An overview of Estonian woodlice (Isopoda, Oniscidea)

An overview of the Estonian terrestrial isopod fauna is given, based on literature data and material collected from 1984 to 2021. The identified material consisted of 10915 specimens belonging to 14 species and collected from 172 localities throughout Estonia. In combination with previous data from the literature data, there are now reliable records of 16 species of woodlice from Estonia. Two species, viz. Platyarthrus hoffmannseggii Brandt, 1833 and Hyloniscus riparius (C. Koch, 1838), are new for the fauna. The latter has probably colonised Estonia recently and range expansions have been reported elsewhere. The data on Philoscia muscorum (Scopoli, 1763) are dubious, and this species is currently excluded from the Estonian list.

Contribution to the knowledge of the terrestrial isopod fauna of Lithuania

The present survey provides records on terrestrial isopods from southern and north-western parts of Lithuania. Isopods were sampled manually by checking substrates in eight habitats (several types of forest and anthropogenic environment) between 2014 and 2016. In total, seven species were recorded. The common European species Trachelipus rathkii was noted as the most frequent isopod in all studied habitats from southern Lithuania. Porcellionides pruinosus, found in the habitat of anthropogenic activity, was recorded for the first time from Lithuania. Based on the data of the present study and previous surveys, the 14 species of terrestrial isopods are recorded in Lithuania and the current state of knowledge about Lithuanian isopod is summarised.

Preliminary data on terrestrial isopods from some railways in Dobruja, eastern Romania

In July 2020 we analyzed the terrestrial isopod assemblages from different (mostly abandoned) railway constructions in Dobruja, eastern Romania. We identified 10 terrestrial isopod species, of which the most abundant and frequent were Porcellionides pruinosus (Brandt, 1833) and Armadillidium vulgare Latreille, 1804. We identified species that, in Romania, are present only in Dobruja: Leptotrichus pilosus Dollfus, 1905 and Trachelipus squamuliger (Verhoeff, 1907). Most of the species are common, generalist or synanthropic, connected to dry and open habitats. In abandoned railway-stations the number of species/samples was low (at most two), but at the base of a stone railway bridge in Babadag forest six species were found.

Experimental evidence of Wolbachia introgressive acquisition between terrestrial isopod subspecies

Wolbachia are the most widespread endosymbiotic bacteria in animals. In many arthropod host species, they manipulate reproduction via several mechanisms that favour their maternal transmission to offspring. Among them, cytoplasmic incompatibility (CI) promotes the spread of the symbiont by specifically decreasing the fertility of crosses involving infected males and uninfected females, via embryo mortality. These differences in reproductive efficiency may select for the avoidance of incompatible mating, a process called reinforcement, and thus contribute to population divergence. In the terrestrial isopod Porcellio dilatatus, the Wolbachia wPet strain infecting the subspecies P. d. petiti induces unidirectional CI with uninfected individuals of the subspecies P. d. dilatatus. To study the consequences of CI on P. d. dilatatus and P. d. petiti hybridization, mitochondrial haplotypes and Wolbachia infection dynamics, we used population cages seeded with different proportions of the two subspecies in which we monitored these genetic parameters five and seven years after the initial set up. Analysis of microsatellite markers allowed evaluating the degree of hybridization between individuals of the two subspecies. These markers revealed an increase in P. d. dilatatus nuclear genetic signature in all mixed cages, reflecting an asymmetry in hybridization. Hybridization led to the introgressive acquisition of Wolbachia and mitochondrial haplotype from P. d. petiti into nuclear genomes dominated by microsatellite markers of P. d. dilatatus. We discuss these results with regards to Wolbachia effects on their host (CI and putative fitness cost), and to a possible reinforcement that may have led to assortative mating, as possible factors contributing to the observed results.