Abstract
Body and horn morphology of two rhinoceros beetle species (Chalcosoma Caucasus F. and C. atlas L.) was observed in six allopatric (one of the two species occurs within the same geographical area) and three sympatric (both of them occur) locations. Across allopatric locations, the ranges of elevational distribution partially overlapped between the two species. In sympatric locations, C. Caucasus occurred at higher elevational range than C. atlas with little overlap of elevational distribution between the two species. Both species showed a clear male dimoiphism in all locations, that is, a minor morph with smaller body and rudimentary horns and the major morph with larger body and disproportionally large horns. Across allopatric locations, the sizes of the corresponding morphs partially overlapped between the two species. In sympatric locations, the sizes of each morph of C. Caucasus were greater than those of its corresponding morph in allopatric locations, whereas those of C. atlas were smaller than those in allopatric locations. Thus, in sympatric locations, the size of each morph of C. Caucasus was distinctly larger than that of the corresponding morph of C. atlas and there were little dimensional overlaps between the corresponding morphs of the two species. It is possible that the two species responded behaviorally to the presence of each other and the resultant elevational habitat shift caused the morphological differences. The magnitudes of intraspecific variation in body size and male dimorphic divergence of the two species did not differ significantly between allopatry and sympatry. These results suggest that habitat shift and phenotypic body size displacement in sympatry of these species took place in response to the presence of the other species avoiding interspecific competition without changing intraspecific variability.
Published Version
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