Hirohashi Noritaka, Iwata Yoko
Oki Marine Biological Station; Education and Research Center for Biological Resources; Shimane University; Oki, Shimane, Japan.
Atmosphere and Ocean Research Institute; University of Tokyo; Kashiwa, Chiba, Japan.
Commun Integr Biol. 2013 Nov 1;6(6):e26729. doi: 10.4161/cib.26729. Epub 2013 Oct 9.
Some coastal squids exhibit male dimorphism (large and small body size) that is linked to mating behaviors. Large "consort" males compete with other, rival males to copulate with a female, and thereby transfer their spermatophores to her internal site around the oviduct. Small "sneaker" males rush to a single female or copulating pair and transfer spermatophores to her external body surface around the seminal receptacle near the mouth. We previously found that in Loligo bleekeri, sneaker sperm are ~50% longer than consort sperm, and only the sneaker sperm, once ejaculated from the spermatophore (sperm mass), form a cluster because of chemoattraction toward their own respiratory CO2. Here, we report that sperm clusters are able to move en masse. Because a fraction of ejaculated sperm from a sneaker's spermatophore are eventually located in the female's seminal receptacle, we hypothesize that sperm clustering facilitates collective migration to the seminal receptacle or an egg micropyle. Sperm clustering is regarded as a cooperative behavior that may have evolved by sperm competition and/or physical and physiological constraints imposed by male mating tactics.
一些沿海鱿鱼表现出与交配行为相关的雄性二态性（体型大小不同）。体型较大的“配偶型”雄鱿鱼与其他竞争雄鱿鱼争夺与雌鱿鱼交配的机会，从而将精荚传递到雌鱿鱼输卵管周围的内部位置。体型较小的“偷情型”雄鱿鱼会冲向单个雌鱿鱼或正在交配的雌雄鱿鱼对，并将精荚传递到雌鱿鱼口部附近受精囊周围的体表。我们之前发现，在剑尖枪乌贼中，偷情型精子比配偶型精子长约50%，而且只有偷情型精子从精荚（精子团）中射出后，会因对自身呼吸产生的二氧化碳产生化学吸引而形成簇。在此，我们报告精子簇能够整体移动。由于偷情型雄鱿鱼精荚中射出的一部分精子最终会位于雌鱿鱼的受精囊中，我们推测精子聚集有助于集体迁移到受精囊或卵孔。精子聚集被视为一种合作行为，可能是通过精子竞争和/或雄性交配策略所施加的物理和生理限制而进化而来的。
