Localization of bacterial communities within gut compartments across Cephalotes turtle ants.

Microbial communities within the animal digestive tract often provide important functions for their hosts. The composition of eukaryotes' gut bacteria can be shaped by host diet, vertical bacterial transmission, and physiological variation within the digestive tract. In several ant taxa, recent findings have demonstrated that nitrogen provisioning by symbiotic bacteria makes up for deficiencies in herbivorous diets. Using 16S rRNA amplicon sequencing and qPCR, this study examined bacterial communities at a fine scale across one such animal group, the turtle ant genus Cephalotes We analyzed the composition and colonization density across four portions of the digestive tract to understand how bacterial diversity is structured across gut compartments, potentially allowing for specific metabolic functions of benefit to the host. In addition, we aimed to understand if caste differentiation or host relatedness influences the gut bacterial communities of Cephalotes ants. Microbial communities were found to vary strongly across Cephalotes gut compartments in ways that transcend both caste and host phylogeny. Despite this, caste and host phylogeny still have detectable effects. We demonstrated microbial community divergence across gut compartments, possibly due to the varying function of each gut compartment for digestion.IMPORTANCE Gut compartments play an important role in structuring the microbial community within individual ants. The gut chambers of the turtle ant digestive tract differ remarkably in symbiont abundance and diversity. Furthermore, caste type explains some variation in the microbiome composition. Finally, the evolutionary history of the Cephalotes species structures the microbiome in our study, which elucidates a trend in which related ants maintain related microbiomes, conceivably owing to co-speciation. Amazingly, gut compartment-specific signatures of microbial diversity, relative abundance, composition, and abundance have been conserved over Cephalotes evolutionary history, signifying that this symbiosis has been largely stable for over 50 million years.

Extreme Insolation: Climatic Variation Shapes the Evolution of Thermal Tolerance at Multiple Scales.

The climatic variability hypothesis (CVH) is a cornerstone of thermal ecology, predicting the evolution of wider organismal thermal tolerance ranges in more thermally variable environments. Thermal tolerance ranges depend on both upper and lower tolerance limits (critical thermal maxima [[Formula: see text]] and critical thermal minima [[Formula: see text]]), which may show different responses to environmental gradients. To delineate the relative effects of mean and extreme temperatures on thermal tolerances, we conducted a within-latitude comparative test of CVH predictions for army ants (Dorylinae) at multiple scales: across elevations, in seasonal versus aseasonal forests, and in subterranean versus surface microhabitats. Consistent with the CVH, thermally buffered subterranean species had narrower thermal tolerance ranges. Both [Formula: see text] and [Formula: see text] decreased with elevation for subterranean species. In contrast, aboveground species (those exposed to insolation) showed a decrease in [Formula: see text] but no change in [Formula: see text] across elevations. Furthermore, greater seasonal temperature variation in dry forests correlated with increased [Formula: see text] but not [Formula: see text]. These patterns suggest that [Formula: see text] and [Formula: see text] respond to different abiotic selective forces: habitat-specific exposure to extreme insolation corresponds to [Formula: see text] differences but not to [Formula: see text] variation. We predict that increasingly frequent heat spikes associated with climate change will have habitat-specific physiological consequences for ectothermic animals. Models predicting climate change impacts should account for species microhabitat uses and within-latitude differences in temperature seasonality.

Author Correction: Herbivorous turtle ants obtain essential nutrients from a conserved nitrogen-recycling gut microbiome.

The originally published version of the Supplementary Information file associated with this Article contained an error in Supplementary Figure 3. Panel b was inadvertently replaced with a duplicate of panel a. The error has now been fixed and the corrected version of the Supplementary Information PDF is available to download from the HTML version of the Article.

Herbivorous turtle ants obtain essential nutrients from a conserved nitrogen-recycling gut microbiome.

Nitrogen acquisition is a major challenge for herbivorous animals, and the repeated origins of herbivory across the ants have raised expectations that nutritional symbionts have shaped their diversification. Direct evidence for N provisioning by internally housed symbionts is rare in animals; among the ants, it has been documented for just one lineage. In this study we dissect functional contributions by bacteria from a conserved, multi-partite gut symbiosis in herbivorous Cephalotes ants through in vivo experiments, metagenomics, and in vitro assays. Gut bacteria recycle urea, and likely uric acid, using recycled N to synthesize essential amino acids that are acquired by hosts in substantial quantities. Specialized core symbionts of 17 studied Cephalotes species encode the pathways directing these activities, and several recycle N in vitro. These findings point to a highly efficient N economy, and a nutritional mutualism preserved for millions of years through the derived behaviors and gut anatomy of Cephalotes ants.