FOUR KEY AREAS
Behavior/DTAGs
Goal:
To identify diving patterns that allow us to relate the cellular adaptations that enable whales to withstand hypoxia during deep dives to their diving behaviors.
Marine mammal diving
Looking at marine mammal diving can reveal behavioral adaptations that allow the whales to prepare physiologically and behaviorally for deep dives. This allows us to connect cellular adaptations to diving behavior. For example, extreme deep diving exposes marine mammals to repeated cycles of hypoxia and reoxygenation, conditions that would normally cause oxidative stress and cellular damage. Their ability to tolerate long dives reflects strong cellular resilience and tightly regulated physiological stress responses.
DTAGs as a tool
DTAGs are digital acoustic tags attached to whales that record sound and movement to reconstruct their underwater behavior. In this study, DTAGs collected data including high-resolution echolocation buzzes and clicks, tri-axial acceleration, pressure, and depth. Our collection of recordings includes 38 pilot whales (Globicephala macrorhynchus) and 4 Ziphius cavirostris, which we analyze using MatLab. Using this data, we can quantify how whales respond behaviorally to physiological stress during dives, including changes in stroke patterns, energy expenditure, oxygen use, and recovery strategies (see more on computational work below).
Computational Work
Our computational work examines parameters such as minimum specific acceleration (MSA) and dive depths to identify behavioral and physiological patterns that prime whales for deep dives. By mapping these dives, we seek to better understand how repeated hypoxia is managed at the cellular level and how these adaptations may be rooted in long-term genetic and evolutionary processes.
Cellular Resilience
Goal:
To characterize cetacean cellular behavior in vitro and relate it to the broader evolutionary context of their physiology
Cell Structure
Using microscopy, we can examine the morphology of whale fibroblasts in vitro under hypoxic conditions, revealing distinct cellular phenotypes. Through techniques such as immunofluorescence staining, we have observed significantly more mitochondria in goose-beaked whale fibroblasts. This leads us to ask how this contributes to hypoxia resilience?
Cell Performance
Studying cell performance reveals how effectively cells function under different conditions, such as hypoxia, and allows us to identify factors and cellular processes that affect cell health, metabolism, and activity. To compare cellular responses between terrestrial and marine mammals, whale, human, and bovine cells are exposed to various conditions, including hypoxia. We measure several metabolic factors, such as spare respiratory capacity, cell cycle kinetics, and abundance of macromolecules. Our work on cellular performance ties into our work on whale behaviors. Cellular performance may help explain how diving-adapted species maintain tissue integrity under low-oxygen conditions, since species evolved for prolonged diving are more likely to preserve cellular function during hypoxia.
Genes & Cellular Processes
We apply a variety of techniques such as RT-qPCR, Seahorse assays, gene knockdown and knockout, and multi-omics analysis to better understand the genes and cellular processes involved in hypoxia tolerance. Specifically, one of our key interests focuses on frataxin (FXN) and fatty acid metabolism in Ziphius. Our work builds on previous experiments where we have observed that (1) the frataxin (FXN) expression levels are elevated in Ziphius cells as compared to humans, (2) that in comparison to humans, Ziphius cells accumulate little to no lipid droplets under hypoxia, and (3) that adding the fatty acid transporter carnitine, as well as the free fatty acid palmitate, can increase the spare respiratory capacity of Ziphius cells.
Genetic Adaptations
Goal:
To understand how evolutionary changes in the genome support physiological and cellular specifications for hypoxia-tolerance in whales
Population Genetics
We are able to use population genetics to understand how natural selection has shaped hypoxia tolerance in Tursiops spp. (bottlenose dolphin), specifically T. truncatus and the recently recognized T. erebennus. Analyzing population genetics allows us to observe patterns of genetic variation and place hypoxia-related traits into an evolutionary context. This population-level perspective bridges population-level genetic patterns with the physiological and cellular mechanisms being studied throughout the lab.
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Our current work involves using genome-wide variation data to examine current and historical population structure, genetic diversity, and evolutionary history across populations.
In addition, we are currently performing a methodological comparison between partial genome sequencing (RAD-seq) and whole genome sequencing (re-seq) approaches to evaluate how data resolution affects downstream analysis and its interpretation in population studies.
Stress
Acute & Chronic Stress
Goal:
To help build up our knowledge on how anthropogenic stressors can affect whales at different levels.
Environmental stressors (e.g., sound pollution, chemical pollution, prey shortages from overfishing) can be classified as either acute or chronic. The duration of the stressor influences which stress signals and hormones are released in marine mammals.
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Our work examines hormones involved in both acute and chronic stress responses. Acute stress and chronic stress are intrinsically tied together, as repeated acute stress events lead to a chronic stress response.
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We simulate stress in cell culture by exposing cells to adrenal hormones associated with acute and chronic stress responses (catecholamines, glucocorticoids, and mineralocorticoids). Combined with hypoxia treatment, we assess the impacts to cellular function using western blots, cell imaging, qPCR, and RNAsequencing.
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Sonar exposure can be examined using DTAGs by detecting shifts in dive behavior and movement dynamics, allowing us to quantify how anthropogenic sound alters whale behavior and potentially exacerbates physiological stress during deep dives.
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Ultimately, understanding the stress response is vital for improving the management of marine ecosystems and better predicting whale health and conservation status.