Benefits of Autonomous Selfing Under Unpredictable Pollinator Environments

Abstract

Pollinator unpredictability favors evolutionary shifts from outcrossing to autonomous selfing, which provides reproductive assurance. Our goal was to quantify the reproductive assurance benefit of autonomous selfing and the stochastic nature of pollinator‐mediated pollen receipt using three wild populations of the annual species Collinsia verna (Scrophulariaceae) over three years. The timing of autonomous self‐pollination in C. verna ranges from competing to delayed, with more than half of the autonomous pollen arriving late in floral life. Floral density, identity of insect floral visitors, and visitation rate varied within and among years, with significant variation in pollinator community between years within populations. Pollinator failure reduced fruit set within and among populations across years. However, reproductive assurance selfing increased fruit set on average by 8% overall and up to 30% in one population. Despite this fitness benefit, fruit set (=Σfruits/Σflowers) estimated in pollinator‐exclusion cages was significantly less than the fruit set in paired open‐pollinated plots. In a series of experiments, we found no difference in fruit set from self‐ vs. outcross pollen, ruling out early inbreeding depression. However, flowers, hand‐outcrossed at the same time that autonomous selfing naturally occurs, produced significantly more fruits relative to flowers that received pollen only through autonomous selfing. These results suggest that pollen type (self/outcross) is less important to fruiting success than is the timing or efficiency of autonomous pollination relative to vector‐mediated pollination. Our results support the reproductive assurance hypothesis and suggest that autonomous selfing in C. verna is adaptive under variable pollinator conditions. Fruit set results from both pollinator‐delivered and autonomous self‐pollen, suggesting a “best of both worlds” scenario, with mixed mating a likely outcome.

Effect of variation in herkogamy on outcrossing within a population of Gilia achilleifolia

“…The difference between our estimates and that of Schoen (1982a) may be due to temporal variation in some environmental factors such as pollinator availability. A few studies have investigated temporal variation in outcrossing rates between consecutive years; some studies reported relatively consistent outcrossing rates across consequent years (Humphreys and Gale, 1974;Kesseli and Jain, 1985;Holtsford and Ellstrand, 1989;El-Kassaby et al, 1993), whereas others reported large temporal variation similar to what we found in this study (Moran and Brown, 1980;Barrett et al, 1993;Kalisz and Vogler, 2003). However, we cannot rule out a possible, but unlikely explanation that sampling bias in our study caused the underestimation of the outcrossing rate.…”

Mixed Mating in Homostylous Species: Genetic and Experimental Evidence from an Alpine Plant with Variable Herkogamy,Primula halleri

“…The probability of pollination can be heightened through higher floral attractiveness, achieved via more conspicuous floral displays (Müller 1881; Arroyo et al 2006) or greater floral longevity (Bingham and Orthner 1998). Alternatively, pollinator reliance can be reduced by promoting reproductive assurance via autonomous self-pollination (Kalisz and Vogler 2003;Arroyo et al 2006;Eckert et al 2006). Decreased reliance on pollinators requires self-compatibility.…”

Impact of Insect Pollinator Group and Floral Display Size on Outcrossing Rate

“…Poor pollen transfer among flowers creates conditions of pollen limitation which in turn select for autogamous selfing as a mechanism to provide reproductive assurance (Kalisz and Vogler 2003;Kalisz et al 2004). Different pollinators could distinctly affect pollen limitation and consequently levels of autogamous selfing.…”