Dissertations, Theses, and Capstone Projects

Date of Degree

6-2026

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy

Program

Biology

Advisor

Sebastion Alvarado

Committee Members

David Lahti

Weigang Qiu

Paul Forlano

Lauren Chapman

Subject Categories

Behavior and Ethology | Evolution | Integrative Biology | Marine Biology

Keywords

cephalopods

Abstract

Evolutionary pressures force organisms to adapt and change for survival over generations through mutation. However, mutational change takes time and often results in extinction rather than species persistence. To enhance survival, species often employ phenotypic plasticity, allowing temporary changes to keep up with selection pressures. One of the most obvious traits that can change is animal pigmentation, which is highly utilized amongst a species for identification, communication, and defense. An animal's ability to adapt to changing environments often requires the coordination of multiple traits, yet the interactions among multiple plastic traits within individuals remain poorly understood. My work investigated phenotypic plasticity in response to environmental change across vertebrate and invertebrate model systems.

Chapter 1: I utilized the African cichlid Astatotilapia burtoni to investigate how the environment shapes body coloration and behavior using multiple behavioral assays. I evaluated the behavior of Astatotilapia burtoni between their blue and yellow phenotype. By rearing cichlids in specific color environments, I generated color-induced territorial males and report distinct behavioral differences between territorial and non-territorial males of both colors. Additionally, I observed differences between territorial males of each color. Blue males are more reproductively inclined and prefer direct aggression compared to their yellow counterparts. This study shows that coloration and behavior are interconnected plastic traits.

Chapter 2: I investigated the role of pigment morphology in the big fin reef squid Sepioteuthis lessoniana. In contrast to the slower morphological change that occurs in most vertebrates, cephalopods are known for quickly responding to visual cues and for temporarily changing color to camouflage themselves. The big fin reef squid is a pelagic species that exhibits multiple strategies to help camouflage such as rapid color change, speed, and inking. I investigated how their basal morphological pigment structure differs in response to a habituated visual environment during maturation and the transition from a pelagic to a semi-benthic lifestyle. The analysis revealed that rearing environment, age, and body region influenced the density and expansion of multiple types of pigment cells utilized by S. lessoniana to camouflage. For all pigment cell types, the ventral region contained larger pigment cells than the dorsal region. Environmental-related differences among black-pigment cells were observed and sustained across all age groups.

Chapter 3: I studied Euprymna berryi, the hummingbird bobtail squid, a benthic species that uses pigmentation and behavioral strategies, such as burying in sediment, to camouflage itself. This species lacks the extensive repertoire of pigment cell types found in other cephalopods. Results show that the pigment cells differ significantly between body regions (ventral and dorsal) but are not influenced by the rearing environment. However, at the behavioral level, individuals reared in different environments show distinct phenotypes when exposed to novel environments. Across these multiple species, I demonstrated how visual ecology affects an organism's phenotypic plasticity at the cellular, molecular, and behavioral levels.

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