Offspring performance in three cleistogamous Viola species

Seed germination and seedling/juvenile fitness in the cleistogamous perennials Viola hirta, V. mirabilis, and V. riviniana were investigated during three growing seasons, to compare the performance of chasmogamously (CH) and cleistogamously (CL) derived progeny. For V. hirta and V. mirabilis the effects of sibling competition were examined, for V. riviniana the effects of interspecific (grass) competition. Seed abortion and seed weight were also taken into account as fitness measures. In none of the species, seed abortion rate differed between CH and CL capsules. In V. mirabilis and V. riviniana, CL seeds had a lower germination rate than CH seeds. In V. hirta the two seed types did not differ in germinability. Mortality did not differ between the two seedling types in any of the species. In V. hirta and V. riviniana, CL progeny had shorter mean length of largest leaf than CH progeny. In V. mirabilis plant size did not differ between progeny types. Sibling competition had little effect on offspring performance, but grass competition increased mortality and reduced plant size of V. riviniana progeny. The two progeny types did not differ in their response to sibling and grass competition. The differences in performance between progeny types could be attributable to inbreeding depression in the CL phase, but the slightly lower fitness of CL offspring is probably balanced by their lower production costs. It is suggested that a dimorphic reproductive system is maintained in perennial Viola species to maximize total seed output in the face of environmental variation.