The Tiburon jewelflower (Streptanthus glandulosus niger, Brassicaceae) is a critically endangered annual plant that is restricted to serpentine soils. This plant was once more widespread across the Tiburon peninsula of Marin County, CA, but in the last century its geographic range has constricted, its populations have declined in size, gene flow between the only two remaining wild populations has been eliminated. Numerous collections of plants were made in the early 1900s, prior to massive housing development in the 1950s, and are housed in Herbaria. Additionally, seeds were collected in 1997 and 2002 by the US Fish and Wildlife Service as part of a seed banking effort. Using herbarium specimens and leaf tissue grown from the seeds collected by USFWS, we quantified the neutral marker diversity of historical populations to assess historic levels of diversity. Present-day populations show a near total absence of polymorphism at all marker loci and we wanted to know if this was a result of recent population decline combined with isolation, or if this lack of diversity was present historically.
Results/Conclusions
We used 14 polymorphic microsatellite loci to assess the genetic diversity in the present day populations and in the historic populations. Results thus far indicate that for 10 of the 14 loci the historic samples are monomorphic and identical to the present day populations. While this may reflect a worrisome lack of genetic diversity due to drift and/or inbreeding that restricts the populations’ evolutionary potential, it does not rule out the possibility of strong local adaptation, which we expect to see in this species. This is consistent with previous work that has shown that neutral marker diversity does not predict variation in quantitative traits involved in local adaptation. The fact that the lack of diversity found in the present day populations was also present in the historic samples, suggests that this may be the case. We are conducting experiments to test for local adaptation between sites and between habitat types within a single site, as well as measuring DNA sequence polymorphism. Whether this species is locally adapted and/or highly inbred is crucial information for developing an effective conservation plan.