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Ecological Genetics of White Campion (Silene latifolia ) Seed Banks: A Comparison of Light and Dark Germination Among Maternal Families

Kelly N. Kiefer, Katherine R. Okey, and Patricia A. Peroni

Department of Biology, Davidson College

ABSTRACT

Many plant species maintain a seed bank. These seed banks may function as reservoirs of genetic variation. Such genetic banks could influence responses to novel selective pressures and ameliorate the effects of inbreeding when population size becomes small. However, inadequate knowledge exists for most species on whether or not differential survival of genotypes in the seed bank actually occurs. Although a seed bank can serve as the genetic "memories" of populations, these "memories" may be selective.
White campion, a dioecious perennial herb, has served as the subject of a metapopulation investigation in SW VA for the past decade. Seed dispersal is extremely limited which means that the seed banks could stabilize the dynamics of population fragments by providing means of reestablishing a population and/or by minimizing the effects of inbreeding in a small population. Peroni and Armstrong (in prep) and Peroni, Boozer, Whitehead, Marshall, Kiefer, and Okey (in prep) documented the existence of white campion seed banks, but have little information on the ecological genetics of these pools.
We chose to manipulate one environmental factor experienced by buried seeds (darkness), and used maternal families of seeds to address the following questions.

1. Do maternal families vary in ability to germinate in the dark?
2. How does the relative performance of the maternal families in the dark compare with the performance in the light?

A significant interaction effect (family*treatment) was found for the Whittaker population. Viability differed significantly between the populations, but not among families within the populations. No correlation between mass and percent germination within the populations was found.

METHODS

Seeds were collected from 2 populations of Silene latifolia in Eggleston, VA, during summer of 1996.

5 families were selected from each population (10 families total).

Fifty seeds per family were assigned to light treatment and 50 seeds were assigned to dark treatment.

Each seed was placed in a cell well plate containing sand and dH20.

Cell well plates were placed in a light (14 hr light/ 10 hr dark) or dark incubator (22oC).

At day 11, germination for each seed was tallied.

Ungerminated seeds from light treatment were tested for viability.

Experiment was repeated switching incubators.

CONCLUSIONS

Maternal families of white campion display differing abilities to germinate in the dark.

Relative performance in the light cannot always predict a family's relative performance in the dark.

The differences in germination observed among maternal families could reflect heritable differences and/or maternal environment effects. However, since we found no correlation between mean family seed mass and percent germination in either treatment, we suspect that the differences among families are genetic in nature.

The white campion seed bank may contain only a selective subset of the genetic variation found in a given seed crop.

IDEAS FOR FUTURE INVESTIGATION

Conduct controlled crosses in the greenhouse to control for variable maternal environment effects, and repeat the investigation.

Compare seed survival of maternal families or different controlled crosses during burial in the field.

Determine if inbred and outcrossed seeds vary in their ability to survive burial (investigation underway).

Acknowledgements

Much gratitude to Katherine Okey and Wyatt Rivens for invaluable help and to Dr. Patricia Peroni for her expert advice throughout this project.