To understand geographic body size variation in an insect species, various factors including habitat temperature, correlation between life history traits, and food availability must be examined. Carabus (Ohomopterus) japonicus is univoltine, feeds exclusively on earthworms during its larval stage, and shows a clinal body size variation along the habitat temperature gradient in northern Kyushu, Japan. Carabus japonicus occurs at both high and low altitudes; at high altitudes it coexists with a larger species, C. (O.) dehaanii. At low altitudes, C. japonicus shows larger body sizes. We sought to determine whether this increase in body size is only an adaptation to high habitat temperatures in the absence of C. dehaanii, and examined the life history of C. japonicus and seasonal trends in prey earthworms at six sites between altitudes of 30 and 980 m. While high-altitude populations used the entire warm season for reproduction and larval development, low-altitude populations showed shorter periods of reproductive activity and larval incidence coincided with seasonal trends in earthworm abundance. Thus, C. japonicus attained larger body sizes at lower altitudes without a notable extension of their juvenile period. At lower altitudes, earthworms grew faster and reached sizes, which may be too large for predation by small carabid larvae. Large females had higher fecundity, and laid larger eggs, from which larger first instar larvae hatch. The large body size of C. japonicus in warm habitats may thus be an adaptation not only for high fecundity, but also for producing large first instar larvae to more efficiently prey on large earthworms.
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1 June 2017
Factors Related to Altitudinal Body Size Variation in the Earthworm-Eating Ground Beetle Carabus japonicus
Yutaka Okuzaki,
Teiji Sota
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Zoological Science
Vol. 34 • No. 3
June 2017
Vol. 34 • No. 3
June 2017
Body size evolution
character release
converse Bergmann cline
earthworm
genus Carabus
reproductive interference
subgenus Ohomopterus