RESUMEN

Heritable endosymbionts widely occur in arthropod and nematode hosts. Among these endosymbionts, Wolbachia has been extensively detected in many arthropods, such as insects and crustaceans. Maternal inheritance is the most basic and dominant mode of transmission of Wolbachia, and it might regulate the reproductive system of the host in four ways: feminization, parthenogenesis, male killing, and cytoplasmic incompatibility. There is a relatively high percentage (10%) of thelytokous species in Oribatida, a suborder under the subclass Acari of arthropods, but the study of the endosymbionts in oribatid mites is almost negligible. In this paper, we detected endosymbiotic bacteria in two parthenogenetic oribatid species, Nothrus anauniensis Canestrini and Fanzago, 1877, which has never been tested for endosymbionts, and Oppiella nova, in which Wolbachia and Cardinium have been reported before. The results showed that Wolbachia was first found in N. anauniensis with an infection rate of 100% across three populations. Phylogenetic analysis showed that Wolbachia in N. anauniensis belonged to the supergroup K, marking the second supergroup of Wolbachia found in oribatid mites. Unlike previous studies, our study did not detect Wolbachia in O. nova, leading to the exclusion of Wolbachia's role in mediating thelytoky in this species.

RESUMEN

Heritable endosymbionts have been observed in arthropod and nematode hosts. The most-known among them is Wolbachia. Although the bacterium was previously identified in oribatid mites (Acari: Oribatida), it was not assigned to any phylogenetic group. Endosymbionts have a profound influence on their hosts, playing various functions that affect invertebrate's biology such as changing the way of reproduction. Oribatida provide the very unique examples of groups in which even whole families appear to be thelytokous, so we considered that it is worth to investigate the occurrence of endosymbiotic microorganisms in oribatid mites, especially that the knowledge on the symbionts occurrence in this invertebrate group is negligible. We report for the first time Wolbachia in oribatid mite Gustavia microcephala. The sequences of 16S rDNA, gltA, and ftsZ genes of the endosymbiont from the mite showed the highest similarity to Wolbachia found in Collembola. Phylogenetic analysis based on single gene and concatenated alignments of three genes revealed that the bacteria from G. microcephala and Collembola were related and clustered together with supergroup E. Relatively close relationship of Wolbachia from oribatid and collembolan hosts might mean at the evolutionary scale that horizontal transfer of bacteria between these two groups of invertebrates may take place.

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RESUMEN

We determined the occurrence of intracellular endosymbionts (Wolbachia, Cardinium, Arsenophonus, Rickettsia, Spiroplasma, Hamiltonella, flavobacteria, and microsporidia) in oribatid mites (Acari: Oribatida) with the use of PCR technique. For the first time we looked for and detected Wolbachia in parthenogenetic oribatid mite Ceratozetes thienemanni Willmann, 1943. The 16S rDNA, gatB, hcpA, and gltA sequences of Wolbachia in C. thienemanni showed the highest similarity (≥ 90%) to the genes of Wolbachia from springtails (Collembola) and oribatid mite Gustavia microcephala. We found the unique sequence 5'-GGGGTAATGGCC-3' in 16S rDNA of Wolbachia from C. thienemanni and collembolan representing group E. The phylogeny of Wolbachia based on the analysis of single genes as well as concatenated alignments of four bacterial loci showed that the bacteria from C. thienemanni belonged to Wolbachia group E, like the endosymbionts from springtail hosts and G. microcephala. Considering coexisting of representatives of Oribatida and Collembola in the same soil habitat and similar food, it is possible that the source of Wolbachia infection was the same. Residues of dead invertebrates could be in organic matter of their soil food, so the scenario of infection transferred by eating of remains of soil cohabitates is also possible. It could explain the similarity and relationship of the Wolbachia in these two arthropod groups. Oribatid mite C. thienemanni is a parthenogenetic mite which is a unique feature in the genus Ceratozetes. Moreover, this species, within the entire genus Ceratozetes, is characterized by the most northerly distribution. It is difficult to determine either it is parthenogenesis or the presence of endosymbionts that are in some way responsible for this kind of evolutionary success. Maybe we are dealing here with a kind of synergy of both factors?

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