A Phylogenetic Survey of Dental Sexual Dimorphism in Chondrichthyan Fishes of the North Carolina Coast

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A Phylogenetic Survey of Dental Sexual Dimorphism
in Chondrichthyan Fishes of the North Carolina
Coast

• By Justin Speaks

Faculty Advisor Dr. Thomas Lankford
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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.

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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
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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?

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The Species List

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Relationship Between Sharks and Rajiformes
batoid fishes
8 Orders of Sharks (350 spp.)
12 families 62 genera 456 spp.
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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.
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Example of Tooth Photography Method

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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

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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 Sexual Dimorphism in the
  Atlantic Stingray, Dasyatis sabina. Journal of
  Experimental Biology June 1996 vol 199, pp.
  2297-2306