Evolution of diversity : analysis of species and speciation in Hemiandrus ground wētā : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Zoology, Massey University, New Zealand
Patterns of biodiversity and endemism in New Zealand are explored, with a focus on the ground weta genus Hemiandrus. I first investigated factors that determined regional levels of endemism using a generalised linear model based on analysis of 2322 species of endemic New Zealand invertebrates. I found that widespread species are uncommon in New Zealand and most invertebrates occupied few regions. Number of endemic species per region was positively correlated with total number of species and size of the region 3 million years ago. Within one clade of Hemiandrus I found that North and South Islands differed in how they were occupied: South Island had many species with small non-overlapping ranges, whereas North Island was largely dominated by a single species. This is likely due to differences in age of different parts of New Zealand, yet this pattern was absent in another clade of ground weta species, showing that properties of species themselves also have a large impact on species ranges and speciation.
I applied several strategies to the Hemiandrus maculifrons species complex to test putative species boundaries (chapter 3). I compared morphological methods (Gaps in Continuous Characters across Geography (GCCG)) and genetic methods (Bayesian Species Delimitation, Rosenberg's P(AB), P(Randomly Distinct), P ID(Liberal)). Some of these strategies indicated that all or nearly all mtDNA clades tested represented separate species, while others indicated that no clades were likely to be distinct species. I concluded that H. maculifrons comprises three species (plus an under-sampled microendemic species, chapter 4); a conclusion that is discordant with the results of the “species delimitation” methods but consistent with other genetic, morphological and distributional data.
Since the genus Hemiandrus was thought to comprise only nine named species but dozens of alleged species, I tested whether the purported diversity accurately reflected biological diversity in the genus or whether it was exaggerated due to speculative classification (chapter 5). To do this, I applied traditional techniques to search for qualitative or quantitative differences between individuals using a model where species are separately evolving lineages that form separate genotypic clusters with no or few intermediates when in contact (Mallet 1995). Most proposed operational taxonomic units were supported, but some names appear to be synonymies while others appear to encompass more diversity than previously recognised. I concluded that Hemiandrus comprises at least 25 species, but as specimens representing all tag-names1
1 A tag-name is an informal name that indicates an entity that may be a separate species, monophyletic group or separate interbreeding population of uncertain taxonomic rank (Leschen et al. 2009).
were not available, additional diversity may exist within Hemiandrus than recognised here.
Phylogenetic analysis of mtDNA sequences identified two major clades within New Zealand Hemiandrus. Using nuclear markers and morphological traits I found strong support for these two clades. Derived shared traits were identified that can determine to which clade each species belongs. Concordance between genetic markers (four loci) and morphology resolved evolutionary relationships from which I propose dividing the group into two separate genera.