Tests of Rensch's rule in the Japanese fireflies Luciola cruciata and L. lateralis
Director, Laboratory of Biology
Key words: Rensch's rule, Luciola cruciata, Luciola lateralis, major axis analysis.
Luciola cruciata and L. lateralis are unlikely to conform to Rensch's rule.
Rensch's rule states that sexual size dimorphism increases with body size in animals where males are the larger sex and decreases with body size in those where females are the larger sex (Rensch, 1950; Fairbairn, 1997). There have been many studies on this rule, but it is not yet examined in fireflies where females are larger.
Iguchi (2007) examined the validity of this rule in the Japanese fireflies Luciola cruciata and L. lateralis collected at 14 sites in Nagano Prefecure, Japan (Fig. 1). Part of the data were obtained from Mitsuishi (1990). Male and female body lengths were measured, and then allometry between male and female body lengths was calculated by major axis analysis (Warton et al. 2006).
In the regression of female body length on male body length, the slope of the allometric equation was greater than 1 in both species (p < 0.02 for L. cruciata and p = 0.35 for L. lateralis, Fig. 2). This indicates that although females are the larger sex, sexual size dimorphism increases with body size in both species.
Neither firefly species is likely to conform to Rensch's rule, although the allometric slope was not significant in L. lateralis.
Fairbairn, D. J. (1997) Allometry for sexual size dimorphism: pattern and process in the coevolution of body size in males and females. Annual review of ecology and systematics 28: 659-687.
Iguchi, Y. (2007) Tests of Rensch's rule in the Japanese fireflies Luciola cruciata and L. lateralis. Zenkoku Hotaru Kenkyukai-shi (an annual journal of the Japan Association for Fireflies Research) 40: 32–34. (in Japanese).
Mitsuishi, T. (1990). Genji botaru (The Genji firefly). The Shinano Mainichi Shimbun, Nagano. (in Japanese).
Rensch, B. 1950, Die Abhängigkeit der relativen Sexualdiffernz von der körpergrösse. Bonner Zoologische Beiträge 1: 58-69.
Warton, D. I., Wright I. J., Falster D. S. and Westoby M. (2006) Bivariate line-fitting methods for allometry. Biological Reviews 81: 259-291.
Fig. 1. Map of study sites in Nagano Prefecure. 1: Iiyama, 2: Shigakogen, 3: Nakano, 4: Shinano, 5: Toyono, 6: Sakanaka, Nagano, 7: Sakayachi, Nagano, 8: Kinasa, Nagano, 9: Ogawa, 10: Miasa, Omachi, 11: Iyari, Omachi, 12: Matsushiro, Nagano, 13: Noguchi, Nagano, 14: Matsuo-kyo, Tatsno.
Fig. 2. Variation in male and female body length in Luciola cruciata and L. lateralis. Dashed line indicates that male body length is equal to female body length. LN denotes natural logarithm.