Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan.
Oki Marine Biological Station, Shimane University, 194 Kamo, Okinoshima, Oki, Shimane 685-0024, Japan.
Curr Biol. 2019 Jan 21;29(2):R48-R49. doi: 10.1016/j.cub.2018.12.010.
How sperm reach ova after mating is one of the central questions in reproductive biology. Many species copulate and store sperm in female reproductive organs until spawning [1]. The way females use stored sperm is closely associated with sperm competition and cryptic female choice. However, it is difficult to observe the process of fertilization in natural spawning, as fertilization usually occurs in some 'hidden place' within the female's body. Here, we report the fertilization process of a squid using a glass plate as a spawning substratum, enabling observation within the female arm crown where the sperm storage organ is located and where fertilization may occur. Additionally, we detail the distribution of sperm around newly spawned eggs. Our observations reveal that: the female places her sperm-storage organ (seminal receptacle) over an egg held within her arm crown and inseminates the eggs one-by-one during attachment to the spawning substratum; sperm pass through a pathway within the jelly layers surrounding an egg; and such direct insemination behavior and the pathway through the egg jelly enables a female squid to externally fertilize her eggs using relatively few sperm. This study is the first to reveal the fertilization process using stored sperm, under female control.
精子在交配后如何到达卵子是生殖生物学中的核心问题之一。许多物种在交配后将精子储存在雌性生殖器官中，直到产卵[1]。雌性利用储存精子的方式与精子竞争和隐蔽性雌性选择密切相关。然而，在自然产卵中很难观察受精过程，因为受精通常发生在雌性体内的某个“隐蔽处”。在这里，我们报告了使用玻璃板作为产卵基质的鱿鱼的受精过程，从而能够在雌性臂冠内观察到精子储存器官所在的位置，以及可能发生受精的位置。此外，我们详细描述了新产卵周围精子的分布。我们的观察结果表明：雌性将其精子储存器官（精囊）放在臂冠内的一个卵子上，并在附着到产卵基质时逐个使卵子受精；精子通过卵子周围的果冻层中的一条通路；这种直接的授精行为和穿过卵果冻的通路使雌性鱿鱼能够使用相对较少的精子对外来卵子进行受精。这项研究首次揭示了在雌性控制下使用储存精子的受精过程。
