Heterosis in crosses between remnant populations of a rare prairie forb: implications for restoration genetics
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Background and Aims
A major goal in both basic and applied evolutionary genetics is understanding the role of drift in shaping genetic variation with fitness consequences. For organisms amenable to controlled crosses, the increased fitness of progeny from between-relative to within-population crosses (heterosis) provides a useful tool to infer historical fixation of partly recessive deleterious alleles by drift and/or bottlenecks. Additionally, heterosis may also provide a unique benefit in regional admixture provenancing for restorations of rare plant species, but empirical data to directly test this idea is lacking.
Methods
We quantified heterosis in crosses between small remnant populations of a rare prairie forb ( Silene regia Sims). We measured early fitness components (seed number per fruit, germination, and juvenile survival) in a controlled environment. Adult fitness components (survival and reproduction) were quantified over two flowering seasons in two different environments, a field common garden simulating the initial stages of a restoration, and a greenhouse. To our knowledge, our study is the first to estimate cumulative fitness for a rare species in conditions of a newly established restoration in the field. Additionally, we provide a unique comparison of heterosis estimated under controlled vs. field conditions.
Key Results
The consequences of between-population crosses for cumulative fitness in the field were strongly positive in two of the populations (132-292% heterosis) and neutral in a third. Heterosis was generally stronger when measured under field conditions and was more likely to be detected for adult fitness components.
Conclusions
Regional admixture provenancing in restorations should be beneficial for this species. We advocate for more research on heterosis in rare species, particularly in restorations. Such restorations can be opportunities for experimental genetics in addition to reestablishing important ecosystem services.
