Hawkmoth Pollinators Decrease Seed Set of a Low-Nectar Petunia axillaris Line through Reduced Probing Time.
ABSTRACT 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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ABSTRACT: Mutualisms are commonly threatened by parasites and cheaters: species that exploit the host-derived resources without providing an adequate service. Here, we summarize mechanisms for the stabilization of obligate defensive ant–plant mutualisms, a typical element of tropical lowland forests. Host plants exert partner choice and can sanction non-defending ants by shedding the domatia that serve as nesting space or ceasing the production of ant rewards. Hosts can also restrict the exploitation of the ant rewards by means of specific biochemical traits that decrease their quality for non-adapted generalist exploiters and, thus, convert them into exclusive rewards. Reward provisioning can even shift the competitive balance between mutualists and exploiters in favor of the mutualists. In turn, plant-ants show adaptations in their colony structure and changes in their digestive capacities that enhance their efficiency in the use of the host-derived resources. Founding queens use plant odors for host choice behavior, and ants not supplied with adequate amounts of EFN decrease their defensive service and thereby exert partner sanctions. Theoretical models and empirical research into mutualisms usually focus on actions that are taken by the host. Using ant-plants as model systems, we are now discovering the importance of contributions that come from the symbiont. This discovery indicates the potential for multiple reciprocal interactions between phenotypically plastic hosts and symbionts, which contribute significantly to what is still considered a miracle: the stability of mutualisms in the presence of exploiters.Biotropica 05/2013; · 2.35 Impact Factor
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ABSTRACT: Mutualisms require protection from non-reciprocating exploiters. Pseudomyrmex workers that engage in an obligate defensive mutualism with Acacia hosts feed exclusively on the sucrose-free extrafloral nectar (EFN) that is secreted by their hosts, a behaviour linking ant energy supply directly to host performance and thus favouring reciprocating behaviour. We tested the hypothesis that Acacia hosts manipulate this digestive specialisation of their ant mutualists. Invertase (sucrose hydrolytic) activity in the ant midguts was inhibited by chitinase, a dominant EFN protein. The inhibition occurred quickly in cell-free gut liquids and in native gels and thus likely results from an enzyme-enzyme interaction. Once a freshly eclosed worker ingests EFN as the first diet available, her invertase becomes inhibited and she, thus, continues feeding on host-derived EFN. Partner manipulation acts at the phenotypic level and means that one partner actively controls the phenotype of the other partner to enhance its dependency on host-derived rewards.Ecology Letters 11/2014; 17:185–192. · 17.95 Impact Factor
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ABSTRACT: In many instances of cooperation, only one individual has both the potential and the incentive to 'cheat' and exploit its partner. Under these asymmetric conditions, a simple model predicts that variation in the temptation to cheat and in the potential victim's capacity for partner control leads to shifts between exploitation and cooperation. Here, we show that the threat of early termination of an interaction was sufficient to induce cleaner wrasse Labroides dimidiatus to feed selectively against their preference (which corresponds to cooperatively eating client fish ectoparasites), provided that their preference for alternative food was weak. Under opposite conditions, cleaners fed selectively according to their own preference (which corresponds to cheating by eating client mucus). By contrast, a non-cleaning fish species, Halichoeres melanurus, failed to adjust its foraging behaviour under these same conditions. Thus, cleaners appear to have evolved the power to strategically adjust their levels of cooperation according to the circumstances.Proceedings of the Royal Society B: Biological Sciences 01/2013; 280(1761):20130553. · 5.68 Impact Factor