[摘要] When populations isolated in allopatry meet in secondary contact, whether they merge depends on whether there is partial premating isolation or selection against hybrids (
Coyne and Orr 2004,
Price 2008). If there is no selection against hybrids, the strength of premating isolating factors (e.g., song differences) can gradually decrease, leading to fusion of the populations. Thus, selection against hybrids plays a critical role in the speciation process, by preventing fusion of differentiated forms and by favoring the evolution of stronger premating isolation. For most pairs of avian taxa in North America, the causes of selection against hybrids are unknown. Although there are a variety of possibilities (e.g., intrinsic genetic incompatibilities, mismatch between morphology of hybrids and environmental niche, inferior mating display of hybrids), there are few data with which to test these. Here, we review the potential importance of molt-scheduling divides and migratory-orientation divides (hereafter “orientation divides”) as general sources of selection against hybrids and suggest tests that could further evaluate these hypotheses.
