Data from: Long-branch attraction and the phylogeny of true water bugs (Hemiptera: Nepomorpha) as estimated from mitochondrial genomes

Background: Most previous studies of morphological and molecular data have consistently supported the monophyly of the true water bugs (Hemiptera: Nepomorpha). An exception is a recent study by Hua et al. (2009; BMC Evol Biol 9: 134) based on nine nepomorphan mitochondrial genomes. In the analysis of Hua et al. (2009), the water bugs in the group Pleoidea formed the sister group to a clade that consisted of Nepomorpha (the remaining true water bugs) + Leptopodomorpha (shore bugs) + Cimicomorpha (assassin bugs and relatives) + Pentatomomorpha (stink bugs and relatives), thereby suggesting that fully aquatic hemipterans evolved independently at least twice. Based on these results, Hua et al. (2009) elevated the Pleoidea to a new infraorder, the Plemorpha. Results: Our reanalysis suggests that the lack of support for the monophyly of the true water bugs (including Pleoidea) by Hua et al. (2009) likely resulted from inadequate taxon sampling. In particular, long-branch attraction (LBA) between the distant outgroup taxa and Pleoidea, as well as LBA among taxa in the ingroup, made Nepomorpha appear to be polyphyletic. We used three complementary strategies to test and alleviate the effects of LBA: (1) the removal of distant outgroups from the analysis; (2) the addition of closely related outgroups; and (3) the addition of a mitochondrial genome from a second family of Pleoidea. We also performed likelihood-ratio tests to examine the support for monophyly of Nepomorpha with different combinations of taxa included in the analysis. Furthermore, we found that specimens of Helotrephes sp. were misidentified as Paraplea frontalis (Fieber, 1844) by Hua et al. (2009). Conclusions: All analyses that included the addition of more taxa significantly and consistently supported the placement of Pleoidea within the Nepomorpha (i.e., supported the monophyly of the traditional true water bugs). Our analyses further support a close relationship between Notonectoidea and Pleoidea within Nepomorpha, and the superfamilies Nepoidea, Ochteroidea, Naucoroidea, and Pleoidea are resolved as monophyletic in all trees with strong support. Our results also confirmed that monophyly of Nepomorpha clearly is not refuted by the mitochondrial genome data.

研究背景：既往绝大多数形态学与分子数据相关研究均一致支持真水生蝽类（true water bugs）的单系群属性，该类群隶属于半翅目（Hemiptera）蝎蝽亚目（Nepomorpha）。仅有一项近期研究例外：Hua等人（2009；《BMC进化生物学》9卷：134）基于9个蝎蝽亚目类群的线粒体基因组开展的分析。在该研究的分析流程中，划蝽总科（Pleoidea）类群形成了一个姊妹支系，该支系与蝎蝽亚目（其余真水生蝽类）+ 细蝽亚目（Leptopodomorpha，岸蝽类）+ 臭虫亚目（Cimicomorpha，猎蝽及近缘类群）+ 盾背蝽亚目（Pentatomomorpha，蝽象及近缘类群）组成的支系构成姊妹群，这一结果提示完全水生的半翅目昆虫至少独立演化了两次。基于上述结果，Hua等人（2009）将划蝽总科（Pleoidea）提升为全新的亚目级阶元——拟蝽亚目（Plemorpha）。
研究结果：我们的重新分析显示，Hua等人（2009）的研究中真水生蝽类（包含划蝽总科Pleoidea）未被支持为单系群，这一结果大概率源于类群取样不足。具体而言，远缘外类群与划蝽总科（Pleoidea）之间存在的长枝吸引（long-branch attraction, LBA）效应，以及内类群内部类群间的长枝吸引效应，使得蝎蝽亚目（Nepomorpha）看似呈现多系群特征。我们采用三种互补策略以检验并缓解长枝吸引的影响：(1) 移除分析中的远缘外类群；(2) 加入近缘外类群；(3) 加入来自划蝽总科（Pleoidea）第二个科的线粒体基因组。此外，我们开展了似然比检验（likelihood-ratio tests），以评估在不同类群组合的分析中，蝎蝽亚目（Nepomorpha）单系群属性所获得的支持度。我们同时发现，Hua等人（2009）曾将Helotrephes sp.标本误鉴定为Paraplea frontalis（Fieber, 1844）。
研究结论：所有纳入更多类群的分析均显著且一致地支持划蝽总科（Pleoidea）隶属于蝎蝽亚目（Nepomorpha）（即支持传统定义下真水生蝽类的单系群属性）。我们的分析进一步证实了仰蝽总科（Notonectoidea）与划蝽总科（Pleoidea）在蝎蝽亚目（Nepomorpha）内的近缘关系；同时，所有系统发育树均以高支持度恢复出四个单系总科：蝎蝽总科（Nepoidea）、肩蝽总科（Ochteroidea）、潜蝽总科（Naucoroidea）以及划蝽总科（Pleoidea）。我们的结果同时证实，线粒体基因组数据并未否定蝎蝽亚目（Nepomorpha）的单系群属性。