Ambient temperature and reproductive success in rodents living at different latitudes.

The concern of this research was with the susceptibility of rodent reproduction to latitudinal acclimatization. More specifically, the relationship between ambient temperature and reproductive success was examined in house mice and deer mice whose ancestors had been trapped in northern versus southern climates (Alberta vs. Texas). Third generation adults of each of these four populations were paired and challenged to breed at -6 degrees, 3 degrees, 23 degrees or 34 degrees C. A 50-day period of gradual temperature adaptation preceded pairing. House mice, regardless of their geographic origin, were found to be relatively insensitive to extreme temperatures. Many pairs of both the Alberta and Texas stocks of this species still produced offspring when maintained at the experimental extremes of -6 degrees and 34 degrees C. In marked contrast, both northern and southern deer mice exhibited relatively narrow temperature ranges within which maximum breeding occurred: -6 degrees to 3 degrees for Texas deer mice and only at 23 degrees C for Alberta deer mice. Thus there is no evidence in either species that reproduction is either less sensitive to cold in northern latitudes or less sensitive to heat in southern latitudes; indeed, somewhat the reverse situation exists in deer mice. Evolutionarily, latitudinal considerations seem to have been of secondary rather than of primary importance in shaping the relationship between ambient temperature and reproduction in these two species.