Sarasota Bay dolphins provide clues to prevent insulin resistance in dolphins and humans

Dolphins can naturally switch diabetes-like states on and off.

In some cases, however, dolphins can develop diseases similar to people with insulin resistance.

In collaboration with the National Marine Mammal Foundation (NMMF) and the Sarasota Dolphin Research Program, a three-year study supported by the Office of Naval Research aims to identify dolphin groups that may be at higher and lower risk of insulin resistance. By doing so, the investigators hope to target new ways to prevent and treat insulin resistance in dolphins.

A new panel of tests was developed and used with Sarasota Bay dolphins to assess their metabolic health. Compared to other groups, Sarasota Bay dolphins had lower insulin, glucose, cholesterol, and triglycerides. These results support that Sarasota Bay dolphins may be better protected against developing insulin resistance compared to other dolphin groups managed under human care. The investigative team is currently exploring how Sarasota Bay dolphin diet, activity, genetics, and environment may prevent insulin resistance. These studies, led by Dr. Stephanie Venn-Watson at the NMMF and SDRP’s Dr. Randall Wells, were recently published in a special issue of Frontiers in Endocrinology: Marine Mammals as Out-of-the-Box Models for Insulin Resistance and Diabetes.

This article was published on pages 16-17 in the January 2014 Nicks n Notches.

Dolphin and stingray interactions

Citizens and tourists of the Sarasota Bay area are well-versed in the “stingray shuffle” to avoid stepping on and being stung by the typically docile, bottom-dwellers found in coastal waters.

But how do stingrays affect bottlenose dolphins?

The Stranding Investigations Program (SIP) at Mote Marine Laboratory provides 24-hour response to stranded marine mammals that are either sick, injured, or dead within the coastal waters of Sarasota and Manatee counties.   The SIP works closely with the Sarasota Dolphin Research Program to identify and recover stranded resident bottlenose dolphins.

Since 1991, 72 resident dolphin have been recovered by the joint programs and upon necropsy (animal autopsy) stingray spines were found in nearly 25% of the dolphins (11 females and 7 males) and suspected in one other case.

How dolphins interact or come into contact with the stingrays is not completely understood.  The stingray barb itself is not always the cause of death, but certainly can contribute to pain and overall poor health.  Often, it is possible to trace the path that the stingray barb took through the dolphin’s body.  The barb generally migrates until it hits something hard, like bone, or the body responds by attempting to wall it off.

In the case of mom, “Jose”, and son, “JOSC”, which are two well-studied Sarasota Bay dolphins typically seen in deep water, both had stingray barbs discovered upon necropsy.  “Jose” stranded on April 12, 2006, emaciated, with a fishing lure in her mouth and a stingray barb that was encapsulated in the right lung.  These findings contributed to “Jose’s” death.  It’s not known if stingray or fishing interaction came first.  The lure would have made it very difficult for “Jose” to hunt and eat, but ultimately, the stingray barb found in the lung was determined to be the cause of death.  For son, “JOSC,” stranded on March 17, 2013, a stingray barb had migrated into the vertebrae, piercing the first vertebra and causing changes to the bones of his skull and surrounding vertebrae. “JOSC” was also emaciated and had severe ulcers in his stomach. As was the case with his mom, “JOSC” died because of the injuries caused by the stingray barb.  These two examples demonstrate how both human and natural factors can harm dolphins and are a good reminder that thorough investigation into the cause of death is important in understanding the threats that these animals face.

This article was published on page 16 in the January 2014 Nicks n Notches.

Microparticles as a biomarker of decompression sickness

Recent studies of stranded marine mammals indicate that exposure to underwater military sonar may induce symptoms consistent with decompression sickness (DCS).

Without a measurable indicator or biomarker, DCS has been difficult to accurately diagnose in marine mammals. As part of the dolphin health assessment project, our team of researchers at Woods Hole Oceanographic Institution, Texas A&M University – Corpus Christi, and University of Maryland is investigating the use of Microparticles (MPs) as a tool to diagnose DCS in marine mammals.

MPs (measured as number/μl plasma) are fragments of various cells, such as platelets that circulate in blood.  Studies of MPs in humans and mice have shown that with increased decompression stress, circulating MPs also increase. The origin and cause of elevated MPs is not clear; however, tissue injury as a result of gas bubble formation from decompression stress is likely a factor.  With support from the many supporters of the Sarasota Dolphin Research Program and the Office of Naval Research, we are collecting and analyzing blood samples from captive Steller sea lions, wild-caught-and-released dolphins, and stranded dolphins in order to verify the use of MPs as a biomarker for DCS.

As part of the Sarasota Dolphin Research Program, we have collected blood samples from healthy dolphins in Sarasota Bay.  In 2012 and 2013, we analyzed blood samples from nearly 40 dolphins to determine baseline MPs values.  Our next step is to collect and analyze blood samples from single and mass-stranded dolphins in Cape Cod in early 2014 to compare against the baseline MPs levels from Sarasota dolphins.  We will also perform statistical analyses of all data by utilizing associated morphometric data, environmental variables, and health assessment parameters collected during the sampling events.

Preliminary results from a related study in Steller sea lions support the use of MPs as a biomarker for decompression stress.  We measured MPs in Steller sea lions before and after experimental dive trials.  Compared to Pre-dive MPs, Post-dive MPs increased on average by 303% at 3 hours and 458% at 24 hours.  This Steller sea lion study provides preliminary verification that MPs may potentially be used as biomarker for DCS in marine mammals.  Although data collection and analyses are ongoing, confirmation of MPs as a diagnostic tool could have significant implications for marine mammal conservation by improving management decisions during a stranding event.

 This article was published on 15 in the January 2014 Nicks n Notches.

Evaluating stress hormones in bottlenose dolphins

As inhabitants of a constantly changing coastal environment, estuarine bottlenose dolphins are exposed to a variety of internal and external stressors. Their stress response is modulated by various hormones, several of which are secreted from the adrenal and thyroid glands.

The objective of this study was to use data from long-term capture-release projects conducted in Sarasota Bay to evaluate influential factors (for example, demographic, seasonal, temporal, physical, and sampling) related to individual variation in circulating concentrations of adrenal and thyroid hormones commonly considered to be involved in the marine mammalian stress response (cortisol, aldosterone, T3, TT4, and FT4).

Previous studies have implicated the influence of these variables on the secretion of these hormones following exposure to various stressors; however most of these studies relied upon short-term data or single-sampling events.  Our study, funded by the Office of Naval Research, used hormone concentrations measured in blood samples collected during capture-release events during 2000-2012.   In total, 185 observations representing 121 individuals (61 males, 60 females) were used for statistical analyses to examine associations between stress hormone measurements and factors such as sex, age, sexual maturity, time of day, length, mass, and elapsed sampling time (the time between capture and blood collection).  Statistical analyses were used to determine that elapsed time and mass were significant influences on cortisol levels, while sex, age, and sexual maturity were associated with thyroid hormone concentrations.

While it is helpful to understand demographic and environmental influences on endocrine hormone concentrations among individuals and across populations, the impact of various biological and artificial stressors cannot be evaluated without a comparison to baseline “normal” values.

Reference intervals provide an opportunity to evaluate an individual’s health status among populations for which baseline data are not available, as they represent a range of expected values for a normal, healthy population.  Results of the analyses to determine influential factors were used to stratify reference intervals for each of the stress hormones.  For example, since elapsed sampling time was significantly associated with cortisol levels, separate reference intervals were calculated for animals sampled in less than 30 minutes following capture and greater than 30 minutes post-capture.  Similarly, reference intervals for T3 were stratified based on sexual maturity, where separate reference intervals were calculated for immature and mature dolphins. Bottlenose dolphin capture-release health assessments have increased in frequency over the past decade due to questions regarding health effects from harmful algal bloom exposure, PCB contamination, and in response to environmental disasters such as the Deepwater Horizon Oil Spill.  In many cases, baseline health data have not been available for these study populations.  Reference intervals, based on unbiased statistical analyses and long-term data, provide an opportunity to quantitatively and objectively compare and evaluate health parameters of individuals for which historical data are unavailable.

This article was published on page 15 in the January 2014 Nicks n Notches.

Genetic susceptibility to red tides

Recent advances in molecular technologies have made it possible to study genetic variation across whole genomes of bottlenose dolphins and other species in the natural environment.

These powerful techniques greatly benefit studies of genetic adaptation, where researchers search for genes linked to higher fitness and health.  In Sarasota Bay, these techniques have greatly enhanced my study of a genetic basis for resistance to harmful algal blooms (HABs) in bottlenose dolphins.

Bottlenose dolphins in central-west Florida, including Sarasota Bay, are exposed to HABs of the toxic dinoflagellate Karenia brevis almost every year.  These HABs, also known as red tides, produce neurotoxins that can be lethal to bottlenose dolphins and other marine animals, such as fish, manatees, sea birds, and sea turtles, but the dolphins in central-west Florida appear to be relatively resistant to the toxin.  I compared bottlenose dolphins that died due to red tide exposure to dolphins that survived, from both central-west Florida and the Florida Panhandle.  Dolphins in the Panhandle appear to be relatively susceptible to red tides and have experienced several large-scale unusual mortality events associated with K. brevis blooms.

My comparisons of live and dead dolphins from apparently resistant and susceptible populations involved thousands of genetic markers from across the bottlenose dolphin genome.  These genetic data are generated using a technique called restriction-associated DNA sequencing, which produces short sequences of DNA representing a subset of the genome.  I found that some variation in these DNA sequences correlates with survival in bottlenose dolphins from both central-west Florida and the Panhandle. These survival-associated DNA sequences may be linked to several genes potentially related to red tide resistance, including genes involved in the immune system, the response to stress, and the generation of neurons.  Overall, this finding of genetic variation associated with survival suggests a genetic basis for resistance to red tides in bottlenose dolphins, and we have identified potential candidate genes that may encode this resistance.

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


This article was published on pages 14-15 in the January 2014 Nicks n Notches.