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Environmental variation in sex ratios and sexual dimorphism in three wind-pollinated dioecious plant species

Citation

Bürli, Sarah; Pannell, John R.; Tonnabel, Jeanne (2022), Environmental variation in sex ratios and sexual dimorphism in three wind-pollinated dioecious plant species, Dryad, Dataset, https://doi.org/10.5061/dryad.z612jm6df

Abstract

Variation in plant sex ratios is often attributable to sex-specific mortality in heterogeneous environments that differentially limit male and female plant reproduction. Yet sexual dimorphism and plastic responses to environmental heterogeneity are common and may co-vary with variation in sex ratios. Here, we show that the sex ratio and the degree of sexual dimorphism for a number of plant traits varied along climatic and elevation gradients in three wind-pollinated dioecious species, Rumex lunaria, Urtica dioica and Salix helvetica. Some of the observed sex-specific responses to climatic variation are consistent with greater sensitivity of females to water scarcity, but most responses rather point to the greater sensitivity of males to ecological stress, consistent with larger male reproductive effort, as has been commonly reported for wind-pollinated plants. In contrast, we found no evidence for variation in either sex ratios or sexual dimorphism expected under sexual selection. Interestingly, sex ratios and sexual dimorphism varied both along distinct and the same ecological axes of variation, suggesting that the evolution of sexual dimorphism in the measured traits was not sufficient to prevent sex-specific mortality.

Methods

We counted males and females and measured plant traits at 14 naturally occurring populations of R. lunaria on the island of Tenerife (Spain) in April 2017, at eleven populations of U. dioica in ‘Le Plateau’ area (Switzerland) in September 2017, and at ten populations of S. helvetica in the Alps (Switzerland) in July 2017. To ensure an unbiased sample, we recorded the sex of every individual identified, moving through the populations in only one direction to avoid sampling any individual more than once. For each species, we counted all individuals up to a maximum of 150 per population.
 
Plant height and canopy width were recorded for all sampled mature flowering individuals in R. lunaria and S. helvetica.
 
For U. dioica, due to its clonal habits, we estimated plant cover for roughly half of the mature individuals identified, using a visual criterion to determine the shape best approximating the plant cover per individual (e.g., circle, ellipse, or rectangle), and we further measured the parameters of the projected shape to assess their cover.
 
For each population, we calculated the operational sex ratio (SR) as the proportion of females divided by the total number of flowering individuals in a population. We further calculated, for each population, two sexual dimorphism indices, one for leaf area and one for plant size, hereafter termed SLD and SSD, respectively. The SLD and SSD were calculated as the log of the ratio of the mean female to the mean male leaf area or plant size, respectively (Smith 1999), with a null expectation of 0 for no difference.
 
We extracted for each population ten bioclimatic variables at a spatial resolution of 1 km 2 from WorldClim global climate layers (Fick and Hijmans 2017) and calculated the principal components (PC) axes of the bioclimatic variables.

Please, find additional details in the Readme file and in the article:

Bürli, S., Pannell, J. R., & Tonnabel, J. (2022). Environmental variation in sex ratios and sexual dimorphism in three wind‐pollinated dioecious plant species. Oikos, e08651. https://doi.org/10.1111/oik.08651

Usage Notes

A detailed README file is available with the datasets.

The data are not standardised and missing values are noted by NA. The data have been checked for outliers.

Relationship between files: the number of the populations refer to the same populations between the files of the same species. For example, the population one for Rumex lunaria refers to the same population one in the following documents "data_SPECIES_pop.csv", "data_SPECIES_indiv.txt" and "data_SPECIES_leaf.txt".

Funding

Swiss National Science Foundation, Award: 31003A_163384

Marie Skłodowska-Curie Actions, Award: 844321