Determinants of male spacing behaviour in Panacanthus pallicornis (Orthoptera: Tettigoniidae)

Panacanthus pallicornis is a neotropical species of katydid endemic to Colombia that inhabits premontane forests, and individuals are found in regenerating (RF) and dense forest (DF) habits. Members of this species are made conspicuous by their colouration, remarkable defensive body thorns and the loud mating calls of the males. Through capture, marking, and recapture, we determined singing-site characteristics in two different natural habitats: an RF and a DF. Using nearest neighbour analysis, we found male distribution tends to uniformity in forest habitats, but in the RF, male distribution is more random. Males also showed preference for high singing sites and these were correlated with host plant height. Although host plants in DF were taller than those in the RF, male's perch preference was independent from the habitat; and in RF, males select lower perches. To investigate if male spacing was a function of the calling song, we manipulated two groups of males from a different population, one group deafened (tympanic membranes torn), and another control group with tympanic membranes intact. Insects were released from a single location in the two different zones of similar area. After a number of days we measured male displacement, and found that the deafened group distribution tended to aggregation, while the control group spread throughout the experimental zone with a random distribution. These results suggest that male spacing behaviour is one of the functions of the calling song. Based on a pre-established phylogenetic framework of the genus Panacanthus, we discuss some implications for the evolution of the calling song of P. pallicornis in both RF and DF.