A molecular phylogeny of Pseudocrangonyx from Japan, including a new subterranean species (Crustacea, Amphipoda, Pseudocrangonyctidae)

Abstract

A subterranean species of pseudocrangonyctid amphipod, Pseudocrangonyx gudariensis Tomikawa & Sato, sp. n., is described from the spring-fed stream Gudari-numa in Hakkoda Mountains, Aomori Prefecture, northern Japan. Pseudocrangonyx gudariensis is morphologically similar to P. coreanus Uéno, 1966 and P. febras Sidorov, 2009 based on its relatively small body size, small number of articles of rami of pleopods, and urosomite 1 without basal setae. However, P. gudariensis is distinguished from those species based on the following characteristics: from P. coreanus, antenna 2 of female without calceoli, palmar margins of gnathopods 1 and 2 with distally notched robust setae, inner margin of inner ramus of uropod 2 with 4 robust setae, and basal part of inner ramus of uropod 2 without slender seta; and from P. febras, carpus of gnathopod 2 without serrate robust setae on posterodistal corners, peduncle of pleopods 1 and 2 with setae, and longer article 2 of uropod 3. Phylogenetic analyses using nuclear 28S rRNA and histone H3, and mitochondrial cytochrome c oxidase subunit I and 16S rRNA markers showed that P. gudariensis is placed among known Pseudocrangonyx Akatsuka and Komai, 1922 species. However, its exact phylogenetic position within the genus could not be determined. The polyphyly of the Japanese Pseudocrangonyx species indicates that multiple colonization events of Pseudocrangonyx ancestors to the Japanese Archipelago could have occurred. The reliability of the past Pseudocrangonyx records from Japan is briefly discussed.

A new species of the genus Pseudocrangonyx (Crustacea, Amphipoda, Pseudocrangonyctidae) from Korea

“…Pseudocrangonyx daejeonensis is also similar to P. febras Sidorov, 2009 and P. gudariensis Tomikawa and Sato in Tomikawa et al (2016) in having 1) relatively smaller body size, 2) eyes completely absent, and 3) urosomite 1 without basal setae. However, P. daejeonensis is distinguished from these two species by the following features: from P. febras (features of P. febras in parentheses), 1) antenna 1 shorter than 0.4 times as long as body length (longer than 0.7 times), 2) peduncular article 2 of antenna 1 0.5 (0.7) times as long as article 1, 3) palp article 2 of mandible with 3 (7) setae, 4) carpus of male gnathopod 2 without serrate robust setae on posterodistal corner (with serrate robust setae), 5) fewer articles of pleopodal rami, up to 4 (more, up to 6), 6) inner ramus of uropod 1 with 2 inner marginal robust setae (5 inner and 3 outer marginal robust setae), 7) outer ramus of uropod 1 without setae (with 2 robust setae), and 8) inner ramus of uropod 2 with inner robust seta (3–4 inner and 2–3 outer marginal robust setae); from P. gudariensis (features of P. gudariensis in parentheses), 1) basal part of inner ramus of uropod 1 with 1 slender setae (with 3 slender setae), 2) outer ramus of uropod 1 without setae (with 2 setae), 3) inner margin of inner ramus uropod 2 with 1 robust setae (with 4 robust setae), and 4) telson lobe with 1 robust seta apically (with 2 robust setae apically).…”

“…Methods of the genomic DNA extraction, PCR and DNA sequencing were performed following Tomikawa et al (2016). Accordingly, nine DNA sequences of nuclear 28S rRNA, histone H3, COI and 16S rRNA from three Korean Pseudocrangonyx specimens were newly obtained in this study, and deposited into the International Nucleotide Sequence Database Collaboration (INSDC) through the DNA Data Bank of Japan (Table 1).…”

“…The OTU set for phylogenetic analyses was almost identical to that used in the previous phylogenetic analyses in Tomikawa et al (2016) with the DNA sequences of P. elegantulus Hou in Zhao and Hou (2017) (Table 1). The alignments of H3 and COI were trivial, as no indels were observed.…”

“…Amphipod species of the genus Pseudocrangonyx Akatsuka & Komai, 1922 have been known from subterranean waters and springs in Japan, the Korean Peninsula, Eastern China, and the Far East of Russia (Sidorov and Holsinger 2007; Tomikawa et al 2016; Zhao and Hou 2017). Among the 22 known species of Pseudocrangonyx , only two species were recorded in Korean waters (Uéno 1966): P. asiaticus Uéno, 1934 and P. coreanus Uéno, 1966.…”

“…Because recent systematic studies of Pseudocrangonyx in other regions have shown high species diversity within this genus (e.g., Tomikawa et al 2016), it is highly possible that the true species diversity of Pseudocrangonyx amphipods inhabiting the Korean Peninsula remains under-estimated.…”