Precopulatory mate guarding and mating in Tachidius discipes (Copepoda: Harpacticoida)

Precopulatory mate guarding and mating behaviour of Tachidius discipes Giesbrecht, 1881, has been analysed using a video camera mounted on a microscope. Males preferably accompany fourth or fifth stage female copepodids during precopulatory mate guarding; only rarely are third copopodid stages guarded. Rare cases of males clasping juvenile males are also known. Males are active during mate guarding and constantly change the site of attachment of their antennules. This behaviour may ensure continued association of the adult male with the juvenile copepodid when the latter moults during the mate guarding phase. The final moult of the female, once observed only, lasts only 2 minutes. Copulation immediately follows but is preceded by the male’s control of the genital field of the female. This is done by the second, third and fourth legs of the male sliding over the female’s genital field. Males copulate only with virgin females. A male will also copulate with a female that he has not guarded during her juvenile state. Previously inseminated adult females are rejected. Their condition is recognized even when the spermatophore has fallen off and when no egg sac is carried. Copulation takes only a few seconds. The spermatophore is transferred without the aid of any appendage and the male separates from the female shortly afterwards. Males of T. discipes were found to have either one or two spermatophores in their gonoduct. Those with two were able to inseminate two females within about two to three hours. After the first or, in the case of a male with two spermatophores, after two copulations, 12.5 to 24 hours elapsed before he was able to inseminate another virgin female. Females are passive when investigated by a male and make no attempt to repel him. In T. discipes, a species exhibiting typical precopulatory mate guarding, male choice is a strongly expressed behaviour while female choice is not expressed.