Surviving glacial ages within the Biotic Gap: phylogeography of the New Zealand cicada Maoricicada campbelli
New Zealand is an ideal location in which to investigate the roles of landscape and climate change on speciation and biogeography. An earlier study of the widespread endemic cicada Maoricicada campbelli (Myers) found two phylogeographically distinguishable major clades – northern South Island plus North Island (northern-SI + NI) and Otago. These two clades appeared to have diverged on either side of an area of the South Island known as the Biotic Gap. We sampled more intensively to test competing theories for this divergence. We aimed to discover if M. campbelli had survived within the Biotic Gap during recent glacial maxima, and if predicted areas of secondary contact between the two major clades existed. Location
New Zealand. Methods
We analysed mitochondrial DNA sequences (1520 bp; 212 individuals; 91 populations) using phylogenetic (maximum likelihood, Bayesian), population genetic (analysis of molecular variance) and molecular dating methods (Bayesian relaxed clock with improved priors). Results
We found strong geographical structuring of genetic variation. Our dating analyses suggest that M. campbelli originated 1.83–2.58 Ma, and split into the two major clades 1.45–2.09 Ma. The main subclades in the northern-SI + NI clade arose almost simultaneously at 0.69–1.03 Ma. Most subclades are supported by long internal branches and began to diversify 0.40–0.78 Ma. We found four narrow areas of secondary contact between the two major clades. We also found a difference between calling songs of the Otago vs. northern-SI + NI clades. Main conclusions
Phylogeographical patterns within M. campbelli indicate an early Pleistocene split into two major clades, followed by late Pleistocene range expansion and in situ population differentiation of subclades. The northern-SI + NI clade diversified so rapidly that the main subclade relationships cannot be resolved, and we now have little evidence for a disjunction across the Biotic Gap. Structure within the main subclades indicates rapid divergence after a common bottlenecking event, perhaps attributable to an extremely cold glacial maximum at c. 0.43 Ma. Clade structure and dating analyses indicate that M. campbelli survived in many refugia during recent glacial maxima, including within the Biotic Gap. The narrow overlap between the two major clades is attributed to recent contact during the current interglacial and slow gene diffusion. The two major clades appear to be in the early stages of speciation based on genetic and behavioural differences.
Document Type: Research Article
Publication date: 2009-04-01