水生動物 第 2020 巻 令和 2 年 3 月 Morphometric approaches reveal sexual differences in the carapace shape of the horsehair crab, Erimacrus isenbeckii (Brandt, 1848) Kenji Toyota1,2*, Kentaro Izumi3, Takashi Ichikawa4, Tsuyoshi Ohira1, Ken Takeuchi2,5 1Department of Biological Sciences, Faculty of Science, Kanagawa University, 2946 Tsuchiya, Hiratsuka, Kanagawa, 259-1293, Japan. 2Department of Biological Science and Technology, Faculty of Industrial Science and Technology, Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo 125-8585, Japan. 3Faculty & Graduate School of Education, Chiba University, 1-33 Yoyoi-cho, Inage-ku, Chiba-shi, Chiba 263-8522, Japan. 4Tokyo University of Agriculture, 196 Yasaka, Abashiri-shi, Hokkaido, 099-2493, Japan. 5Department of Biological Science and Technology, Faculty of Industrial Science and Technology, Tokyo University of Science, 102-1 Tomino, Oshamambe-cho, Yamakoshi-gun, Hokkaido, 049-3514, Japan *Corresponding author; e-mail:
[email protected]. Abstract Animal shape has become sophisticated through evolution or phenotypic plasticity to adapt and survive changing environmental conditions. Sexual differences, which are sex-specific characteristics, form an important research topic that has also long fascinated biologists. Morphometrics is a traditional approach that enables the quantitative description and interpretation of variation in shape based on morphological features. In this study, we attempted to apply two morphometrics approaches (landmark-based or measurement-based) to identify sexual dimorphic traits in the carapace of the horsehair crab, Erimacrus isenbeckii (Brandt, 1848). Both approaches revealed that its carapace showed apparent sexual dimorphism, enabling the discrimination of the male and female carapace with more than 90 % accuracy. Moreover, the landmark-based approach found that carapace shape showed fluctuating asymmetry as well as directional asymmetry in both males and females.