Does Size Matter: Effects of Dorsal Fin Morphology and Body Size on Hierarchy Formation in Lythrypnus dalli
Faculty Mentor Information
Dr. Devaleena Pradhan, Idaho State University; and Makenzie Reed, Idaho State University
Presentation Date
7-16-2026
Abstract
Elaborate postural displays of threat prior to escalation of aggressive combat is vital to minimize injury and conserve energy during establishment of dominance hierarchies. The size-advantage hypothesis states that individuals of a larger body size obtain higher social rank. However, predicting status based on a single feature neglects the subtle nuances of other morphological, behavioral, and endocrinological processes involved in communication between conspecifics. Bluebanded gobies, Lythrypnus dalli, are social fish that use aggressive interactions to form hierarchies of one dominant male and multiple subordinate females. While larger body size is usually associated with dominance, smaller fish with longer dorsal fins can also achieve a higher rank. We aim to parse out the contribution of additional morphological features during hierarchy formation. We hypothesize that while standard length will have a significant effect, additional morphological and endocrinological measures will affect hierarchy formation. Fish were placed in pairs with morphological combinations ranging from similar and different standard lengths and dorsal fin lengths. After seven days, a winner was determined based on behavioral measures, fish were photographed for morphological feature analysis and fins clipped for future endocrinological analysis. Differentiating the multimodal communication of aggressive signaling will allow for a better understanding of hierarchy establishment.
Does Size Matter: Effects of Dorsal Fin Morphology and Body Size on Hierarchy Formation in Lythrypnus dalli
Elaborate postural displays of threat prior to escalation of aggressive combat is vital to minimize injury and conserve energy during establishment of dominance hierarchies. The size-advantage hypothesis states that individuals of a larger body size obtain higher social rank. However, predicting status based on a single feature neglects the subtle nuances of other morphological, behavioral, and endocrinological processes involved in communication between conspecifics. Bluebanded gobies, Lythrypnus dalli, are social fish that use aggressive interactions to form hierarchies of one dominant male and multiple subordinate females. While larger body size is usually associated with dominance, smaller fish with longer dorsal fins can also achieve a higher rank. We aim to parse out the contribution of additional morphological features during hierarchy formation. We hypothesize that while standard length will have a significant effect, additional morphological and endocrinological measures will affect hierarchy formation. Fish were placed in pairs with morphological combinations ranging from similar and different standard lengths and dorsal fin lengths. After seven days, a winner was determined based on behavioral measures, fish were photographed for morphological feature analysis and fins clipped for future endocrinological analysis. Differentiating the multimodal communication of aggressive signaling will allow for a better understanding of hierarchy establishment.