Image: Cryptocercus punctulatus © Nancy Moran.
Host-specific assemblages typify gut microbial communities of related insect species
Zakee L Sabree and Nancy A Moran. 2014. Springer Plus 3: 138. DOI: 10.1186/2193-1801-3-138
Abstract Mutualisms between microbes and insects are ubiquitous and facilitate exploitation of various trophic niches by host insects. Dictyopterans (mantids, cockroaches and termites) exhibit trophisms that range from omnivory to strict wood-feeding and maintain beneficial symbioses with the obligate endosymbiont, Blattabacterium, and/or diverse gut microbiomes that include cellulolytic and diazotrophic microbes. While Blattabacterium in omnivorous Periplaneta is fully capable of provisioning essential amino acids, in wood-feeding dictyopterans it has lost many genes for their biosynthesis (Mastotermes and Cryptocercus) or is completely absent (Heterotermes). The conspicuous functional degradation and absence of Blattabacterium in strict wood-feeding dictyopteran insects suggest that alternative means of acquiring nutrients limited in their diet are being employed. A 16S rRNA gene amplicon resequencing approach was used to deeply sample the composition and diversity of gut communities in related dictyopteran insects to explore the possibility of shifts in symbiont allegiances during termite and cockroach evolution. The gut microbiome of Periplaneta, which has a fully functional Blattabacterium, exhibited the greater within-sample OTU diversity and abundance variability than those of Mastotermes and Cryptocercus, whose Blattabacterium have reduced nutrient provisioning capabilities. Heterotermes lacks Blattabacterium and a single operational taxonomic unit that was 95% identical to a Bacteroidia-assigned diazotrophic endosymbiont of an anaerobic cellulolytic protist termite gut inhabitant samples consistently dominates its gut microbiome. Many host-specific OTUs were identified in all host genera, some of which had not been previously detected, indicating that deep sampling by pyrotag sequencing has revealed new taxa that remain to be functionally characterized. Further analysis is required to uncover how consistently detected taxa in the cockroach and termite gut microbiomes, as well as the total community, contribute to host diet choice and impact the fate of Blattabacterium in dictyopterans.
Effects of watershed land use on sources and nutritional value of particulate organic matter in temperate headwater streams
Yue Han Lu, Elizabeth A. Canuel, James E. Bauer, R. M. Chambers. 2014. Aquatic Sciences in press. DOI: 10.1007/s00027-014-0344-9
Abstract Suspended particulate organic matter (POM) in headwater streams is an important source of food and energy to stream food webs. In order to determine the effects of watershed land use on the sources and characteristics of POM, we compared the lipid composition of POM (fatty acid, aliphatic alcohol and sterol) from streams influenced by different types of watershed land use. Eight first-order streams discharging to the York River Estuary (Virginia, USA) were sampled during baseflow conditions bi-monthly from February to November 2009, including streams draining forest-dominated, pasture-dominated, cropland-dominated, and urban land-dominated watersheds. Allochthonous vs. autochthonous lipids showed that POM in most of these streams was dominated by allochthonous sources (59.5 ± 14.2 vs. 39.6 ± 14.5 % for aliphatic alcohols and 52.9 ± 11.5 vs. 34.1 ± 10.3 % for sterols). The relative abundance of allochthonous vs. autochthonous lipid inputs to POM varied as a function of land use type. POM in streams draining forest-dominated watersheds contained a higher proportion of allochthonous lipids and a lower proportion of autochthonous lipids than the streams influenced by human land use. The contribution of bacterial fatty acids differed significantly among sampling times (P = 0.003), but not among land use types (P = 0.547). Stepwise linear regression model selected nitrate and temperature as the best predictors of variation in bacterial inputs to POM. Proxies used to assess the nutritional value of POM potentially available to stream consumers included C:N ratios, and the concentrations of total long-chain polyunsaturated fatty acids, eicosapentaenoic acid, arachidonic acid, and cholesterol. None of these nutritional proxies differed among sampling months (P ≥ 0.171), but the proxies showed that the nutritional value of POM in forest streams was lower than in urban streams. Collectively, these findings suggest that human land use in upstream watersheds alters the source composition and nutritional value of stream POM, which not only impacts food quality for stream biota, but also potentially changes the characteristics of OM reaching downstream ecosystems
Wet hibernacula promote inoculative freezing and limit the potential for cryoprotective dehydration in the Antarctic midge, Belgica antarctica
Yuta Kawarasaki, Nicholas M. Teets, David L. Denlinger, Richard E. Lee Jr. 2014. Polar Biology in press. DOI: 10.1007/s00300-014-1475-0
Abstract The terrestrial midge, Belgica antarctica, occupies a diverse range of microhabitats along the Antarctic Peninsula. Although overwintering larvae have the physiological potential to survive by freezing or cryoprotective dehydration, use of the latter strategy may be constrained by inoculative freezing within hibernacula. To investigate the influence of microhabitat type on larval overwintering, we selected four substrate types that differed markedly in their composition and hydric characteristics. Organic content of these substrates ranged from 14 to 89 %. High organic content was associated with higher values for saturation moisture content (up to 2.0 H2O g−1 dry mass) as well as elevated levels of field moisture content. Seasonal values of field moisture content remained near or above the saturation moisture value for each microhabitat type, and when larvae were cooled in substrates rehydrated to field-based levels, they were unable to avoid inoculation by environmental ice, regardless of substrate type. Consequently, our data suggest that wet hibernacula would force most larvae to overwinter in a frozen state. Yet, dehydrated larvae were collected in April during the seasonal transition to winter suggesting that spatial and temporal variations in precipitation and microhabitat conditions may expose larvae to dehydration and promote larval overwintering in a cryoprotectively dehydrated state.