Brown
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How many species of giraffe are there in Africa? David M. 1 Brown and Nicholas J. 2 Georgiadis 1. University of California, Los Angeles; 2. Mpala Research Centre RATIONALE • • • • • • • Nuclear DNA: THE GENETIC HISTORY OF POPULATIONS AND SPECIES The genus Giraffa in Africa is comprised of phenotypically distinct groups, currently classified as nine ‘subspecies’. Are the different groups reproductively isolated, and perhaps different species? Or do the different groups interbreed, and will their distinctiveness disappear over time? Arguments have surrounded these questions for over 100 years. The different giraffe groups have hybridized in captivity. What does this variation mean in evolutionary terms? What are the evolutionary dynamics of giraffes in the wild? NJ Athi18 Athi23 ChyuluM2 TarangireM2264 LoboM2081 TarangireM2235 TarangireM2249 Athi3 Athi5 Athi6 Athi21 Athi13 Athi2 Chyulu17 Chyulu25 4868 4856 5017 Chyulu5 Chyulu4 Chyulu1 Athi25 2271 5016 5026 Chyulu20 Athi8 SamburuRe4812 Niger10 Niger18 RumaRoGR40 OlJogiRe2 OlJogiRe15 OlJogiRe26 OlJogiRe3 OlJogiRe8 Samburu3 OlJogi2 MFNPF3 MFNPM2 MFNPM5 Kruger12 Kruger2 Kruger4 Niger13 GN30 Kruger3 Niger5 Niger14 Samburu4 GN16 GN22 MFNPM3 MFNPF2 MFNPF1 4814 4812 4810 ENPF8 Kruger1 Kruger11 OlJogi16 OlJogi18 Kruger15 Kruger7 Kruger13 ENPF1 ENPF2 ENPF3 ENPM1 ENPM5 ENPM6 KHBM1 HSBM2 ENPM3 HNBF3 Kruger8 Okapi1 APPROACH We examined genetic variation in the mitochondrial and nuclear genomes of free-ranging individual giraffes from six taxonomic giraffe subspecies. We are tested whether the giraffe subspecies: • Are genetically isolated from each other: Is genetic isolation recent or deep in evolutionary time? • Are hybridizing with each other: Is hybridization rare or common? • Biopsy-dart samples were collected from 397 free-ranging individual giraffes representing six subspecies: * Giraffa camelopardalis peralta (W) from Niger * G.c. rothschildi (N) from Uganda and Western Kenya * G.c. reticulata (R) from Kenya * G.c. tippelskirchi (M) from Kenya and Tanzania * G.c. angolensis (S) from Namibia * G.c. capensis (S) from South Africa Microsatellites: hypervariable sections of DNA *17 different microsatellite markers *397 individual giraffes from six taxonomic groups: * peralta (W) N=28 * tippelskirchi (M) N=142 * rothschildi (N) N=81 * capensis (S) N=27 * reticulata (R) N=80 *angolensis (S) N=38 Mitochondrial DNA: MATERNAL HISTORY Mitochondrial DNA is maternally inherited and does not capture the genetic history of males in a species. • 656 nucleotide fragment starting in cytochrome b extending through tRNAs to control region. • Okapi was used as the ‘outgroup’ for reconstruction of the phylogenetic tree. • There were 37 unique mtDNA sequences (haplotypes) found in 266 individuals. Haplotypes 1PeraltaA 2PeraltaB 3RothsA 4RothsB 5RothsC 6ReticA 7ReticB 8ReticC 9ReticD 10ReticE 11ReticF 12ReticG 13MasaiA 14MasaiB 15MasaiC 16MasaiD 17MasaiE 18MasaiF 19MasaiG 20MasaiH 21MasaiI 22MasaiJ 23MasaiK 24MasaiL 25MasaiM 26MasaiN 27MasaiO 28CapensisA 29CapensisB 30AngolensisA 31AngolensisB 32AngolensisC 33AngolensisD 34AngolensisE 35AngolensisF 36AngolensisG 37AngolensisH Peralta Niger Rothschildi Murchison Falls Western Kenya Reticulata Samburu Meru Ol Jogi Tippelskirchi Athi Chyulu Naivasha Tara Manyara n g i r e Serengeti Capensis Kruger Angolensis Etosha Table 1. Distribution of mtDNA haplotypes by sampling location • peralta (W) N=22; rothschildi (N) N=51; reticulata (R) N=63; tippelskirchi (M) N=83; capensis (S) N=12, angolensis (S) N=35 • Each taxonomic subspecies has a unique set of mtDNA haplotypes • No haplotypes were shared between groups Hoanib 7 15 25 16 8 2 1 7 5 2 1 5 2 11 8 1 1 6 13 9 4 1 13 4 7 5 2 2 1 tippelskirchi peralta reticulata rothschildi angolensis capensis Masai (tippelskirchi) giraffes have a unique SNP (single nucleotide polymorphism) in the FES intron sequence, distinguishing them from all others. Fig. 3. FES: cladogram of single-copy nuclear intron sequences, representing: * peralta (W) N=5 * rothschildi (N) N=10 * reticulata (R) N=14 * tippelskirchi (M) N=27 * capensis (S) N=10 * angolensis (S) N=11 capensis angolensis Southern Africa capensis+angolensis Masai (tippelskirchi) Reticulated (reticulata) Western Africa peralta+rothschildi Population clusters of composite microsatellite genotypes CONCLUSIONS Mitochondrial DNA • Each of the sampled groups has a unique set of haplotypes (Reticulated, Rothschilds, Peralta, Masai, Angolensis, Capensis). • Exceptions to monophyly may be due to retention of ancestral polymorphism, or hybridization at range boundaries, for example, between tippelskirchi females and reticulata males in the Athi Plains region. • Since there is no evidence for nuclear DNA hybridization between them, it is likely that recurrent backcrossing of hybrid females to tippelskirchi males replaced the reticulata genome in hybrid individuals over many generations. NJ 2 2 1 1 2 Okapi 2 17MasaiE 19MasaiG 20MasaiH 15MasaiC 1 2 14 1 3 1 3 18MasaiF 14MasaiB 11 1 3 7 2 2 1 tippelskirchi 21MasaiI 16MasaiD 22MasaiJ 24MasaiL 23MasaiK 25MasaiM 26MasaiN 27MasaiO 13MasaiA 12ReticG OlJogi10Hap15 10ReticE 8ReticC 9ReticD 7ReticB 1PeraltaA 2PeraltaB 1 1 17 1 Fig. 2. (right) Phylogenetic tree of mitochondrial haplotypes • Each group is monophyletic with exception of one Masai haplotype grouping with reticulated giraffes. • In general, giraffes of different morphotypes are not interbreeding in the wild. 3RothsA 5RothsC reticulata peralta rothschildi 4RothsB 6ReticA 32AngolensisC 33AngolensisD 35AngolensisF 31AngolensisB 30AngolensisA 37AngolensisH 36AngolensisG 34AngolensisE 28CapensisA capensis 29CapensisB 1 change angolensis Nuclear DNA: Microsatellites • Microsatellite genotypes cluster into 4 major nuclear DNA pools: Reticulated, Rothschilds + Peralta, Masai, Angolensis + Capensis • Each gene pool is equivalent of a monophyletic group (no interbreeding between them) • Some evolutionary force has kept reticulata and tippleskirchi reproductively isolated from each other: *Ecological selection for climate or some other factor? *Sexual selection? • The population genetic structure of giraffes in the wild conflicts with the currently held classification of ‘9 subspecies’. • There are at least four distinct groups of giraffes that, based on genetic evidence, appear to be reproductively isolated from each other in the wild. • These groups may correspond with different species of giraffe.
