title: Comparative analyses of animal-tracking data reveal ecological significance of endothermy in fishes.
abstract: Despite long evolutionary separations, several sharks and tunas share the ability to maintain slow-twitch, aerobic red muscle (RM) warmer than ambient water. Proximate causes of RM endothermy are well understood, but ultimate causes are unclear. Two advantages often proposed are thermal niche expansion and elevated cruising speeds. The thermal niche hypothesis is generally supported, because fishes with RM endothermy often exhibit greater tolerance to broad temperature ranges. In contrast, whether fishes with RM endothermy cruise faster, and achieve any ecological benefits from doing so, remains unclear. Here, we compiled data recorded by modern animal-tracking tools for a variety of free-swimming marine vertebrates. Using phylogenetically informed allometry, we show that both cruising speeds and maximum annual migration ranges of fishes with RM endothermy are 2-3 times greater than fishes without it, and comparable to nonfish endotherms (i.e., penguins and marine mammals). The estimated cost of transport of fishes with RM endothermy is twice that of fishes without it. We suggest that the high energetic cost of RM endothermy in fishes is offset by the benefit of elevated cruising speeds, which not only increase prey encounter rates, but also enable larger-scale annual migrations and potentially greater access to seasonally available resources.
authors.affiliation: National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan; Department of Polar Science, SOKENDAI (The Graduate University for Advanced Studies), Tachikawa, Tokyo 190-8518, Japan; watanabe.yuuki@nipr.ac.jp.
authors.forename: Yuuki Y
authors.initials: YY
authors.lastname: Watanabe
authors.affiliation: Alaska Department of Fish and Game, Homer, AK 99603;
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Goldman
authors.affiliation: Marine Science Institute, University of California, Santa Barbara, CA 93106;
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Caselle
authors.affiliation: Institute for Ocean Conservation Science, School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11794-5000; and.
authors.forename: Demian D
authors.initials: DD
authors.lastname: Chapman
authors.affiliation: Scottish Oceans Institute, School of Biology, University of St. Andrews, St. Andrews KY16 8LB, Scotland, United Kingdom.
authors.forename: Yannis P
authors.initials: YP
authors.lastname: Papastamatiou
mesh_terms: D000222:Adaptation, Physiological; D025041:Animal Migration; D000818:Animals; D005075:Biological Evolution; D001831:Body Temperature; D001835:Body Weight; D004777:Environment; D005399:Fishes / Q000502:physiology*; D010802:Phylogeny; D012621:Seasons; D012754:Sharks; D013550:Swimming; D022722:Thermogenesis / Q000235:genetics* / Q000502:physiology*
keywords: body temperature; marine predator; migration; swim speed