title: Heterozygosity, gender, and the growth-defense trade-off in quaking aspen.
abstract: Although plant growth is generally recognized to be influenced by allocation to defense, genetic background (e.g., inbreeding), and gender, rarely have those factors been addressed collectively. In quaking aspen (Populus tremuloides Michx.), phenolic glycosides (PGs) and condensed tannins (CTs) constitute up to 30 % of leaf dry weight. To quantify the allocation cost of this chemical defense, we measured growth, defense chemistry, and individual heterozygosity (H obs at 16 microsatellite loci) for male and female trees in both controlled and natural environments. The controlled environment consisted of 12 juvenile genets grown for 3 years in a common garden, with replication. The natural environment consisted of 51 mature genets in wild populations, from which we sampled multiple ramets (trees) per genet. Concentrations of PGs and CTs were negatively correlated. PGs were uncorrelated with growth, but CT production represented a major cost. Across the range of CT levels found in wild-grown trees, growth rates varied by 2.6-fold, such that a 10 % increase in CT concentration occurred with a 38.5 % decrease in growth. H obs had a marked effect on aspen growth: for wild trees, a 10 % increase in H obs corresponded to a 12.5 % increase in growth. In wild trees, this CT effect was significant only in females, in which reproduction seems to exacerbate the cost of defense, while the H obs effect was significant only in males. Despite the lower growth rate of low-H obs trees, their higher CT levels may improve survival, which could account for the deficit of heterozygotes repeatedly found in natural aspen populations.
authors.affiliation: Division of Science and Mathematics, University of Minnesota, Morris, 600 E. 4th St., Morris, MN, 56267, USA. colect@morris.umn.edu.
authors.forename: Christopher T
authors.identifier: 0000-0003-1192-6960
authors.initials: CT
authors.lastname: Cole
authors.affiliation: Department of Biology, Utah Valley University, Orem, UT, 84058, USA.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Stevens
authors.affiliation: Division of Science and Mathematics, University of Minnesota, Morris, 600 E. 4th St., Morris, MN, 56267, USA.
authors.forename: Jon E
authors.initials: JE
authors.lastname: Anderson
authors.affiliation: Department of Entomology, University of Wisconsin-Madison, Madison, WI, 53706, USA.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Lindroth
mesh_terms: D004777:Environment; D006579:Heterozygote; D018515:Plant Leaves; D032107:Populus / Q000235:genetics*; D014197:Trees
keywords: Allocation cost; Condensed tannin; Heterozygote advantage; Phenolic glycoside; Phenylpropanoid pathway