Movement propensity differs in two morphs of the plainfin midshipman, Porichthys notatus

Alternative reproductive tactics occur when there is within-sex variation in how individuals achieve reproduction. Although these discrete alternative tactics have been well studied in a reproductive context, little is known about non-reproductive behavioural and cognitive differences between reproductive types. Using the plainfin midshipman fish, Porichthys notatus, a species with two distinct male reproductive tactics, we investigated whether individuals employing different tactics vary in movement propensity and spatial navigation ability. In this toadfish species, guarders (Type I males) build nests, acoustically court females, and provide parental care, while sneakers (Type II males) use stealth to enter nests and steal fertilizations. We hypothesized that because sneakers are thought to find multiple nests over the reproductive season, they would be better navigators. We tested guarders and sneakers in a T-maze and found that although sneakers swam faster on average, guarders unexpectedly completed the maze more frequently and more directly, taking a shorter path to the end than sneakers. Guarders also made fewer mistakes over time, entering the incorrect arm of the maze less frequently across subsequent trials within a day, whereas sneakers entered the incorrect arm more frequently over subsequent trials. We discuss how differences in motivation and the saliency of sensory cues could explain these findings. Our results demonstrate that in the plainfin midshipman the two male reproductive morphs differ in spatial task completion and movement propensity, extending our knowledge of behavioural differences in alternative reproductive tactics to a non-reproductive context.