evolutionary attributes of headfirst prey manipulation and.pdf

NOTES Evolutionary attributes of headfirst prey manipulation and swallowing in piscivores T. E. REIMCHEN Department of Biology, University of Victoria, P. 0. Box 1700, Victoria, B. C., Canada V8W 2Y2 Received December 3, 1990 REIMCHEN, T. E. 1991. Evolutionary attributes of headfirst prey manipulation and swallowing in piscivores. Can. J. Zool. 69: 2912-2916. Headfirst swallowing of fish prey is mon attribute of gape-limited predators, conferring the presumed advantage of reduced esophageal abrasion. I evaluate swallowing orientation using cutthroat trout (Oncorhynchus clarki) as predator and three- spine stickleback (Gasterosteus aculeatus) as prey. Field data indicate that orientation is random when prey diameter is less than one-half the gape of the predator, but this increases to 90% headfirst orientation as prey diameter approaches and exceeds the maximum gape, consistent with the suspected reduction in abrasion. Experimental data show two additional advantages to headfirst orientation. Following capture, there is a 2- to 5-fold reduction in escape rate of the prey, and among prey that were swallowed, the manipulation period is substantially reduced (mean 29 vs. 8 1 s for headfirst and tailfirst orientation, respectively), the differences being most accentuated at large prey sizes. REIMCHEN, T. E. 1991. Evolutionary attributes of headfirst prey manipulation and swallowing