Undergraduate Honors Thesis Projects

Date of Award

Spring 4-8-2020

Document Type

Honors Paper

Degree Name

Zoo and Conservation Science-BS


Biology & Earth Science


Dr. Sarah Bouchard

First Committee Member

Dr. Sarah Bouchard

Second Committee Member

Dr. David Sheridan

Third Committee Member

Dr. John Tansey


Plasticity, intraspecific competition, Agalychnis callidryas, Anaxyrus americanus, anuran, mesocosm, oviposition, homogenizer

Subject Categories

Developmental Neuroscience | Molecular and Cellular Neuroscience | Terrestrial and Aquatic Ecology



Plasticity is the ability of an organism to respond to environmental variation by expressing different phenotypes. In Red-eyed treefrog tadpoles, Agalychnis callidryas, competitive environments induce long guts and short tails. Despite having a larger gut, tadpoles reared with competition do not increase intake when food becomes available. Pilot data suggest that this is because they have lower metabolic rates. The ability to maintain a larger gut with a depressed metabolic rate is confusing because guts are energetically expensive, and suggests that another energetic trade-off is taking place. The purpose of this study was to investigate the effect of intraspecific competition on metabolic rate and organ size plasticity in Agalychnis callidryas tadpoles to determine if differences in metabolic rate are associated with differences in organ size. A. callidryas tadpoles were reared at low and high density in outdoor mesocosms in Gamboa, Panama. Once they reached a standard size, we measured their metabolic rate and dissected and weighed their guts, livers, pancreases, and brains. Additionally, we analyzed effects on the following brain components: forebrain, optic tectum, and medulla oblongata. We also conducted a comparative study of American toads, Anaxryus americanus, which were reared at low, high, and extra high density. We measured metabolic rates and organs as in the Red-eyed treefrog study. Additionally, to understand differences in the brain at the cellular level, we determined brain cell nuclear density and size. For both species, we predicted that competition would decrease growth and metabolic rates, increase gut mass, and decrease overall brain mass. We also predicted that high-density tadpoles would have larger optic tecta and smaller medulla oblongatas and forebrains. Competition induced lower metabolic rates in A. callidryas. This was associated with smaller livers, pancreases, and brains, but not differences in gut mass. Competition did not induce lower metabolic rates or smaller livers and brains in A. americanus, but extra-high densities did. Competition induced smaller optic tecta and forebrains in both species, but smaller medulla oblongatas were only observed in A. callidyras. There were no differences observed in A. americanus brain nuclei density or nuclei diameter across treatments. We concluded that A. callidryas exhibits a stronger metabolic response to competition than A. americanus, and that this response may be facilitated by changes in organ size. The naturally higher larval schooling densities that A. americanus have relative to A. callidryas may explain the differences between species.