Character displacement of a learned behavior and its implications for ecological speciation

Cultural evolution may accelerate speciation, but most support for this hypothesis is limited to cases of allopatric speciation through random cultural drift. In contrast, cultural evolution’s role in non-allopatric speciation (i.e., speciation with gene flow) has been less explored. One clade in which cultural evolution may have figured prominently in speciation with gene flow includes the conifer-seed-eating finches in the red crossbill (Loxia curvirostra) complex. Here we focus on Cassia crossbills (L. sinesciuris; an ecotype recently split taxonomically from red crossbills) that learn social contact calls from their parents. Previous work found that individuals modify their calls throughout life such that they become increasingly divergent from a sympatric red crossbill ecotype. This open-ended modification of calls could lead to character displacement if it causes population-level divergence in call structure that, in turn, reduces maladaptive heterospecific flocking. Heterospecifi...