A loss of genetic diversity can be both a cause and a consequence of population decline. Genetic diversity is often associated with higher fitness and population persistence and is likely to be crucial in determining whether populations can adapt to a rapidly changing climate.
We quantified genetic diversity in largest remaining population of the Endangered serpentine endemic, Streptanthus glandulosus niger (Brassicaceae) using 10 polymorphic microsatellite markers. We then used herbarium specimens to assess past levels of diversity and compared this to the present-day population. The herbarium samples were collected between 1902 and 1954, prior to the largescale housing development that greatly reduced the size of S. g. niger populations.
Results/Conclusions
Allelic richness was low but not significantly different in both the historic and contemporary populations (historic AR=6.5 and contemporary AR=6.37). The effective number of alleles is significantly lower in the contemporary population (AE=3.3) compared to the historic population (AE=2.6). Both expected and observed heterozygosity were higher historically (HE=6.5; HO=5.86) than they are today (HE=5.6; HO=4.8). Further, the degree of inbreeding was moderate historically (FIS=0.105) but more pronounced in the contemporary population (FIS=0.141). Finally, weak to moderate genetic divergence between the historic and contemporary populations is evident from the FST value (0.066).
These observed changes in the contemporary population may reflect a worrisome lack of genetic diversity due to drift and/or inbreeding which may restrict the populations’ evolutionary potential. We are conducting experiments to test for inbreeding depression and whether the population retains the capacity for adaptive evolution despite low diversity in neutral markers. Both pieces of information are crucial for developing an effective conservation plan as well as understanding the role of genetic diversity in population persistence.