Bone mineral density (BMD) in the pectoral flipper of the common bottlenose dolphin, Tursiops truncatus, was examined to address the need to define a comprehensive target site for clinical osteodensitometric assessment and to establish ranges of observed bone density values for this species. Radii were analyzed using dual energy X-ray absorptiometry (DXA), the accepted standard in human medical studies. Multiple loci within the radius were identified and assessed for their correlation to BMD of the entire bone. Radii BMD were also examined for differences based on sex, age, total body length, handedness, geographical affinity, and nutritional status at time of death. No statistically significant differences were observed in BMD measurements for male and female dolphins or right and left flippers. Additionally, no statistically significant differences were observed based on geographical region or nutritional status at time of death. These results support the inclusion of all specimens used in this study as a descriptive reference dataset for bone density values in bottlenose dolphins and detail a primary skeletal site for clinical assessment of bone density for the species. The values utilized in this study represent the largest dataset published on BMD in any wildlife or marine mammal species to date.
In the skeletal specimens analyzed, BMD increased with age and body length; however, the variance of bone density values that was observed at any given age was of such magnitude that it precludes the use of this single parameter as a reliable estimator of age. The clinical measurement of an individual’s bone density at any given time is a direct reflection of that individual’s skeletal health. Reducing osteodensitometry to a static age estimation tool would inherently disregard the biological and physiological function of calcified tissues. Variation of bone density values at any given age may be an indicator of altered skeletal health due to numerous factors including overall health, nutritive status, contaminant exposure, body condition, or metabolic and endocrine related disorders.
Despite its accuracy, precision, and widespread use, DXA has limitations and clinical shortcomings. The technology is not appropriate for all healthcare and screening applications due to the inherent use of radiation, large size of units, relatively high associated costs, and limited access and availability. Quantitative ultrasound (QUS) methods for bone assessment have demonstrated potential to determine bone quality and to provide information about BMD. QUS is beneficial in that it is portable, nondestructive, noninvasive, less expensive than X-ray technology, and does not expose patients or technicians to radiation. To circumvent limitations in traditional radiographic bone density assessment, a custom QUS device and protocols were developed for assessment of live bottlenose dolphins. In laboratory measurements on disarticulated pectoral flippers collected post-mortem, a strong correlation was established between BMD as measured with QUS and DXA. Initial trials to develop clinical protocols and establish ultrasonic assessment of bone as non-aversive were conducted on dolphins managed under human care. Findings support the application of quantitative ultrasonic assessment of bone density to assess skeletal health in free-ranging dolphins during capture-release health assessments and in populations of dolphins under human care.
Bottlenose dolphins are utilized as indicators of ecosystem health in capture-release health assessments. BMD measurements have not previously been incorporated into these projects despite evidence that exposure to a suite of anthropogenic contaminants, episodic prey depletion events, and resultant malnutrition lead to decreased bone density in laboratory animals and wildlife species. To establish bone density as a useful health and life history parameter for the bottlenose dolphin, normative reference ranges must be established from healthy individuals in order to facilitate evaluation of health and disease status of individuals from impacted populations and habitats. Repeatability assays were conducted on dolphins under human care to define the precision error for this novel QUS application. Ultrasonic bone density assessments of live, free-ranging dolphins were conducted during capture-release health assessments from 2014–2019. Individuals were selected from this long-term population study for the development of a normative bone density dataset of dolphins with nutritive body condition within normal limits and the lack of obvious disease or health issues. This study represents the first use of QUS to assess bone density in a marine mammal species, and the BMD values as assessed with QUS represent the first normative BMD dataset for live, free-ranging marine mammals. Application of this technology during capture-release health assessments adds a valuable resource to biologists and wildlife veterinarians investigating dolphin and overall ecosystem health.
Future studies and applications are suggested to investigate associations between anthropogenic contaminant exposure and BMD in free-ranging dolphins and renal dysfunction or metabolic disorder and BMD in managed care dolphins. Continued long-term monitoring of bone density in live, free-ranging bottlenose dolphins using the established reference population will allow for more in-depth investigation of life history questions, particularly with regard to large-scale prey mortality events associated with toxic algal blooms and resultant malnutrition. Technological advancements to assess BMD in additional skeletal sites is encouraged to facilitate additional research questions that may not be as readily addressed using the pectoral flipper as an examination site.
|Commitee:||Buckley, Bradley, Podrabsky, Jason, Wells, Randall, Butler, Virginia|
|School:||Portland State University|
|School Location:||United States -- Oregon|
|Source:||DAI-A 81/6(E), Dissertation Abstracts International|
|Subjects:||Animal sciences, Zoology, Museum studies|
|Keywords:||Bone density, Ecosystem health, Marine mammal, Marine mammal health assessments, Osteodensitometry, Quantitative ultrasound|
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