A discrete neuropeptide difference between two hybridizing grasshopper subspecies

Population divergence can be detected by the divergence of functional and neutral characters. Under some circumstances, it is desirable to have available a character that is discretely expressed in either of the diverging genomes, rather than the evaluation of qualitative variation of continuous characters. In the present study, we investigated mass peaks of peptide hormones in a model system of population divergence, the hybrid zone of two Chorthippus parallelus subspecies in the French–Spanish Pyrenees. Mass spectra from neuroendocrine tissues have previously been identified as species-specific and may have a sufficient resolution to vary at the subspecies level. For the first time, we succeeded in the detection of a subspecies-specific expression of neuropeptides collected from single individuals. Mass spectra sampled from populations across the C. parallelus grasshopper hybrid zone indicated neuropeptide identity between the sexes and within sample sites. The distribution of a single distinct but variable peptide signal, however, very closely followed the cline of the hybrid zone as derived from the mean variation in several continuous characters. The identity of this peptide in populations from the northern Pyrenees and central Europe supports a neuropeptide differentiation of preglacial origin. The observed differentiation in the peptide profile of the two subspecies demonstrates that a peptidomic approach may be a promising perspective to reconstruct reproductive isolation in an insect hybrid zone.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 541–548.