Male brood care without paternity increases mating success

We investigate under which conditions we can expect the evolution of costly male care for unrelated offspring, when the benefit of such care is in the form of increased mating success. This applies to male helping behavior that cannot be explained as paternal care because the male's own offspring does not benefit from his behavior. Our model shows that caring for others' offspring can be a stable strategy for males, if a male that does not "help" loses mating opportunities, for example if females discriminate against non-helping males as mating partners. This is possible when females are polyandrous. Increasing population density decreases the parameter region where male care is stable. Male care is also more likely to be stable when male mortality rate is higher than that of females. We discuss the results with special reference to the golden egg bug Phyllomorpha laciniata, where females lay eggs on conspecifics, often on males before mating. Males therefore carry mostly unrelated eggs. We investigate how oviposition rate and female mating rate influences when egg carrying is an evolutionary stable strategy. We conclude that in the golden egg bug, male egg carrying could be explained as a form of mating investment. Copyright 2004.