Macquarie Island House mice: A genetical isolate on a sub‐Antarctic island

Abstract

Macquarie Island (54°37'S; 158°54'E) lies half‐way between Australia and the Antarctic Continent, 400 miles from the nearest land. Its climate is wet, windy, cool and cloudy. The mean annual temperature is 4.7°C, and ranges only from 3.1°C in the coldest month to 6.7°C in the warmest. Despite these inclement conditions, House mice (Mux museulus) live over most of the island (up to at least 1000 feet), and apparently thrive. They breed all the year round. Their diet seems to be largely the seeds of the Macquarie cabbage (Stilocarpa polaris), supplemented by insects.The object of the study was to determine the effect of life in an equable but stressful environment for the mice. The animals were not remarkable in any morphological traits, although they were fairly large and had relatively short tails. However six of 17 gene‐loci investigated electrophoretically were polymorphic. The average heterozygosity was 6.8%, similar to mice living under much more fluctuating conditions in the Northern Hemisphere. The frequency of the Hbbd allele decreased from 71 ± 6 % in mice under three months of age to 54±5% in older ones. This change was most marked in animals caught well away from human habitation.