Genetic evidence of population subdivision among Masai giraffes separated by the Gregory Rift Valley in Tanzania

Giraffe mothers across a valley carry ancient genetic differences. Tanzania’s Gregory Rift escarpments separate the Serengeti and Tarangire ecosystems, placing steep cliffs between populations of Masai giraffes. Their DNA offered a way to investigate whether animals had crossed this landscape and reproduced, even long before anyone could observe their journeys.

George Lohay, Derek Lee and colleagues analysed whole genomes from 100 giraffes and a shorter mitochondrial sequence from 320 animals sampled across six protected areas. They compared DNA inherited from both parents with mitochondrial DNA inherited through mothers, then examined the terrain for possible routes between populations. Differences between those two genetic histories could reveal whether males and females had contributed differently to past connections.

The main eastern and western populations carried deeply separated maternal lineages, suggesting little female-mediated exchange over hundreds of thousands of years. Nuclear DNA suggested more recent male-mediated exchange, though its timing is uncertain. Lake Manyara giraffes complicated the division, combining western maternal ancestry with substantial eastern nuclear ancestry. The team proposed conserving eastern and western Masai giraffes as separate evolutionary units, not declaring new species. Their practical priority was maintaining connections among populations on each side of the escarpments, where fragmentation could further isolate already differentiated animals.