Genetic connectivity and population structure of African savanna elephants (Loxodonta africana) in Tanzania

Increasing human population growth, exurban development, and associated
habitat fragmentation is accelerating the isolation of many natural areas
and wildlife populations across the planet. In Tanzania, rapid and ongoing
habitat conversion to agriculture has severed many of the country’s former
wildlife corridors between protected areas. To identify
historically-linked protected areas, we investigated the genetic structure
and gene flow of African savanna elephants in Tanzania using
microsatellite and mitochondrial DNA markers in 688 individuals. Our
results indicate distinct population genetic structure within and between
ecosystems across Tanzania, and reveal important priority areas for
connectivity conservation. Elephants sampled from the Tarangire-Manyara
ecosystem appear marginally, yet significantly isolated from elephants
sampled from the greater Serengeti ecosystem (mean FST = 0.03), where two
distinct subpopulations were identified.Unexpectedly, elephants in the
Lake Manyara region appear to be more closely related to those across the
East African Rift wall in the Ngorongoro Conservation Area than they are
to the neighboring Tarangire subpopulations. We concluded that the Rift
wall has had a negligible influence on genetic differentiation up to this
point, but differentiation may accelerate in the future because of ongoing
loss of corridors in the area. Interestingly, relatively high genetic
similarity was found between elephants in Tarangire and Ruaha although
they are separated by >400 km. In southern Tanzania, there was
little evidence of female-mediated gene flow between Ruaha and Selous,
probably due to the presence of the Udzungwa Mountains between them.
Despite observing evidence of significant isolation, the populations of
elephants we examined generally exhibited robust levels of allelic
richness (mean AR = 9.96), heterozygosity (mean µHE = 0.73), and effective
population sizes (mean Ne = 148). Our results may inform efforts to
restore wildlife corridors between protected areas in Tanzania in order to
facilitate gene flow for long-term survival of elephants and other
species.