August 13, 2013
Principal Investigator: Matthew S. Leslie, Marine Mammal Genetics Program
Millions of dolphins were accidentally killed in the tuna fishery of the Eastern Tropical Pacific (ETP). The killing has largely stopped (only about 1000 dolphins still die in the fishery each year), but the dolphin populations haven't recovered as predicted. One of the most important questions still needing an answer is, "How many populations are there?” The answer to this question is crucial for setting limits on the number of dolphins that can be killed in a given area, which is critical for recovery of the dolphin populations.
Significant differences in skull features and overall size/shape of the dolphins were used to define a subspecies of the coastal spotted dolphin (Stenella attenuata graffmani) in this area, which are distinct from the offshore pantropical subspecies (S. a. attenuata). The same methods were also used to divide spinner dolphins into three subspecies: Central American spinner dolphins (Stenella longirostris centroamericana), Eastern spinner dolphins (S. l. orientalis), and Pantropical spinner dolphins (S l. l.). We have reason to believe that there are populations within these subspecies that have not yet been discovered.
We are collecting DNA sequence data from these dolphins to try to detect these populations. DNA data from the whole mitochondrial genome show little population structure in both species, even across subspecies. This indicates geneflow between the subspecies, which may make this a very difficult question to answer. We are now collecting large volumes of nuclear DNA using a "genome scan" approach. This method should provide sufficient statistical power to detect even small differences between populations.
Spinner and spotted dolphins live in all the tropical seas of the world. But how did they get there and how are the animals in different oceans related? Using samples from around the globe and collecting data using a "genome scan" approach, we will try to uncover the evolutionary history of these two species. This includes examining a proposed spinner dolphin hybrid zone in the eastern tropical Pacific using a combination of genomics, skull measurements and oceanographic. We are collecting DNA data from teeth from museum specimens in order to combine genetic data with measurement data. These data will enable us to describe this hybrid zone in great detail, and hopefully yield insight into how marine mammal species originate in the oceanic environment.