Rs. Burton et Bn. Lee, NUCLEAR AND MITOCHONDRIAL GENE GENEALOGIES AND ALLOZYME POLYMORPHISM ACROSS A MAJOR PHYLOGEOGRAPHIC BREAK IN THE COPEPOD TIGRIOPUS-CALIFORNICUS, Proceedings of the National Academy of Sciences of the United Statesof America, 91(11), 1994, pp. 5197-5201
The genetic structure of natural populations is frequently inferred fr
om geographic distributions of alleles at multiple gene loci. Surveys
of allozyme polymorphisms in the tidepool copepod Tigriopus californic
us have revealed sharp genetic differentiation of populations, indicat
ing that gene flow among populations is highly restricted. Analysis of
population structure in this species has now been extended to include
nuclear and mitochondrial gene genealogies. DNA sequences of the mtDN
A-encoded cytochrome-c oxidase subunit I gene from 21 isofemale lines
derived from seven populations reveal a phylogeographic break between
populations north and south of Point Conception, California, with sequ
ence divergence across the break exceeding 18%, the highest level of m
tDNA divergence yet reported among conspecific populations. Divergence
between populations based on 22 sequences of the nuclear histone H1 g
ene is geographically concordant with the mitochondrial sequences. In
contrast with previously studied nuclear genes in other sexually repro
ducing metazoans, the H1 gene genealogy from T. californicus shows no
evidence of recombination. The apparent absence of intragenic recombin
ants probably results from the persistent lack of gene flow among geog
raphically separated populations, a conclusion strongly supported by a
llozyme data and the mitochondrial gene genealogy. Despite strong popu
lation differentiation at allozyme loci, the phylogeographic break ide
ntified by the DNA sequences was not evident in the allozyme data.