Comparative morphology of the reproductive system and germ cells of Amblyomma ticks (Acari: Ixodidae): A contribution to Ixodidae systematics

Among arthropods, ticks of the genus Amblyomma are of great medical and veterinary importance and present phylogenetic and taxonomic divergences given polymorphisms and phenotypic plasticity between subpopulations. Generally, the male reproductive system and spermatozoon exhibit diversified morphology and ultrastructure species-specific, bringing new possibilities for phylogenetic and taxonomic issues. Therefore, the present study aimed to describe and compare the morphology of the male reproductive system and its germ cells of Amblyomma aureolatum, A. sculptum, and A. triste, intending to identify possible diagnostic features. Couples of the three tick's species were kept in colony, infested on rabbits and collected over 12 days of feeding. The males had their reproductive systems dissected, fixed and processed for histology and scanning electron microscopy. The results obtained here allowed the description of spermiogenesis stages and the comparison of spermatids morphology in the last stage of development. Furthermore, the testis of A. triste present an isthmus connecting the distal region of both, while in the other two species this structure could not be observed. Some anatomical features were identified which can be used for taxonomic and phylogenetic studies, like the presence or absence of the isthmus connecting testis, spV cell shape, the shape of the operculum and the presence or absence of the rim on its base.