Origins of the Domesticated House Mouse

My use of the terms wild, domestic, and commensal follow Bruell (1970). Domestic strains have been raised in captivity for several generations and their breeding is controlled by humans; wild mice are populations whose reproduction is not controlled by humans. Wild mice can be further classified by the degree of association with humans: commensal mice live in close association with human structures, aboriginal mice live predominantly independent of human dwellings and are endemic to that area. Bruell (1970) uses "feral" to refer to mice that have secondarily returned to the aboriginal mode of existence. However, the more commonly accepted use of feral (e.g., Allaby 1991) is to describe domesticated forms (e.g., horses, goats, dogs, cats) that have reverted to a wild condition. In any case, the foregoing classifications are not absolute; for example, house mice populations may be commensal during the winter months, but may inhabit fields and woodlands during the summer (Berry 1981b; cf. Kaufman and Kaufman 1990). We know of no reports of self-sustaining feral house mouse populations. In fact, even deliberate attempts to introduce lab mice into nature have been unsuccessful (e.g., Berry et al., 1982).

Robert Hooke in 1664 was apparently the first to use a house mouse in scientific experiments (Masson 1940, cited in Festing and Lovell 1981), although mice had been kept and bred by "fanciers" throughout antiquity (Keeler 1931). Regular breeding in the laboratory did not start until sometime around 1850 and C. L. Little is credited with establishing the first inbred strain (DBA) in 1909 (Festing and Lovell 1981). The most immediate ancestors of the modern laboratory strains of mice were derived from private stocks in Europe, eastern North America, and perhaps Japan (Keeler 1931; Morse 1978; Festing and Lovell 1981).

Modern laboratory mice are thought to be hybrids of three forms: Mus musculus musculus, Mus musculus domesticus, and Mus musculus castensus (also referred to as M. m. molossinus in some literature). Most of the domestic mice of Europe and North America are primarily descendents of Mus domesticus (Yonekawa et al. 1980; Ferris et al. 1982; Ferris et al. 1983; Tucker et al. 1992). However, M. spretus, M. macedonius, and M. spicilgus all form viable F1 offspring with Mus musculus in the laboratory (Avner et al. 1988) and the derivation of laboratory strains may also include additional chromosomal segments from one or more of these species (Blank et al. 1986). All of the common laboratory strains of mice contain the M. domesticus mitochondrial DNA genome (Ferris et al. 1983). Furthermore, many, but not all of the strains of inbred mice carry the same M. domesticus mtDNA haplotype (Ferris et al. 1983). In contrast, most, but not all, of the strains carry the M. musculus Y chromosome (Bishop et al. 1985; Tucker et al. 1992).

Although the historical records for mice are extensive (e.g., see reviews in Morse 1978; Festing 1979; Lyon and Searle 1989), records are generally not adequate to identify the ancestral populations of the founder individuals for a particular strain (Atchley and Fitch 1993). For example, many of the modern strains used in North America can be traced back to A. Lathrop's colony in Granby, Massachusetts (Potter 1978; Festing and Lovell 1981). The founder individuals for Lathrop's colony are not known, but are thought to include imported mice of several subspecies obtained from other private collectors plus wild mice caught locally (Potter 1978). A detailed phylogeny based on molecular and biochemical data is now available for many of the common inbred strains of mice which can be used to confirm the historical records (e.g., Fitch and Atchley 1985; Atchley and Fitch 1991, 1993; reviews in Sage et al. 1993). The phylogenetic results are usually, but not always, consistent with the historical accounts (Atchley and Fitch 1993).

Substantial genetic evidence indicates that the different laboratory strains do not all share a common origin (Tucker et al. 1992; Atchley and Fitch 1993); in other words, present-day laboratory house mice are not derived from a mouse "Eve" (cf. Ferris et al. 1982)! Some strains are clearly hybrid in origin, containing genes from three or more species of Mus (see above; e.g., BALB/c, C57BL/6J); other strains, such as the "so-called Swiss-Webster" mouse (Lynch 1969), were apparently not derived as hybrids (see above; e.g., SJL/J, SWR/J). Recent molecular evidence indicates that both the inbred and random-bred lines derived from the original stocks of Dr. Carol J. Lynch (see below) are pure Mus domesticus (Tucker et al. 1992; Atchley and Fitch 1993). The ICR strain of house mouse used by our laboratory is derived from Lynch's strains, and therefore is not of hybrid origin.

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