PARENT SESSION
Oral Session #65: Evolutionary Ecology/ Population Genetics. Presiding: G. Gerrish.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Hall of Ideas J.
Experimental studies of adaptation in Clarkia xantiana (Onagraceae): Character variation across a subspecies border.
Eckhart, Vincent1, Geber, Monica2, McGuire, Chris3, 1 2 3
ABSTRACT- Explaining distribution limits and discerning causes of adaptive variation among populations are central objectives in ecology. We addressed these objectives with transplant experiments across a subspecies border. Clarkia xantiana ssp. xantiana and C. xantiana ssp. parviflora are annuals with contrasting phenology (e.g., ssp. xantiana flowers later) and morphology (e.g., ssp. xantiana has larger flowers and leaves). The subspecies are distributed parapatrically along a precipitation gradient; ssp. parviflora occupies arid regions. We analyzed variation in 12 ssp. parviflora populations and 6 ssp. xantiana populations, at 3 sites (one well within each subspecies' range and one at the subspecies border), in 2 growing seasons (an unusually wet winter and an unusually dry winter). Subspecies distinctions remained clear within sites and years. Within-subspecies variation along the precipitation gradient mimicked between-subspecies differences seen at a larger scale. Phenology and morphology exhibited between-year effects concordant with genetic differences (e.g., flowering was earlier and petals were shorter in the dry year and in populations from dry areas). Among-site variation was not always concordant with genetic differences (e.g., petals were not shortest at the driest site). Developmental traits exhibited subspecies-environment interactions, a pattern that possibly arose because the flowering-time difference caused the subspecies to experience contrasting conditions in shared locations. Though some observed patterns of phenotypic plasticity might facilitate adaptation, interactions and sign differences between genetic and environmental effects may limit adaptation and geographic ranges.
KEY WORDS: species borders, phenotypic plasticity, adaptation, Clarkia xantiana