Behavioral aspects of sperm competition in cuttlefish, Sepia officinalis (Sepioidea : Cephalopoda)

Sexual selection studies in cephalopods indicate that sperm competition is a central feature of their mating systems, yet this has not been studied ex perimentally in any detail. In 1998 we staged 20 matings of the cattlefish, Sepia officinalis L., in the laboratory. Males rapidly initiated mating in the "head-to-head" position, with no apparent courtship. Mating lasted an average of 10 min (range 7 to 14 min). For the first 6 min (on average 63% of the mating duration), the male flushed strong jets of water directly at the female's buccal membrane, which sometimes resulted in the expulsion of parts of spermatangia placed there in recent matings. Then, in a single dis crete movement that lasted an average of only 14 s, the male's modified fou rth left arm - the hectocotylus - wrapped around a single large bundle of s permatophores (ca. 150 to 300) and transferred them to the female's buccal membrane. For the remainder of the mating (average 3 min, range 1.5 to 5.0 min), the hectocotylus repeatedly broke the spermatophores open, and manipu lated them, so that sperm were released and many spermatangia were attached along the ventral buccal membrane, near the paired seminal receptacles. Ap proximately 140 spermatangia were attached in rows 3 to 5 deep around the v entral buccal membrane in a single mating; the rest were usually discarded during mating. Histology revealed that each of the seminal receptacles cons ists of a series of sperm storage bulbs connected by a central duct, which leads to a single pore at the surface of the buccal membrane. Baseline data on sperm motility were obtained, but the mechanism by which sperm enter th e seminal receptacle remains unknown. Females seemed to initiate terminatio n of mating, then males guarded their mates temporarily. These results, com bined with other recent laboratory experiments, provide evidence that sperm competition may be a major feature of the mating system of S. officinalis.