This document discusses the endangered plant Castilleja mollis which grows in only two locations on Santa Rosa Island. It is concerned that the population may be declining due to hybridization with the widespread native Castilleja affinis. Studies from 1995-2007 found the C. mollis population declining as temperatures increased. If hybrids with C. affinis are more heat tolerant, they may replace C. mollis over time. The document summarizes genetic and mapping research on the two populations since the 1990s which shows differing trends between the sites and evidence of hybridization. Ongoing work aims to understand the genetics and impacts of hybridization on C. mollis survival in light of climate change challenges.

1. Is hybridization between an endemic and a widespread native plant cause for conservation concern?
Soft-leaved island paintbrush (Castilleja mollis) on Santa Rosa Island
Kathryn McEachern– U.S. Geological Survey, Ventura, California, USA
Diane Thomson, Bryan Thines, Elizabeth Medford - Keck Science Dept., Claremont Colleges, Claremont, California, USA
Is this a Problem?
The Thirteen Plant Taxa from the Northern Channel Islands Recovery Plan (U.S. Fish
& Wildlife Service, 2000) states that one of the recovery criteria for endangered
species is to preserve genetic diversity. There is concern about possible hybrid
contamination with Castilleja affinis at Carrington Point. Demographic studies 1995-
2007 indicated that C. mollis populations are declining as air temperatures increase,
driven by mortality in small plants. If C. affinis ssp. affinis and the hybrids are more
heat tolerant than C. mollis will we see more of them within the C. mollis population
in the future? Is this a conservation problem, or is this natural selection that
ultimately saves the C. mollis lineage?
Soft-leaved island paintbrush
(Castilleja mollis)
Castilleja mollis is an endangered plant
that grows only in two locations on Santa
Rosa Island. In both places it inhabits a
thin band at the coastal margin right at
the bluff edge.
Hybrids (Castilleja mollis x Castilleja affinis ssp. affinis)
Plants appearing to be hybrids of Castilleja mollis x Castilleja affinis ssp. affinis with a
range of characteristics of both occur throughout the area occupied by C. mollis.
Habitats
C. mollis grows on terraces at Jaw Gulch and bluffs at Carrington Point, sites about
14 kilometers apart on the north side of Santa Rosa Island. Island vegetation was
damaged severely by livestock introduced in the mid-1800s. Elimination of cattle in
1998, and deer and elk in 2011, have resulted in improved habitat conditions.
Carrington PointJaw Gulch
FIELD MAPPINGTHE SPECIES AND THEIR HYBRIDS GENETIC RESEARCH
1990s vs 2012 Expansion or contraction?
We mapped Castilleja mollis in 1994 and 1999, and again 2010 - 2012, to determine
whether C. mollis has expanded in response to non-native ungulate removal.
Mapping was much more detailed in 2010-2012, using more modern techniques, so
comparisons are approximate. The maps showed different trends at the two sites.
Acknowledgements
We want to thank many folks who have helped map and monitor
Castilleja mollis in the field over the years, including Katie Chess,
Kathy Rindlaub, Darla Rugel, Dirk Rodriguez, Clark Cowan, Emily
Schultz, Lauren Cole, Ruth Oliver, Ken Niessen and many seasonal
technicians. Ken Niessen produced the GIS graphics for this poster.
This work has been funded by USGS and NPS grants and base funds,
and NSF grants DEB0236070 and 0950106.
CNPS 16 Januaray 2015
Coastal Indian paintbrush
(Castilleja affinis ssp. affinis)
Castilleja affinis ssp. affinis is a native
plant widespread in California, also
found on other Channel Islands. It
grows in close proximity to C. mollis in
both habitats, spreading upslope and
inland from the coastal margin
inhabited by C. mollis.
2003 Random amplification of polymorphic DNA (RAPD)
In 2003, we conducted a pilot study (Bushakra and McEachern 2003) to investigate
Castilleja mollis genetic diversity within and between the two habitats, and to see if
there was genetic evidence of hybridization with C. affinis ssp. affinis.
(Bushakra, Jill M. and Kathryn McEachern. 2003. Genetic Assessment for Castilleja mollis. Page 14 in D. Garcelon and C. Schwemm,
eds. 6th California Islands Symposium Presentation Abstracts. The Institute for Wildlife Studies, Arcata, California and National Park
Service, Channel Islands National Park, Ventura, California.)
2012 Distribution of hybrids
During the 1990s mapping we noticed that hybrid plants appeared among the C.
mollis population, but they were not common.
In 2010 - 2012, we mapped locations of C. mollis, C. affinis ssp. affinis, and their
hybrids. Again, we see differences between the two sites.
Genetic studies 2015
In 2012 we collected tissue samples from C. mollis, C. affinis ssp. affinis and
apparent hybrids in and around the C. mollis population at both sites. Subsequent
lab work identified a genetic marker that shows promise for distinguishing pure C.
mollis and C. affinis ssp. affinis from each other and hybrids.
In 2013-14, we collected tissue samples from tagged individuals in demography
monitoring plots. Future work will first focus on genotyping as many of these
individuals as possible. This will allow us to confirm that patterns observed based
on phenotype in the field are supported by genetic data. Then we will be able to link
genetic type with survivorship and growth data, to test whether hybrids perform
differently than pure C. mollis.
Conclusion
Climate change poses some new and interesting challenges for conservation
genetics. Small population size and isolation can generate endemic plant diversity,
but also may be barriers to adaptation under rapidly changing environmental
conditions. Hybridization with common relatives may be an avenue for rare
endemics to persist, but in and of itself might be considered a form of extinction.
This system provides an excellent opportunity to explore these issues.
At Jaw Gulch C. mollis has disappeared
from the most inland, upslope places
inhabited in the 1990s.
At Carrington Point, C. mollis has
contracted and expanded laterally along
the coastal margin, but has not lost or
gained ground upslope and inland.
At Jaw Gulch, most of the area is
occupied by “pure” C. mollis, but
several C. affinis ssp. affinis individuals
and hybrids are mixed in at the western
edge of the population.
At Carrington Point, most of the C.
mollis are growing intermixed with
hybrids and also some C. affinis ssp.
affinis.
Cleaved Amplified Polymorphic Sequence (CAPS)
markers differentiate between C. mollis and C. affinis
ssp. affinis. Agarose gel electrophoresis of amplified
5.8S rDNA sequences cut or uncut with restriction
enzyme BsrBI. “+RE” identifies samples cut with BsrBI
restriction enzyme.
Preliminary results based on RAPD
analysis suggested that the diversity
between sites is the same as the
diversity within a single site. This could
indicate the fragmentation of a larger
continuous population since the
introduction of grazers to the island. C.
mollis was distinguishable from C. affinis
ssp. affinis with the RAPD primers. There
was enough data to suggest that
introgression with C. affinis ssp. affinis is
occurring.