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.