Characterizing the genetic and behavioural consequences of contact between previously geographically isolated lineages provides insights into the mechanisms underlying diversification and ultimately speciation. The spring peeper (Pseudacris crucifer) is a widespread Nearctic chorus frog with six divergent mitochondrial DNA (mtDNA) lineages, many of which came into secondary contact during the Holocene. We examined genetics, morphology, advertisement calls and female preference for two lineages that began diverging in allopatry in the Pliocene and now overlap in southwestern Ontario, Canada. We found non-coincident clines in mtDNA and nuclear DNA, mirroring directionality of premating isolation barriers. We also found divergence in a range of traits between these two lineages, displacement in male call attributes and female preference for calls of their natal lineage in sympatry. Hybrids were morphologically distinct from both parental lineages, but hybrid male calls were acoustically intermediate. Female hybrids showed asymmetrical preference for Eastern male calls. These results considered together provide evidence of either unidirectional hybridization or selection against hybrids, potentially implying reproductive character displacement. Our work demonstrates the utility of integrated, multi-character approaches to understanding the processes of divergence and the nature of speciation.

Genotypic_Acoustic_Morphological_Preference_Data_PseudacrisThis file contains 5 worksheets: worksheet 1 describes identifiers used throughout data set; worksheet 2 (Genotypes (G)) encompasses 14 columns of microsatellite and mtDNA data; worksheet 3 (Call (C)) encompasses 21 columns of mean acoustic data; worksheet 4 (Morphology (M)) encompasses 11 columns of mean morphological measurements; worksheet 5 (Female Preference (F)) encompasses 6 columns of phonotaxis experimental results. For more detail refer to Methods and Table 1.Stewart et al Heredity 2015 DRYAD.xlsx