Testing the use/disuse hypothesis: pectoral and leg muscle changes in captive barnacle geese Branta leucopsis during wing moult

Abstract

SUMMARYPrevious studies on wild moulting waterfowl have demonstrated that flight and leg muscles experience periods of hypertrophy and atrophy. This is thought to be in response to the change in use of the locomotor muscles as described in the use/disuse hypothesis. We tested this hypothesis using captive barnacle geese. Forty geese were dissected before, during and after wing moult, to determine the changes in mass and functional capacity of the flight and leg muscles. Physiological cross sectional areas (PCSA) and mean fascicle lengths of functional muscle groups were calculated to ascertain the force-producing capabilities of the flight and leg muscles. At the onset of moult, flight muscle mass was at a minimum, having atrophied by 35% compared with premoult levels, but it returned to pre-moult levels by the end of wing moult. By contrast, the leg muscles hypertrophied during wing moult by 29%, and the PCSA of individual muscle groups increased substantially. Increases in mass, PCSA and fascicle length of individual leg muscle groups during moult suggest that, when flightless, the leg muscles are functionally adapted to provide greater force and/or manoeuvrability to the birds, to aid ground-based escape from predators. Through studying captive animals that are unable to fly, it has been possible to conclude that the major changes in leg and flight muscle in moulting captive geese cannot be explained through use or disuse. Instead, changes seem to be compensatory or to occur in anticipation of changes in locomotor patterns.

Predicting the rate of oxygen consumption from heart rate in barnacle geeseBranta leucopsis: effects of captivity and annual changes in body condition

“…Froget et al, 2001;Nudds and Bryant, 2001), and also increase the cost of locomotion (the net cost of transport). However, our results suggest that the changes in the cardiovascular system in response to gains in body fat may be systematic, as the relationship between f H and V O2 did not change significantly between five out of the six of the sampling periods, despite significant changes in body mass, body composition and total body fat (Portugal et al, 2007;Portugal, 2008;Portugal et al, 2009).…”

“…Bevan et al, 1995;Green et al, 2001;. Here, for the first time, we provide this relationship from six points in the annual cycle, for a species that exhibits significant seasonal changes in body mass, body composition and abdominal temperature, even when in captivity (Portugal et al, 2007;Portugal, 2008;Portugal et al, 2009).…”

“…However, the experiments in both studies were performed at similar times in the annual cycle. Recent work on captive barnacle geese has demonstrated that they undergo changes in body mass, body composition and abdominal temperature similar to those of wild geese (Portugal et al, 2007;Portugal, 2008;Portugal et al, 2009). For example, despite ad libitum access to food, captive geese lost approximately 25% of their body mass during their annual wing moult, while simultaneously experiencing an increase in the resting rate of metabolism of approximately 80% (Portugal et al, 2007).…”

Wild geese do not increase flight behaviour prior to migration

“…There is evidence to suggest that flight muscles have the capacity to hypertrophy without an increase in use or a simultaneous increase in body mass [6]. It is possible that this endogenous capacity for muscle hypertrophy observed in waterfowl previously ( [6], see also [20]) may have contributed to the apparent lack of requirement for increased flight and muscle training prior to migration.…”

“…However, evidence now exists to the contrary and suggests that in captive birds at least, their muscles have the capacity to hypertrophy and atrophy without any change in muscle use or exercise levels. These changes are largely independent of the external environment or behaviour [5,6]. This suggests that changes in muscle architecture can not only be a result of increased exercise [7], but some birds may also have an endogenous capacity for muscle hypertrophy [5,6].…”