By Martin Mendez, PhD, Columbia University
Studying the relationships between environmental heterogeneity and spatial population structure for marine species is fundamental to increase our understanding of marine populations and to enhance conservation strategies. I took on this issue as part of my PhD dissertation, focusing on two coastal cetaceans: Franciscana dolphins in coastal South America, and humpback dolphins off the coasts of South Africa, Mozambique, Tanzania and Oman. Specifically, I used remote sensing oceanographic information to look for abrupt spatial changes in environmental conditions (environmental breaks) in these areas, and combined this information with genetic data to evaluate population structure for both species. Ultimately, the goal was to assess if the environmental breaks coincide spatially with the genetic structure observed.
The Franciscana dolphin work, published in the journals Conservation Genetics and Molecular Ecology, shows significant population structure between dolphins occurring in Brazilian, Uruguayan and Argentinean waters, and suggests further genetic structure within the groups of animals collected in Argentina. In addition, our analyses show a concordant spatial arrangement of the genetic and environmental breaks for the populations off Argentina, and provide evidence suggesting that a mechanism termed here “isolation by environmental distance” may explain some of the observed patterns. The humpback dolphin work, under review in the journal Heredity, shows regional oceanographic breaks that are concordant to the strong and highly significant genetic structure of this species in the study area, and suggests that surface currents and ocean color properties may play a significant role in dispersal of humpback dolphins in this region. All in all, this type of multidisciplinary work has allowed us to take a more comprehensive look at the relationships between mobile marine populations and their environment, and is currently contributing to the conservation of both species through more specific management recommendations.
Other aspects explored in my dissertation include an assessment of genetic and demographic impacts of by-catch to Franciscana dolphins (currently under review in the journal PLoS ONE) and an evaluation of the effectiveness of the Marine Protected Areas in Latin America (published in the journal Latin American Journal of Aquatic Mammals). I graduated in May 2010 and was honored with the Columbia University Distinction for my PhD Dissertation.
We acknowledge support from Martin Mendez’s Dissertation Committee, Fundación Aquamarina, the local fishermen in Buenos Aires, Sackler Institute for Comparative Genomics at the American Museum of Natural History, Mote Marine Laboratory, Chicago Zoological Society, Wildlife Trust Alliance, Fundación Vida Silvestre, Columbia University and the Argentinean Government.