Data_Sheet_1_Olfactory System Morphology Suggests Colony Size Drives Trait Evolution in Odorous Ants (Formicidae: Dolichoderinae).docx

In social insects colony fitness is determined in part by individual worker phenotypes. Across ant species, colony size varies greatly and is thought to affect worker trait variation in both proximate and ultimate ways. Little is known about the relationship between colony size and worker trait evolution, but hypotheses addressing the role of social structure in brain evolution suggest workers of small-colony species may have larger brains or larger brain regions necessary for complex behaviors. In previous work on odorous ants (Formicidae: Dolichoderinae) we found no correlation between colony size and these brain properties, but found that relative antennal lobe size scaled negatively with colony size. Therefore, we now test whether sensory systems scale with colony size, with particular attention to olfactory components thought to be involved in nestmate recognition. Across three species of odorous ants, Forelius mccooki, Dorymyrmex insanus, and D. bicolor, which overlap in habitat and foraging ecology but vary in colony size, we compare olfactory sensory structures, comparing those thought to be involved in nestmate recognition. We use the visual system, a sensory modality not as important in social communication in ants, as a control comparison. We find that body size scaling largely explains differences in eye size, antennal length, antennal sensilla density, and total number of olfactory glomeruli across these species. However, sensilla basiconica and olfactory glomeruli in the T6 cluster of the antennal lobe, structures known to be involved in nestmate recognition, do not follow body size scaling observed for other structures. Instead, we find evidence from the closely related Dorymyrmex species that the larger colony species, D. bicolor, invests more in structures implicated in nestmate recognition. To test for functional consequences, we compare nestmate and non-nestmate interactions between these two species and find D. bicolor pairs of either type engage in more interactions than D. insaus pairs. Thus, we do not find evidence supporting a universal pattern of sensory system scaling associated with changes in colony size, but hypothesize that observed differences in the olfactory components in two closely related Dorymyrmex species are evidence of a link between colony size and sensory trait evolution.

在社群昆虫的群落中，个体工蚁的表型特征在一定程度上决定了群落的适应性。在蚂蚁物种之间，群落的规模存在显著差异，且普遍认为这会在近端和终极层面上影响工蚁性状的变异。关于群落规模与工蚁性状进化的关系知之甚少，但关于社会结构在脑进化中作用的假设提出，小型群落物种的工蚁可能拥有更大的脑部或更大的脑区，这些脑区对于复杂行为是必需的。在先前对有气味的蚂蚁（Formicidae: Dolichoderinae）的研究中，我们发现群落规模与这些脑部特性之间没有相关性，但发现相对触角叶的大小与群落规模呈负相关。因此，我们现在检验感官系统是否与群落规模成比例，特别是关注被认为涉及同巢识别的嗅觉成分。在三种有气味的蚂蚁物种——Forelius mccooki、Dorymyrmex insanus 和 D. bicolor 中，这些物种在栖息地和觅食生态学上存在重叠，但在群落规模上存在差异，我们比较了嗅觉感官结构，特别是那些被认为涉及同巢识别的结构。我们将视觉系统，在蚂蚁的社会交流中并不那么重要的感官模态，作为对照比较。我们发现，身体大小比例在很大程度上解释了这些物种之间眼睛大小、触角长度、触角感毛密度和嗅觉球体总数的差异。然而，已知参与同巢识别的触角叶T6簇中的感毛基锥和嗅觉球体并不遵循其他结构观察到的身体大小比例。相反，我们从密切相关的 Dorymyrmex 物种中找到证据，表明大型群落物种 D. bicolor 在涉及同巢识别的结构上投入更多。为了测试功能后果，我们比较了这两种物种的同巢和非同巢之间的互动，发现 D. bicolor 的任意一对都比 D. insanus 的对参与更多的互动。因此，我们没有发现支持与群落规模变化相关的感官系统比例普遍模式的证据，但假设在两个密切相关的 Dorymyrmex 物种中观察到的嗅觉成分差异是群落规模与感官性状进化之间联系的证据。