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Size and architectural traits as ontogenetic determinants of fitness in a phenotypically plastic annual weed ( Amaranthus albus )
Author(s) -
Cheplick Gregory P.
Publication year - 2002
Publication title -
plant species biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.419
H-Index - 36
eISSN - 1442-1984
pISSN - 0913-557X
DOI - 10.1046/j.1442-1984.2002.00075.x
Subject(s) - biology , genotype , trait , allometry , phenotypic plasticity , weed , gene–environment interaction , nutrient , genetic variation , inbred strain , botany , horticulture , agronomy , ecology , genetics , gene , computer science , programming language
Plasticity of size and architectural traits, and their importance to reproductive fitness, were estimated in relation to nutrient availability in the annual Amaranthus albus . Seeds from seven field‐collected genotypes were used to rear a first generation under uniform conditions. Seed families (inbred lines) from four first‐generation plants per genotype were used to rear a second generation in a glasshouse for 10 weeks. Nine plants per family were regularly fertilized, while nine others were unfertilized. Size was estimated at 5, 8, and 10 weeks; architectural traits were recorded at 8 weeks (no. branches) and 10 weeks (no. branches and branch length). Fitness was assessed by the number of seeds per plant. Because traits were intercorrelated, size‐scaled architectural traits were generated and allometric analyses performed. Genetic variation was analyzed for the second generation among inbred lines of the original genotypes, and among families within each genotype. For fertilized and unfertilized groups, early size (volume occupied at 5 weeks) and branch length per mass were significant determinants of fitness. The number of branches per size explained a smaller proportion of the variance in fitness. Genotype by treatment interaction was apparent for some traits, indicating genetic variation for plasticity, but plasticity of size did not change over ontogeny. Significant effects of genotype on size and architectural traits, and fitness, were detected mostly in the unfertilized group. Thus, selection is most likely to differentiate among genotypes in nutrient‐poor environments. Lengthening of multiple branches increases seed output throughout the season, and genotypes with longer branches per unit mass have a selective advantage. Because early size is correlated with seed output, ontogenetic plasticity in response to improved soil resources allows opportunistic increases in fitness.