A rapidly evolving cricket produces percussive vibrations: how, who, when, and why

Sexual signals are often transmitted through multiple modalities (e.g.,
visual and chemical), and under selection from both intended and
unintended receivers. A nuanced understanding of sexual signal evolution
is important since they play a critical role in diversification. We
recently documented percussive substrate-borne vibrations in the Pacific
field cricket (Teleogryllus oceanicus), a species that uses airborne
acoustic and chemical signals to attract and secure mates. The airborne
signals of Hawaiian T. oceanicus are currently undergoing rapid evolution;
at least five novel male morphs have arisen in the past 20 years. Nothing
is yet known about the newly discovered percussive substrate-borne
vibrations, so we ask ‘how’ they are produced, ‘who’ produces them (e.g.,
population, morph), ‘when’ they produce them (e.g., whether they are
plastic), and ‘why’ (e.g., do they play a role in mating). We show that
the vibrations are produced exclusively by males and during courtship via
foreleg drumming. One novel morph, purring, produces quieter airborne
songs and is more likely to drum than the ancestral morph. However,
drumming behavior is also contextually plastic for some males; when we
removed the ability of males to produce airborne song, ancestral males
became more likely to drum, whereas two novel morphs were equally likely
to drum regardless of their ability to produce song. Opposite our
prediction, females were less likely to mate with males who drummed. We
discuss why that might be and describe what we can learn about complex
signal evolution from this newly discovered behavior.