The Male Primary Sex Ratio Bias in Goose Eggs Early in the Laying Season: A Pilot Study

In bird eggs, the theoretical expectation of a primary sex ratio (at conception) of 50:50 males/females often fails to materialize. Using PCR technology for sex verification in this pilot study, we evaluated the primary sex ratio of 128 fertilized domestic goose eggs (Anser anser) early in the laying season. Over 24 consecutive days of egg collection, 37% more males were found (58% males vs. 42% females). This male-biased trend gradually declined over the period, but an excess of males was still observed. Among the factors for predicting the male sex ratio bias in a particular goose was the egg weight, i.e., heavier eggs tended towards a male phenotype. The embryo sex of the first egg laid and the egg weight change dynamics over the laying period were also noted. The correlation between actual and predicted data was calculated, taking into account three parameters, and found to be 0.724. To explain the effect of an implicit random/non-random process more adequately, we introduced the concept of biased randomness. As well as being of academic interest, research on sex ratio bias is crucial for goose breeding/reproduction programs and important as a step towards understanding the physiological mechanisms that underly sex ratio bias in these animals.