Host Sanctions and Pollinator Cheating in the Fig Tree- Fig Wasp mutualism. K. Charlotte Jander and Edward Allen Herre.

In this study, the authors looked to answer the question, “What prevents one partner from reaping the benefits of the interaction with-out paying the costs?” This is the definition of a cheater; one fig who is able to reproduce within the fig without spending the time or energy to help the fig to pollinate. This is therefore a disruption to the life-cycle of the fig to fig-wasp mutualism. In addition, they looked at the affect of host sanctions on wasp fitness. The study was really important to do given the questions of cheaters and how this might disrupt the very old mutualism in the future.

In order to do this study they looked at six monoecious fig species, four of which were actively pollinated, and two passively pollinated figs near the Panama Canal in the Republic of Panama. They used field experiments and direct observations in order to measure sanction strength which is determined based on the total life span of the pollinating fig and whether or not she actively served as pollinator. In order to find the cheaters they "screened natural populations of pollinator waspss for individuals that did not carry pollen" (Jander). Once they had gathered the field observations they performed experiments in the lab by pairing one pollinating and one non-pollinating fig wasp with each fig.

They found three major findings from doing this study. "First we show that host sanctions against non-cooperative symbionts vary dramatically in form and intensity across fig species. Second, we document the existence of pollen-free individuals ('cheaters') within the otherwise mutualistic pollinator wasp species. Third, across the actively pollinated fig species, we show that the proportion of pollen-free wasps is negatively correlated with sanction strength" (Jander)

This study indicated that sanction strengths vary dramatically from basal to active species and that cheaters do exist in mutualistic symbioses. "In contrast, the passively pollinated fig species showed no evidence of sanctions" (Jander). The findings that they made indicate that despite previous beliefs, the stability of the mechanisms surrounding the fig tree and fig wasp symbiosis may not be fixed. In addition, it is rare to find “cheaters” in a mutualistic relationship, but because this study proved that “cheaters” exist, we can understand why sanctions are important in mutualistic relationships so as to limit the amount of “cheaters” present in the symbiosis. Given that cheaters are disruptive to the traditional symbiotic association of these two organisms, there need be some sort of compensation, which is then the host sanctions. The host sanctions are critical for keeping the number of cheaters to a minimum. As expected, an increase in cheaters could disrupt the cycle of the mutualism entirely, therefore it is important that this be studied in order to know whether some new trend is leading to an increase in cheaters and therefore threatening the success of fig trees.

In addition to finding that cheaters do exist and that there are effects on fitness as a result of host sanctions, they also found a correlation between passive and active pollination and the presence of host sanctions. When reviewing the results, that fact that host sanctions were found in all actively pollinated fig species, but not in passively pollinated fig species shows that as natural selection favored the actively pollinated fig species, so did the evolution of strong host sanctions to protect against cheaters. The new information found on this mechanism supplies new insight into the mechanism behind cheaters but also how the system responds with host sanctions in the actively pollinating fig species. Due to the lesser amount of production in the actively pollinating species, the cheater wasps are able to fake pollination and reproduce in the flowers. The passively pollinating fig species does not have to worry about this because it produces so much that the danger of cheaters is greatly lessened. While passive verses active was previously understood, this research is helping to explain how that specifically affects the symbiotic association between fig trees and fig wasps.

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