Body cooling and the diving capabilities of muskrats (Ondatra zibethicus): A test of the adaptive hypothermia hypothesis

Animal Models for Investigating the Central Control of the Mammalian Diving Response

“…The first cardiac interval after submersion is usually the longest, and upon resurfacing heart rate increases to the pre-dive level within 5 s (Drummond and Jones, 1979 ). Qualitatively similar results have also been found using implantable heart rate transmitters (Gilbert and Gofton, 1982 ; MacArthur and Karpan, 1989 ; McCulloch and Jones, 1990 ; Signore and Jones, 1995 , 1996 ; Hindle et al, 2006 ; Shereshkov et al, 2006 ; Figure 1 ). However, although all data indicate that an immediate and substantial bradycardia accompanies every voluntary dive in muskrats, the extent of the bradycardia can vary with the nature of the dive.…”

“…In muskrats underwater exercise is accompanied by an increase in energy expenditure which approaches that of surface swimming (Fish, 1983 ; MacArthur and Krause, 1989 ). In thermoneutral water estimated oxygen consumption of diving muskrats ranges between 2.05 and 2.49 ml O 2 /g/h (MacArthur and Krause, 1989 ; MacArthur et al, 2003 ; Hindle et al, 2006 ), and the proportionality coefficient for diving metabolic rate (DMR) is 2.73 times that of BMR (DMR = 1908.8M 0.74 ; MacArthur et al, 2001 ). The relationship between mass and total body oxygen stores (which combines lung, blood, and muscles oxygen stores) is 33.7M 1.09 , giving a calculated ADL of 61.4M 0.37 (MacArthur et al, 2001 ).…”

“…Decreasing water temperature also produces an intensification of bradycardia during exploratory and foraging dives (MacArthur and Karpan, 1989 ) as well as during forced submergence (Thornton et al, 1978 ). Diving heart rate also decreases as core body temperature decreases (MacArthur and Karpan, 1989 ; Hindle et al, 2006 ), which may be related to a more intense abdominal vasoconstriction (MacArthur and Krause, 1989 ). Adult muskrats are rather tolerant of hypothermia, but do not use hypothermia to maximize underwater submergence during routine diving through a depression of metabolic rate (Hindle et al, 2006 ).…”

“…Diving heart rate also decreases as core body temperature decreases (MacArthur and Karpan, 1989 ; Hindle et al, 2006 ), which may be related to a more intense abdominal vasoconstriction (MacArthur and Krause, 1989 ). Adult muskrats are rather tolerant of hypothermia, but do not use hypothermia to maximize underwater submergence during routine diving through a depression of metabolic rate (Hindle et al, 2006 ). Indeed, muskrats may defer thermoregulatory costs associated with cold water diving until the post-dive recovery period (MacArthur, 1986a ; Hindle et al, 2006 ).…”

The Oxygen-Conserving Potential of the Trigeminocardiac Reflex

“…[31][32][33] As a result, whereas the blood supply to the heart meets myocardial oxygen demand, myocardial oxygen consumption decreases. [39][40][41][42][43][44] Although these changes are universal in at least vertebrates, diving animals developed additional mechanisms facilitating their survival during prolonged periods without breathing. 31 Interestingly, apnea itself is not oxygen conserving; rather, its function is to prevent the lungs from filling with water or noxious fumes.…”