The evolution of sticks; quantifying clasper morphology across a hybrid zone in the stick insect genus Clitarchus

Shelley Myers *1, Thomas Buckley 2, Gregory Holwell 3


1 Landcare Research & University of Auckland
2 Landcare Research, 231 Morrin Road, Auckland, 1072, New Zealand
3 University of Auckland, 261 Morrin Road Tamaki Campus, Glen Innes, Auckland, 1142, New Zealand

A hybrid zone is the geographic area where two species can meet and form offspring.  It is common for the offspring of hybridising species to have reduced fitness. The theory of reinforcement predicts that prezygotic barriers will evolve between hybridising groups and there will be selection against hybridisation. In the Far North of New Zealand, the widely-distributed stick insect species Clitarchus hookeri is replaced by an ecologically similar and undescribed species of Clitarchus. These species are differentiated on the basis of male terminalia (specifically the claspers), egg morphology and mitochondrial DNA. Populations sampled between the two species show intermediate morphology. The aim of our research is to quantify the intra- and interspecific variation in clasper structure of Clitarchus populations across Northland. It is likely that variation in genital structures represents the differing abilities of males to control mating duration, and that those males with hybrid clasper phenotype suffer from a reduction in fitness. Quantification of clasper structure will provide a basis for addressing the questions: Does variation in morphology correspond to differences in mating behaviour? And does morphological variation reflect reproductive isolation? The research presented will cover the methods behind complex morphological quantification and demonstrate the relationship with speciation. 


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