Environmental and genetic determinants of the male forceps length dimorphism in the European earwig Forficula auricularia L. |
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Authors: | J L Tomkins |
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Institution: | (1) School of Biological Sciences University of Liverpool, P.O. Box 147, Liverpool, L69 3BX, UK, GB |
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Abstract: | Male dimorphisms are particularly conspicuous examples of alternative reproductive strategies. The male forceps length dimorphism
in the European earwig Forficula auricularia has long been considered an example of a status- (body size) dependent male dimorphism. In this paper, I test three hypotheses
relating to the dimorphism of F. auricularia. First, that the dimorphism is status dependent and determined by nutrition. Second, that the dimorphism is a density-dependent
adaptation. Third, that there is a genetic basis to population differences in morph frequency seen in the field. These hypotheses
were tested by rearing two populations in a split-family rearing design with two diets and two densities. Populations of male
earwigs reared in the common garden differed in forceps length and relative forceps length. The populations also differed
in the morph frequencies, with 40 versus 26% long-forceped males. These results confirm the notion that there is a genotype-by-environment
interaction that determines the morph frequency in a population. There were only minor effects of density on male forceps
length and no influence of density on the male dimorphism. In accordance with the hypothesis that the morphs are status-dependent
alternatives, large-forceped males only arose on the high-protein diet that produced earwigs of a large body size. However,
not all large males produced the long-forceped phenotype. I put forward an extension of the status-dependent dimorphism model
that may account for the pattern of forceps dimorphism in this species.
Received: 18 November 1998 / Received in revised form: 14 May 1999 / Accepted: 25 July 1999 |
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Keywords: | Dermaptera Male dimorphism Alternative strategies |
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