Variation among populations of the endangered plant, Astragalus brauntonii

The federally endangered species, Astragalus brauntonii (Braunton's milkvetch), is a rare short-lived perennial plant found in isolated populations in coastal sage scrub of Southern California's Los Angeles, Ventura, and Orange Counties. Populations are located along the coast and as far inland as Monrovia. Gene flow among populations is severely limited by urban development and large distances between some populations. Though one coastal population had been studied previously, potential differences between inland and coastal populations were unknown. Demographic, vegetative and reproductive attributes were measured in one coastal and five inland populations in 2008 and 2009. The results indicated that there were differences in growth and reproduction among populations. Phenotypic plasticity and/or genetic differences among populations were the likely reasons for this. Therefore, seeds from 4 A. brauntonii populations were germinated and the plants were subjected to common garden and reciprocal transplant experiments. There were significant differences in morphology and survivorship among gardens and populations. More plants survived when grown in the coastal garden than the inland garden. Differences in plant fitness among gardens and transplantation sites pointed to differentiation among populations. Low germination rates, poor seedling survival, and the apparent canalization of some traits suggested that some populations have lower genetic diversity than other populations, though the mechanism for this was unclear. These results indicated that coastal populations may need to be managed differently from those occurring further inland and that some populations may benefit from genetic supplementation.