The genus Gennadas (Benthesicymidae: Decapoda): morphology of copulatory characters, phylogeny and coevolution of genital structures

Species within Gennadas differ from each other largely only in male (petasma) and female (thelycum) copulatory characters, which were restudied in scanning electron microscopy and used as a basis for phylogenetic analyses. Twenty-six petasma characters and 49 thelycum characters were identified. All sixteen recognized species of Gennadas and Aristaeomorpha foliacea (outgroup) were included as terminals. Four robust monophyletic clades were retrieved, described and diagnosed as new species groups. The thelycum characters had greater impact on tree topology and supported deeper nodes than did the petasma characters. We hypothesize that aspects of the thelycum evolved first followed by aspects of the petasma. Relatively more conservative characters include parts of the anterior sternites of the thelycum and of the petasma, while the scuti and protuberances on the thelycum and the shape and subdivisions of the petasma lobes are evolutionary plastic. We identified two groups of copulatory characters, which are likely coupled functionally and interlinked evolutionarily: (1) the external part of the petasma and the posterior part of the thelycum and (2) the internal part of the petasma and anterior part of the thelycum. We reconstruct possible mating position during copulation for each of the new species groups presented here. We also present an updated key to species of Gennadas.

Gennadas属的物种之间，彼此差异主要仅存在于雄性交接器（petasma）与雌性交接器（thelycum）的交配相关形态特征上。本研究通过扫描电子显微镜（scanning electron microscopy）对这些特征进行了重新检视，并以此为基础开展系统发育分析。
本研究共鉴定出26个雄性交接器特征与49个雌性交接器特征。研究纳入了所有已被正式确认的16种Gennadas属物种，以及外类群（outgroup）物种叶形拟对虾（Aristaeomorpha foliacea）作为终端分类单元。
分析结果检索到4个稳健的单系群分支，本研究将其描述并界定为全新的物种组。
雌性交接器特征对系统树拓扑结构的影响程度高于雄性交接器特征，且对更深层级的分类节点具有更强的支持效力。
我们推测，雌性交接器的相关形态特征的演化早于雄性交接器的对应特征。
相对保守的特征包括雌性交接器的前侧腹板以及雄性交接器的部分结构；而雌性交接器上的盾片与突起，以及雄性交接器叶瓣的形态与细分结构则演化可塑性较强。
本研究鉴定出两类可能在功能上偶联、演化上相互关联的交配相关特征：（1）雄性交接器的外部结构与雌性交接器的后部结构；（2）雄性交接器的内部结构与雌性交接器的前部结构。
我们针对本文提出的各个新物种组，重构了其交配过程中可能存在的交配体位。
本研究同时提供了一份更新版的Gennadas属物种检索表。