Biodiversity Data Journal :
Taxonomic Paper
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Corresponding author: Tatsushi Takayanagi (salixalta@gmail.com)
Academic editor: Vesela Evtimova
Received: 16 Apr 2021 | Accepted: 24 Jun 2021 | Published: 08 Jul 2021
© 2021 Tatsushi Takayanagi, Kazunori Yoshizawa
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:
Takayanagi T, Yoshizawa K (2021) The first record of Caenis rivulorum (Ephemeroptera: Caenidae) from Japan. Biodiversity Data Journal 9: e67413. https://doi.org/10.3897/BDJ.9.e67413
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Caenis rivulorum Eaton, 1884 is widely distributed and has been reported from a wide range in the Palearctic Region.
We report this species from Japan for the first time, from five localities of Hokkaido, based on morphology and molecular data.
Ephemeroptera, mayflies, Caenidae, Caenis, Japan, Hokkaido, COI
The genus Caenis Stephens, 1836 (Ephemeroptera: Caenidae) is a cosmopolitan group of mayflies with more than 140 described species and is one of the most diversified genus of mayflies (
Adult mayflies were collected from five distinct localities of Hokkaido in 2019 and 2020 (Fig.
Locations of collecting localities. Loc. 1 Usotan, Hamatonbetsu-cho, Hokkaido, Japan.
Total DNA was extracted from the specimens using Qiagen DNeasy Tissue Kit (QIAGEN, Venlo, The Netherlands). DNA of male adults was extracted from the whole abdomen. The exoskeleton was kept for further observation. DNA of female adults was extracted from the thoracic muscle tissues. The barcode region of COI gene was amplified by the PCR method using the primer set, LCO1490 and HCO2198 (
All sequence data were aligned automatically using MAFFT v.7.429 (
Caenis dimidiata var. rivulorum Eaton, 1884 in
Caenis rivulorum Eaton, 1884 in
Caenis nivea Bengtsson, 1917 in
Caenis nigroforceps Zhou, Gui & Su, 1997 in
Male adults (Fig.
Female adults (Fig.
Body length: 2.6–2.8 mm; fore-wing length: 2.8–3.1 mm; caudal filaments length: 0.8–1.0 mm.
Most features similar to male. Abdomen seems yellow by inner eggs and some brownish pigmentation on surfaces of each segments.
Eggs (Fig.
Longitudinal length ca. 115 μm, latitudinal length ca. 54 μm. Surface fine-granulated, with polar caps on both ends. Micropyle widens to aperture.
Male adults (Fig.
Compared to the European materials examined in
Thorax: Prosterunum triangular (Fig.
Genital characters:
Female adults (Fig.
Female adult C. rivulorum is similar to C. horaria but, by using the following characters, they can be distinguished from C. horaria: mesothorax with fin-shaped process (absent in C. horaria) (Fig.
Eggs (Fig.
The features of eggs similar to C. horaria. According to
TIM2+F+I+G4 substitution model was selected as the best fit model according to BIC (Bayesian Information Criterion). By the Maximum Likelihood analysis of COI sequences, the present samples were clustered with the German C. rivulorum (Fig.
Mean/Standard deviation/minimum-maximum values (%) of intraspecific pairwise genetic distance (p-distance) between Japanese and European samples. "JP" means "Japanese" materials examined this time.
Species |
C. rivulorum, JP |
C. rivulorum |
C. rivulorum, JP |
0.47/0.40/ 0–0.97 |
11.3/0.19/ 11.0–11.59 |
C. rivulorum |
- |
1.45/0.78/ 0.16–2.42 |
The genital characters of the Japanese specimens agree well with those of the European specimens as described in
According to the morphological observations, we identified the Japanese samples as C. rivulorum, as is noted in Diagnosis, Taxon treatments. However, the genetic difference between Japanese (Hokkaido) samples and European (German) C. rivulorum is significantly larger (> 11%) than 2.2%, which has been generally recognised as a level of divergence delimiting species across diverse insect taxa (
The Japanese fauna of the genus Caenis are poorly studied. The following two named species have been reported from Japan to date (
In addition, a couple of unidentified species have been reported, based on larval stages: Caenis sp. CA and Caenis sp. CB (
Recently, an additional unidentified species of the genus was reported from Ura-Bandai, Fukushima, Japan (
We thank Yuto Okita and Dr. Tomiko Ito for providing samples, Alyssa L. Suzumura for editing the English manuscript. We are grateful to all reviewers for critical advice.