The Myth of Monogamy: Fidelity and Infidelity in Animals and People by David P. Barash; Judith Eve Lipton Page A
Authors: David P. Barash; Judith Eve Lipton
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studies in which males of different species were removed while their Desde-monas were sexually receptive, in which these males had visual access to their unguarded females, in which the females were removed, in which males witnessed their females in cages with decoy males, and so forth, all looking for possible impact on the males' subsequent behavior, especially his paternal inclinations.
The pattern persists: Genetic paternity correlates with acting paternally. But not always. Especially among some socially monogamous species, males do not consistently reduce their paternal solicitude following behavioral evidence of their mates' infidelity. Maybe they just don't "understand" what has happened, or perhaps their paternal inclinations are so hard wired that they simply don't have enough flexibility to adjust. In any event, it is interesting that the strongest evidence for precise adjustments by males to the EPCs of females comes from cooperatively breeding species such as the dunnock, where several males might be associated with one female. Here, males care for offspring in proportion to their likelihood of being the father; if several males have copulated with one female, each male will provide food, for example, proportional to his degree of sexual access. (More copulating, more food-bringing.) In another cooperatively breeding bird species, the acorn woodpecker, when dominant males are experimen-
undermining the myth: males 49
tally removed from the group, they respond by infanticide, destroying eggs laid while they were out of the reproductive picture. The likelihood is that in such species, males are often exposed to variations in the probability of being fathers; hence, they have the behavioral repertoire to detect such probabilities and to behave accordingly. Perhaps in cases of ostensible monogamy, females are normally so adroit at hiding their EPCs that males have not evolved a response.
There are other interesting avenues connecting EPCs and parental behavior. We have already looked at the peculiar trade-off between mate-guarding and gallivanting, with one precluding the other. Males also appear to be influenced by another balance point: between gallivanting (going in search of EPCs) and staying home to help take care of the kids. As with gallivanting versus mate-guarding, males can't have it both ways; if they are off trying to spread their seed, they cannot very well also be home tending the fruits of that seed.
In many colonially nesting bird species (e.g., terns, herons, social gulls), there is comparatively little EPC activity, perhaps because the females breed synchronously; that is, they are all likely to breed at about the same time. As a result, a male who gallivants runs the risk that his own female will cuckold him. By contrast, most songbirds appear to engage in EPCs if they can. Although they breed seasonally, they are not truly synchronous, so a male can inseminate "his" female, guard her against other males while she is fertile, and then proceed to seek other females who may be just entering their fertile period. Also, many males seem to use a "switching" strategy: After their eggs have hatched, they abandon gallivanting and become doting fathers ... because at this point the genetic payoff exceeds that from seeking EPCs.
For example, male indigo buntings seek EPCs while their mates are incubating--at a time when there is relatively little that the males can do to aid their offspring. Paternal behavior competes with trying to get EPCs: In most species of birds, males provide quite a bit of parental care during chick-rearing, much less during nest-building or incubation. It may be no coincidence that in these early stages of the breeding cycle, males have the prospect of achieving one or more EPCs; hence, they are more likely to gallivant. By the chick-rearing stage, most fertile females have already been inseminated, so the best thing a male can do is help rear the offspring he has (presumably)
The pattern persists: Genetic paternity correlates with acting paternally. But not always. Especially among some socially monogamous species, males do not consistently reduce their paternal solicitude following behavioral evidence of their mates' infidelity. Maybe they just don't "understand" what has happened, or perhaps their paternal inclinations are so hard wired that they simply don't have enough flexibility to adjust. In any event, it is interesting that the strongest evidence for precise adjustments by males to the EPCs of females comes from cooperatively breeding species such as the dunnock, where several males might be associated with one female. Here, males care for offspring in proportion to their likelihood of being the father; if several males have copulated with one female, each male will provide food, for example, proportional to his degree of sexual access. (More copulating, more food-bringing.) In another cooperatively breeding bird species, the acorn woodpecker, when dominant males are experimen-
undermining the myth: males 49
tally removed from the group, they respond by infanticide, destroying eggs laid while they were out of the reproductive picture. The likelihood is that in such species, males are often exposed to variations in the probability of being fathers; hence, they have the behavioral repertoire to detect such probabilities and to behave accordingly. Perhaps in cases of ostensible monogamy, females are normally so adroit at hiding their EPCs that males have not evolved a response.
There are other interesting avenues connecting EPCs and parental behavior. We have already looked at the peculiar trade-off between mate-guarding and gallivanting, with one precluding the other. Males also appear to be influenced by another balance point: between gallivanting (going in search of EPCs) and staying home to help take care of the kids. As with gallivanting versus mate-guarding, males can't have it both ways; if they are off trying to spread their seed, they cannot very well also be home tending the fruits of that seed.
In many colonially nesting bird species (e.g., terns, herons, social gulls), there is comparatively little EPC activity, perhaps because the females breed synchronously; that is, they are all likely to breed at about the same time. As a result, a male who gallivants runs the risk that his own female will cuckold him. By contrast, most songbirds appear to engage in EPCs if they can. Although they breed seasonally, they are not truly synchronous, so a male can inseminate "his" female, guard her against other males while she is fertile, and then proceed to seek other females who may be just entering their fertile period. Also, many males seem to use a "switching" strategy: After their eggs have hatched, they abandon gallivanting and become doting fathers ... because at this point the genetic payoff exceeds that from seeking EPCs.
For example, male indigo buntings seek EPCs while their mates are incubating--at a time when there is relatively little that the males can do to aid their offspring. Paternal behavior competes with trying to get EPCs: In most species of birds, males provide quite a bit of parental care during chick-rearing, much less during nest-building or incubation. It may be no coincidence that in these early stages of the breeding cycle, males have the prospect of achieving one or more EPCs; hence, they are more likely to gallivant. By the chick-rearing stage, most fertile females have already been inseminated, so the best thing a male can do is help rear the offspring he has (presumably)
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