Faculty Research: 6) Ecological adaptation, gene flow, and the potential for hybrid breakdown in restoration projects.

One of the abiding questions in population biology concerns the degree to which novel genes spread in natural populations and how this phenomenon may affect evolutionary and ecological processes. Although a number of studies have been conducted to detect changes in allele frequencies within and between populations, there is a dearth of experimental data documenting the effect of large scale introduction of alien genotypes on resident populations. In the case of plant species, this phenomenon is becoming more common through the accidental spread of seeds and the many attempts to reconstruct native vegetation through restoration activities.

While the introduction of new genotypes may provide benefits to genetically depauperate populations or to those with high genetic load, there are also serious potential risks. For example, hybridization between genotypes representing two populations, each of which is locally adapted to distinct ecological conditions, can result in "hybrid breakdown" if subsequent recombination events break apart coadapted gene complexes.

The extensive grasslands of California provide an excellent model system in which to examine the effects of alien genotype introduction because they have become the focus of many recent restoration projects. The native perennial grass species thought to have dominated these grasslands in the past have been replaced by annual grass species introduced from the Old World. Consequently, there is great interest in increasing the relative abundances of perennial grasses. Over the last ten years, there has been a great deal of financial investment in the study of the factors (e.g., cattle grazing, herbicides, fire, nutrients) that may promote native perennial grass performance. More recently, the restoration of these communities by sowing seeds derived from other locations has been considered to be a desirable alternative to the spread of annual exotics.

Restoration efforts, however, generally rely on the introduction of large quantities of commercially available seeds. The source of these seeds may be unknown or from distant locations, yielding uncertain genetic and ecological effects on local populations. Moreover, hybridization (and hybrid breakdown) between introduced and local populations could have severe consequences where populations exhibit significant local adaptation.

Recent events at Sedgwick Ranch Natural Reserve, a research preserve near the University of California - Santa Barbara, provide a unique opportunity to investigate the influence of alien genotypes on local plant populations. Two large-scale introductions (one representing the introduction of genotypes from Vandenberg Air Force Base), conducted as part of research projects at Sedgwick, have occurred in the last two years. In addition to these two projects, a number of researchers has expressed interest in conducting experiments involving common gardens or introductions at Sedgwick. This is a common situation at biological stations where manipulative experiments are designed to investigate a variety of ecological questions.

My current research effort and collaboration with Dr. Jim Reichman (UCSB)will address several question to which the answers will suggest guidelines for the management of natural reserves (e.g., should the introduction of alien grassland genotypes be permitted?) both in California and elsewhere.

• Is there gene flow between introduced and natural (locally endemic) grassland populations? Here, we are focussing on three California native perennial grass species (Bromus carinatus, Nasella pulchra, and Elymus glaucus) growing both as Sedgwick resident populations and as "alien" genotypes growing in two experiments located at Sedgwick.
• Does the introduction of alien genotypes significantly disrupt the genetic composition of native populations such that evidence of hybrid breakdown in detectable? We aim to use a combination of molecular markers and gene flow models to detect evidence of hybridization between resident and introduced genotypes. Moreover, we will produce F1 and F2 hybrids to transplant into the field to determine whether there is evidence for hybrid breakdown.
• Is there evidence of ecotypic differentiation between populations "endemic" to Sedgwick and those that have been introduced? Reciprocal transplants between genotypes native Sedgwick and those from Vandenberg Air Force Base will be conducted to seek evidence for adaptive differentiation between these genotypes.
• Is there evidence of molecular genetic differentiation (presumably due to drift) between introduced and local populations?
• Are the F1 offspring between local and introduced populations viable? Is there evidence of "hybrid vigor"?
• Does the F2 generation resulting from subsequent backcrossing or crossing between F1's show evidence of hybrid breakdown?

Should we observe strong evidence of hybrid breakdown, not only will this be of interest and concern to current researchers and managers at Sedgwick, but the implications for grassland restoration efforts elsewhere may also be serious.

Current Research Projects

1. Testing the assumptions of sex allocation theory: quantitative genetic variation and covariation among floral traits in the Sand-Spurrey, Spergularia marina (Caryophyllaceae)
2. The evolution of gender-related traits in species with different mating systems: a quantitative genetic comparison of selfing and outcrossing species of Clarkia (farewell-to-spring: Onagraceae)
3. The Evolutionary Significance of Variation in Traits Subject to Ontogenetic Change and Maternal Environmental Effects
4. Genetic and environmental influences on life history, floral traits, and sex allocation in Raphanus sativus (Brassicaceae; wild radish): the stability of genetic parameters across environments.
5. The Detection of the Long-term Outcome of Natural Selection and the Ecological Sorting of Species Among Habitats: Comparative Studies of Plant Reproductive Characters
6. Ecological adaptation, gene flow, and the potential for hybrid breakdown in restoration projects.

Susan Mazer | Research | Publications | Curriculum Vitae

<< Return to Faculty Page