Evidence suggests that the
mitochondrial (mt)
DNA of anthozoans is evolving at a slower tempo than their nuclear
DNA; however, parallel surveys of nuclear and
mitochondrial variations and calibrated rates of both synonymous and nonsynonymous substitutions across taxa are needed in order to support this scenario. We examined species of the
scleractinian coral genus
Acropora, including previously unstudied species, for molecular variations in protein-coding genes and
noncoding regions of both nuclear and mt genomes.
DNA sequences of a
calmodulin (CaM)-encoding gene region containing three
exons, two
introns and a 411-bp mt
intergenic spacer (IGS) spanning the
cytochrome b (
cytb) and
NADH 2 genes, were obtained from 49
Acropora species. The molecular evolutionary rates of coding and
noncoding regions in nuclear and mt genomes were compared in conjunction with published data, including mt
cytochrome b, the control region, and nuclear Pax-C
introns. Direct
sequencing of the mtIGS revealed an
average interspecific variation comparable to that seen in published data for mt
cytb. The
average interspecific variation of the nuclear genome was two to five times greater than that of the mt genome. Based on the calibration of the closure of Panama Isthmus (3.0 mya) and closure of the Tethy Seaway (12 mya),
synonymous substitution rates ranged from 0.367% to 1.467% Ma(-1) for nuclear CaM, which is about 4.8 times faster than those of mt
cytb (0.076-0.303% Ma(-1)). This is similar to the findings in plant genomes that the nuclear genome is evolving at least five times faster than those of
mitochondrial counterparts.
