The ability to modulate the function of muscle is integral to an animal’s ability to function effectively in the face of widely disparate challenges. This modulation of function can manifest through short-term changes in neuromuscular control, but also through long-term changes in force profiles, fatigability, and architecture. However, the relative extent to which shorter-term modulation and longer-term plasticity govern locomotor flexibility remains unclear. Here, we obtain simultaneously-recorded kinematic and muscle activity data of fin and body musculature of an amphibious fish, Polypterus senegalus. After examining swimming and walking behaviour in aquatically-raised individuals, we show that walking behaviour is characterized by greater absolute duration of muscle activity in most muscles when compared with swimming, but that the magnitude of recruitment during walking is only increased in the secondary bursts of fin muscle and in the primary burst of the mid-body point. This localized increase in intensity suggests that walking in P. senegalus is powered in a few key locations on the fish, contrasting with the more distributed, low intensity muscle force that characterizes the stroke cycle during swimming. Finally, the increased intensity in secondary, but not primary, bursts of the fin muscles when walking likely underscores the importance of antagonistic muscle activity to prevent fin collapse, add stabilization, and increase body support. Understanding the principles that underlie the flexibility of muscle function can provide key insights into the sources of animal functional and behavioural diversity.
Kathleen L. Foster, Misha Dhuper, and Emily M. Standen