Male brood care without paternity increases mating success

We investigate under which conditions we can expect the evolutionof costly male care for unrelated offspring, when the benefitof such care is in the form of increased mating success. Thisapplies to male helping behavior that cannot be explained aspaternal care because the male's own offspring does not benefitfrom his behavior. Our model shows that caring for others' offspringcan be a stable strategy for males, if a male that does not"help" loses mating opportunities, for example if females discriminateagainst non-helping males as mating partners. This is possiblewhen females are polyandrous. Increasing population densitydecreases the parameter region where male care is stable. Malecare is also more likely to be stable when male mortality rateis higher than that of females. We discuss the results withspecial reference to the golden egg bug Phyllomorpha laciniata,where females lay eggs on conspecifics, often on males beforemating. Males therefore carry mostly unrelated eggs. We investigatehow oviposition rate and female mating rate influences whenegg carrying is an evolutionary stable strategy. We concludethat in the golden egg bug, male egg carrying could be explainedas a form of mating investment.     

Nonrandom mating preserves intrasexual polymorphism and stops population differentiation in sexual conflict

Evolutionary conflict between the sexes is predicted to lead to sexual arms races in which male adaptations for acquiring mates ("offense" traits) are met by female counteradaptations--for example, to reduce mating rate ("defense" traits). Such coevolutionary chases may be perpetual. However, we show here that the coevolutionary process may also lead to a stable state in which multiple offense-defense trait pairs are maintained. This type of polymorphism below the species level is a result of sexual conflict in combination with nonrandom mating. Our results show that if nonrandom mating occurs with respect to male and female conflict traits, genetic correlations will act to stabilize the trait frequencies so that all morphs are maintained. We discuss the results in special relation to the evolution of female polymorphism in diving beetles and argue that the process we describe may be a general force that maintains polymorphism in other taxa as well.     

Female polymorphism, frequency dependence, and rapid evolutionary dynamics in natural populations

Rapid evolutionary change over a few generations has been documented in natural populations. Such changes are observed as organisms invade new environments, and they are often triggered by changed interspecific interactions, such as differences in predation regimes. However, in spite of increased recognition of antagonistic male-female mating interactions, there is very limited evidence that such intraspecific interactions could cause rapid evolutionary dynamics in nature. This is because ecological and longitudinal data from natural populations have been lacking. Here we show that in a color-polymorphic damselfly species, male-female mating interactions lead to rapid evolutionary change in morph frequencies between generations. Field data and computer simulations indicate that these changes are driven by sexual conflict, in which morph fecundities are negatively affected by frequency- and density-dependent male mating harassment. These frequency-dependent processes prevent population divergence by maintaining a female polymorphism in most populations. Although these results contrast with the traditional view of how sexual conflict enhances the rate of population divergence, they are consistent with a recent theoretical model of how females may form discrete genetic clusters in response to male mating harassment.     

Conflict of interest between sexes over cooperation: a supergame on egg carrying and mating in a coreid bug

In the golden egg bug (Phyllomorpha laciniata Vill. Heteroptera: Coreidae) females lay eggs on the backs of conspecifics, oftenon courting males. Although the bugs do not provide care tothe eggs, this decreases the risk of egg predation. As an effectmales carry many eggs which are not their own. The male andfemale interests are in conflict; females need to find an ovipositionsite, and male fitness depends on the obtained number of matings. By using a very rare modeling approach, a supergame where theindividuals actions change payoffs over time, we show thatcombinations of reciprocating strategies where males obtaina mating in return for a carried egg can be stable. The valueof the mating, to males, is more important than the relatednessto the eggs in gaining their cooperation in carrying eggs. Females may also take advantage of the males without reciprocating.This is especially likely if the probability of future meetingis high and the value of a mating is high for the male. Werelate our results to our own data from empirical studies andexperiments on the species. In the light of the results we discuss the behavior of the bugs in relation to nuptial gifts. We alsodiscuss the general applicability of the supergame approach.