An iconic group of arid-adapted insects is the Australian soil-burrowing cockroaches (Blaberidae: Geoscapheinae), large, wingless insects that evolved burrowing behaviour and associated forms in parallel from wood feeding ancestors in the subfamily Panesthiinae. A particularly problematic taxon within the Geoscapheinae is Geoscapheus dilatatus (Saussure, 1864), which might represent a species complex and whose delimitation has been complicated for decades by the species harbouring polymorphic males. Males can be divided into two main morphs: individuals possessing horn-like protrusions on the anterior margin of the pronotum (‘tuberculate’) and those without these characters (‘non-tuberculate’). A less common, third form consists of individuals that possess tubercles but are far larger than other tuberculate males and occur solely to the north of the species' distribution (‘atypical’ tuberculates). Here, we make use of whole mitochondrial genomes and nuclear ribosomal RNA data from individuals across the range of G. dilatatus to conduct the first phylogenetic analysis of this species to date. We recover all tuberculate males (including atypical forms) as monophyletic and the derived form of G. dilatatus, having evolved only once in this species, whereas non-tuberculate forms are paraphyletic. Fossil-calibrated molecular clock analysis revealed that the divergence between these two forms occurred during the late Miocene approximately 6.7 Mya, concurrent with an expansion of the continent's drier biomes. Environmental niche modelling suggests that tuberculate male forms are more climatically tolerant than their more restricted non-tuberculate counterparts, and both forms' predicted fundamental niches are strongly limited by rainfall. Three species delimitation analyses implemented here failed to consistently delimit G. dilatatus beyond a single species. Ultimately, population genetic approaches paired with additional sampling will be necessary to determine these findings more concretely, but at present, we do not consider the results presented here sufficient to delimit G. dilatatus based on morphological differences found in the species' polymorphic males alone.

中文翻译：

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具有多态雄性的澳大利亚土穴蟑螂的分子系统学和生物地理学，Geoscapheus dilatatus (Blattodea: Blaberidae)

一个标志性的适应干旱的昆虫群是澳大利亚土栖蟑螂（Blaberidae：Geoscapheinae），这种大型无翅昆虫从 Panesthiinae 亚科的以木材为食的祖先平行进化出穴居行为和相关形式。Geoscapheinae 中一个特别成问题的分类群是Geoscapheus dilatatus(Saussure, 1864)，这可能代表了一个物种复合体，几十年来，它的定界一直被包含多态雄性的物种复杂化。雄性可分为两种主要形态：在前胸膜前缘具有角状突起的个体（“结核”）和没有这些特征的个体（“非结核”）。较不常见的第三种形式是具有结节，但远大于其他结节性雄性的个体，仅出现在物种分布的北部（“非典型”结节）。在这里，我们利用整个线粒体基因组和来自G. dilatatus范围内个体的核糖体 RNA 数据进行迄今为止该物种的首次系统发育分析。我们将所有结核雄性（包括非典型形式）恢复为单系和G. dilatatus的衍生形式，在该物种中仅进化一次，而非结核形式是并系的。化石校准的分子钟分析表明，这两种形式之间的分歧发生在中新世晚期大约 6.7 Mya，同时该大陆较干燥的生物群落扩张。环境生态位模型表明，有结核的雄性形态比它们更受限制的非结核性形态更具气候耐受性，并且两种形态的预测基本生态位都受到降雨的强烈限制。这里实施的三个物种定界分析未能一致地定界G. dilatatus超越单一物种。最终，需要结合额外抽样的种群遗传方法来更具体地确定这些发现，但目前，我们认为此处提供的结果不足以根据仅在物种多态性雄性中发现的形态差异来界定G. dilatatus。