Effects of genetic and geographic distance on mating success in the rare sandhill endemic, Erysimum teretifolium (Brassicaceae)

Background/Question/Methods

The Zayante Sandhills of Santa Cruz County, California, are home to a rich diversity of native and endemic plants and animals adapted to their unique soils. One sand parkland endemic, Erysimum teretifolium (Ben Lomond wallflower), is an endangered biennial, herbaceous flower in the Brassicaceae. Naturally isolated by patchy mesic forests, some adaptation of local populations is expected, which could lead to outbreeding depression. In contrast, subpopulations that have been artificially isolated through fragmentation and pollination loss may suffer from inbreeding depression. The objective of this study was to assess whether remnant E. teretifolium individuals have higher or lower fitness when they cross with individuals from more distant remnant populations than they do when crossed within a population or even when they are self-pollinated. In 2010, a captive breeding colony was established from seeds collected from 4 locations across the Zayante Sandhills. Pollination combinations were selected to compare self pollinations with differing degrees of outcrosses. Viable seed production of crosses was analyzed based on geographical distance, and the results were compared with analyses based on genetic distance using microsatellite genotypes.

Results/Conclusions

Average number of viable seeds produced was significantly greater for outcrossed individuals as compared with self-pollinated individuals (P < 0.001), as measured by geographic and genetic distance, these findings illuminate the effects of geography and genetic diversity on reproductive fitness. Self-incompatibility further suggests that insect pollinators may be important for the reproductive success of E. teretifolium, and understanding the composition of insect pollinators and their habitat requirements may be crucial to conserving E. teretifolium.