While A. limatula possesses the ability to acclimate its physiological rates to altered environmental temperatures, acclimation is probably responsible for only a portion of the observed seasonal variation in heart rate. The effect of starvation on heart rate was rapid, measurable and reversible. The large seasonal variation may include a component related to either food availability (algae growth) or to some feeding rhythm. Some correlation between the annual reproductive cycle and heart rate is suggested by the simultaneous occurrence of peak yearly rate and spawning time. Temperature acclimation may be relatively more important in explaining rate differences between microgeographically separated populations, but the presence of a rotational component in the R-T [respiration/temperature] curves of acclimatized animals and the absence of such a component from the curves of animals acclimated in the laboratory indicate that temperature is not the only factor influencing the differences seen in field populations.
