Temporal changes in genetic diversity reveal small-scale invasion dynamics of the Eastern Redcedar (Juniperus virginiana L. var. virginiana) in the Lakeside Daisy State Nature Preserve in Ohio

Abstract

Eastern redcedar (Juniperus virginiana L. var. virginiana) is a native species currently invading open areas and grasslands outside of its original range in the United States. We studied the eastern redcedar’s (ERC) invasion patterns in the Lakeside Daisy State Nature Preserve (LDSNP), a short grass prairie located on the Marblehead Peninsula in Ohio, examining the changes in the genetic diversity and structure of the encroaching population. We investigated the relative importance of long-distance dispersal vs. diffusion in the invasion of this short grass prairie by ERC. We use eight microsatellite marker loci to infer gene flow from external sources vs. within-population recruitment. We found that the older trees in this preserve were less than fifty-years-old, indicating that the population was established between 1970 and 1980. When we grouped trees into five age categories of 10-year increments, we found that the allelic diversity, as indicated by the average number of alleles per locus, increased as the age of the trees decreased. We also found that not all loci were in Hardy-Weinberg Equilibrium, probably due to the arrival of new variants in the preserve. Moreover, heterozygosity remained high, with an excess of heterozygotes in all age groups (F = -0.163 ± 0.046). Principal Coordinate Analysis showed two distinct groups of trees in the LDSNP. Analysis of the cryptic population structure of the ERC trees using STRUCTURE revealed four ancestral clusters in the ERC population. All ancestral clusters are present in all age groups, suggesting that all trees sampled are derived from an admixed population. Furthermore, the high observed heterozygosity and lack of inbreeding in this dioecious species maintained all ancestral clusters over time. Overall, our findings indicate that ERC encroachment of the LDSNP results from multiple and reiterated gene flow events from the edge of the range through animal-mediated seed dispersal.