Abstract: Aggressive behaviour associated with the defence of a territory is thought to impose substantial energy costs and thus to represent a trade-off with other energy-demanding activities. The energy costs of aggressive behaviours, however, have rarely been estimated in the wild, and the overall contribution of territorial defence to daily energy expenditure has never been determined. We studied the activity budget of breeding king penguins, Aptenodytes patagonicus, equipped with heart rate data loggers to estimate the energy costs associated with territory defence in this colonial bird exhibiting very high rates of agonistic interactions. We also assessed whether threat displays imposed lower energy costs than attacks with body contact. During territorial defence (i.e. threats and physical attacks combined), energy expenditure averaged 1.27 times resting metabolic rate. Defence accounted for 13% of the daily time budget and contributed to 2.7% of the total daily energy expenditure. Interactions with body contact cost three times more than threat displays, but accounted for only 16% of the aggressive behaviours recorded. Neither did body mass, body size, penguin sex or breeding stage affect the cost of aggressiveness. Our results are consistent with previous research reporting that fighting imposes significant metabolic costs. However, we found that aggressive behaviour in king penguins was not an expensive activity compared to the total energy budget. Because king penguins go without food and are sleep deprived while breeding, they may have developed behavioural strategies (e.g. lower rates of attacks with body contact) allowing them to defend their territory efficiently at a low energy cost.

Abstract: International Association of Volcanology and Chemi

Abstract: To elucidate the strategy of low temperature adaptation for a cold-adapted family 8 xylanase, the thermal and chemical stabilities, thermal inactivation, thermodependence of activity and conformational flexibility, as well as the thermodynamic basis of these processes, were compared with those of a thermophilic homolog. Differential scanning calorimetry, fluorescence monitoring of guanidine hydrochloride unfolding and fluorescence quenching were used, among other techniques, to show that the cold-adapted enzyme is characterized by a high activity at low temperatures, a poor stability and a high flexibility. In contrast, the thermophilic enzyme is shown to have a reduced low temperature activity, high stability and a reduced flexibility. These findings agree with the hypothesis that cold-adapted enzymes overcome the quandary imposed by low temperature environments via a global or local increase in the flexibility of their molecular edifice, with this in turn leading to a reduced stability. Analysis of the guanidine hydrochloride unfolding, as well as the thermodynamic parameters of irreversible thermal unfolding and thermal inactivation shows that the driving force for this denaturation and inactivation is a large entropy change while a low enthalpy change is implicated in the low temperature activity. A reduced number of salt-bridges are believed to be responsible for both these effects. Guanidine hydrochloride unfolding studies also indicate that both family 8 enzymes unfold via an intermediate prone to aggregation.