Abstract
Males of the katydid Sphagniana sphagnorum form calling aggregations in boreal sphagnum bogs to attract mates. They broadcast frequency-modulated (FM) songs in steady series, each song comprised of two wing-stroking modes that alternate audio and ultrasonic spectra. NN analysis of three populations found mean distances between 5.1 and 8.4 m, but failed to find spacing regularity: in one males spaced randomly, in another they were clumped, but within the clumps spaced at random. We tested a mechanism for maintaining inter-male distances by playback of conspecific song to resident males and analysing song interactions between neighbouring males in the field. The results indicate that the song rate is an important cue for males. Information coded in song rates is confounded by variation in bog temperatures and by the linear correlation of song rates with temperature. The ultrasonic and audio spectral modes suffer different excess attenuation: the ultrasonic mode is favoured at shorter distances (< 6 m), the audio mode at longer distances (> 6 m), supporting a hypothesized function in distance estimation. Another katydid, Conocephalus fasciatus, shares habitat with S. sphagnorum and could mask its ultrasonic mode; however, mapping of both species indicate the spacing of S. sphagnorum is unaffected by the sympatric species.
Highlights
Males of most crickets and katydids (Ensifera, Orthoptera) broadcast songs
The results of the nearest neighbour distance analysis of the spatial distribution of the 66 singing males of S. sphagnorum (Table 1) indicated that this did not differ from a random distribution
Within choruses of singing males, many acoustic insects and anurans maintain a minimum distance from their neighbours, resulting in an exclusive space occupied by their song, even while they are not defending some physical resource
Summary
Males of most crickets and katydids (Ensifera, Orthoptera) broadcast songs. Diverse aspects of this singing behaviour are much studied: the function and evolution of their hearing organs, the effects of acoustic signal differentiation. This broadcast signal can elicit either positive or negative phonotaxis, or aggression in conspecific males (Doolan 1981; Mason 1996). Males display the same aggressive approach to a speaker broadcasting conspecific song. Confirming the repulsive role of song, deafened males no longer display acoustic-mediated spacing
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have