Hawkmoth Pollinators Decrease Seed Set of a Low-Nectar Petunia axillaris Line through Reduced Probing Time

Institute of Biology, University of Neuchâtel, Emile Argand 13, 2009 Neuchâtel, Switzerland.
Current biology: CB (Impact Factor: 9.57). 07/2012; 22(17):1635-9. DOI: 10.1016/j.cub.2012.06.058
Source: PubMed


Although deception of floral pollinators is well known among orchids [1, 2], the majority of animal-pollinated plants secure pollination by nectar rewards. The costs and benefits of nectar production remain poorly understood [3-5]. Here, we developed a crossing design to introgress a low-nectar-volume locus of Petunia integrifolia into the genetic background of P. axillaris. The resulting introgression line resembled P. axillaris but produced only one-third of the nectar volume. When exposed simultaneously to low-nectar and wild-type P. axillaris plants, hawkmoth pollinators reduced their probing duration on low-nectar plants but otherwise did not show any signs of discrimination against these plants. However, reduced probing duration resulted in reduced seed production in the low-nectar plants despite their higher reproductive potential as evidenced by hand pollination. In line with this interpretation, we found a positive correlation between probing duration and seed set, and hawkmoth pollination of low-nectar plants that were manually supplemented with nectar to parental levels yielded seed sets similar to hand pollination. Thus, a simple self-serving pollinator behavior-the adjustment of probing time in response to nectar volume-may select against reducing nectar and protect many plant-pollinator mutualisms against a drift toward parasitism. VIDEO ABSTRACT:

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    • "Possibly because the conflict does not involve interdependencies, the system has yielded experimental evidence for a variety of partner control mechanisms, including punishment, partner switching and social prestige[69,105]. Asymmetric cheating options are highly abundant in mutualisms, with experimental evidence that contingent helping may occur even in plants and insects106107108. For within-species cooperation, evidence for payto-stay in cooperatively breeding systems[109]provides a class of examples for helping acts like brood care or territorial defense, though Hamilton & Taborsky[110]found that if the threat of eviction alone enforces helping, subordinates will not overcompensate for the costs they impose on dominants. "
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    ABSTRACT: Mutual helping for direct benefits can be explained by various game theoretical models, which differ mainly in terms of the underlying conflict of interest between two partners. Conflict is minimal if helping is self-serving and the partner benefits as a by-product. In contrast, conflict is maximal if partners are in a prisoner’s dilemma with both having the pay-off-dominant option of not returning the other’s investment. Here,we provide evolutionary and ecological arguments for why these two extremes are often unstable under natural conditions and propose that interactions with intermediate levels of conflict are frequent evolutionary endpoints. We argue that by-product helping is prone to becoming an asymmetric investment game since even small variation in by-product benefits will lead to the evolution of partner choice, leading to investments by the chosen class. Second, iterated prisoner’s dilemmas tend to take place in stable social groups where the fitness of partners is interdependent, with the effect that a certain level of helping is self-serving. In sum, intermediate levels of mutual helping are expected in nature, while efficient partner monitoring may allow reaching higher levels © 2016 The Author(s) Published by the Royal Society. All rights reserved.
    Full-text · Article · Feb 2016 · Philosophical Transactions of The Royal Society B Biological Sciences
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    • "By virtue of their close mutualistic association, pollinator population density and activity are largely dependent upon floral resource availability and quality (Hanley et al., 2008, 2014; Brandenburg et al., 2012; Scaven and Rafferty, 2013). For example , pollinators typically show fidelity towards plants producing more and higher quality nectar (Lake and Hughes, 1999; Mitchell et al., 2004), such that nectar production directly affects pollinator activity (Klinkhamer and de Jong, 1990; Kudo and Harder, 2005) and pollinator community structure (Potts et al., 2004). "
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    ABSTRACT: Asymmetric warming is one of the distinguishing features of global climate change, in which winter and night-time temperatures are predicted to increase more than summer and diurnal temperatures. Winter warming weakens vernalization and hence decreases the potential to flower for some perennial herbs, and night warming can reduce carbohydrate concentrations in storage organs. This study therefore hypothesized that asymmetric warming should act to reduce flower number and nectar production per flower in a perennial herb, Saussurea nigrescens, a key nectar plant for pollinators in Tibetan alpine meadows. A long-term (6 years) warming experiment was conducted using open-top chambers placed in a natural meadow and manipulated to achieve asymmetric increases in temperature, as follows: a mean annual increase of 0·7 and 2·7 °C during the growing and non-growing seasons, respectively, combined with an increase of 1·6 and 2·8 °C in the daytime and night-time, respectively, from June to August. Measurements were taken of nectar volume and concentration (sucrose content), and also of leaf non-structural carbohydrate content and plant morphology. Six years of experimental warming resulted in reductions in nectar volume per floret (64·7 % of control), floret number per capitulum (8·7 %) and capitulum number per plant (32·5 %), whereas nectar concentration remained unchanged. Depletion of leaf non-structural carbohydrates was significantly higher in the warmed than in the ambient condition. Overall plant density was also reduced by warming, which, when combined with reductions in flower development and nectar volumes, led to a reduction of ∼90 % in nectar production per unit area. The negative effect of asymmetric warming on nectar yields in S. nigrescens may be explained by a concomitant depletion of leaf non-structural carbohydrates. The results thus highlight a novel aspect of how climate change might affect plant-pollinator interactions and plant reproduction via induction of allocation shifts for plants growing in communities subject to asymmetric warming. © The Author 2015. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email:
    Preview · Article · Apr 2015 · Annals of Botany
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    • "Most flowering plants depend primarily on animals for sexual reproduction, offering edible or non-edible rewards to their pollen vectors [1-3]. However, some “deceptive flowers” offer no rewards [4-6]. "
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    ABSTRACT: It is estimated that floral deception has evolved in at least 7500 species of angiosperms, of which two thirds are orchids. Epipactis veratrifolia (Orchidaceae) is a model system of aphid mimicry as aphidophagous hoverflies lay eggs on false brood sites on their flowers. To understand the evolutionary ecology of floral deception, we investigated the pollination biology of E. veratrifolia across 10 populations in the Eastern Himalayas. We reconstructed the phylogeny of Epipactis and mapped the known pollination systems of previously studied species onto the tree. Some inflorescences of E. veratrifolia were so infested with aphids while they were still in bud that the some larvae of hoverflies developed to the third instar while flower buds opened. This indicated that adult female hoverflies were partly rewarded for oviposition. Although flowers failed to secrete nectar, they mimicked both alarm pheromones and aphid coloring of to attract female hoverflies as their exclusive pollinators. Phylogenetic mapping indicate that pollination by aphidophagous hoverflies is likely an ancestral condition in the genus Epipactis. We suggest that the biological interaction of aphid (prey), orchid (primary producer) and hoverfly (predator) may represent an intermediate stage between mutualism and deception in the evolution of pollination-by-deceit in E. veratrifolia. Our analyses indicate that this intermediate stage may be used as a model system to interpret the origin of oviposition (brood site) mimicry in Epipactis. We propose the hypothesis that some deceptive pollination systems evolved directly from earlier (partly) mutualistic systems that maintained the fidelity of the original pollinator(s) even though rewards (nectar/ brood site) were lost.
    Full-text · Article · Mar 2014 · BMC Plant Biology
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