Social rank and not physiological capacity determines competitive success in zebrafish (Danio rerio)

Abstract

Competition for resources shapes ecological and evolutionary relationships. Physiological capacities such as in locomotor performance can influence the fitness of individuals by increasing competitive success. Social hierarchy too can affect outcomes of competition by altering locomotor behaviour or because higher ranking individuals monopolize resources. Here, we tested the hypotheses that competitive success is determined by sprint performance or by social status. We show that sprint performance of individuals measured during escape responses (fast start) or in an accelerated sprint test did not correlate with realized sprint speed while competing for food within a social group of five fish; fast start and accelerated sprint speed were higher than realized speed. Social status within the group was the best predictor of competitive success, followed by realized speed. Social hierarchies in zebrafish are established within 7 days of their first encounter, and interestingly, there was a positive correlation between social status and realized speed 1 and 4 days after fish were placed in a group, but not after 7 days. These data indicate that physiological performance decreases in importance as social relationships are established. Also, maximal physiological capacities were not important for competitive success, but swimming speed changed with social context.

Dynamics of dominance: maneuvers, contests, and assessment in the posture-scale movements of interacting zebrafish

“…In the wild, territorial males are known to aggressively stop other males from accessing spawning sites [38,39]. Zebrafish also live in groups for which contests may help establish a dominance hierarchy [40][41][42].…”

The Potential for Physiological Performance Curves to Shape Environmental Effects on Social Behavior

“…Changes in dominance may also be delayed or may not occur at all if there are carryover effects whereby a dominant individual is more likely to stay dominant ( Hock and Huber, 2009 ), even if the environmental conditions become less favorable for its own phenotype. For example, established social rank can weaken the importance of physiological performance for competitive interactions in some species ( Miln et al, 2021 ).…”

“…Even without dominance hierarchies and aggression, individuals within groups also consistently differ in their ability to exploit resources, such as food, during scramble competition ( David et al, 2011 ). These individual differences can be explained by physiological processes that affect motivation for the resource, sensory perception of the resource and locomotory performance to acquire the resource before competitors ( Miln et al, 2021 ). Differences among individuals in physiological performance curves will affect how resources are distributed within groups depending on the current environmental conditions.…”