Abstract
Understanding the mechanisms that lead organisms to be separated into distinct species remains a challenge in evolutionary biology. Interspecific hybridization, which results from incomplete reproductive isolation, is a useful tool to investigate such mechanisms. In birds, interspecific hybridization is relatively frequent, despite the fact that closed species exhibit morphological and behavioural differences. Evolution of behaviour is difficult to investigate on a large timescale since it does not ‘fossilize’. Here I propose that calls of hybrid non-songbirds that develop without the influence of learning may help in understanding the gradual process that leads to vocal divergence during speciation. I recorded crows produced by the European quail (Coturnix c. coturnix), the domestic Japanese quail (Coturnix c. japonica) and their hybrids (F1, F2 and backcrosses). Most crowing patterns were intermediate to those of the parental species; some were similar to one or the other parental species, or not present in either parental species. I also observed vocal changes in hybrid crows during the breeding season and from one year to the other. This vocal variability resembles those observed during the ontogeny of the crow in quails. It is likely that similar mechanisms involved in vocal changes during ontogeny might have driven vocal divergence in the species of Palearctic quails. I suggest that hybrid crows might have resembled those produced by intermediary forms of quails during speciation.
Highlights
During the speciation process, groups of individuals that had belonged originally to a common ancestor developed morphological, ecological and/or behavioural differences
Confirming previous studies on the acoustic signals of hybrids in different animal groups [5,6,7,8,9,10,11,12,13,29], some hybrids crows were closer to one parental form but most of them presented a mosaic of characteristics of both subspecies
This study is original since hybrid crows were intermediate between the three types of crows produced by the two parental subspecies and not between two parental signals as usually observed
Summary
Groups of individuals that had belonged originally to a common ancestor developed morphological, ecological and/or behavioural differences. These differences led eventually to reproductive isolation that characterizes a new species entity, according to Mayr’s biological concept [1]. Two isolating mechanisms act during the speciation process [2]: postzygotic (hybrid inviability and sterility) and prezygotic (sexual selection, asynchrony of sexual cycles, habitat selection). This isolation is definitely achieved when genetic rearrangements lead to complete reproductive incompatibility. It is interesting to point out that these morphological traits and behaviours are mainly signals assumed to be of crucial importance in sexual selection [5,6,7,8,9,10,11,12,13]
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