Fitness effects of inbreeding and outbreeding on golden paintbrush (Castilleja levisecta): Implications for recovery and reintroduction
In this paper we examine the mating system of Castilleja levisecta and explore the effects of inbreeding and outbreeding on progeny fitness at multiple life history stages. The results have
In this paper we examine the mating system of Castilleja levisecta and explore the effects of inbreeding and outbreeding on progeny fitness at multiple life history stages. The results have direct bearing on reintroduction and recovery actions for the species because the risks associated with inbreeding and outbreeding need to be identified in order to assist with seed selection and genetic management of outplanting activities.
We performed controlled cross-pollination between individuals of differing known heritage. These crosses were of four major types: self-pollination, crosses between siblings, crosses between non-sibling plants from the same source population, and crosses between individuals from different populations. Seeds were collected from wild populations on the San Juan Islands of Washington state.
Castilleja levisecta appears to be almost completely self-incompatible, and seed-set appears to increase as the genetic relationship among mating individuals becomes more distant.
For example, inbreeding, including selfing and inbreeding among siblings (which, on average, share 50% of their alleles), reduced seed production and plant growth of the F1 generation significantly when compared to crosses between non-siblings from the same or different populations. Inbreeding depression was not detected in seed germination or flowering rate, but this may be because of insufficient statistical power due to the small sample sizes available for the inbred treatments. Outbreeding depression was not detected at any level in our study of seed set and F1 plant traits. Instead, we found significant increases in fitness of plants produced by crosses of individuals from different populations. Future investigation into Castilleja breeding is recommended to better understand the risks of both inbreeding and outbreeding depression.