CLEISTOGAMY IN MICROLAENA POLYNODA (GRAMINEAE): AN EXAMINATION OF SOME MODEL PREDICTIONS

Abstract

A population of the cleistogamous grass, Microlaena polynoda, was investigated to determine some of the factors responsible for adjusting the balance between reproduction by chasmogamous (CH) and cleistogamous (CL) flowers, the tissue costs associated with the two reproductive modes, the fate of progeny produced by each mode, and the genetic diversity of the progeny. Cleistogamous flower production begins earlier in the season than CH flower production. There is a distinct threshold of low light intensity below which mostly CL flowers are produced. Paternal expenditure per plant is an order of magnitude larger for the CH than the CL component. The opposite relation holds for maternal expenditure. Increased maternal expenditure in the CL component may be due to greater fertilization success and retrieval of paternal costs. Cleistogamous seeds are dispersed later than CH seeds. Following dispersal, the spikelet encloses the CL seed but not the CH seed, and is responsible for inducing dormancy. The ratio of seedlings arising from CH seeds to that from CL seeds in a natural habitat is significantly lower than the ratio of estimated numbers of CH to CL seeds produced. There were no detectable polymorphisms among ten presumptive enzyme loci assayed. Many of the features associated with CH and CL reproduction in M. polynoda are in accord with the theoretical requirements for the evolution of closed flower self‐pollination and the maintenance of two distinct methods of reproduction.