《自然》：美科学家发现微生物也会“耕种”

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2 k' u* ]+ t+ A1 T/ g4 x盘基网柄菌具有“播种”其食物细菌的行为
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耕种行为并非人类的专利，研究人员发现一种真核微生物也会播种并收获自己的食物——细菌。0 i5 U0 G( V4 E5 Y- B' a' X( Z

# \) |' h1 t, k5 n' x$ j* o- w, R新一期英国《自然》杂志刊登报告说，美国赖斯大学的研究人员发现一些盘基网柄菌具有这种农业行为。盘基网柄菌是黏菌的一种，虽然名字中带个“菌”字，却并不是通常说的细菌，而是属于真核生物。它通常以单细胞形态存在，以细菌为食，但当某处的食物变得匮乏时，大量盘基网柄菌就会聚集到一起，形成黏液状的多细胞有机体，集体迁徙到别的地方。$ b, T4 l# m! O6 C3 M
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过去人们一直认为盘基网柄菌只会这样四处“游猎”，但本次研究发现，有的盘基网柄菌在找到可作为食物的细菌后，并不将其完全吃掉，而是留下一部分作为“种子”，在集体迁徙时也带上这些“种子”，到达新地方后再进行“播种”，以收获更多细菌。研究人员在报告中风趣地称这些盘基网柄菌为“农民”。3 H5 G- c) c: o  [$ s

6 K, u- X& K$ S7 B2 M! z领导研究的德布拉·布罗克说，盘基网柄菌有很多种，研究只发现其中一部分具有这种行为。具有这种能力的盘基网柄菌在食物稀缺环境下要比其他同类更具竞争力。 4 [2 n; H' D! B4 Z) S# [
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Primitive agriculture in a social amoeba4 s4 ~" K7 E$ G- D" Q7 X
Debra A. Brock,Tracy E. Douglas,David C. Queller& Joan E. Strassmann
# [! M+ Y; l# g8 L* e! iNature Volume: 469, Pages: 393–396 Date published: (20 January 2011) DOI: doi:10.1038/nature09668 8 Q. w- @. J9 X4 X' R# p* e  F6 c2 C
http://www.nature.com/nature/jou ... ll/nature09668.html
. ?2 S4 C% ]3 Q/ D' `! |# C* h2 qAgriculture has been a large part of the ecological success of humans1. A handful of animals, notably the fungus-growing ants, termites and ambrosia beetles2, 3, 4, have advanced agriculture that involves dispersal and seeding of food propagules, cultivation of the crop and sustainable harvesting5. More primitive examples, which could be called husbandry because they involve fewer adaptations, include marine snails farming intertidal fungi6 and damselfish farming algae7. Recent work has shown that microorganisms are surprisingly like animals in having sophisticated behaviours such as cooperation, communication8, 9 and recognition10, 11, as well as many kinds of symbiosis12, 13, 14, 15. Here we show that the social amoeba Dictyostelium discoideum has a primitive farming symbiosis that includes dispersal and prudent harvesting of the crop. About one-third of wild-collected clones engage in husbandry of bacteria. Instead of consuming all bacteria in their patch, they stop feeding early and incorporate bacteria into their fruiting bodies. They then carry bacteria during spore dispersal and can seed a new food crop, which is a major advantage if edible bacteria are lacking at the new site. However, if they arrive at sites already containing appropriate bacteria, the costs of early feeding cessation are not compensated for, which may account for the dichotomous nature of this farming symbiosis. The striking convergent evolution between bacterial husbandry in social amoebas and fungus farming in social insects makes sense because multigenerational benefits of farming go to already established kin groups.
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演化过程
, ?6 {$ v0 ]9 u2 ^5 L7 NI、 单细胞生物群体行为（细菌菌落、真菌集落、原虫群落等）9 f: R; j5 d. Z/ T" f0 m
II、 多细胞生物组织行为（本帖的盘基网柄菌、大型真菌、粘虫、水螅、水母等）$ ]( R0 _3 R; Z+ k
III、高等生物组织器官分工（哺乳动物、禽类、鱼类等）
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