This study is directed toward understanding the process of feeding stimulation ("refeeding signal") that has been suggested to operate below a body mass threshold or critical metabolic status in spontaneously fasting birds. Behavior and egg temperature (T(egg)) were continuously monitored by video monitoring and biotelemetry, respectively, in fasting-incubating king penguins kept in a pen to prevent relief by the partner until spontaneous egg abandonment. Penned birds fasted 10 days more and lost 1.2 kg more than birds relieved normally by their partner, abandoning the egg about 1 wk after reaching a critical body mass. Definitive egg abandonment was preceded by transitory abandonments of progressively increasing duration during which time the birds went further and further away from their egg. There were marked interindividual differences but on average transitory abandonments began 36 +/- 5 h before the definitive abandonment and were paralleled by resumption of display songs signaling the readiness of the bird to depart for feeding. T(egg) was maintained at around 35.7 degrees C during normal incubation but significantly decreased the last 2 days before egg abandonment. These changes are interpreted as reflecting a stimulation to refeed at a threshold body mass corresponding to a critical fat store depletion. Thus the fasting-incubating king penguin appears to be an interesting animal model for understanding the long-term metabolic control of feeding behavior in relation to energy status.

No abstract

Spatial distribution of motor endplates affects the shape of the electrical activity recorded from muscle. In order to provide information for realistic models of action potential propagation within muscles, we assembled three-dimensional maps of the motor endplates of the rat medial gastrocnemius (MGM) and lateral gastrocnemius (MGL) muscles. The maps were assembled from histological cross sections stained for acetylcholinesterase activity. Within MGL, the motor endplates formed three columns along its longitudinal axis. Within MGM, the motor endplates were arranged in a leaf-like body that shifted obliquely from proximal to distal. As inferred from the proximo-distal distribution of the cross-sectional projection area, the majority of the motor endplates were concentrated in the middle of MGL and in the distal third of MGM. Regions of maximal motor endplate concentration are considered most suitable for injections of neuroactive substances, such as neuronal tracers. The assembled maps of the gastrocnemius muscles can be used as guides for such injections within the motor endplate zones.

Groscolas, R. 2001. Restoration of body mass in King Penguins after egg abandonment at a critical energy depletion stage: early vs late breeders. -J. Avian Biol. 32: 303-310.In fasting-incubating seabirds, it has been proposed that egg abandonment and refeeding should be induced when a low body mass (BM) threshold is attained, thus ensuring adult survival at the expense of immediate breeding. In the context of life-history trade-offs in long-lived birds, we have tested this hypothesis by comparing short-term survival and restoration of BM in King Penguins Aptenodytes patagonicus that abandoned their egg to those that were relieved normally by their mate at the end of the first incubation shift. Since King Penguins have an extended laying period, the possible influence of seasonal factors was also examined by comparing early and late breeders. Forty incubating males were experimentally forced to fast until egg abandonment by preventing relief by the female. At egg abandonment of both early and late breeding males, BM was below the BM threshold, fasting duration was eight days (about 30%) longer than for relieved birds, and plasma uric acid level was elevated (signature of increased body protein catabolism, phase III of fasting). All abandoning birds survived and came back from sea at a BM similar to that of relieved penguins. The duration of the foraging trip of abandoning early breeders was the same as that of relieved birds, and some abandoning birds engaged in a new breeding attempt. Abandoning late breeders, however, made foraging trips twice as long as those of relieved males. This difference can be explained by time constraints rather than nutritional constraints, abandoning early breeders having enough time left in the breeding season to engage in a new breeding attempt in contrast to abandoning late breeders. These observations lend support to the suggestion that not only BM but also an internal clock intervene in the decision to engage in breeding or not. By preventing a lethal energy depletion ashore and by acting at a fasting stage where the capacity to restore BM at sea is unaffected, abandonment at a low body condition threshold plays a major role in the trade-off between adult penguin survival and reproduction.