Table_1_Body Size and Symmetry Properties of Termite Soldiers Under Two Intraspecific Competition Scenarios.XLSX

Single-piece nesting termites live and forage in the same piece of wood throughout their life, which limit their colony size. In certain species, more than one colony thrive in a given piece of wood (multicolonial substrate) and intraspecific competition become important in this limited resource, as has been reported in Zootermopsis nevadensis (Hagen, 1858) and Neotermes chilensis (Blattodea: Kalotermitidae) (Blanchard, 1851). The effects of such competition have been described mainly at population and colony levels rather than at the individual level. In eusocial insects such as termites, intraspecific competition constitutes a stress factor imposed to a colony as a whole and should also cause developmental instability in soldiers produced under such conditions. Investment in the production of soldiers involves a trade-off between colony maintenance costs and defense benefits. Hence, we hypothesize that body size and fluctuating asymmetry, two indicators of developmental instability, will increase when two or more colonies of N. chilensis share a piece of wood (high intraspecific competition scenario). Our results showed that soldiers developing in multicolonial substrates were indeed larger and more asymmetric than soldiers developing in unicolonial substrates. The large body size in a soldier could improve its chance to win a physical contest with a non-nestmate opponent; thus, despite the high cost to produce large soldiers in small colonies, larger soldier production could be an adaptative strategy to avoid being outcompeted. However, the effects of deviations from perfect symmetry on soldier performance are not clear.

单块木材栖居的白蚁终其一生都在同一块木材中筑巢与觅食，这一特性限制了其种群规模。在部分物种中，单块木材内可存活多个蚁群（多蚁群基质，multicolonial substrate），此时种内竞争（intraspecific competition）在这一有限资源环境中变得至关重要，这一点已在新等白蚁（Zootermopsis nevadensis，Hagen, 1858）与智利新白蚁（Neotermes chilensis，Blattodea: Kalotermitidae，Blanchard, 1851）的相关研究中得到证实。目前针对这类种内竞争的研究多聚焦于种群与蚁群层面，而非个体层面。在白蚁这类真社会性昆虫（eusocial insects）中，种内竞争会作为整体应激因子作用于蚁群，同时也会导致在此条件下产生的兵蚁出现发育不稳定现象。兵蚁的生产投入需要在蚁群维持成本与防御收益之间进行权衡。因此我们提出假说：当智利新白蚁的两个或更多蚁群共享一块木材时（即高种内竞争场景），作为发育不稳定两项指标的体型大小与波动不对称（fluctuating asymmetry）程度均会上升。研究结果显示，在多蚁群共存基质中发育的兵蚁，其体型确实比单蚁群基质中的兵蚁更大，不对称程度也更高。兵蚁体型较大可提升其与非巢伴对手进行物理对抗时的获胜概率；因此，尽管小型蚁群生产大型兵蚁的成本高昂，但增加大型兵蚁的产出或许是一种避免被竞争淘汰的适应性策略。然而，完美对称性偏差对兵蚁功能表现的影响目前仍不明确。