Abstract
Interspecific crosses between Viviparus contectus males and V. ater females were successful (53 per cent of intraspecific V. ater fecundity), whereas the reverse combination was almost sterile (1.2 per cent of intraspecific V. contectus fecundity). The hybrid offspring had a high survival rate (99 per cent in the first year) and a male-biased sex ratio (84 per cent males). F1 hybrids were fertile inter se and in all six backcross combinations tested. Some of the backcrosses had fecundities similar to intraspecific control crosses. Hybrid females produced more offspring in backcrosses with V. contectus males than with V. ater males, suggesting that the higher fecundity of V. contectus as compared with V. ater can be inherited paternally. The male-biased sex ratio of hybrids suggests that the female is the heterogametic sex in Viviparus. The male-biased sex ratio and the high fecundity of hybrids of both sexes in backcrosses are compatible with Coyne's (Coyne, J. A. 1992 Nature, 355, 511–515) hypothesis of a composite nature of Haldane's rule. The high fecundity of hybrids also implies that introgression may occur in natural populations.
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Trüb, H., Ribi, G. High fecundity of hybrids between the sympatric snail species Viviparus ater and V. contectus (Gastropoda: Prosobranchia). Heredity 79, 418–423 (1997). https://doi.org/10.1038/hdy.1997.176
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DOI: https://doi.org/10.1038/hdy.1997.176