Even the “oldest profession” that figured so prominently in Mr. Spitzer’s demise is old news. Nonhuman beings have been shown to pay for sex, too. Reporting in the journal Animal Behaviour, researchers from Adam Mickiewicz University and the University of South Bohemia described transactions among great grey shrikes, elegant raptorlike birds with silver capes, white bellies and black tails that, like 90 percent of bird species, form pair bonds to breed. A male shrike provisions his mate with so-called nuptial gifts: rodents, lizards, small birds or large insects that he impales on sticks. But when the male shrike hankers after extracurricular sex, he will offer a would-be mistress an even bigger kebab than the ones he gives to his wife  for the richer the offering, the researchers found, the greater the chance that the female will agree to a fly-by-night fling.

In another recent report from the lubricious annals of Animal Behaviour entitled “Payment for sex in a macaque mating market,” Michael D. Gumert of Hiram College described his two-year study of a group of longtailed macaques that live near the Rimba ecotourist lodge in the Tanjung Puting National Park of Indonesia. Dr. Gumert determined that male macaques pay for sex with that all-important, multipurpose primate currency, grooming. He saw that, whereas females groomed males and other females for social and political reasons  to affirm a friendship or make nice to a dominant  and mothers groomed their young to soothe and clean them, when an adult male spent time picking parasites from an adult female’s hide, he expected compensation in the form of copulation, or at the very least a close genital inspection. About 89 percent of the male-grooming-female episodes observed, Dr. Gumert said in an interview from Singapore, where he is on the faculty of Nanyang Technological University, “were directed toward sexually active females” with whom the males had a chance of mating.

Significantly, males adjust their grooming behavior in a distinctly economic fashion, paying a higher or lower price depending on the availability and quality of the merchandise and competition from other buyers. “What led me to think of grooming as a form of payment was seeing how it changed across different market conditions,” Dr. Gumert said. “When there were fewer females around, the male would groom longer, and when there were lots of females, the grooming times went down.” Males also groomed females of high rank considerably longer than they did low-status females with nary a diamond to their page.

Commonplace though adultery may be, and as avidly as animals engage in it when given the opportunity, nobody seems to approve of it in others, and humans are hardly the only species that will rise up in outrage against wantonness real or perceived. Most female baboons have lost half an ear here, a swatch of pelt there, to the jealous fury of their much larger and toothier mates. Among scarab beetles, males and females generally pair up to start a family, jointly gathering dung and rolling and patting it into the rich brood balls in which the female deposits her fertilized eggs. The male may on occasion try to attract an extra female or two  but he does so at his peril. In one experiment with postmatrimonial scarabs, the female beetle was kept tethered in the vicinity of her mate, who quickly seized the opportunity to pheromonally broadcast for fresh faces. Upon being released from bondage, the female dashed over and knocked the male flat on his back. “She’d roll him right into the ball of dung,” Dr. Barash said, “which seemed altogether appropriate.”

In the case of the territorial red-backed salamander, males and females alike are inclined to zealous partner policing and will punish partners they believe to have strayed: with threat displays, mouth nips and throat bites, and most coldblooded of all, a withdrawal of affection, a refusal to engage. Be warned, you big lounge lizard: it could happen to you.