Ignored pattern in studies of local adaptations: When the grass is greener on the allopatric site

Recently, the focus within microevolutionary studies has been on the ecological divergence of populations. One subset of this research field includes studies on local adaptation. This approach is useful for studying whether or not adaptive spatial variation takes place in a metapopulation context. There is growing body of research studying local adaptations of populations, and much of this has used a formal test for assessing the existence of local adaptation. According to Kawecki and Ebert (2004), the “Local vs. foreign” criterion is fulfilled if the local population has higher fitness than other populations in its own locality and “Home vs. away” is fulfilled if a population has higher fitness in the sympatric than allopatric environment. Interestingly, interpretation of results not fulfilling these criteria has received scant attention even though the question of how to measure local adaptation is vital for the study field. At present, there is an extensive volume of published results showing other kinds of patterns than those proposed by the “Local vs . foreign” or “Home vs . away” criteria. Here, we highlight one of these alternative patterns that we believe may have an adaptive background and may show local adaptation not recognized by the above-mentioned criteria.