Consequences of the Evolutionary Loss of a Sexual Signal in the Field Cricket Teleogryllus oceanicus
- Author(s): Gray, Brian
- Advisor(s): Zuk, Marlene
- et al.
Evolutionary events have potentially dramatic implications for organisms. I took advantage of an evolutionary event, the loss of a sexual signal in the field cricket Teleogryllus oceanicus, to elucidate the potential consequences of such a change. In some Hawaiian populations, males possess a wing mutation, flatwing, that precludes song production, rendering them obligately silent. Signal loss has the effect of altering the acoustic landscape experienced by all crickets, representing a change in the social environment. Previous studies indicate that the lack of acoustic input alters several phenotypic traits, perhaps by changing perceived population density. I investigated the role of the acoustic environment in mediating male reproductive investment and aggressive behavior. Males reared in song-dense environments, representing populations with many rivals, invested more in the ejaculate but were less aggressive than males from silent environments.
In addition, because flatwing males lack the ability to produce song, they face difficulties in attracting mates, since females locate males by responding to calling song. In some other species with multimodal communication, individuals may compensate for the temporary loss of a signal modality by switching to or increasing the use of an alternative, pre-existing modality. Communication in my study species involves acoustic and chemical cues, so I predicted that males lacking the ability to produce song would compensate by producing more attractive chemical cues. A female-response assay showed that females responded to chemical cues from both normal-winged and flatwing males, but did not exhibit a preference for either, indicating that flatwing males do not compensate for a lack of song with chemical cues.
Further, on the Hawaiian islands, calling males are subject to lethal parasitism from an acoustically-orienting North American parasitoid fly, Ormia ochracea, and males in parasitized populations do not live as long as males from unparasitized populations. Given that flatwing males are unable to produce song and are thus protected from parasitism from O. ochracea, I predicted that flatwing males would have a greater average age than their normal-winged counterparts in the same population. Contrary to my predictions, flatwing males were not older than normal-winged males.