Research Article |
Corresponding author: Kôji Sasakawa ( ksasa@chiba-u.jp ) Academic editor: Thorsten Assmann
© 2018 Kôji Sasakawa, Hirotarô Itô.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Sasakawa K, Itô H (2018) Taxonomic notes on the ground beetles in the genus Trephionus Bates, 1883 from central Honshu, Japan (Coleoptera, Carabidae, Sphodrini, Synuchina). ZooKeys 742: 91-104. https://doi.org/10.3897/zookeys.742.23752
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Trephionus Bates, 1883, a Japanese endemic genus in the subtribe Synuchina (Coleoptera, Carabidae, Sphodrini), is revised taxonomically based mainly on the shape of the endophallus, a membranous inner sac everted from the aedeagus of the male genitalia. Three known species from central Honshu, T. kinoshitai Habu, 1954; T. shibataianus Habu, 1978; and T. babai Habu, 1978, are re-defined based on this genital character, and five new species are described from the region: T. cylindriphallus Sasakawa, sp. n., T. niumontanus Sasakawa, sp. n., T. inexpectatus Sasakawa & Itô, sp. n., T. abiba Sasakawa & Itô, sp. n., and T. bifidilobatus Sasakawa & Itô, sp. n. The observed interspecies differences in endophallus morphology are discussed in terms of the species-level phylogeny and genus-level taxonomy of Trephionus.
Cryptic species, endophallus, male genitalia, new species, phylogeny, taxonomy
Trephionus Bates, 1883 is a Japanese endemic genus in the subtribe Synuchina (Coleoptera, Carabidae, Sphodrini) that is distributed in Honshu, Shikoku, and Kyushu (
Our recent research demonstrated that the morphological characteristics of the male endophallus are also taxonomically useful in Trephionus. In this study, we revise two species distributed widely in central Honshu: T. kinoshitai Habu, 1954 and T. shibataianus Habu, 1978. Based on the endophallus morphology, the two species and a related species, T. babai Habu, 1978, are re-defined, and five new species are described. The implications of these results for the species-level phylogeny and genus-level taxonomy of Trephionus are discussed.
Specimens from various localities in central Honshu were examined (Fig.
To investigate male genital characters, all male specimens other than a male of T. kinoshitai were dissected. The endophallus was everted by injecting toothpaste (White & White; LION, Tokyo, Japan) using an insulin syringe with a pre-attached 29-gauge needle (SS-10M2913; TERUMO, Tokyo, Japan). A new terminology for characters on the endophallus is proposed herein because homologies of most characters between Trephionus and other carabid species could not be established. Body length was measured from the mandible apices to the elytral end. To represent the size/shape of some body parts, the following three measurements are defined: (i) the pronotum index (PI) calculated as the width at the widest part divided by the width at the level of postero-marginal setae, which was used by
Distribution of Trephionus spp. in central Honshu based on specimens with unambiguous identities. ◆ T. nikkoensis ★ T. mikii ■ T. kinoshitai ▼ T. cylindriphallus sp. n. ▲ T. niumontanus sp. n. ● T. babai ○ T. subcavicola △ T. shibataianus ◇ T. inexpectatus sp. n. ☆ T. abiba sp. n. □ T. bifidilobatus sp. n. The type localities of T. nikkoensis, T. mikii, and T. subcavicola, which were not examined in this study, are shown, although the validities of their species statuses remain to be examined.
The eight species are similar to each other and share the following adult morphological character states.
External characters (Figs
Pronotum moderately convex, widest at apical 1/4–1/3; anterior margin emarginated, narrower than posterior margin (measured at the level of the postero-marginal setae); anterior angles rounded at apex; lateral margins arcuate except near the base, where roughly sinuate; two marginal setae on each side, anterior setae near widest pronotal point and posterior setae at the posterior end of lateral margins; posterior margin slightly emarginated at median area, arcuate anterolaterally in lateral areas, with the curvature stronger than that of the lateral margins; posterior angles not denticulate; pronotal surface smooth except for posterior margin, which is slightly punctate in some specimens; median line distinct in the middle, but rudimentary or absent near anterior or posterior margins; laterobasal impressions single, wide, moderately concave; both sides of the impressions connected with moderately depressed transverse line.
Elytra oblong, moderately convex; shoulders and apices rounded, not denticulate; intervals barely convex; scutellar stria present, not connected to stria 1; stria 1 connected to stria 2 behind basal margin; one setigerous puncture between the connection of stria 1 and stria 2 and at anterior end of stria 2; interval 3 lacks setigerous punctures. Male sternum 7 lacks sexual characteristics. Legs slender; mid and hind first tarsal segment sulcate outer side in all species, on inner side in some species; tarsal claws smooth inside, not denticulate.
Male genital characters (Figs
Female genital characters: Gonocoxite 2 digitate and slender, with one ensiform seta on both medial and lateral side; apical nematiform seta absent.
Trephionus
kinoshitai
:
Synuchus
nikkoensis
kinoshitai
:
5♂1♀, Kamishiro asl. ca. 1084 m, Mt. Shirouma, Hakuba-mura, Nagano Pref. (36.739801°N, 137.813480°E), 7–16.IX.2014 (Pitfall traps baited with 10% acetic acid), K. Sasakawa leg.
Similar to T. cylindriphallus sp. n. and T. niumontanus sp. n. in having secondary setae on dorsal side of mid and hind tarsal segment 5, but distinguished from the former by distinctly sinuate lateral margin of pronotum near base and from the latter by smaller body.
Body length: ♂, 8.7–10.2 mm (mean ± SD: 9.5 ± 0.61 mm, n = 5); ♀, 9.0 mm (n = 1). PI: ♂, 1.21–1.29 (mean: 1.27, n = 5); ♀, 1.25 (n = 1). Head and pronotum black; elytra blackish brown to black. Pronotal lateral margins sinuate before hind angles (Fig.
Holotype: ♂, Kawamata, University Forest in Chichibu, The University of Tokyo, Ôtaki, Chichibu-shi, Saitama Pref., 16.X.2009, N. Nishiyama leg. Paratypes: 1♂2♀, same data as the holotype; 1♂3♀, same locality as the holotype (1♂, 17.X.2008, K. Ômura leg.; 1♀, 1.IX.2005, Ômura leg.; 1♀, 6.X.2005, Ômura leg.; 1♀, 10.IX.2009, K. Nishiyama leg.); 1♂, Ôjiro near Abe Pass, Minobu-cho, Yamanashi Pref., 1–2.X.2003, K. Sasakawa leg.; 1♂, Shimakura-rindô, asl. ca. 1000 m, Ôshika-mura, Nagano Pref., 14.IX.1998, M. Hama leg.
Similar to T. kinoshitai and T. niumontanus sp. n. in having secondary setae on dorsal side of mid and hind tarsal segment 5, but distinguished from the former by barely sinuate lateral margin of pronotum near base and from the latter by smaller body.
Body length: ♂, 8.9–9.8 mm (mean ± SD: 9.4 ± 0.36 mm, n = 5); ♀, 8.2–10.0 mm (mean ± SD: 9.3 ± 0.84 mm, n = 5). PI: ♂, 1.23–1.25 (mean: 1.24, n = 5); ♀, 1.19–1.24 (mean: 1.22, n = 5). Dorsal surface blackish brown to black. Pronotal lateral margins before hind angles barely sinuate (Fig.
The name refers to the robust, cylindrical shape of the endophallus.
Trephionus
kinoshitai
:
Holotype: ♂, Mt. Kunimi, asl. ca. 480 m, Fukui-shi, Fukui Pref., 27.VI.2012, S. Inoue leg. Paratypes: 1♀, same data as the holotype; 2♀, Mino-cho, asl. ca. 480 m, Fukui-shi, Fukui Pref., 27.VI.2012, S. Inoue leg.
Similar to T. kinoshitai and T. cylindriphallus sp. n. in having secondary setae on dorsal side of mid and hind tarsal segment 5, but distinguished by larger body.
Body length: ♂, 10.6 mm (n = 1); ♀, 10.9 mm (mean ± SD: 10.9 ± 0.03 mm, n = 2). PI: ♂, 1.23 (n = 1); ♀, 1.25–1.26 (n = 2). Dorsal surface black. Pronotal lateral margins sinuate before hind angles (Fig.
The name refers to the Niu Mountains, where the type specimens were collected.
Trephionus
babai
:
1♂2♀, Mt. Ishikiri (entrance of the Ishikiri Cave), Haguro, Tainai-shi, Niigata Pref. (38.051608°N, 139.435625°E), 7–9.X.2017, H. Itô leg.
Similar to T. nikkoensis in general appearance and the absence of secondary setae on dorsal side of mid and hind tarsal segment 5, but distinguished by wider pronotum and elytral microsculpture, which is isodiametric in T. babai, but moderately transverse mesh in T. nikkoensis (see Habu, 1978). Distinguished from sympatric T. abiba sp. n. by larger body and less sinuate pronotal lateral margin near the base.
Body length: ♂, 9.3 mm (n = 1); ♀, 9.8–10.3 mm (n = 2). PI: ♂, 1.30 (n = 1); ♀, 1.34–1.37 (n = 2). Dorsal surface black. Pronotal lateral margins before hind angles barely sinuate (Fig.
Trephionus
shibataianus
:
1♂, Karasawa Spa, Chino-shi, alt. ca. 1900 m (the foot of Mt. Naka, the Yatsugatake Mountains), Nagano Pref., 13–28.VIII.1999, R. Shimoyama leg.
Diagnosis. Similar to T. subcavicola Uéno and three species to be described below in having truncate apex of aedeagus. Readily distinguished from T. subcavicola by the absence of inner sulcus of mid and hind tarsal segment 1 (present in T. subcavicola;
Body length: ♂, 8.4 mm (n = 1). PI: ♂, 1.19 (n = 1). Head and pronotum black; elytra blackish brown to black. Pronotal lateral margins sinuate before hind angles (Fig.
Holotype: ♂, Kitazawa Pass, alt. ca. 2000 m, Hase-mura, Nagano Pref., 7–15.X.1998, M. Hama leg.
Readily distinguished from T. subcavicola by the absence of inner sulcus of hind tarsal segment 5 (
Body length: ♂, 8.8 mm (n = 1). PI: ♂, 1.26 (n = 1). Dorsal surface black. Pronotal lateral margins slightly sinuate before hind angles (Fig.
The name refers to the unexpected discovery of this species, which is externally similar to other congeneric species with simple aedeagus apex such as T. kinoshitai, T. cylindriphallus and T. babai.
Holotype: ♂, Mt. Ishikiri (entrance of the Ishikiri Cave), Haguro, Tainai-shi, Niigata Pref. (38.051754°N, 139.435703°E), 23.V.2013, H. Itô leg. Paratype: 1♀, same data as the holotype.
Among the species with truncate aedeagal apex, similar to T. shibataianus and T. bifidilobatus sp. n. in having small body. Distinguished from the former by larger PI (i.e., wider pronotum) and from the latter by blacker dorsal surface (Figs
Body length: ♂, 8.1 mm (n = 1); ♀, 9.8 mm (n = 1). PI: ♂, 1.27 (n = 1); ♀, 1.31 (n = 1). Head and pronotum black; elytra blackish brown to black (Fig.
The name is an anagram of the specific name of the sympatric species T. babai.
Holotype: ♂, Kotosawa, alt. ca. 310 m, Mitake, Oume-shi, Tokyo (35.795931°N, 139.168746°E), 10–12.IX.2009, K. Sasakawa leg.
Diagnosis. Similar to T. shibataianus and T. abiba sp. n. in having truncate aedeagal apex and small body, but distinguished by larger PI (i.e., wider pronotum) and reddish brown elytra.
Body length: ♂, 8.2 mm (n = 1). PI: ♂, 1.32 (n = 1). Head and pronotum black, elytra reddish brown. Pronotal lateral margins sinuate before hind angles (Fig.
The name refers to the bifid apex of the dorsoapical lobe of the endophallus.
Dorsal view of Trephionus species: 2 T. kinoshitai, male from Mt. Shirouma 3 T. cylindriphallus sp. n., holotype male 4 T. niumontanus sp. n., holotype male 5 T. babai, male from Mt. Ishikiri 6 T. shibataianus, male from Mt. Naka 7 T. inexpectatus sp. n., holotype male 8 T. abiba sp. n., holotype male 9 T. bifidilobatus sp. n., holotype male.
Left lateral (a) and dorsal (b) views of the endophallus and ventral view of the aedeagal apex (c) of Trephionus spp.: 10 T. kinoshitai from Mt. Shirouma 11 another specimen of T. kinoshitai from Mt. Shirouma, showing directions and examples of measurements for descriptions 12 T. cylindriphallus sp. n., holotype male; 13 T. cylindriphallus sp. n., a paratype male from Abe Pass 14 T. niumontanus sp. n., holotype male 15 T. babai from Mt. Ishikiri; 16 T. shibataianus from Mt. Naka 17 T. inexpectatus sp. n., holotype male 18 T. abiba sp. n., holotype male 19 T. bifidilobatus sp. n., holotype male. Abbreviations: AW, the width of the aedeagus at the ostium from the dorsal view; BD, the basal diameter of the lobe from dorsal view; da, dorsoapical lobe; db, dorsobasal lobe; go, gonopore; lb, left laterobasal lobe; rb, right laterobasal lobe; sl, sclerotized lobe.
This study revealed that Trephionus has diversified in terms of the male endophallus and there are “cryptic species” that can be distinguished only by the endophallus. These findings indicate the need for re-definition of the known Trephionus species based on this genital morphology. To this end, new specimens from the type localities will be required for most species because the dissection of the membranous parts of the genitalia, such as the endophallus, is usually difficult in old specimens and because the type specimens of all of the known Trephionus were collected over 40 years ago (
Interspecies differences in endophallus morphology and distribution give insights into the phylogeny and differentiation of Trephionus. Of the eight species treated here, T. kinoshitai, T. cylindriphallus, and T. niumontanus are considered to be closely related because they share a character that is found only in a few species of Synuchina, i.e., secondary setae on the dorsal side of the mid and hind last tarsal segments (
Our results also provide insights into the genus-level taxonomy. Despite the marked morphological diversification, the endophallus of all of the species examined has two lobes in common: the dorsoapical and sclerotized lobes. Regarding the dorsoapical lobe, a similar lobe has been reported in some groups of Carabidae (e.g.,
We thank M. Takahashi (Matsumoto) and S. Inoue (Fukui) for offering important specimens. This study was partly supported by the Japan Society for the Promotion of Science (JSPS) to KS (nos. 25830150 and 17K15171).