The sexual reproduction(conjugation) between opposite mating types are led by the collaborative synthesis of trisporic acid. It is produced 4-dehydrotrisporic acid and trisporol. The former one is produced by the [+] strain produces and the latter one is produced by the [-] strain produces. A high level of trisporic acid leads to the formation of zygophores, dissolving contact region and formation of a thick-walled, heavily pigmented zygospore with diploid nuclei.
Very informative and well-labelled photo.