“This was like the animal kingdom’s version of true romance versus arranged marriages,” said consortium collaborator Lee Drickamer, who spearheaded the house-mouse component. Drickamer, who has written several popular textbooks on animal behavior, heads the biological sciences department at Northern Arizona University.

Turns out that romance trumps random matchmaking: Similar patterns emerged among all consortium-studied vertebrates.

Like other vertebrates in the study, pipefish produced higher quality young when parents got a preferred mate.

“In virtually all these studies,” Gowaty said, “offspring viability was lower when individuals were reproducing with partners they didn’t prefer.”

Added Anderson, “It made us believe that there could be something to this idea that mating-strategy behavior may be based on natural selection.”

Among house mice, for example, matches based on romance had greater odds of bearing young. “It made no difference whether females or males did the choosing,” Drickamer said. “Differences between attraction and random arrangement showed up in the sheer numbers of litters produced.”

Mouse pups born to romance-based couples survived longer, under both lab and field conditions. The pups built better nests, staked out larger territories as adults and got caught in live traps less often. Sons usually won dominance competitions and daughters had higher pregnancy rates. The findings — published in the journal Animal Behaviour (February 2000 and January 2003) — also contradict the well-established parental-investment theory, which holds that whichever sex invests more reproductive resources also is choosier about a partner.

“For the father, the only cost is sperm, but the mother gestates, lactates and has an additional care-giving period,” said Gowaty, who collaborated on the mouse studies. Yet the male subjects were just as choosy as the females.

For mallards, mate choice not only favored romance, according to Gowaty and avian endocrinologist Cynthia Bluhm, but also provided ammunition for the compensation theory: Unlike younger ducks in arranged partnerships, older moms in the same bind laid larger, heavier eggs and their ducklings were similar in size and condition to ducklings born to older moms who mated with their most-preferred drake. “First-year females didn’t (or couldn’t) compensate when mated with males they didn’t like,” Gowaty said. “Their ducklings were at a significant disadvantage.” The mallard research was published last September in Animal Behaviour. The lone exception to romance’s advantage occurred among cockroaches. All four mating combinations yielded similar results for offspring viability, according to Gowaty. While no one could explain why, she proffered one possibility: a genetic similarity among individuals in the 50-year-old colony.

“Yet this study also showed that females mated to males they did not like died significantly sooner than females mated to males they did like,” Gowaty said. “That suggests that there are significant costs to females that reproduced with males they did not like.”