Date of Award

Spring 2019

Degree Name

Bachelor of Science

Major

Biology

First Advisor

Kent D. Dunlap

Second Advisor

Daniel G. Blackburn

Third Advisor

Claire T. Fournier

Abstract

Brain cell proliferation is an important form of brain plasticity that has been sparsely studied in natural populations. Killifish, Rivulus hartii, from the freshwater streams of Trinidad are a remarkable organism for understanding how brain plasticity is influenced by both internal and environmental factors. Through extensive ecological studies in the region, Trinidadian killifish have been used to determine how predation directly effects brain cell proliferation and brain size. In wild populations, waterfalls in the streams block predator movements upstream, thereby creating distinct populations of killifish – i.e., killifish living with abundant predators (high predators, HP) and killifish living with no predators (Rivulus-only, RO). In the present study, fish were caught in HP and RO locations from three replicate streams at a total of six populations. In a common garden study, the F1 population from the same RO and HP streams were reared in captivity under the same living conditions. Immunocytochemistry for proliferating cell nuclear antigen (PCNA) was performed on brains from both wild and common garden killifish to quantify the amount of cell proliferation in the forebrain and midbrain. In the wild, killifish from HP streams had significantly more cell proliferation throughout the brain indicating that predator presence enhances cell proliferation non-specifically. In captivity, fish derived from HP streams also had increased cell proliferation, showing that the population differences in the wild are likely due to intrinsic, evolved genetic differences among populations. This combined study suggests that predation has caused brain cell dynamics in RO and HP killifish to differ genetically, since the results from the common garden experiment paralleled the findings from the field study.

Comments

Senior thesis completed at Trinity College, Hartford CT for the degree of Bachelor of Science in Biology.

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