RESUMEN
Species of mites (Chelicerata: Arachnida) show a great variety of structures of the female gonads. In both evolutionary lines, Acariformes and Parasitiformes, the panoistic ovary, in which all germline cysts differentiate into oocytes, and the meroistic ovary, in which the oocytes grow supported by the nurse cells, have been documented. A less pronounced variation in the gonad structure could be expected at lower systematic levels, hence, we ask about the degree of differences within the family that is subordinate to Acariformes and represents the cohort Parasitengona. Based on the members of Trombidiidae (Acariformes: Trombidiformes, Parasitengona, Trombidioidea), we test the hypothesis that the general ovary type is constant at the family level. Our previous research on the female gonad in Allothrombium fuliginosum revealed that the meroistic ovary occurs in these mites. Here, we proceed with a detailed insight into the ovary structure in A. fuliginosum and examine the structure of the female gonad in other members of Trombidiidae, focusing on the following representatives of its nominotypical genus Trombidium: Trombidium brevimanum, Trombidium holosericeum, Trombidium heterotrichum, and Trombidium latum. For all species, studied with light, fluorescence, and transmission electron microscopy, we could confirm the presence of the meroistic ovary that is highly similar with respect to general architecture. The germline cysts show similarities in general morphology and the mode of germline cell differentiation; they consist of a few nurse cells and one oocyte. The connection between the nurse cells and oocytes is maintained by trophic cords that serve for the transport of organelles and macromolecules. Our results confirm the constancy of the structure of the female gonad at the intrageneric level and provide further support for the hypothesis on the lack of differences at the intrafamily level.
Asunto(s)
Ácaros , Ovario , Animales , Femenino , Ovario/ultraestructura , Ovario/anatomía & histología , Ácaros/anatomía & histología , Ácaros/ultraestructura , Oocitos/ultraestructuraRESUMEN
In arthropods of the subphylum Chelicerata a panoistic ovary, in which all germline cells differentiate into oocytes, prevails. Among the chelicerates, mites are believed to show a great variety of the structure of the female gonads. In general, the knowledge of the ovarian structure in mites is fragmentary and patchy. In both evolutionary lines, Acariformes and Parasitiformes, apart from the panoistic ovary, the meroistic ovary, in which the oocytes grow supported by their sibling cells, the nurse cells, occurs. The presence of the meroistic ovary is considered an apomorphic state. Previous studies revealed a various structure of the meroistic ovary in different mite taxa, and the differences came down, inter alia, to a different number and location of the nurse cells in relation to the oocytes. Here we provide a comprehensive review of the structure of the Chelicerata ovary, with special reference to the mite ovary. We also provide our preliminary results of the analysis of ovarian structure in two representatives of terrestrial Parasitengona (Acariformes), Allothrombium fuliginosum (Trombidiidae) and Erythraeus cinereus (Erythraeidae), performed using light, confocal and electron transmission microscopy. The analyses allowed for verification of data published before. In A. fuliginosum we showed the presence of the nurse cells in the ovarian wall, so the ovary should be classified as meroistic. In meroistic ovary of E. cinereus we found that each oocyte is connected to several mononucleated nurse cells. The verification of literature data and broadening the knowledge of the structure of the female gonad in mites, will result in estimating the usefulness of the ovary traits in phylogenetic analyses and will provide the basis for inference about the directions of evolutionary changes of female gonad at lower systematic levels.