The evolution of shape in the wing dimorphic cricket, Allonemobius socius
1998
Roff, D.A. | Bradford, M.J.
Many traits which show only two phenotypic morphs are polygenically determined. For such traits the threshold model of quantitative genetics provides a suitable theoretical basis for the estimation of genetic parameters and response to selection. A consequence of this model is that traits correlated to the threshold trait are predicted to change, both in terms of their overall mean value and their morph-specific values. The cricket Allonemobius socius is wing dimorphic with the morphs also showing differences in the shape of the thorax. In this paper we present a quantitative genetic analysis of shape variation in relation to wing morph in A. socius. Overall size, as measured by the first principal component, has a high heritability (0.64 and 0.63 for females and males, respectively), as also does shape, as measured by the first principal component of a size-adjusted principal component analysis (PCA), (0.40, 0.25). However, size is neither phenotypically nor genetically correlated with wing morph, whereas shape is highly correlated, both phenotypically (0.64, 0.49) and genetically (0.80, 0.46), with wing morph. An analysis of the correlated response of shape to selection on the incidence of macroptery predicts that within populations the two morphs will remain different in shape, but different morphs from separate populations may be very similar in shape.
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