Range-wide study in a sexually polymorphic wild strawberry reveals climatic and soil associations of sex ratio, sexual dimorphism, and sex chromosomes

The contemporary environment, which influences local resource pools and mate access, is rapidly changing in the Anthropocene, posing unique challenges for sexually polymorphic plants. A landscape scale understanding of climate and soil drivers of sex-specific factors can help predict how global change will impact these species.

Using ~7,000 herbarium and iNaturalist specimens we determine how sex ratio, sexual dimorphism, and sex chromosomes vary with geographic, climatic and soil gradients in Fragaria virginiana and whether these conform to predictions from theory.

Sex ratio was hermaphrodite/male-biased and was driven more by soil attributes than climatological ones. Sex ratio-environment associations matched predictions for subdioecious species in the West but for gynodioecious species in the East. Climatic, not soil factors, affected sexual dimorphism in traits related to carbon acquisition but not mate access (petal size and flowering time). Greater sexual dimorphism was due to one sex being more responsive (females for leaf length and hermaphrodite/male for runnering while flowering) to precipitation or temperature. Sex chromosome variation was biased towards the ancestral type and frequencies varied with different environmental factors between East-West regions.

A landscape-level perspective of environmental drivers of sex-specific factors provides insight into how anthropogenic disturbance may impact sexually polymorphic species.

Methods
Briefly, we downloaded digitized, imaged herbarium records of Fragaria virginiana from online herbarium databases (iDigBio, GBIF, the Consortium of Pacific Northwest Herbaria, and the Consortium of Intermountain Herbaria) and iNaturalist records. We filtered out all digital records which were missing geolocation coordinates (latitude, longitude) or a collection date. We scored imaged records for flower sex, flowering time (collection date), presence of collection-year runners, and measured petal and leaf length and width on a subset of herbarium records. We additionally used targeted primers to characterize the sex determining region (SDR) haplotypes on a subset of herbarium records, which we had sampled in-person and requested from specific herbaria. To associate sex ratio, petal/leaflet phenotype, flowering time (from collection date), runner presence and SDR haplotypes with spatial and climate variables we gathered data on elevation, temperature and precipitation (from the CRU time series dataset), and soil nitrogen and bulk density (from the SoilGrids dataset). Herbarium records were binned into east and west regions using a dividing meridian of 102° W (natural gap in the continent-wide range). Temperature and precipitation averages were estimated for the coldest (winter) and warmest (summer) months for each record, averaging the monthly temperature for the month of collection and the two preceeding months for 10 years prior to the collection year of the record (10-year pre-collection climatological means). Together these data were used to conduct the analyses presented in the linked manuscript.