Demographic History, Not Mating System, Explains Signatures of Inbreeding and Inbreeding Depression in a Large Outbred Population

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.

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THE ROLE OF INBREEDING DEPRESSION AND MATING SYSTEM IN THE EVOLUTION OF HETEROSTYLY

Evolution ◽

10.1111/evo.12123 ◽

2013 ◽

Vol 67 (8) ◽

pp. 2309-2322 ◽

Cited By ~ 13

Author(s):

Jennifer J. Weber ◽

Stephen G. Weller ◽

Ann K. Sakai ◽

Olga V. Tsyusko ◽

Travis C. Glenn ◽

...

Keyword(s):

Mating System ◽

Inbreeding Depression

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Mating system of Calluna vulgaris: self-sterility and outcrossing estimations

Canadian Journal of Botany ◽

10.1139/b97-148 ◽

1998 ◽

Vol 76 (1) ◽

pp. 37-42 ◽

Cited By ~ 3

Author(s):

Grégory Mahy ◽

Anne-Laure Jacquemart

Keyword(s):

Mating System ◽

Inbreeding Depression ◽

Calluna Vulgaris ◽

Pollen Tubes ◽

Outcrossing Rate ◽

Evolutionary Significance ◽

Mixed Mating ◽

Mixed Mating System ◽

Cross Pollination ◽

Mating System Evolution

The evolutionary significance of a mixed mating system is currently under debate. Calluna vulgaris (L). Hull, a widespread European shrub, is likely to undergo mixed mating because of geitonogamy. Mating system was investigated in three populations of C. vulgaris by means of greenhouse controlled crosses, pollen tube observations, and outcrossing rate estimations from allozyme markers. The species is highly self-sterile, most probably as a result of early inbreeding depression. Mean fruit set and mean seed number per fruit following hand self-pollination were 48 and 13%, respectively, of those following cross-pollination. Pollen tubes produced by self pollen penetrated the ovary with the same success as those from cross-pollination. Multilocus estimates of the outcrossing rates ranged from 0.71 to 0.90, and two estimates were significantly different from 1.00. Calluna vulgaris could thus be classified as being mixed mating with predominant allogamy. Single-locus estimates did not differ significantly from multilocus estimates suggesting that biparental inbreeding did not contribute to the apparent selfing rate. The maintenance of high early inbreeding depression despite an intermediate level of selfing is discussed with respect to recent theories on mating system evolution. Key words: Calluna vulgaris, mating system, self-sterility, pollen tubes, outcrossing rate, inbreeding depression.

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