Peromyscus leucopus (White footed mouse) neonates.
Keywords: mouse, peromyscus, white, foot, neonateWhite-footed mice are seasonal breeders in northern climates. In southern populations, breeding may occur year-round. Gestation length is about three weeks long (22 days) but may be longer because mice can experience embryonic diapause with delayed implantation. In that respect, they are similar to mink, bats etc.
Figure 1. These neonates were taken from a dog that just eaten and regurgitated them (!). Note here that Peromyscus leucopus (like all mice, rats, canids, felids and others) give birth to young that are hairless, blind and deaf, resembling premature fetuses in precocious species. Species such as mice are referred to as altricial (the antonym of precocious). Image size: 1200 x 964 px
Figure 2. Young, white footed mice, about to be weaned. Similar to puppies and kittens, the eyes of neonates usually open about 2 weeks after birth yet weaning occurs just one week later! Therefore, these mice (from the same location as the neonates in figure 1) were presumed to be approximately three weeks old; well developed yet still with their mother (not shown). Image size:1270 x 1026 px
Peromyscus leucopus has a remarkable reproductive capacity. Weaned at approximately three weeks of age, they reach puberty at only 6 weeks of age. With an estrous cycle every 4 to 6 days, gestation lengths of only 21 days and virtually no postpartum anestrus, they have at least 3 or 4 litters a year. Incidentally, this pales by comparison with domestic mice (Mus musculus) which may have up ten per litters per year. Each litter of white footed mice contains 2 to 9 young, similar to the litter size of domestic mice. Litter size peaks at the fifth or sixth litter, then decreases.
White-footed mice may live several years in captivity but in the wild, there is complete population replacement almost each year.
Selected references:
1. Animal diversity.org. University of Michigan: Peromyscus leucopus
2. Jackson labs. Murine reproduction
3. Ptak, G.E. Embryonic Diapause is conserved across mammals. www.plosone.org Volume 7. Iss. 3 e33027
