Behavioural response to songs between genetically diverged allopatric populations of Darwin’s small tree finch in the Galápagos

Empirical data that identify contemporary mechanisms of divergence shed
light on how species could multiply. In this study, we measured population
genetic structure, song syllable diversity, and response to simulated
intruder song in Darwin’s small tree finch (Camarhynchus parvulus) on
Santa Cruz and Floreana Islands, Galápagos archipelago. Our aim was to
test whether the magnitude of contemporary behavioural response in
resident birds was consistent with patterns of genetic or cultural
differences between populations. We analysed genetic structure and the
occurrence of song syllable types, and experimentally measured the
response of resident birds to intruder bird song from different
geographical origin (i.e., island) or syllable type. We discovered a weak
signal of population genetic structure between Santa Cruz and Floreana
Islands. While some song syllables occurred on both islands, others were
unique to each island; Santa Cruz Island males used more unique syllables
than Floreana Island males. Both Santa Cruz and Floreana resident males
discriminated their response towards a simulated intruder song based on
the geographical origin of the intruder song, but not on the syllable type
sung by the intruder. We conclude that the populations are diverging in
genetic and cultural traits and identified a signal of contemporary
behavioural response that could maintain divergence upon secondary
contact.