Call Timing in Male-Male Acoustical Interactions and Female Choice in the Midwife Toad Alytes obstetricans

Male midwife toads emit a short, tonal advertisement call. Previous studies have shown that two nearby males engaged in acoustical competition (duet) increase their calling rate. We address the question of whether acoustical competition is expressed in the temporal adjustment of the calls of nearby calling males. One male emits its calls typically immediately after the emission of a nearby male with an approximate phase angle of 80°. Variation in timing of calls is correlated with the size of the calling male (as inferred by call frequency). Playback experiments with females show that the timing of calls between interacting males can influence the choice of a mate. Females prefer duets of males calling with a phase angle of 180° rather than 90° and prefer males responding to calls over males initiating the duets.

Fig. 1.

Oscillograms of two Alytes obstetricans males. Caller A (black) leads the duet, the calls of B (grey) are lagging. Intervals A-A and B-B are the individual intercall intervals, intervals A-B and B-A are the between-individual call latencies

Fig. 2.

Response Time (RT) to the stimulus and expected response time (AT; grey, stimuli; black, responses). (A) A single response between two stimuli; (B) two responses between stimuli

Fig. 3.

Alternatives presented in the phonotaxis experiments. (A) Large male (black) and small male (grey) alternating their calls with a phase angle of 180° (upper channel) versus large male and small male alternating their calls with a phase angle of 90° (lower channel). (B) Large male always leading the call exchanges versus large male always following the call exchanges

Fig. 4.

Interval between calls (mean, standard error, sample size) of three pairs of males (A and B) when both males of a pair are calling (A-A and B-B intervals) and call interval of male B when male A ceases to call (B-B interval, B alone)

Fig. 5.

Relationship between response time (RT) and average time (AT) in the four playback tests (Random: stimulus with medium frequency emitted at random intervals; Low: low-frequency stimulus; Medium: medium-frequency stimulus; High: high-frequency stimulus; mean + standard error)

Fig. 6.

Interval between calls in two Alytes obstetricans males calling isolated (dotted line) and during the period of acoustical stimulation (solid line; horizontal line is interval between stimuli). (A) The intercall interval diminishes to adjust to the interval between stimuli. (B) Prior to the stimulus, the intercall interval of the isolated calling male matches approximately the intercall interval of the stimulus; thus, the male does not alter its call interval during playback

Accepted: 20 May 2000