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Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

ORCID

https://orcid.org/0000-0002-7394-9079

Date of Award

Spring 2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Department of Biology

Advisor(s)

Christopher S. Rose

Janet C. Daniel

Derek S. Strong

Abstract

Amphibians occupy an intermediate phylogenetic position between fish and tetrapods, making amphibians an essential model for understanding the evolution of air breathing organs in vertebrates. Amphibians have a uniquely biphasic life style allowing them to occupy aquatic and terrestrial habitats and to use multiple organs for gas exchange at different stages of life. This initial independence from lung breathing means that amphibians are developing their lungs while they are using them, which opens up the possibility that their rate of lung development is controlled in part by their breathing behavior. As such, amphibians provide a starting point for examining the evolution of lung development in vertebrates. Two objectives were investigated: first, lung morphogenesis is described for Lithobates sylvaticus, Anaxyrus americanus, and Ambystoma maculatum, and second, average and maximum lung lengths were compared to four independent variables: development (stage), age, size (weight), and frequency of breathing to see if any of these variables were predictors of lung growth. Lungs appeared early in development for L. sylvaticus and midway through larval development for A. americanus and A. maculatum. Lung morphogenesis generally occurred by the appearance of lungs, the expansion of lung lumen, the appearance of folds, the extension of folds into septa, and the septa connecting to form a septa network. The extension of folds into septa and the septa network did not occur in A. maculatum. Stage and age were predictors of lung length in all three species, weight was a predictor in L. sylvaticus and A. maculatum, and breathing frequency was an additional predictor for A. maculatum. The strongest relationships between lung length and a predictor had an R-squared value of 50% and were seen in A. americanus for age to both average and maximum lung length and for A. maculatum for stage to maximum lung length. These data provide an initial description in lung morphology and development in the first tetrapod vertebrates offering a starting point to understand the evolution of lung morphogenesis in the tetrapod vertebrates that amphibians gave rise to, the fish that amphibians evolved from, and the fish that might have convergently evolved lungs.

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