An evaluation of the potential for hybridization between Castilleja levisecta and C. hispida
Catilleja levisecta (Golden paintbrush) is listed as Endangered Species by the US Fish and Wildlife Department. The Recovery Plan for C. levisecta identifies population reintroduction, development of propagation methods, and studies of the
Catilleja levisecta (Golden paintbrush) is listed as Endangered Species by the US Fish and Wildlife Department. The Recovery Plan for C. levisecta identifies population reintroduction, development of propagation methods, and studies of the pollination biology of the species as high priority actions to meet recovery objectives. A second paintbrush species, C. hispida (harsh paintbrush), also occurs in prairies along the Puget Trough and Willamette Valley. This is a larval host plant for Taylor’s checkerspot butterfly, another endangered species, and restoration with both paintbrush species is under consideration for improving butterfly habitat. There is concern, however, that plantings of the two species at the same site could lead to hybridization and alteration of the endangered C. levisecta genotype. In this report, we present the results of controlled crosses between these species. In addition, we examine the geographic distribution of diploid and polyploidy forms in these species, and discuss the implications of our findings.
Our studies found no evidence of post-pollination reproductive barriers to gene flow between C. hispida and C. levisecta from seed set to germination, and growth through flower production in F1 hybrids. Pollen viability, however, appears to be reduced in hybrid individuals compared to parental forms, which may weaken the ability of hybrids to interbreed or form successful back crosses to their parental species.
However, the risk to Castilleja levisecta of genetic swamping from C. hispida appears to be relatively low and manageable. The degree to which hybridization creates a conservation risk for C. levisecta depends on the fitness and fertility of crossed progeny, and the likelihood that inter-specific hybridizations will occur in the wild. We have shown that C. levisecta and C. hispida can produce viable progeny, but that these hybrids have reduced pollen viability. Further, because C. levisecta is diploid, the risk of gene flow between these two species would likely be lowest at sites of sympatry involving polyploid forms of C. hispida. Polyploid C. hispida may be identified based on flower morphology and other traits. Thus, it may be possible to optimize conservation efforts through site selection and reintroduction strategies that limit contact between C. levisecta and diploid C. hispida, and where some degree of proximity is unavoidable, make sure that the C. hispida on site is polyploid.