"Phenotypic Plasticity in a Population of Ecotone Tarweeds" 

Defense of the dissertation took place on October 27, 2006.

Presently, manuscripts of dissertation chapters are being reviewed for publication.

Abstract of dissertation:

Morphological variation in Deinandra fasciculata growing across a scrub/meadow ecotone was analyzed to determine the reason for the variation, and discover patterns within that variation.  Eight common gardens were established to test the effect of soil (treatment 1) versus genotype (treatment 2) on F1 progeny of a tarweed ecotone population.  A natural distribution study was conducted as a control to compare the ex situ common garden results with the natural population.  Analysis of variance, reaction norms, and correlations were calculated on data collected at each phenological stage during the plantís annual life history.  Results indicate that differences in several variable characters across the ecotone are due to phenotypic plasticity, rather than genetic differentiation of ecotypes.  Biomass was larger in the meadow gardens, as well as height, but number of branches was greater in the scrub gardens.  However, natural distribution indicates higher branch to height (B/H) and branch to capitulum (B/C) ratios on the scrub-side, but not greater branching, suggesting in situ, ex situ differences.

A reciprocal transplant experiment was performed on 36 ecotone tarweeds to determine environmental effects in situ.  Results suggest that ratio of branches to capitulae (B/C) was higher on meadow transplants in scrub soil than vice-versa.  The two sides of the ecotone were studied to determine differences in soil composition and plant water potential.  Results indicate that scrub-side plants have higher water potentials, suggesting that more water is available to the scrub-side tarweeds than the meadow-side tarweeds.  Meadow-side soil nitrogen content was much higher (order of magnitude), possibly explaining differences in height across the ecotone.  A watering regimen experiment was conducted to test the effects of water availability as a potential environmental cue stimulating phenotypic plasticity.  Results suggest that decreasing water over time to experimental plants decreased the number of branches, depending on the phenology.  It appears that the ecotone tarweed population has adapted to this heterogeneous environment by reducing potential loss of fitness on the nutrient-impoverished scrub side, which results in shorter plants, by using increased water availability on the scrub-side as a cue to increase B/C ratio and thus number of flowers relative to size.

Ph.D. in botany conferred by Claremont Graduate University, through Rancho Santa Ana Botanic Garden.

Major Professor: Dr. J. Mark Porter.

Correspondence: kovnatgd@lavc.edu