Meeting Abstract

54.9  Saturday, Jan. 5  Complexity in the suction feeding mechanism mitigates a diet tradeoff in centrarchid fishes. COLLAR, David; University of California, Davis dccollar@ucdavis.edu

Tradeoffs are pervasive in organismal design and often shape ecological diversification. Structures that perform multiple functions are subject to several, often-opposing selection pressures, which may limit their evolution. The size of a fish�s buccal cavity is subject to a performance tradeoff between the volume of water it can engulf and the magnitude of the pressure drop generated inside it. However, suction pressure is also determined by the force capacity of cranial muscles and their mechanical advantage. I tested whether this complexity in the feeding mechanism mitigates the consequences of the tradeoff for diet evolution. I applied a well-resolved phylogeny to calculate independent contrasts and performed a principal components analysis on contrasts of diet variables. The first diet principal component (PC) loads with changes in the contribution of fish and crayfish and is associated with change in buccal volume but not with suction pressure. The second diet PC loads with changes in the contribution of aquatic insect larvae and is correlated with evolution of suction pressure but is unrelated to buccal volume. Thus, the performance tradeoff is not realized as a diet tradeoff; increases in buccal volume are associated with increases in the amount of large, evasive prey but come at little or no cost to insectivory, and enhancements in suction capacity are linked to increased insectivory but do not appreciably influence piscivory or crayfish predation. The consequences of the tradeoff for diet evolution are lessened because changes in suction capacity associated with the second diet PC result from change in cranial features other than the buccal cavity. These results demonstrate that functional complexity is capable of promoting resource diversification in the face of a tradeoff.