Nectar alkaloids decrease pollination and female reproduction in a native plant |
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Authors: | Email author" target="_blank">Lynn?S?AdlerEmail author Rebecca?E?Irwin |
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Institution: | (1) Department of Plant, Soil and Insect Science, University of Massachusetts, Amherst, MA 01003, USA;(2) Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA |
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Abstract: | The evolution of floral traits may be shaped by a community of floral visitors that affect plant fitness, including pollinators
and floral antagonists. The role of nectar in attracting pollinators has been extensively studied, but its effects on floral
antagonists are less understood. Furthermore, the composition of non-sugar nectar components, such as secondary compounds,
may affect plant reproduction via changes in both pollinator and floral antagonist behavior. We manipulated the nectar alkaloid
gelsemine in wild plants of the native perennial vine Gelsemium sempervirens. We crossed nectar gelsemine manipulations with a hand-pollination treatment, allowing us to determine the effect of both
the trait and the interaction on plant female reproduction. We measured pollen deposition, pollen removal, and nectar robbing
to assess whether gelsemine altered the behavior of mutualists and antagonists. High nectar gelsemine reduced conspecific
pollen receipt by nearly half and also reduced the proportion of conspecific pollen grains received, but had no effect on
nectar robbing. Although high nectar gelsemine reduced pollen removal, an estimate of male reproduction, by one-third, this
effect was not statistically significant. Fruit set was limited by pollen receipt. However, this effect varied across sites
such that the sites that were most pollen-limited were also the sites where nectar alkaloids had the least effect on pollen
receipt, resulting in no significant effect of nectar alkaloids on fruit set. Finally, high nectar gelsemine significantly
reduced seed weight; however, this effect was mediated by a mechanism other than pollen limitation. Taken together, our work
suggests that nectar alkaloids are more costly than beneficial in our system, and that relatively small-scale spatial variation
in trait effects and interactions could determine the selective impacts of traits such as nectar composition. |
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