Light alters calling-song characteristics in crickets

Abstract

Communication is crucial for mate choice and thus for the survival and fitness of most species. In the cricket, females choose males according to their calling-song attractiveness and, exhibiting positive phonotaxis, they approach the chosen male. Light has been widely reported to induce changes in crickets' daily activity patterns, including the males' stridulation behavior. It had remained unknown, however, whether light also affects the calling-song properties and thus may consequently also alter female choice. Here, we present a novel semi-automated process, enabling the analysis of calling-song properties in an extremely large sample size of recording sections from males subjected to lifelong light:dark (LD) or constant light (LL) conditions. Our findings revealed that the LD calling songs consisted of longer chirps, longer inter-syllable intervals and a higher proportion of 4-syllable chirps compared with those of LL males. We also conducted some preliminary female choice experiments suggesting that females (reared in LD conditions) exposed to playbacks of male calling songs exhibit a preference towards LD over LL recordings. We therefore conclude that illumination conditions such as constant light affect the male crickets' calling-song properties in a manner that may be discernible to the females. It remains unclear, however, how and to what extent female mate choice and the species' overall fitness are affected by these changes.

Keywords: Gryllus bimaculatus; Bioacoustics; Computational analysis; Intraspecific communication; Sexual selection; Stridulation.

Fig. 1.

Time series representation of the Gryllus bimaculatus male cricket stridulation. (A) The crickets' calling song consists of chirps and inter-chirp intervals. (B) An enlarged view of the shaded square from A, showing that each chirp comprises 3 or 4 syllables. (C) An enlarged view of the shaded square from B: the solid bar denotes one chirp; the dotted bar denotes the inter-chirp interval. (D) An enlarged view of the shaded square from C: the solid bar indicates one syllable; the dotted bar denotes the inter-syllable interval.

Fig. 2.

A screen capture of the time series representation of the automated detection of a male cricket's calling-song properties. (A) Detection of the onset and offset of syllables and (B) their grouping into 3- and 4-syllable chirps. The vertical lines at the onset and offset points of each syllable provide visual validation of the automated detection process.

Fig. 3.

Lifelong exposure to constant light affects calling-song properties of G. bimaculatus males, expressed as a decrease in the median chirp duration and increased variance. Medians are colored orange; the average stridulation of each individual male cricket is represented by a dot. Light:dark (LD), n=16; constant light (LL), n=22. Asterisks indicate significance (Welch t-test: ***P<0.001).

Fig. 4.

Calling-song properties of male crickets reared under lifelong LD or LL lighting conditions. The dominant frequency (A), mean number of chirps (B) and mean number of syllables (C) did not differ significantly between the two lighting conditions. However, both the mean chirp duration (D) and the mean inter-chirp interval duration (E) differed significantly between LD and LL (nested t-test: **P<0.01, ***P<0.001).

Fig. 5.

Distribution and proportion of 1-, 2-, 3-, 4- and 5-syllable chirps in the calling-song recordings of male crickets reared under lifelong LD or LL conditions. The 3- and 4-syllable chirps (green and blue, respectively) are the most dominant, comprising >98% of the total (LD: 23.54% and 75.07%; LL: 46.99% and 51.17%, respectively); 2-syllable chirps (red) comprise <2% of the total. In both LD and LL, 1- or 5-syllable chirps were practically absent.

Fig. 6.

Calling-song properties of male crickets reared under lifelong LD or LL illumination. A total of 3500 chirps were analyzed from each of five sound recordings for each of the five experimental crickets per treatment. Lifelong lighting conditions significantly affected 3-syllable (A) and 4-syllable (B) chirp duration. It did not affect syllable duration for either 3-syllable (C) or 4-syllable chirps (D). However, lifelong constant illumination did significantly affect the inter-syllable interval duration in both 3-syllable (E) and 4-syllable (F) chirps. Asterisks indicate significance (nested t-test: *P<0.05, **P<0.01).