THE ROLE OF GENES OF LARGE EFFECT ON INBREEDING DEPRESSION IN MIMULUS GUTTATUS
- 1 December 1999
- Vol. 53 (6), 1678-1691
- https://doi.org/10.1111/j.1558-5646.1999.tb04553.x
Abstract
Severe inbreeding depression is routinely observed in outcrossing species. If inbreeding load is due largely to deleterious alleles of large effect, such as recessive lethals or steriles, then most of it is expected to be purged during brief periods of inbreeding. In contrast, if inbreeding depression is due to the cumulative effects of many deleterious alleles of small effect, then it will be maintained in the face of periodic inbreeding. Whether or not inbreeding depression can be purged with inbreeding in the short term has important implications for the evolution of mating systems and the probability that a small population will go extinct. In this paper I evaluate the extent to which the tremendous inbreeding load in a primarily outcrossing population of the wildflower, Mimulus guttatus, is due to alleles of large effect. To do this, I first constructed a large outbred "ancestral" population by randomly mating plants collected as seeds from a natural population. From this population I formed 1200 lines that were maintained by self-fertilization and single seedling descent: after five generations of selling, 335 lines had survived the inbreeding process. Selection during the line formation is expected to have largely purged alleles of large effect from the collection of highly inbred lines. Because alleles with minor effects on fitness should have been effectively neutral, the inbreeding depression due to this class of genes should have been unchanged. The inbred lines were intercrossed to form a large, outcrossed "purged" population. Finally, I estimated the fitness of outbred and selfed progeny from the ancestral and purged populations to determine the contribution of major deleterious alleles on inbreeding depression. I found that although the average fitness of the outcrossed progeny nearly doubled following purging, the limited decline in inbreeding depression and limited increase in inbred fitness indicates that alleles of large effect are not the principle cause of inbreeding depression in this population. In aggregate, the data suggest that lethals and steriles make a minority contribution to inbreeding depression and that the increased outbred fitness is due primarily to adaptation to greenhouse conditions.Keywords
Funding Information
- National Science Foundation
This publication has 62 references indexed in Scilit:
- Correlations among traits associated with herbivore resistance and pollination: implications for pollination and nectar robbing in a distylous plantAmerican Journal of Botany, 2006
- Measures of Phenotypic Selection Are Biased by Partial InbreedingEvolution, 1996
- Mutation Accumulation and the Extinction of Small PopulationsThe American Naturalist, 1995
- Purging inbreeding depression and the probability of extinction: full-sib matingHeredity, 1994
- Effects of Different Levels of Inbreeding on Fitness Components in Mimulus guttatusEvolution, 1993
- Genetic analysis of inbreeding depression caused by chlorophyll-deficient lethals in Mimulus guttatusHeredity, 1992
- Fitness Rebound in Serially Bottlenecked Populations of the House FlyThe American Naturalist, 1990
- Mutation-selection balance and the evolutionary advantage of sex and recombinationGenetics Research, 1990
- Inbreeding Depression Doesn't Matter: The Genetic Basis of Mating-System EvolutionEvolution, 1988
- The effects of inbreeding on rate of development and on fertility inDrosophila SubobscuraJournal of Genetics, 1955