Sex and the cost of reproduction through the life course of an extremely long-lived herb.

Abstract

Despite being central concepts for life history theory, little is known about how reproductive effort and costs vary with individual age once plants have started to reproduce. We conducted a 5-year field study and estimated age-dependent reproductive effort for both sexes in the extraordinarily long-lived dioecious plant Borderea pyrenaica. We also evaluated costs of reproduction on vital rates for male and female plants, both by examining effects of differences in individual reproductive effort under natural conditions, and by conducting a flower removal experiment, aimed at decreasing reproductive effort. Reproductive effort was fairly constant and independent of age for males, which may reflect a strategy of adjusting overall reproductive output by spreading reproduction over the life course. Females had a higher total effort, which first increased and then decreased with age. The latter may be a response to an increasing reproductive value-an inverse of a terminal investment-or a sign of reproductive senescence due to an age-related physiological decline. Seed production was lower in plants with higher previous reproductive effort and this effect increased with age. We found no evidence for costs of reproduction on other vital rates for either sex. Experimental flower removal only resulted in progressively more negative effects on flower production in older male plants, whereas female vital rates were unaffected. Overall, this study demonstrates that not only sex, but also age influences resource allocation trade-offs and, thus, plant life history evolution.