Christopher K. Beachy, Kiswendsida C. OuedraogoDepartment 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-HypothesesTemperature and Thyroid hormone have an effect on cranial metamorphosis of Desmognathus quadramaculatus

II-BackgroundDescription of Plethodontidae salamanders -Variable life cycle -Sensitivity to Temperature and Thyroid hormone

Effect of temperatureEffect on metamorphosisHigh temperature effectLow temperature effectStructures affected during metamorphosisExternal structures: the skinInternal structures: skeletal elementsEffect of Thyroid hormoneCriteria of TH actionTH concentrationSize-age of the animal

III-Materials and Method Characteristics of the salamandersLarval sizePlace of collectionGott Farm Creek, Bald Mountains, NC

Experimental ProcedureNumber of salamandersHabitatRoomBoxes: 8*3*4 LWH110g sands100g gravel250 Ml of distilled waterHouse : CoolersVariation in TemperatureBeginning of the experimentLow temperature (7 C, 11C)In the course of the experimentHigh temperature (11C, 15C)TH treatmentTH (1.2*10-8 M )Control ( 0.0 M)

Variation in the intensity of the treatment factorsTemperature1 C every two daysThyroid hormone1.2*10-8 M every two weeksFour final treatment groups11C and 4.8*10-8 M15 C and 4.8*10-8 M11 C and control15 C and control

Evaluation of the internal metamorphosisThe idea of the Bone-Cartilage evaluationDouble-Staining TechniqueThe idea of the number of teeth and hyobranchial apparatusFour Dermatocranial elementsVomerParasphenoidPterygoidMaxillaHyobranchial ApparatusCeratohyal (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 analysisMultivariate Analysis of Variance=0.05Test statistics: Wilks LambdaPearson CorrelationIdentification of the nature of the effects of the factorsIdentification of the patterns of skeletal elements development

IV-ResultsTemperature effectThe changes in the hyobranchial apparatusChanges in the shapeReduction in the number of structuresThe four bonesVomerRemodeling of the vomerReduction in the number of teethParasphenoid tooth patchFormation and formation of the teethMaxillaFormation and formation of teethPterygoidRegression and complete disappearance

Thyroid HormoneNo effect of Thyroid hormone

Multivariate Analysis

SourceWilksFPTemperature0.1111.07

Summary of Pearson Correlation

V-Discussion TemperatureEffect of temperature on amphibiansSimilarity in the actionNature of the similarityPossible conclusion: temperature action is beyond the simple stimulation for regressive or progressive development of skeletal elements

Thyroid Hormonesensitivity 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 metamorphosisPossible factors:Mechanical stress:Internal mechanical stress:Interaction between skeletal elementsExternal mechanical stress:Action of muscles and feeding system on the skeletal elementsMechanical 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.