Molecular Population Genetics of the Male and Female Mitochondrial DNA Molecules of the California Sea Mussel,Mytilus californianus

Abstract

The presence of two gender-associated mitochondrial genomes in marine mussels provides a unique opportunity to investigate the dynamics of mtDNA evolution without complications inherent in interspecific comparisons. Here, we assess the relative importance of selection, mutation, and differential constraint in shaping the patterns of polymorphism within and divergence between the male (M) and female (F) mitochondrial genomes of the California sea mussel, Mytilus californianus. Partial sequences were obtained from homologous regions of four genes (nad2, cox1, atp6, and nad5) totaling 2307 bp in length. The M and F mtDNA molecules of M. californianus exhibited extensive levels of nucleotide polymorphism and were more highly diverged than observed in other mytilids (overall Tamura-Nei distances .40%). Consistent with previous studies, the M molecule had significantly higher levels of silent and replacement polymorphism relative to F. Both genomes possessed large numbers of singleton and low-frequency mutations that gave rise to significantly negative Tajima's D values. Mutation-rate scalars estimated for silent and replacement mutations were elevated in the M genome but were not sufficient to account for its higher level of polymorphism. McDonald-Kreitman tests were highly significant at all loci due to excess numbers of fixed replacement mutations between molecules. Strong purifying selection was evident in both genomes in keeping the majority of replacement mutations at low population frequencies but appeared to be slightly relaxed in M. Our results suggest that a reduction in selective constraint acting on the M genome remains the best explanation for its greater levels of polymorphism and faster rate of evolution.

Restricted gene flow in Chilean barnacles reflects an oceanographic and biogeographic transition zone

“…However, there are abundant cases of effectively panmictic gene flow in species distributed even lower in the intertidal (e.g. Harley et al 2006, Ort & Pogson 2007. The physiological environment along both the NAP and SAP coasts could also drive patterns of local adaptation in species like B. glandula and N. scabrosus; while the recognized clines ( Fig.…”

The environmentally tuned transcriptomes ofMytilusmussels

“…The origins of Mytilus can be traced back to the North Pacific Ocean (Seed, 1992;Vermeij, 1991) where the four species, Mytilus californianus, Mytilus trossulus, Mytilus edulis and Mytilus galloprovincialis, shared a common ancestor approximately 7.6 mya (Ort and Pogson, 2007). The California mussel M. californianus represents a distinct lineage from the other three species, which make up the blue mussel species complex (Ort and Pogson, 2007;Seed, 1992).…”

“…The California mussel M. californianus represents a distinct lineage from the other three species, which make up the blue mussel species complex (Ort and Pogson, 2007;Seed, 1992). The blue mussels shared a common ancestor approximately 3.5 mya, when M. edulis diverged from M. trossulus in the North Atlantic (Heath et al, 1995;Vermeij, 1991).…”

Transcriptomic responses to heat stress in invasive and native blue mussels (genus Mytilus): molecular correlates of invasive success

“…To this end, we developed a novel oligonucleotide microarray that contained 11,506 genes based on sequences available for two congeners of Mytilus, M. galloprovincialis and the ribbed mussel, Mytilus californianus. Mytilus californianus is an out-group species that is approximately 7.6 million years diverged from M. galloprovincialis and M. trossulus (Ort and Pogson, 2007). Hybridization to the array thus involved both homologous and heterologous hybridizations, leaving 8874 of the probes, representing 4488 different genes, with sufficient binding to be studied.…”