Limited flexibility in female Pacific field cricket (Teleogryllus oceanicus) exploratory behaviors in response to perceived social environment

Abstract

How populations adapt, or not, to rapid evolution of sexual signals has important implications for population viability, but is difficult to assess due to the paucity of examples of sexual signals evolving in real time. In Hawaiian populations of the Pacific field cricket (Teleogryllus oceanicus), selection from a deadly parasitoid fly has driven the rapid loss of a male acoustic signal, calling song, that females use to locate and evaluate potential mates. In this newly quiet environment where many males are obligately silent, how do phonotactic females find mates? Previous work has shown that the acoustic rearing environment (presence or absence of male calling song) during late juvenile stages and early adulthood exposes adaptive flexibility in locomotor behaviors of males, as well as mating behaviors in both sexes that helps facilitate the spread of silent (flatwing) males. Here, we tested whether females also show acoustically induced plasticity in walking behaviors using laboratory‐reared populations of T. oceanicus from Kauai (HI; >90% flatwings), Oahu (HI; ~50% flatwings), and Mangaia (Cook Islands; no flatwings or parasitoid fly). Though we predicted that females reared without song exposure would increase walking behaviors to facilitate mate localization when song is rare, we discovered that, unlike males, female T. oceanicus showed relatively little plasticity in exploratory behaviors in response to an acoustic rearing environment. Across all three populations, exposure to male calling song during development did not affect latency to begin walking, distance walked, or general activity of female crickets. However, females reared in the absence of song walked slower and showed a marginally non‐significant tendency to walk for longer durations of time in a novel environment than those reared in the presence of song. Overall, plasticity in female walking behaviors appears unlikely to have facilitated sexual signal loss in this species.

Direct and indirect effects of sexual signal loss on female reproduction in the Pacific field cricket (Teleogryllus oceanicus)

“…It is unclear why the sexes would differ in reproductive physiological plasticity, but other studies have also found sex-specific differences following the spread of flatwing in Kauai. For instance, Kauai females show less socially-induced plasticity in gene expression (Pascoal et al, 2018) and walking behaviors (Balenger & Zuk, 2015;Heinen-Kay, Strub, & Zuk, 2018) than males.…”

When Does Sexual Signal Exploitation Lead to Signal Loss?

“…Males from Kauai also walk around more when raised in the absence of calling song, which should increase the likelihood of a chance encounter with a female or calling male (Balenger and Zuk, 2015). As noted above, females reared in a song-less environment are also more phonotactic and express lower mating thresholds Swanger and Zuk, 2015), though they do not show similar flexibility in exploratory behaviors (Heinen-Kay et al, 2018).…”