The male reproductive strategy of a deep-sea squid: sperm allocation, continuous production, and long-term storage of spermatophores in Histioteuthis miranda

Squid are semelparous organisms. Much of what we know about squid reproduction relates to females, because few studies have addressed males and, although males are similarly challenged by semelparity, it remains virtually unknown what tactics squid have evolved to allocate sperm to spermatophores. The male reproductive strategy of the deep-sea squid Histioteuthis miranda was examined by describing the male reproductive anatomy, which appears unique among cephalopods, and by quantifying spermatophore production and sperm allocation. The species produces and stores spermatophores over a considerable period of continuous somatic growth. Body size and spermatophore length (SpL) are positively correlated, and the size difference between spermatophores stored by a single individual was up to 270%. Individuals had between 136 and 2276 spermatophores inside their reproductive system, and spermatophores may be stored for as long as 4.5 months. The relationship between SpL and the mass of sperm per spermatophore was polynomial, demonstrating that larger spermatophores did not necessarily contain more sperm. The unique male morphology and the continuous production and long-term storage of spermatophores in H. miranda seem to allow the species to increase the window in which reproduction can take place, a strategy that may be valuable in the deep-sea environment.