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Reproductive allocation and the long-term costs of reproduction in Siparuna grandiflora, a dioecious neo-tropical shrub

Authors


Adrienne B. Nicotra, Research School of Biological Sciences, Australian National University, Canberra, ACT 0200, Australia (fax 612 6249 5095; e-mail nicotra@rsbs.anu.edu.au).

Abstract

1 Using a combination of observational and experimental approaches, both allocation of resources to reproduction (often called the direct cost of reproduction) and the subsequent long-term costs (the indirect, delayed or demographic cost) associated with reproductive allocation to male and female function in Siparuna grandiflora (Siparunaceae), a tropical dioecious shrub, were examined.

2 The objectives were to determine whether females allocate more biomass or nitrogen per reproductive episode than males, and whether there is a long-term cost of reproduction in terms of subsequent growth or reproduction for either sex. If there is no long-term cost of reproduction, then reproduction may be viewed as free in an evolutionary sense.

3 As is generally the case in dioecious species, females allocated more biomass and nitrogen to reproduction than males. Females also showed delayed costs of reproduction in terms of decreased growth and subsequent reproduction, whereas males did not.

4 The lack of measurable delayed costs in males suggests that with the evolution of dioecy, selection has reduced delayed costs of reproduction in S. grandiflora males. In contrast, females that were prevented from reproducing were able to re-allocate resources to growth, and produced more stem length on average than males. This re-allocation response may have evolved to reduce delayed costs of reproduction in females over time frames longer than that considered in the present study.

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