Abstract:
Summit metabolism (Msum), the maximum rate of resting metabolic
thermogenesis, has been found to be broadly correlated with climatic
variables and the use of heterothermy in some endotherms. Far less
is known about Msum and metabolic expansibility [ME, the ratio of
Msum to basal metabolic rate (BMR)] in bats compared with many
other endotherm taxa. We measured BMR and Msum during winter
and summer in captive and wild populations of a pteropodid from the
southern subtropics, Wahlberg’s epauletted fruit bat (Epomophorus
wahlbergi) in Pretoria, South Africa. The Msum of fruit bats ranged
from 5.178±0.611 W (captive, summer) to 6.006±0.890 W (captive,
winter), and did not vary significantly between seasons. In contrast,
BMR decreased by 17–25% in winter. The combination of seasonally
stable Msum but flexible BMR resulted in ME being significantly higher
in winter than in summer, ranging from 7.24±1.49 (wild, summer) to
13.11±2.14 (captive, winter). The latter value is well above the typical
mammalian range. Moreover, both Msum and ME were significantly
higher in captive bats than in wild individuals; we speculate this
represents a phenotypic response to a reduction in exerciseassociated
heat production while in captivity. Our data for E.
wahlbergi, combined with those currently available for other
chiropterans, reveal that Msum in bats is highly variable compared with
allometrically expected values for other mammals.
