Distinct Patterns of Co-Evolution Among Protist Symbionts of Neoisoptera Termites

Obligate symbionts often exhibit some degree of co-speciation with their hosts. One prominent example is the symbiosis between termites and their wood-feeding hindgut protists. This symbiosis is mutually obligate, vertically inherited by anal feeding, and it predates the emergence of termites from their cockroach ancestors. Termites and their symbiotic protists might therefore be expected to have congruent phylogenies, but symbiont loss, transfer, and independent diversification can impact the coevolutionary history to varying degrees. Here, we have characterized the symbiotic protist communities of eight Neoisoptera species from three families in order to gauge the phylogenetic congruence between each lineage of protists and their hosts. Using microscopy and 18S rRNA gene sequencing of individually isolated protist cells, we identified protists belonging to the Parabasalia genera Pseudotrichonympha, Holomastigotoides, Cononympha, and Cthulhu. Pseudotrichonympha were present in all of the investigated termites, with a strong pattern of codiversification with hosts, consistent with previous studies. The phylogeny of Holomastigotoides indicates several instances of diversification that occurred independently of the hosts’ diversification, along with lineage-specific symbiont loss. Cononympha occurs only in Heterotermitidae and Psammotermes. Surprisingly, the small flagellate Cthulhu is widespread and exhibits cophylogeny with its hosts. This study demonstrates that different symbiont lineages can show different coevolutionary patterns, even within the same host.