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

Abstract

Founder effects, together with access to unoccupied ecological niches, may allow rodent populations on isolated islands to evolve constellations of life-history traits that distinguish them from their mainland relatives, for example in body size, litter size, and longevity. In particular, low intrinsic mortality risks on islands with reduced predator numbers and not subject to harsh winter climates may in principle support the development of stocks with extended longevity. Conversely, the conditions under which laboratory rodents are typically bred are thought to select for genotypes that produce large, rapidly maturing races with high early reproductive rates but diminished longevity. To test these ideas, and to generate new mouse stocks suitable for genetic and molecular analysis of the processes that time life-history events, we have developed speci®c pathogen-free stocks from mice trapped from three distinct populations: the U.S. mainland (Idaho) and the tropical Paci®c islands Majuro and Pohnpei. Mice from all three locations were found to be shorter and lighter, to have smaller litters, and to have higher faecal corticosterone levels than mice of a genetically heterogeneous stock derived from four common laboratory inbred strains. Among the wild-derived stocks, mice from Pohnpei and Majuro were signi®cantly lighter and shorter than Idahoderived animals, even in populations kept from birth under identical housing conditions. Litter size and reproductive success rates did not differ signi®cantly among the three wild-derived stocks. Although further work will be needed to see if, as predicted, the wild-derived stocks differ from one another and from laboratory mice in longevity, these stocks provide useful tools for genetic dissection of factors that regulate body size and reproductive success.

Mapping ecologically relevant social behaviours by gene knockout in wild mice

“…As a proof of concept of the applicability and scientific advantages of studying gene function on the genetic background of wild-derived house mice (Mus musculus), we backcrossed a commercially available inbred laboratory knockout mouse line with pathogenfree rederived wild mice (see Methods). Pathogen-free rederived wild mice were generated through the cross-fostering of newborn offspring from free-living wild-caught mice by post-partum CD-1 laboratory female mice 20 .…”

“…The genetic background of the laboratory TrpC2 mice was C57BL/6J Â 129S1/Sv. Wild house mice were trapped in the fields (Idaho, USA) near livestock barns and kept under laboratory conditions for seven generations as an outbred stock of pathogen-free wild mice 20 . Wild-backcrossed mice were produced by 10-generation backcrossing of laboratory TrpC2 mice with wild house mice.…”

Big mice die young: early life body weight predicts longevity in genetically heterogeneous mice

“…Our new data suggest that this relationship may be a general one, not restricted to the products of artificial selection for extremes in growth rate or body size. It is noteworthy that laboratory-adapted mouse stocks, such as the progenitors of the inbred lines from which our UM-HET3 mice are derived, are larger in body weight (Miller et al ., 2000b) and body dimensions (Harper et al , unpublished observations) than laboratory-raised stocks derived from recently wild-trapped progenitors. Furthermore, the small size of wild-derived mice is associated with an increase of 24% in mean life span and a 16% increase in maximum life span of the longest lived animals (Miller et al ., unpublished observations).…”

Are mice calorically restricted in nature?

“…Increased food consumption by mice leads to faster growth, earlier sexual maturation, larger body size and enhanced fertility in adulthood (Eisen et al ., 1980;Singleton et al ., 2001), and it is well documented that laboratory mice have been selected for enhanced reproductive rate compared with wild mice (Berry, 1969;Clark & Price, 1981;Miller et al ., 2000Miller et al ., , 2002. Thus the conditions in a standard commercial mouse breeding facility will favour genetic variants that reproduce well and also eat more than other genotypes.…”