2.3 Environmental Variables
To identify environmental factors that could act as agents of selection
on circadian period, we analyzed data for 19 bioclimatic variables in
the WorldClim dataset (Fick and Hijmans 2017) for each of our population
sites. For the analysis of environmental data, values for the climate
variables collected at 30-s resolution (~1
km2) were utilized, including mean annual temperature
and annual precipitation and measures of peak and low temperature and
moisture through the year. As soil variables were not found in any
online database for the areas of the experimental B .stricta populations, we collected soil samples and analyzed soil
features from each of the 30 population sites. At each site, along a
10-m transect, we measured soil temperature and moisture. We also
collected three soil samples; in the lab, we measured soil pH, soil
electrical conductivity, soil moisture, bulk density, and soil texture
(as percent of silt, sand, and clay composition).