Fig 1.
Appearance, range, and collection location of the animals used in this study.
(A) An adult meadow jumping mouse, showing the long tail and large hind limbs used for jumping locomotion. (B) The range of Zapus hudsonius in much of North America. The collection location is marked with a red circle. Map was adapted from map tiles by Stamen Design under Creative Commons (CC BY 3.0), using data by OpenStreetMap under the Open Database License (ODbL). (C) Aerial imagery of the trapping location within the Bolton Flats Wildlife Management Area, with the collection areas delineated with dotted yellow lines. (D) A meadow within the trapping area, shown here at the end of the trapping season following partial mowing by the state wildlife agency.
Table 1.
Species captured during three years of Zapus collection.
Fig 2.
Captive breeding of Zapus results in a male-biased sex ratio and a high proportion of single-sex litters.
(A) Meadow jumping mouse pups visible in an opened nest box. These animals are approximately 17 days old. (B) Histogram of possible gestation lengths from 39 successful matings; impossible lengths were removed from the frequency distribution according to the number of times they were out of bounds given the breeder pairing and separation dates. (C) The distribution of litter size (number of weaned pups) from each of 32 litters (mean = 4 pups). (D) Histogram of litter sex ratio (fraction male) in our colony, determined from sexes of weaned animals in 32 litters. Note the unusually large number of all-female and all-male litters.
Fig 3.
Photoperiod controls pre-hibernation fattening in wild-caught and captive-reared meadow jumping mice.
(A) Body mass by age of 15 captive-born meadow jumping mice that were housed under long photoperiod (16L:8D) which inhibited pre-hibernation fattening. (B) Body mass of animals captured near the end of the active season (black lines, circles, n = 10) or born to a female that was pregnant while captured (red lines, triangles, n = 4) and held at long photoperiod (16L:8D). Animals captured at the end of summer fattened for hibernation despite the long photoperiod; captive-born animals did not fatten. (C) Periods of exposure to short photoperiod (12L:12D, shaded red) are sufficient to induce pre-hibernation fattening in animals that were held at long (16L:8D) photoperiod after capture. (D) A meadow jumping mouse that has prepared for hibernation by fattening. (E) A meadow jumping mouse curled up in typical posture used during torpor. The nest box lid and nest were opened to view the animal. (F) A partially uncurled animal that was found torpid at 20° C ambient temperature. Full arousal takes around 10 minutes at this temperature [24].
Fig 4.
Short photoperiod and low temperature induce hibernation in captive-reared meadow jumping mice.
Body mass (A-D) and average daily food consumption (E-H) are shown for control conditions (16L:8D, 20° C) and three hibernation induction conditions. Data are marked black during the period when the corresponding animal was found torpid. (A) Body mass of control animals in an environmental chamber (open circles, n = 5), or colony housing room (closed circles, n = 5). (B) Body mass at 20° C and 8L:16D, n = 5. (C) Body mass at 12° C and 8L:16D, n = 5. (D) Body mass at 7° C and 8L:16D, n = 5. (E) Average daily food consumption of control animals in an environmental chamber (open circles, n = 5), or colony housing room (closed circles, n = 5). (F) Average daily food consumption at 20° C and 8L:16D, n = 5. (G) Average daily food consumption at 12° C and 8L:16D, n = 5. (H) Average daily food consumption at 7° C and 8L:16D, n = 5.
Fig 5.
Ambient temperature affects pre-hibernation weight gain and food consumption in captive meadow jumping mice.
Captive-reared meadow jumping mice in hibernation induction conditions (8L:16D and 20°C, 12°C, or 7°C) show trends toward earlier weight gain (A) and earlier onset of torpor (B) at lower temperatures. (C) Maximum attained body mass is significantly increased in all hibernation induction conditions (shaded gray) versus controls. Means differed significantly by ANOVA (F = 30.92, p < 0.0001) and asterisks indicate adjusted p-values from Dunnett’s multiple comparisons test between control and each induction condition: 20°C (p = 0.0007), 12°C (p < 0.0001), and 7°C (p < 0.0001). (D) Daily food consumption at maximum attained body mass is significantly increased at 7° C and 12° C, but not 20°C. Induction conditions are shaded gray. Means differed significantly by ANOVA (F = 11.10, p = 0.0001) and asterisks or ‘ns’ (not significant) indicate adjusted p-values from Dunnett’s multiple comparisons test between control and each induction condition: 20°C (p = 0.9964), 12°C (p = 0.0166), and 7°C (p = 0.0001) (E-G) The relationship between body weight and food consumption is shown at 20°C (panel E), 12° C (panel F), and 7°C (panel G). Red best fit lines increase in slope as temperature falls, illustrating the interaction between body mass and temperature with respect to food consumption.
Fig 6.
Circadian activity of captive meadow jumping mice before and during hibernation.
Body mass (blue lines) and food consumption measurements (red lines) from animals that did (A) or did not (B) enter torpor at 8L:16D and 7° C. For the same animals that did (C) and did not (D) enter torpor, the total daily activity (fraction of 24 hour period active) is shown with black lines, and the fraction of total activity that occurred during the light phase is show with orange lines. The intervals shaded light gray in panels A and C correspond to the 14-day periods shown in actograms E-J, where the dark phase is shaded gray and activity outside the nest box is represented as black bars. (E) First 14 days of activity. Hibernation induction conditions began after a 4-day acclimation period. (F,G) Before hibernation, daily activity begins at the onset of the dark phase. (H) At the start of hibernation, activity outside the nest box becomes sporadic and no longer aligns with photoperiod. (I) Mid-hibernation, essentially no activity occurs outside the nest box. (J) Late in hibernation, some activity occurs that either does or does not align with photoperiod.