Research Article |
Corresponding author: Yûsuke N. Minoshima ( minoshima@kmnh.jp ) Academic editor: James Liebherr
© 2019 Yûsuke N. Minoshima.
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:
Minoshima YN (2019) First known larva of omicrine genus Psalitrus d’Orchymont (Coleoptera, Hydrophilidae). Deutsche Entomologische Zeitschrift 66(1): 107-118. https://doi.org/10.3897/dez.66.34300
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The larval morphology of the water scavenger beetle Psalitrus yamatensis Hoshina & Satô, 2005 is described based on a specimen collected from Fukuoka Prefecture, Kyushu, Japan. This is the first description of the larval morphology of the hydrophilid genus Psalitrus d’Orchymont, 1919, as well as the first description of larval chaetotaxy of the tribe Omicrini. Species-level identification of the larva was performed using DNA barcoding of a molecular marker: a 658 bp fragment of the mitochondrial cytochrome oxidase I. A description including chaetotaxy of head capsule and head appendages, diagnosis, and illustrations of the larva is provided. Psalitrus larvae can be distinguished from other known larvae of the tribe Omicrini by the morphology of the head and legs. The larva shares characters with other known larvae of Omicrini; potential plesiomorphies are shared with Cylominae and aquatic hydrophilids; some characters are also shared with larvae of Megasternini and Sphaeridiini.
chaetotaxy, COI, DNA barcoding, immature stages, Omicrini, water scavenger beetle
The tribe Omicrini, comprising 15 genera worldwide, is a group of small, terrestrial hydrophilid beetles belonging to the subfamily Sphaeridiinae (
Psalitrus d’Orchymont, 1919 is an omicrine genus containing 36 species from the Afrotropical, Oriental, Palaearctic, and Australian regions (
A tiny larva of a terrestrial hydrophilid resembling omicrine larvae was recently collected in Kitakyushu, Kyushu Island, Japan. The larva was collected together with two omicrine species: Psalitrus yamatensis Hoshina & Satô, 2005 and Peratogonus reversus. In this study, the larva is identified using a DNA barcoding method, described as the first known larva of the genus Psalitrus, and compared with other known larvae of the Sphaeridiinae and Cylominae.
A single larva extracted from leaf litter using Tullgren funnels was available for study (Table
List of specimens and GenBank Accession Number used in this study. AD: adult; L: larva.
Taxon | Stage | Extraction ID | Locality data / reference | Accession No. |
---|---|---|---|---|
Psalitrus yamatensis | L | YNME#16-9 | JAPAN: Fukuoka Pref., Kitakyushu-shi, Yahata-nishi-ku, Narumizu, Gôtôyama, 33°51.16’N, 130°46.51’E, 170 m; leaf litter; 11 Jun. 2016; YN Minoshima (Loc#2016-11) | LC484174 |
Psalitrus yamatensis | AD | YNME#85 | Same as above (Loc#2016-11) | LC484175 |
Psalitrus yamatensis | AD | YNME#86 | Same as above (Loc#2016-11) | LC484176 |
Psalitrus yamatensis | AD | YNME#16-4 | JAPAN: Ôita Pref., Nakatsu-shi, Hon-yabakei-machi, Atoda, 33°28.57’N, 131°11.81’E, 120 m; leaf litter; 28 May 2016; YN Minoshima (Loc#2016-8) | LC484173 |
Peratogonus reversus | AD | YNME#16-2 | Same as above (Loc#2016-8) | LC484172 |
Armostus ohyamatensis | AD | YNME#90 | Same locality as Loc#2016-11; see |
LC422744 |
Pairwise distances between individuals in analysis expressed as a percentage of nucleotide differences (p-distances).
1 | 2 | 3 | 4 | 5 | |
---|---|---|---|---|---|
1. Larva (YNME16-9) | |||||
2. Psalitrus yamatensis (YNME16-4) | 0.0% | ||||
3. Psalitrus yamatensis (YNME85) | 0.0% | 0.0% | |||
4. Psalitrus yamatensis (YNME86) | 0.0% | 0.0% | 0.0% | ||
5. Peratogonus reversus (YNME16-2) | 15.7% | 15.5% | 15.5% | 15.5% | |
6. Armostus ohyamatensis (LC422744) | 17.9% | 17.8% | 17.8% | 17.8% | 18.4% |
The specimen was examined using a Leica MZ16 (Leica Microsystems, Wetzlar) and an Olympus BX50 (Olympus, Tokyo). Illustrations were prepared with the aid of a drawing tube attached to the BX50; line drawings were prepared using the software Paint Tool SAI (Systemax Inc., Tokyo). Photographs were taken with digital cameras (Olympus OM-D E-M5 Mark II and E-M1 Mark II) attached to an Olympus SZX12 and the BX50. Composite images were created using focus stacking software Helicon Focus (Helicon Soft Ltd, Kharkov). Photographs were subsequently adapted in Adobe Photoshop Lightroom and Photoshop CC (Adobe Systems Inc., San Jose) as needed.
Morphological terminology follows
Total genomic DNA was extracted from the whole body using a DNeasy Blood & Tissue Kit (Qiagen, Hilden) (
Pairwise p-distance analysis (Table
Larva of Psalitrus can be distinguished from other known omicrine larvae (Omicrus Sharp, 1879, Peratogonus, and unidentified larva of Noteropagus or Paromicrus) by: (1) nasale with four distinct teeth; (2) asymmetrical median projection on nasale absent; (3) epistomal lobe absent; (4) mentum very deeply emarginate dorsally; and (5) legs four-segmented.
The Psalitrus larva is also similar to other terrestrial sphaeridiine larvae; however, it can be distinguished by the addition of following combination of characters: (1) coronal line absent; (2) PA6 and PA13 absent; (3) antennomere 2 with a small basal additional pore dorsally; (4) antennal sensorium slender, long; (5) mandibles almost symmetrical, both mandibles with two teeth; (6) MN1 close to MN2; (7) MN2–4 forming a triangular group; (8) maxillae symmetrical; (9) maxilla with well-sclerotised inner appendage; (10) submentum without large lateral extension; (11) labium without hypopharyngeal lobe; (12) LA10 stout seta; (13) legs short, four-segmented; and (14) median lobe of spiracular atrium with median emargination posteriorly.
1 presumably first instar larva; see Table
See generic diagnosis.
General morphology. Length 1.2 mm in the specimen fixed by ethanol; head width 0.2 mm. Body (Fig.
Head. Head capsule subquadrate (Fig.
Antenna (Fig.
Mandibles (Fig.
Maxilla (Fig.
Labium (Fig.
Thorax. Thoracic segments bearing microtrichiae, which may catch and securely keep the dirt on its integument, except for ventral area between legs; this area bare and not bearing dust as other parts. Prothorax slightly wider than head capsule (Fig.
Abdomen 10-segmented, widest in anterior half, then tapering posteriad (Fig.
Primary chaetotaxy of head. Frontale (Fig.
Parietale (Fig.
Head appendages. Antenna (Fig.
Mandibles (Fig.
Maxilla (Fig.
Labium (Fig.
Adults and the larva were collected from leaf litter (for the photograph of collecting locality, see
Sphaeridiinae | Cylominae | |||||
Omicrini | Coelostomatini | Protosternini | Sphaeridiini | Megasternini | ||
Nasale | With teeth | With median projection to aggregated teeth-like projection | Without teeth | With a median projection | Without teeth | With/Without teeth |
Asymmetrical median projection on nasale | Present/absent | Absent | Absent | Absent | Absent | Absent |
Epistomal lobe | Present/absent | Present | Present | Absent | Absent | Present |
Notch on left side of nasale | Absent | Absent | Absent | Present | Present | Absent |
FR2 | Absent | Present | Present | Present | Present | Present |
FR7 | Present | Present | Present | Absent | Absent | Present |
PA6 | Absent | Present | Present | Present | Present | Present |
Mandibles | Symmetrical | Symmetrical/Asymmetrical | Symmetrical/Asymmetrical | Asymmetrical | Asymmetrical | Symmetrical/Asymmetrical |
Stipes | Symmetrical | Symmetrical | Symmetrical/Asymmetrical | Asymmetrical | Asymmetrical | Symmetrical/Slightly asymmetrical |
Chaetotaxy of inner face of stipes | MX7–11 | gMX2 | MX7–11 | gMX2 | gMX2 | MX7–11/gMX2 |
MX17 | Absent | Present | Present | Present | Absent | Present |
Hypopharyngeal lobe | Absent | Present/Absent | Absent | Present | Present | Present/Absent |
LA9 | Absent | Present | Present | Absent | Absent | Present |
LA10 | Stout | Trichoid | Trichoid | Trichoid | Trichoid | Trichoid |
LA11 | Absent | Present/Absent | Present | Present | Absent | Present |
LA12 | Absent | Present/Absent | Present | Present | Present | Present |
Legs | Reduced to 4 segments/5-segmented | 5-segmented | 5-segmented | Short rod-like, 5-segmented | Reduced, unsclerotized to 2-segmented | 5-segmented |
Basal additional pore on dorsal surface antennomere 2 | Present | Absent | Absent | Absent | Present | Absent |
The larva of Psalitrus shows us multiple differences from other known larvae of Omicrini (Omicrus, Peratogonus, and an unidentified larva of Noteropagus/Paromicrus;
The phylogenetic position of the members of Omicrini, which is an early-diverging clade within the subfamily Sphaeridiinae (
The Psalitrus larva have distinct teeth on the nasale (Fig.
Asymmetry of mandibles and maxillae are characteristics of megasternine and sphaeridiine larvae. Asymmetry of mandibles has evolved multiple times in different clades within Hydrophilidae, including Coelostomatini and Protosternini; in contrast, asymmetry of maxillae is less common in Hydrophilidae (
Legs of Psalitrus larva are well sclerotised but short and reduced to four segments (Figs
This is the first detailed description of the larval chaetotaxy of Omicrini. Even though only one larva is available in this study and intraspecific variation is therefore still unclear, the chaetotaxy of Psalitrus larva shows apparent differences from the other larvae of Sphaeridiinae. Homology of some setae are still unclear, further investigations of omicrine larvae are essential to solve the homology of the sensilla.
Absence of FR2 (Fig.
On the parietale (Fig.
Arrangements of mandibular sensilla MN1–3 (forming a transverse row) and MN2–4 (forming a triangular group) (Fig.
The inner face of stipes of maxilla bears five setae (MX7–11) (Fig.
The arrangement of LA1 and LA2 is unique, as LA1 is posterolateral to LA2 in other known hydrophilid larvae. The character state of LA10 (stout setae; Fig.
Psalitrus larva have characters shared with other known larvae of Omicrini, including potential synapomorphies of the tribe, the presumable plesiomorphies shared with aquatic hydrophilids and Cylominae, and the supposed derived characters, which are shared with Megasternini + Sphaeridiini, for an adaptation to terrestrial habitats.
I am grateful to Martin Fikáček (National Museum, Praha, Czech Republic) for his critical reading and helpful comments on the draft. I thank Miguel Archangelsky (LIESA-CIEMEP, Esquel, Argentina) and Andrew E. Z. Short (University of Kansas, Lawrence, USA) for valuable comments on the manuscript. Article processing charge was generously supported by the Museum für Naturkunde, Berlin, Germany. This study was supported by Fujiwara Natural History Foundation (2017) and JSPS KAKENHI Grant Number JP17K15187.