Jl. Patton et al., GENE GENEALOGY AND DIFFERENTIATION AMONG ARBOREAL SPINY RATS (RODENTIA, ECHIMYIDAE) OF THE AMAZON BASIN - A TEST OF THE RIVERINE BARRIER HYPOTHESIS, Evolution, 48(4), 1994, pp. 1314-1323
Sequence variation in the mitochondrial cytochrome b gene was examined
in the arboreal spiny rat, Mesomys hispidus, collected at 15 sites al
ong the Rio Jurua in western Amazonia, Brazil, to determine the import
ance of riverine barriers in the diversification of this taxon. Twenty
individual haplotypes were uncovered, most of which were unique to si
ngle localities but some of which were shared among adjacent sites eit
her along or across the river. Genealogical analyses suggest that gene
flow is limited and, in combination with the unique distribution of m
ost haplotypes, suggest that populations of this species are strongly
substructured along the river. Thus, most sharing of haplotypes betwee
n adjacent localities is probably caused by historical association rat
her than to ongoing gene flow. Two haplotype clades were uncovered, bu
t these correspond to headwaters versus mouth areas, not to opposite s
ides of the river, as would be expected by the Riverine Barrier Hypoth
esis. Moreover, haplotype sharing across the river was greater at its
mouth than in the headwaters, a pattern opposite that expected if the
river were a substantive barrier. Broader scale phylogeographic patter
ns of this species show that both clades have relationships to areas w
ell outside the Rio Jurua basin. This suggests that the basin represen
ts a relatively recent point of invasion between two more broadly dist
ributed and differentiated geographic units of the species.