VIRUS INFECTION AND THE EVOLUTION OF SEX IN FLOWERING PLANTS

摘要

Advantage of sex remains an unanswered question. According to the Red Queen hypothesis, pathogen-driven selection can provide a general advantage for sex. However, evidence supporting this hypothesis is still circumstantial. The geminivirus-Eupatoriumsystem provides an excellent opportunity to test the Red Queen hypothesis for the evolution of sex. E. makinoi (Asteraceae), a common perennial in Japan, consists of sexual and asexual (agamospermous) populations (Watanabe et al. 1982, Watanabe and Yahara 1984), and the asexual populations suffer infection of geminivirus at much higher frequencies than the sexual populations (Yahara and Oyama 1993). Geminivirus infection causes the specific reduction of chlorophylls and light-harvesting chlorophyll binding proteins, which results in high mortality under low light conditions (Funayama et al. 1997). Thus, virus infection is one of the major mortality factors in asexual populations of E. makinoi in the field (Yahara and Oyama 1993).