Fast and reliable decisions for a dynamic song parameter in field crickets

Abstract

We investigated the choice of female crickets for a dynamic song parameter (chirp rate) on a walking compensator, and the underlying neuronal basis for the choice in the form of discharge differences in the pair of AN1-neurons driving the phonotactic steering behaviour. Our analysis reveals that decisions about chirp rate in a choice situation are made fast and reliably by female crickets. They steered towards the higher chirp rate after a delay of only 2.2-6 s, depending on the rate difference between the song alternatives. In this time period, the female experienced only one to two additional chirps in the song model with the higher rate. There was a strong correlation between the accumulated AN1 discharge difference and the amount of steering towards the side with the stronger response.

Fig. 1

Lateral steering of a single female towards song models differing in the chirp rate in a no-choice-situation (a), and when offered a choice between two alternatives differing in the chirp rate as indicated (b). All tracks are recordings over 1 min. Note the dependency of the amount of steering on absolute chirp rate in (a), and on the chirp rate difference in the choice situation (b). The average lateral steering (±1 SD) for 14 females in a choice between song alternatives differing in chirp rate is shown in (c)

Fig. 2

Averaged phonotactic steering of eight females in a choice between two song alternatives differing in their chirp rate by 10, 20 or 30 chirps/min. The analysis in (a) shows the first six-seconds after the onset of both stimuli (time zero) at a higher temporal resolution. The threshold lateral deviation, where females started to steer significantly towards one of the two alternative song models was studied using the phonotactic paths of females under symmetrical stimulation. Under these conditions, females track into a forward direction (lateral deviation zero), with some random and meandering steering towards either side. For eight females we calculated the average ±1 SD of lateral steering in each subsequent time segment of 2 ms (shaded area in a). The time when females exceeded this threshold (dashed line and arrows) was considered as the first time when they significantly steered towards one song model (see also arrows in b). b Stimuli in the choice situations with chirp rate differences of 10, 20 and 30 chirps/min

Fig. 3

Correlation between the discharge difference in the responses of the pair of AN1-neurons, as a result of chirp rate differences, and the degree of lateral deviation (N=14). Chirp rate differences of 10 and 20/min were tested for stimulus pairs of 120 versus 130 and 140 versus 150 chirps/min, and pairs of 130 versus 150 and 150 versus 170 chirps/min, respectively. Differences of 30 and 50 chirps/min were tested for pairs of 120 versus 150, and 120 versus 170 chirps/min, respectively. The discharge differences were calculated for the time of the phonotactic path of 1 min. Error bars represent standard deviations