ELEPHANTS WITHOUT BORDERS: HISTORICAL AND CONTEMPORARY GENETIC CONNECTIVITY IN TANZANIA

Open Access
- Author:
- Lohay, George Martin
- Graduate Program:
- Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 07, 2019
- Committee Members:
- Douglas Cavener, Dissertation Advisor/Co-Advisor
Stephen Wade Schaeffer, Committee Chair/Co-Chair
Katriona Shea, Committee Member
George H Perry, Committee Member
John Edward Carlson, Outside Member
Anna Bond Estes, Special Member - Keywords:
- African Savanna elephants
Population structure
genetic connectivity
corridors
fecal-centric
microsatellite markers
simple sequence repeats (SSRs)
mitochondrial DNA (mtDNA)
habitat loss
habitat fragmentation
wildlife corridors
age and sex structure
Amelogenin gene (AMELX/Y) - Abstract:
- African savanna elephants (Loxodonta africana) are ecologically important as ecosystem engineers and socio-politically as revenue earners for national economies and local communities. However, their population has declined due to poaching and loss of habitat as a result of an increase in the human population. Habitat loss and fragmentation makes most protected areas isolated because of blocking of wildlife corridors. This study covered four ecosystems (Serengeti, Tarangire-Manyara, Selous, and Ruaha) in Tanzania which have the largest elephant populations in the country to determine the extent of genetic diversity and population structure nuclear and mitochondrial DNA markers. We wanted to establish historical genetic connectivity using mitochondrial DNA and contemporary gene flow using microsatellite markers from DNA obtained non-invasively from fecal samples. We specifically wanted to determine if there is gene flow between the Serengeti and Tarangire-Manyara ecosystems and whether the genetic structure has substantially changed over the past 50 years. We assumed that the Greater Rift Valley between two ecosystems would also act a barrier to the gene flow. We collected 800 elephant fecal samples from the four ecosystems and performed genetic analyses at the Pennsylvania State University. Our results showed that the Serengeti elephants are genetically distinct from the Tarangire-Manyara. Elephants from Ngorongoro showed an admixture between the two ecosystems. We also identified that there was a higher genetic similarity of elephants between Ngorongoro and Lake Manyara compared to Lake Manyara and Tarangire. Also, Tarangire and Ruaha elephants shared the same population structure although they are more than 400 km apart. Within the Serengeti ecosystem, we identified two population clusters from south and north of the Serengeti. Our results suggest that even without any physical barriers, there is genetic differentiation. The analysis of nuclear and mitochondrial DNA showed significant population differentiation between the Ruaha and Selous ecosystems. We further found no evidence for female-mediated gene flow between Ruaha and Selous. Only 4% of elephants sampled in Ruaha shared a haplotype with the Selous Game Reserve. We also developed a novel fecal-centric approach to assess the age and sex structure of elephants and validated it with a rapid demographic assessment. We compared the sex ratio of elephants between Serengeti National Park, Ngorongoro Conservation Area and Maswa Game Reserve which have different protection status. In Serengeti, the sex ratio for adult age classes was skewed in favor of females whereas, in Ngorongoro, the sex ratio was skewed in favor of males for elephants older than 25 years. Although poaching is the main explanation for the observed sex ratio in Serengeti, we speculate that differential survival rates between males and female could explain the differences in sex ratio, particularly for young elephants. Our findings provide baseline information about historical connectivity using the mitochondrial DNA and recent gene flow (using nuclear markers) between protected areas in Tanzania. This information may be used to inform laws to protect the existing wildlife corridors or to restore the blocked corridors. We have highlighted some wildlife corridors that may have been or are still very important for the elephants based on our data; these would be suitable targets for conservation and restorations