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Hybridisation is commonly observed in geographical zones of contact between distinct lineages. These contact zones have long been of interest for biogeographers because they provide insight into the evolutionary and ecological processes that influence the distribution of species as well as the process of speciation. Here we review research on hybrid zones and zones of past introgression, both terrestrial and marine, in Aotearoa New Zealand. Many of New Zealand's hybrid zones occur between lineages or species that diverged prior to the Last Glacial Maximum (LGM), with numerous divergences dating to the early Pleistocene or Pliocene. Few secondary contact zones have been detected in terrestrial plants and in marine taxa. This may reflect a lack of the intensive sampling required to detect hybrid zones in these groups but for plants may also indicate widespread Pleistocene survival across the country. Lastly, we suggest avenues for research into New Zealand hybrid zones that are likely to be fruitful. [ABSTRACT FROM AUTHOR]

Documenting natural hybrid systems builds our understanding of mate choice, reproductive isolation and speciation. The stick insect species Clitarchus hookeri and C. tepaki differ in their genital morphology and hybridize along a narrow peninsula in northern New Zealand. We utilize three lines of evidence to understand the role of premating isolation and species boundaries: (a) genetic differentiation using microsatellites and mitochondrial DNA; (b) variation in 3D surface topology of male claspers and 2D morphometrics of female opercular organs; and (c) behavioural reproductive isolation among parental and hybrid populations through mating crosses. The genetic data show introgression between the parental species and formation of a genetically variable hybrid swarm. Similarly, the male and female morphometric data show genital divergence between the parental species as well as increased variation within the hybrid populations. This genital divergence has not resulted in reproductive isolation between species, instead weak perimating isolation has enabled the formation of a hybrid swarm. Behavioural analysis demonstrates that the entire mating process influences the degree of reproductive isolation between species undergoing secondary contact. Mechanical isolation may appear strong, whereas perimating isolation is weak. [ABSTRACT FROM AUTHOR]