Importance of pause between spider courtship vibrations and general problems using synthetic stimuli in behavioural studies

Abstract

Abstract. Effectiveness of natural stimuli (recorded and replayed male vibratory courtship signals) in eliciting a female's vibratory response was compared with that of synthetic stimuli in a plant-dwelling spider (Cupiennius salei). Specifically, the role of interseries (pauses between consecutive male series) was evaluated. Effectiveness was assessed by the number of responding females and the number of responses per female per stimulus. In case of both synthetic and natural stimuli, effectiveness increases with increasing duration of interseries in both measures. Interseries are thus represented in the female's innate releasing mechanism. However, synthetic stimuli are less effective (about 55%) than natural stimuli (set 100%). With decreasing interseries, the number of female responses per unit time sharply increases in case of playback of natural stimuli, but only slightly in case of synthetic stimuli. Since males courting on plants decrease interseries as soon as a female responds, thus facilitating their orientation, the data obtained with natural stimuli much better fit natural male courtship behaviour. This finding brings into question the validity of the synthetic stimulus. In the bioacoustics literature there is neither consensus on the effectiveness of a synthetic stimulus necessary to qualify it for behavioural analysis nor on how to measure effectiveness. We propose three measures: the percentage of responding animals, the action pattern of the response and the number of responses. It may be crucial, particularly when addressing evolutionary questions, to use either natural stimuli or synthetic stimuli (nearly) as effective as natural stimuli to avoid biased sampling of experimental animals and results difficult to interpret in biological terms.

The effect of temperature on the temporal structure of the vibratory courtship signals of a spider (Cupiennius salei Keys.)

“…The male signal's effectiveness in eliciting the female response increases with increasing duration of the interseries (Schmitt et al 1993). Since the repetition rate (number of responses, min-a) of the female is temperature dependent the maximum number of female responses per min is determined by the ambient temperature as well.…”

“…Since the repetition rate (number of responses, min-a) of the female is temperature dependent the maximum number of female responses per min is determined by the ambient temperature as well. For C. salei it is about 2 at 20~ It is therefore reasonable that with increasing duration of the interseries (decreasing the repetition rate of the interseries) the effectiveness of the female response increases as well, if it is calculated as the relative number of responses of a particular female to the number of male signals (Schmitt et al 1993).…”

“…By using synthetic male vibratory signals the importance of various signal parameters for eliciting a female response could be determined and thereby filter properties of the female innate releasing mechanism (IRM) defined. According to Schmitt et al (1993) not only the microstructure contained in one series of male syllables but also the timing of the complete series (macro-structure of the signal) is represented in the IRM of the female.…”

Mechanism of signal production in the vibratory communication of the wandering spider Cupiennius getazi (Arachnida, Araneae)

“…The behavioural significance of this reciprocal vibratory communication over distances of up to at least 3.8 m (Schmitt et al 1993 for C. coccineus) is to ensure mutual location and appeasement of the mates. It is also important for species recognition by the female, which responds preferentially to signals of conspecific males (Barth and Schmitt 1991).…”

“…Behavioural studies with C. salei have shown that the opisthosomal signals (and not, however, the pedipalpal signals) are necessary and sufficient to elicit the female's response (Schiich and Barth 1990). The probability of a female's response is determined by the main frequencyJ of the syllables, the temporal structure of the series and the pause duration between consecutive series (Schiich and Barth 1990;Schmitt et al 1993Schmitt et al , 1994.…”