Analysis of Mitochondrial DNA from

Chimpanzees in Tanzania

Timothy Comar, April Bednarski, and Douglas Green

Lake Tanganyika AreaChimpanzee Habitats

• Gombe

• Tongwe

• Mahale

Satellite ImageGombe

Mahale

Tongwe

Phylogeny of Tanzanian Chimpanzees

GombeFig. 5, clade 4

GombeFig. 5, clade 1

MixedFig. 5, part of clade 2(one Mahale omitted)

TongweFig. 5, part of clade 2

GombeFig. 5, clade 3 (minus northern species)

Fig. 1

Our Analysis Morin, et. al.

Clade 1 all Gombe (7 sequences) all Gombe (7 sequences)

Clade 2

two separate clades Gombe (2 seqs) / Mahale (2 seqs) (one Mahale seq omitted by mistake) Twonge (5 seqs) / Mahale (1 seq)

two “subclades”

Gombe (2 seqs) / Mahale (3 seqs) Twonge (5 seqs) / Mahale (1 seq) (plus 1 northern sequence)

Clade 3 all Gombe (2 sequences) Gombe (2 sequences) + northern (5 seqs)

Clade 4 all Gombe (8 sequences) Gombe (8 sequences) + northern (4 seqs)

Table 1

Comparing Phylogenies with Morin et. al. (Table 1)

Our analysis included sequence data only from the Tanzanian sites: Gombe (L), Tongwe (N), Mahale (M). Morin’s study included these sites and three sites north of Tanzania: Uganda (I), Rawanda (J), Burundi (K).

Morin et. al. reported four clades for the eastern subspecies, P. troglodytes schwienfurthii. They also reported finding “some geographic differentiation” between these clades, with intermediate Gombe-type sequences scattered among them.

We also found four clades that were essentially identical to Morin’s (minus the northern species). However, we found a greater degree of geographic differentiation: two of our four clades consisted entirely of sequences from a single collection site, a third clade contained only 1 sequence from a foreign site, and the fourth clade was mixed.

HYPOTHESES:

1. Genetic divergence is recent: Human activity has fragmented the habitat, cutting reducing gene flow between Gombe and Twonge

2. Genetic divergence is ancient: Gombe and Twonge have experienced reduced gene flow due to long-term natural conditions

3. Genetic differences are not due to divergence. Reduction in population sizes due to human activity has put both populations through a “bottleneck,” resulting in two genetically distinct “founding” populations”

4. Twonge is a relatively new population – founder’s effect has resulted in low genetic diversity

5. Variation seen in the Gombe region could be from recent movement of chimpanzees to this area after being pushed out of other habitats

QUESTIONS:

1. Why are the Gombe and Twonge populations genetically disjoint?

2. Why is the Gombe population genetically more diverse than Twonge?

3. Can we explain the branches of the phylogenetic tree based on chimpanzee habitat and social structure?

4. Are the two Gombe groups that were noted by Jane Goodall in 1972 seen in the phylogenetic tree?

Jane Goodall Observations in Gombe

• Gombe National Park set up as protected area in 1968

• Chimpanzees thought to be migrating to Gombe National Park area as old habitats are destroyed

• Jane Goodall observed two social groups of chimpanzees in Gombe in 1970’s

Changes in environment that result in increased fragmentation of chimpanzee habitat since 1970’s includes deforestation, agricultural changes, and an increasein human population

• The Tongwe population was historically isolated from other groups of chimps. This is expressed in the significantly fewer number of mutations observed for population than observed for the other Tanzanian chimp populations.

• The significant genetic diversity observed in the Gombe population indicates that these chimps were most likely not isolated for a long period of time. Even though two genetically and socially distinct groups emerged over time, the genetic evidence suggests that isolation for these groups is very recent. (That is, there is no clear evidence of inbreeding for a significantly large number of generations.)

• The evidence may further suggest that the Gombe chimps interacted with other groups of chimps.

• The small population size is not statistically large enough to conclude that divergence occurred with in the last 30 years.

Results of genetic analysis (counting base changes in the multiple sequence alignment)

• ~20/300 site changes seen between all the collected Tanzania sequences

• When randomly choose 5 Gombe sequences, see 15/300 changes

• When choose 5 Tangwe forest sequences, see 2/300 changes

• Out of 4 Mahale sequences, see 2/300 changes

Human mitochondrial DNA mutation rate is estimated to be 2.5/site/Myr or 1 change/33 generations1, so 20 sites difference per 30 years is too great to be based on 30 years of evolution

1Parsons, Thomas J., et al., A high observed substitution rate in the human mitochondrial DNA control region, Nature Genetics vol. 15, April 1997, pp. 363-367

http://www.imagingnotes.com/winter03/pintea.htm

Satellite Photo of Deforestation (red) in Gombe

Land Cover

Gombe

Mahale

Tongwe

Population DensityGombe

Mahale

Tongwe

Future Direction

• More information about where in the sequence data was collected within the Gombe National Park

• More accurate measurement of mutation rate needed to draw conculsions about molecular clock