Abstract
Interspecific hybrid incompatibility, including inviability and sterility, is important in speciation; however, its genetic basis remains largely unknown in vertebrates. Crosses between male chickens and female Japanese quails using artificial insemination can generate intergeneric hybrids; however, the hatching rate is low, and hatched hybrids are only sterile males. Hybrid development is arrested frequently during the early embryonic stages, and the sex ratio of living embryos is male-biased. However, the development and sex ratio of hybrid embryos have not been comprehensively analyzed. In the present study, we observed delayed embryonic development of chicken-quail hybrids during the early stage, compared with that of chickens and quails. The survival rate of hybrids decreased markedly during the blastoderm-to-pre-circulation stage and then decreased gradually through the subsequent stages. Hybrid females were observed at more than 10 d of incubation; however, the sex ratio of hybrids became male-biased from 10 d of incubation. Severely malformed embryos were observed frequently in hybrids. These results suggest that developmental arrest occurs at various stages in hybrid embryos, including a sexually non-biased arrest during the early stage and a female-biased arrest during the late stage. We discuss the genetic basis for hybrid inviability and its sex bias.
Highlights
Interspecific hybrid incompatibility, including inviability and sterility, is important in speciation; its genetic basis remains largely unknown in vertebrates
Previous studies on chicken-quail F1 hybrids showed that the fertilization rate in this interspecific cross was 5.4–25.3%32,33,37,38 and that development was arrested in 42.9–62.8% of fertilized eggs during the extraembryonic membrane formation
The GSP chicken line, which was used for this analysis, has been maintained as a closed colony and is highly inbred[44,45]; quails used in the analysis were a commercial line exhibiting high genetic heterogeneity[46,47]
Summary
Interspecific hybrid incompatibility, including inviability and sterility, is important in speciation; its genetic basis remains largely unknown in vertebrates. Hybrid development is arrested frequently during the early embryonic stages, and the sex ratio of living embryos is male-biased. Malformed embryos were observed frequently in hybrids These results suggest that developmental arrest occurs at various stages in hybrid embryos, including a sexually non-biased arrest during the early stage and a female-biased arrest during the late stage. Hybrid inviability and sterility in birds is more severe in the ZW heterogametic sex than ZZ homogametic sex[7,8,14]. Hybrid inviability in birds occurs frequently during the embryonic stage[16,17,18,19,20,21]. Bird hybrids would provide new genetic insight into hybrid incompatibility
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