Reproductive proteins are among the fastest evolving in the proteome, often due to the consequences of positive selection, and their rapid evolution is frequently attributed to a coevolutionary process between interacting female and male proteins. Such a process could leave characteristic signatures at coevolving genes. One signature of coevolution, predicted by sexual selection theory, is an association of alleles between the two genes. Another predicted signature is a correlation of evolutionary rates during divergence due to compensatory evolution. We studied female–male coevolution in the abalone by resequencing sperm lysin and its interacting egg coat protein, VERL, in populations of two species. As predicted, we found intergenic linkage disequilibrium between lysin and VERL, despite our demonstration that they are not physically linked. This finding supports a central prediction of sexual selection using actual genotypes, that of an association between a male trait and its female preference locus. We also created a novel likelihood method to show that lysin and VERL have experienced correlated rates of evolution. These two signatures of coevolution can provide statistical rigor to hypotheses of coevolution and could be exploited for identifying coevolving proteins a priori. We also present polymorphism-based evidence for positive selection and implicate recent selective events at the specific structural regions of lysin and VERL responsible for their species-specific interaction. Finally, we observed deep subdivision between VERL alleles in one species, which matches a theoretical prediction of sexual conflict. Thus, abalone fertilization proteins illustrate how coevolution can lead to reproductive barriers and potentially drive speciation.
The present study was conducted to evaluate the genetic diversity and relationships of 9 native Japanese long-tailed chicken breeds (Shoukoku, Koeyoshi, Kurokashiwa, Minohiki, Ohiki, Onagadori, Satsumadori, Toumaru, and Toutenkou) together with 2 commercial breeds (White Leghorn and White Plymouth Rock), using 40 polymorphic microsatellite markers covering 23 linkage groups. The 8 breeds mentioned, except for Shoukoku and 2 commercial breeds, were believed to be descendants derived from crossings of the ancestor of Shoukoku and some other breeds. Three to 14 alleles per locus were detected across all the breeds. The mean number of alleles per locus, the mean unbiased expected heterozygosity, and the mean polymorphic information content ranged from 2.60 (Minohiki) to 4.07 (Shoukoku), from 0.293 (Koeyoshi) to 0.545 (Satsumadori), and from 0.250 (Koeyoshi) to 0.478 (Satsumadori), respectively. The mean fixation coefficient of subpopulation within the total population of 9 Japanese long-tailed breeds showed that approximately 38% of the genetic variation was caused by breed differences and 62% was due to differences among individuals. Toumaru had the largest number of breed-specific alleles with relatively high (>20%) frequency. In the phylogenetic tree of 11 breeds constructed by the neighbor-joining method from modified Cavalli-Sforza chord genetic distance measure, White Leghorn and White Plymouth Rock clustered together apart from the Japanese breeds. Among the Japanese long-tailed breeds, Toumaru, Kurokashiwa, and Koeyoshi showed relatively far distance from the other breeds. The Ohiki, Onagadori, Shoukoku, and Toutenkou were grouped into the same branch. Minohiki and Satsumadori were also clustered together. Kurokashiwa was not genetically close to Shoukoku, differing from a traditional hypothsis. It was confirmed in the present study that the microsatellite is a suitable tool to evaluate genetic diversity and relationships in chicken breeds.
We examined population genetic structure by means of microsatellite analysis among 7 Japanese flounder (Paralichthys olivaceus) populations collected from coastal sea areas around Japan. As was expected, all of the 11 microsatellite loci examined were variable in all populations (number of alleles per locus, 15.2-18.2; average of expected heterozygosity, 0.74-0.78). Eleven population pairs in 21 possible pairwise comparisons showed significant genetic heterogeneity associated with allele frequency distributions or fixation index (F(ST)). Modified Cavalli-Sforza chord distance (D(A)) and Nei's standard genetic distance (D(ST)) ranged from 0.051 to 0.090, and from 0.000 to 0.025, respectively. There was evidence that the populations assessed in this study were not drawn from a single panmictic population; however, it appears that Japanese flounder populations around Japan are not well-structured, as an estimate of the fixation index value among the 7 localities was very low (F(ST) = 0.0025).
This study presents linkage maps for the Pacific abalone (Haliotis discus hannai) based on 180 microsatellite DNA markers. Linkage mapping was performed using three F 1 outbred families, and a composite linkage map for each sex was generated by incorporating map information from the multiple families. A total of 160 markers are placed on the consolidated female map and 167 markers on the male map. The numbers of linkage groups in the composite female and male maps are 19 and 18, respectively; however, by aligning the two maps, 18 linkage groups are formed, which are consistent with the haploid chromosome number of H. discus hannai. The female map spans 888.1 cM (Kosambi) with an average spacing of 6.3 cM; the male map spans 702.4 cM with an average spacing of 4.7 cM. However, we encountered several linkage groups that show a high level of heterogeneity in recombination rate between families even within the same sex, which reduces the precision of the consolidated maps. Nevertheless, we suggest that the composite maps are of significant potential use as a scaffold to further extend the coverage of the H. discus hannai genome with additional markers.
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