SREL Reprint #2082






Hsiu-Ping Liu1,2,* Jeffry B. Mitton1, Shi-Kuei Wu2

1Department of Environmental, Population, Organismic Biology,
University of Colorado, Campus Box 334, Boulder, CO 80309-0334,
Telephone: (303) 492-8956, Email: (J.B. Mitton)

2University of Colorado Museum, Zoology Section,
Campus Box 315, Boulder, CO 80309-0315,
Telephone: (303) 492-7359, Email: (S.-K. Wu)

*Current Address: Savannah River Ecology Laboratory,
University of Georgia, Drawer E, Aiken, SC 29802,
Telephone: (803) 725-7095, Email: (H.-P. Liu)

Key words. - Allozymes, Anodonta, mtDNA, doubly uniparental inheritance

The mtDNA haplotypes of males differ from the mtDNA haplotypes of females; the average sequence divergence between male and female mtDNA is 6.8%. Separate maternal and paternal transmission and the lack of recombination between these systems has allowed mutations to accumulate, producing highly differentiated mtDNAs. The M and F types of mtDNA differ by 10%-20% in the blue mussel, Mytilus edulis (Fisher and Skibinski 1990; Hoeh et al. 1991).
Allozyme polymorphisms, maternal mtDNA and paternal mtDNA reveal disparate degrees of genetic differentiation among populations of the giant floater. The differentiation revealed by allozymes and maternal mtDNA is slight, while the differentiation revealed by paternal mtDNA is great. The discrepancy in the magnitudes of differentiation can not be explained by differences in gene flow between males and females. One hypothesis to explain the disparate degrees of mtDNA differentiation focuses upon the modes of inheritance and the genetic environments within males and females. In the blue mussel, males carry both types of mtDNA in their somatic tissues, but females usually have only the F type mtDNA. Thus, the F type mtDNA must operate in isolation in females, but the M type mtDNA works in the presence of the F type mtDNA in males (Skibinski et al. 1994; Zouros et al. 1994). If this is also the case for Anodonta grandis grandis, selective constraints might be less restrictive for the M type mtDNA, allowing faster evolution and greater differentiation. This hypothesis is consistent with high estimates of evolutionary rates in chloroplast DNA (cpDNA) from non-photosynthetic species (Wolfe et al. 1992).
Although heteroplasmy for the M and F mitochondria is commonly found in the somatic tissues of male blue mussels (Fisher and Skibinski 1990; Hoeh et al. 1991; Zouros et al. 1992), we found no evidence of heteroplasmy for the M and F mtDNAs in our samples. However, heavy infestations of water mites in the mantle and gill tissues forced us to use only gonadal tissue for extraction of DNA. Because males preferentially package the M type mitochondria into sperm, the exclusive use of gonadal tissue precluded detection of heteroplasmic males (Skibinski et al. 1994; Zouros et al. 1994; Hurst and Hoekstra 1994).

SREL Reprint #2082

Liu, H.P., J.B. Mitton, and S.K. Wu. 1996. Paternal mitochondrial DNA differentiation far exceeds maternal mitochondrial DNA and allozyme differentiation in the freshwater mussel, Anodonta grandis grandis. Evolution 50:952-957.

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