Influence of non-lethal costs of reproduction on life history evolution in a long-lived orchid

Background/Question/Methods

Understanding the selective forces that shape reproductive strategies is a central goal of evolutionary ecology. Selection on the timing of reproduction is well studied in semelparous organisms because the cost of reproducing (death) can be easily incorporated into demographic models. Iteroparous organisms also exhibit delayed reproduction and experience reproductive costs, although these are not necessarily lethal. How non-lethal costs shape iteroparous life histories remains unresolved. We analyzed long-term demographic data for the iteroparous orchid Orchis purpurea from two habitat types (light and shade). We incorporated non-lethal costs into integral projection models to identify the flowering size and size-dependent flowering effort that maximize fitness.

Results/Conclusions

In both habitats flowering plants had lower growth rates and this cost was greater for smaller plants. We detected an additional growth cost of fruit production in the light habitat. Observed flowering sizes were remarkably consistent with fitness optima in both habitats. We also estimated optimal parameters for size-dependent flowering effort but found a strong mismatch with observed flower production. Our study highlights the role of context-dependent non-lethal reproductive costs as selective forces in the evolution of iteroparous life histories and provides a novel and broadly applicable approach to studying the evolutionary demography of iteroparous organisms.