Population Genetics and Conservation Implications of Hippopotamus in Cross River, South South Nigeria

Hippopotamus populations in Nigeria have declined dramatically due to hunting and habitat loss, and the fragmented nature of remaining groups raises concerns about genetic diversity and population viability. This study applied population genetic analyses to hippo populations inhabiting the Cross River system in South South Nigeria to assess genetic diversity, population structure, and connectivity. Faecal DNA samples were collected non-invasively from eleven sites along the Cross River and its tributaries. Microsatellite genotyping was performed at fifteen loci following DNA extraction and amplification. Genetic diversity indices, population differentiation statistics, and assignment tests were used to characterise population structure. Effective population size was estimated using linkage disequilibrium and temporal methods. Results revealed low to moderate genetic diversity across all sample sites, with mean allelic richness of 4.2 and observed heterozygosity of 0.48. Significant genetic differentiation was detected between northern and southern river sub-populations, consistent with reduced movement across dam structures and heavily settled river reaches. Effective population size estimates were critically low in three sub-populations, raising concern about inbreeding depression. Bayesian clustering identified two genetically distinct management units. The study provides the first population genetic assessment of Nigerian hippos and recommends targeted management interventions including dam passage facilitation and anti-poaching efforts focused on critically small sub-populations along the Cross River. Keywords: hippopotamus, population genetics, Cross River, conservation genetics, South South Nigeria.