Functional trade-offs and innovation shape the adaptive landscape of aquatic mammal feeding.

Functional trade-offs are inherent in phenotypes due to the need to balance multiple competing selection pressures. Traditionally regarded as constraints on evolution, trade-offs have recently been reframed as facilitators of adaptation via the changing relative importance of competing functions. Here, we examine these ideas through the lens of aquatic mammal feeding, testing a behavioral aquatic feeding framework where feeding strategies form an evolutionary continuum from terrestrial to increasingly more specialized water-based feeding styles. Specifically, we hypothesized that suction, suction filter, and ram filter feeding would have adaptive peaks closer together than raptorial feeding, and that taxa follow the functionally optimal evolutionary path (Pareto front) between adaptive peaks. Constructing morphofunctional adaptive landscapes from cetacean mandibles revealed strong support for this framework. Surprisingly, most cetaceans do not lie along the Pareto front between peaks, suggesting that novel functional innovations- most likely the specialized cetacean auditory pathway-are also influencing mandibular evolution.