Female mating status affects mating and male mate-choice in the copepod genus Acartia

Mating in many copepod species is not random; moreover, individuals have preferences for certain qualities in their mates. This study tested whether female mating status (virgin versus mated) affects mate choice in males in the copepod species Acartia tonsa and Acartia hudsonica, both in laboratory and field populations. In addition, the costs and benefits associated with mating twice versus once for females of both species were tested in laboratory studies. In both A. tonsa and Acartia hudsonica, males mated more frequently with virgin females compared with females that had already mated, suggesting that female reproductive status is important for mating and mate choice. Frequencies of females carrying double spermatophores in the field (at three sites and seasonally within a site) were consistently low, implying that mate choice for female reproductive status is present in natural populations as well. In Acartia hudsonica, the frequency of females carrying double spermatophores was positively related to spermatophore volume and male and female sizes, but negatively related to temperature. No such relationships were found for A. tonsa. However, the frequency of females carrying double spermatophores decreased as the season progressed. In both copepod species, there was no difference in the number of nauplii produced, length of fertilization or lifespan between females that had mated twice compared with those that had mated only once. Hence, there was no particular cost or benefit to mating a second time. Our findings suggest that female reproductive status is important for mating success in these two coastal copepod species and that this is most likely due to male mate-choice.