Does the female seahorse still prefer her mating partner after a period of separation?

For species showing sexual monogamy, once one male and one female form a mating pair bond, they will be faithful to each other in subsequent breeding events. However, if their pair bond is broken for some reason, do they continue to prefer their partner when they come together again for mating? In other words, can the broken pair bond of sexually monogamous species be repaired? This is an interesting question but not yet well answered. To address this question, in the present study we used the lined seahorse (Hippocampus erectus), a typical sexually monogamous species, to study the partner preference of a female individual who experienced a complete separation followed by a reunion with her partner. Our main findings are as follows: (i) The female seahorse no longer prefers her partner after a separation, whether it is a former partner or a recent partner. No preference for partner-males may indicate that the broken pair bond cannot be repaired. (ii) The female seahorse maintains sexual fidelity to her partner in the absence of separation. However, once the health of her partner decreases, the female will switch mate, and her courtship with the new partner can take place during the pregnancy of her original partner. The first finding may provide insight into whether monogamous species still have an opportunity to reselect a new partner in the future to correct their poor choice once they have mated with a low-quality partner. The answer is that they can still gain an opportunity as long as the pair bonds with their current partners are broken. The second finding may reveal the conditions and timing at which a female seahorse switches her mate. These findings help us better understand the mating system of the seahorse H. erectus.