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

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.

Life history of chorus cicada, an endemic pest of kiwifruit (Cicadidae: Homoptera)

“…Both adults and immature cicadas feed on xylem sap, the latter as soil-dwelling nymphs. The chorus cicada Amphipsalta zelandica (Boisduval) is an endemic New Zealand species widespread in the North and South Islands (Larivière et al 2010;Marshall et al 2012). The fifth and final instar nymphs emerge from soil and moult to adults on any upright structure, leaving exuviae that can persist for over a year.…”

Phylogeography of six codistributed New Zealand cicadas and their relationship to multiple biogeographical boundaries suggest a re‐evaluation of the Taupo Line

“…b). A previously studied cicada, Amphipsalta cingulata , shows a genetic split between clades north and south of the Taupo Line (except one individual found north of Auckland), but this differentiation is far too recent to have been caused by the sea strait and there are no large differences in genetic diversity across the line (Marshall et al ., ). Another cicada, Notopsalta sericea , is restricted to the North Island and does show a genetic break near the Taupo Line, but this split is also recent ( c .…”

“…Another cicada, Notopsalta sericea , is restricted to the North Island and does show a genetic break near the Taupo Line, but this split is also recent ( c . 1 Ma) and is more likely to be attributable to Cockayne's Line (below) and tectonic uplift (Marshall et al ., ).…”

“…this study and others; see Wallis & Trewick, ). Very recent northern‐clade diversifications, as in the cicada Amphipsalta cingulata (Marshall et al ., ), are attributable to more recent climate cycles. This area is known to contain many unique organisms, not only because of its Pliocene history, but also recent endemic speciation (Spencer et al ., ), making it a priority area for conservation management (Buckley et al ., , ).…”

“…Our studies of New Zealand cicadas from a wide variety of habitats (forests, open dry habitats, dense forest, forest edge, scrub; Marshall et al ., ; this study) have failed to find strong support for the Taupo Line as a biogeographically significant break between clades or a demarcation of a shift in patterns of diversity. Of the three proposed Taupo lines (Fig.…”