Despite the fact that outbreeding has often been suggested as a method for combating the negative fitness effects of inbreeding, the consequences of outbreeding remain unclear. Outbreeding may have either positive effects through heterosis or negative effects, as in the case of outbreeding depression. Using a combination of genetic data, field surveys and a common-garden, mesocosm experiment, we evaluated the effects of inbreeding and outbreeding on population-level fitness correlates in the wood frog, Rana sylvatica, a species that shows evidence of adaptation to local environmental conditions at a relatively small spatial scale.
Results/Conclusions
Populations with low levels of inbreeding had larger population sizes and increased survivorship in the common garden experiment than more inbred and more outbred populations and had a trend for increased survivorship in the field relative to more outbred populations. While the results corroborate the long-held view that high levels of inbreeding negatively impact populations, the results also suggest that natural levels of outbreeding can be an important concern. In fact, slight levels of inbreeding can actually be beneficial. The results provide a warning for conservation programs that utilize outbreeding for controlling inbreeding depression, since even natural levels of outbreeding can have detrimental effects on populations.