Although natural populations of most species exhibit a 1:1 sex ratio, biased sex ratios are known to be associated with non-Mendelian inheritance, as in sex-linked meiotic drive and cytoplasmic inheritance (Charnov 1982; Hurst 1993). We show how cultural inheritance, another type of non-Mendelian inheritance, can favor skewed primary sex ratios and propose that it may explain the female-biased sex ratios commonly observed in reptiles with environmental sex determination (ESD). Like cytoplasmic elements, cultural traits can be inherited through one sex. This, in turn, favors skewing the primary sex allocation in favor of the transmitting sex. Female nest-site philopatry is a sex-specific, culturally inherited trait in many reptiles with ESD and highly female-biased sex ratios. We propose that the association of nest-site selection with ESD facilitates the maternal manipulation of offspring sex ratios toward females.

Corresponding Editor: T. Mousseau