Vogel Kevin J, Moran Nancy A
Department of Ecology and Evolutionary Biology, Biological Sciences West, Room 301, 1041 E. Lowell St., The University of Arizona, Tucson, AZ 85721-0088, USA.
EEB West Campus, Yale University, PO Box 27388, West Haven, CT 06516-7388, USA.
Insects. 2011 Sep 16;2(3):423-34. doi: 10.3390/insects2030423.
Obligate nutritional symbioses require balance between the energetic needs of the host and the symbiont. The resident symbiont population size within a host may have major impacts on host fitness, as both host and symbiont consume and supply metabolites in a shared metabolite pool. Given the massive genome degradation that is a hallmark of bacterial endosymbionts of insects, it is unclear at what level these populations are regulated, and how regulation varies among hosts within natural populations. We measured the titer of the endosymbiont Buchnera aphidicola from different clones of the pea aphid, Acyrthosiphon pisum, and found significant variation in titer, measured as Buchnera genomes per aphid genome, among aphid clones. Additionally, we found that titer can change with the age of the host, and that the number of bacteriocytes within an aphid is one factor likely controlling Buchnera titer. Buchnera titer measurements in clones from a sexual cross indicate that the symbiont genotype is not responsible for variation in titer and that this phenotype is likely non-heritable across sexual reproduction. Symbiont titer is more variable among lab-produced F₁ aphid clones than among field-collected ones, suggesting that intermediate titer is favored in natural populations. Potentially, a low heritability of titer during the sexual phase may generate clones with extreme and maladaptive titers each season.
专性营养共生需要宿主和共生体的能量需求之间保持平衡。宿主内共生体的种群数量可能对宿主健康产生重大影响，因为宿主和共生体都在一个共享的代谢物池中消耗和供应代谢物。鉴于大规模的基因组降解是昆虫细菌内共生体的一个标志，目前尚不清楚这些种群在何种水平上受到调控，以及自然种群中不同宿主之间的调控方式如何变化。我们测量了豌豆蚜不同克隆体中内共生菌蚜虫内共生菌的滴度，发现以每个蚜虫基因组中的蚜虫内共生菌基因组数来衡量，不同蚜虫克隆体的滴度存在显著差异。此外，我们发现滴度会随着宿主年龄的变化而改变，并且蚜虫体内含菌细胞的数量是可能控制蚜虫内共生菌滴度的一个因素。对有性杂交克隆体中蚜虫内共生菌滴度的测量表明，共生体基因型与滴度变化无关，并且这种表型在有性繁殖过程中可能不可遗传。与田间采集到的蚜虫克隆体相比，实验室培育的F₁蚜虫克隆体中的共生体滴度变化更大，这表明中等滴度在自然种群中更受青睐。在有性阶段，滴度的低遗传性可能会导致每个季节产生具有极端和适应不良滴度的克隆体。
