For better or worse: Benefits and costs in a linked pollination/herbivory interaction.
Bronstein, Judith*,1, Davidowitz, Goggy1, Huxman, Travis1, 1 University of Arizona, Tucson, AZ
ABSTRACT- Certain mutualists appear to inflict such high costs on their partners that it is perplexing how they have evolved and are able to persist. Addressing this issue has been hampered by difficulties in measuring the costs and benefits of mutualism in comparable currencies, and by a persistent focus on the perspective of only one of the two partners. The interaction between the perennial herb Datura wrightii and the hawkmoth Manduca sexta, which in the southwestern US is both a major pollinator and a highly damaging herbivore of D. wrightii, offers many advantages for taking a physiological approach to the reciprocal forces that shape and constrain mutualism. In this talk we focus on the costs and benefits experienced by the plant. We present experimental and observational evidence that the benefits of pollination by M. sexta are smaller than expected: D. wrightii is highly self-compatible, and has several alternative hawkmoth pollinators. Furthermore, M. sexta (as well as the alternate pollinators) spend much of their time nectaring at Agave, a plant they do not appear to effectively pollinate; when they do visit D. wrightii flowers, they transport Agave pollen into them. It seems likely that costs of herbivory might frequently outweigh the benefits M. sexta confers. However, the costs inflicted by the herbivorous larvae also appear to be much smaller than expected. We present physiological evidence that the underground tuber of D. wrightii subsidizes remarkably rapid regrowth following herbivore damage. However, newly regrown leaves have reduced photosynthetic rates. We present a general physiological model that links herbivory with reproductive effort, and demonstrate how it can be used as a first step towards linking the costs and benefits of M. sexta to D. wrightii via a common energetic currency.
Key words: mutualism, herbivory, pollination, Lepidoptera
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