STRUCTURE AND HISTORY OF AFRICAN ELEPHANT POPULATIONS .1. EASTERN ANDSOUTHERN AFRICA

Patterns of restriction site variation within mitochondrial DNA (mtDNA ) of 270 individuals were used to examine the current structure of sav anna elephant populations and to infer historical patterns of gene flo w across eastern and southern Africa. Elephants have a complex populat ion structure characterized by marked subdivision at the continental l evel (F-st = 0.39; 95% confidence interval 0.19-0.58), and isolation b y distance at the regional level. However, phylogeographic analysis re vealed evidence of protracted gene flow across the continent. First, o ne relatively derived haplotype was found at all sampling locations. S econd, haplotypes representing exceptionally divergent (up to 8.3%) mi tochondrial clades were found to coexist at distant (>2,000 km) sampli ng locations. In the few other species characterized by sympatric indi viduals bearing such divergent haplotypes, all such individuals were f ound to coexist within limited geographical regions. Accordingly, pron ounced mitochondrial divergence within populations is often attributed to ancestral isolation in allopatry, followed by secondary contact. T he patterns within elephants do not accord with ancestral isolation in allopatry. Given the exceptional mobility of elephants, a geographica l barrier is unlikely to have obstructed gene flow between regions for long enough to produce the observed mitochondrial divergence. Rather, the patterns are consistent with the more parsimonious hypothesis, ba sed on neutral coalescent theory, that gene flow has maintained a suff iciently large effective population size (>50,000 females) for represe ntatives of clades that diverged at least 4 million years ago to have persisted by chance within a population that was subdivided, but not s trictly isolated in allopatry.