Morphological differentiation following experimental bottlenecks in the butterfly Bicyclus anynana (Nymphalidae)

The consequences of population bottlenecks for morphological differentiation were investigated experimentally in the Afrotropical butterfly Bicyclus anynana (Satyrinae). A genetically variable laboratory population was used to establish daughter populations differing in the severity of the founding bottleneck (two, six, 20 and c . 300 individuals), with four to six replicate lines per treatment. Nine quantitative traits of the hind wing were measured (wing area and eight wing pattern characters) in the founders, F 1 , F 2 and F 3 generations. A tenth character, egg weight, was measured in all lines in F 3 . The validity of the neutral additive model was tested by regressing the observed phenotypic variance among replicate lines ( V d ) at F 3 against the expected additive genetic variance among lines (2 F t V A0 , where F t is the coefficient of inbreeding at generation t and V A0 is the additive genetic variance in the base population). This analysis was performed for the first six principal components of the wing character set, and using two series of F t estimates, one obtained from demographic parameters, the other from molecular markers. Overall, V d was slightly less than expected, perhaps as a result of some characters being subject to weak stabilizing selection, but the general picture was one of close concordance with the prediction of the neutral additive model. Plots of phenotypic line means, from the parental generation through to F 3 , illustrate that the observed differentiation was essentially entirely due to the initial sampling event. Egg weight showed a similar pattern of differentiation. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 107–115.