Monogamous female seahorses cheat on their male partners when they can鈥檛 smell them any more.
鈥淪eahorses can express incredible loyalty and affection once a pair has bonded during the reproductive season,鈥� says Dong Zhang at the Chinese Academy of Fishery Sciences in Shanghai.
The curvy-tailed couples usually stay together for months or years. They live within a few metres of each other and meet up at daylight for 鈥渕orning greetings鈥� that reinforce their bond 鈥� swimming in parallel, brightening their hues and 鈥渄ancing鈥�, says Zhang.
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They reproduce through male pregnancy after the female deposits her eggs into the male鈥檚 abdominal brood pouch. The couple takes a mating break during the 12 to 20 days the male is pregnant, but then they mate again within 48 hours after he gives birth.
Zhang and his team wondered what kept the female faithful during the waiting time and how she distinguished her mate from other males. They tested 200 pairs of virgin, lab-raised lined seahorses (Hippocampus erectus) in various situations. They allowed them to couple up, placing a female and her pregnant mate in a tank with a second male that had just given birth, which may have made him more attractive because he had proven to be fertile, says Zhang.
Then they placed the pregnant mate either in a mesh cage, an opaque open-ended pipe or a transparent plastic bag. These barriers respectively blocked morning greetings, vision or odours.
After the mate gave birth, the researchers let all three seahorses swim freely. If a female hadn鈥檛 been able to see or greet her mate during pregnancy, she still chose him over the other male, except for a few rare cases in which a female didn鈥檛 choose either male, says Zhang.
However, 75 per cent of the females that hadn鈥檛 been able to smell their enclosed mates chose the other male. It is possible that while the mate was in the transparent bag, the female forgot his scent and got used to the other male鈥檚 odours, says Zhang.
Behavioural Processes
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