Muscle plasticity of Inuit sled dogs in Greenland

Abstract

SUMMARYThis study examined flexible adjustments of skeletal muscle size, fiber structure, and capillarization in Inuit sled dogs responding to seasonal changes in temperature, exercise and food supply. Inuit dogs pull sleds in winter and are fed regularly throughout this working season. In summer, they remain chained to rocks without exercise, receiving food intermittently and often fasting for several days. We studied two dog teams in Northern Greenland (Qaanaaq) where dogs are still draught animals vital to Inuit hunters, and one dog team in Western Greenland (Qeqertarsuaq) where this traditional role has been lost. Northern Greenland dogs receive more and higher quality food than those in Western Greenland. We used ultrasonography for repeated muscle size measurements on the same individuals, and transmission electron microscopy on micro-biopsies for summer-winter comparisons of muscle histology, also within individuals. At both study sites, dogs' muscles were significantly thinner in summer than in winter -atrophy attributable to reduced fiber diameter. Sarcomeres from West Greenland dogs showed serious myofilament depletion and expansion of the sarcoplasmatic space between myofibrils during summer. At both study sites, summer samples showed fewer interfibrillar and subsarcolemmal mitochondria, and fewer lipid droplets between myofibrils, than did winter samples. In summer, capillary density was higher and inter-capillary distance smaller than in winter, but the capillaryto-fiber-ratio and number of capillaries associated with single myofibers were constant. Increased capillary density was probably a by-product of differential tissue responses to condition changes rather than a functional adaptation, because thinning of muscle fibers in summer was not accompanied by reduction in the capillary network. Thus, skeletal muscle of Inuit dogs responds flexibly to changes in functional demands. This flexibility is based on differential changes in functional components: mitochondrial numbers, lipid droplet size, and the number of contractile filaments all increase with increasing workload and food supply while the capillary network remains unchanged.

Musculoskeletal architecture of the prey capture apparatus in salamandrid newts with multiphasic lifestyle: does anatomy change during the seasonal habitat switches?

“…Structural seasonal changes in the musculoskeletal system, however, have not been studied in any salamanders to date. Nevertheless, such changes are not unlikely as seasonal muscle plasticity was documented previously in other vertebrates where they are associated with seasonally changing functional demands (Fl€ uck, 2006;Gerth et al 2009;Nowell et al 2011).…”

“…However, muscle plasticity does not exclusively rely on muscle volume or PCSA changes, and other factors, such as changes in the capillary network and supply area of the muscles, changes in myofibril ultrastructure or molecular mechanisms (Boonyarom & Inui, ; Flück, ; Gerth et al. ) may be considered in future studies.…”

“…Nevertheless, such changes are not unlikely as seasonal muscle plasticity was documented previously in other vertebrates where they are associated with seasonally changing functional demands (Flück, ; Gerth et al. ; Nowell et al. ).…”

Craniomandibular Trauma and Tooth Loss in Northern Dogs and Wolves: Implications for the Archaeological Study of Dog Husbandry and Domestication

“…Working dogs, particularly those used for tasks such as pulling sleds, have very elevated metabolic rates due to high activity levels [74]–[75]. Correspondingly, such dogs require significant caloric intake to maintain their energy balance [76]. Keeping dogs can be costly for humans in terms of time and energy—one has to purchase, hunt, fish, and forage in order to provision them [58], and at times these efforts may be unsuccessful or insufficient.…”

Scaling matters: incorporating body composition into Weddell seal seasonal oxygen store comparisons reveals maintenance of aerobic capacities

“…Weddell seal locomotor muscles contained primarily MHC I and IIA (Kanatous et al 2002(Kanatous et al , 2008, and other MHC isoforms were rare and/or not present in all individuals. In terrestrial mammals, such as humans, mice and rats, and sled and raccoon dogs, numerous aerobic aspects of muscles atrophy quickly during periods of inactivity and food deprivation (i.e., myofibers atrophy, capillary and mitochondrial densities drop, Mb and aerobic enzyme activities decrease, and MHC shifts from slow to fast-types; Lindboe et al 1982;Baldwin and Haddad 2001;Flück 2006;Gerth et al 2009;Kinnunen et al 2015). Conversely, in Weddell seals, the great oxidative potential of muscles was reflected by stable CS and HOAD enzyme activities, in addition to high and relatively invariant Mb concentrations.…”