THE MALES DILEMMA - INCREASED OFFSPRING PRODUCTION IS MORE PATERNITY TO STEAL

Large potential effects of male care on the number of offspring female s successfully raise are not sufficient to select for caring males bec ause of the pervasive importance of mating competition. Males face a v ersion of 'the social dilemma', in which increased production increase s the pay-off for theft, Models of the allocation of male effort parti tioned between caring for babies and competing for paternity show that the optimal allocation to care is very low under a wide range of cond itions. Like sex allocation where the alternatives are male versus fem ale function or sons versus daughters? the pay-offs to one alternative are always strongly frequency dependent. Because that alternative (ma le function, sons, male mating effort) pays so well when rare, it cann ot remain rare under most conditions. Here we consider the consequence s of partitioning mating effort into mate guarding and all other forms of mating conflict. If a male gets all his partner's conceptions whil e guarding, gaining them at a constant rate, there are two possible re gions of stability. The evolutionarily stable strategy (ESS) depends o n a parameter scaling the decisiveness of (non-guarding) mating confli ct. When marginal returns from conflict decrease with scale, almost al l effort goes into guarding. When marginal returns increase, the ESS d evotes all effort to mating. Even when the potential effect of care is large, male equilibrium strategies allocate little effort to it. We a lso report the results of computer simulations showing that care incre ases if gains from guarding saturate quickly, so that a male is assure d of the paternity of most of his partner's offspring with little guar ding, and consequently the pool of unguarded conceptions open to compe tion shrinks sharply. But even when the male's dilemma is very much re duced, it still substantially limits the allocation to care. The resul ts of both computer simulations and mathematical analysis converge wit h other lines of evidence that mating has much stronger effects than p arenting in shaping male strategies.