Kessler & Helitschke 2009
I won’t be at PAInt on Wednesday, but here are some potential discussion topics:
1.) The authors suggest that pollinator attraction to a flower could be reduced by herbivore defense mechanisms in two ways: either by a trade off mechanism where plants invest less in flower attractiveness to produce more defense or by a byproduct mechanism in which the same defense chemicals reduce pollinator attraction in the flower (which is claimed to be a non-adaptive mechanism). What other mechanisms could lead to this same outcome? Do you believe that the adaptive or non-adaptive mechanism is more common in nature? (Note: the authors do say that these two mechanisms are not mutually exclusive and are at two ends of a continuum, but I still think that a debate on adaptive vs. non-adaptive mechanisms is worthwhile)
2.) Theoretically, should nectar or pollen secondary metabolites be under stronger selection from pollinators? Could you find general patterns of selection strength across pollinator guilds?
3.) In the case study, the authors found that bees are less likely to visit flowers of damaged plants, perhaps as a response to altered pollen chemistry (resulting from an induced defense). Would there be times when it would be beneficial (in terms of reproductive fitness, of course) for a plant to not induce stronger defense compounds in order to maintain high flower visitation? How would you model this tradeoff?
In addition to everything Josh mentioned:
–The authors found that typically defensive compounds (i.e. rutin and chlorogenic acid) were found in all flower tissues, and mentioned that perhaps those chemicals cued tissue-specific responses. Are there situations where it is adaptive to have a inter-tissue chemical signal be defensive? Are there situations where the converse is true?
–Solanum has poricidally dehiscing anthers, and, as mentioned by the authors, will not release pollen unless the anther cone is vibrated. If leaf VOC’s (or any other signal) dissuades pollinators from landing on flowers so dramatically, what would be the adaptive significance of decreased SAS/herkogamy as a response to herbivory in obligate insect pollinated species?
— The case study combined a South American Solanum species with a bumble bee native to the Eastern United States. Though Bombus impatiens is a common surrogate for native bees in manipulative experiments, do you believe that the historical isolation of these species (in an evolutionary sense) would have an affect on the interactions observed? To phrase the question in another way, is this species level interaction between non-cooccurring plants and insects broadly generalizable?
–In the discussion section the authors mention a third hypothesis for decreased pollinator visitation not touched on by Josh. The suggestion that the change in VOC bouquet might be unfamiliar to pollinators, and thus decreases floral visitation, functions under the assumption that VOC’s are not inherently attractive or non-attractive to pollinators, but rather novel compounds dissuade pollinators. On the other hand individual pollinator turn-over rate can be fairly high. If bee response was purely due to differences in floral VOC bouquet, how would pollinator lifespan affect the selective pressures on chemical defense.
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UNR Plant-Animal Interactions Graduate Reading Group
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