EEOB Publications April 1 - April 30
Multiple concurrent and convergent stages of genome reduction in bacterial symbionts across a stink bug family
Alejandro Otero-Bravo & Zakee L. Sabree. 2021. Scientific Reports volume 11, Article number: 7731. https://doi.org/10.1038/s41598-021-86574-8
Nutritional symbioses between bacteria and insects are prevalent and diverse, allowing insects to expand their feeding strategies and niches. A common consequence of long-term associations is a considerable reduction in symbiont genome size likely influenced by the radical shift in selective pressures as a result of the less variable environment within the host. While several of these cases can be found across distinct insect species, most examples provide a limited view of a single or few stages of the process of genome reduction. Stink bugs (Pentatomidae) contain inherited gamma-proteobacterial symbionts in a modified organ in their midgut and are an example of a long-term nutritional symbiosis, but multiple cases of new symbiont acquisition throughout the history of the family have been described. We sequenced the genomes of 11 symbionts of stink bugs with sizes that ranged from equal to those of their free-living relatives to less than 20%. Comparative genomics of these and previously sequenced symbionts revealed initial stages of genome reduction including an initial pseudogenization before genome reduction, followed by multiple stages of progressive degeneration of existing metabolic pathways likely to impact host interactions such as cell wall component biosynthesis. Amino acid biosynthesis pathways were retained in a similar manner as in other nutritional symbionts. Stink bug symbionts display convergent genome reduction events showing progressive changes from a free-living bacterium to a host-dependent symbiont. This system can therefore be used to study convergent genome evolution of symbiosis at a scale not previously available.
Synergism between local‐ and landscape‐level pesticides reduces wild bee floral visitation in pollinator‐dependent crops
Elias H. Bloom Thomas J. Wood Keng‐Lou James Hung John J. Ternest Laura L. Ingwell Karen Goodell Ian Kaplan Zsofia Szendrei. 2021. https://doi.org/10.1111/1365-2664.13871
The hazard pesticides pose to pollinators are well‐understood from laboratory studies. However, the field‐level response of pollinators to pesticide use in agroecosystems is not well‐established, nor is it clear if synergisms between pesticides affect pollinator visitation to crops.
Here, we evaluated if fungicide and insecticide use posed a hazard to wild and honeybees at 87 cucurbit—pumpkin, cucumber, watermelon—farms in the Midwestern United States. We also evaluated if synergisms between local‐ (i.e. focal cucurbit field) and landscape‐level (i.e. surrounding crops) pesticide use influence wild and honeybee visitation to crop flowers.
We found that bees were exposed to pesticides above regulatory levels of concern and that synergisms between a few local insecticides and landscape‐level fungicides reduced wild bee visitation to cucurbit flowers. Honey and bumblebee visitation to crops was not strongly influenced by synergisms between pesticides used at the local and landscape level.
Synthesis and applications. We found pesticides posed hazards to honey and wild bee species. However, pesticides were less likely to affect short‐term visitation rates of honeybees compared with wild bee species. Thus, there is a need for changes in pesticide use at large spatial scales to reduce reliance on honeybees and maximize wild bee visitation to pollinator‐dependent crops. We suggest that a multifaceted approach, involving collaborations between farmers, consumers and policymakers, will be fruitful to promote changes in pesticide use and wild bee pollinators.
Determinants of invertebrate community structure in glacial‐melt streams of southeast Tibet
Heather Fair Peter C. Smiley Jr Roman Lanno. 2021. https://doi.org/10.1111/fwb.13716
A widely examined predictive model of invertebrate community dynamics in glacial‐melt streams describes longitudinal changes in community structure with changing water temperature and channel stability with increasing distance from glaciers. Previous studies conducted in Europe, Greenland, New Zealand, and South America have supported the predictions of the invertebrate model and contributed to its refinement. However, none has evaluated if the model fits invertebrate community dynamics over a full range of distances from the glacier and water temperature conditions within glacial‐melt streams in southeast Tibet.
We sampled invertebrates and measured water temperature, specific conductivity, turbidity, and associated glacier‐related variables within 14 sites in three subalpine glacial‐melt catchments in southeastern Tibet's Three Parallel Rivers region during 2010, 2011, 2013, and 2015. Our sites encompassed a temperature gradient from the upstream metakryal sites (maximum summer water temperature <2°C) to the furthest downstream site (maximum summer temperature >10°C) near the Mekong River.
We evaluated the relationships of invertebrate community structure with in situ water temperature and channel stability which are the focal habitat variables in the invertebrate model. The additional habitat variables of distance from the glacier, glacier size, conductivity, and turbidity were evaluated to see if these were more important determinants of community structure than in situ water temperature and channel stability.
Minimum and in situ water temperatures were positively correlated with distance from the glacier but Pfankuch Channel Stability Index bottom scores were not. Thus, the physical template within our study area differed from the expected template of the invertebrate model.
Similar to the invertebrate model, in situ water temperature by itself or combined with Pfankuch index best explained five invertebrate response variables. In contrast with the invertebrate model, conductivity and turbidity best explained invertebrate taxa richness, density, and the site scores of the first and second detrended correspondence analysis axes of relative abundance.
The invertebrate model predicts that only Diamesinae will occur in metakryal sites. However, in our metakryal sites we frequently captured 13 taxa (two Nemouridae morphotypes, Diamesinae, Orthocladiinae, Rhyacophila, Epeorus, Taeniopterygidae, Baetis, Capnia, Simuliidae, Limnephilidae, Himalopsyche, and Collembola).
Invertebrate‐habitat relationships and taxa occurrence trends in glacial‐melt catchments in southeast Tibet differed from the invertebrate model predictions. Our findings highlight the need to develop a regional version of the invertebrate model applicable to Asian glacial‐melt streams with unstable stream channels throughout their catchments and that do not freeze in the winter.
Predicting migration routes for three species of migratory bats using species distribution models
Jamin G. Wieringa, Bryan C. Carstens, H Lisle Gibbs. 2021. PeerJ 9:e11177 https://doi.org/10.7717/peerj.11177
Understanding seasonal variation in the distribution and movement patterns of migratory species is essential to monitoring and conservation efforts. While there are many species of migratory bats in North America, little is known about their seasonal movements. In terms of conservation, this is important because the bat fatalities from wind energy turbines are significant and may fluctuate seasonally. Here we describe seasonally resolved distributions for the three species that are most impacted by wind farms (Lasiurus borealis (eastern red bat), L. cinereus (hoary bat) and Lasionycteris noctivagans (silver-haired bat)) and use these distributions to infer their most likely migratory pathways. To accomplish this, we collected 2,880 occurrence points from the Global Biodiversity Information Facility over five decades in North America to model species distributions on a seasonal basis and used an ensemble approach for modeling distributions. This dataset included 1,129 data points for L. borealis, 917 for L. cinereus and 834 for L. noctivagans. The results suggest that all three species exhibit variation in distributions from north to south depending on season, with each species showing potential migratory pathways during the fall migration that follow linear features. Finally, we describe proposed migratory pathways for these three species that can be used to identify stop-over sites, assess small-scale migration and highlight areas that should be prioritized for actions to reduce the effects of wind farm mortality.
Solvent choice influences final toxicity results in Thamnocephalus platyurus bioassay when exposed to microcystin -LR
Carissa Hipsher, Joel Barker, Roman Lanno, Allison MacKay. 2021. https://doi.org/10.1016/j.toxicon.2021.04.010
Cyanobacterial blooms present a threat to many waterbodies around the world used for drinking water and recreational purposes. Toxicology tests, such as the Thamnotoxkit-F which uses the cladoceran T. platyurus, have been employed to assess the health hazards that these blooms may pose to the public. However, reported median lethal concentrations (LC50) of microcystin -LR to T. platyurus vary significantly from one study to the next. The variation in solvent type and concentrations used to dissolve microcystin -LR in preparation for toxicity experiments may be contributing to the variations in LC50 values found in the literature. The primary goal of this study was to determine what solvents and their corresponding concentrations can be used for microcystin -LR testing using T. platyurus without artifactually impacting LC50 values. All toxicity testing was completed using glassware as polystyrene containers have been shown to sorb microcystin. Microcystin -LR LC50 values for T. platyurus were determined using United States Environmental Protection Agency (US EPA) moderately hard standard freshwater as a control for comparison with systems that were prepared using dimethyl sulfoxide or methanol to dissolve microcystin -LR. Low levels of dimethyl sulfoxide (2%) or methanol (1%) did not impact LC50 values of microcystin -LR to T. platyurus compared to US EPA moderately hard standard freshwater diluted in microcystin -LR. However, higher levels of dimethyl sulfoxide (4%) and methanol (1.4% and 4%) did lower the LC50 for microcystin -LR to T. platyurus, consistent with the toxicity of these solvents to T. platyurus when dosed in the absence of microcystin -LR. Researchers need to report the type and concentrations of solvents used in toxicity tests using cyanotoxins in order to ensure that results can be intercompared appropriately. Furthermore, researchers need to use caution when using organic solvents such as dimethyl sulfoxide or methanol to ensure that these solvents are not causing significant mortality in toxicity testing.
Influence of Stocking Practices, Predation, and Reservoir Characteristics on the Growth and Recruitment of Saugeye
Richard R. Budnik, Jahn L. Kallis, Elizabeth A. Marschall. 2021. North American Journal of Fisheries Management. https://doi.org/10.1002/nafm.10624
Saugeye (female Sander vitreus X male S. canadensis) are stocked annually into Ohio reservoirs to maintain popular recreational fisheries. The growth and recruitment of stocked saugeye are highly variable among years and reservoirs, with the causes of this variability not well understood. Using a multi‐year (2004‐2019), multi‐reservoir (6 reservoirs) dataset, we implemented mixed‐effects models and an information theoretic approach to identify possible predictors of saugeye post‐stocking growth and recruitment. Top‐performing models (ΔAICc < 2) explained 38‐40% of the variation in stocked saugeye growth (N = 4 models) and 36‐47% of the variation in stocked saugeye recruitment (N = 9 models). Specifically, our growth models identified stocking day of year and mean summer (July‐August) water temperature as significant predictors, with saugeye experiencing higher daily growth rates when fish were stocked earlier in the year and when summer water temperatures were warmer. Based on the results from our recruitment models, stocking density was identified as the only significant predictor, with greater stocking densities leading to stronger stocked saugeye recruitment. From these relationships, we predict that saugeye fishery production will be greater when managers stock greater densities of saugeye earlier in the year and when summer reservoir temperatures are higher. Despite identifying significant predictors, our models could not explain much of the variation in stocked saugeye growth and recruitment, revealing the complexity of growth and recruitment processes in Ohio reservoirs.
Phylogenetically diverse diets favor more complex venoms in North American pitvipers
Holding, Matthew L. ; Strickland, Jason L. ; Rautsaw, Rhett M. ; Hofmann, Erich P. ; Mason, Andrew J. ; Hogan, Michael P. ; Nystrom, Gunnar S. ; Ellsworth, Schyler A. ; Colston, Timothy J. ; Borja, Miguel ; Castañeda-Gaytán, Gamaliel ; Grünwald, Christoph I. ; Jones, Jason M. ; Freitas-de-Sousa, Luciana A. ; Viala, Vincent Louis ; Margres, Mark J. ; Hingst-Zaher, Erika ; Junqueira-de-Azevedo, Inácio L. M. ; Moura-da-Silva, Ana M. ; Grazziotin, Felipe G. ; Gibbs, H. Lisle ; Rokyta, Darin R. ; Parkinson, Christopher L. PNAS April 27, 2021 118 (17) e2015579118; https://doi.org/10.1073/pnas.2015579118
The role of natural selection in the evolution of trait complexity can be characterized by testing hypothesized links between complex forms and their functions across species. Predatory venoms are composed of multiple proteins that collectively function to incapacitate prey. Venom complexity fluctuates over evolutionary timescales, with apparent increases and decreases in complexity, and yet the causes of this variation are unclear. We tested alternative hypotheses linking venom complexity and ecological sources of selection from diet in the largest clade of front-fanged venomous snakes in North America: the rattlesnakes, copperheads, cantils, and cottonmouths. We generated independent transcriptomic and proteomic measures of venom complexity and collated several natural history studies to quantify dietary variation. We then constructed genome-scale phylogenies for these snakes for comparative analyses. Strikingly, prey phylogenetic diversity was more strongly correlated to venom complexity than was overall prey species diversity, specifically implicating prey species’ divergence, rather than the number of lineages alone, in the evolution of complexity. Prey phylogenetic diversity further predicted transcriptomic complexity of three of the four largest gene families in viper venom, showing that complexity evolution is a concerted response among many independent gene families. We suggest that the phylogenetic diversity of prey measures functionally relevant divergence in the targets of venom, a claim supported by sequence diversity in the coagulation cascade targets of venom. Our results support the general concept that the diversity of species in an ecological community is more important than their overall number in determining evolutionary patterns in predator trait complexity.