Developmental stability of insecticide resistant phenotypes in blowfly; a result of canalizing natural selection

Abstract

Maynard Smith et al.¹ have recently suggested that newly evolved phenotypes will be more variable than long-established ones when developmental constraints have evolved through canalizing selection in which similar phenotypic expression is stabilized across a range of genotypes². There is as yet little evidence for this^1,3. Fluctuating asymmetry¹ (random differences between left and right sides of a normally bilaterally symmetric organism) has been used to indicate developmental stability and to define environmental or genetic stresses on development^4–14. Here we show that insecticide-resistant phenotypes of the Australian sheep blowfly, Lucilia cuprina, show greater fluctuating asymmetry than susceptible phenotypes when resistance first evolves, and that continued use of an insecticide after resistance develops leads to a return in the asymmetry of resistant phenotypes to the level of susceptibles. The asymmetry of resistant phenotypes increases during repeated back-crossing to a susceptible strain, suggesting that developmental stability may be modified by selection.