Fig. 1.

The predictions for the experiment. a If females can manipulate male investment using a cue to which only males respond, proportional investment by the male should increase with increasing androgen level in the foster eggs. There is no clear prediction for the relationship between proportional investment by the male and the original egg androgen levels. b If females can manipulate male investment using a cue to which both sexes respond, the proportional investment by the male should increase with increasing androgen level in the original eggs of the nest. This is because a female that lays eggs with high androgen levels should reduce her responsiveness to the androgen-mediated cue(s) of the chicks. There is no clear prediction for the relationship between the proportional investment by the male and foster egg androgen levels