Artificial seed aging reveals the invisible fraction: Implications for evolution experiments using the resurrection approach
Non-random mortality is a key driver of evolution, but mortality that occurs early in life leaves adult traits of individuals that died unknown. This can lead to the invisible fraction problem, which causes difficulty in measuring selection and evolution in natural and experimental populations. Furthermore, seeds or other propagules that are stored intentionally or that persist in dormant states in nature can experience storage conditions that alter adult traits. Invisible fraction and storage condition effects can cause bias in evolutionary studies such as those using the resurrection approach of comparing ancestors and descendants in common environments. To investigate invisible fraction and storage condition effects, we subjected seeds of Brassica rapa Fast Plants to artificial aging under hot, humid conditions. We grew plants from artificially aged seeds alongside unaged control seeds for two generations and measured morphological and phenological traits on adult plants. We found that the plants from artificially aged seeds flowered later than those from unaged seeds in both the first and second generation, indicating storage condition and invisible fraction biases. However, the difference in flowering time was smaller in the second generation, indicating that the refresher generation decreased the storage condition effect. We also found that seeds that survived artificial aging were smaller than seeds that did not survive, indicating a potential physical basis for non-random mortality in storage. These results suggest that invisible fraction and storage condition effects can bias the results of resurrection experiments, and that the proper storage of seeds for use in resurrection experiments, as well as a refresher generation, are critical for valid results. The results also demonstrate that artificial aging can be used as a tool for studying mortality of propagules in nature, such as in soil seed banks, thus providing insight into evolutionary processes that would otherwise remain obscure.
KeywordsAdaptation Brassica rapa Climate change Contemporary evolution Missing data problem Phenology Seed storage
We thank the Fordham University Honors Program for providing support to S.D. for his research.
This work was supported by grants from the National Science Foundation (DEB-1142784 and IOS-1546218) to S.J.F., and an NSERC Discovery Grant to A.E.W.
Compliance with ethical standards
Conflict of interest
The authors declare no conflicts of interest.
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