Effect of transatlantic transport on reproduction of agouti and nonagouti deer mice, Peromyscus maniculatus

In conjunction with establishing colonies of deer mice in the UK, effects of transportation on reproduction in agouti (A) and nonagouti (a) deer mice were assessed. Adults were shipped via ground courier and air freight from Northampton, Massachusetts, USA to Sutton Bonington, Leicestershire, England in February and June. Deer mice were paired upon arrival in Sutton Bonington, whereas matched controls were paired in the original colonies at shipping. To assess reproduction, the following variables were monitored for 110 days for all 96 pairs: number of pairs producing Litters, time from pairing to birth, interlitter interval, Litter size at birth, and litter size at weaning. Generally, shipping suppressed litter production and delayed its timing, but had less effect on litter size. Overall, 32 of 48 control pairs (67%) produced 69 litters compared with 37 litters from 21 of 48 pairs (44%) after shipping. Pairing-to-first-litter intervals were approximately two oestrous cycles shorter in control animals (39 vs 53 days). Averaged over all litters, litter size was higher in control pairs (4.4 vs 4.0). With respect to genotype, control agouti deer mice were less productive than nonagouti animals, but they reproduced better than nonagoutis after shipping. In control animals, colourmorphs did not differ with respect to litter production or timing, but agouti pairs had smaller litters (first litter: A: 3.1, a: 4.2) and this difference increased at successive litters (third litter A: 3.9, a: 6.0). After shipping, agouti animals produced more litters (A: 22, a: 15), and did so earlier (pairing to birth: A: 47 days, a: 60 days), as well as more frequently (interlitter interval: A: 32 days, a: 51 days). Litter size was also more similar between genotypes after shipping (A: 4.0, a: 4.1). Overall, control agouti animals produced 37% fewer offspring than nonagouti pairs (A: 116 neonates, a: 185 neonates), but after shipping agouti deer mice produced 43% more offspring than nanagouti animals (A: 87 neonates, a: 61 neonates). In sum, transport stress suppressed reproduction for several weeks after shipping and this suppression was exacerbated in nonagouti deer mice.