The quantitative genetics of wing dimorphism under laboratory and 'field' conditions in the cricket Gryllus pennsylvanicus
1997
Roff, D.A. | Simons, A.M.
Laboratory estimates of the heritability of threshold traits indicate a typically large additive genetic component. In natural populations, it has been suggested that the heritability might be considerably reduced owing to environmental variation. No test of this hypothesis for threshold traits has been undertaken. In this paper, such a test is reported using wing dimorphism in the cricket, Gryllus pennsylvanicus. A full-sib, split-family design was used, one half of each family being raised under constant conditions in the laboratory, and the second raised in cages outside at the site from which the parents were originally collected. Pitfall-trap data indicated that nymphs in the field cages grew similarly to individuals in the natural population. Heritability of wing dimorphism in the laboratory was larger than heritability in the 'field' (0.70 vs. 0.21). However, analysis of variation across environments suggested that the genetic correlation was close to or even 1.00: this is supported by the estimate of the genetic correlation of 0.94. Thus selection in the laboratory environment will mirror the responses expected in the field. Laboratory estimates of heritability can therefore be useful indices of field values. These results do not support the hypothesis that heritabilities of threshold traits are reduced to insignificant values under natural conditions. More experiments are required to test the generality of this result and its consequences for the evolution of threshold traits in natural populations.
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