Abstract
Specialization in plant–insect interactions is an important driver of evolutionary divergence; yet, plant traits mediating such interactions are poorly understood. In this study, we investigated how flower color and floral scent are related to seed predation by a seed-eating pollinator. We used field-transplanted recombinant F2 hybrids between Silene latifolia and S. dioica that are the preferred and alternative hosts of the moth Hadena bicruris and crosses within these species for comparison. We scored seed predation and flower color and analyzed floral scent. Pinker S. dioica-like flowers and emission of α-pinene decreased the odds of seed predation while emission of benzyl acetate and 6-methyl-5-hepten-2-one increased the odds of seed predation. Emission of these compounds did not differ significantly between the two Silene species. Our results suggest that flower color plays an important role in the specific interaction of H. bicruris with its preferred host S. latifolia. The compounds α-pinene, benzyl acetate and 6-methyl-5-hepten-2-one could represent non-specific deterrents and attractants to ovipositing moths. Alternatively, emission of these compounds could be related to herbivory or pathogen attack and act as a signal for host quality. This would weaken the predictability of the plant's costs and benefits of the interaction and act to maintain an imperfect degree of specialization.
Highlights
Specialization in plant–insect interactions, for example in plantpollinator interactions, is an important mechanism driving diversification in both plants and insects [1,2,3]
Seed predation rate was very low in S. dioica (3.2% of the plants infested, N = 31), and differed significantly from the substantial seed predation rate in S. latifolia (55.6%, N = 18, X2 = 15.00, P = 0.0001)
Emission of a-pinene decreased and emission of benzyl acetate and 6-methyl-5-hepten-2-one increased odds of primary seed predation. These compounds were present in the floral scent of the two Silene species in our study suggesting that they are not related to the specific interaction of H. bicruris with S. latifolia
Summary
Specialization in plant–insect interactions, for example in plantpollinator interactions, is an important mechanism driving diversification in both plants and insects [1,2,3]. Hawk moths (Manduca species), for example, are pollinating herbivores of Sacred Datura (Datura wrightii) and of wild tobacco (Nicotiana attenuata) In these systems, both male and female moths are attracted by flower color and scent while oviposition choices by female moths were based on nectar volume or on volatile compounds perceived by female moths [9,10,11,12]. Pollination benefits for Nicotiana attenuata were maximized by the presence of both attractants and deterrents for moths as this increased the number of different plants visited [11]. Such a combination of attractants and deterrents could be common [13], and may be expected where pollinators damage plants through their larvae. More investigations on floral traits are needed to understand their role in the interactions of plants with pollinating seed predators/ herbivores, especially under field conditions
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