Stacy C. Farina

Modelling tooth–prey interactions in sharks: the importance of dynamic testing

The shape of shark teeth varies among species, but traditional testing protocols have revealed no predictive relationship between shark tooth morphology and performance. We developed a dynamic testing device to quantify cutting performance of teeth. We mimicked head-shaking behaviour in feeding large sharks by attaching teeth to the blade of a reciprocating power saw fixed in a custom-built frame. We tested three tooth types at biologically relevant speeds and found differences in tooth cutting ability and wear. Teeth from the bluntnose sixgill (Hexanchus griseus) showed poor cutting ability compared with tiger (Galeocerdo cuvier), sandbar (Carcharhinus plumbeus) and silky (C. falciformis) sharks, but they also showed no wear with repeated use. Some shark teeth are very sharp at the expense of quickly dulling, while others are less sharp but dull more slowly. This demonstrates that dynamic testing is vital to understanding the performance of shark teeth.

Look before you leap: Visual navigation and terrestrial locomotion of the intertidal killifish Fundulus heteroclitus

Mummichogs (Fundulus heteroclitus; Cyprinodontiformes) are intertidal killifish that can breathe air and locomote on land. Our goals were to characterize the terrestrial locomotion of mummichogs and determine their method of navigation towards water in a terrestrial environment. We used high-speed video to record behavior during stranding experiments and found that mummichogs use a tail-flip jump to move overland, similarly to other Cyprinodontiformes. However, mummichogs also prop themselves upright into a prone position between each jump, a previously undescribed behavior. After becoming prone, mummichogs rotate about their vertical axis, directing the caudal fin towards the water. Then, they roll back onto their lateral aspect and use a tail-flip behavior to leap into a caudally-directed, ballistic flight path. We conducted experiments to determine the sensory stimulus used to locate a body of water by placing mummichogs on a square platform with one side adjacent to a sea table. Under artificial light, mummichogs moved towards the sea table with a higher frequency than towards the other sides. Under dark conditions, mummichogs did not show a preference for moving towards the sea table. When the surface of the water was covered with reflective foil, mummichogs moved towards it as if it were a body of water. These results suggest that mummichogs primarily use visual cues, specifically reflected light, to orient towards the water. The uprighting behavior that mummichogs perform between terrestrial jumps may provide an opportunity for these fish to receive visual information that allows them to safely return to the water. J. Exp. Zool. 325A:57-64, 2016.

Undulation frequency affects burial performance in living and model flatfishes.

Flatfishes bury themselves under a thin layer of sand to hide from predators or to ambush prey. We investigated the role of undulation frequency of the body in burial in five species of flatfishes (Isopsetta isolepis, Lepidopsetta bilineata, Hippoglossoides elassodon, Parophrys vetulus, and Psettichthys melanostictus). High-speed videos show that undulations begin cranially and pass caudally while burying, as in forward swimming in many other fishes. The flatfishes also flick the posterior edge of their dorsal and anal fins during burial, which may increase the total surface area covered by substrate. We built a simple physical model - a flexible, oval silicone plate with a motorized, variable-speed actuator - to isolate the effect of undulation frequency on burial. In both the model and actuated dead flatfish, increased undulation frequency resulted in an increase in the area of sand coverage. Complete coverage required an undulation frequency of no more than 10Hz for our models, and that was also sufficient for live flatfishes. The model shows that undulation is sufficient to bury the animal, but live flatfishes showed a superior ability to bury, which we attribute to the action of the median fins.

Aquatic burst locomotion by hydroplaning and paddling in common eiders (Somateria mollissima)

ABSTRACT Common eiders (Somateria mollissima) are heavy sea-ducks that spend a large portion of their time swimming at the water surface. Surface swimming generates a bow and hull wave that can constructively interfere and produce wave drag. The speed at which the wavelengths of these waves equal the waterline length of the swimming animal is the hull speed. To increase surface swimming speed beyond the hull speed, an animal must overtake the bow wave. This study found two distinct behaviors that eider ducks used to exceed the hull speed: (1) ‘steaming’, which involved rapid oaring with the wings to propel the duck along the surface of the water, and (2) ‘paddle-assisted flying’, during which the ducks lifted their bodies out of the water and used their feet to paddle against the surface while flapping their wings in the air. An average hull speed (0.732±0.046 m s−1) was calculated for S. mollissima by measuring maximum waterline length from museum specimens. On average, steaming ducks swam 5.5 times faster and paddle-assisted flying ducks moved 6.8 times faster than the hull speed. During steaming, ducks exceeded the hull speed by increasing their body angle and generating dynamic lift to overcome wave drag and hydroplane along the water surface. During paddle-assisted flying, ducks kept their bodies out of the water, thereby avoiding the limitations of wave drag altogether. Both behaviors provided alternatives to flight for these ducks by allowing them to exceed the hull speed while staying at or near the water surface. Summary: Eider ducks are able to exceed their hull speed through the use of two kinematically distinct aquatic surface burst locomotive behaviors.

Biomechanics: Boxed up and ready to go

Flow-tank experiments and fluid-dynamics simulations refute the idea that water movements over the body of boxfishes are a stabilizing influence, instead showing that the fishs shape amplifies destabilizing forces to improve manoeuvrability.

Evolution of the Branchiostegal Membrane and Restricted Gill Openings in Actinopterygian Fishes

A phylogenetic survey is a powerful approach for investigating the evolutionary history of a morphological characteristic that has evolved numerous times without obvious functional implications. Restricted gill openings, an extreme modification of the branchiostegal membrane, are an example of such a characteristic. We examine the evolution of branchiostegal membrane morphology and highlight convergent evolution of restricted gill openings. We surveyed specimens from 433 families of actinopterygians for branchiostegal membrane morphology and measured head and body dimensions. We inferred a relaxed molecular clock phylogeny with branch length estimates based on nine nuclear genes sampled from 285 species that include all major lineages of Actinopterygii. We calculated marginal state reconstructions of four branchiostegal membrane conditions and found that restricted gill openings have evolved independently in at least 11 major actinopterygian clades, and the total number of independent origins of the trait is likely much higher. A principal component analysis revealed that fishes with restricted gill openings occupy a larger morphospace, as defined by our linear measurements, than do fishes with nonrestricted openings. We used a decision tree analysis of ecological data to determine if restricted gill openings are linked to certain environments. We found that fishes with restricted gill openings repeatedly occur under a variety of ecological conditions, although they are rare in open‐ocean pelagic environments. We also tested seven ratios for their utility in distinguishing between fishes with and without restricted gill openings, and we propose a simple metric for quantifying restricted gill openings (RGO), defined as a ratio of the distance from the ventral midline to the gill opening relative to half the circumference of the head. Functional explanations for this specialized morphology likely differ within each clade, but its repeated evolution indicates a need for a better understanding of diversity of ventilatory morphology among fishes. J. Morphol. 276:681–694, 2015.

Functional morphology of gill ventilation of the goosefish, Lophius americanus (Lophiiformes: Lophiidae)

The goosefish, Lophius americanus, is a dorso-ventrally compressed marine fish that spends most of its life sitting on the substrate waiting to ambush prey. Species in the genus Lophius have some of the slowest ventilatory cycles recorded in fishes, with a typical cycle lasting more than 90s. They have a large gill chamber, supported by long branchiostegal rays and ending in a siphon-like gill opening positioned underneath and behind the base of the pectoral fin. Our goals were to characterize the kinematics of gill ventilation in L. americanus relative to those of more typical ray-finned fishes, address previous assertions about ventilation in this genus, and describe the anatomy of the gill opening. We found that phase 1 of ventilation (during which both the buccal and gill chamber are expanding) is greatly increased in duration relative to that of typical ray-finned fishes (ranging from 62 to 127s), and during this phase, the branchiostegal rays are slowly expanding. This slow expansion is almost visually imperceptible, especially from a dorsal view. Despite this unusually long phase 1, the pattern of skeletal movements follows that of a typical actinopterygian, refuting previous assertions that Lophius does not use its jaws, suspensorium, and operculum during ventilation. When individuals were disturbed from the sediment, they tended to breathe more rapidly by decreasing the duration of phase 1 (to 18-30s). Dissections of the gill opening revealed a previously undocumented dorsal extension of the adductor hyohyoideus muscle, which passes from between the branchiostegal rays, through the ventro-medial wall of the gill opening, and to the dorsal midline of the body. This morphology of the adductor hyohyoideus shares similarities with that of many Tetraodontiformes, and we suggest that it may be a synapomorphy for Lophiiformes+Tetraodontiformes. The specialized anatomy and function of the gill chamber of Lophius represents extreme modifications that provide insight into the potential limits of the actinopterygian gill ventilatory system.