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1. Termite Presence and Feeding on Loblolly Pine Wood Differs Among Four Root-Infecting Bluestain (ophiostomatoid) Fungal Species

   https://doi.org/10.1093/ee/nvab052  

   Clay, Natalie A; Siegert, Courtney; Tang, Juliet D; Little, Nathan S; Eckhardt, Lori G; Riggins, John J (June 2021, Environmental Entomology)

   Hajek, Ann (Ed.)

   Abstract Bark beetles and root weevils can impact forests through tree death on landscape scales. Recently, subterranean termites have been linked to these beetles via the presence of bluestain fungi (Ascomycota: Ophiostomataceae), which are vectored to trees by beetles. However, only a small subset of bluestain species have been examined. Here, we tested whether termite-bluestain association patterns in the field reflect termite feeding preference in laboratory choice trials. We documented the presence of four bluestain fungi (Leptographium procerum (W.B. Kendr.), L. terebrantis (Barras & Perry), Grosmannia huntii (Rob.-Jeffr.), and G. alacris (T.A. Duong, Z.W. de Beer & M.J. Wingf.) in the roots of 2,350 loblolly pine trees in the southeastern United States and whether termites were present or absent on these roots and paired this with laboratory choice feeding trials. Termites were found 2.5-fold on tree roots with at least one bluestain fungus present than tree roots without bluestain fungi. Although termites in this study and others were associated with L. procerum, L. terebrantis, and marginally G. huntii, termites only showed preferential feeding on wood inoculated with G. huntii in laboratory trials. This suggests that increased termite presence on wood with bluestain fungi may be driven by factors other than increased wood palatability. Termites could thus disproportionately affect wood turnover rates for specific pools (e.g., bark beetle and root weevil attacked trees) and in some cases (e.g., G. huntii) accelerate wood decomposition. This study supports the growing evidence that the association between subterranean termites and bluestain fungi is spatially and taxonomically widespread. 

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2. Assessing the Australian Termite Diversity Anomaly: How Habitat and Rainfall Affect Termite Assemblages

   https://doi.org/10.3389/fevo.2021.657444  

   Clement, Rebecca A.; Flores-Moreno, Habacuc; Cernusak, Lucas A.; Cheesman, Alexander W.; Yatsko, Abbey R.; Allison, Steven D.; Eggleton, Paul; Zanne, Amy E. (April 2021, Frontiers in Ecology and Evolution)

   null (Ed.)

   Termites are important ecosystem engineers in tropical habitats, with different feeding groups able to decompose wood, grass, litter, and soil organic matter. In most tropical regions, termite abundance and species diversity are assumed to increase with rainfall, with highest levels found in rainforests. However, in the Australian tropics, this pattern is thought to be reversed, with lower species richness and termite abundance found in rainforest than drier habitats. The potential mechanisms underlying this pattern remain unclear. We compared termite assemblages (abundance, activity, diversity, and feeding group composition) across five sites along a precipitation gradient (ranging from ∼800 to 4,000 mm annual rainfall), spanning dry and wet savanna habitats, wet sclerophyll, and lowland and upland rainforests in tropical North Queensland. Moving from dry to wet habitats, we observed dramatic decreases in termite abundance in both mounds and dead wood occupancy, with greater abundance and activity at savanna sites (low precipitation) compared with rainforest or sclerophyll sites (high precipitation). We also observed a turnover in termite species and feeding group diversity across sites that were close together, but in different habitats. Termite species and feeding group richness were highest in savanna sites, with 13 termite species from wood-, litter-, grass-, dung-, and soil-feeding groups, while only five termite species were encountered in rainforest and wet sclerophyll sites—all wood feeders. These results suggest that the Australian termite diversity anomaly may be partly driven by how specific feeding groups colonized habitats across Australia. Consequently, termites in Australian rainforests may be less important in ecosystem processes, such as carbon and nutrient cycling during decomposition, compared with termites in other tropical rainforests. 

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3. Coarse woody debris decomposition assessment tool: Model development and sensitivity analysis

   https://doi.org/10.1371/journal.pone.0251893  

   Dai, Zhaohua; Trettin, Carl C.; Burton, Andrew J.; Jurgensen, Martin F.; Page-Dumroese, Deborah S.; Forschler, Brian T.; Schilling, Jonathan S.; Lindner, Daniel L. (June 2021, PLOS ONE)

   Hui, Dafeng (Ed.)

   Coarse woody debris (CWD) is an important component in forests, hosting a variety of organisms that have critical roles in nutrient cycling and carbon (C) storage. We developed a process-based model using literature, field observations, and expert knowledge to assess woody debris decomposition in forests and the movement of wood C into the soil and atmosphere. The sensitivity analysis was conducted against the primary ecological drivers (wood properties and ambient conditions) used as model inputs. The analysis used eighty-nine climate datasets from North America, from tropical (14.2° N) to boreal (65.0° N) zones, with large ranges in annual mean temperature (26.5°C in tropical to -11.8°C in boreal), annual precipitation (6,143 to 181 mm), annual snowfall (0 to 612 kg m -2 ), and altitude (3 to 2,824 m above mean see level). The sensitivity analysis showed that CWD decomposition was strongly affected by climate, geographical location and altitude, which together regulate the activity of both microbial and invertebrate wood-decomposers. CWD decomposition rate increased with increments in temperature and precipitation, but decreased with increases in latitude and altitude. CWD decomposition was also sensitive to wood size, density, position (standing vs downed), and tree species. The sensitivity analysis showed that fungi are the most important decomposers of woody debris, accounting for over 50% mass loss in nearly all climatic zones in North America. The model includes invertebrate decomposers, focusing mostly on termites, which can have an important role in CWD decomposition in tropical and some subtropical regions. The role of termites in woody debris decomposition varied widely, between 0 and 40%, from temperate areas to tropical regions. Woody debris decomposition rates simulated for eighty-nine locations in North America were within the published range of woody debris decomposition rates for regions in northern hemisphere from 1.6° N to 68.3° N and in Australia. 

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4. Wood fibers are a crucial microhabitat for cellulose- and xylan- degrading bacteria in the hindgut of the wood-feeding beetle Odontotaenius disjunctus

   https://doi.org/10.3389/fmicb.2023.1173696  

   Schwarz, Melbert; Beza-Beza, Cristian F.; Mikaelyan, Aram (June 2023, Frontiers in Microbiology)

   IntroductionWood digestion in insects relies on the maintenance of a mosaic of numerous microhabitats, each colonized by distinct microbiomes. Understanding the division of digestive labor between these microhabitats- is central to understanding the physiology and evolution of symbiotic wood digestion. A microhabitat that has emerged to be of direct relevance to the process of lignocellulose digestion is the surface of ingested plant material. Wood particles in the guts of some termites are colonized by a specialized bacterial fiber-digesting microbiome, but whether this represents a widespread strategy among insect lineages that have independently evolved wood-feeding remains an open question. MethodsIn this study, we investigated the bacterial communities specifically associated with wood fibers in the gut of the passalid beetleOdontotaenius disjunctus. We developed a Percoll-based centrifugation method to isolate and enrich the wood particles from the anterior hindgut, allowing us to access the wood fibers and their associated microbiome. We then performed assays of enzyme activity and used short-read and long-read amplicon sequencing of the 16S rRNA gene to identify the composition of the fiber-associated microbiome. ResultsOur assays demonstrated that the anterior hindgut, which houses a majority of the bacterial load, is an important site for lignocellulose digestion. Wood particles enriched from the anterior hindgut contribute to a large proportion of the total enzyme activity. The sequencing revealed thatO. disjunctus, like termites, harbors a distinct fiber-associated microbiome, but notably, its community is enriched in insect-specific groups ofLactococcusandTuricibacter. DiscussionOur study underscores the importance of microhabitats in fostering the complex symbiotic relationships between wood-feeding insects and their microbiomes. The discovery of distinct fiber-digesting symbionts inO. disjunctus, compared to termites, highlights the diverse evolutionary paths insects have taken to adapt to a challenging diet. 

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5. Protist symbionts of termites: diversity, distribution, and coevolution

   https://doi.org/10.1111/brv.13038  

   Gile, Gillian H. (December 2023, Biological Reviews)

   ABSTRACT 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. 

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