“…All these traits are considered to contribute to a behavioral phenotype adapted to cold ambient temperatures (Barnett, 1956;Barnett and Dickson, 1984a, b, 1986, 1989Barnett et al, 1975;Glaser and Lustick, 1975;Lynch, 1973Lynch, , 1977Lynch, , 1980Hegmarm, 1972, 1973;Lynch and Possidente, 1978;Lynch et al, 1976;Muul, 1968;Pearson, 1960). Natural populations ofMus domesticus (Lynch, 1992;Plomin and Manosevitz, 1974) and Peromyscus (King et al, 1964) show a geographic cline in nest-building behavior, in which northern populations build larger nests compared to southern populations. In these natural populations of Mus domesticus nest-building behavior is positively correlated with nest-building at 4~ and body weight (Lynch, 1992).…”