Bracewell Ryan R, Six Diana L
Department of Ecosystem and Conservation Sciences The University of Montana 32 Campus Drive Missoula Montana 59812.
Ecol Evol. 2015 Oct 19;5(21):5109-19. doi: 10.1002/ece3.1772. eCollection 2015 Nov.
The importance of symbiotic microbes to insects cannot be overstated; however, we have a poor understanding of the evolutionary processes that shape most insect-microbe interactions. Many bark beetle (Coleoptera: Curculionidae, Scolytinae) species are involved in what have been described as obligate mutualisms with symbiotic fungi. Beetles benefit through supplementing their nutrient-poor diet with fungi and the fungi benefit through gaining transportation to resources. However, only a few beetle-fungal symbioses have been experimentally manipulated to test whether the relationship is obligate. Furthermore, none have tested for adaptation of beetles to their specific symbionts, one of the requirements for coevolution. We experimentally manipulated the western pine beetle-fungus symbiosis to determine whether the beetle is obligately dependent upon fungi and to test for fine-scale adaptation of the beetle to one of its symbiotic fungi, Entomocorticium sp. B. We reared beetles from a single population with either a natal isolate of E. sp. B (isolated from the same population from which the beetles originated), a non-natal isolate (a genetically divergent isolate from a geographically distant beetle population), or with no fungi. We found that fungi were crucial for the successful development of western pine beetles. We also found no significant difference in the effects of the natal and non-natal isolate on beetle fitness parameters. However, brood adult beetles failed to incorporate the non-natal fungus into their fungal transport structure (mycangium) indicating adaption by the beetle to particular genotypes of symbiotic fungi. Our results suggest that beetle-fungus mutualisms and symbiont fidelity may be maintained via an undescribed recognition mechanism of the beetles for particular symbionts that may promote particular associations through time.
共生微生物对昆虫的重要性再怎么强调也不为过；然而，我们对塑造大多数昆虫与微生物相互作用的进化过程却知之甚少。许多树皮甲虫（鞘翅目：象甲科，小蠹亚科）物种参与了与共生真菌的所谓专性互利共生关系。甲虫通过利用真菌补充其营养匮乏的食物而受益，而真菌则通过甲虫获得资源运输而受益。然而，只有少数甲虫 - 真菌共生关系经过实验操作来测试这种关系是否是专性的。此外，还没有人测试甲虫是否适应其特定的共生体，这是协同进化的要求之一。我们通过实验操作西部松小蠹 - 真菌共生关系，以确定甲虫是否绝对依赖真菌，并测试甲虫对其一种共生真菌Entomocorticium sp. B的精细尺度适应性。我们从单个种群中饲养甲虫，分别与E. sp. B的本地分离株（从甲虫起源的同一种群中分离）、非本地分离株（来自地理上遥远的甲虫种群的遗传上不同的分离株）或不与真菌一起饲养。我们发现真菌对西部松小蠹的成功发育至关重要。我们还发现本地和非本地分离株对甲虫适合度参数的影响没有显著差异。然而，育雏成虫未能将非本地真菌纳入其真菌运输结构（菌囊），这表明甲虫对共生真菌的特定基因型具有适应性。我们的结果表明，甲虫 - 真菌互利共生关系和共生体保真度可能通过甲虫对特定共生体的一种未描述的识别机制得以维持，这种机制可能随着时间推移促进特定的关联。
