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The symbiosis between termites and their hindgut protists is mutually obligate and vertically inherited. It was established by the late Jurassic in the cockroach ancestors of termites as they transitioned to wood feeding. Since then, protist symbionts have been transmitted from host generation to host generation by proctodeal trophallaxis (anal feeding). The protists belong to multiple lineages within the eukaryotic superphylum Metamonada. Most of these lineages have evolved large cells with complex morphology, unlike the non‐termite‐associated Metamonada. The species richness and taxonomic composition of symbiotic protist communities varies widely across termite lineages, especially within the deep‐branching clade Teletisoptera. In general, closely related termites tend to harbour closely related protists, and deep‐branching termites tend to harbour deep‐branching protists, reflecting their broad‐scale co‐diversification. A closer view, however, reveals a complex distribution of protist lineages across hosts. Some protist taxa are common, some are rare, some are widespread, and some are restricted to a single host family or genus. Some protist taxa can be found in only a few, distantly related, host species. Thus, the long history of co‐diversification in this symbiosis has been complicated by lineage‐specific loss of symbionts, transfer of symbionts from one host lineage to another, and by independent diversification of the symbionts relative to their hosts. This review aims to introduce the biology of this important symbiosis and serve as a gateway to the diversity and systematics literature for both termites and protists. A searchable database with all termite‐protist occurrence records and taxonomic references is provided as a supplementary file to encourage and facilitate new research in this field. [ABSTRACT FROM AUTHOR]

Aim We analysed data from an insect host ( Cryptocercus punctulatus) and its maternally-inherited obligate bacterial endosymbiont ( Blattabacterium cuenoti str . punctulatus) to address the following: (1) to what extent do these species exhibit cophylogenetic structure, (2) do the spatial-genetic structures of these species differ, and (3) what is the relative importance of codivergence versus other events in explaining congruence, or instances of incongruence, between their molecular phylogenies? Location The southern Appalachian Mountains, USA. Methods We conducted fine-scale population-level sampling and screening of DNA sequence variation in two mitochondrial genes from the host, and four genic or intergenic regions from the endosymbiont. Inferences were made using analyses that have the potential to identify isolated instances of cophylogenetic discord, uncover subtle differences in geographic locations of genetic discontinuities, and disentangle different evolutionary processes that contributed to observed patterns. Results The host and its endosymbiont showed similar phylogenetic and geographic patterns. Cophylogenetic analyses revealed that while topological discord is rare (and restricted within major clades), some instances are potentially non-negligible. Assessments of spatial-genetic structure showed that most abrupt breaks occur in the same locations, but they differ in strength, again underscoring some subtle discordance. The main process generating observed patterns was inferred to be codivergence due to host-tracking; however, incomplete lineage sorting seems likely to have also played a minor role. Main conclusions Our overarching finding of strong congruence is reflected by broader-scale cophylogenetic studies of related Cryptocercus and Blattabacterium taxa. Accordingly, we suggest that members of this symbiosis may provide an excellent opportunity for investigating geographic scaling of processes that affect biogeographic patterns. However, fine-scale sampling coupled with geospatial analyses detected rare and/or minor discordances that appeared to be localized within the most deeply dissected topographic regions of the southern Appalachian Mountains, and these warrant further exploration. [ABSTRACT FROM AUTHOR]

Basal termites possess two developmental features that eusocial Hymenoptera lack: the majority of colony members are juveniles whose somatic and reproductive development is temporarily or permanently suspended, and individual development is characterized by extreme phenotypic plasticity. An examination of the literature indicates that the basis for these unique ontogenetic characters is not the prolongation of a pronymphal stage into postembryonic development, as recently suggested. Like other hemimetabolous insects, termites have three embryonic cuticles, and the pronymphal (EC3) cuticle is shed during or shortly after hatch. Nonetheless, a different developmental landmark, dorsal closure, occurs later during embryogenesis in termites than it does in their cockroach relatives, clearly indicating ontogenetic repatterning from an ancestral state. An alternate hypothesis for the origin of isopteran phenotypic plasticity becomes apparent if we remain focused on the phylogenetic and social context of termite evolution. Altricial development occurs in both vertebrate and invertebrate taxa, evolves in response to the parental environment, and is displayed by two distantly related, biparental, wood-feeding cockroaches, including Cryptocercus, the sister-group to termites. It is therefore likely the condition was present in subsocial termite ancestors, and played a complex, multidimensional role in the transition to eusociality. Most relevant to current arguments is that a shift in responsibility for the care of altricial dependents, from parents to the first nutritionally independent nymphs in the family (alloparents), resulted in the developmental stasis of alloparents at a relatively young age. Because early instar cockroaches are not metamorphically competent, these young alloparents would have provided a novel developmental template on which selection could act. [ABSTRACT FROM AUTHOR]

Trichonympha is one of the most complex and visually striking of the hypermastigote parabasalids—a group of anaerobic flagellates found exclusively in hindguts of lower termites and the wood-feeding cockroach Cryptocercus—but it is one of only two genera common to both groups of insects. We investigated Trichonympha of Cryptocercus using light and electron microscopy (scanning and transmission), as well as molecular phylogeny, to gain a better understanding of its morphology, diversity, and evolution. Microscopy reveals numerous new features, such as previously undetected bacterial surface symbionts, adhesion of post-rostral flagella, and a distinctive frilled operculum. We also sequenced small subunit rRNA gene from manually isolated species, and carried out an environmental polymerase chain reaction (PCR) survey of Trichonympha diversity, all of which strongly supports monophyly of Trichonympha from Cryptocercus to the exclusion of those sampled from termites. Bayesian and distance methods support a relationship between Trichonympha species from termites and Cryptocercus, although likelihood analysis allies the latter with Eucomonymphidae. A monophyletic Trichonympha is of great interest because recent evidence supports a sister relationship between Cryptocercus and termites, suggesting Trichonympha predates the Cryptocercus-termite divergence. The monophyly of symbiotic bacteria of Trichonympha raises the intriguing possibility of three-way co-speciation among bacteria, Trichonympha, and insect hosts. [ABSTRACT FROM AUTHOR]

Nitrogen fixation by gut microorganisms is one of the crucial aspects of symbiosis in wood-feeding termites since these termites thrive on a nitrogen-poor diet. In order to understand the evolution of this symbiosis, we analysed the nitrogenase structural gene nifH in the gut microbial communities. In conjunction with the published sequences, we compared approximately 320 putatively functional NifH protein sequences obtained from a total of 19 termite samples that represent all the major branches of their currently proposed phylogeny, and from one species of the cockroach Cryptocercus that shares a common ancestor with termites. Using multivariate techniques for clustering and ordination, a phylogeny of NifH protein sequences was created and plotted variously with host termite families, genera, and species. Close concordance was observed between NifH communities and the host termites at genus level, but family level relationships were not always congruent with accepted termite clade structure. Host groups examined included basal families (Mastotermitidae, Termopsidae, Kalotermitidae, as well as Cryptocercus), the most derived lower termite family Rhinotermitidae, and subfamilies representing the advanced and highly diverse apical family Termitidae (Macrotermitinae, Termitinae, and Nasutitermitinae). This selection encompassed the major nesting and feeding styles recognized in termites, and it was evident that NifH phylogenetic divergence, as well as the occurrence of alternative nitrogenase-type NifH, was to some extent dependent on host lifestyle as well as phylogenetic position. [ABSTRACT FROM AUTHOR]