Costs and benefits of fruiting to future reproduction in two dormancy-prone orchids

1 Reproduction is expected to occur at a cost to survival, growth or future reproduction. However, trade-offs in long-lived, clonal herbs have proven difficult to assess, particularly when they are prone to adult dormancy. 2 We assessed the costs of fruiting in a study of two species of lady's slipper orchid, Cypripedium candidum and C. parviflorum, growing sympatrically in a wet meadow in north-eastern Illinois, USA, from 2000 to 2005. 3 First, we characterized flowering and fruiting in both populations. We found some differences between species, with 68.6 +/- 5.7% (mean +/- SE) and 43.5 +/- 1.4% of sprouting plants flowering, while 33.6 +/- 10.0% and 33.5 +/- 8.1% of flowering plants fruited in C. candidum and C. parviflorum, respectively. 4 Next, we tested the survival, sprouting and flowering response to current fruiting using multistate mark-recapture statistics. The best-fit model posited no cost of fruiting. However, according to a model parsimonious with the best-fit model, fruiting may have resulted in a small cost to survival visible primarily in small-sized individuals of C. parviflorum (decrease from 0.846 in non-fruiting but flowering plants to 0.824 in fruiting plants). In all cases, fruiting resulted in an increased probability of future flowering, suggesting that reproduction may have a higher priority in resource allocation than survival. 5 Finally, we tested the effects of fruiting on future fruiting using logistic regression for two years in which fruiting was particularly high, but detected no change in the probability of fruiting after fruiting. 6 Fruiting may increase in response to internal cues, perhaps related to nutrient uptake or storage, in addition to the obvious effects of pollination. The result may be that plants with greater access to nutrients or with greater stored reserves are more likely to flower each season. We suggest a need for further research exploring the internal mechanisms governing fruiting response in long-lived, clonal herbs.