Cost of reproduction in a gender-switching forest understory herb, Coptis laciniata

Background/Question/Methods

Cost of reproduction is difficult to demonstrate because plants in favorable microsites accumulate enough resource to flower, but also accumulate resources so quickly that the resource cost of seed production is masked.  I studied costs of reproduction over four years in 200 permanently marked individuals of Coptis laciniata, a clonal forest understory herb in the buttercup family, in the Cascade Mountains of Oregon.  Because Coptis is exceedingly shade tolerant, it is similar to the understory orchids for which cost of reproduction has been possible to demonstrate.  In contrast, however, it is clonal and exhibits gender switching, with plants that are bisexual in one year often reproducing strictly as males in the next year. 

Results/Conclusions

Bisexual ramets had the largest leaves (3.45cm), male ramets had the second largest (3.05cm) and non-flowering ramets had the smallest (2.26cm).  Cost of reproduction was not evident in leaf size or reproductive output, with number of fruit produced in one year serving as a positive predictor of number of fruit in the second year.  Ramets that produced many fruits were more likely to shrink, and ramets that had produced the most fruits over the three year study period were not the largest ramets, but these patterns were not statistically significant given the current sample size.  Interestingly, ramets in high light microsites had smaller leaves than those in lower light microsites, and yet produced more fruits, suggesting that larger leaves are produced in response to a low light environment and do not reflect levels of stored resources.  In contrast, cost of reproduction was evident in the patterns of gender switching.  Bisexual ramets had a 42% chance of remaining bisexual for another year, a 40% chance of becoming male, and a 18% chance of becoming non-flowering, and only an 11% chance of remaining bisexual for all three study years.  Ramets that would switch to being male in the next year had smaller leaves (3.42cm) than ramets that continued to be bisexual (3.64cm). Males and non-flowering ramets had a 65% chance of remaining in the same state from one year to another, and only a 6% chance of becoming bisexual.  A third way to show cost of reproduction would be through natural or experimental removal of flowering stalks.  Of ten ramets that underwent herbivory in the second year, 80% were bisexual again the next year, compared with 38% of those that produced mature fruit.