Thursday, February 18, 2016

Dolphin DNA

Photo credit: http://blog.nus.edu.sg/lsm1303student2013/2013/04/11/deadly-alliances-male-common-bottlenose-dolphins-engage-in-sexually-coercive-mating-behaviour-in-gangs/
          I read a book one time about a girl who fell overboard during a tropical boating expedition.  Somehow the crew didn’t notice her absence and left her, stranded, in the middle of the ocean.  Worried, alone, and exhausted, the girl was rescued by a friendly dolphin, who gave her a ride back to the boat.

Regardless of how unrealistic this story is, I can’t help being captivated by the majestic beauty of these marine mammals.  When I think of Marine Biology, my mind quickly creates this heroic rescue by the dolphin pod.  So without further ado, we can proceed to the science surrounding these beautiful creatures.

Although microorganisms can be useful indicators for various aspects of marine ecology, dolphins and other large marine organisms are important to study because of their large size.  Contaminants to the marine environment can actually be identified and estimated using samples from dolphins.  Along the same lines, the health of a marine habitat can be evaluated by assessing the health of animals farther up the food chain such as dolphins.  It was with these aspects in mind that a team of nine researchers joined forces to sequence and assess the DNA of five Tursiops truncatus (bottlenose dolphin) populations.  They published their multidisciplinary results in 2015.

DNA was collected from blood samples from dolphins in the following locations:
  • Beaufort, NC
  • Sarasota Bay, FL
  • Saint Joseph Bay, FL
  • Sapelo Island, GA
  • Brunswick, GA

Samples were collected from 69 dolphins total, 30 males and 39 females collectively from these five locations between 2005 and 2010.  The team evaluated 30 control genes to verify the species.  Additionally, blubber samples were examined for the presence of polychlorinated biphenyls (PCB), which are persistent organic pollutants that are banned in many countries including the US.

Photo credit: http://www.brandoncole.com/photos_bottlenose_dolphins.htm

Since this was a new technique, the capabilities of the microassay was evaluated through the completion of this project.  It identified seven genes that correctly differentiated the dolphins by sex as well as 153 genes that were expressed differently depending on whether dolphins were part of Gulf or Atlantic populations.  The researchers found that the genomes of the dolphins from the two locations in Georgia – Sapelo Island and Brunswick – did not contain significant differences, so they were regarded as one population.  Specific differences were noted between the genomes when gender was consistent and population was assessed, such as specific genomic differences between a male Gulf dolphin and a male Atlantic dolphin.  The researchers expressed concern about drawing many conclusions about the sexes individually due to low sample sizes, so statistical analysis was focused on the group of both sexes together.

Georgia dolphins were found to be significantly different than the other dolphins in 69 of the 153 genes that were assessed.  The differences among both male and female members of the respective populations each fell into four categories, as you can see in the table below.

Male
Female
Development and Differentiation
Transcription and Translation
Wound Healing and Tumor Prevention
Immune Response
Inflammatory Response
Cell Development and Growth
Metabolism of Foreign Chemicals
Metabolism of Foreign Chemicals

The differences between Georgia dolphins and other dolphins generally center around immune response, so blubber was analyzed.  The research team found that Georgia dolphins deal with more PCBs than the other populations, most likely due to their proximity to the Linden Chemicals and Plastics plant on the Georgia coast.  Not only is it clear that the Atlantic habitat off the coast of Georgia is contaminated with PCBs, we can see that these toxins are genetically – and thus, physiologically – affecting the marine organisms there.  A quick search online shows that PCBs have been linked to decreased lymphocyteresponses and negative reproductive effects in dolphins, not to mention their prey and consumers.  After identifying the PCB level in the Georgia dolphin population, the researchers were able to identify specific genes that reflect this differing level of contaminants, which will make future assessments easier.

Overall, this method of genetically analyzing Tursiops truncates is quite informative about the marine environments that were studied.  I appreciate the interdisciplinary nature of this paper, as it integrates genetics so flawlessly into the field of marine biology.  Who knows if I’ll ever befriend a dolphin, but they are fascinating to study and beautiful to see!

Reference:

2 comments:

  1. It sounds like this paper was measuring gene expression levels, and which genes were down or upregulated. They then tried to correlate the change in gene expression with PCB contamination. Is this correct?

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  2. Yes, that is correct. Thank you for clarifying!

    ReplyDelete