Structure and biology of house mouse populations that plague irregularly: an evolutionary perspective

In Australia, populations of mice occasionally irrupt into plagues, mainly in the southern and eastern grain-growing regions. Mus domesticus was the only member of the subgenus Mus identified from a genetic survey of animals collected from four states. Little is known of the origin of these mice but they probably came from Europe where plagues do not occur. We examined whether mice have evolved the ability to plague since their colonization by comparing some population parameters of Australian, European and North American mice. Their helminth fauna were contrasted to gauge the importance of founder effects on the evolution of mice in Australia. Australian mice share 52% (12 of 23) of the helminths found in mice in Europe and North America. Those not shared mainly had indirect life cycles. The absence of species could be explained by a strong founder effect or the lack of suitable intermediate hosts near Australian ports. There was no evidence that population structure or diet had evolved differently. Population abundance was different in field populations especially during the build-up and irruption of plagues. These differences were related to better breeding by mice in Australia in field environments; average number of embryos per litter was substantially higher and breeding seasons longer. Genetic change is not the only explanation for this increased productivity-a combination of lack of interspecific competition from other granivores and more favourable climatic conditions may be responsible. All things considered, there was no compelling evidence that Australian mice have evolved the ability to plague. Their ability to respond to good conditions by increasing litter size beyond that recorded elsewhere supports the notion that control of mouse productivity is an appropriate management option for plague prevention.