Graduation Term

2015

Degree Name

Master of Science (MS)

Department

School of Biological Sciences

Committee Chair

Victoria A. Borowicz

Abstract

Baptisia alba macrophylla, a native, herbaceous perennial legume, produces inflorescences with a large number of flowers, yet matures relatively few fruits. We hypothesized that the number of seeds matured by B. alba macrophylla is maximized based on resource availability at each stage of development, but this optimal number is further compromised by extrinsic factors including pollen limitation and pre-dispersal seed predation by the weevils Apion rostrum and Tychius sordidus. To test this hypothesis, we conducted a field experiment at two sites: (i) the John English Prairie, located in Hudson, IL, and also (ii) the Sugar Grove Nature Center and Funks Grove, located in McLean County, IL. Whole plants were randomly assigned to one of two fertilizer treatments (no fertilizer, application of a granular fertilizer prior to first flowering and again post flowering) and one of two seed predation treatments (no insect barrier, application of Tanglefoot® insect barrier). Individual flowers were then assigned to one of two pollination treatments (open pollination, open pollination supplemented with hand-pollinated outcrossing) in an alternating manner.

At the John English Prairie, flowers that were supplemented with hand pollination initiated significantly more fruits per flower than flowers that were not supplemented with hand pollination, but neither nutrient treatment nor predation treatment affected fruit initiation at this site. There were no significant effects of nutrient treatment, pollen treatment or predation treatment on fruit maturation at the John English Prairie. No statistical analysis was conducted on the number of seeds matured per fruit at this site because all but three fruits experienced complete reproductive failure (=zero seeds) due to pre-dispersal seed predation by T. sordidus. Further, it can be concluded that pre-dispersal seed predation has an overwhelming and devastating effect on seed maturation in this population.

At Sugar Grove Nature Center and Funks Grove, flowers that were supplemented with hand pollination initiated significantly more fruits per flower than flowers that were not supplemented with hand pollination, but this did not translate to greater fruit and/or seed production. Nutrient treatment did not have significant effects on fruit initiation, fruit maturation or seed maturation at this site. Application of Tanglefoot® significantly increased the number of initiated fruits that reached maturity. Likewise, plants treated with Tanglefoot® matured significantly more seeds per fruit than control plants. Further, pre-dispersal seed predation by A. rostrum significantly reduced reproductive output of B. alba macrophylla by limiting the number of fruits and seeds matured, but neither resource availability nor pollen availability were significant factors during any stage of offspring development.

This study demonstrates that the number of seeds matured by B. alba macrophylla was severely reduced by pre-dispersal seed predation by weevil larvae, but neither resource availability nor pollen availability significantly affected the total number of seeds matured by this native legume. Pollen supplementation increased fruit initiation at both sites, but these populations are not pollen limited because this effect did not translate to greater fruit and/or seed production. Further, the results of this study indicate that B. alba macrophylla is neither nutrient limited nor pollen limited, but pre-dispersal seed predation by the weevils A. rostrum and T. sordidus significantly reduces reproductive output of B. alba macrophylla during fruit and seed maturation.

Access Type

Thesis-Open Access

DOI

http://doi.org/10.30707/ETD2015.Hembrough.A

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