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Phylogeography and history of giant Galápagos tortoises

January 1, 2002

We examined the phylogeography and history of giant Galápagos tortoise populations based on mitochondrial DNA sequence data from 161 individuals from 21 sampling sites representing the 11 currently recognized extant taxa. Molecular clock and geological considerations indicate a founding of the monophyletic Galápagos lineage around 2–3 million years ago, which would allow for all the diversification to have occurred on extant islands. Founding events generally occurred from geologically older to younger islands with some islands colonized more than once. Six of the 11 named taxa can be associated with monophyletic maternal lineages. One, Geochelone porteri on Santa Cruz Island, consists of two distinct populations connected by the deepest node in the archipelago-wide phylogeny, whereas tortoises in northwest Santa Cruz are closely related to those on adjacent Pinzón Island. Volcan Wolf, the northernmost volcano of Isabela Island, consists of both a unique set of maternal lineages and recent migrants from other islands, indicating multiple colonizations possibly due to human transport or multiple colonization and partial elimination through competition. These genetic findings are consistent with the mixed morphology of tortoises on this volcano. No clear genetic differentiation between two taxa on the two southernmost volcanoes of Isabela was evident. Extinction of crucial populations by human activities confounds whether domed versus saddleback carapaces of different populations are mono- or polyphyletic. Our findings revealed a complex phylogeography and history for this tortoise radiation within an insular environment and have implications for efforts to conserve these endangered biological treasures.

Publication Year 2002
Title Phylogeography and history of giant Galápagos tortoises
DOI 10.1554/0014-3820(2002)056[2052:PAHOGG]2.0.CO;2
Authors A. Caccone, G. Gentile, J.P. Gibbs, T. H. Fritts, H. L. Snell, J. Betts, J.R. Powell
Publication Type Article
Publication Subtype Journal Article
Series Title Evolution
Index ID 1015235
Record Source USGS Publications Warehouse
USGS Organization Fort Collins Science Center