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1 August 2011 Male Dimorphism in the Harem-Forming Gnathiid Isopod Elaphognathia discolor (Crustacea: Isopoda)
Katsuhiko Tanaka, Eijiroh Nishi
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Previously unreported males of a gnathiid isopod were found in reproductive aggregations of the harem-forming gnathiid Elaphognathia discolor. Although the male gnathiids were small in size and morphologically different from E. discolor males, the male sexual organ, appendix masculina, was similar to that of E. discolor males, and possible conspecific larvae and females of the small male gnathiid were never found. In the laboratory, the small male gnathiids as well as male E. discolor successfully copulated with female E. discolor, and the development of embryos in female brood pouches was observed. Offspring of small male gnathiids develop to adults of E. discolor after molting three times, or small male gnathiids after molting two times. Thus, the small male gnathiid was concluded to be an alternative male form compared to the regular large male form of E. discolor. This male polymorphism was thought to have a genetic basis, since no small male specimens appeared in offspring of regular E. discolor males. Field sampling showed that a regular large male formed a harem composed of one large male and several females and never coexisted with other large males as previously reported. However, small males were often found together with large males. Therefore, small males are thought to be sneakers intruding into harems dominated by large males.

© 2011 Zoological Society of Japan
Katsuhiko Tanaka and Eijiroh Nishi "Male Dimorphism in the Harem-Forming Gnathiid Isopod Elaphognathia discolor (Crustacea: Isopoda)," Zoological Science 28(8), 587-592, (1 August 2011).
Received: 20 December 2010; Accepted: 1 January 2011; Published: 1 August 2011
gnathiid isopod
male dimorphism
small male
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