Social learning by mate‐choice copying increases dispersal and reduces local adaptation

Frequency-dependence may moderate fitness costs linked to reduced bird song complexity

Animal cultures can undergo rapid changes associated with innovations, revolutions or population decline. Where a rapid shift results in reduced complexity of cultural behaviours, it may have fitness consequences for individuals. Here, we report a dramatic shift in the dominant song type of critically endangered wild regent honeyeaters Anthochaera phrygia. Between 2015 and 2019, most males in the Blue Mountains sang a typical regent honeyeater song (typical Blue Mountains song), but 5%-10% sang an abbreviated version of the song with half the number of syllables (the clipped Blue Mountains song), which was associated with lower pairing success. Since 2020, the proportion of males singing the clipped Blue Mountains song has increased to 50%-75% each year. The likelihood of successful pairing in these males showed a significant concomitant increase, suggesting that the fitness costs associated with the abbreviated song decreased as it became the dominant song type. Our results suggest that the fitness consequences of loss of song complexity in declining and fragmented populations may be ameliorated by frequency-dependent shifts in song type preference.

Mate-choice copying accelerates species range expansion

Mate-choice copying is a type of social learning in which females can change their mate preference after observing the choice of others. This behaviour can potentially affect population evolution and ecology, namely through increased dispersal and reduced local adaptation. Here, we simulated the effects of mate-choice copying in populations expanding across an environmental gradient to understand whether it can accelerate or retard the expansion process. Two mate-choice copying strategies were used: (i) when females target a single individual and (ii) when females target similar individuals. We also simulated cases where the male trait singled out by females with mate choice maps perfectly onto his genotype or is influenced by genotype-by-environment interactions. These rules have different effects on the results. When a trait is determined by genotype alone, populations where copier females target all similar males expand faster and the number of potential copiers increased. However, when preference is determined by genotype-by-environment interactions, populations where copier females target a single male had higher dispersal and also expand faster, but the potential number of copiers decreases. The results show that mate-choice copying can accelerate the expansion process, although its adaptiveness depends on the information animals use in different contexts.