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Hybrid sterility is a critical step in the evolution of reproductive barriers between diverging taxa during the process of speciation. Recent studies of young subspecies of the house mouse revealed a multigenic nature and frequent polymorphism of hybrid sterility genes as well as the recurrent engagement of the meiosis-specific gene PR domain-containing 9 (Prdm9) and X-linked loci. Prdm9 -controlled hybrid sterility is essentially chromosomal in nature, conditioned by the sequence divergence between subspecies. Depending on the Prdm9 interallelic interactions and the X-linked Hstx2 locus, the same homologs either regularly recombine and synapse, or show impaired DNA DSB repair, asynapsis, and early meiotic arrest. Thus, Prdm9 -dependent hybrid sterility points to incompatibilities affecting meiotic recombination as a possible mechanism of reproductive isolation between (sub)species. House mouse subspecies provide excellent models of early stages of speciation. They show incomplete reproductive isolation with the formation of hybrid zones and polymorphic hybrid sterility genes. Genetic control of hybrid sterility is multigenic, with recurrent involvement of Prdm9 and X-linked loci, including Hstx2. The Dobzhansky–Miller incompatibility between Prdm9 and Hstx2 relates to meiotic recombination and homologous chromosome pairing during the first meiotic prophase. Fertility of Mus musculus musculus × Mus musculus domesticus F1 hybrid females homozygous for the M. musculus musculus Hstx2 locus disproves the dominance theory of Haldane's rule in this particular hybrid sterility model. [ABSTRACT FROM AUTHOR]

We propose an application of network analysis to determine which traits and behaviors predict fertilizations within and between populations. This approach quantifies how reproductive behavior between individuals shapes patterns of selection and gene flow, filling an important gap in our understanding of the connection between evolutionary processes and emergent patterns. [ABSTRACT FROM AUTHOR]

Hybrid zones, where two genetic groups come in contact, provide valuable opportunities for testing whether reproductive isolation is complete between the groups. The intertidal goby Chaenogobius annularis comprises a group in the Sea of Japan and another group in the Pacific Ocean that exhibit a substantial level of genetic divergence; however, it is unclear whether they are reproductively isolated. In this study, we analyzed six populations sampled around a transition zone (approximately 300 km) between the two major groups, i.e., along the Sanriku coast of the northeastern Pacific coastline of the Japanese Archipelago, using mitochondrial DNA sequences of the cytochrome b gene, the allozyme loci of malate dehydrogenase, and eight microsatellite DNA loci. We detected considerable genetic admixture in the Taro population located at the center of the transition zone, where most individuals (98%) appeared to be post-F 2 hybrids. Bayesian clustering analysis, mitochondrial DNA phylogenetic tree, and private alleles in the allozyme and microsatellite DNA loci demonstrated that contemporary gene flow has been negligible between the hybrid population and either of the two groups. These findings demonstrate the long-term isolation and self-sustaining nature of this population after ancient hybridization. [ABSTRACT FROM AUTHOR]

Crassostrea ariakensis is widely distributed in the estuaries of China and has the advantages of wide salinity adaptation and strong resistance, but the artificial aquaculture of C. ariakensis is mainly concentrated in southern China. Long-term geographical isolation resulted in genetic variation between the northern and southern C. ariakensis populations. In this study, the reproductive isolation between two independent population of C. ariakensis was evaluated by hybridization. Results showed that the fertilization rate, cleavage rate and D Larval rate of interpopulation hybrids (NS- northern ♂ × southern ♀ and SN- southern ♂ × northern ♀) were significantly lower than those of intrapopulation inbreed groups (SS and NN). Moreover, southern maternal larvae (SS and NS) have significant survival advantages. The growth trend between the two sites was very different in early stage (from 90th to 210th day), but it was consistent in late stage (from 210th to 480th day), with a significant decreasing trend of SS > NS > SN > NN. The survival rates of SN and NS was significantly higher than that of NN, indicating that the high temperature tolerance and stress resistance of hybrids were improved. The positive maternal effect advantages (MEAs) at most time points of both sites demonstrated that parental origin, especially the maternal origin, had a significant effect on the survival and growth of progeny. Hybrid advantages (HAs) for growth of both sites were opposite, and positive HAs of survival accounted for most of both sites, indicating that environmental conditions and survival could significantly affect the growth, and interpopulation hybrids did not necessarily always show positive HAs. Moreover, the maternal origin would affect the shell shape and shell hardness, resulted in NS similar to SS and SN similar to NN, respectively. Additionally, all interpopulation hybrids could produce mature gametes. These results confirmed that there was no serious reproductive isolation between the two populations. The southern maternal groups, especially SS, had better growth and survival advantages, could be used as good new strains for large-scale breeding in southern China, and also provided basic data for the commercial promotion of C. ariakensis in southern China. • First systematic comparison of the southern and northern populations of Crassostrea ariakensis and hybrids in southern China. • No serious reproductive isolation between two populations, although interpopulation hybrids had significantly low hatching rate. • The maternal origin would affect the shell shape and hardness of offspring, and the hybrids were fully fertile. • The south maternal groups, especially SS, had better performance, could be used as excellent strains for commercial breeding in southern China. [ABSTRACT FROM AUTHOR]