INBREEDING EFFECTS IN A GYNODIOECIOUS POPULATION OF THE COLONIZING SPECIES TRIFOLIUM HIRTUM ALL

The demographic consequences of one and two generations of selfing were examined in a gynodioecious population of rose clover (Trifolium hirtum). Seeds collected from a roadside population were used to create an experimental population that consisted of seeds of open-pollinated individuals (S₀ ), and seeds obtained after one (S₁ ) and two (S₂ ) generations of selfing. Seeds from the three groups were equally likely to germinate. However, inbreeding effects were observed in the vigor and survivorship of the seedlings. The proportion of the transplanted seedlings that reached the reproductive stage was 0.42, 0.31, and 0.14 for the S₀ , S₁ , and S₂ groups, indicating a reduction of 26% and 66% by one and two generations of selfing, respectively. Inbreeding effects on reproductive components of fitness were nonsignificant. Groups were compared by multiplicative fitness functions based on germination, survival to reproduction, and fecundity. The relative fitness of the S₁ and S₂ groups were 0.64 and 0.23 relative to the S₀ group, representing a reduction in lifetime fitness of 36% and 77%, respectively. The differences in relative fitness among the groups were caused mainly by differences in survivorship. Thus, inbreeding depression is apparently an important factor in the maintenance of the gynodioecious breeding system in rose clover.