Kelber Christina, Rössler Wolfgang, Roces Flavio, Kleineidam Christoph Johannes
Department of Behavioral Physiology and Sociobiology, Biozentrum, University of Wurzburg, Wurzburg, Germany.
Brain Behav Evol. 2009;73(4):273-84. doi: 10.1159/000230672. Epub 2009 Jul 29.
Ants of the tribe Attini are characterized by their obligate cultivation of symbiotic fungi. In addition to the complex chemical communication system of ants in general, substrate selection and fungus cultivation pose high demands on the olfactory system of the Attini. Indeed, behavioral studies have shown a rich diversity of olfactory-guided behaviors and tremendous odor sensitivity has been demonstrated. To allow fine-tuned behavioral responses, adaptations within the olfactory system of the Attini are expected. We compared the number, volumes and position of the glomeruli (functional units) of the antennal lobe of 25 different species from all three major Attini groups (lower, higher and leaf-cutting Attini). The antennal lobes of all investigated Attini comprise a high number of glomeruli (>257). The highest number (630) was found in Apterostigma cf. mayri. This species is at a basal position within the Attini phylogeny, and we suggest that a high number of glomeruli might have been advantageous in the evolution of the advanced olfactory systems of the Attini. In the leaf-cutting Attini, an extremely large glomerulus (macroglomerulus) near the antennal nerve entrance was recently described in two species. Preliminary results show that this macroglomerulus is involved in processing of trail-pheromone information. In our comparative study, we find this macroglomerulus in all investigated leaf-cutting Attini, but in none of the lower and higher Attini species. It is found only in large workers, and for all investigated species it is located close to the entrance of the antennal nerve. Our results indicate that the presence of a macroglomerulus in large workers of leaf-cutting Attini is a derived over-expression of a trait in the polymorphic leaf-cutting species. It presumably represents an olfactory adaptation to elaborate foraging and mass recruitment systems, and adds to the complexity of division of labor and social organization known for this group.
Attini族蚂蚁的特点是专一地培育共生真菌。除了蚂蚁普遍具有的复杂化学通讯系统外，基质选择和真菌培育对Attini族蚂蚁的嗅觉系统提出了很高的要求。事实上，行为研究表明，它们具有丰富多样的嗅觉引导行为，并且已证明其具有极高的气味敏感性。为了实现精细调节的行为反应，预计Attini族蚂蚁的嗅觉系统会有适应性变化。我们比较了来自Attini族所有三个主要群体（低等、高等和切叶蚁Attini）的25个不同物种触角叶中神经小球（功能单位）的数量、体积和位置。所有被研究的Attini族蚂蚁的触角叶都包含大量的神经小球（>257个）。在近似迈氏无刺蚁（Apterostigma cf. mayri）中发现的神经小球数量最多（630个）。该物种处于Attini族系统发育的基部位置，我们认为大量的神经小球可能在Attini族先进嗅觉系统的进化中具有优势。在切叶蚁Attini中，最近在两个物种中描述了触角神经入口附近有一个极大的神经小球（大神经球）。初步结果表明，这个大神经球参与追踪信息素信息的处理。在我们的比较研究中，我们在所有被研究的切叶蚁Attini中都发现了这个大神经球，但在低等和高等Attini物种中均未发现。它仅在大型工蚁中发现，并且对于所有被研究的物种，它都位于触角神经入口附近。我们的结果表明，切叶蚁Attini大型工蚁中存在大神经球是该多态切叶蚁物种中一种性状的衍生过度表达。它可能代表了一种嗅觉适应，以适应精细的觅食和大规模招募系统，并增加了该群体已知的劳动分工和社会组织的复杂性。
