A Physiological Analysis of Color Vision in Batoid Elasmobranchs

The potential for color vision in elasmobranchs has been studied in detail; however, a high degree of variation exists among the group. Evidence for ultraviolet (UV) vision is lacking, despite the presence of UV vision in every other vertebrate class. An integrative physiological approach was used to investigate color and ultraviolet vision in cownose rays and yellow stingrays, two batoids that inhabit different spectral environments. Both species had peaks in UV, short, medium, and long wavelength spectral regions in dark-, light-, and chromatic-adapted electroretinograms. Although no UV cones were found with microspectrophotometric analysis, both rays had multiple cone visual pigments with λmax at 470 and 551 nm in cownose rays (Rhinoptera bonasus) and 475, 533, and 562 nm in yellow stingrays (Urobatis jamaicensis). The same analysis demonstrated that both species had rod λmax at 500 and 499 nm, respectively. The lens and cornea of cownose rays maximally transmitted wavelengths greater than 350 nm and greater than 376 nm in yellow stingrays. These results support the potential for color vision in these species and future investigations should reveal the extent to which color discrimination is significant in a behavioral context

Green fishing: Sustainable seafood of the Georgia Coastal Plain

Dr. Christine Bedore, Assistant Professor, Department of Biology ($31,808.00) Promoted sustainability of local marine resources of the Georgia Coastal Plain in order to educate GS students to raise awareness about the importance of making sustainable choices with respect to seafood

Sexual Dimorphism in the Dentition of Pelagic Stingrays, Pteroplatytrygon violacea

The elasmobranch fishes are a group of vertebrates that have evolved a multi-functional mouth that is involved in mating behavior. Sexually dimorphic changes have been observed, which include epidermal thickening in females and seasonal changes in male dentition. Male Atlantic stingray (Dasyatis sabina) dentition changes from molariform to pointed during the mating season, which allows them to better grasp the females to successfully mate . Pelagic stingrays (Pteroplatytrygon violacea) are in the same family (Dasyatidae) as Atlantic stingrays and are likely to undergo seasonal changes in dentition as well. However, pelagic stingrays possess pointed symphyseal teeth to aid in feeding on teleosts and squid. Therefore, it is unknown if pelagic stingrays also undergo seasonal changes in dentition to aid in mating. Pelagic stingray jaws were collected from commercial fisherman. Tissue was dissected from each jaw and the number of teeth in the files and rows was recorded. The tooth next to the symphyseal tooth in the second row of the upper jaw was extracted and photographed. Photographs were digitized and analyzed for shape with various software programs. Results show that sexual dimorphism in pelagic stingrays is seen between male and female teeth (P=0.01). There were no significant differences in males and females between mating and non-mating seasons (P=0.06, P=0.55). The number of tooth rows increased significantly according to disc width in upper jaws in both sexes. The number of tooth rows in the lower jaws of males also increased significantly. There is no significant difference in tooth files in upper or lower jaws in both sexes. However, number of tooth files are significantly different between males and females

Effects of Temperature and Anesthesia on Visual Temporal Resolution in Elasmobranch Fishes

An organism’s ability to track moving objects, or temporal resolution, has been correlated to habitat and lifestyle, and can be further modulated by temperature and light intensity fluctuations within the environment. Photopic (bright-light/day time) vision is typically faster than scotopic (dim-light/night time) because visual sensitivity is greater in dim light and integration time must be slowed to allow for capture of the maximum number of photons. Higher temperatures result in increased temporal resolution in both endothermic and non-endothermic fishes. Previous studies have used either anesthetized or paralyzed fishes to determine temporal resolution, measured as the maximum critical flicker fusion frequency (CFFmax). However, sedation with the anesthetic, tricaine methanesulfonate (MS-222), is thought to suppress sensory system responses, although empirical evidence is lacking. Therefore, we quantified scotopic and photopic CFFmax in the yellow stingray, Urobatis jamaicensis, at the extremes of its temperature range, 20°C and 30°C, and immobilized with anesthesia, MS-222, or a paralytic, Pavulon. Both low temperature and anesthesia (MS-222) reduced CFFmax. With an increase of 10°C, CFFmax doubled from 12Hz to 25.3Hz (photopic) under Pavulon, whereas CFFmax increased by only 4Hz, from 6.7Hz to 10.7Hz (photopic) under MS-222 anesthesia. In general, MS-222 anesthesia minimized the effects of both temperature and light-adaptation compared to Pavulon. Yellow stingray CFFmax was similar to the skate, another benthic batoid, but slower than shark species studied with the same technique. These results illustrate the effects of light adaptation, temperature, and anesthesia on visual function within the elasmobranch fishes

Sexual Dimorphism in the Dentition of Basal Vertebrates

Elasmobranch fishes are among a small group of vertebrates that use their mouth to bite their mate during courtship and copulation. Because the teeth of males are under selective pressure to facilitate both feeding and grasping of the females, there exists the potential for conflicting selective demands on the tooth morphology, where the tooth shape optimal for one behavior may be suboptimal for the other. Various elasmobranch species have been documented to exhibit sexual dimorphisms in tooth morphology with males typically possessing more cuspidate teeth, presumably to facilitate grasping the female during mating. Male Atlantic stingrays (Dasyatis sabina) demonstrate seasonally dynamic changes in dentition, from molariform teeth during the non-mating season to cuspidate teeth during the mating season. Thisseasonal change in tooth shape is documented for only a single species so it remains unknown whether this is a widespread phenomenon. Pelagic stingrays (Pteroplatytrygon violacea) are in the same family (Dasyatidae) as Atlantic stingrays but feed on teleost and squid prey which present similar demands on the male tooth morphology as the slippery body of their female mates. If the tooth morphology of pelagic stingrays is sexually dynamic and males undergo a seasonal change in tooth shape, it suggests that dynamic teeth are likely widespread throughout the batoids. Pelagic stingray jaws were collected monthly from commercial fisherman for a full year. the number of tooth files and rows did not differ between the sexes and ranged from 20-35 tooth rows and 5-10 tooth files in both upper and lower jaws. Upper jaw symphyseal teeth were extracted for shape analysis, Qualitative differences in tooth shape were observed between males and females throughout the year, and males demonstrated different tooth shapes between mating and non-mating seasons. male Pelagic stingray teeth were more strongly cuspidate than female teeth especially late in the mating season (April) when the teeth have rotated to the outermost functional position. Male Teeth fromthe non-mating season (November) showed a more rounded triangular shape. a Procrustes superimposition with relative warp analysis was employed to quantify the differences between the sexes and between mating and non-mating seasons. The observation that male tooth morphology changes seasonally, even in a piscivorous species, indicates that this is a widespread phenomenon

Distribution and relative abundance of scalloped (Sphyrna lewini) and Carolina (S. gilberti) hammerheads in the western North Atlantic Ocean

The scalloped hammerhead (Sphyrna lewini) and its cryptic congener, Carolina hammerhead (S. gilberti), are sympatrically distributed in the western North Atlantic Ocean. Because the species are indistinguishable based on external morphology, little research focused on Carolina hammerheads exists. In this study, the distribution of Carolina hammerheads in waters of the United States off the east coast (U.S. Atlantic) and Gulf of Mexico (Gulf) was examined and their abundance relative to scalloped hammerheads assessed by genetically identifying 1231 individuals using diagnostic single nucleotide polymorphisms. Both species were found in the U.S. Atlantic, where 27 % of individuals were Carolina hammerheads, but only scalloped hammerheads were identified in the Gulf. In Bulls Bay, SC, a well-known hammerhead nursery, assessment of relative abundance from May to September showed scalloped hammerheads were more abundant May-June and Carolina hammerheads more abundant July-September. Results of this study suggest Carolina hammerheads have a spatially limited distribution in the western North Atlantic and highlight the importance of Bulls Bay as a nursery for the species. In addition, the results suggest Carolina hammerheads may comprise a non-trivial proportion of what is considered the U.S. Atlantic scalloped hammerhead stock and should be considered in future decisions regarding management of the hammerhead complex