在追求雌烏賊的過(guò)程中,，小個(gè)子的雄烏賊是無(wú)法戰(zhàn)勝大塊頭的競(jìng)爭(zhēng)對(duì)手的，因此它們?cè)V諸一種卑鄙的伎倆：在最后關(guān)頭釋放它們的精子,。
在一只雌烏賊選擇一只大個(gè)的雄烏賊之后,，后者會(huì)將它的精子包放入前者的輸卵管中，這些精子會(huì)與雌烏賊一直呆在一起直至其產(chǎn)卵,，這樣一來(lái),，其他雄烏賊便沒(méi)有機(jī)會(huì)橫刀奪愛(ài)了。
但是小塊頭的烏賊會(huì)在這對(duì)甜蜜的戀人附近閑逛,，并在雌烏賊排卵的一剎那搶過(guò)去與其交配,。
這些矮個(gè)子的羅密歐會(huì)將它們的精子包放在雌烏賊的體外，靠近其精子儲(chǔ)存器官的位置——位于雌烏賊的口腔下方,。
隨著雌烏賊將它的卵子沉入海底,，這些精子也會(huì)使其中的一些卵子受精。
盡管這些卑鄙的雄性并不會(huì)像它的競(jìng)爭(zhēng)對(duì)手那樣讓那么多的卵子受精,，但這依然是一個(gè)有效的手段,。
研究人員在8月9日的《BMC進(jìn)化生物學(xué)》雜志上報(bào)告了這一研究成果。
實(shí)驗(yàn)室研究同時(shí)表明,，盡管體型較小,，但小烏賊的精子卻要比大烏賊的大。這并不是因?yàn)榇笠稽c(diǎn)的精子比小一點(diǎn)的精子更有優(yōu)勢(shì),，它們之所以大是因?yàn)檫@些精子必須禁得起雌烏賊體外的嚴(yán)酷環(huán)境,。(生物谷 Bioon.com)
doi:10.1186/1471-2148-11-236
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PMID:
Why small males have big sperm: dimorphic squid sperm linked to alternative mating behaviours
Yoko Iwata, Paul Shaw, Eiji Fujiwara, Kogiku Shiba, Yasutaka Kakiuchi, Noritaka Hirohashi
(provisional)Background Sperm cells are the target of strong sexual selection that may drive changes in sperm structure and function to maximize fertilisation success. Sperm evolution is regarded to be one of the major consequences of sperm competition in polyandrous species, however it can also be driven by adaptation to the environmental conditions at the site of fertilization. Strong stabilizing selection limits intra-specific variation, and therefore polymorphism, among fertile sperm (eusperm). Here we analyzed reproductive morphology differences among males employing characteristic alternative mating behaviours, and so potentially different conditions of sperm competition and fertilization environment, in the squid Loligo bleekeri. Results Large consort males transfer smaller (average total length = 73 um) sperm to a female's internal sperm storage location, inside the oviduct; whereas small sneaker males transfer larger (99 um) sperm to an external location around the seminal receptacle near the mouth. No significant difference in swimming speed was observed between consort and sneaker sperm. Furthermore, sperm precedence in the seminal receptacle was not biased toward longer sperm, suggesting no evidence for large sperm being favoured in competition for space in the sperm storage organ among sneaker males. Conclusion sHere we report the first case, in the squid Loligo bleekeri, where distinctly dimorphic eusperm are produced by different sized males that employ alternative mating behaviours. Our results found no evidence that the distinct sperm dimorphism was driven by between- and within-tactic sperm competition. We propose that presence of alternative fertilization environments with distinct characteristics (i.e. internal or external), whether or not in combination with the effects of sperm competition, can drive the disruptive evolution of sperm size.
