Metabolism, size, and environmental influences on vision in the fiddler crab, Minuca pugnax
Date
2025
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
For many organisms, vision is a fundamental sensory modality influencing behaviors such as photoperiod perception, predator avoidance, and social interactions. In fiddler crabs, visual function is closely linked to ecological need, which influences key optical and energetic properties that may affect visual performance. This study explores how metabolism, morphology, and environmental parameters shape key aspects of vision in the fiddler crab, Minuca pugnax. ☐ I assessed metabolic rate, temporal resolution of vision, irradiance sensitivity, and eye morphometrics across a range of masses in M. pugnax. To measure metabolic rate, I used the proxies of dry mass-adjusted oxygen consumption rate and tissue mass-adjusted oxygen consumption rate, both of which decreased with an increase in the respective mass unit used. For temporal resolution of vision, I developed a new method of analysis using electroretinographic data to measure critical flicker fusion frequency (CFF) using a Lomb-Scargle periodogram that I then applied to M. pugnax. Electroretinography was also utilized for irradiance sensitivity to determine logK as a parameter to measure sensitivity. Both irradiance sensitivity and temporal resolution increased with metabolic rate and decreased with mass, irradiance sensitivity being an unexpected trend. Finally, histological analysis of M. pugnax eyes determined that all aspects of a compound eye facet increase with mass, which was an expected trend. Optical sensitivity values obtained from morphological measurements of the eyes were also found to increase with mass. Collectively, these findings suggest that smaller crabs have an increased need for visual speed due to faster movement relative to their body size and being more vulnerable to predators. These smaller crabs have a heightened metabolic capacity per unit body mass and smaller eyes to support this visual performance. ☐ To understand the influence of chronic temperature acclimation on metabolism and vision in M. pugnax, I applied the relationship between metabolic rate and temporal resolution of vision to a latitudinal study, as latitudinal plasticity in metabolic rate is already known to exist in fiddler crabs. Air temperature for National Estuarine Research Reserve sites in Narragansett Bay, Rhode Island; St. Jones, Delaware; and North Inlet-Winyah Bay, South Carolina, showed increased mean but decreased variability with decreasing latitude. I collected M. pugnax from near these three locations and conducted respirometry and critical flicker fusion frequency experiments at 15ºC, 20ºC, and 25ºC. As latitude increased, M. pugnax populations upregulated metabolic capacity and were less thermally sensitive, consistent with their colder and more variable chronic thermal acclimation conditions. CFF values showed no statistical significance across location or temperature aside from an increase in CFF with temperature in the southernmost population, suggesting that vision is less plastic than metabolism. Other factors, such as morphological or energetic adaptations to deal with ecological pressures, may keep this constant across latitudes. ☐ This study describes both the energetic and morphological influences on vision in M. pugnax and how these factors are shaped by acclimatization. As climate change continues to raise the temperatures of coastal marshes, the physiology of organisms that live in them will likely also be affected similarly. This study’s focus on metabolic plasticity and visual performance under varying thermal conditions provides insights into how these crabs may adapt to a changing climate. By understanding these physiological responses, we can better predict the resilience of M. pugnax and similar species to future environmental changes, informing conservation strategies for coastal ecosystems.
Description
Keywords
Critical flicker fusion frequency, Fiddler crabs, Latitudinal gradient, Metabolism, Vision