Offspring performance in three cleistogamous Viola species

Seed germination and seedling/juvenile fitness in the cleistogamous perenni als Viola hirta, V. mirabilis, and V. riviniana were investigated during th ree growing seasons, to compare the performance of chasmogamously (CH) and cleistogamously (CL) derived progeny. For V. hirta and V. mirabilis the eff ects 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 capsu les. In V. mirabilis and V. riviniana, CL seeds had a lower germination rat e than CH seeds. In V. hirta the two seed types did not differ in germinabi lity. 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 p erformance, but grass competition increased mortality and reduced plant siz e of V. riviniana progeny. The two progeny types did not differ in their re sponse 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 s uggested that a dimorphic reproductive system is maintained in perennial Vi ola species to maximize total seed output in the face of environmental vari ation.