Phylogeography and species delimitation in the New Zealand endemic, genetically hypervariable harvestman species, Aoraki denticulata (Arachnida, Opiliones, Cyphophthalmi) Rosa Fernández A,B and Gonzalo Giribet A A Museum of Comparative Zoology, Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford St, Cambridge, MA 02138, USA. B Corresponding author. Email: rfernandezgarcia@g.harvard.edu Abstract. Aoraki denticulata, a widespread mite harvestman endemic to the NW South Island of New Zealand, was postulated to constitute an old lineage with deep genetic history. Expanding on previous studies, we explored its genetic diversity and population structure, phylogeography and diversification patterns. We also examined the systematic implications of such a complex scenario through species delimitation analyses under coalescent-based and barcoding gap discovery methodologies. Our results depict the deep evolutionary history of the A. denticulata lineage, which shows high geographic structure and low genetic connectivity among modern populations. Aoraki denticulata is further subdivided into three lineages: a lineage presently inhabiting the northern region of the Southern Alps (and including the subspecies A. d. major), a second lineage in the north-eastern part of the sampled land, and a third one occupying the south-eastern localities. When using species delimitation methods based on coalescence approaches, large numbers of cryptic species were estimated. Based on morphological and biological evidence, we thus argue that these methods may overestimate species in cases in which genetic divergence is unusually large and discuss the systematic implications of our findings. Additional keywords: biogeography, DNA barcoding, lineage diversification, Pettalidae, species delimitation. Received 8 February 2014, accepted 1 August 2014, published online 12 September 2014 Introduction New Zealand constitutes an excellent but challenging biogeographic framework for evolutionary studies. As Diamond (1997: p. 3) put it, ‘New Zealand is biologically the closest thing we can come to exploring another planet’. This archipelago has an extraordinary degree of endemicity (Gibbs 2006), comparable with few other places (except, perhaps, Madagascar), yet a recent review of biogeographic studies did not reveal any single consistent pattern in the distribution of species-level phylogenetic diversity (Wallis and Trewick 2009; Trewick et al. 2011). The modern New Zealand originated after the Zealandia block (also called Tasmantia) split off the Antarctic margin of East Gondwana ca. 80 Mya (Sanmartín 2002). Zealandia thus separated from what was to become Australia, Antarctica and South America, following the opening of the Tasman Sea. From ~60–24 Ma, Zealandia gradually stretched, thinned and submerged, finally resulting in a major marine drowning event – the Oligocene marine transgression – in which Zealandia was putatively reduced to a few low-lying islands (Cooper 1989; Cooper and Millener 1993; Cooper and Cooper 1995; Campbell and Hutching 2007; Landis et al. 2008; Trewick and Bland 2012). Dispersal has been subsequently recognised as the main driving force shaping the diversity in modern New Zealand (e.g. McGlone 2005; Waters and Craw 2006; Trewick et al. 2007). Of all the documented examples of endemic fauna in New Zealand, harvestmen constitute one of the oldest animal groups (e.g. Giribet and Boyer 2010). Among all the species belonging to these ancient survivors, Aoraki denticulata, an old lineage belonging to the cyphophthalmid family Pettalidae and endemic to the NW South Island (Boyer et al. 2007), represents a challenging model. A previous phylogeographic study exploring the population genetics of this relatively widespread cyphophthalmid species identified high genetic variability, with up to 20% of divergence in the mitochondrial marker cytochrome c oxidase subunit I (COI), a large number of haplotypes, and within species divergences as deep as those between morphologically distinct species in the same genus (Boyer et al. 2007). This study failed to identify any morphological characters fixed in particular populations, therefore supporting the species status of A. denticulata, at least at the level of morphology. These morphological and genetic data were interpreted to suggest a different evolutionary history than those of the rest of the cyphophthalmid species of New Zealand, but others sustain that this may be a case of cryptic diversity (e.g. Schönhofer and Martens 2010), in part due to the Journal compilation Ó CSIRO 2014 www.publish.csiro.au/journals/is CSIRO PUBLISHING Invertebrate Systematics, 2014, 28, 401–414 http://dx.doi.org/10.1071/IS14009