1 August 2012 The Inheritance of Intrasexual Dimorphism in Female Diving Beetles (Coleoptera: Dytiscidae)
Toshio Inoda, Roger Härdling, Souichirou Kubota
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Many species of Dytiscus diving beetles exhibit intrasexual dimorphism, e.g., the elytra is smooth in some females and grooved in others. However, the expression of the grooves and whether they are a product of heredity or the environment remain unknown. One Japanese species, Dytiscus sharpi sharpi Wehncke, 1875, also shows female dimorphism, with grooved and smooth morphs, while D. sharpi validus Régimbart, 1899, only has a single morph (the grooved type). A hybrid of the two species should therefore provide a means of sorting out how the grooves are inherited. We found two independent wetlands of D. sharpi sharpi in Chiba Prefecture, Japan. One was a place where a high proportion of grooved females lived, and the others had high proportions of smooth females. After five to eight generations of beetles from two populations with different proportions of grooved females were reared under aquarium conditions constituting a common garden design, i.e., water temperature, water depth, and presence of a plant for oviposition, the differences remained. We mated smooth virgin females of D. sharpi sharpi with males of D. sharpi validus to obtain hybrid offspring. The elytral traits of the hybrid females produced only grooved forms. These results suggested that the female dimorphism is determined by genetics, and that the grooved morph was dominant over the smooth one, independent of environmental factors. In addition, the hybrid insects did not differ from the two subspecies insects in larval survivorship, pupation success, or sex ratio. They also showed neither morphological abnormality nor reduced survival.

© 2012 Zoological Society of Japan
Toshio Inoda, Roger Härdling, and Souichirou Kubota "The Inheritance of Intrasexual Dimorphism in Female Diving Beetles (Coleoptera: Dytiscidae)," Zoological Science 29(8), 505-509, (1 August 2012). https://doi.org/10.2108/zsj.29.505
Received: 4 April 2011; Accepted: 1 March 2012; Published: 1 August 2012
diving beetles
elytral groove
intrasexual dimorphism
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