Christopher K. Beachy, Kiswendsida C. Ouedraogo
Department of Biology, Minot State University, 500 University Avenue West, Minot, North Dakota 58707,
USA
Cranial development in a miniaturized form of the salamander Desmognathus quadramaculatus:Roles of temperature and thyroid hormone.
I-Hypotheses
Temperature and Thyroid hormone have an effect on cranial
metamorphosis of Desmognathus quadramaculatus
II-Background
• Description of Plethodontidae salamanders
-Variable life cycle
-Sensitivity to Temperature and Thyroid
hormone
• Effect of temperature– Effect on metamorphosis
• High temperature effect• Low temperature effect
– Structures affected during metamorphosis• External structures: the skin• Internal structures: skeletal elements
• Effect of Thyroid hormone– Criteria of TH action
• TH concentration• Size-age of the animal
III-Materials and Method • Characteristics of the salamanders
– Larval size– Place of collection
• Gott Farm Creek, Bald Mountains, NC
• Experimental Procedure
– Number of salamanders– Habitat
• Room– Boxes: 8*3*4 LWH– 110g sands– 100g gravel– 250 Ml of distilled water
• House : Coolers
– Variation in Temperature• Beginning of the experiment
– Low temperature (7 C, 11C)
• In the course of the experiment– High temperature (11C, 15C)
– TH treatment• TH (1.2*10-8 M )• Control ( 0.0 M)
– Variation in the intensity of the treatment factors• Temperature
– 1 C every two days
• Thyroid hormone– 1.2*10-8 M every two weeks
– Four final treatment groups• 11C and 4.8*10-8 M• 15 C and 4.8*10-8 M• 11 C and control• 15 C and control
– Evaluation of the internal metamorphosis• The idea of the Bone-Cartilage evaluation
– Double-Staining Technique
• The idea of the number of teeth and hyobranchial apparatus– Four Dermatocranial elements
» Vomer» Parasphenoid» Pterygoid» Maxilla
– Hyobranchial Apparatus» Ceratohyal (1)» Basibranchials(2)» Ceratobranchials(2)» Epibranchials (4)
Skull of larvae Desmognathus quadramaculatus (dorsal view)
Skull of adult Desmognathus quadramaculatus (dorsal view)
Skull of adult Desmognathus quadramaculatus (ventral view)
• The statistical analysis
– Multivariate Analysis of Variance =0.05• Test statistics: Wilk’s Lambda
– Pearson Correlation• Identification of the nature of the effects of the factors• Identification of the patterns of skeletal elements development
IV-Results• Temperature effect
– The changes in the hyobranchial apparatus• Changes in the shape• Reduction in the number of structures
– The four bones• Vomer
– Remodeling of the vomer– Reduction in the number of teeth
• Parasphenoid tooth patch– Formation and formation of the teeth
• Maxilla– Formation and formation of teeth
• Pterygoid– Regression and complete disappearance
• Thyroid Hormone– No effect of Thyroid hormone
Multivariate Analysis
Source Wilk’s F P
Temperature 0.11 11.07 <0.001
Thyroxin 0.69 0.64 0.716
Temperature*Thyroxin 0.54 1.22 0.373
Temperature Effect
R2 = 0.6564 R2 = 0.5043 R2 = 0.6897 R2=0.601
R2 = 0.2325 R2 = 0.6545 R2 = 0.5808 R2=0.771
0
50
100
150
200
250
300
350
400
1 2Temperature
Number of elements
Vomer teeth
Teeth patch
Pterygoidteeth
Maxillae teeth
Totalnumtee
HyobranchialApparatus
masvariatio8
score
Linear(Maxillaeteeth)Linear(Totalnumtee)
Linear(HyobranchialApparatus)Linear(masvariatio8)
Linear (score)
Summary of Pearson Correlation
Correlation
R2 = R2 = 0.7887 R2 = R2 = 0.0853
-20
0
20
40
60
80
100
120
140
160
0 20 40 60
Vomer teeth
Teeth on the other elements
Teeth patch
Pterygoid teeth
Maxillae teeth
Totalnumtee
V-Discussion
• Temperature– Effect of temperature on amphibians– Similarity in the action
• Nature of the similarity
• Possible conclusion: temperature action is beyond the simple stimulation for regressive or progressive development of skeletal elements
• Thyroid Hormone
– sensitivity to TH is not related only to metamorphic salamanders.
– Insensitivity to TH is not the matter of only non-metamorphic salamanders.
– TH may be a secondary factor in metamorphosis• Possible factors:
– Mechanical stress:
» Internal mechanical stress:Interaction between skeletal elements
» External mechanical stress:Action of muscles and feeding system on the skeletal elements
– Mechanical stress-inducing factors:Temperature
ACKNOWLEDGEMENT Special Thanks to:-The Faculty of the Biology Department of Minot State University and Dr Richard Barkosky-The International Students Office particularly: .Mrs. Ronnie Walker and her family: .Mr. Gary Loper .Beth .Sarah .Davis-Minot Community particularly: .Mr. Tim Eighmy .Mrs. Kathy Hammond .Mrs. Shirley Hintz .Mrs. Margret Lowe .Mr. Berb Williams-Mr. Stuart Melby and Mrs. Karen Melby-Dr David McCormack in the Mathematics Department.