GENDER VARIATION IN A RED MAPLE POPULATION (ACER RUBRUM; ACERACEAE): A SEVEN-YEAR STUDY OF A “POLYGAMODIOECIOUS” SPECIES

Abstract

Red maple trees have been described as having a complex breeding system, categorized as “polygamodioecious.” However, the seven-year, quantitative investigation of 79 trees presented here shows that the breeding system is relatively simple, using the gender equations of Lloyd (1980). Out of the entire maple population, 55 individuals are constant males while 4 individuals are inconstant males that on occasion produce some female inflorescences. Twelve individuals are constant females and 6 individuals are inconstant females that on occasion produce some male inflorescences. Only 2 of the plants have a functional gender which fluctuates dramatically in successive years between maleness and femaleness. It might be predicted that maple plants may specialize in one gender at a small size and switch over to produce both pollen and ovules at a larger size. However, these data show that plants of inconstant gender are not larger than plants of constant gender. Further, the inconstant plants actually appear to have a lower mean fitness than plants of constant gender. These results suggest that inconstancy in red maple gender does not increase fitness and may be an example of an imperfectly developed canalization process.