Male egg carrying in Phyllomorpha laciniata is favoured by natural not sexual selection

Two hypotheses could explain the evolution of paternal care: caring males are more attractive to females and mate more often (sexual selection); males care when the benefits in terms of offspring survival exceed the costs (natural selection). To test these hypotheses we used Phyllomorpha laciniata: females can choose whether to lay eggs on plants or on conspecifics, and the extent to which males carry eggs varies between populations. Our results do not support the sexual selection hypothesis: females did not choose to mate with egg-carrying males in either natural populations or experimental contexts. We compared two populations that differ in the extent of male egg carrying and we show that in the population where male egg carrying was more prevalent, parasitism pressure was higher. Field experiments revealed that, in the population with high parasitism rate, egg mortality as a result of parasitoid attack was up to 10 times higher on plants than on conspecifics. Egg carrying is thus an effective strategy that protects eggs against parasitoids. We conclude that the main benefit derived by males from egg carrying is an increase in offspring survival, and that males are sensitive to interpopulation differences in egg mortality risks. Male care in this system has evolved despite intermediate levels of paternity certainty because the impact on offspring survival is high, and the costs in terms of loss of mating opportunities low. Thus, our findings support the natural selection hypothesis, although additional work on more populations is needed to verify this.