Neural and behavioral evolution in an eavesdropper with a rapidly evolving host.

The diversification of animal communication systems is driven by the interacting effects of signalers, signal receivers, and the environment. Yet, the critical role of unintended receivers, like eavesdropping enemies, has been underappreciated. Furthermore, contemporary evolution of animal signals is rare, making it difficult to directly observe this process.

Surviving the serenade: how conflicting selection pressures shape the early stages of sexual signal diversification.

Understanding how the early stages of sexual signal diversification proceed is critically important because these microevolutionary dynamics directly shape species trajectories and impact macroevolutionary patterns. Unfortunately, studying this is challenging because signals involve complex interactions between behavior, morphology, and physiology, much of which can only be measured in real-time. In Hawaii, male Pacific field cricket song attracts both females and a deadly parasitoid fly.

A novel cricket morph has diverged in song and wing morphology across island populations.

Divergence of sexual signals between populations can lead to speciation, yet opportunities to study the immediate aftermath of novel signal evolution are rare. The recent emergence and spread of a new mating song, purring, in Hawaiian populations of the Pacific field cricket (Teleogryllus oceanicus) allows us to investigate population divergence soon after the origin of a new signal. Male crickets produce songs with specialized wing structures to attract mates from afar (calling) and entice them to mate when found (courtship).

Decoupling of sexual signals and their underlying morphology facilitates rapid phenotypic diversification.

How novel phenotypes evolve is challenging to imagine because traits are often underlain by numerous integrated phenotypic components, and changes to any one form can disrupt the function of the entire module. Yet novel phenotypes do emerge, and research on adaptive phenotypic evolution suggests that complex traits can diverge while either maintaining existing form-function relationships or through innovations that alter form-function relationships. How these alternate routes contribute to sexual signal evolution is poorly understood, despite the role of sexual signals in generating biodiversity.

Behavioral responses of a parasitoid fly to rapidly evolving host signals.

Animals eavesdrop on signals and cues generated by prey, predators, hosts, parasites, competing species, and conspecifics, and the conspicuousness of sexual signals makes them particularly susceptible. Yet, when sexual signals evolve, most attention is paid to impacts on intended receivers (potential mates) rather than fitness consequences for eavesdroppers. Using the rapidly evolving interaction between the Pacific field cricket, , and the parasitoid fly, , we asked how parasitoids initially respond to novel changes in host signals.

Responses of intended and unintended receivers to a novel sexual signal suggest clandestine communication.

Inadvertent cues can be refined into signals through coevolution between signalers and receivers, yet the earliest steps in this process remain elusive. In Hawaiian populations of the Pacific field cricket, a new morph producing a novel and incredibly variable song (purring) has spread across islands. Here we characterize the current sexual and natural selection landscape acting on the novel signal by (1) determining fitness advantages of purring through attraction to mates and protection from a prominent deadly natural enemy, and (2) testing alternative hypotheses about the strength and form of selection acting on the novel signal.