Vertically transmitted bacterivorous nematodes are consistent nest inhabitants in the Azteca-Cecropia ant-plant mutualism

Nematodes play key roles in natural and agricultural ecosystems. They contribute to organic matter transformation and the stability of soil food webs. Beyond their free-living forms, many nematode lineages have evolved in close associations with insects, ranging from mutualistic and commensal to parasitic interactions. Recent studies have revealed that nematodes are common in tropical ant–plant mutualisms and are particularly relevant in ant-made organic matter piles, or “patches”, within ant nests. To investigate nematode community dynamics during ant colony growth and their consistency across closely related ant species, we analysed patches from 65 ant colonies of the Azteca-Cecropia ant-plant mutualism using 18S rRNA metabarcoding combined with morphology-based quantification methods. Bacterivorous nematodes from the order Rhabditida were present in all samples, regardless of the ant or plant species and the colony developmental stage. Members of Tylenchida and Dorylaimida were also detected, though sporadically. Our results support the previously proposed vertical transmission of bacterivorous nematodes from mother to daughter colonies as well as horizontal transmission among patches within the same ant colony. Moreover, nematode community composition remained stable throughout colony development but varied between ant species. These findings demonstrate that nematodes constitute a persistent and functionally important component of this ant–plant mutualism.