Vision is not necessary for size-selective zooplanktivory in aquatic salamanders

Abstract

Vision is usually implicated as the sensory modality employed in size-selective zooplanktivory by aquatic vertebrates. I tested this generalization for nocturnally active salamanders by offering sighted and enucleated Ambystoma maculatum larvae a choice of large vs. small, or normally coloured vs. artificially darkened Daphnia, a natural prey. Salamanders in all treatments took the largest Daphnia and exhibited similar high feeding rates. There was no preference for artificially darkened Daphnia, as would be expected if visual cues predominate. Together these results indicate that vision is not exclusively responsible for size-selective predation by nocturnal salamanders. The often stated or implied assumption that size selectivity indicates visual predation in aquatic vertebrates should thus be questioned.