Veronica R Morris

On average, ten new dams are being built every year in the US (Gleick 2000). Dams create lakes with artificially fluctuating water levels. Plants living in moisture zones around dammed lakes experience novel selective pressures and might have adapted to their local environments (Ali 2006).

One mechanism that can speed adaptation to new environments, especially when the new environment is close to the undisturbed area, is reproductive isolation. This limits gene flow between organisms in nearby habitats with differing selective pressures. Plants can develop reproductive barriers in less than 100 generations (Hendry et al 2007). Folsom Lake was created in 1955 by damming the American River. Water levels fluctuate as the lake fills with winter rains and spring snowmelt, and drops as water is used for hydroelectric power and irrigation during the dry season. Lake levels are usually highest in May and lowest in November (CA Dept of Water Res). Lupinus nanus, a native annual, grows in the inundation zone around the lake. Winter lake plants germinate in December, at the start of the rainy season, and are inundated by water as the lake rises in spring. Winter upland plants grow a short distance away, are under no pressure from fluctuating lake levels and flower a few weeks later. Summer plants, which are previously unreported in this species, germinate after the lake drops in June and flower in November.

The following two questions allow me to address my main interest, which is whether L. nanus is undergoing rapid adaptive evolution to anthropogenic lake level fluctuation at Folsom Lake. 1) What is the population structure and gene flow between the populations? 2) Are observed changes in flowering time influenced by genetics, the environment, or both?

Determining whether the populations are distinct and how much gene flow occurs between them will indicate the potential for local adaptation in these populations. If there is a high degree of gene flow and the populations are highly mixed, it is unlikely that any local adaptation has taken place. If there is little gene flow and the populations are separate, the populations may be adapting to the anthropogenic lake levels with flowering time providing the necessary reproductive isolation.

It appears that winter lake and winter upland populations are separate due to the distance between them and their differences in flowering time. However, we cannot tell whether winter lake and summer lake plants are two separate populations reproducing independently, or if seeds produced in one growing season germinate immediately for the next growing season. I have developed 23 microsatellite loci for L. nanus, and will use these to determine the population structure and gene flow between populations.

Germination time differences between populations could be under genetic control, suggesting reproductive isolation is occurring. However, germination differences might also be a result of environmental factors, and may not be reflecting evolution of different populations. It could also be a combination of environmental and genetic factors. To address this, I will perform a reciprocal transplant experiment growing plants from each population in the other two environments. If germination is under genetic control, the plants in the new environment will germinate at the same time as their counterparts from their original environment. However if we observe plants in the new environment germinating at the same time as the plants naturally found in that environment, observed germination differences are probably under environmental control.

Veronica R Morris

Local adaptation of Lupinus nanus to anthropogenically fluct

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