Report on Iridovirus Iiv-31 (Iridoviridae, Iridovirus) Infecting Terrestrial Isopods (Isopoda, Oniscidea) in Japan

Crustaceana 85 (10) 1269-1278

REPORT ON IRIDOVIRUS IIV-31 (IRIDOVIRIDAE, IRIDOVIRUS) INFECTING TERRESTRIAL ISOPODS (ISOPODA, ONISCIDEA) IN JAPAN

BY

S. KARASAWA1,4), J. TAKATSUKA2) and J. KATO3) 1) Faculty of Education, Fukuoka University of Education, Munakata, Fukuoka 811-4192, Japan 2) Forest Entomology Division, Forestry and Forest Products Research Institute, Matsunosato 1, Tsukuba, Ibaraki 305-8687, Japan 3) Takezono, Tsukuba, Ibaraki 305-0032, Japan

ABSTRACT We conducted a comprehensive review of blue isopods in Japan by collecting isopod species from eight sites located on three Japanese islands (Honshu, Kyushu and Okinawajima). We also interviewed Japanese soil-fauna researchers and retrieved data from the Internet detailing isopod collections in Japan. From analysis of the complete data set, we conclude that a total of eight species from six families (i.e., Ligiidae, Alloniscidae, Philosciidae, Armadillidae, Porcellionidae and Armadillidiidae), excluding two unidentified species, have been observed at 18 Japanese sites. The distributional range of the blue isopods covered the whole of Japan (from Okinawajima Island to Hokkaido). Examination of transmission electron microscope (TEM) images revealed non-enveloped virions in the epithelial cell cytoplasm of the blue coloured Armadillidium vulgare (Latreille, 1804) from Japan. We designed primers for amplifying partial sequences from the major capsid protein (MCP) gene from invertebrate iridescent viruses (IIVs). The predicted amino acid sequences of the MCP gene from IIV isolated from the blue coloured isopods, A. vulgare, Porcellio scaber Latreille, 1804, Burmoniscus kathmandia (Schmalfuss, 1983), and Ligidium koreanum Flasarová, 1972, collected from Japan, were completely congruent with IIV-31 from the U.S.A. However, nucleotide sequence analysis showed that genetic variation exists among the IIV-31 species collected from the four collection sites in Japan and the North American IIV-31 species.

RÉSUMÉ Nous avons conduit une étude exhaustive des isopodes bleus au Japon en échantillonnant les espèces d’isopodes de huit sites localisés sur trois îles japonaises (Honshu, Kyushu et Okinawajima). Nous avons aussi interrogé des chercheurs japonais spécialistes de la faune du sol et récupéré des données disponibles sur internet détaillant les précédentes collection d’isopodes au Japon. A partir de l’analyse complète des données, nous concluons qu’ un total de huit espèces provenant de six familles (c’est-à-dire, Ligiidae, Alloniscidae, Philosciidae, Armadillidae, Porcellionidae et Armadillidiidae), en excluant deux espèces non identifiées, ont été observées sur 18 sites japonais. L’aire de répartition

4) e-mail: [email protected] © Koninklijke Brill NV, Leiden, 2012 DOI:10.1163/15685403-00003116 1270 S. KARASAWA, J. TAKATSUKA & J. KATO des isopodes bleus couvre tout le Japon (de l’île de Okinawajima à Hokkaido). L’observation des images de microscopie électronique à transmission (TEM) révèle des virions sans enveloppe dans le cytoplasme des cellules épithéliales d’Armadillidium vulgare (Latreille, 1804) du Japon. Des amorces ont été définies pour amplifier les séquences partielles du gène de la principale protéine de la capside (MCP) à partir de virus iridescents d’invertébrés (IIVs). La séquence prédite d’acides aminés du gène MCP de IIV isolée à partir des isopodes, A. vulgare, Porcellio scaber Latreille, 1804, Burmoniscus kathmandia (Schmalfuss, 1983), et Ligidium koreanum Flasarová, 1972, collectés au Japon a été complètement conforme avec IIV-31 des U.S.A. Cependant, l’analyse des séquences des nucléotides a montré qu’une variation génétique existe parmi le IIV-31 entre les espèces collectées à partir des quatre sites japonais et les IIV-31 des espèces nord américaines.

INTRODUCTION

Purple-blue isopods have been collected from terrestrial isopod communities in some regions of the world. In 1980, Cole & Morris (1980) and Federici (1980) found that the striking coloration of the isopods was caused by infection with inver- tebrate iridescent viruses (IIVs). IIVs are large ichosahedron-shaped DNA viruses belonging to the family Iridoviridae; there are currently two genera, Iridovirus and Chloriridovirus, recognized in this family (Chinchar et al., 2005). The genus Iri- dovirus contains viruses that have been isolated from several different orders of invertebrates and have particles (in ultrathin section) of around 120-130 nm in dia- meter. Due to limited genome sequence data, only two viruses in this genus, IIV-1 and IIV-6, currently have species status. Another 11 viruses are regarded as tenta- tive species within this genus. In contrast, the genus Chloriridovirus comprises a single viral species that has a particle size of about 180 nm diameter (in ultrathin section); within this genus, IIV-3 was originally isolated from mosquitoes. The virus studied in 1980 by Federici had a diameter of about 140 nm (negative stain) and icosahedral symmetry. The same study designated the viruses isolated from Armadillidium vulgare (Latreille, 1804) and Porcellio dilatatus Brandt, 1833 as IIV-31 and IIV-32, respectively. More recently, however, the virus infecting terrestrial isopods is considered a tentative species designated IIV-31 within the genus Iridovirus (cf. Chinchar et al., 2005). Infected isopods are light blue to violet in colour, have decreased photo and water responsiveness, and a shorter life span than non-infected individuals (Federic, 1980; Wijnhoven & Berg, 1999). Viral infection can also affect intra- and inter-specific interactions in terrestrial isopods (Grosholtz, 1992). Williams (2008) compiled a list of the natural host species for IIVs and established that 108 invertebrate host species had been reported in the literature, and that 19 of these species were terrestrial isopods. Isopods with the blue coloration that is the characteristic sign of IIV infection have been reported in the United States, United Kingdom, Netherlands, France, former Czechoslovakia and the Russian Federation (Hess & Poinar, 1984; Wijnhoven & Berg, 1999;