71.1 Jan. 7 Does growth rate differ across altitudes in deer mice? RUSSELL, GA*; HAMMOND, KA; Univ. of California, Riverside; Univ. of California White Mountain Research Station; Univ. of California, Riverside email@example.com
When faced with a hypoxic challenge (e.g. high altitude), young growing mammals may respond by using energy that otherwise would have been allocated to growth. For example, an organism may accelerate growth of those organs or organ systems involved with oxygen acquisition at the cost of decreased whole animal growth rate or individual organ size. Alternatively, growth rate or adult size may not be compromised at high altitude. To investigate whether growth rate is different between low and high altitude, we measured body mass, snout-rump length (SR), and hindfoot length (HF) from 3-42 days of age in two groups of deer mice (Peromyscus maniculatus): the first group underwent gestation and growth at elevation 340 m (low-born, LB); the second developed at 3800 m (high-born, HB). We fitted each character to a Gompertz growth curve and compared overall curve shape by entering the coefficients into an ANCOVA, using litter size, parity, and family as covariates. Curve shape for SR differed between natal altitudes; the upper asymptote was higher and initial length was higher in LB mice. Curve shape for body mass also differed between natal altitudes: the upper asymptote was higher and the slope of the curve was steeper in LB mice. The absence of curve shape differences for HF may be because it is already ~50% of adult size at our first measurement, which results in less differentiation in later measurements. By contrast, SR and mass are <50% of adult size at first measurement, so there is space for differentiation in later measurements. Our models predict no difference in HF, but they do predict larger body size (as measured by SR) and faster mass gain in LB mice. One interpretation of these data is that HB mice are repartitioning growth energy elsewhere, resulting in smaller body size and slower growth rate.