Influence of genetic variation on susceptibility to harmful algal blooms

 Map of study areas in the Florida Panhandle (A) and central-west Florida (B) indicating the location of sample collection for live coastal (blue stars) and estuarine (black circles) bottlenose dolphins and dolphin strandings during UMEs in the Panhandle in 1999 (blue circles) and 2004 (black stars) and during HABs between 1992 and 2006, including a UME in 2005-2006, in central-west Florida (blue circles).
Map of study areas in the Florida Panhandle (A) and central-west Florida (B) indicating the location of sample collection for live coastal (blue stars) and estuarine (black circles) bottlenose dolphins and dolphin strandings during UMEs in the Panhandle in 1999 (blue circles) and 2004 (black stars) and during HABs between 1992 and 2006, including a UME in 2005-2006, in central-west Florida (blue circles).

This past year marks the successful completion of my dissertation research on bottlenose dolphin susceptibility to harmful algal blooms (HABs), otherwise known as red tides. Over the past five years, through collaboration with the Sarasota Dolphin Research Program and NOAA Fisheries, I have used genetic techniques to investigate apparent differences in red tide resistance among bottlenose dolphins from central-west Florida and the Florida Panhandle.

Red tides in the Gulf of Mexico refer to naturally occurring dense blooms of the dinoflagellate algae, Karenia brevis, which produce neurotoxins. Exposure to these toxins can be lethal to fish, sea birds, sea turtles, and marine mammals, and can cause illness in humans. Several unusual mortality events (UMEs) of dolphins in Florida have been attributed to red tides. The goal of my research was to investigate if dolphins that have been frequently exposed to red tides historically have evolved resistance to the algal toxins. To test this hypothesis, I compared genetic variation between dolphins that died due to red tides and dolphins that survived red tide exposure, looking for a genetic signal that was more commonly observed in one group over the other. I included dolphins from both estuarine and coastal populations of bottlenose dolphins in central-west Florida (including Sarasota Bay) and the Florida Panhandle (see map).

I found that the frequency of some genetic markers varied significantly between live and dead dolphins, suggesting there may be some genetic basis to red tide resistance. The significant genetic markers were found within the dolphin genome nearby to genes involved in immune, nervous, and detoxification systems. A closer look at dolphin sodium channel genes, which encode the biological binding site of the toxin, revealed no significant differences. Unlike other neurotoxin-resistant systems (e.g., garter snakes that prey on toxic newts and clams exposed to HABs in New England), bottlenose dolphins have not adapted to red tide exposure via adaptations to the toxin binding site. Instead, the dolphin immune system, particularly the major histocompatibility complex, may play a previously undescribed role in red tide resistance. Overall, I conclude that genetics is likely one of several factors that influence the susceptibility of individual bottlenose dolphins to red tide exposure.

This research was supported by the Duke University Marine Lab, the American Fisheries Society, the PADI Foundation, and a Katherine Goodman Stern Fellowship. Samples were generously provided by the NOAA Fisheries SEFSC DNA Archives and the Sarasota Dolphin Research Program.

This article was published on page 15 in the November 2014 issue of Nicks n Notches

 

 

The Sarasota Bay dolphin diet may provide important clues to prevent diabetes

Just like people, some dolphins are susceptible to prediabetes, also called metabolic syndrome. This syndrome includes elevated insulin, glucose, triglycerides, fatty liver disease, and associated iron overload. While metabolic syndrome is not a direct cause of death in dolphins, it is a chronic condition that – when removed – may help dolphins live longer, healthier lives. Thanks to funding from the Office of Naval Research, the National Marine Mammal Foundation has been working with the Sarasota Dolphin Research Program for several years to find out why some dolphins get this disease, while others do not.

Through a series of publications featured in a special Frontiers in Endocrinology issue, ‘Marine mammals as outside the box models for insulin resistance and type 2 diabetes,’ some important clues have been discovered. First, Sarasota Bay dolphins had lower insulin, glucose, triglycerides, and iron in their blood compared to dolphins with metabolic syndrome. Second, Sarasota Bay dolphins and the fish they eat had different types of nutrients compared to dolphins with metabolic syndrome (and the fish they eat). Third, metabolic syndrome in dolphins was not associated with either higher stress (indicated by a stress-related hormone, cortisol) or higher body mass index (i.e. body weight).

Common Sarasota Bay bottlenose dolphin prey fish including a scaled sardine, a type of clupeid. Note: measures are in centimeters and the four photos are not to the same scale.
Common Sarasota Bay bottlenose dolphin prey fish including a scaled sardine, a type of clupeid. Note: measures are in centimeters and the four photos are not to the same scale.

Current studies are focusing on nutrients in dietary fish that may protect dolphins against developing prediabetes. If we can find the right combination of nutrients that prevent or treat prediabetes in dolphins, this may provide critical clues on how to prevent and treat diabetes in people.

This article was published on page 15 in the November 2014 issue of Nicks n Notches

Deep breaths

Dr. Cynthia Smith and Dr. Jen Langan performing an ultrasound examination.
Dr. Cynthia Smith and Dr. Jen Langan performing an ultrasound examination.

Bottlenose dolphins take rapid breaths that begin with an explosive exhalation and are followed by a deep inhalation. The dolphin then holds its breath while it swims, forages, interacts with others, and then returns to the surface of the water for another breath. These deep breaths are held for up to several minutes at a time. Dolphins also use more of their lung volume than humans for each breath, being as efficient as possible while they are at the surface to breathe.

So now imagine that the air is polluted. What happens when a dolphin takes deep, full breaths of polluted air, and then holds that breath while it swims, forages, or interacts with others? With their deep, prolonged breath holds, and the fact that dolphins don’t have noses or nasal turbinates to filter air, we would expect even more contamination to reach their lungs than in a human breathing the same air. While their respiratory adaptations serve them well for diving and living in the ocean, they may also make them more vulnerable to lung injury and infection.

To evaluate lung health in a live dolphin, ultrasound is a valuable diagnostic tool that offers a rapid assessment. The dolphin body is well-suited for ultrasound, as their skin is smooth and hairless, so doesn’t require any preparation before conducting the exam.   Current ultrasound units are powerful enough to penetrate the blubber of a dolphin and rugged enough to use on a salty research vessel. Exams can either be performed in-water or on the deck of the research vessel.

Determining what is ‘normal’ for a wild dolphin would be challenging if we didn’t have decades of experience working with animals in human care. By providing long-term health care to dolphins and routinely performing ultrasound examinations to monitor their well-being, we have characterized variations of normal conditions in the lung and defined disease states. This information now serves as a reference point for interpreting ultrasound results from wild dolphins, and helps us understand how lung health may be impacted in the face of an environmental disaster, long-term contamination, or infectious disease outbreak.

Since 2011, we have been collecting standardized pulmonary (lung) ultrasound data on Sarasota Bay dolphins. Pulmonary abnormalities detected are divided into the following categories: (1) pleural effusion, or fluid surrounding the lungs; (2) superficial pulmonary nodules, or <2cm round/ovoid foci of non-aerated lung; (3) pulmonary masses, or 2cm or greater well-defined areas of non-aerated lung; (4) alveolar-interstitial syndrome, or evidence of reduced air in the lung and replacement of air with cellular infiltrate, and (5) pulmonary consolidation, where fluid or cellular infiltrate is occupying the alveolar spaces in the lungs. During the exam, numerous images are captured to document the findings in each dolphin’s lungs. After the field exam is performed and abnormalities recorded, our sonographer (CRS)-radiologist (MI) team goes through each animal’s data set and then assigns an overall lung score: normal, mild, moderate, or severe. To date, the vast majority of Sarasota Bay dolphins evaluated have been assigned either normal or mild lung disease scores, and no dolphins have received a severe lung disease score. We will continue to collect lung ultrasound data for each animal as a critical part of their medical record, as well as further develop this baseline of essential data for comparisons to other populations of bottlenose dolphins to study the impact of environmental factors on lung health.

This article was published on page 12-13 in the November 2014 issue of Nicks n Notches

 

 

Markers of decompression stress

Recent studies have suggested a link between mass stranding of beaked whales and the use of naval mid-frequency sonar. The whales experienced symptoms that were similar to those caused by gas bubbles in human divers. These reports have increased the concern that anthropogenic sound, such as that created by military sonar or during seismic exploration, may harm marine animals. It has been suggested that alteration in physiology or diving behavior may increase the risk of decompression sickness (DCS). A diagnostic tool for DCS in dolphins is very desirable.

Bubble formation is believed to be the crucial event in the etiology of DCS, but the role bubbles play in the disease process remains unclear. Recent studies have shown that Microparticles (MPs) correlate with the level of decompression stress in both the mouse and human. MPs are particles between 0.3 to 3 µm in size that are shed from various cells. MPs are present in stranded dolphins and they can be detected by standard assays. Thus, MPs may be suitable biomarkers to assess decompression stress. The study is aimed at verifying a relationship between decompression stress and MPs in sea lions and then transferring this knowledge to assess decompression stress of cetaceans in the field. We collaborated with the Chicago Zoological Society health assessments in Sarasota to sample dolphins when they are first restrained, during examination on deck, and back in the water, to get baseline data for shallow-swimming and out-of-the-water dolphins.

In total, 123 blood samples from 58 wild-caught-and-released dolphins in Sarasota Bay, Florida, were analyzed for MPs over the 2012 to 2014 period. The samples were obtained Pre-, Mid-, and Post-procedure. Preliminary analyses of data from the first 2 years of this study found an apparent increase in MP count with removal of the animal from the water, but subsequent analysis of all MP counts now available for this study showed no significant impact of removal from, or return to the water. This work is supported by the Office of Naval Research.

This article was published on page 11 in the November 2014 issue of Nicks n Notches

Use of overhead imaging for body condition assessment

six-rotor remote-controlled helicopter (foreground) at ready
Unmanned aerial vehicle imaging system (foreground), a six-rotor remote-controlled helicopter with a downward-facing digital camera, developed by researchers at the Duke Marine Lab and the Woods Hole Oceanographic Institution to measure dolphin body condition.

The body or nutritional condition of dolphins can significantly affect survival, reproductive success, and susceptibility to disease through impacts on immune function. In addition, it can be a sensitive indicator of prey abundance and individual feeding success, as well as the presence of disease. Thus, assessing the body condition of animals is critical for monitoring the health of dolphin populations. However, current methods of measuring body condition in free-ranging dolphins require capturing, restraining and sampling individuals directly through capture-release health assessments, which are expensive and logistically complex, and are not feasible in many situations. With a grant from the Association of Zoos & Aquariums Conservation Endowment Fund (through funding from the Disney Worldwide Conservation Fund), and a fellowship grant from the Morris Animal Foundation, we designed and built a low-cost remote-controlled unmanned aerial vehicle (UAV) to remotely measure the body condition of cetaceans at sea.

The UAV, which has a digital camera, is designed to be launched from a small boat and to hover precisely over individual animals and collect photographs for detailed measurements of body size and shape (a technique called aerial photogrammetry), which then can be used to derive indices of body condition. Initial field testing of the UAV system was conducted over bottlenose dolphins being temporarily held in large net corrals during capture-release health assessments in Sarasota Bay. These initial trials enabled us to compare measurements (such as total body length and girth) obtained from the aerial photographs with those obtained directly from the animals during capture-release events and, thus, assess the accuracy of our technique.

Our next step will be to use the UAV system to collect measurements of body condition from resident bottlenose dolphins during year-round boat surveys in Sarasota Bay, and to conduct comparisons based on the animals’ sex, age, and reproductive class, as well as comparisons between seasons and between healthy and unhealthy individuals. Our novel health assessment technique could be used in the future to help determine whether capture-release health evaluations of bottlenose dolphins are warranted in areas of concern. In addition, our methodology could be applied to a wide variety of marine mammal species that have yet to be studied in this manner.

This article was published on page 10 in the November 2014 issue of Nicks n Notches