Pollinator limitation on reproductive success in Iris tuberosa

Giuseppe Pellegrino

doi:10.1093/aobpla/plu089

Abstract

Variation in plant and floral size can have conflicting effects on pollination and fruit production in flowering plants. This research examines the contributions of plant height, flower size and pollinator visitation to reproductive success in four populations of Iris tuberosa. The plants were pollinated exclusively by hymenopteran species, primarily during sunny days. Pollination supplementation increased the proportion of flowers that matured into fruit, with 95 % fruit set for hand-pollinated compared with 74.15 % for naturally pollinated flowers. The pollinator visitation rate and the proportion of fruit produced were not significantly different between tall and short plants or between small and large flowers. Furthermore, the increase in plant size and floral display did not increase the frequency of pollinator visitations and so did not increase the fruit set. Thus, despite the widespread effects of flowering plant size on pollinator attraction and plant reproduction in other species, these effects are lacking in I. tuberosa. This study quantifies the role of pollinators in the reproductive success of I. tuberosa. Pollinators visited tall/short plants and large/small flowers in equal proportion, suggesting that plant and floral display size do not affect pollinator attraction and reproductive success in I. tuberosa. These results suggest that sexual reproduction of I. tuberosa is fairly limited by pollinators and not by resource limitation.

Highlights

Plants should invest in flower production until visitation yields the amount of pollen necessary to produce the maximum number of seeds that resources can support (Haig and Westoby 1988), and plants would be simultaneously limited by resources and by pollen
Plant and floral size Plant height of I. tuberosa ranged from 18.00 to 39.50 cm (Table 1), and there were no significant differences between the populations with regard to average plant length (F3,77 1⁄4 0.97, P 1⁄4 0.28 by analysis of variance (ANOVA))
Nine species were recognized as effective pollinators belonging to five genera of Hymenoptera (Andrena, Anthophora, Colletes, Lasioglossum and Xylocopa)

Summary

Introduction

Plants should invest in flower production until visitation yields the amount of pollen necessary to produce the maximum number of seeds that resources can support (Haig and Westoby 1988), and plants would be simultaneously limited by resources and by pollen. The frequency and potential consequences of pollen limitation for plant populations and communities have been intensely explored during the last few decades (Ashman et al 2004; Garcıa-Camacho and Totland 2009; Gomez et al 2010; Harder and Aizen 2010). Pollinator limitation of female reproduction occurs when an inadequate supply of pollen limits fruit set below the level possible given the plant’s available resources. A decrease in pollinator frequency (i.e. number of visits) is likely to decrease the quantity of pollen deposited onto the stigma (Ashman et al 2004), reducing fruit and seed set (Bierzychedek 1981; Matsui et al 2001; Pellegrino et al 2005; Aizen and Harder 2007). Limitation of fruit and seed production by insufficient pollinator visitation is common and ubiquitous across angiosperms (Ashman et al 2004; Knight et al 2005)

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