An Australian forest fire wipes out over $92\%$ of a population of terrestrial gastropodan slugs. The slug's gene pool originally consisted of $4$ alleles for dermis color CM $,$ CS$,$ CB and CA$$ these occurred at frequencies of$0\mathrm{.}3,0\mathrm{.}4.0\mathrm{.}1$ and $0\mathrm{.}2$ respectively. After the fire the slug's gene pool now consists of only $2$ alleles $$CS $,$ and CB$$at frequencies of$0\mathrm{.}2,0\mathrm{.}8$ respectively.$$This type of forest fire mediated reduction in allelic variation is called