Female preference for symmetric calls in a grasshopper

Abstract

Grasshoppers produce calls by alternating use of a row of pegs on the two hind legs. The number of pegs per row in the grasshopper Myrmeleotettix maculatus demonstrated fluctuating asymmetry as shown by signed right-minus-left number of pegs having a frequency distribution not differing from a normal distribution with a mean value of zero. Peg asymmetry was significantly negatively related to mean number of pegs per leg. Peg asymmetry was relatively larger than asymmetry in femur length. A larger degree of peg asymmetry resulted in a larger degree of asymmetry in maximum frequency of chirps and asymmetry in the duration of chirps produced by the two legs. Calls produced by males with experimentally manipulated numbers and asymmetries of pegs were used in a female phonotaxis experiment. Females preferred calls of males with a larger and more symmetrical number of pegs. Peg asymmetry differed in a field sample of mated and unmated males with mated males having a smaller degree of peg asymmetry. These results demonstrate that females can discriminate male asymmetry directly on the basis of calls.