All Mixed Up: How Do Hybrids Fit Into The Picture?

Hybrids are a symbol of complexity. For several decades these mixed species have challenged ecologists who study their role in ecological communities. Ecologists are still asking themselves the question: Are plant and animal hybrids viable contributors to ecosystems or just evolutionary blunders? The Special Feature in the March issue of Ecology focuses on hybridization and the current research encompassing this issue.

Indeed, researchers are intrigued by the unique genetic makeup of hybrid species that merit evolutionary distinction from their parental generations. Researchers at the University of Georgia, Department of Genetics conducted a study challenging the existing paradigms that minimize the importance of hybridization in ecological settings. Michael Arnold et al. in their paper "Natural Hybridization: How Low Can You Go and Still Be Important?" state that hybrids are in fact viable evolutionary components of communities, and in some cases, more fit than their parents. Because hybridization enhances genetic variation, Arnold states, "…hybrid genotypes can be more fit than parental genotypes in novel environments."

In contrast, Catherine Moulia from the Laboratoire de Parasiologie Compare in France presents a different scenario. Her research on hybrid mice reveals that they are more prone to parasite attack than their parental counterparts (Mus mus musculus and M. m. domesticus). Her review of the parasitism of animal hybrids not only suggests an evolutionary implication of parasites. It also stresses that this implication of parasites is very similar in animal and in plant hybrids.

According to some studies reviewed by Moulia, "By taking advantage of hybrid susceptibility, parasites could enhance their range and therefore abundance within an ecosystem."

Her paper, titled "Parasitism of Plant and Animal Hybrids: Are Facts and Fates the Same?" demonstrates how hybrids impact the population dynamics of parasite species and how these parasites in turn could impact the evolution of hybridizing species.

Robert Fritz from Vassar College investigates the environmental and genetic factors that lead to plant hybrid fitness.

"Genetic composition is an important factor in determining fitness, as hybrids have the capacity to develop either enhanced or decreased fitness," says Fritz. However, environmental conditions and interactions of hybrids in different environments are equally important.

Fritz proposes a new theoretical model that he calls the "ecological resistance gradient model." The model supports his studies of environmental effects on hybrid fitness.

Other advances, such as those in molecular technology, are allowing researchers to better classify and study hybrid lifestyles. The application of these techniques will enable them to monitor genetic stocks of rare species that are potentially threatened by hybrid invasion. This and other evolutionary concerns will be addressed as ecologists begin to better understand the roles hybrids play in ecosystems.

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