From sneaky to bully: reappraisal of male squid dimorphism indicates ontogenetic mating tactics and striking ejaculate transition

摘要

The expression of alternative reproductive tactics (ARTs) is often influenced by the environmental cues and intrinsic conditions experienced by each male, and it may be reversible or permanent. In male loliginid squid, ARTs include consorts and sneakers, which differ in behaviour, body size, sperm deposition site, and morphology and functioning of ejaculates. Here, we describe intermediate-sized males in the squid Doryteuthis plei (Blainville, 1823) that produce sneaker-like, consort-like and intermediate ejaculates. In addition, age estimates show that sneakers and intermediate males are younger than consorts. Our findings suggest that ARTs in this species may be ontogenetically expressed. Such a transition between phenotypes requires dramatic anatomical and physiological reorganization of the male reproductive system, not only to produce different-structured spermatophores, but also to generate sperm with distinct behaviour, both of which are compatible with the switch in sperm deposition site. These findings demonstrate that this peculiar mating system may also fit the current predictions of ARTs.