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By Justin Speaks

A Phylogenetic Survey of Dental Sexual Dimorphism in Chondrichthyan Fishes of the North Carolina Coast. By Justin Speaks. Faculty Advisor: Dr. Thomas Lankford. Mating Behavior. Typical for male to bite female prior to and during copulation, leaving what are called mating scars.

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By Justin Speaks

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  1. A Phylogenetic Survey of Dental Sexual Dimorphism in Chondrichthyan Fishes of the North Carolina Coast By Justin Speaks Faculty Advisor: Dr. Thomas Lankford

  2. Mating Behavior • Typical for male to bite female prior to and during copulation, leaving what are called mating scars. • Sharks and Rajiformes practice in vitro fertilization.

  3. What is Dental Sexual Dimorphism? • A difference in tooth shape between males and females. • Some stingrays have displayed this on a seasonal basis • Sharper teeth during mating seasons Photo courtesy of Florida Museum of Natural History Ichthyology Department

  4. Research Questions • Do other species of ray or skate, or even sharks with similar dentition, display this adaptation? • Hypothesis: Dental Sexual Dimorphism is widespread among Chondrichthyan species who posses flat, crushing dentition. • Is this a new evolutionary trend or something that has been passed down the lineage of cartilaginous fishes? • Will we be able to determine mating seasons for those species that are currently unknown?

  5. The Species List

  6. Relationship Between Sharks and Rajiformes bullhead sharks dogfish sharks mackerel sharks ground sharks angel sharks carpet sharks skates & rays cow sharks saw sharks chimaeras “batoid fishes” 8 Orders of Sharks (350 spp.) 12 families 62 genera 456 spp.

  7. How to Answer These Questions • Bottom trawl collections once a month for twelve months (May ’06-April ’07) • New Methods • Pictures of dentition will be taken immediately upon capture so as to release all animals alive. • We will survey sex, size, ovulation and mating scars (in females only) • Photo record will be compiled and interpreted as it is collected. Trawls will collect in Onslow Bay, from Cape Fear to Cape Lookout.

  8. Example of Tooth Photography Method

  9. Why Answer These Questions? • Basic information for the scientific record. • Which species exhibit this adaptation • Mating seasons • Evolution • Information for Fisheries Biologists • Reduce by-catch during mating seasons

  10. References Kajiura, Stephen M.; Sebastian, Agustin P.; Tricas, Timothy C. Dermal Bite Wounds as Indicators of Reproductive Seasonality and Behavior in the Atlantic Stingray, Dasyatis sabina. Environmental Biology of Fishes: 2000; vol. 58, pp. 23-31 Kajiura, Stephen M.; Tricas, Timothy C. Seasonal Dynamics of Dental SexualDimorphism in the Atlantic Stingray, Dasyatis sabina. Journal of Experimental Biology: June 1996; vol 199, pp. 2297-2306

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