Sarasota Dolphin Research Program

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Genetic susceptibility to red tides
By Kristina Cammen, PhD student, Duke University

SEM image of a Pseudo-nitzschia frustule. Photo Credit: Steve Morton (NOAA Marine Biotoxins Program).

Red tides, which are a common occurrence in the Gulf of Mexico, can have drastic negative impacts on many marine species. In the past decade, four Unusual Mortality Events (UMEs) of bottlenose dolphins have been attributed to Karenia brevis, the red tide algal species that produces neurotoxic brevetoxins. Three of the UMEs occurred in the Florida Panhandle in 1999-2000, 2004, and 2005-2006 resulting in a total of over 300 dolphin mortalities. One UME occurred in central-west Florida in 2005-2006, killing at least 79 dolphins. Bottlenose dolphins from these two regions appear to differ significantly in their susceptibility to red tides. Central-west Florida experiences red tides almost annually, but only one dolphin UME has occurred. In contrast, only a few red tides have been reported in the Panhandle, and these red tides often result in dolphin mortalities. We are currently investigating the hypothesis that this difference in susceptibility is due to genetic differences between populations.

Historical exposure to red tides could have resulted in differential selection at certain genes related to brevetoxins. Adaptation to a common threat can result in resistance in an exposed population and susceptibility in a naīve population. Specifically, we are evaluating genetic variation at detoxification enzymes such as cytochrome P450 and glutathione, as well as immune system genes such as the MHC. Additionally, we are studying genes that code for the voltage-gated sodium channel in neurons, the primary target for brevetoxins.

We plan to compare genetic variation at these genes among dolphins from the Panhandle and Sarasota Bay. Samples from live healthy animals, collected during health assessment capture-release operations, will be compared to samples collected and archived from dead animals that stranded during red tides. We hope to identify genetic variation that is found more commonly in either live or dead animals and associate this variation with susceptibility to red tides. We can then evaluate if the Panhandle population contains more individuals with genes associated with susceptibility. Additionally, we may be able to apply these concepts to other dolphin populations in the Gulf of Mexico to determine which populations are more likely to experience mortality events in the future when red tides occur. Our research is supported by funding from the Duke University Marine Lab, and samples were provided by SDRP and NMFS SEFSC Marine Mammal Molecular Genetics Laboratory.