Limited, episodic diversification and contrasting phylogeography in a New Zealand cicada radiation.

David C Marshall,Kathy B R Hill,Chris Simon,Thomas R Buckley,Katharine A Marske,Colleen Chambers

doi:10.1186/1471-2148-12-177

Abstract

BackgroundThe New Zealand (NZ) cicada fauna contains two co-distributed lineages that independently colonized the isolated continental fragment in the Miocene. One extensively studied lineage includes 90% of the extant species (Kikihia + Maoricicada + Rhodopsalta; ca 51 spp.), while the other contains just four extant species (Amphipsalta – 3 spp. + Notopsalta – 1 sp.) and has been little studied. We examined mitochondrial and nuclear-gene phylogenies and phylogeography, Bayesian relaxed-clock divergence timing (incorporating literature-based uncertainty of molecular clock estimates) and ecological niche models of the species from the smaller radiation.ResultsMitochondrial and nuclear-gene trees supported the monophyly of Amphipsalta. Most interspecific diversification within Amphipsalta-Notopsalta occurred from the mid-Miocene to the Pliocene. However, interspecific divergence time estimates had large confidence intervals and were highly dependent on the assumed tree prior, and comparisons of uncorrected and patristic distances suggested difficulty in estimation of branch lengths. In contrast, intraspecific divergence times varied little across analyses, and all appear to have occurred during the Pleistocene. Two large-bodied forest taxa (A. cingulata, A. zelandica) showed minimal phylogeographic structure, with intraspecific diversification dating to ca. 0.16 and 0.37 Ma, respectively. Mid-Pleistocene-age phylogeographic structure was found within two smaller-bodied species (A. strepitans – 1.16 Ma, N. sericea – 1.36 Ma] inhabiting dry open habitats. Branches separating independently evolving species were long compared to intraspecific branches. Ecological niche models hindcast to the Last Glacial Maximum (LGM) matched expectations from the genetic datasets for A. zelandica and A. strepitans, suggesting that the range of A. zelandica was greatly reduced while A. strepitans refugia were more extensive. However, no LGM habitat could be reconstructed for A. cingulata and N. sericea, suggesting survival in microhabitats not detectable with our downscaled climate data.ConclusionsUnlike the large and continuous diversification exhibited by the Kikihia-Maoricicada-Rhodopsalta clade, the contemporaneous Amphipsalta-Notopsalta lineage contains four comparatively old (early branching) species that show only recent diversification. This indicates either a long period of stasis with no speciation, or one or more bouts of extinction that have pruned the radiation. Within Amphipsalta-Notopsalta, greater population structure is found in dry-open-habitat species versus forest specialists. We attribute this difference to the fact that NZ lowland forests were repeatedly reduced in extent during glacial periods, while steep, open habitats likely became more available during late Pleistocene uplift.

Highlights

The New Zealand (NZ) cicada fauna contains two co-distributed lineages that independently colonized the isolated continental fragment in the Miocene
cytochrome oxidase I (COI) sequences of the four species formed strongly supported monophyletic groups, and Amphipsalta was recovered as a monophyletic group (91% ML bootstrap), but A. zelandica and A. cingulata were only weakly supported as sister-taxa (Figure 3)
Models for A. cingulata yielded similar geographic projections, with much of lowland North Island (NI) projected as climatically suitable under modern conditions, and no refugia projected for the LGM (Figure 6)

Summary

Introduction

The New Zealand (NZ) cicada fauna contains two co-distributed lineages that independently colonized the isolated continental fragment in the Miocene. 20 taxa), and Rhodopsalta Dugdale (3 taxa), which are related to New Caledonian cicadas [4,5]. Species of this clade are distributed across all three main islands (North, South, Stewart; see Figure 1 and Figure 2) and several outer islands, and together they inhabit a variety of low- and mid-elevation habitats [6,7,8,9]. Molecular-clock studies suggest that diversification in both Kikihia and Maoricicada began around 6–7 Ma and accelerated through the Pliocene as mountain-building increased temperature and moisture contrasts throughout NZ and isolated populations geographically [1,2,10]

Results

Discussion

Conclusion