Local adaptation to serpentine and non-serpentine soils in Collinsia sparsiflora

Abstract

Question: Are populations of a native California annual plant locally adapted to serpentine and non-serpentine soils? Study species: Collinsia sparsiflora (Scrophulariaceae s.l ), which grows both on and off serpentine soils. Field sites: We studied six populations at the McLaughlin University of California Natural Reserve, in the North Coast Range of California. All sites were within 1 km of each other, but were notably variable for a number of soil characters, including concentrations of calcium and magnesium, key factors in serpentine soils. Methods: We conducted reciprocal transplant experiments in 2002 and 2003. The 2002 experiment involved four study populations, two serpentine and two non-serpentine. In 2003, an additional population on each soil type was included in a second reciprocal transplant study. Seeds generated in greenhouse crosses were planted reciprocally into each population, providing replication within the soil types. Results: Both experiments demonstrated the presence of significant reciprocal adaptation to soil type. We also observed variation in phenology between transplants on the two soil types. We conclude that plants from these six populations represent two distinct, soil-specific ecotypes, raising questions about the relative role of selection and gene flow in promoting genetic differentiation in these contrasting environments.