Life cycle expression of inbreeding depression in Eucalyptus regnans and inter-generational stability of its mixed mating system

Author:

Griffin A Rod12,Potts Brad M13,Vaillancourt René E13,Bell J Charles4

Affiliation:

1. School of Natural Sciences, University of Tasmania, Tasmania, Australia

2. GTI Pty. Ltd, Sandy Bay, Tasmania, Australia

3. ARC Training Centre for Forest Value, Australia

4. Army Ave, Tanilba Bay, NSW, Australia

Abstract

Abstract Background and Aims Many plants exhibit a mixed mating system. Published models suggest that this might be an evolutionarily stable rather than a transitional state despite the presence of inbreeding depression, but there is little empirical evidence. Through field experimentation, we studied the role of inbreeding depression in eliminating inbred progeny from the reproductive cohort of the forest tree Eucalyptus regnans, and demonstrate a stable mixed primary mating system over two successive generations. Methods Two field experiments were conducted using seed from natural populations. We sowed open-pollinated seeds to simulate a natural regeneration event and determined isozyme genotypes of dominant and suppressed individuals over 10 years. We also planted a mixture of open-pollinated, outcross and selfed families with common maternal parentage; monitored survival of cross types over 29 years; and determined the percentage of outcrosses in open-pollinated seed from a sample of reproductively mature trees using microsatellite analysis. Key Results Both experiments demonstrated progressive competitive elimination of inbred plants. By 29 years, the reproductive cohort in the planted experiment consisted only of outcrosses which produced seed which averaged 66 % outcrosses, similar to the estimate for the parental natural population (74 %). Conclusions Selective elimination of inbred genotypes during the intense intra-specific competition characteristic of the pre-reproductive phase of the life cycle of E. regnans results in a fully outcrossed reproductive population, in which self-fertility is comparable with that of its parental generation. The mixed mating system may be viewed as an unavoidable consequence of the species’ reproductive ecology, which includes the demonstrated effects of inbreeding depression, rather than a strategy which is actively favoured by natural selection.

Funder

CSIRO Divison of Forestry and Forest Products

Publisher

Oxford University Press (OUP)

Subject

Plant Science

Reference68 articles.

1. Inbreeding depression in benign and stressful environments;Armbruster;Heredity,2005

2. Development of even-aged stands of Eucalyptus regnans F Muell in Central Victoria;Ashton;Australian Journal of Botany,,1976

3. Fire in tall open forests (wet sclerophyll forests).;Ashton,1981

4. Regeneration in a pole-stage forest of Eucalyptus regnans subjected to different fire intensities in 1982;Ashton;Australian Journal of Botany,1996

5. Selection in natural populations;Barber;Heredity,1965

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