Diving experience and the aerobic dive capacity of muskrats: does training produce a better diver?

Abstract

SUMMARY We tested the hypothesis that the body oxygen stores, aerobic dive limit(ADL) and dive performance of muskrats can be enhanced by dive-conditioning in a laboratory setting. We compared several key variables in 12 muskrats trained to swim a 16 m underwater course to a feeding station (`divers') with those of 12 animals precluded from diving but required to travel identical distances in water to feed (`surface swimmers'). Acclimated muskrats assigned to each group were trained concurrently over a 9–11 week period. We observed significant gains in the haematocrit (P=0.0005) and blood haemoglobin concentration (P=0.015) of `divers', but not `surface swimmers'. The post-training blood O2 store calculated for `divers' (22.9 ml O2 kg–1) was nearly 26% higher than that (18.2 ml O2 kg–1) derived for `surface swimmers'(P=0.03). Dive-conditioning had no apparent effect on lung volume,whole blood and plasma volumes, nor on the glycogen level and buffering capacity of skeletal muscles. Cardiac and skeletal muscle myoglobin levels were also similar in both test groups following training. The mean total body oxygen store of `divers' (37.8ml O2 STPD kg–1) was 13.5% higher (P=0.037) than for `surface swimmers' (33.3 ml O2 STPD kg–1), an increase attributed entirely to the gain in blood O2 storage capacity of the former group. However,owing to a slightly higher estimate of diving metabolic rate in dive-conditioned animals, the calculated ADL for this group (61.3 s) was indistinguishable from that of `surface swimmers' (61.8 s). Few differences were observed in the post-training dive behaviour of `surface swimmers' and`divers', a finding consistent with the strong similarity in their calculated aerobic dive capacities.

Do seasonal changes in metabolic rate facilitate changes in diving behaviour?

“…Increased oxygen availability during diving was induced in tufted ducks (Aythya fuligula) by training them to dive for longer (Stephenson et al, 1989). However, a similar increase induced by training in muskrats (Ondatra zibethicus) was again cancelled out by an increase in V O ∑ during diving (MacArthur et al, 2003). In the current study, we do not know how, or even whether, oxygen stores varied.…”

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

“…The resting oxygen consumption of muskrats in air ranges between 0.78 and 0.85 ml O 2 /g/h (MacArthur and Krause, 1989; MacArthur and Campbell, 1994; MacArthur et al, 2003), while resting oxygen consumption in thermoneutral water (29–30°C; MacArthur, 1984a) is 0.77 ± 0.04 ml O 2 /g/h (Fish, 1983). In a laboratory study of recently captured animals, the allometric relationship between mass (M) and basal metabolic rate (BMR) of field acclimatized adult muskrats is BMR = 700M 0.68 (Campbell and MacArthur, 1998).…”

“…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).…”

“…Younger muskrats likely are more dependent than adults on anaerobic metabolism during diving, as there is a greater tendency for smaller and younger muskrats to exceed their ADLs (MacArthur et al, 2001). During ontological development in muskrats there is a concurrent increase in diving experience, and so the effect of dive training was specifically investigated in a laboratory study that used a 9- to 11-week dive training protocol (MacArthur et al, 2003). MacArthur et al (2003) found that dive training produces a 26% increase in blood oxygen stores, due mainly to increases in hematocrit and hemoglobin concentration, and a 13.5% increase in mean total body oxygen stores compared with muskrats restricted to surface swimming.…”

“…During ontological development in muskrats there is a concurrent increase in diving experience, and so the effect of dive training was specifically investigated in a laboratory study that used a 9- to 11-week dive training protocol (MacArthur et al, 2003). MacArthur et al (2003) found that dive training produces a 26% increase in blood oxygen stores, due mainly to increases in hematocrit and hemoglobin concentration, and a 13.5% increase in mean total body oxygen stores compared with muskrats restricted to surface swimming. However, the diving oxygen consumption of dive-trained muskrats (2.22 ml O 2 /g/h) is 14.4% greater than for swim-trained muskrats (1.94 ml O 2 /g/h), and consequently the calculated ADL is indistinguishable between the two groups (61.3 s for divers and 61.8 s for swimmers; MacArthur et al, 2003).…”