EVALUATING THE DESIGN OF MATE-CHOICE EXPERIMENTS - THE EFFECT OF AMPLEXUS ON MATE CHOICE BY FEMALE BARKING TREEFROGS, HYLA-GRATIOSA

The proper design of mate-choice experiments is critical to detecting and characterizing mating preferences. Female anuran amphibians tested in mate-choice experiments are almost always collected in amplexus (i .e. after they have chosen a mate); it has been assumed that these fem ales are as discriminating as they are before they enter amplexus. Thi s assumption was tested by testing females of the barking treefrog, Hy la gratiosa, twice within the same night, once before they entered amp lexus ('before' test) and once after ('after' test). Two such experime nts were conducted in which females were given a choice between two ca lls that differed either in repetition rate or fundamental frequency. In both experiments, the proportion of females choosing each alternati ve did not differ between the before and after tests. Some females swi tched their choice between the before and after tests; in both experim ents, equal numbers of females switched in one direction as in the oth er. The response of females in the after tests was not affected by eit her the time that they had spent in amplexus or the time of night when they were tested. Females that had not been tested earlier in the sea son took significantly less time to make their choice in the after tes t than in the before test, but females that had been previously tested did not. The results support the assumption that female anuran amphib ians captured in amplexus are as discriminating as they are when first selecting mates in natural choruses. (C) 1996 The Association for the Study of Animal Behaviour