Whole-genome Analysis of Giraffe Supports Four Distinct Species.

Species is the fundamental taxonomic unit in biology and its delimitation has implications for conservation. In giraffe (Giraffa spp.), multiple taxonomic classifications have been proposed since the early 1900s.(1) However, one species with nine subspecies has been generally accepted,(2) likely due to limited in-depth assessments, subspecies hybridizing in captivity,(3,4) and anecdotal reports of hybrids in the wild.(5) Giraffe taxonomy received new attention after population genetic studies using traditional genetic markers suggested at least four species.(6,7) This view has been met with controversy,(8) setting the stage for debate.(9,10) Genomics is significantly enhancing our understanding of biodiversity and speciation relative to traditional genetic approaches and thus has important implications for species delineation and conservation.(11) We present a high-quality de novo genome assembly of the critically endangered Kordofan giraffe (G. camelopardalis antiquorum)(12) and a comprehensive whole-genome analysis of 50 giraffe representing all traditionally recognized subspecies. Population structure and phylogenomic analyses support four separately evolving giraffe lineages, which diverged 230-370 ka ago. These lineages underwent distinct demographic histories and show different levels of heterozygosity and inbreeding. Our results strengthen previous findings of limited gene flow and admixture among putative giraffe species(6,7,9) and establish a genomic foundation for recognizing four species and seven subspecies, the latter of which should be considered as evolutionary significant units. Achieving a consensus over the number of species and subspecies in giraffe is essential for adequately assessing their threat level and will improve conservation efforts for these iconic taxa.