title: Lineage fusion in Galápagos giant tortoises.
abstract: Although many classic radiations on islands are thought to be the result of repeated lineage splitting, the role of past fusion is rarely known because during these events, purebreds are rapidly replaced by a swarm of admixed individuals. Here, we capture lineage fusion in action in a Galápagos giant tortoise species, Chelonoidis becki, from Wolf Volcano (Isabela Island). The long generation time of Galápagos tortoises and dense sampling (841 individuals) of genetic and demographic data were integral in detecting and characterizing this phenomenon. In C. becki, we identified two genetically distinct, morphologically cryptic lineages. Historical reconstructions show that they colonized Wolf Volcano from Santiago Island in two temporally separated events, the first estimated to have occurred ~199 000 years ago. Following arrival of the second wave of colonists, both lineages coexisted for approximately ~53 000 years. Within that time, they began fusing back together, as microsatellite data reveal widespread introgressive hybridization. Interestingly, greater mate selectivity seems to be exhibited by purebred females of one of the lineages. Forward-in-time simulations predict rapid extinction of the early arriving lineage. This study provides a rare example of reticulate evolution in action and underscores the power of population genetics for understanding the past, present and future consequences of evolutionary phenomena associated with lineage fusion.
authors.affiliation: Department of Biology, University of Mississippi, Oxford, MS, 38677, USA.
authors.forename: Ryan C
authors.initials: RC
authors.lastname: Garrick
authors.forename: Edgar
authors.initials: E
authors.lastname: Benavides
authors.forename: Michael A
authors.initials: MA
authors.lastname: Russello
authors.forename: Chaz
authors.initials: C
authors.lastname: Hyseni
authors.forename: Danielle L
authors.initials: DL
authors.lastname: Edwards
authors.forename: James P
authors.initials: JP
authors.lastname: Gibbs
authors.forename: Washington
authors.initials: W
authors.lastname: Tapia
authors.forename: Claudio
authors.initials: C
authors.lastname: Ciofi
authors.forename: Adalgisa
authors.initials: A
authors.lastname: Caccone
mesh_terms: D000818:Animals; D004272:DNA, Mitochondrial / Q000235:genetics; D004484:Ecuador; D019143:Evolution, Molecular; D005260:Female; D005788:Gene Pool; D014644:Genetic Variation; D005828:Genetics, Population; D006824:Hybridization, Genetic; D062312:Islands; D018895:Microsatellite Repeats; D008957:Models, Genetic; D017422:Sequence Analysis, DNA; D014426:Turtles / Q000145:classification / Q000235:genetics*
chemical_list: D004272:DNA, Mitochondrial
keywords: Galápagos; biodiversity; conservation; evolutionary history; introgressive hybridization