Greater degree of body size plasticity in males than females of the rhinoceros beetle Trypoxylus dichotomus
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Female body size is more sensitive to the environmental conditions during development than male body size in many insect species with female-biased sexual size dimorphism (SSD) (i.e., females are larger than males). However, the sexual difference in body size plasticity is largely unknown in species with male-biased SSD. Here, I conducted a laboratory experiment using low- and high-quality diets to examine sexual differences in body size plasticity in the male-larger rhinoceros beetle Trypoxylus dichotomus Linnaeus, 1771 (Coleoptera: Scarabaeidae). I found that male body size was much more greatly affected by nutritional status than female body size. The stronger condition dependency in male body size is likely associated with sexual selection for male body size. Furthermore, in wild-caught beetles, males showed larger body size differences between years within populations, while the body size of females was more constant. Within populations and years, male body size also showed greater variation than female body size. In addition, SSD of field-caught beetles was usually much smaller than that of lab-reared beetles of corresponding populations. Thus, the stronger condition dependency of male body size in this species probably has profound effects on the variation of observed body size and SSD among and within populations.
KeywordsColeoptera Intrasexual selection Life-history traits Phenotypic plasticity Scarabaeidae Sexual size dimorphism (SSD)
I would like to thank Dr. Takuma Takanashi, Hiroshi Makihara and Aika Kawachi for their help in collecting beetles and morphological measurement. I am very grateful to the two anonymous reviewers and the associate editor for valuable comments on the manuscript. This study was supported by JSPS Grant-in-Aid for Research Activity Start-up, Grant number 17H06901.
- Bonduriansky R (2007) The evolution of condition-dependent sexual dimorphism. Am Nat 169:9–19Google Scholar
- DeBlock M, Stoks R (2008) Short-term larval food stress and associated compensatory growth reduce adult immune function in a damselfly. Ecol Entomol 33:796–801Google Scholar
- Fairbairn DJ (2005) Allometry for sexual size dimorphism: testing two hypotheses for Rensch’s rule in the water strider Aquarius remigis. Am Nat 166:69–84Google Scholar
- Lovich JE, Gibbons JW (1992) A review of techniques for quantifying sexual size dimorphism. Growth Dev Aging 56:269–269Google Scholar
- Maekawa M (2005) A preliminary study on movement of beetles living on sappy trees in a secondary oak forest in rural landscape, central Japan. Bull Inst Nat Educ Shiga Heights 42:13–16 (in Japanese) Google Scholar
- Stillwell RC, Morse GE, Fox CW (2007) Geographic variation in body size and sexual size dimorphism of a seed-feeding beetle. Am Nat 170:358–369Google Scholar