Science Topics: Forest Genetics
Conservation Biology using Molecular and Quantitative Genetic Techniques
The Wright lab is focused on a number of projects with an overall goal to gain understanding of major issues in conservation biology through the use of molecular and quantitative genetic techniques.
Habitat fragmentation is of major concern to conservation biology, and is considered one of the four threats by the Forest Service. To understand the long-term dynamics of human-caused habitat fragmentation, the Wright lab studies the conservation genetics of naturally fragmented populations using Serpentine soils in California as a model system. Serpentine soils are a particularly nasty place for plants to grow. They contain high levels of heavy metals, are low in nutrients and have a low Calcium: Magnesium (Ca:Mg) ratio, which leads to an odd ionic balance in the soils. Rather than being barren wastelands, many plants are adapted to grow on serpentine soils. Serpentine and non-serpentine soils are a naturally fragmented habitat, with serpentine and non-serpentine soils occurring in close proximity. The Wright lab focuses on species that grow both on and off of serpentine soils. Listed below are some of our current projects.
Adaptation to serpentine soils in Collinsia sparsiflora
We have worked extensively with a native annual plant, Collinsia sparsiflora, which grows on and off of serpentine soils. We have demonstrated local adaptation to serpentine soils in this species through 2 reciprocal transplant experiments using 3 serpentine and 3 non-serpentine sites. The results of these studies clearly show that plants grow best on their home soil type- in both directions (see graph below). That is, plants from serpentine habitats grow best in serpentine habitats, and plants from non-serpentine habitats do best in non-serpentine habitats. This result is fairly remarkable in that the distance between study sites is less that 1 km, with the closest two sites being 75 meters apart. Obviously, these results have practical implications for management of serpentine areas. For example, restoration efforts need to focus on collecting locally adapted seeds, as using non-serpentine seed-sources in serpentine areas may lead to a failure in restoration efforts.
This finding of local adaptation to serpentine and non-serpentine soils has lead to a series of other research directions in both the field and the lab. We are using microsatellite, AFLP and SNP markers to study population differentiation and gene flow between and within populations growing on and off of serpentine soils. These results are showing strong evidence for gene flow between the populations, with little differentiation between serpentine and non-serpentine populations. This result is very surprising, given the result of the reciprocal transplant experiment, illustrating the importance of combing field and molecular results.
In collaboration with K. Davies, J. McKay, A. McCall and J. Lau, we have conducted a larger field experiment, where we used a model created by K. Davies (University of Colorado) to predict the performance of C. sparsiflora in well-characterized habitats. We planted seeds into a range of habitats, and determined that the predictions of the model were accurate, and that we had successfully described the niche of C. sparsiflora. Moreover, further analysis revealed that the serpentine ecotype has a different niche than the non-serpentine ecotype, as we were not able to predict the performance of non-serpentine plants. Studies such as these are important for understanding the distribution of species, and will play a critical role in predicting and understanding the future impacts of global climate change.
Tolerance of serpentine soils in ponderosa pine
We are investigating a reciprocal transplant experiment established in 1970 by J. Jenkinson, a PSW scientist. Trees were planted reciprocally between serpentine and non-serpentine sites in El Dorado County. Our results show that even in a long-lived, wind-pollinated species, growing in very different habitats only 1.4 km apart, the results are similar to those obtained for C. sparsiflora- local adaptation to both serpentine and non-serpentine soil habitats. We have also collected allozyme data from the surviving trees, and have archived DNA from each surviving tree in the plantations. We are currently focused on the development of markers to use in this experiment. This study is potentially very useful as most P. ponderosa seed zones are based on climate and altitude data, and do not consider soil characteristics.