2.2. Determination of males’ mating readiness
In order to select Ch. biguttulus males with high mating
readiness as potential reproductive partners in subsequent
experiments we stimulated 14 mature males on 6 consecutive
days after their isolation from females with the recording of a
female song. Individual male grasshoppers were transferred to an
arena that was heated by a heating lamp from above to constant
30 8C. The record of female stridulation was presented at an
intensity of 60 dB SPL to the right or to the left side of the body via a
loudspeaker (Sound Craft Conrad DT 25 P). The acoustic stimulus
consisted of 27 repetitions of a female song sequence of 1.5 s
duration separated by 3.3 s long pauses. Recognition of female
song elicits a uniform series of male reactions (von Helversen and
von Helversen, 1983). We rated the intensities of the males’
reactions to stimulation with female song with the following
scores: 0, no reaction; 1, stridulation; 2, turning toward the sound
source; 3, jumping or walking toward the sound source. The
maximal response of each individual male on each day following
separation from females was determined and the days were ranked
with respect to the maximal response intensities (higher ranks
accord to higher maximal responses; equal ranks were assigned to
days with equal maximal responses). After an overall Friedman
test, a post hoc Wilcoxon–Wilcox test for multiple comparisons of
matched samples was applied to compare the rank sums of the
different experimental days. Males used in this experiment were
not included in the experiments with females described above.