title: Body ram, not suction, is the primary axis of suction-feeding diversity in spiny-rayed fishes.
abstract: Suction-feeding fishes exhibit diverse prey-capture strategies that vary in their relative use of suction and predator approach (ram), which is often referred to as the ram-suction continuum. Previous research has found that ram varies more than suction distance among species, such that ram accounts for most differences in prey-capture behaviors. To determine whether these findings hold at broad evolutionary scales, we collected high-speed videos of 40 species of spiny-rayed fishes (Acanthomorpha) feeding on live prey. For each strike, we calculated the contributions of suction, body ram (swimming) and jaw ram (mouth movement relative to the body) to closing the distance between predator and prey. We confirm that the contribution of suction distance is limited even in this phylogenetically and ecologically broad sample of species, with the extreme suction area of prey-capture space conspicuously unoccupied. Instead of a continuum from suction to ram, we find that variation in body ram is the major factor underlying the diversity of prey-capture strategies among suction-feeding fishes. Independent measurement of the contribution of jaw ram revealed that it is an important component of diversity among spiny-rayed fishes, with a number of ecomorphologies relying heavily on jaw ram, including pivot feeding in syngnathiforms, extreme jaw protruders and benthic sit-and-wait ambush predators. A combination of morphological and behavioral innovations has allowed fish to invade the extreme jaw ram area of prey-capture space. We caution that while two-species comparisons may support a ram-suction trade-off, these patterns do not speak to broader patterns across spiny-rayed fishes.
authors.affiliation: Department of Evolution and Ecology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA sjlongo@ucdavis.edu.
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Longo
authors.affiliation: Department of Evolution and Ecology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: McGee
authors.affiliation: Department of Biological Sciences, Towson University, Towson, MD 21252, USA.
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Oufiero
authors.affiliation: Department of Infectious Diseases and Pathology, College of Veterinary Medicine, University of Florida, PO Box 110880, Gainesville, FL 32611, USA.
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Waltzek
authors.affiliation: Department of Evolution and Ecology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Wainwright
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D005247:Feeding Behavior / Q000502:physiology*; D005399:Fishes / Q000502:physiology*; D009055:Mouth; D011235:Predatory Behavior; D013550:Swimming
keywords: Acanthomorpha; Constraint; Continuum; Jaw ram; Prey capture; Ram–suction