Rio Rita V M, Wu Yi-Neng, Filardo Giovanni, Aksoy Serap
Department of Epidemiology and Public Health, Yale University School of Medicine, 606 LEPH, New Haven CT 06510, USA.
Proc Biol Sci. 2006 Apr 7;273(1588):805-14. doi: 10.1098/rspb.2005.3399.
Symbiotic associations often enhance hosts' physiological capabilities, allowing them to expand into restricted terrains, thus leading to biological diversification. Stable maintenance of partners is essential for the overall biological system to succeed. The viviparous tsetse fly (Diptera: Glossinidae) offers an exceptional system to examine factors that influence the maintenance of multiple symbiotic organisms within a single eukaryotic host. This insect harbours three different symbionts representing diverse associations, coevolutionary histories and transmission modes. The enterics, obligate mutualist Wigglesworthia and beneficial Sodalis, are maternally transmitted to the intrauterine larvae, while parasitic Wolbachia infects the developing oocyte. In this study, the population dynamics of these three symbionts were examined through host development and during potentially disruptive events, including host immune challenge, the presence of third parties (such as African trypanosomes) and environmental perturbations (such as fluctuating humidity levels). While mutualistic partners exhibited well-regulated density profiles over different host developmental stages, parasitic Wolbachia infections varied in individual hosts. Host immune status and the presence of trypanosome infections did not impact the steady-state density levels observed for mutualistic microbes in either sex, while these factors resulted in an increase in Wolbachia density in males. Interestingly, perturbation of the maternal environment resulted in the deposition of progeny harbouring greater overall symbiont loads. The regulation of symbiont density, arising from coadaptive processes, may be an important mechanism driving inter-specific relations to ensure their competitive survival and to promote specialization of beneficial associations.
共生关系通常会增强宿主的生理能力，使其能够拓展到受限的生存环境中，从而导致生物多样性的增加。伙伴之间的稳定维持对于整个生物系统的成功至关重要。胎生采采蝇（双翅目：舌蝇科）提供了一个独特的系统，可用于研究影响单个真核宿主内多种共生生物维持的因素。这种昆虫携带着三种不同的共生体，它们代表了不同的共生关系、共同进化历史和传播方式。肠道共生体、专性互利共生菌维氏菌和有益菌索氏菌通过母体传递给子宫内的幼虫，而寄生性沃尔巴克氏体则感染发育中的卵母细胞。在本研究中，通过宿主发育过程以及在潜在的干扰事件期间，包括宿主免疫挑战、第三方（如非洲锥虫）的存在和环境扰动（如湿度水平波动），对这三种共生体的种群动态进行了研究。虽然互利共生伙伴在不同宿主发育阶段表现出调控良好的密度分布，但寄生性沃尔巴克氏体感染在个体宿主中存在差异。宿主免疫状态和锥虫感染的存在对两性中互利共生微生物的稳态密度水平均无影响，而这些因素导致雄性中沃尔巴克氏体密度增加。有趣的是，母体环境的扰动导致携带更高总体共生体负荷的后代的产生。由共同适应过程产生的共生体密度调控可能是驱动种间关系以确保其竞争性生存并促进有益共生关系专业化的重要机制。
