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：既往多数基于形态学与分子数据的研究，均一致支持真水生蝽类（半翅目：潜蝽次目Nepomorpha）的单系性。唯一例外是Hua等人2009年发表于《BMC进化生物学（BMC Evol Biol）》第9卷第134页的一项研究，该研究基于9个潜蝽次目类群的线粒体基因组序列。在Hua等人2009年的分析中，划蝽总科（Pleoidea）的水生蝽类构成了一支演化支的姊妹群，该演化支包含潜蝽次目（其余真水生蝽类）、宽蝽次目（Leptopodomorpha，岸蝽类）、猎蝽次目（Cimicomorpha，猎蝽类及其近缘类群）以及蝽次目（Pentatomomorpha，蝽类及其近缘类群），这一结果提示完全水生的半翅目类群至少独立演化两次。基于上述结果，Hua等人2009年将划蝽总科（Pleoidea）提升为新次目普莱莫蝽次目（Plemorpha）。

研究结果：本研究的重新分析表明，Hua等人2009年的研究未能支持真水生蝽类（包含划蝽总科Pleoidea）的单系性，该问题可能源于类群取样不足。具体而言，远缘外类群与划蝽总科（Pleoidea）之间的长枝吸引（long-branch attraction, LBA），以及内类群类群间的长枝吸引，导致潜蝽次目（Nepomorpha）呈现出多系性的表象。本研究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）添加亲缘关系较近的外类群；（3）添加划蝽总科（Pleoidea）第二个科的线粒体基因组序列。本研究还开展了似然比检验，以评估不同类群组合的分析中，潜蝽次目（Nepomorpha）单系性所获得的支持度。此外，本研究发现Hua等人2009年将Helotrephes sp.（Helotrephes属未定种）误鉴定为额突拟划蝽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）隶属于潜蝽次目（Nepomorpha），即支持传统意义上真水生蝽类的单系性。本研究的分析进一步支持潜蝽次目（Nepomorpha）内的仰蝽总科（Notonectoidea）与划蝽总科（Pleoidea）存在密切亲缘关系；同时，在所有具有高支持度的系统发育树中，负子蝽总科（Nepoidea）、宽蝽总科（Ochteroidea）、固蝽总科（Naucoroidea）以及划蝽总科（Pleoidea）均被恢复为单系类群。本研究结果同时证实，线粒体基因组数据并未否定潜蝽次目（Nepomorpha）的单系性。