A bilateral gynandromorph Orange-tip Anthocharis cardamines: Some observations

摘要

A strikingly aberrant Orange-tip Anthocharis cardamines was photographed by Mark Coates at Askham Bog (VC64 Mid-west Yorkshire) on 13 June 2016 (see front cover). It shows a fine example of bilateral gynandromorphy where the insect is half male (in this case the left-side of the butterfly) and half female (right-side). This rare and intriguing sport of nature arises from the loss of one of the sex chromosomes from an initially typically developing homogametic1 sex zygote. If the loss of one Z chromosome occurs at the first mitotic division (when the fertilised cell first divides into two) then the zygote will produce one cell with two same-sex (ZZ) chromosomes and one cell with a single Z sex chromosome. The possession of the two Z sex chromosomes in a cell steers development along the male path while the possession of only one Z sex chromosome steers development along the female path. In all subsequent cell divisions one half of the cells will code for male and the other half for female. The resulting adult is entirely male on one side and entirely female on the other side (see Plate 2, centre pages) - the adult butterfly is perfectly bisected sexually.