Department of Ecology and Evolutionary Biology, University of Connecticut, 75 N, Eagleville Rd, Storrs, CT 06269, USA.
BMC Evol Biol. 2012 Sep 11;12:177. doi: 10.1186/1471-2148-12-177.
The 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.
Mitochondrial 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.
Unlike 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.
新西兰（NZ）蝉类群包含两个共同分布的谱系，它们在中新世独立殖民了这个孤立的大陆碎片。一个广泛研究的谱系包括 90%的现存物种（Kikihia + Maoricicada + Rhodopsalta；约 51 种），而另一个谱系仅包含四个现存物种（Amphipsalta-3 种+Notopsalta-1 种），研究较少。我们研究了这些物种的线粒体和核基因系统发育和系统地理学、贝叶斯松弛时钟分歧时间（包括基于文献的分子钟估计不确定性）以及较小辐射物种的生态位模型。
线粒体和核基因树支持 Amphipsalta 的单系性。Amphipsalta-Notopsalta 内的大多数种间多样化发生在中新世中期到上新世。然而，种间分歧时间估计值置信区间较大，高度依赖于假定的树先验，未校正和父系距离的比较表明分支长度的估计存在困难。相比之下，种内分歧时间在各分析中变化不大，似乎都发生在更新世。两个大型森林物种（A. cingulata、A. zelandica）表现出最小的系统地理学结构，种内多样化可追溯到约 0.16 和 0.37 Ma。在两个较小体型的物种（A. strepitans-1.16 Ma，N. sericea-1.36 Ma）中发现了中更新世年龄的系统地理学结构，它们栖息在干燥开阔的栖息地。与种内分支相比，独立进化物种的分支较长。回溯到末次冰盛期（LGM）的生态位模型与 A. zelandica 和 A. strepitans 的遗传数据集相符，表明 A. zelandica 的范围大大缩小，而 A. strepitans 的避难所则更为广泛。然而，无法为 A. cingulata 和 N. sericea 重建 LGM 栖息地，这表明它们在我们缩小的气候数据中无法检测到的小生境中存活。
与 Kikihia-Maoricicada-Rhodopsalta 分支表现出的大型和连续多样化不同，同期的 Amphipsalta-Notopsalta 谱系包含四个相对较老（早期分支）的物种，它们只表现出近期的多样化。这表明要么是一段没有物种形成的长时间稳定期，要么是一次或多次灭绝事件已经修剪了辐射。在 Amphipsalta-Notopsalta 中，在干燥开阔栖息地的物种中发现了更大的种群结构，而不是森林特化物种。我们将这种差异归因于这样一个事实，即在冰期期间，新西兰低地森林的范围一再缩小，而在更新世晚期抬升期间，陡峭、开阔的栖息地可能变得更加可用。
