Regulation of reproductive success in the biennial plant, Hydrophyllum appendiculatum
Wolfe, Lorne Mark
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https://hdl.handle.net/2142/19870
Description
Title
Regulation of reproductive success in the biennial plant, Hydrophyllum appendiculatum
Author(s)
Wolfe, Lorne Mark
Issue Date
1990
Doctoral Committee Chair(s)
Berenbaum, May R.
Department of Study
Biology
Discipline
Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Botany
Biology, Ecology
Agriculture, Plant Culture
Language
eng
Abstract
The major goal of this study was to determine the relative importance of genetic and environmental sources of variation in reproductive success in Hydrophyllum appendiculatum (Hydrophyllaceae), a biennial, self-compatible, outcrossing, insect-pollinated, forest understory herb. Observations conducted in two populations over three flowering seasons (1987-1989) revealed that survival, flower production, and seed production varied spatially and temporally. While some of this variance was probably due to rainfall patterns, seed production was negatively affected by an unidentified pathogen and a weevil that consumed flowers and developing seeds.
A series of greenhouse experiments was conducted to determine the effects of mating system and physical environment on variation in seed size: seed weight in this species ranges from 5-60 mg. Plant mating system was important: outcrossed seeds were heavier than selfed seeds. Seed size was affected by neither the distance separating pollen donors and recipients nor by the number of pollen donors siring offspring with inflorescences. Although mother-offspring regression for seed weight yielded a significant positive relationship, controlled breeding designs revealed no differences among paternal half-sib families, indicating that little or no additive genetic variance exists for seed size. On the other hand, large differences among maternal half-sib families implied maternal effects. Manipulations of the maternal physical environment showed that plants growing under high light conditions had heavier seeds than did shaded plants but that soil types and fertilizer addition had no effect. Within individuals, seed size declined through the season. Seed weight was developmentally constrained by flower size: larger flowers produced larger seeds.
Field and greenhouse studies showed that the effects of seed characters (seed size, seed genotype) and emergence date are expressed at different stages of the life cycle. Generally, seedlings that emerged earlier and those derived from larger seeds developed into larger seedlings which had greater survival. While emergence date effects persisted longer, seed size effects waned rapidly with time. Fitness differences between selfed and outcrossed progeny due to inbreeding depression were barely detectable in the first year of growth but became progressively more pronounced in the second, or reproductive year.
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