Reproductive Photoresponsiveness: Selection for Genetic Variants
In the figures is shown the change in the frequency of reproductive photoresponsiveness in P leucopus after three-four generations selected FOR and AGAINST that trait. Approximately 50% of the parental generation (P) were responsive, ie experienced reduced reproductive abilities when exposed to a short photoperiod. Selected photoresponsive mice were bred to produce the F1 generation, and in like manner an subsequent generations were produced. Similarly, sequential generations were produced from parents to be non-responsive to photoperiods.
Peromyscus leucopus from Michigan (Heideman and Bronson, 1991)
Peromyscus leucopus from Williamsburg, Virginia (Heideman et al., 1999)
This is a clear demonstration that both of these populations of Peromyscus leucopus manifest selectable genetic variation for photoperiod responsiveness. It is noteworthy that continued selection for responsiveness or non-responsiveness fails to produce groups of mice all of whom expressing one phenotype or the other. Mechanisms must exist to prevent full penetrance of the genetic trait to ensure a level of phenotypic variability necessary to accommodate the variations in seasonal severity from year to year.
Heideman PD, Bronson FH. 1991. Characteristics of a genetic polymorphism for reproductive photoresponsiveness in the white-footed mouse (Peromyscus leucopus). Biol Reprod 44:1189-1196.
Heideman PD, Bruno TA, Singley JW, Smedley JV. 1999. Genetic variation in photoperiodism in Peromyscus leucopus: geographic variation in an alternative life-history strategy. J Mammal 80:1232-1242.