Читать книгу Extreme Insects - Richard Jones - Страница 15

NAME	bilateral gynandromorph various species, but particularly prominent in butterflies
LOCATION	this example was bred in captivity
ATTRIBUTE	half male and half female

Insects are usually either wholly male or wholly female. In extremely rare situations, however, there appears an individual that is exactly half one sex and half the other – a bilateral gynandromorph – and nowhere is this more striking than when it involves a butterfly. In butterflies, as in most animals, sex is determined by the chromosomes. Females have two X chromosomes (XX) and males have just one (XO). Butterfly sperm contains either an X or no-sex chromosome.

In this marsh fritillary butterfly (Euphydryas aurinia) the sperm that originally fertilised the egg contained an X chromosome so the offspring was due to be XX, female. But after the very first cell division into two, one of the XX cells (female) somehow lost an X and became XO (male). Throughout the many millions of further cell divisions in the growing caterpillar and during metamorphosis in the chrysalis the right-hand side of the insect stayed female while the left-hand side had become male. When the final adult butterfly emerged from its pupa, it continued to be right half female and left half male.

Gynandromorphs are very rare and unlikely to survive. Neither male nor female sexual organs are functional. Some striking butterfly specimens occur where males and females have different wing patterns. In the case of the marsh fritillary, males are significantly smaller than females. This specimen was reared as part of a genetic study. In the wild all it could have achieved in life would have been a terminal spiral flight.