Pattern of specificity in the tripartite symbiosis between Barteria plants, ants and Chaetothyriales fungi

Abstract

The two sympatric ant-plant sister species Barteria fistulosa and B. dewevrei have hollow branches (called domatia) in which ants nest. Each plant is colonized by a single colony of one of three ant species, Tetraponera aethiops, T. latifrons or Crematogaster sp. In addition, two sister strains of Chaetothyriales fungi can also be hosted within domatia of these Barteria. To test for association specificity between the three types of partners we investigated the association pattern in two localities, Kessala and Bigoundou, in Gabon. Plants and ants were identified by morphology and fungi by molecular typing. In Kessala we found a preferential association between B. fistulosa, T. aethiops and the fungal strain Y1 on the one hand, and B. dewevrei, T. latifrons and the fungal strain Y9 on the other hand. Crematogaster ants were found in B. dewevrei, in plants that had smaller domatia than those colonized by Tetraponera. In Bigoundou we found mostly B. fistulosa, which were mostly colonized by T. aethiops. However, the two fungal strains were equally represented. This tripartite symbiosis shows association specificity, the pattern of which can vary across sites. Association specificity and site variation are probably related to ecological conditions but these still need to be identified.