3.6 n&v 509 MH

NATURE | VOL 429 | 3 JUNE 2004 | www.nature.com/nature 517 Family conflicts are of professional interest not only to agony aunts but to evolutionary biologists as well. A case to exercise the latter has just appeared in Proceedings of the Royal Society, where James Curley and colleagues describe their manipulations of a mouse gene, Peg3. This gene is of particular interest because it is known to influence maternal behaviour, but is also inherited in an unusual fashion. Conflicts between mother, father and offspring take several forms. Newborns in a species that provides parental care often demand more than a mother is willing to give. The interest of the mother is to ensure that the needs of her offspring are met while retaining the ability to take care of other or future offspring; the interest of an offspring is to get as many resources as possible for itself, regardless of the interests of its siblings or mother. Fathers’ interests may coincide with those of the offspring, particularly if there is uncertainty that he will father other or future offspring in this family and the mother provides all the care. Conflicting selection pressures can therefore arise. If the behaviour is genetically influenced, that raises questions about how such family conflicts are resolved over evolutionary time. Curley and colleagues have applied modern techniques to investigate the genetics of such conflicts in mice. The Peg3 gene they studied is paternally expressed: that is, the mother’s copy of the gene is turned off in the offspring. This phenomenon, known as ‘imprinting’, is predicted to have evolved in genes whenever there are asymmetries in the evolutionary interests of parents in the behaviour directed towards offspring. But whose behaviour is affected? Is the action of Peg3 expressed in mothers or in offspring? Because individuals only express the Peg3 gene they inherit from their father, it is possible to generate mouse families in which the mother expresses the functional Peg3 gene product but the offspring don’t, and vice Behavioural genetics