Progressive colonization and restricted gene flow shape island-dependent population structure in Galápagos marine iguanas (Amblyrhynchus cristatus)
- Equal contributors
1 Department of Ecology and Evolutionary Biology and Yale Institute for Biospheric Studies - Molecular Systematics and Conservation Genetics Laboratory, New Haven, Connecticut 06511, USA
2 Current address: Department of Animal Behaviour, University of Bielefeld, D-33501 Bielefeld, Germany
3 Current address: Marine Biology Laboratory, University of Mons-Hainaut, 7000 Mons, Belgium
4 Department of Biology, University of British Columbia Okanagan, Kelowna, British Columbia V1V 1V7, Canada
5 Galápagos National Park, Puerto Ayora, Galápagos, Ecuador
6 Museum of Southwestern Biology, Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA
7 Department of Biology, Tor Vergata University, 00133 Rome, Italy
8 Ornis italica, Piazza Crati 15, 00199 Rome, Italy
9 36 Carew Rd, Hamden, CT 06517, USA
BMC Evolutionary Biology 2009, 9:297 doi:10.1186/1471-2148-9-297Published: 22 December 2009
Marine iguanas (Amblyrhynchus cristatus) inhabit the coastlines of large and small islands throughout the Galápagos archipelago, providing a rich system to study the spatial and temporal factors influencing the phylogeographic distribution and population structure of a species. Here, we analyze the microevolution of marine iguanas using the complete mitochondrial control region (CR) as well as 13 microsatellite loci representing more than 1200 individuals from 13 islands.
CR data show that marine iguanas occupy three general clades: one that is widely distributed across the northern archipelago, and likely spread from east to west by way of the South Equatorial current, a second that is found mostly on the older eastern and central islands, and a third that is limited to the younger northern and western islands. Generally, the CR haplotype distribution pattern supports the colonization of the archipelago from the older, eastern islands to the younger, western islands. However, there are also signatures of recurrent, historical gene flow between islands after population establishment. Bayesian cluster analysis of microsatellite genotypes indicates the existence of twenty distinct genetic clusters generally following a one-cluster-per-island pattern. However, two well-differentiated clusters were found on the easternmost island of San Cristóbal, while nine distinct and highly intermixed clusters were found on youngest, westernmost islands of Isabela and Fernandina. High mtDNA and microsatellite genetic diversity were observed for populations on Isabela and Fernandina that may be the result of a recent population expansion and founder events from multiple sources.
While a past genetic study based on pure FST analysis suggested that marine iguana populations display high levels of nuclear (but not mitochondrial) gene flow due to male-biased dispersal, the results of our sex-biased dispersal tests and the finding of strong genetic differentiation between islands do not support this view. Therefore, our study is a nice example of how recently developed analytical tools such as Bayesian clustering analysis and DNA sequence-based demographic analyses can overcome potential biases introduced by simply relying on FST estimates from markers with different inheritance patterns.