Increased competitiveness of nematode sperm bearing the male X chromosome
Increased competitiveness of nematode sperm bearing the male X chromosome
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DOI：
10.1073/pnas.94.1.185
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发表时间：
1997-01-07
影响因子：
11.1
通讯作者：
Ward, S
中科院分区：
文献类型：
--
作者：
LaMunyon, CW;Ward, S
无法独立繁殖的雄性后代代表了有性繁殖的成本。通过自体受精线虫 Caenarhabditis briggsae 产生雌雄同体后代，可以消除这一成本。然而，这些雌雄同体可以通过与雄性交配来异型杂交。从男性获得的精子中有一半不含有性染色体，因此会产生男性后代。因此，与雄性交配应该付出产生雄性后代的成本。我们发现雄性精子优先于雌雄同体精子，从而实现最大程度的异交，但雄性后代的出现在交配后延迟。这种延迟是由于携带 X 的雄性精子在与无 X 的精子的竞争中胜出而造成的。携带 X 的精子相对于无 X 精子的竞争优势仅限于男性精子；它并没有发生在产生两种类型精子的突变雌雄同体中。布里格斯染色体对精子竞争力的影响尚未在其他物种中观察到，这表明 X 染色体已经进化出一种减数分裂驱动形式，自私地提高了携带该染色体的精子相对于不携带该染色体的精子的竞争力。因此，C. briggsae 中发现的多水平精子竞争力最大限度地提高了交配后的异型杂交，同时延迟了产生雄性后代的成本。
Male offspring, which cannot reproduce independently, represent a cost of sexual reproduction. This cost is eliminated by the production of hermaphroditic offspring in the self-fertilizing nematode Caenarhabditis briggsae. However, these hermaphrodites can outcross by mating with males. Half the sperm received from males contain no sex chromosome and therefore give rise to male progeny. Mating with males should thus impose the cost of making male offspring. We found that male sperm took immediate precedence over hermaphrodite sperm, resulting in maximized outcrossing, but the appearance of male progeny was delayed after mating. This delay is caused by the male X-bearing sperm outcompeting their nullo-X counterparts. The competitive advantage of X-bearing sperm over nullo-X sperm is limited to sperm from males; it did not occur in a mutant hermaphrodite that produces both types of sperm. The chromosomal effect on sperm competitiveness in C. briggsae, which has not been observed in other species, suggests that the X chromosome has evolved a form of meiotic drive, selfishly increasing the competitiveness of sperm that bear it over those that do not. Thus, the multiple levels of sperm competitiveness found in C. briggsae maximize outcrossing after mating while delaying the cost of making male offspring.