A cladistic and comparative analysis of kinematic components of the fast-start of fishes, with a note on body size constraints.

The fast-start is an ecologically relevant behavior pattern in fishes. The present article analyses the distribution of five continuous kinematic traits (latency for response initiation, time to maximum angular velocity, time to maximum displacement velocity, maximum angular velocity, and maximum displacement velocity) in eight of the eleven species described in Eaton (66:65-81, 1977). Phylogenetic generalized least square estimation of ancestor states demonstrated evolutionary changes in maximum angular velocity and maximum displacement velocity, consistent with species differences in the same variables. These changes in maximum velocity are also correlated (phylogenetically independent contrasts) with the mean body sizes of all species, pointing to the possibility that body size was an evolutionary constraint on maximum velocities. The conservation of the other traits suggest that they are mainly constrained by neural control, and a trade-off between neural and body size-constraints is proposed ex hypothesi.