Abstract
A prerequisite for the evolutionary stability of pollinating seed-consuming mutualisms is that each partner benefits from the association. However, few studies of such mutualism have considered the benefit gained by the pollinators. Here, we determined how the pollinating seed-predators ensure the provisioning of their offspring in the recently discovered mutualism between Rheum nobile and Bradysia flies. The correlation between flower fate and fly oviposition was examined. Floral traits and patterns of variation in fruit abortion and fly oviposition were investigated to determine whether female flies exhibit preferences for particular flowers when laying eggs. Indole-3-acetic acid (IAA) was quantified to determine whether female flies manipulate host physiology. Flowers that flies oviposited on had a significantly lower probability of fruit abortion compared with intact flowers. Females did not exhibit oviposition preference for any of the floral traits examined. There was no significant correlation between fruit abortion and fly oviposition in terms of either flower position or timing of flowering. IAA concentrations in oviposited flowers were significantly higher than in intact flowers. Our results suggest that oviposition by the mutualistic seed-consuming pollinator Bradysia sp., greatly reduces the probability of fruit abortion of its host, R. nobile; this may be attributed to the manipulation of host physiology through regulating IAA levels.
Highlights
Effect Fruit set Pollination Year Pollination ×year Error Fruit abortion rate Pollination Year Pollination ×year Error
Since egg laying by pollinating seed-consumers typically occurs much earlier than seed development, it would be beneficial if ovipositing females could ‘predict’ which flowers were most likely to set seed and have a low probability of fruit abortion, e.g., if they could actively select sites that are most favorable for growth and survival of their offspring
In addition to choosing oviposition sites ‘wisely’, some insect herbivores are thought to be able to manipulate the physiology of host plants by controlling hormones so as to enhance the resources available for larval growth, as seed development is regulated by a variety of hormone signals[22,23,24]
Summary
Effect Fruit set Pollination Year Pollination ×year Error Fruit abortion rate Pollination Year Pollination ×year Error. Our preliminary investigations found that the probability of fruit abortion for flowers in which eggs have been laid by Bradysia flies was lower than flowers not selected for oviposition, suggesting that ovipositing flies are good at choosing superior flowers that will develop into mature fruits, or that they or their offspring are able to manipulate the physiology of their host, Rheum nobile, to ensure fruit development so as to provide sufficient food resources. We determined the role of several floral traits in influencing pollinating seed-predator oviposition choices and the effects of flower position and flowering sequence on fruit set, fruit abortion and oviposition patterns.
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