Bacterial Associates of a Gregarious Riparian Beetle With Explosive Defensive Chemistry

Bombardier beetles (Carabidae: Brachininae) are well known for their unique explosive defensive chemistry. These beetles are found in riparian corridors throughout the American Southwest, where they commonly form large diurnal multispecies aggregations in moist areas under rocks, in crevices, and in leaf litter. Using high throughput 16S amplicon sequencing, we provide the first microbiome survey of a bombardier beetle, Brachinus elongatulus, collected from two sites in Arizona. Two bacterial taxa were present in all individuals sampled: Enterococcus and Dysgonomonas. Enterococcus has been implicated in the production of fecal aggregation pheromone components, which have been shown to regulate aggregation in the German cockroach; it is possible that Enterococcus plays a similar role in Brachinus. Dysgonomonas was found in all the secretory cells of the defensive system and gut samples. Additional studies are needed to determine if these microbes play a role in these beetles’ unique chemical defense. Results also show that the majority of B. elongatulus individuals collected from both sites were infected with Spiroplasma. Many Spiroplasma are intracellular, vertically transmitted insect symbionts that may manipulate host reproduction (e.g., cause male-killing) or provide resistance to nematodes and/or parasitoid wasps. Defensive protection could be especially beneficial to B. elongatulus, which are frequently parasitized by horsehair worms (Nematomorpha). In sum, findings suggest several testable hypotheses on the effects bacteria may have on bombardier beetle behavior and physiology

The Direct and Ecological Costs of an Ant-Plant Symbiosis

How strong is selection for cheating in mutualisms? The answer depends on the type and magnitude of the costs of the mutualism. Here we investigated the direct and ecological costs of plant defense by ants in the association between Cordia nodosa, a myrmecophytic plant, and Allomerus octoarticulatus, a phytoecious ant. Cordia nodosa trees produce food and housing to reward ants that protect them against herbivores. For nearly 1 year, we manipulated the presence of A. octoarticulatus ants and most insect herbivores on C. nodosa in a full-factorial experiment. Ants increased plant growth when herbivores were present but decreased plant growth when herbivores were absent, indicating that hosting ants can be costly to plants. However, we did not detect a cost to ant colonies of defending host plants against herbivores. Although this asymmetry in costs suggests that the plants may be under stronger selection than the ants to cheat by withholding investment in their partner, the costs to C. nodosa are probably at least partly ecological, arising because ants tend scale insects on their host plants. We argue that ecological costs should favor resistance or traits other than cheating and thus that neither partner may face much temptation to cheat.Organismic and Evolutionary Biolog

Invasive Plants in U. S. National Wildlife Refuges: A Coordinated Research Project Using Undergraduate Ecology Students

Answering large-scale questions in ecology can involve time-consuming data compilation. We show how networks of undergraduate classes can make these projects more manageable and provide an authentic research experience for students. With this approach, we examined the factors associated with plant species richness in US national wildlife refuges. We found that the richness of harmful invasive plants and the richness of native plants were positively correlated in mainland refuges but negatively correlated in island refuges. Nonnative richness and invasive richness were also positively correlated with colonization pressure as indicated by nonnative richness around each refuge. Associations between refuge characteristics and invasive plants varied substantially among regions, with refuge area and habitat diversity important predictors of invasion in some regions but not in others. Our results serve to identify the refuges that are most susceptible to plant invasion and demonstrate the potential value of a new model for education and research integration

What Do Unions Do for Economic Performance?

Twenty years have passed since Freeman and Medoff's What Do Unions Do? This essay assesses their analysis of how unions in the U.S. private sector affect economic performance - productivity, profitability, investment, and growth. Freeman and Medoff are clearly correct that union productivity effects vary substantially across workplaces. Their conclusion that union effects are on average positive and substantial cannot be sustained, subsequent evidence suggesting an average union productivity effect near zero. Their speculation that productivity effects are larger in more competitive environments appears to hold up, although more evidence is needed. Subsequent literature continues to find unions associated with lower profitability, as noted by Freeman and Medoff. Unions are found to tax returns stemming from market power, but industry concentration is not the source of such returns. Rather, unions capture firm quasi-rents arising from long-lived tangible and intangible capital and from firm-specific advantages. Lower profits and the union tax on asset returns leads to reduced investment and, subsequently, lower employment and productivity growth. There is little evidence that unionization leads to higher rates of business failure. Given the decline in U.S. private sector unionism, I explore avenues through which individual and collective voice might be enhanced, focusing on labor law and workplace governance defaults. Substantial enhancement of voice requires change in the nonunion sector and employer as well as worker initiatives. It is unclear whether labor unions would be revitalized or further marginalized by such an evolution

Bacterial Associates of a Gregarious Riparian Beetle With Explosive Defensive Chemistry

Bombardier beetles (Carabidae: Brachininae) are well known for their unique explosive defensive chemistry. These beetles are found in riparian corridors throughout the American Southwest, where they commonly form large diurnal multispecies aggregations in moist areas under rocks, in crevices, and in leaf litter. Using high throughput 16S amplicon sequencing, we provide the first microbiome survey of a bombardier beetle, Brachinus elongatulus, collected from two sites in Arizona. Two bacterial taxa were present in all individuals sampled: Enterococcus and Dysgonomonas. Enterococcus has been implicated in the production of fecal aggregation pheromone components, which have been shown to regulate aggregation in the German cockroach; it is possible that Enterococcus plays a similar role in Brachinus. Dysgonomonas was found in all the secretory cells of the defensive system and gut samples. Additional studies are needed to determine if these microbes play a role in these beetles' unique chemical defense. Results also show that the majority of B. elongatulus individuals collected from both sites were infected with Spiroplasma. Many Spiroplasma are intracellular, vertically transmitted insect symbionts that may manipulate host reproduction (e.g., cause male-killing) or provide resistance to nematodes and/or parasitoid wasps. Defensive protection could be especially beneficial to B. elongatulus, which are frequently parasitized by horsehair worms (Nematomorpha). In sum, findings suggest several testable hypotheses on the effects bacteria may have on bombardier beetle behavior and physiology.University of the Arizona, Office for Research and Discovery, Faculty Seed Grants Program, Microbiome Discovery and its Influence on Beetle-Ant Symbiosis; National Science Foundation [1556813]; U.S. National Institutes of Health PERT Training Grant [K12GM000708]Open access journal.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Data from: No evidence that gut microbiota impose a net cost on their butterfly host

Gut microbes are believed to play a critical role in most animal life, yet fitness effects and cost benefit-tradeoffs incurred by the host are poorly understood. Unlike most hosts studied to date, butterflies largely acquire their nutrients from larval feeding, leaving relatively little opportunity for nutritive contributions by the adult’s microbiota. This provides an opportunity to measure whether hosting gut microbiota comes at a net nutritional price. Since host and bacteria may compete for sugars, we hypothesized that gut flora would be nutritionally neutral to adult butterflies with plentiful food, but detrimental to semi-starved hosts, especially when at high density. We held field-caught adult Speyeria mormonia under abundant or restricted food conditions. Since antibiotic treatments did not generate consistent variation in their gut microbiota, we leveraged inter-individual variability in bacterial loads and OTU abundances to examine correlations between host fitness and the abdominal microbiota present upon natural death. We detected strikingly few relationships between microbial flora and host fitness. Neither total bacterial load nor the abundances of dominant bacterial taxa were related to butterflies’ fecundity, egg mass, or egg chemical content. Increased abundance of a Commensalibacter species did correlate with longer host lifespan, while increased abundance of a Rhodococcus species correlated with shorter lifespan. Contrary to our expectations, these relationships were unchanged by food availability to the host and were unrelated to reproductive output. Our results suggest the butterfly microbiota comprise parasitic, commensal, and beneficial taxa that together do not impose a net reproductive cost, even under caloric stress

Butterfly microbiome and community metabolic profiling data (open format)

Butterfly metadata, microbiome data (16s and ITS OTU tables; microbial taxonomic identifications; and representative fasta sequences for the OTUs) and gut community metabolic profiling (Biolog assay) data in .csv and .txt formats. See README file for additional information about individual files

R script and R-formatted data

This directory includes an R script that generates the figures from the associated manuscript, as well as butterfly metadata, microbiome (16s and ITS) data, and community metabolic profiling data in the .Rdata format. See the README for more information about individual files

Ravenscraft2019_Data

qPCR data (bacterial 16S and butterfly ef1a), microbiome data (16S OTU tables; bacterial taxonomy, phylogenetic tree, and representative fasta sequences of the OTUs), cumulative butterfly metadata (over the lifespan) and daily butterfly metadata in .csv and .txt formats. See README file for detailed descriptions of individual files

Data from: Structure and function of the bacterial and fungal gut microbiota of Neotropical butterflies

The relationship between animals and their gut flora is simultaneously one of the most common and most complex symbioses on Earth. Despite its ubiquity, our understanding of this invisible but often critical relationship is still in its infancy. We employed adult Neotropical butterflies as a study system to ask three questions: First, how does gut microbial community composition vary across host individuals, species and dietary guilds? Second, how do gut microbiota compare to food microbial communities? Finally, are gut flora functionally adapted to the chemical makeup of host foods? To answer these questions we captured nearly 300 Costa Rican butterflies representing over 50 species, six families and two feeding guilds: frugivores and nectivores. We characterized bacteria and fungi in guts, wild fruits and wild nectars via amplicon sequencing and assessed the catabolic abilities of the gut microbiota via culture-based assays. Gut communities were distinct from food communities, suggesting that the gut environment acts as a filter on potential colonists. Nevertheless, gut flora varied widely among individuals and species. On average, a pair of butterflies shared 21% of their bacterial species and 6% of their fungi. Host species explained 25-30% of variation in microbial communities while host diet explained 4%, suggesting that non-dietary aspects of host biology play a large role in structuring the butterfly gut flora. Much of the variation between species correlated with host phylogeny. Host diet was related to gut microbial function: compared to frugivores, nectivores’ gut flora exhibited increased catabolism of sugars and sugar alcohols and decreased catabolism of amino acids, carboxylic acids and dicarboxylic acids. Since fermented juice contains more amino acids and less sugar than nectar, it appears that host diet filters the gut flora by favoring microbes that digest compounds abundant in foods. By quantifying the degree to which gut communities vary among host individuals, species and dietary guilds and evaluating how gut microbial composition and catabolic potential are related to host diet, this study highlights the linkages between structure and function in one of the most complex and ubiquitous symbioses in the animal kingdom