Genetic population structure of coastal tucuxi dolphins in Southern Brazil
By Paulo A.C. Flores, PhD, Deborah A. Duffield, PhD, and Paulo Simões-Lopez, PhD

The marine tucuxi inhabits river and lake systems of Amazonia, the lower Orinoco River, and coastal marine waters from southern Brazil north to at least Nicaragua. For more than 10 years, Paulo Flores has been studying marine tucuxi at the southern extent of the species’ range, in Baía Norte of the Florianópolis region of Brazil. His work, including his Earthwatch Institute photographic identification studies since 2001 that include Randall Wells as co-PI, has demonstrated the existence of a long-term resident population of tucuxi that appears to be isolated from other populations, based on distance from other documented populations. This population is subjected to human impacts from gill-net fishing (for which incidental dolphin take has been documented), boat traffic, and coastal development. The degree of risk from human threats to this population remains to be evaluated, as more information is needed on population structure and the degree of isolation.

As a collaboration between Brazilian and U.S. scientists, we initiated a study of the genetic structure of the population of marine tucuxi inhabiting Baía Norte, taking advantage of existing samples from stranded tucuxi recovered from Baía Norte. Teeth from stranded tucuxi were used as a source of genetic material to begin to evaluate the genetic variability in the population (teeth from museum specimens were provided by Dr. Simões-Lopes). Genetic variability were assessed by two methods: 1) mitochondrial DNA haplotypes, to examine phylogeographic distinctions between the resident population and samples from other areas, and 2) DNA microsatellites, to investigate the population structure of this resident group.

Total genomic DNA was extracted from 36 individuals. Mitochondrial DNA (mtDNA) was amplified with three primers of different sizes: 130 base pairs (bp), 230 and 540, with successful amplification from both the 130 and 230bp for 34 of the 36 samples (individuals). An ~ 230bp mtDNA sequence of the control region was obtained, which overlaps with Sotalia sequences from GenBank and Cunha et al. (2005) from a phylogenetic study along the Brazilian coast. The sequences obtained from 33 individuals were excellent but all identical, producing only one haplotype which is identical to the sequence reported as the only one for south-southeastern Brazil by Cunha et al. (2005) as found in GenBank. Therefore, at the level we analyzed, no genetic variability was found in our sample, which included 15 males, 10 females and five individuals with no gender identification (calves, juveniles and adults) from Baia Norte, as well as one male and five other individuals from Baia de Babitonga, located about 200 km to the North. Microsatellite analyses continue.

We were able to consistently extract DNA from teeth of museum/scientific collection material. These protocols will be extremely helpful for other researchers with access to such material from museums or scientific and stranding network collections, especially in Latin America where the subject species occurs, for future molecular studies. We have banked DNA for 34 individuals, which is likely to represent the largest sampling for a discrete population of marine tucuxi to date. Support for this project was provided by the Chicago Board of Trade, Dolphin Biology Research Institute, and the Whale and Dolphin Conservation Society