title: Progressive colonization and restricted gene flow shape island-dependent population structure in Galápagos marine iguanas (Amblyrhynchus cristatus).
abstract: BACKGROUND
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Ecology and Evolutionary Biology and Yale Institute for Biospheric Studies - Molecular Systematics and Conservation Genetics Laboratory, New Haven, Connecticut 06511, USA. sebastian.steinfartz@uni-bielefeld.de
authors.forename: Sebastian
authors.initials: S
authors.lastname: Steinfartz
authors.forename: Scott
authors.initials: S
authors.lastname: Glaberman
authors.forename: Deborah
authors.initials: D
authors.lastname: Lanterbecq
authors.forename: Michael A
authors.initials: MA
authors.lastname: Russello
authors.forename: Sabrina
authors.initials: S
authors.lastname: Rosa
authors.forename: Torrance C
authors.initials: TC
authors.lastname: Hanley
authors.forename: Cruz
authors.initials: C
authors.lastname: Marquez
authors.forename: Howard L
authors.initials: HL
authors.lastname: Snell
authors.forename: Heidi M
authors.initials: HM
authors.lastname: Snell
authors.forename: Gabriele
authors.initials: G
authors.lastname: Gentile
authors.forename: Giacomo
authors.initials: G
authors.lastname: Dell'Olmo
authors.forename: Alessandro M
authors.initials: AM
authors.lastname: Powell
authors.forename: Adalgisa
authors.initials: A
authors.lastname: Caccone
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics; D004484:Ecuador; D005260:Female; D051456:Gene Flow; D014644:Genetic Variation; D005828:Genetics, Population; D007076:Iguanas / Q000235:genetics*; D019901:Locus Control Region; D008297:Male; D018895:Microsatellite Repeats
chemical_list: D004272:DNA, Mitochondrial