Growth–defense tradeoffs differ by gender in dioecious trembling aspen ( Populus tremuloides)

Abstract

Growth–defense tradeoffs are foundational to plant defense theory, but few studies have addressed the role of plant gender in such tradeoffs. We used an experimental trial garden of mature, dioecious Populus tremuloides trees to assess gender-based differences in growth, defense, and growth–defense tradeoffs. Male trees were 9% larger than female trees in terms of diameter-at-breast height (dbh) and had levels of defense chemicals [phenolic glycosides (PGs) and condensed tannins (CTs)] similar to those of females. Although male and female aspen had roughly similar levels of growth and defense, growth–defense tradeoffs differed markedly by gender. Growth of males was not related to either PG or CT concentrations, while growth of females was positively correlated with PG concentrations and negatively correlated with CT concentrations. Higher levels of PGs, if present throughout the life of a tree, may be protective against herbivores and result in greater growth over time.