Muñoz-Muñoz Francesc, Ramoneda Josep, Pagès Nonito, Pujol Nuria, Talavera Sandra
Departament de Biologia Animal, de Biologia Vegetal i d'Ecologia, Facultat de Biociències, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain.
Departament de Biologia Animal, de Biologia Vegetal i d'Ecologia, Facultat de Biociències, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain.
J Invertebr Pathol. 2016 Mar;135:1-9. doi: 10.1016/j.jip.2016.01.008. Epub 2016 Jan 22.
Mermithidae is a family of endoparasitic nematodes known to cause intersexuality in arthropods. Intersexes of the genus Culicoides parasitized by mermithids have been the object of several studies aiming to describe their particular morphology. Culicoides intersexes are specimens with male genitalia and feminized sexually dimorphic structures, i.e. antennae, mouthparts and wings. To date, these specimens have only been described qualitatively and a quantitative approach supported by statistical analysis is lacking. Here we conduct morphometric analyses of sexually dimorphic structures in a sample of Culicoides circumscriptus that includes 34 intersexes with the aim of describing precisely the intersexual morphology. The morphology of antennae and the mouthparts was studied by multivariate statistical analysis of linear measures, and wing form by implementing geometric morphometrics techniques. While intersex wings proved to have a similar size to male wings, their shape was intermediate between males and females. However, when allometric shape variation was removed, the wing shape of intersexes was almost identical to that of females. The intersex antennae were morphometrically of the female type, especially when size variation was considered. In contrast, the measured mouthparts (the labrum and the third palpal segment) were halfway between males and females, even when body size was considered. Overall, the antennae and the wings showed a higher degree of feminization than the mouthparts. These findings indicate that the degree of feminization depends both on the morphological structure and on body size. Moreover, we propose that the feminization of the wings and antennae has an adaptive meaning for the parasite, which would favor female-like traits in order to access more easily its breeding sites, where the parasite has plenty of new hosts to infect. Female-like antennae would be beneficial to detect these sites, while having female-like wings would favor the host's capacity of dispersal to these sites.
索线虫科是一类内寄生线虫，已知会导致节肢动物出现雌雄间性现象。被索线虫寄生的库蠓属雌雄间性个体一直是多项旨在描述其特殊形态学研究的对象。库蠓雌雄间性个体是具有雄性生殖器以及雌性化的两性异形结构（即触角、口器和翅膀）的标本。迄今为止，这些标本仅进行了定性描述，缺乏统计学分析支持的定量研究方法。在此，我们对包括34个雌雄间性个体的局限库蠓样本的两性异形结构进行了形态测量分析，目的是精确描述雌雄间性形态。通过对线性测量数据进行多变量统计分析研究触角和口器的形态，采用几何形态测量学技术研究翅膀形态。虽然雌雄间性个体的翅膀大小与雄性翅膀相似，但其形状介于雄性和雌性之间。然而，去除异速生长形状变异后，雌雄间性个体的翅膀形状几乎与雌性相同。从形态测量学角度来看，雌雄间性个体的触角属于雌性类型，尤其是考虑到大小变异时。相比之下，所测量的口器部分（上唇和第三下唇节）即使考虑身体大小，也介于雄性和雌性之间。总体而言，触角和翅膀比口器表现出更高程度的雌性化。这些发现表明，雌性化程度既取决于形态结构，也取决于身体大小。此外，我们认为翅膀和触角的雌性化对寄生虫具有适应性意义，这有利于其具备类似雌性的特征，以便更轻松地进入其繁殖场所，在那里寄生虫有大量新宿主可供感染。类似雌性的触角有利于探测这些场所，而具有类似雌性的翅膀则有利于宿主向这些场所扩散。
