“Mating opportunity increases with synchrony of flowering among years more than synchrony within years in a non-masting perennial”

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Amy Waananen, Gretel Kiefer, Jennifer L. Ison, and Stuart Wagenius (Sep 2018)

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Timing of mating among years matters as much, or more, than timing within years, even in non-masting species

Three Echinacea flower heads, one shedding pollen, demonstrate variation in within-year flowering phenology.
(Credit: Gretel Kiefer)

Plants can’t actively search for mates, so timing of flowering is critical for their reproduction. For years, research has characterized patterns of reproduction among years in species that “mast,” or show dramatic variation in annual reproductive effort—think of forest floors littered with oak tree acorns in a mast year, sudden blooms of desert annuals after rain, or bamboos, which grow for decades until they invest all their resources in one fatal reproductive episode. For these species, flowering synchronously with their neighbors, i.e. flowering in the same year or years, is critical for finding a mate. Although reproduction in non-masting species may also vary from year to year, reproductive synchrony of these species is usually studied within seasons (i.e., the days individuals flower relative to their neighbors). In this study, the authors investigate the extent to which among- and within-year flowering synchrony influences individuals’ number of potential mates in a non-masting species. They used an 11-year dataset of flowering phenology of the long-lived perennial herb, Echinacea angustifolia. Surprisingly, they found that among-year synchrony contributed to variation in individuals’ long-term mating opportunities 39% more than within-year synchrony. This finding is important because it is demonstrates that among-year timing of reproduction may be an important determinant of mating opportunity not only in masting species, but also for many other species in which population reproduction varies among years.


Abstract

The timing and synchrony of mating activity in a population may vary both within and among years. With the exception of masting species, in which reproductive activity fluctuates dramatically among years, mating synchrony is typically studied within years. However, opportunities to mate also vary among years in non-masting iteroparous species. We demonstrate that studying only within-year flowering synchrony fails to accurately quantify variation in mating opportunity in an experimental population (n = 286) of a non-masting species, Echinacea angustifolia. We quantified individuals’ synchrony of flowering within and among years and partitioned the contribution of each measure to mean daily mating potential, the number of potential mates per individual per day, averaged over every day it flowered during the 11-year study period. Individual within- and among-year synchrony displayed wide variation and were weakly correlated. In particular, among-year synchrony explained 39% more variation in mean daily mating potential than did within-year synchrony. Among-year synchrony could have underappreciated significance for mating dynamics in non-masting species.