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Individual variation in metabolic traits of wild nine-banded armadillos (Dasypus novemcinctus), and the aerobic capacity model for the evolution of endothermy

Patrice Boily

Department of Biological Sciences, University of New Orleans, New Orleans, LA 70148, USA

View larger version (13K): [in a new window]   Fig. 1. Relationship between peak metabolic rate (PMR; A) or basal (BMR; B) and body mass. Both BMR (r=0.64, P<0.001) and PMR (r=0.50, P<0.005) were significantly related to mass and differed significantly between sampling years (P<0.001).

View larger version (17K): [in a new window]   Fig. 2. Correlation between peak (PMR) and basal (BMR) metabolic rates represented as whole-animal (A; r=0.62, P<0.001) and mass-independent (B; r=0.45, P<0.005) values.

View larger version (15K): [in a new window]   Fig. 3. Relationship between mass-independent peak (A; PMR) or basal metabolic rates (B; BMR) and rectal temperature. Rectal temperatures were measured at the same time as BMR or PMR. Mass-independent BMR was significantly (r=0.81, P<0.001) correlated with rectal temperature, but mass-independent PMR was not (P=0.13). Solid horizontal lines represent mean metabolic rate calculated (assuming a Q10 of 3) if rectal temperatures were 38°C instead of the observed average of 33.9°C for mass-independent BMR and 32.5 for mass-independent PMR. Dashed horizontal lines represent predicted values for eutherian mammals of similar size (mean 4.2 kg) according to Lovegrove (2000) for mass-independent BMR and Taylor et al. (1981) for mass-independent PMR.

View larger version (12K): [in a new window]   Fig. 4. Typical example of temporal changes in chamber temperature (A), rectal temperature (B) and rates of gas exchange (O2 and CO2; C) of an armadillo during cold-exposure. Time zero indicates the start of cold-exposure. In this example, it took 35 min for peak rectal temperature (36.0°C) to occur and 123 min for peak CO2 (93.6 ml min-1) and O2 (110.6 ml min-1) to occur.

View larger version (20K): [in a new window]   Fig. 5. Relationship between the time at which peak O2 or CO2 occurred and the time at which peak rectal temperature occurred in armadillos following the start of cold-exposure. Data points above the solid line represent experimental trials in which the peak rectal temperature occurred before the peak O2 and vice versa. Individuals (N=3) for which the time at peak rectal temperature has a value of zero did not exhibit the typical cold-induced increase in rectal temperature.

View larger version (12K): [in a new window]   Fig. 6. Typical example of changes in baseline O2 and CO2 concentration occurring while heliox was circulated through an empty metabolic chamber. Five other trials were conducted, and all yielded similar results.