Differential muscular myosin heavy chain expression of the pectoral and pelvic girdles during early growth in the king penguin (Aptenodytes patagonicus) chick

Abstract

SUMMARYContinuous growth, associated with a steady parental food supply, is a general pattern in offspring development. So that young chicks can acquire their locomotor independence, this period is usually marked by a fast maturation of muscles, during which different myosin heavy chain (MyHC) isoforms are expressed. However, parental food provisioning may fluctuate seasonally, and offspring therefore face a challenge to ensure the necessary maturation of their tissues when energy is limited. To address this trade-off we investigated muscle maturation in both the pectoral and pelvic girdles of king penguin chicks. This species has an exceptionally long rearing period (1year), which is prolonged when parental food provisioning is drastically reduced during the sub-Antarctic winter. Approximately 1month post hatching, chicks acquire a functional pedestrian locomotion, which uses pelvic muscles, whereas swimming, which uses the pectoral muscles, only occurs 1year later. We therefore tested the hypothesis that the MyHC content of the leg muscles reaches a mature state before those of the pectoral muscles. We found that leg muscle MyHC composition changed with the progressive acquisition of pedestrian locomotion, whereas pectoral muscle fibres reached their mature MyHC profile as early as hatching. Contrary to our predictions, the acquisition of the adult profile in pectoral muscles could be related to an early maturation of the contractile muscular proteins, presumably associated with early thermoregulatory capacities of chicks, necessary for survival in their cold environment. This differential maturation appears to reconcile both the locomotor and environmental constraints of king penguin chicks during growth.

Fibre types in primary ‘flight’ muscles of the African Penguin (Spheniscus demersus)

“…; Erbrech et al . ). In the present study, we detected the presence of a slow fibre population that has not been observed in other Sphenisciformes.…”

“…; Erbrech et al . ), it is possible that only superficial muscle was sampled, accounting for the lack of slow fibres. As many experiments use biopsy samples from the pectoralis and supracoracoideus (Williams et al .…”

“…; Erbrech et al . ). As fibre type composition of the Aptenodytes species may not be representative of Spheniscus penguins, we used histochemical and immunohistochemical methods to determine the fibre type composition of African penguin pectoralis, supracoracoideus and latissimus dorsi muscles.…”