Data from: Mitochondrial function predicts dominance status in brown trout

In social hierarchies, winning contests confers better access to food,
shelter, and reproductive opportunities. Clear dominance relationships are
often apparent even when opponents are matched for experience, age, size,
and other obvious characteristics. One explanation for this could be
among-individual differences in mitochondrial function, since this could
be associated with the cellular allocation of energy to
dominance-associated traits. Here, we tested whether the dominance status
of juvenile brown trout (Salmo trutta) was related to their mitochondrial
function. We determined each fish’s dominance status by staging a series
of contests for a feeding territory in an artificial stream tank;
observations of colouration, food acquisition, and aggressive behaviour
allowed the assignment of dominance. Mitochondrial function (the capacity
for ATP production, and the efficiency with which ATP is produced) was
then measured in the muscles used for swimming, analysed at the level of
both homogenised tissue and isolated mitochondria. We found that a fish’s
net phosphorylation efficiency (i.e., the efficiency with which ATP is
produced) was a significant predictor of its dominance-associated
colouration and the level of aggression it exhibited towards an opponent.
However, a fish’s overall dominance status was instead predicted by its
capacity for oxidative phosphorylation (i.e. ATP production capacity).
Moreover, oxidative phosphorylation was also a significant predictor of
whether a fish would be categorised as being subordinate or dominant in a
binary classification. While it is now well established that
organism-level metabolism is a fundamental trait linking an individual’s
ecology, physiology and life history, it is only relatively recently that
the causes of among-individual variation in this trait have been
investigated, with a shift in focus towards the ways in which energy is
produced at a cellular level. By showing that mitochondrial function is
related to competitive ability, this study exemplifies how cellular energy
production can influence contest outcomes and thus the architecture of
social hierarchies.