Testing for evolutionary change in restoration: A genomic comparison between ex situ, native and commercial seed sources of Helianthus maximiliani

Authors: BRAASCH, JOSEPH - North Dakota State University; DI SANTO, LIONEL - North Dakota State University; TARBLE, ZACH - North Dakota State University; Prasifka, Jarrad; HAMILTON, JILL - North Dakota State University

Submitted to: bioRxiv
Publication Type: Pre-print Publication
Publication Acceptance Date: 6/28/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary: Both common and rare plant species are key components of plantings for habitat restoration. Success of restoration plantings can depend on whether the seeds used are adapted to the location where they are planted, but also whether they have enough genetic diversity to survive in a natural, unpredictable environment. Because restoration plantings require large amounts of seed, commercial sources of seed are often needed. In this study, a perennial sunflower commonly used in pollinator plantings in the United States, Maximilian sunflower, was used to compare the genetic diversity of seeds from four different types of sources (existing wild populations, stored seed from historic collections in wild populations, commercial seed suppliers, and seed bred for a specific purpose other than conservation). Compared to existing wild populations, commercial seed had high levels of genetic diversity, but clearly differed from wild populations. It also appeared that stored seed from historic collections in the wild might not have captured all of the diversity in those populations because of how the seeds were collected. These results are important to various groups involved in plantings for habitat restoration, including landowners, conservation managers, commercial seed producers, and researchers, and suggest that more communication between these groups could help improve the success of future restoration plantings.

Technical Abstract: Globally imperiled ecosystems often depend upon collection, propagation, and storage of seed material for use in restoration. However, during the restoration process demographic changes, population bottlenecks, and selection can alter the genetic composition of seed material, with potential impacts for restoration success. The evolutionary outcomes associated with these processes have been demonstrated using theoretical and experimental frameworks, but no studies to date have examined the impact these processes have had on the seed material maintained for conservation and restoration. In this study, we compare genomic variation across seed sources used in conservation and restoration for the perennial prairie plant Helianthus maximiliani, a key component of restorations across North American grasslands. We compare individuals sourced from contemporary wild populations, ex situ conservation collections, commercially produced restoration material, and two populations selected for agronomic traits. Overall, we observed that ex situ and contemporary wild populations exhibited a similar genomic composition, while four of five commercial populations and selected lines were differentiated from each other and other seed source populations. Genomic differences across seed sources could not be explained solely by isolation by distance nor directional selection. We did find evidence of sampling effects for ex situ collections, which exhibited significantly increased coancestry relative to commercial populations, suggesting increased relatedness. Interestingly, commercially sourced seed appeared to maintain an increased number of rare alleles relative to ex situ and wild contemporary seed sources. However, while commercial seed populations were not genetically depauperate, the genomic distance between wild and commercially produced seed suggests differentiation in the genomic composition could impact restoration success. Our results point towards the importance of genetic monitoring of species used for conservation and restoration as they are expected to be influenced by the evolutionary processes that contribute to divergence during the restoration process.