Oliver Kerry M, Moran Nancy A, Hunter Martha S
Department of Entomology, University of Arizona, 410 Forbes Building, Tucson, AZ 85721, USA.
Proc Biol Sci. 2006 May 22;273(1591):1273-80. doi: 10.1098/rspb.2005.3436.
Symbiotic associations between animals and inherited micro-organisms are widespread in nature. In many cases, hosts may be superinfected with multiple inherited symbionts. Acyrthosiphon pisum (the pea aphid) may harbour more than one facultative symbiont (called secondary symbionts) in addition to the obligate primary symbiont, Buchnera aphidicola. Previously we demonstrated that, in a controlled genetic background, A. pisum infected with either Serratia symbiotica or Hamiltonella defensa (called R- and T-type in that study) were more resistant to attack by the parasitoid Aphidius ervi. Here, we examined the consequences of A. pisum superinfected with both resistance-conferring symbionts. We found that an A. pisum line co-infected with both S. symbiotica and H. defensa symbionts exhibits even greater resistance to parasitism by A. ervi than either of the singly infected lines. Despite this added benefit to resistance, superinfections of S. symbiotica and H. defensa symbionts appeared rare in our survey of Utah A. pisum symbionts, which is probably attributable to severe fecundity costs. Quantitative polymerase chain reaction estimates indicate that while the density of H. defensa is similar in singly and superinfected hosts, S. symbiotica densities increased dramatically in superinfected hosts. Over-proliferation of symbionts or antagonistic interactions between symbionts may be harmful to the aphid host. Our results indicate that in addition to host-symbiont interactions, interactions among the symbionts themselves probably play a critical role in determining the distributions of symbionts in natural populations.
动物与遗传微生物之间的共生关系在自然界中广泛存在。在许多情况下，宿主可能会被多种遗传共生体重复感染。豌豆蚜（Acyrthosiphon pisum）除了专性初级共生体蚜虫内共生菌（Buchnera aphidicola）外，可能还携带有不止一种兼性共生体（在该研究中称为次级共生体）。此前我们证明，在可控的遗传背景下，感染了共生致病杆菌（Serratia symbiotica）或防御汉氏菌（Hamiltonella defensa）（在该研究中分别称为R型和T型）的豌豆蚜对寄生蜂豌豆蚜茧蜂（Aphidius ervi）的攻击具有更强的抵抗力。在此，我们研究了豌豆蚜被两种赋予抗性的共生体重复感染的后果。我们发现，同时感染共生致病杆菌和防御汉氏菌的豌豆蚜品系对豌豆蚜茧蜂寄生的抵抗力比单一感染的品系更强。尽管这种抗性有额外的益处，但在我们对犹他州豌豆蚜共生体的调查中，共生致病杆菌和防御汉氏菌的重复感染似乎很少见，这可能是由于严重的繁殖成本所致。定量聚合酶链反应估计表明，虽然防御汉氏菌在单一感染和重复感染宿主中的密度相似，但共生致病杆菌在重复感染宿主中的密度显著增加。共生体的过度增殖或共生体之间的拮抗相互作用可能对蚜虫宿主有害。我们的结果表明，除了宿主 - 共生体相互作用外，共生体自身之间的相互作用可能在决定自然种群中共生体的分布方面起着关键作用。
