Mouse (Mus musculus) stocks derived from tropical islands: new models for genetic analysis of life-history traits

Founder effects, together with access to unoccupied ecological niches, may allow rodent populations on isolated islands to evolve constellations of li fe-history traits that distinguish them from their mainland relatives, for example in body size, litter size, and longevity. In particular, low intrin sic mortality risks on islands with reduced predator numbers and not subjec t to harsh winter climates may in principle support the development of stoc ks with extended longevity. Conversely, the conditions under which laborato ry rodents are typically bred are thought to select for genotypes that prod uce large, rapidly maturing races with high early reproductive rates but di minished longevity. To test these ideas, and to generate new mouse stocks s uitable for genetic and molecular analysis of the processes that time life- history events, we have developed specific pathogen-free stocks from mice t rapped from three distinct populations: the U.S. mainland (Idaho) and the t ropical Pacific islands Majuro and Pohnpei. Mice from all three locations w ere found to be shorter and lighter, to have smaller litters, and to have h igher faecal corticosterone levels than mice of a genetically heterogeneous stock derived from four common laboratory inbred strains. Among the wild-d erived stocks, mice from Pohnpei and Majuro were significantly lighter and shorter than Idaho-derived animals, even in populations kept from birth und er identical housing conditions. Litter size and reproductive success rates did not differ significantly among the three wild-derived stocks. Although further work will be needed to see if, as predicted, the wild-derived stoc ks differ from one another and from laboratory mice in longevity, these sto cks provide useful tools for genetic dissection of factors that regulate bo dy size and reproductive success.