Inbreeding depression and differential maladaptation shape the fitness trajectory of two co-occurring Eucalyptus species
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The fitness trajectory of long-lived forest species with mixed mating systems is shaped by a dynamic interplay between endogenous (inbreeding depression) and exogenous (environmental maladaptation) factors. Using two eucalypt species, we show that the timing and translation of inbreeding depression from growth to survival through size-dependent mortality may vary between species and may intensify under climate stress.
Inbreeding is an important issue in evolutionary biology and breeding, as it can reduce genetic diversity and fitness and ultimately limit the adaptive response of populations to environmental stress. This is particularly relevant to forest tree species, such as eucalypts, which have a mixed mating system and long-generation intervals.
Examine the role of inbreeding depression on the fitness trajectory of two eucalypt species, Eucalyptus globulus and E. ovata.
Survival, growth, and reproduction of controlled-crossed self and outcross, as well as open-pollinated progeny of each species grown in a common garden field trial were assessed over a 28-year period and analysed using mixed effect models.
Inbreeding depression resulted in the purging of inbred progeny through size-dependent mortality with the most death of inbreds occurring between 4 and 13 years. After this period, differential maladaptation of the species was the dominant cause of mortality, associated with a period of drought and high temperatures, and it was evident first in the selfed populations.
This study demonstrates the dynamic nature of the selective process in purging inbred progeny from a population, with inbreeding depression the dominant factor early in stand development, leading to older stands being dominated by outcrosses.
KeywordsEucalyptus globulus Eucalyptus ovata Mixed mating Drought Heat stress Selection
The authors thank the North Forest Products (and subsequently Gunns Limited and Forico Pty Limited) for the provision and maintenance of the trial site.
Contribution of the co-authors
Conceptualization: BMP, HN, and PAH; methodology and data analysis: HN, PAH, and BMP; data collection and curation: PT and HN; writing, reviewing, and editing: HN, PAH, REV, and BMP.
The trial was established under an Australian Research Council (ARC) National Research Fellowship awarded to BMP. The final measurements and collation of data were undertaken as part of an ARC Linkage Grant LP140100506, which is obtained in partnership with the Southern Tree Breeding Association. HN acknowledges receipt of a Tasmania Graduate Research Scholarship.
Compliance with ethical standards
Statement on data availability
Conflicts of interest
The authors declare that they have no conflict of interest.
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