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Population
trends and
distribution of genetic variation in western lowland gorillas:
Implications for conservation
E. Jean Wickings,1
Nicola M. Anthony,2 Mireille Bawe-Johnson,1
Stephen L. Clifford,1 Kate A.
Abernethy,1 Fiona Maisels,3 and Michael W.
Bruford4
1Unité de
Génétique des Ecosystèmes
Tropicaux, Centre
International de Recherches Medicales de Franceville (CIRMF), Gabon, 2School
of Biological Sciences, University of New Orleans, 3WCS-Gabon,
Libreville, Gabon, 4School of Biosciences, Cardiff
University, United Kingdom
Abstract
In addition to
the
historical pressures of hunting and habitat fragmentation, current
gorilla
populations are under intense local risk of extinction from
haemorrhagic viral
fever (Ebola). Recent estimates have shown drastic declines of up to
50% of the
total population, with local losses of up to 90%. Estimates of genetic
variability
using mitochondrial sequences from the hypervariable region (HV-1) of
the
D-loop in western lowland gorillas reveal a high genetic diversity and
a
complex historical genetic structure that may be tied to ice age
changes in
tropical forest cover.
After removing
nuclear
translocations and recombinant sequence artefacts, two geographically
defined
and highly divergent haplogroups (C, D) are found in western lowland
gorillas
and each of these is further subdivided into subgroups (C1, C2, D1-3).
The
northern-most haplogroup C (Nigeria, Cameroon and northern Gabon) shows
the highest
overall diversity, with similar haplotypes (C1) found in Cross River,
Ebo
Forest and Lobeke gorillas. Gene flow occurs across the Sanaga River,
whereas
the Sangha River separates C2 (Dja, Cameroon and north-east Gabon) and
D2 (Central
African Republic, CAR) subgroups. Haplogroup D is less variable
although widely
distributed from Equatorial Guinea and Monts de Cristal, Gabon (D1),
CAR (D2)
and southern and central Gabon and Congo (D3). The least variable
subgroup (D3),
comprising relatively few, closely related haplotypes, dominates the
southern
part of the western lowland gorilla range. Gorillas in north-eastern
Gabon show
a mixture of haplotypes (C2, D2 and D3).
Disease progression
models imply recent passage of Ebola through areas of current low
gorilla
density in south-eastern Cameroon, northen Gabon and central Congo,
avoiding
the Sangha-Dzanga Triangle where ape densities remain high.
Conservation
efforts should focus not only on areas of current high gorilla density
or distinct
genetic composition, but also on areas where Ebola has decimated
populations,
to monitor their recovery and residual genetic variability. Thus we highlight the
need for additional resources for re-surveying “Ebola affected” areas
and
continuing genetic monitoring of their great ape populations. |