DOI: 10.5061/dryad.sqv9s4n2j
title: Earlier spring reduces potential for gene flow via reduced flowering synchrony across an elevational gradient

description: Premise: One of the best-documented ecological responses to climate
 warming involves temporal shifts of phenological events. However, we lack
 an understanding of how phenological responses to climate change vary
 among populations of the same species. Such variability has the potential
 to affect flowering synchrony among populations and hence the potential
 for gene flow. Methods: To test if an earlier start of the growing season
 affects the potential for gene flow among populations, we quantified the
 distributions of flowering times of two spring-flowering plants (Trillium
 erectum and Erythronium americanum) over six years along an elevation
 gradient. We developed a novel model-based metric of potential gene flow
 between pairs of populations to quantify the potential for pollen-mediated
 gene flow based on flowering phenology. Results: For both species
 investigated, earlier onset of spring led to greater separation of peak
 flowering dates across the elevation gradient. For T. erectum, but not E.
 americanum, this was also associated with a reduction in potential gene
 flow. Conclusion: Our study suggests that climate change could decrease
 gene flow via phenological separation among populations along climatic
 gradients. We also provide a novel method for quantifying potential
 pollen-mediated gene flow using data on flowering phenology, based on a
 quantitative, more biologically interpretable model than other available
 metrics.
description: Two
 elevational transects, approximately 800m apart, were established in 2013
 on the east-facing slope of Mont St-Joseph within the park (see Lajoie and
 Vellend 2015). Each transect comprises six 26 m x 4 m plots (104
 m<sup>2</sup>), with 55-85 m of elevation between plots. Plots
 were established only in areas under full tree canopy to avoid disturbed
 habitats and wetland areas. Our focal species were selected given their
 high abundance and presence across most of the elevational gradient. The
 focal species were present in five plots per transect (absent at the
 highest elevation), covering an elevation gradient from 697 m to 951 m
 a.s.l. The geographic distance between plots varied from 123m for adjacent
 plots up 914m for the two most distant plots on different
 transects. Each plot was divided into 26 2m × 2m
 subplots in which the number of flowers of <i>Trillium
 erectum</i> and <i>Erythronium americanum</i> was
 recorded approximately every 4 days throughout the flowering season for
 six years, 2013-2018 inclusive. Flowers were included in the count from
 the start of flower opening to the start of flower senescence (identified
 by signs of drying, wrinkling, or discoloration of petals or sepals).
 Since flower abundance decreased with elevation, for high-elevation plots
 (850 m and higher), we also recorded individuals within less than 2 m from
 the plots to obtain enough data to determine the flowering start, peak and
 end; the number of individuals was standardised to correspond to the
 density of individuals in an area of 104 m<sup>2</sup> (the
 area of one plot).