No evidence for early inbreeding depression in planted seedlings of Eucalyptus caesia, an anciently fragmented tree endemic on granite outcrops
Selection against inbred progeny is a well-documented phenomenon in natural and experimental populations of trees with mixed mating systems. This inbreeding depression can be expressed at multiple life stages, including early seedling development. Eucalyptus caesia, a long-lived tree that is endemic to granite outcrops in south-west Australia, has an anciently fragmented population structure, low levels of heterozygosity and limited genetic interconnection between stands and small population sizes. To test whether purging of genetic load may have facilitated the persistence of E. caesia on its granite rock habitat, we assessed the early growth and survivorship of seedlings in a common garden trial. A total of 120 seedlings from eight maternal trees were planted in four plots at the study site. Seedling growth rate and survivorship were assessed over 26 months against familial background and level of individual heterozygosity. We found no significant variation in the early growth or survivorship of selfed or outcrossed seedlings, or between seedlings with low or high levels of individual heterozygosity. These results support the hypothesis that purging of genetic load may have reduced the negative impacts of inbreeding in seedlings of E. caesia.
KeywordsHeterozygosity Inbreeding depression Ancient fragmentation Eucalyptus caesia
We thank Chris and Sheina Murphy for their kindness, support and permission to plant seedlings on their property. Sheina helped plant the seedlings, and Chris prepared a first-class field lunch. We also thank Stephen D. Hopper for discussions that improved the manuscript and supervision of NB during the project. This project was partly funded by an Australian Research Council Grant (DP140103357) to SDH, SLK and RD Phillips and by a Holsworth Wildlife Research Endowment—Equity Trustees Charitable Foundation and Wiley Fundamental Ecology Award from the Ecological Society of Australia to NB, who was supported by an Australian Government Research Training Program (RTP) Scholarship at the University of Western Australia.
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