Experimental results and theoretical predictions.

Red and blue colourings correspond to genes of maternal and paternal origin, respectively. Orange and brown colourings correspond to genes expressed in the pup and the mother, respectively. Gray colouring corresponds to genes contributing to the phenotype but not considered in the current experiment. Arrowed and crossed-out rectangles correspond to expressed and silenced genes, respectively. All possible pairings between the wild type Grb10 and the loss-of-function mutant Grb10KO in the pup and mother are presented in a 2 × 2 matrix. In each cell, we indicate (i) the experimental result in white over grey background and (ii) the theoretical prediction in black. The amount of milk a pup obtains results from a tension between offspring demand and maternal supply. Eliminating genes that maintain this tension (by rendering them nonfunctional) alters the amount of milk the pup obtains. (A) If the mother is more related to the recipients of allo-maternal care through her father, then in the pup, demand-inhibitor (DI) genes should be paternally silenced and demand-enhancer (DE) genes should be maternally silenced; in the mother, supply-inhibitor (SI) genes should be maternally silenced and supply-enhancer (SE) genes should be paternally silenced; and so, as Grb10 is maternally expressed in pup and mother, this gene is predicted to be a DI in the pup and a SE in the mother, and the corresponding predicted 2 × 2 matrix of pup weights exactly matches that observed in the experiment. (B) If the mother is more related to the recipients of allo-maternal care through her mother, then in the pup, DI genes should be paternally silenced and DE genes should be maternally silenced; in the mother, SI genes should be paternally silenced and SE genes should be maternally silenced; and so, as Grb10 is maternally expressed in pup and mother, this gene is predicted to be a DI in the pup and a SI in the mother, and the corresponding predicted 2 × 2 matrix of pup weights only partially matches that observed in the experiment. Accordingly, the kinship theory suggests that, in the natural setting in which GI has evolved, the mother is more related to the recipients of her allo-maternal care through her father than through her mother.