Plasticity of flower longevity in alpine plants is increased in populations from high elevation compared to low elevation populations

Judith Trunschke,Jürg Stöcklin

doi:10.1007/s00035-016-0176-4

Abstract

Flower longevity is an adaptive trait, optimized to balance reproductive success against the costs of flower maintenance. The trait is highly plastic in response to pollination success, and numerous studies report increased flower longevity in high elevation environments, where diversity, abundance, and activity of pollinators are low. However, few studies have experimentally investigated how flower longevity varies with pollination intensity within and among populations. We studied flower longevity of six alpine species under three pollination intensity treatments (hand-pollination, natural pollination, pollinator exclusion) at 1600 m vs. 2600 m a.s.l. at the Furka Pass, Central Swiss Alps. We hypothesized, (1) that flower longevity is generally increased in population at high elevation, and (2) that the increase in flower longevity when pollination fails is stronger in populations at high elevation compared to low elevation. Hand-pollination did not decrease flower longevity in any of the studied populations and rarely increased natural seed production suggesting no pollination limitation at both elevations. This was supported by similar pollinator visitation rates, pollinator efficiency, and pollination effectivity. Pollinator exclusion significantly increased flower longevity, but only in populations of three species at low elevation, whereby in all populations of the six species at high elevation, indicating a higher plasticity of flowers in populations at high elevation compared to populations from lower elevation. We suggest that the higher plasticity of flower longevity in alpine populations is of advantage in their unpredictable pollination environment: Increased flower longevity compensates for low pollination in unsuitable periods guaranteeing a minimum reproduction, while the capacity to senescence rapidly after successful pollination saves redundant floral costs in suitable periods.

Highlights

Flower longevity is defined as the time in which a flower remains open and functional, and is a crucial feature for a plants’ reproductive success as it directly determines the time available for pollinator visitations, and, pollen removal and deposition (Primack 1985; Ashman and Schoen 1994)
To test the hypotheses of a general increase and a higher plasticity of flower longevity in high elevation populations, we studied two populations for each of six alpine species occurring at a difference of 1000 m elevation in the Central Swiss Alps, and experimentally manipulated pollination success at both elevations by three pollination treatments: open control pollination, supplemental hand-pollination, and pollinator exclusion
The number of pollen grains delivered to recipient stigmas differed significantly among species with the lowest average pollen deposition found for Primula (22 ± 6) and the highest average pollen deposition recorded for Campanula (1152 ± 62; means across elevation and time periods; Tables S2 and S3; Fig. 2b)

Summary

Introduction

Flower longevity is defined as the time in which a flower remains open and functional, and is a crucial feature for a plants’ reproductive success as it directly determines the time available for pollinator visitations, and, pollen removal and deposition (Primack 1985; Ashman and Schoen 1994). Flowers are costly organs, and their longevity might be determined to balance the rate at which male and female fitness accrue over time against the daily costs of floral maintenance, with short-living flowers when fitness accrual rates and maintenance costs are high and long-living flowers when fitness accrual rates and maintenance costs are low (Schoen and Ashman 1995). Flower longevity might be limited by the high carbon (Ashman and Schoen 1997) and water (Teixido and Valladares 2015) demand of flower development and the maintenance of reproductively functional flowers. Temporal and spatial variation of both the biotic and abiotic environment interplays in determining potential and actual flower longevities in natural populations resulting in amongand within-population variation in flower longevity

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