Extrinsic and Intrinsic Factors Controlling Reproduction in an Annual Plant
Lee, Thomas Dale
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https://hdl.handle.net/2142/68205
Description
Title
Extrinsic and Intrinsic Factors Controlling Reproduction in an Annual Plant
Author(s)
Lee, Thomas Dale
Issue Date
1980
Department of Study
Plant Biology
Discipline
Botany
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Botany
Language
eng
Abstract
The objectives of the study were to (1) determine what factors limit fruit and seed production in the annual legume Cassia fasciculata Michx., and (2) determine the extent of and basis for selective fruit maturation in this plant species. Cassia fasciculata is an herbaceous plant that inhabits prairies, open woods, and waste places. Manual addition of pollen to flowers in the field increased the number of fruit initiated per inflorescence, but did not increase the number of fruit matured, suggesting that fruit production was not pollinator limited. Removal of rapidly growing fruits resulted in growth and maturation of fruits that normally would not have matured, suggesting that resources limited fruit production. In four populations studied 24 - 70% of initiated fruits matured, 12 - 40% were aborted or died, 3 - 31% were still developing at the time of plant death, and 6 - 12% were lost to predators. In fruits that matured, between 23 and 73% of initiated seeds reached maturity, 22 - 43% were aborted, and 0 - 49% were lost to seed predators. The data indicate that seed production was limited by either resources or seed predators. Demographic studies indicated that resource limitation resulted from either resource shortages or insufficient time to acquire these resources.
Several hypotheses were advanced to explain why C. fasciculata initiates a greater number of fruits than can usually be matured. Available data suggest that extra fruits are selected for by year to year unpredictability in resources during fruit filling and because they provide the opportunity for selective fruit maturation.
Demographic analysis of flowers and fruits in field populations demonstrated that fruits did not mature in the order initiated, although early initiated fruits did have a higher probability of maturation. Fruits initiated early in the season tended to grow slowly at first, whereas those initiated later tended to grow rapidly; this growth pattern dampened the effect of the order of fruit initiation on maturation sequence.
Two glasshouse experiments were conducted to test the hypothesis that more outcrossed fruits were matured than selfed fruits, but in both cases the hypothesis was rejected. Two experiments were also conducted to test the hypothesis that fruits with a large number or percentage of fertilized ovules were selectively matured. This hypothesis was supported by both glasshouse experiments and field observations. Percentage of fertilized ovules seemed to be more clearly related to fruit growth and maturation than was number of fertilized ovules. Natural selection may favor individuals that mature fruits with high percentage fertilization because such fruits (1) may be more resource efficient because they contain less pericarp per seed, (2) may provide better dispersal of seed, or (3) may contain high-quality seed owing to increased gamete competition.
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