Path analysis of local adaptation in two ecotypes of the annual plant Diodia teres Walt. (Rubiaceae).
Reciprocal transplant experiments were conducted to measure local adaptation in morphologically distinct ecotypes of the weedy annual dicot poorjoe (Diodia teres). Local ecotypes were generally favored in comparisons of survival, growth, and seed production. Pathcoefficient analysis was used to estimate coefficients of a model of causal relations among fitness components (nge-specific sizes and seed production) and to examine how differences in growth between ecotypes over a succession of phases lead to selection against introduced ecotypes at the level of seed production. The path-coefficient analysis revealed large differences between ecotypes in performance over many intervals and in many relations between fitness components. However, differences did not occur at all growth stages, and introduced ecotypes were superior in several comparisons. Path-coefficient analysis offers insights into the comparative adaptation of ecotypes beyond those possible from analyses that do not account for causal relations among fitness components. By focusing attention on life-history stages at which fitness differences arise between ecotypes, it can facilitate investigations of ecophysiological and other mechanisms underlying adaptive differences among ecotypes.
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