Structure and dynamics of natural populations of polyploid trilliums

Abstract

To confirm predominant self-pollination in natural populations ofTrillium apetalon (2n=4x=20, SSUU), chromosome constitutions of endosperms (2n=30, SSSUUU) fertilized in nature were analyzed for the patterns of H-segments of cold-treated chromosomes. The endosperms were of two kinds: homo-constitutions in which three chromosomes in each of the ten sets of homologues were of the same patterns of H-segments and hetero-constitutions in which one chromosome in a set of three homologous chromosomes was different from the other two. Out of 30 endosperms, 27 (90%) were of homo-constitutions and only three (10%) were of hetero-constitutions. Since the population consisted of various homokaryotypes in which each of the ten pairs of homologous chromosomes was homozygous for the patterns of H-segments, the endosperms of homo-constitutions were the result of self-pollination, and those of hetero-constitutions were from cross-pollination.

Due to pollination tests conducted in two natural populations, many good seeds were found in the fruits from both open-pollinated flowers and those covered with cotton-bags. In striking contrast, no good seeds were found in the fruits from flowers castrated and pollinated in the open-air.

An additional evidence of predominant self-pollination and occasional cross-pollination was given by analyzing spatial distribution of plants of various karyotypes in a population.