In these groups the duet allows the sexes to establish a pair bond that may eventually lead to copulation and, more importantly, duetting behaviour develops over a considerable time, often reinforcing an existing relationship. The largest literature on duetting or antiphonal singing exists for birds and primates (see review by Farabaugh, 1982). The treatment of homopteran signalling as a duet may encourage a careful re-examination of calling and searching strategies in this large and diverse group of insects. Thus sporadic evidence of fixed temporal strategies exists within the Homoptera, in which the putative duet induces males rather than females to adopt a searching role. One case of call interaction in cicadas provides a classic example of costs of male searching as part of a duet in homopteran signalling (Gwynne, 1987). Nuhardiyati, 1998), for most species the female reply is seldom fixed in its latency and so workers have not considered variation in reply latency as an important aspect of signalling in these groups. Although duetting may occur in some species of plant hopper (e.g. Similarly, many leaf and plant hoppers produce calls in response to males, and these calls either increase male searching patterns ( Claridge, 1985) or may assist males in locating receptive females ( Shaw et al., 1974 Ichikawa, 1976 Booij, 1982). In these cases the temporal organization between call and responding courtship signal is seldom fixed and few would consider such acts of acoustic courtship as a duet. For example, drosophilid fruit flies produce long and complex courtship patterns in which females may signal their presence and willingness to mate ( Bennet-Clark et al., 1980 Crossley et al., 1995). Many insects incorporate sound as part of the courtship display but not all of these constitute duets. To draw common threads from studies on male–female signalling in insects, the remarkable bioluminescent interactions of fireflies ( Buck & Case, 2002) and interactions based on substrate vibration have been included.
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For this reason, although many of the ideas developed around chorusing behaviour also apply to duetting, the voluminous literature on male call interactions has been excluded from this review (see Schwartz, 1991 Greenfield, 1994a, b, 2002). However, such a term suggests a loosely structured interaction rather than one with low temporal variance between initiating and reply signals.Ī stereotypic interaction is possible between calling males, and although interactions may involve just two males, and therefore qualify as a duet, more often calling males are part of a chorus of aggregated individuals. Other authors have used the more conservative term dialogue for male–female signal interactions (e.g. The most compelling aspect of the term used in animal communication, and hence its use in this review, is that there are only two participants whose signal interaction is marked by the predictable and stereotyped temporal association between initiating call and the reply. For biologists who study duetting behaviour in birds, primates, ungulates, frogs or arthropods, the interaction is between the sexes. When alternative tactics exist in nature, males may decrease the intensity of their call, insert a trigger pulse that signals to the female the end of its complex call, or males may even add a masking signal that obscures the competing signal.Ī duet is usually considered as an acoustic interaction between two partners. Under these circumstances, reply latencies often increase, creating an opportunity for alternative male tactics. However, in those species in which the initiating male call is under selection through female choice, the male call is predictably longer and occasionally more complex. In cases in which the male's initiating signal is extremely short, reply latencies become indicators of species' recognition. For insects, the key element of a duet for species' recognition is low variance in the reply latency of females.
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As defined, the duet has distinct temporal characteristics and these are compared with acoustic interactions among males in those species that exhibit male–male synchrony and alternation. The mechanisms of the duet are examined first, followed by evolution and the associated change in searching strategies of each sex. Duetting is reviewed principally in Orthoptera but also in Plecoptera, Hemiptera, Neuroptera and bioluminescence in the Coleoptera. Insect duets are characterized by low variance in the reply latency of the female (the time between a key element in the male call and the onset of the female's response). Unlike avian duets, in which females may initiate the interaction, among insects the duet starts with the male, and the female usually provides a brief reply. Duetting between the sexes in insects involves the use of airborne acoustic signals, substrate vibration and bioluminescence.