Functional regionalization of the pectoral fin of the benthic longhorn sculpin during station holding and swimming N. K. Taft 1 , G. V. Lauder 2 & P. G. A. Madden 2 1 Graduate Program in Organismic and Evolutionary Biology, University of Massachusetts Amherst, Amherst, MA, USA 2 Museum of Comparative Zoology, Harvard University, Cambridge, MA, USA Keywords fish; sculpin; benthic; swimming; locomotion; three-dimensional kinematics; pectoral fin. Correspondence Natalia K. Taft, Graduate Program in Organismic and Evolutionary Biology, University of Massachusetts Amherst, 211 Morrill Science Center South, 611 North Pleasant St, Amherst, MA 01003, USA. Email: natashak@bio.umass.edu Editor: Jean-Nicolas Volff Received 11 February 2008; revised 1 May 2008; accepted 9 May 2008 doi:10.1111/j.1469-7998.2008.00472.x Abstract Studies of the kinematics of the pectoral fins in fishes have focused on fins as devices for propulsion or maneuvering. Studying pectoral fin function in benthic fishes is an opportunity to understand how the fins are used in a broader range of fin-based behaviors, especially those involving substrate contact. Morphological specializations of the pectoral fins, hypothesized adaptations for substrate contact, have been described for several benthic fish groups. These specializations include, but are not limited to, reduced webbing between ventral rays as well as thickening and shortening of these rays compared with the dorsal rays. Our focal species, the benthic longhorn sculpin, Myoxocephalus octodecimspinosus, possesses these morphological specializations, which divide the fin loosely into dorsal and ventral regions. Our goal was to investigate the functional consequences of these specializations, if any. First, we used high-speed video to examine the motion of the pectoral fins during swimming and station holding on the bottom, the first such study for a benthic fish. We found that longhorn sculpin do not oscillate their pectoral fins during swimming. Rather, the pectoral fins are held in a steady laterally extended posture. Oscillations of the body, median fins and caudal fin are used for propulsion. The shape of the fin also changes dramatically as the fish moves from station holding to swimming. Second, we measured the curvature of the individual fin rays that support and control the shape and movement of the pectoral fins. We did this to examine whether morphological specialization of the fin rays influences fin ray curvature. Individual fin rays in different fin regions show consistently different patterns of bending regardless of behavior. We propose that the pectoral fin is divided into functional as well as morphological regions. The fin rays in each functional region have distinct roles during swimming and substrate contact. Introduction The transition from a pelagic to a benthic lifestyle has occurred in several groups of fishes (Aleev, 1969; Gosline, 1994). This shift has been accompanied by morphological changes in the structure of the pectoral fins (Gosline, 1994). The pectoral fins of most fishes are used for propulsion, maneuverability and/or stability in the water column (Walk- er & Westneat, 2002; Drucker & Lauder, 2003; Drucker, Walker & Westneat, 2006). However, the pectoral fins of benthic fishes are often used for behaviors involving sub- strate contact. For example, pectoral fins aid in digging, burrowing, probing, clinging, crawling, supporting the body of the fish at rest or actively resisting displacement in flow during station holding (Lundberg & Marsh, 1976; Webb, 1989; Brandstatter et al., 1990; Gosline, 1994; Jamon et al., 2007). It has been hypothesized that the pectoral fins of benthic fishes evolved from an ancestral pelagic condition (Gosline, 1994). Specifically, it has been suggested that the benthic pectoral fin evolved from a condition of a relatively uniform morphology into a benthic morphology character- ized by distinct dorsal and ventral morphological regions, the ventral region specialized for substrate contact (Wagner, 1989). In this study, we explore the morphological and func- tional specializations of the pectoral fins in the scorpaeni- form fish Myoxocephalus octodecimspinosus, the longhorn sculpin. Our goal is to better understand regionalization of the pectoral fins in benthic fishes. Scorpaeniform fishes are a group noted for diversity of morphological adaptations, including regionalization, of the pectoral fins associated with a benthic lifestyle (Gosline, 1994). The evolution of regionalization may provide a way to decouple the conflict- ing functional demands of swimming and substrate contact on the pectoral fins (Brandstatter et al., 1990). However, functional differences in the morphologically distinct re- gions of the pectoral fins in benthic fishes have not been examined previously. Journal of Zoology Journal of Zoology ]] (2008) 1–9 c  2008 The Authors. Journal compilation c  2008 The Zoological Society of London 1 Journal of Zoology. Print ISSN 0952-8369