Males of the microscopic annelid family Dinophilidae use their prominent glandomuscular copulatory organ (penis) to enzymatically dissolve the female’s epidermis and thereafter inject sperm. In order to test for putative conserved copulatory structures and neural orchestration across three dinophilid species, we reconstructed the reproductive myo- and neuroanatomy and mapped immunoreactivity patterns against two specific neurotransmitter markers with reported roles in invertebrate male mating behaviour (FVRIamide, MIP) and three general neural markers (acetylated α-tubulin, serotonin, FMRFamide). Seminal vesicles (one or two pairs), surrounded by a thin layer of longitudinal and circular muscles and innervated by neurites, are found between testes and copulatory organ in the larger males of Dinophilus vorticoides and Trilobodrilus axi, but are missing in the only 0.05 mm long D. gyrociliatus dwarf males. The midventral copulatory organ is in all species composed of an outer muscular penis sheath and an inner penis cone. Neurites encircle the organ equatorially, either as a ring-shaped circumpenial fibre mass or as dorsal and ventral commissures, which are connected to the ventrolateral nerve cords. All three examined dinophilids show similar immunoreactivity patterns against serotonin, FMRFamide, and FVRIamide in the neurons surrounding the penis, supporting the hypotheses about the general involvement of these neurotransmitters in copulatory behaviour in dinophilids. Immunoreactivity against MIP is restricted to the circumpenial fibre mass in D. gyrociliatus and commissures around the penis in T. axi (but not found in D. vorticoides), indicating its role in controlling the copulatory organ. The overall myo- and neuroanatomy of the reproductive organs is rather similar in the three studied species, suggesting a common ancestry of the unpaired glandomuscular copulatory organ and its innervation in Dinophilidae. This is furthermore supported by the similar immunoreactivity patterns against the tested neurotransmitters around the penis. Smaller differences in the immunoreactivity patterns around the seminal vesicles and spermioducts might account for additional, individual traits. We thus show morphological support for the putatively conserved role of FMRFamide, FVRIamide, MIP and serotonin in dinophilid copulatory behaviour.

中文翻译：

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支配器官的神经在整个Dinophilidae（Annelida）中显示常见的FMRFamide，FVRIamide，MIP和5-羟色胺免疫反应模式，表明它们在交配行为中的保守作用

显微镜下的无肢线螨科Dinophilidae的雄性使用其突出的腺肌交配器官（阴茎）以酶的方式溶解雌性的表皮，然后注入精子。为了测试假定的守恒交配结构和三个嗜蝇类物种的神经编排，我们重建了生殖肌和神经解剖结构，并针对两种特定的神经递质标记物绘制了免疫反应性模式，这些标记物在无脊椎动物雄性交配行为（FVRIamide，MIP）和三种一般性神经标记（乙酰化的α-微管蛋白，5-羟色胺，FMRFamide）。在较大的Dinophilus vorticoides和Trilobodrilus axi雄性雄性动物的睾丸和交配器官之间，发现有精囊（一对或两对），周围有一层薄薄的纵向和环形肌肉，并被神经突支配。但仅在0.05毫米长的D. gyrociliatus矮公中失踪。在所有物种中，腹中部交配器官由外部肌肉阴茎鞘和内部阴茎锥组成。神经突起以环形的环状纤维团或背侧和腹侧连合的方式赤道环绕器官，并连接到腹侧神经索。所有三个检查的亲液体对阴茎周围神经元中的血清素，FMRF酰胺和FVRI酰胺具有相似的免疫反应模式，支持有关这些神经递质普遍参与亲液体交配行为的假说。针对MIP的免疫反应性仅限于D. gyrociliatus中的周缘纤维团和A. axi的阴茎周围的连合（但在D. vorticoides中未发现），说明其在控制交配器官中的作用。在这三个研究物种中，生殖器官的整体肌肉和神经解剖学非常相似，这表明未配对的腺体肌交配器官及其在Dinophilidae中的神经支配关系是共同的。此外，针对阴茎周围被测神经递质的类似免疫反应模式也支持了这一点。精囊和精囊周围的免疫反应模式的较小差异可能解释了其他个体特征。因此，我们显示形态上支持FMRFamide，FVRI酰胺，MIP和5-羟色胺在嗜亲性交配行为中的保守作用。提示未配对的腺体肌肉交配器官及其在恐龙科中的神经支配。此外，针对阴茎周围被测神经递质的类似免疫反应模式也支持了这一点。精囊和精囊周围的免疫反应模式的较小差异可能解释了其他个体特征。因此，我们显示形态上支持FMRFamide，FVRI酰胺，MIP和5-羟色胺在嗜亲性交配行为中的保守作用。提示未配对的腺体肌肉交配器官及其在恐龙科中的神经支配。此外，针对阴茎周围被测神经递质的类似免疫反应模式也支持了这一点。精囊和精囊周围的免疫反应模式的较小差异可能解释了其他个体特征。因此，我们显示形态上支持FMRFamide，FVRI酰胺，MIP和5-羟色胺在嗜亲性交配行为中的保守作用。精囊和精囊周围的免疫反应模式的较小差异可能解释了其他个体特征。因此，我们显示形态上支持FMRFamide，FVRI酰胺，MIP和5-羟色胺在嗜亲性交配行为中的保守作用。精囊和精囊周围的免疫反应模式的较小差异可能解释了其他个体特征。因此，我们显示形态上支持FMRFamide，FVRI酰胺，MIP和5-羟色胺在嗜亲性交配行为中的保守作用。