1. Evolutionary history of gorillas inferred from complete mitochondrial DNA sequences
Das R1, Hergenrother SD1, Lurie-Marino M1, Soto-Calderón ID2,3, Anthony NM2, Jensen-Seaman MI1
1Department of Biological Sciences, Duquesne University, Pittsburgh, PA, USA
2Department of Biological Sciences, University of New Orleans, New Orleans, LA, USA
3Biology Institute, University of Antioquia, Medellín, Colombia 
Introduction
Phylogenetic tree with time scale (in Mya)
Results
- Genetic verification
Gorilla populations are found in equatorial Africa in two widely separated regions (aerial distance ~ 1000 km): West Africa and East/Central Africa. Currently there are two recognized gorilla ‘species’, Western gorilla (Gorilla gorilla) and Eastern gorilla (Gorilla beringei), but taxonomy is under debate.
The Eastern gorilla populations are currently assigned to the subspecies G. b. beringei (Mountain gorilla) and G. g. graueri (Eastern Lowland gorilla). The Western gorilla populations are assigned to the subspecies G. g. gorilla (Western Lowland gorilla) and G. g. diehli (Cross River gorilla).
Chimp-Bonobo vs. Eastern-Western gorilla genetic distance comparison
sp.
mtDNA segment
Chimp-Bonobo
Eastern-Western gorilla
Only light strand gene: NADH6
0.021
0.016
D-Loop
0.105
0.106
12 heavy strand genes combined
0.046
0.041
Overall
0.040
0.036
Eastern-Western gorilla split time statistically similar to chimpanzee-bonobo split time (P = 0.17).
Selection
Only 13 Transitions in 22 t-RNA genes among gorillas
Ka/Ks<1 (P <0.001) for all protein-coding genes for all taxa pairs. Sign of strong purifying selection.
Major Questions Addressed
Eastern and Western gorillas are the same ‘species’ or different? How different?
When did Eastern-Western gorilla diverge?
Major biogeographical event involved in the split of Eastern and Western gorillas?
Sex biased gene flow?
When did Eastern Lowland and Mountain gorillas diverge?
Major Findings from the D-Loop dataset
The split time between Eastern Lowland gorilla and the Mountain gorilla comes to 0.94 Mya (Calibrated with the Western/Eastern gorilla split time)
Conclusions
Methods
Taxa Pair
Split time (in Mya)
95% CI
MONKEY-HOMINOID
35.269
ORANG-AFRICAN APES
16.133
GORILLA-HOMO/PAN
8.618
HUMAN-CHIMP 6
CHIMP-BONOBO
2.164
EASTERN-WESTERN GORILLA
1.861
SPLIT WITHIN WESTERN GORILLA
0.375
HUMAN-NEANDERTHAL
0.576
Same biogeographical events may have caused the split between Western & Eastern gorilla, and chimpanzee & bonobo (Pleistocene forest refugia, or formation of major rivers).
In terms of genetic distances, Western and Eastern gorilla are similar to chimp and bonobo: consistent with two-species classification of gorilla.
Published Molecular data show gene flow may have persisted between Eastern and Western gorilla until ~ 77,700 years ago: male mediated gene flow (Thalmann et al. 2006).
Sequenced complete Mitochondrial genome from one Western gorilla (“Chipua” ID# PR00622) and one Eastern gorilla (“M’kubwa” ID# PR00206), both from Coriell Institute for Medical Research (Camden, NJ).
14 additional published mitochondrial genomes included in analysis.
Two Data subsets used:
Entire Mitochondrial genome, excluding D-Loop (15599 bp)
Twelve Heavy strand protein-coding genes (10887 bp)
Additional published D-Loop sequences of Eastern Lowland and Mountain gorillas analyzed.
Acknowledgements
BEAST used for the Bayesian MCMC analysis
Pairwise distances calculated in MEGA 5.0
For dating, nodes were calibrated with human-chimp split of 6 Mya
Only 12 Heavy strand protein coding genes’ results are shown. The other data subset shows the same trend
Analyses
The work was funded by NIH (NIGMS) grant R15GM to N. M. Anthony
Thanks to Carlos Guerrero and TJ Firneno of Duquesne University Core Sequencing Facility for technical assistance.
Thanks to Sarah Carnahan-Craig, Amanda Colvin, Alicia Martinez.