An inquiry into suspected hybridisation in zones of overlap involving species of the genus Kikihia (Homoptera : Tibicinidae)

Abstract

The objective of this study is to test the hypothesis that hybridisation is occurring today between two species of New Zealand cicadas Kikihia subalpina (Hudson) and Kikihia cutora cumberi (Fleming). The morphological intermediacy of the putative hybrids, and the apparent close phylogenetic relationship of the taxa are investigated as this provides the best support for this hypothesis. Species status of specimens was determined a priori using acoustic character as this is a central component in the mate recognition system. The recognition concept of species is employed in this study rather than the "biological" species concept. The application of a biometrical technique, (Anderson's Hybrid Index) enabled an objective assessment of species status to be made based only on phenetic criteria. Only one phenetic hybrid was identified representing 0.15% of the total sample (N = 687). It was collected at a site well outside the zone of introgression. The close correlation between the two classifications, applying acoustic character, and that based on an assessment of overall phenetic similarity, suggested that the phenetic intermediacy of putative hybrids was not due to hybridisation. The employment of a unique signal-response system "co-adapted" in terms of the signaller (male) and receiver (female) is suggested as the basis of genetic isolation. The characters indicative of genetic relationship between the two taxa are pleisiomorphic from a cladistic framework and provide no information regarding the phylogenetic relationship of the taxa. They also provide no basis for the postulate of genetic relationship based on phenetic criteria. A new species morphologically identical to the putative hybrids is described and its relationship to the two taxa is central to resolving the hypothesis. It was identified on the basis of unique acoustic characters. Detailed studies of the acoustic structure of all three species, and extensive fieldwork observations suggest that acoustic character is central to conspecific mate recognition. Consequently, there may be no genetic relationship between the species in spite of marked overlap in morphology. The stability of the acoustic structure in all populations of the three taxa throughout their distributional ranges suggests that all three represent discrete genetic communities of reproduction.