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How to build a pectoral fin: functional morphology and steady swimming kinematics of the spotted ratfish (Hydrolagus colliei)

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Aquatic flight is the primary locomotor mode for many animals, including penguins and other diving birds, turtles, and fishes, where labriform and rajiform swimming have been the focus of much interest. However, despite its interesting phylogenetic placement, little is known about the aquatic flight of the sister lineage to the elasmobranchs, the chimaerids. This study investigates the pectoral fin morphology of the spotted ratfish (Hydrolagus colliei (Lay and Bennett, 1839)) as a possible factor underlying the kinematics of their steady swimming by comparing muscle mass, distribution, and abductor to adductor ratio with those of a closely related shark (Squalus acanthias L., 1758). Despite fundamental differences in swimming mode, abductor to adductor muscle ratio did not differ between species (P = 0.49). However, the muscle ratio in the spotted ratfish was similar to the range determined in other flapping labriform swimmers. Ratfish had larger, distally placed pectoral fin muscles relative to body size than dogfish (P < 0.0001) possibly aiding in fine control. Stroke amplitude remained constant across body size (P = 0.26) and relative swimming speed (P = 0.23) in the ratfish, whereas the downstroke was significantly faster than the upstroke (P = 0.006). The similar muscle ratio, despite differences in stroke phases, may be explained by physiological or in vivo recruitment differences between abductors and adductors in the ratfish.

Le vol aquatique est le mode principal de locomotion de plusieurs animaux, dont les manchots et autres oiseaux plongeurs, les tortues et les poissons, chez lesquels on s’est beaucoup intéressé à la nage labriforme et la nage rajiforme. Cependant, on connaît peu de choses sur le vol aquatique des chiméridés, la lignée sœur des élasmobranches, malgré leur position phylogénique intéressante. Notre étude examine la morphologie de la nageoire pectorale de la chimère d’Amérique (Hydrolagus colliei (Lay et Bennett, 1839)) comme facteur sous-jacent potentiel de la cinématique de leur nage régulière soutenue, en comparant la masse musculaire, la répartition des muscles et le rapport des abducteurs-adducteurs avec les mêmes caractères chez un requin fortement apparenté (Squalus acanthias L., 1758). Malgré des différences fondamentales dans le mode de nage, le rapport des abducteurs-adducteurs ne diffère pas entre les deux espèces (P = 0,49). Cependant, le rapport des muscles chez la chimère d’Amérique correspond à l’étendue observée chez d’autres nageurs labriformes qui battent des nageoires. Les chimères possèdent des muscles en position distale dans les nageoires pectorales de plus grande taille par rapport à la taille corporelle que les aiguillats (P < 0,0001), ce qui aide peut-être au contrôle à l’échelle fine. L’amplitude du battement reste constante quelles que soient la taille corporelle (P = 0,26) et la vitesse relative de nage (P = 0,23) chez la chimère, alors que l’abaissée est significativement plus rapide que la remontée (P = 0,006). Les rapports musculaires semblables, malgré les différences dans les phases du battement, peuvent s’expliquer par des différences physiologiques, ou in vivo, de recrutement entre les muscles abducteurs et adducteurs chez la chimère.

Document Type: Research Article

Publication date: 2010-08-01

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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