Showing papers by "Susannah K. S. Thorpe published in 2009"

Orangutans employ unique strategies to control branch flexibility

Abstract: Orangutans are the largest habitually arboreal mammal. For them, as for all arboreal mammals, access to the abundant fruits and narrowest gaps found among the thin peripheral branches of tree crowns poses considerable safety risks and energetic demands. Most arboreal primates use flexed-limb postures to minimize problems caused by branch compliance and instability. Here, we show that Sumatran orangutans employ unique locomotor strategies to control compliance and allow access to the terminal branch niche for feeding and gap crossing. We calculated a "stiffness score," which is a measure of the flexibility of the supports on which orangutans moved. We found that certain locomotor behaviors clearly are associated with the most compliant supports; these behaviors appear to lack regular limb sequences, which serves to avoid the risk of resonance in branch sway caused by high-frequency, patterned gait. Balance and increased stability are achieved through long contact times between multiple limbs and supports and a combination of pronograde (horizontal) and orthograde (vertical) body postures, used both above branches and in suspension underneath them. Overall, adult females seem to be the most conservative in their travel, selecting more solid and secure supports than males and adolescents. These results have implications for understanding locomotor diversity in fossil and extant apes and for orangutan conservation and reintroduction programs.

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

Abstract: SUMMARY Previous 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 pre-moult 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.