, Spencer C. H. — 2018-12-11 Wind pollination has evolved from insect pollination in numerous angiosperm lineages and is associated with a characteristic syndrome of morphological traits. The traits initiating transitions to wind pollination and the ecological drivers involved are poorly understood. Here, we examine this problem in Thalictrum pubescens, an ambophilous (insect and wind pollination) species that probably represents a transitional state in the evolution of wind pollination in some taxa. We investigated wind-induced pollen release by forced harmonic motion by measuring stamen natural frequency (fn), a key vibration parameter, and its variability among nine populations. We assessed the repeatability of fn over consecutive growing seasons, the effect of this parameter on pollen release in a wind tunnel, and male reproductive success in the field using experimental manipulation of the presence or absence of pollinators. We found significant differences among populations and high repeatability within genotypes in fn. The wind tunnel assay revealed a strong negative correlation between fn and pollen release. Siring success was greatest for plants with lower fn when pollinators were absent; but this advantage diminished when pollinators were present. Our biomechanical analysis of the wind-flower interface has identified fn as a key trait for understanding early stages in the transition from insect to wind pollination.
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Data from: The spatial ecology of sex ratios in a dioecious plant: relations between ramet and genet sex ratios
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Timerman, David; Barrett, Spencer C. H.; Barrett, Spencer C.H. — 2019-01-17 1. In clonal dioecious plants, the frequency and spatial distribution of flowering ramets contains information on the underlying genet sex ratio. These measures can also provide insight on potential ecological mechanisms causing variation and bias in sex ratios among populations. 2. We used a novel likelihood-based approach and spatial clustering model to estimate the genet sex ratios from flowering ramet data collected from 32 populations of dioecious Thalictrum pubescens, a clonal species from eastern N. America that occupies moist wetland and forested environments. We investigated sex ratios of seed families, clone size, patterns of flowering and plant height to determine potential causes of sex ratio bias. 3. Flowering ramet sex ratios varied considerably among populations but were significantly male-biased. Seed families grown to flowering also exhibited the same degree of male bias. Both models predicted close correspondence between ramet and genet sex ratios. The likelihood model revealed that gender differences in ramet production could not account for biased sex ratios. The spatial clustering model indicated that ramets were significantly clustered at two spatial scales and estimated similar cluster sizes and densities for both sexes. There was no evidence for spatial segregation of the sexes. Both sexes were equally likely to flower in consecutive years and repeated bouts of flowering had no effect on ramet height. 4. Synthesis. Our analyses suggest that the widespread occurrence of male-biased sex ratios in T. pubescens is unlikely to result from sexual differences in clonal growth or habitat preferences. The bias appears to become established early in the life cycle, perhaps at the seed stage as consequence of local resource competition.

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(Author: Timerman, David)

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