All the spermatangia on a female were implanted by single-pair copulation in giant squid Architeuthis dux

Abstract Deep-ocean biology has been the least explored—although rapidly growing—area of research. In particular, behavior, reproduction and ecology of deeper-living squids remain poorly documented due to the extreme difficulties of encountering and capturing them. Here we report on a mature/maturing female giant squid, Architeuthis dux, caught as by-catch in a fishery set-net. Microsatellite paternity analysis was carried out on the implanted spermatangia scattered widely over the body surface. Using genomic DNA from 42 Architeuthis individual muscle tissue specimens, four polymorphic microsatellite markers were developed, of which three were used for genotyping. Surprisingly, it was found that all 66 of the successfully genotyped spermatangia located on five different body parts were derived from a single male, suggesting that only single-pair copulation can lead to entire sperm loading. From this result and previous findings, the possibilities of the reproductive mode of this species are explored in the light of postcopulatory sexual selection mechanisms.