Historical contingency in species interactions: towards niche-based predictions.

The way species affect one another in ecological communities often depends on the order of species arrival. The magnitude of such historical contingency, known as priority effects, varies across species and environments, but this variation has proven difficult to predict, presenting a major challenge in understanding species interactions and consequences for community structure and function. Here, we argue that improved predictions can be achieved by decomposing species' niches into three components: overlap, impact and requirement. Based on classic theories of community assembly, three hypotheses that emphasise related, but distinct influences of the niche components are proposed: priority effects are stronger among species with higher resource use overlap; species that impact the environment to a greater extent exert stronger priority effects; and species whose growth rate is more sensitive to changes in the environment experience stronger priority effects. Using nectar-inhabiting microorganisms as a model system, we present evidence that these hypotheses complement the conventional hypothesis that focuses on the role of environmental harshness, and show that niches can be twice as predictive when separated into components. Taken together, our hypotheses provide a basis for developing a general framework within which the magnitude of historical contingency in species interactions can be predicted

Forager bees (Apis mellifera) highly express immune and detoxification genes in tissues associated with nectar processing.

Pollinators, including honey bees, routinely encounter potentially harmful microorganisms and phytochemicals during foraging. However, the mechanisms by which honey bees manage these potential threats are poorly understood. In this study, we examine the expression of antimicrobial, immune and detoxification genes in Apis mellifera and compare between forager and nurse bees using tissue-specific RNA-seq and qPCR. Our analysis revealed extensive tissue-specific expression of antimicrobial, immune signaling, and detoxification genes. Variation in gene expression between worker stages was pronounced in the mandibular and hypopharyngeal gland (HPG), where foragers were enriched in transcripts that encode antimicrobial peptides (AMPs) and immune response. Additionally, forager HPGs and mandibular glands were enriched in transcripts encoding detoxification enzymes, including some associated with xenobiotic metabolism. Using qPCR on an independent dataset, we verified differential expression of three AMP and three P450 genes between foragers and nurses. High expression of AMP genes in nectar-processing tissues suggests that these peptides may contribute to antimicrobial properties of honey or to honey bee defense against environmentally-acquired microorganisms. Together, these results suggest that worker role and tissue-specific expression of AMPs, and immune and detoxification enzymes may contribute to defense against microorganisms and xenobiotic compounds acquired while foraging

Dynamic magnetic susceptibility of systems with long-range magnetic order

The utility of the tunnel diode resonator (TDR) as an instrument for the study of magnetically ordered materials has been expanded beyond simple demonstration purposes. Results of static applied magnetic field dependent measurements of the dynamic magnetic susceptibility, χ, of various ferromagnetic (FM) and antiferromagnetic (AFM) materials showing a range of transition temperatures (1-800 K) are presented. Data were collected primarily with a tunnel diode resonator (TDR) at different radio-frequencies (∼10-30 MHz). In the vicinity of TC local moment ferromagnets show a very sharp, narrow peak in χ which is suppressed in amplitude and shifted to higher temperatures as the static bias field is increased. Unexpectedly, critical scaling analysis fails for these data. It is seen that these data are frequency dependent, however there is no simple method whereby measurement frequency can be changed in a controllable fashion. In contrast, itinerant ferromagnets show a broad maximum in χ well below TC which is suppressed and shifts to lower temperatures as the static bias field is increased. The data on itinerant ferromagnets are fit to a semi-phenomenological model that suggests the sample response is dominated by the uncompensated minority spins in the conduction band. Concluding remarks suggest possible scenarios to achieve frequency resolved data using the TDR as well as other fields to which the apparatus may be applied

Mycorrhizal abundance affects the expression of plant resistance traits and herbivore performance

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98805/1/jec12111.pd

Trump-induced anxiety among Latina/os

During the 2016 election, Donald Trump castigated unauthorized immigrants as “murderers and rapists.” During his presidency, he continued the use of this rhetoric, explicitly linking unauthorized migrants to threatening narratives. Here, we consider three questions: Did Donald Trump and his immigration positions serve as an “anxiety trigger” for Latina/os? Are individuals with contextually stigmatized attributes especially sensitive to Trump and his policy proposals? Is Spanish language itself, an attribute negatively stigmatized in the context of the immigration issue, sufficient to increase deportation anxiety? Utilizing survey experiments of Latina/os, we demonstrate that exposure to a Trump immigration cue is sufficient to increase anxiety about deportation. We also demonstrate that stigmatized attributes predict anxiety, but do not moderate the effect of the Trump cue. Lastly, we provide evidence that survey language affects anxiety among Latina/os. In Studies 1 (n = 736) and 2 (n = 1,040), we show that exposure to information about Trump’s immigration agenda significantly increases reports about deportation anxiety. In Study 3 (n = 1,734), we show that the Trump exposure condition induces heightened anxiety but that Latina/o attributes (language proficiency and use, immigration status, assessed phenotype) and identity strength have an independent effect on deportation anxiety. In Study 4 (n = 775), we randomized bilingual respondents into Spanish or English language survey protocols and found that comparable bilinguals exposed to Spanish language report higher levels of anxiety compared to English-language survey takers

Whose Phenotype is it Anyway? The Complex Role of Species Interactions and Resource Availability in Determining Plant Defense Phenotype and Community Consequences.

The expression of plant defense is influenced by resource availability and biotic interactions, with consequences for herbivores and plant fitness. While the majority of plants associate with mycorrhizal fungi, which dramatically affect plant resource status, the role of these belowground interactions in shaping the expression of plant defense is poorly understood. In addition, plant-herbivore interactions affect plant growth and defense, but their effects on mycorrhizal interactions can vary dramatically. I hypothesized that changes in plant resource status and subsequent defense expression may mediate the interactions between mycorrhizal fungi and aboveground herbivores. Drawing from current knowledge of resource mutualisms, I hypothesized that the carbon costs and nutrient benefits of hosting mycorrhizal fungi would predict a nonlinear effect of mycorrhizae on the expression of plant defense. An experimental manipulation of the abundance and identity of mycorrhizal fungi associating with Asclepias syriaca revealed mycorrhizal colonization nonlinearly affected the expression of plant defense, although the shape of the response to increasing fungal colonization depended on the plant trait examined. In particular, traits (eg. trichomes, plant biomass) that increased with the concentration of phosphorus responded unimodally to mycorrhizal colonization as predicted, while those traits that were putatively carbon-limited (eg. latex and toughness) declined with fungal colonization. I also manipulated carbon available to plants and examined changes in plant defense and the effects of herbivores on mycorrhizal fungi. Growth under elevated CO2 increased plant biomass by 15% and toughness by 40%, but decreased cardenolide concentration by 20% and had little effect on trichome density. Herbivory by either aphids or caterpillars had no effect on mycorrhizal colonization when plants were grown in ambient CO2, but herbivory dramatically increased mycorrhizal colonization under elevated CO2. Taken together, these results indicate that fungi and aboveground herbivores interact through changes in plant resource status and defense phenotype and exert strong influence on the expression of plant defense phenotype. In addition, these experiments revealed substantial genetic variation within a single population of A. syriaca in the expression of plant defense and in response to mycorrhizal colonization and carbon addition, indicating the potential for evolutionary adaptation to changing environmental conditions.Ph.D.Ecology and Evolutionary BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/86373/1/raleva_1.pd