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Volley (= SRU) detail

Volley (= SRU) detail

FIGURE 10.5 Duetting responses at 25°C (upper oscillographs in (a) and (b)) by an individual of Chrysoperla plorabunda to a stimulus signal (lower oscillographs in (a) and (b)) which gradually increases (a) or decreases (b) in SRU period. This species has a single-volley SRU (c). SRU duration of both stimulus signals was held constant at the species mean, 636 msec (25°C). Initial SRU period for both stimuli was 1230 msec (also the species mean at 25°C). In (a), the period of the stimulus increased to a maximum of 2280 msec; in (b), the period of the stimulus decreased to a minimum of 610 msec. Note that the individual is able to maintain perfect synchrony with the stimulus, regardless of whether the period of the latter markedly increases or decreases.

very recent: genetic distances and nucleotide sequence divergences among the song species are vanishingly small (Wells, 1994; Henry et al., 1999).

A prediction of this model of speciation is that the genetic architecture of song phenotype should be simple, consisting of relatively few genes of large effect. Indeed, the results of a hybridisation experiment between C. downesi and C. plorabunda showed that song features segregated in a manner consistent with simple architecture (Henry, 1985). Furthermore, in a Bayesian Castle-Wright analysis of song data from C. plorabunda X C. johnsoni, Henry et al. (2002b) showed that as few as one "genetic element" might be responsible for a crucial duetting difference between those two species. If these conclusions continue to receive support from future studies, Chrysoperla will be seen as a rare exemplar of rapid, sympatric speciation caused by sexual selection acting on chance mutational differences in mating signals.

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