Research on the genetic susceptibility of Florida bottlenose dolphins to red tides has continued over the past year with some interesting new developments involving the addition of a genomics approach.
This project investigates populations of estuarine and coastal bottlenose dolphins in the Florida Panhandle and central-west Florida, including Sarasota Bay.
Dolphins in these two regions appear to differ in their susceptibility to harmful algal blooms, or red tides, of the toxic algal species . My research tests the hypothesis that this difference in susceptibility is due to the evolution of resistance over time in areas, like central-west Florida, that have been historically and regularly exposed to red tides.
To search for evidence of evolved resistance, I initially analyzed a set of candidate genes that are thought to be involved in the process of toxin exposure, including immune system genes, detoxification enzymes, and the biological target of the toxin. This past year, I added a new complementary approach to the research project in order to search for evidence of evolved resistance across the dolphin genome more broadly. This genomics approach uses a newly developed technique known as restriction site associated DNA (RAD) sequencing, which provides DNA sequence information from thousands of sites located throughout the genome. I will look for variation in this sequence data and analyze the frequency of variants in different groups of bottlenose dolphins. For example, I will compare dolphins from central-west Florida to those from the and compare dolphins that survived red tides to those that died due to toxin exposure. Although the sequence data provided by RAD sequencing is not necessarily linked to a function, like the candidate genes listed above, it may be possible to determine the function of any sequence that shows an interesting pattern of variation by comparing it to the dolphin genome available online and genes of known function in other organisms.
While the candidate gene approach takes advantage of previous knowledge of red tide intoxication to select genes of interest, RAD sequencing is an unbiased approach to searching for a signal of evolved resistance across the genome. The analysis of both complementary approaches, which is still in progress, will help us determine if there is a genetic basis for resistance to red tide in bottlenose dolphins. Any of susceptibility that we identify could be used to evaluate the susceptibility of additional dolphin populations and estimate the likelihood of dolphin mortality events should future red tides occur.
This research has been supported by funding from the Duke University Marine Lab, the PADI Foundation, and the American Fisheries Society. Samples were provided by the Sarasota Dolphin Research Program and the NOAA Fisheries SEFSC Marine Mammal DNA Archives.
This article was published on page 23 in the January 2013 Nicks n Notches.