The role of Pleistocene refugia and rivers in shaping gorilla genetic diversity in central Africa

doi:10.1073/pnas.0704816105

The role of Pleistocene refugia and rivers in shaping gorilla genetic diversity in central Africa

*Department of Biological Sciences, University of New Orleans, New Orleans, LA 70148;
^†School of Biosciences, Cardiff University, Cardiff CF10 2TL, United Kingdom;
^§Centre International de Recherches Médicales de Franceville, B.P. 769, Franceville, Gabon;
^¶School of Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, United Kingdom;
^‖Institut de Recherche en Ecologie Tropicale, B.P. 180, Makokou, Gabon; and
**Wildlife Conservation Society, Bronx Zoo, 185th Street and Southern Boulevard, Bronx, NY 10460

Edited by Jeffrey Rogers, Southwest Foundation for Biomedical Research, San Antonio, TX, and accepted by the Editorial Board November 6, 2007 (received for review May 23, 2007)

Abstract

The role of Pleistocene forest refugia and rivers in the evolutionary diversification of tropical biota has been the subject of considerable debate. A range-wide analysis of gorilla mitochondrial and nuclear variation was used to test the potential role of both refugia and rivers in shaping genetic diversity in current populations. Results reveal strong patterns of regional differentiation that are consistent with refugial hypotheses for central Africa. Four major mitochondrial haplogroups are evident with the greatest divergence between eastern (A, B) and western (C, D) gorillas. Coalescent simulations reject a model of recent east–west separation during the last glacial maximum but are consistent with a divergence time within the Pleistocene. Microsatellite data also support a similar regional pattern of population genetic structure. Signatures of demographic expansion were detected in eastern lowland (B) and Gabon/Congo (D3) mitochondrial haplogroups and are consistent with a history of postglacial expansion from formerly isolated refugia. Although most mitochondrial haplogroups are regionally defined, limited admixture is evident between neighboring haplogroups. Mantel tests reveal a significant isolation-by-distance effect among western lowland gorilla populations. However, mitochondrial genetic distances also correlate with the distance required to circumnavigate intervening rivers, indicating a possible role for rivers in partitioning gorilla genetic diversity. Comparative data are needed to evaluate the importance of both mechanisms of vicariance in other African rainforest taxa.

Footnotes

^‡To whom correspondence should be addressed. E-mail: nanthony{at}uno.edu
Author contributions: K.A.A., L.J.T.W., E.J.W., and M.W.B. designed research; N.M.A., M.J.-B., and S.L.C. performed research; K.J., K.A.A., C.E.T., S.A.L., L.J.TW., and J.F.U. contributed new reagents/analytic tools; N.M.A., J.F.U., and M.W.B. analyzed data; and N.M.A. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. J.R. is a guest editor invited by the Editorial Board.
Data deposition: The sequences reported in this paper have been deposited in the GenBank database (accession nos. EU305296–EU305397).
This article contains supporting information online at www.pnas.org/cgi/content/full/0704816105/DC1.