Facilitating the recovery of insect communities in restored streams by increasing oviposition habitat.

Recruitment limitation is known to influence species abundances and distributions. Recognition of how and why it occurs both in natural and in designed environments could improve restoration. Aquatic insects, for instance, rarely reestablish in restored streams to levels comparable to reference streams even years after restoration. We experimentally increased oviposition habitat in five out of 10 restored streams in western North Carolina to test whether insect egg-laying habitat was limiting insect populations in restored streams. A main goal was to test whether adding oviposition habitat in the form of rocks that partially protrude above the water surface could be used to increase the abundance and richness of stream insect eggs and larval insects in restored streams. Adding egg-laying habitat enhanced several response variables (e.g., protruding rocks, number of eggs, egg masses, egg morphotype richness, and oviposition habitat stability) to levels similar to those found in reference streams. Following the addition of protruding rocks, egg mass abundance increased by 186% and richness by 77% in restored-treated streams. Densities of larval insects that attached their eggs to protruding rocks showed an overall pattern consistent with treatment effects due to the combination of nonsignificant and significant increases of several taxa and not just one taxon. Our results indicate that these stream insect populations are limited by oviposition habitat and that adding egg-laying habitat alleviated this component of recruitment limitation. However, the weaker larval response indicates that additional post-recruitment factors, such as egg or larval mortality, may still be limiting a full recovery of larval insect abundances in these restored streams. This study shows the importance of integrating information from animal life histories, ecology, and geomorphology into restoration practices to improve the recovery of aquatic insects, which are commonly used to assess water quality and the biological efficacy of stream restoration.

Individual preferences, government policy, and COVID-19: A game-theoretic epidemiological analysis.

Purpose: The ongoing COVID-19 pandemic imposes serious short-term and long-term health costs on populations. Restrictive government policy measures decrease the risks of infection, but produce similarly serious social, mental health, and economic problems. Citizens have varying preferences about the desirability of restrictive policies, and governments are thus forced to navigate this tension in making pandemic policy. This paper analyses the situation facing government using a game-theoretic epidemiological model. Methodology: We classify individuals into health-centered individuals and freedom-centered individuals to capture the heterogeneous preferences of citizens. We first use the extended Susceptible-Exposed-Asymptomatic-Infectious-Recovered (SEAIR) model (adding individual preferences) and the signaling game model (adding government) to analyze the strategic situation against the backdrop of a realistic model of COVID-19 infection. Findings: We find the following: 1. There exists two pooling equilibria. When health-centered and freedom-centered individuals send anti-epidemic signals, the government will adopt strict restrictive policies under budget surplus or balance. When health-centered and freedom-centered individuals send freedom signals, the government chooses not to implement restrictive policies. 2. When governments choose not to impose restrictions, the extinction of an epidemic depends on whether it has a high infection transmission rate; when the government chooses to implement non-pharmacological interventions (NPIs), whether an epidemic will disappear depends on how strict the government's restrictions are. Originality/value: Based on the existing literature, we add individual preferences and put the government into the game as a player. Our research extends the current form of combining epidemiology and game theory. By using both we get a more realistic understanding of the spread of the virus and combine that with a richer understanding of the strategic social dynamics enabled by game theoretic analysis. Our findings have important implications for public management and government decision-making in the context of COVID-19 and for potential future public health emergencies.

Consequences of climate-induced range expansions on multiple ecosystem functions.

Climate-driven species range shifts and expansions are changing community composition, yet the functional consequences in natural systems are mostly unknown. By combining a 30-year survey of subalpine pond larval caddisfly assemblages with species-specific functional traits (nitrogen and phosphorus excretion, and detritus processing rates), we tested how three upslope range expansions affected species' relative contributions to caddisfly-driven nutrient supply and detritus processing. A subdominant resident species (Ag. deflata) consistently made large relative contributions to caddisfly-driven nitrogen supply throughout all range expansions, thus "regulating" the caddisfly-driven nitrogen supply. Whereas, phosphorus supply and detritus processing were regulated by the dominant resident species (L. externus) until the third range expansion (by N. hostilis). Since the third range expansion, N. hostilis's relative contribution to caddisfly-driven phosphorus supply increased, displacing L. externus's role in regulating caddisfly-driven phosphorus supply. Meanwhile, detritus processing contributions became similar among the dominant resident, subdominant residents, and range expanding species. Total ecosystem process rates did not change throughout any of the range expansions. Thus, shifts in species' relative functional roles may occur before shifts in total ecosystem process rates, and changes in species' functional roles may stabilize processes in ecosystems undergoing change.

Preoperative SARS-CoV-2 infection increases risk of early postoperative cardiovascular complications following noncardiac surgery.

As the coronavirus disease 2019 (COVID-19) pandemic progresses to an endemic phase, a greater number of patients with a history of COVID-19 will undergo surgery. Major adverse cardiovascular and cerebrovascular events (MACE) are the primary contributors to postoperative morbidity and mortality; however, studies assessing the relationship between a previous severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and postoperative MACE outcomes are limited. Here, we analyzed retrospective data from 457,804 patients within the N3C Data Enclave, the largest national, multi-institutional data set on COVID-19 in the United States. However, 7.4% of patients had a history of COVID-19 before surgery. When comorbidities, age, race, and risk of surgery were controlled, patients with preoperative COVID-19 had an increased risk for 30-day postoperative MACE. MACE risk was influenced by an interplay between COVID-19 disease severity and time between surgery and infection; in those with mild disease, MACE risk was not increased even among those undergoing surgery within 4 wk following infection. In those with moderate disease, risk for postoperative MACE was mitigated 8 wk after infection, whereas patients with severe disease continued to have elevated postoperative MACE risk even after waiting for 8 wk. Being fully vaccinated decreased the risk for postoperative MACE in both patients with no history of COVID-19 and in those with breakthrough COVID-19 infection. Together, our results suggest that a thorough assessment of the severity, vaccination status, and timing of SARS-CoV-2 infection must be a mandatory part of perioperative stratification.NEW & NOTEWORTHY With an increasing proportion of patients undergoing surgery with a prior history of COVID-19, it is crucial to understand the impact of SARS-CoV-2 infection on postoperative cardiovascular/cerebrovascular risk. Our work assesses a large, national, multi-institutional cohort of patients to highlight that COVID-19 infection increases risk for postoperative major adverse cardiovascular and cerebrovascular events (MACE). MACE risk is influenced by an interplay between disease severity and time between infection and surgery, and full vaccination reduces the risk for 30-day postoperative MACE. These results highlight the importance of stratifying time-to-surgery guidelines based on disease severity.

Species-specific traits predict whole-assemblage detritus processing by pond invertebrates.

Functional trait diversity determines if ecosystem processes are sensitive to shifts in species abundances or composition. For example, trait variation suggests detritivores process detritus at different rates and make different contributions to whole-assemblage processing, which could be sensitive to compositional shifts. Here, we used a series of microcosm experiments to quantify species-specific coarse and fine particulate organic matter (CPOM and FPOM) processing for ten larval caddisfly species and three non-caddisfly species in high-elevation wetlands. We then compared trait-based models including life history, dietary, and extrinsic traits to determine which traits explained interspecific variation in detritus processing. Finally, we compared processing by mixed caddisfly assemblages in microcosms and natural ponds to additive predictions based on species-specific processing to determine if single-species effects are additive in multi-species assemblages. We found considerable interspecific variation in biomass-specific CPOM (13-fold differences) and FPOM (8-fold differences) processing. Furthermore, on a mass-specific basis, amphipods, chironomids, and caddisflies processed similar amounts of detritus, suggesting non-shredder taxa could process more than previously recognized. Trait models including dietary percent detritus, development rate, body size, and wetland hydroperiod explained 81 and 57% of interspecific variation in CPOM and FPOM processing, respectively. Finally, species-specific additive predictions were strikingly similar to mixed-assemblage processing in microcosms and natural ponds, with the largest difference being a 15% overestimate. Thus, additivity of species-specific processing suggests single-species rates may be useful for understanding functional consequences of shifting assemblages, and a trait-based approach to predicting species-specific processing could support generating additive predictions of whole-assemblage processing.

Good clinical practice improves rigor and transparency: Lessons from the ACTIVE trial.

Clinical trials are governed by principles of good clinical practice (GCP), which can strengthen the achievement of rigor, reproducibility, and transparency in scientific research. Rigor, reproducibility, and transparency are key for producing findings with greater certainty. Clinical trials are closely supervised, often by a clinical trial coordinating center, data safety and monitoring board, and a funding agency, with policies that are a manifestation of GCP and support rigor, reproducibility, and transparency. The multisite Advanced Cognitive Training for Independent and Vital Elderly (ACTIVE) study is an example clinical trial of relevance to a psychology and aging audience that utilized many protocols that can be applied to single-laboratory designs, including a manualized protocol with accompanying scientific rationale, predefined analysis plans, standardization of procedures across field sites, assurance of competence of study staff in study procedures, transparent coding/entry/transmittal of data, regular quality assurance, and open publication of data. Despite substantial resource discrepancies between the two, single-laboratory studies can model the GCP principles utilized in large clinical trials to provide an excellent foundation for rigor, reproducibility, and transparency. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Understanding the evolution of nutritive taste in animals: Insights from biological stoichiometry and nutritional geometry.

A major conceptual gap in taste biology is the lack of a general framework for understanding the evolution of different taste modalities among animal species. We turn to two complementary nutritional frameworks, biological stoichiometry theory and nutritional geometry, to develop hypotheses for the evolution of different taste modalities in animals. We describe how the attractive tastes of Na-, Ca-, P-, N-, and C-containing compounds are consistent with principles of both frameworks based on their shared focus on nutritional imbalances and consumer homeostasis. Specifically, we suggest that the evolution of multiple nutritive taste modalities can be predicted by identifying individual elements that are typically more concentrated in the tissues of animals than plants. Additionally, we discuss how consumer homeostasis can inform our understanding of why some taste compounds (i.e., Na, Ca, and P salts) can be either attractive or aversive depending on concentration. We also discuss how these complementary frameworks can help to explain the evolutionary history of different taste modalities and improve our understanding of the mechanisms that lead to loss of taste capabilities in some animal lineages. The ideas presented here will stimulate research that bridges the fields of evolutionary biology, sensory biology, and ecology.

Videogame and Computer Intervention Effects on Older Adults' Mental Rotation Performance.

Objective: This article examined older adults' performance on two components of a mental rotation task (reaction time and rotation rate) in a home-based intervention study of videogame (Crazy Taxi [CT]) and computerized cognitive training (PositScience InSight). Materials and Methods: Participants were randomized to one of three groups: one group played an off-the-shelf videogame (i.e., CT), the second group engaged in a computerized training program focused on fast perceptual comparisons, visuospatial working memory, rapid scanning of a visual array and pattern recognition, visual discrimination, and selective and divided attention and processing speed (i.e., InSight), and the third (control) group received no training. Training in the two intervention conditions consisted of 60 training sessions of 1 hour each, which were completed in 3 months (5 hours a week). As part of a larger study, participants received mental rotation testing, which was administered immediately before (baseline), after (post-test), and 3 months after (follow-up) training. Results: Although the InSight group showed greater improvements in rotation rate at the immediate post-test, by the 3-month follow-up, the combined treatment groups (CT and InSight) had improved more than controls. Conclusion: The improvements in mental rotation performance found at 3-month follow-up add additional support to previous research, showing visuospatial benefits of both videogame play and cognitive training in older adults. Common elements of both interventions may include expansion of the attentional field of view and faster visual comparison efficiency.

Examining the determinants of eHealth usage among elderly people with disability: The moderating role of behavioural aspects.

BACKGROUND: Existing studies have demonstrated that behavioural barriers impede eHealth usage among senior citizens. However, thus far, no analysis of how such barriers affect elderly people with disabilities (PwD) has been conducted. Thus, the study investigates the predictors of eHealth usage among elderly PwD. METHODS: Using data from a 2018 nationwide disability survey comprising 14,798 respondents in Australia, multivariate logistic regression models are used to predict the relationship between eHealth usage and the various characteristics of respondents, including access to information and communication technologies (ICTs), socioeconomic status, and level of education. RESULTS: Although most participants (approximately 88%) have access to ICTs, few (only around 9%) have used eHealth services. The results show a number of factors are associated with an increased likelihood of using eHealth services, including higher educational attainment (odds ratio [OR] = 3.12, 95% confidence interval [CI]: 2.38, 4.24), employment (OR = 1.43, 95% CI: 1.06, 1.94), higher household income (OR = 1.39, 95% CI: 1.00, 1.96), and ICT access (OR = 15.92, 95% CI: 10.51, 27.01). The probability of eHealth use is lower for the oldest-old (OR = 0.35, 95% CI: 0.22, 0.45). In addition, the estimates from interaction effects suggest the effect of ICT penetration on use of eHealth falls by a negligible amount because of resistive attitudinal barriers (OR = 0.01, 95% CI: 0.01, 0.06). CONCLUSION: Given the challenges of ageing populations and pandemics, such as COVID-19, eHealth services are a vital part of an effective, inclusive, and robust health care system. This study demonstrates the presence of a significant digital divide among elderly PwD and suggests that public and private efforts should be made to increase the availability of ICT infrastructure. Training could also increase inclusion in this regard.

Does ICT maturity catalyse economic development? Evidence from a panel data estimation approach in OECD countries.

To date, definitions of information and communication technology (ICT) development used in quantitative studies on the relationship between economic development and ICT are incomplete and often based on single indicators. Thus, this study investigates the link between ICT maturity and economic development in the Organisation of Economic Cooperation and Development (OECD) countries. A novel composite index of ICT maturity that includes previously neglected dimensions of ICT maturity, such as affordability and quality of internet connectivity, is utilised. The baseline estimations using the feasible generalised least squares indicate that ICT maturity is associated with an increase in economic development by 1%-3.8% in OECD countries. These findings have been cross-validated by applying the generalised method of moments estimation. Results imply that the holistic development of ICT, including infrastructure, skills, and affordability, can augment economic development.

Determinants of ICT usage for healthcare among people with disabilities: The moderating role of technological and behavioural constraints.

Existing studies have demonstrated that people with disabilities (PwD) face a range of technological and behavioural barriers to successful adoption of information and communication technology (ICT)-enabled health services. However, there has been little examination and no scholarly consensus on the relative impact of each factor. This study investigates the determinants of ICT usage for health care among PwD. Using national-level disability survey data in Australia, several multivariate hierarchical regression models are deployed to predict the relationship between ICT-enabled health service adoption and the explanatory variables. In addition, several measures of the overall goodness-of-fit are estimated for each model. The results indicate that age, gender, income, level of education, language proficiency and geographical remoteness are significant predictors of ICT-enabled health care usage among PwD. It is also found that technological constraints have a stronger moderating effect than behavioural factors. This provides valuable insight for policymakers and private organisations on which approaches and interventions are most likely to narrow the digital disability divide.

The Mediating Effect of Information and Communication Technology Usages on the Nexus Between Assistive Technology and Quality of Life Among People with Communication Disability.

This study aims to investigate the mediating effect of information and communication technology (ICT) on the nexus between quality of life (QoL) and assistive technology among people with communication disabilities. Using a national-level disability survey data in Australia, this study employs a series of causal mediation models based on counterfactual framework for mediation analysis. The results indicate that about 61% to 73% of the impact of assistive technology on QoL among people with communication disabilities is mediated through ICT use. Furthermore, it is evident that the degree of communication impairment partially moderates the impact of ICT-enabled assistive technology on QoL. The findings of the study have several practical implications. First, this study indicates that better integration of assistive technology with ICT will enhance the quality of people with communication disabilities. The second broad recommendation is that improved accessibility with affordable high-speed broadband Internet can deliver services that people with disabilities need.

Recall and Recognition Discriminability in Parkinson's Disease and Huntington's Disease.

BACKGROUND: Parkinson's disease (PD) and Huntington's disease (HD) are two neurodegenerative diseases affecting frontal-striatal function and memory ability. Studies using the original California Verbal Learning Test (CVLT) to examine recall and recognition abilities between these groups have produced mixed findings. Some found that individuals with HD demonstrate worse recall and recognition than those with PD, whereas others reported comparable performance. OBJECTIVE: We utilized multiple indices of recall and recognition discriminability, provided by the second and third editions of the CVLT (CVLT-II and CVLT-3, respectively), that allow for a more thorough assessment of more nuanced aspects of verbal memory function. METHODS: We examined differences between individuals with PD (n = 72) and those with HD (n = 77) on CVLT-II indices of recall discriminability (immediate, short delay free and cued, long delay free and cued) and recognition discriminability (total, source, semantic, and novel) using standardized scores while controlling for education and Dementia Rating Scale-2 scores. RESULTS: The HD group performed significantly worse than the PD group on all measures of recall and recognition discriminability (ps < 0.05), and group differences were associated with large Cohen's d effect sizes. CONCLUSIONS: Our findings suggest that individuals with HD are more impaired than individuals with PD in more nuanced aspects of recall and recognition memory function. These CVLT indices yield more thorough assessments of recall and recognition memory function and have the potential to improve efforts to characterize and distinguish profiles of memory loss in different neurodegenerative populations, including PD and HD.

Bilateral Internal Mammary Artery Use in Diabetic Patients: Friend or Foe?

BACKGROUND: Bilateral internal mammary artery (BIMA) grafting in diabetic patients undergoing coronary artery bypass grafting remains controversial. Our study compared morbidity and mortality between (1) diabetic and nondiabetic BIMA patients and (2) diabetic BIMA versus diabetic patients who underwent left internal mammary artery (LIMA) grafting only. METHODS: Patients who underwent isolated coronary artery bypass grafting from July 2011 to June 2016 at any of the 10 Maryland Cardiac Surgery Quality Initiative centers were propensity scored across 16 variables. Diabetic BIMA patients were matched 1:1 by nearest neighbor matching to nondiabetic BIMA patients and were separately matched 1:1 to diabetic LIMA patients. We calculated observed-to-expected (O/E) ratios for composite morbidity/mortality, operative mortality, unplanned reoperation, stroke, renal failure, prolonged ventilation, and deep sternal wound infection and compared ratios among matched populations. RESULTS: During the study period, 812 coronary artery bypass grafting patients received BIMA grafts, including 302 patients (37%) with diabetes. We matched 259 diabetic and nondiabetic BIMA patients. O/E ratios were higher in matched diabetic (versus nondiabetic) BIMA patients when comparing composite morbidity/mortality, reoperation, stroke, renal failure, and prolonged ventilation (all O/E ratios >1.0); however, the O/E ratio for operative mortality was higher in nondiabetic BIMA patients. We additionally matched 292 diabetic BIMA to diabetic LIMA patients. Diabetic BIMA patients had a higher O/E ratio for composite morbidity/mortality, operative mortality, stroke, renal failure, and prolonged ventilation. CONCLUSIONS: In this statewide analysis, diabetic patients who received BIMA grafts (compared with diabetic patients with LIMA grafts or nondiabetic patients with BIMA grafts) had higher O/E ratios for composite morbidity/mortality as a result of higher O/E ratios for major complications.

Pharmacology, pharmacokinetics, and metabolism of the DNA-decoy AYX1 for the prevention of acute and chronic post-surgical pain.

Background AYX1 is an unmodified DNA-decoy designed to reduce acute post-surgical pain and its chronification with a single intrathecal dose at the time of surgery. AYX1 inhibits the transcription factor early growth response protein 1, which is transiently induced at the time of injury and triggers gene regulation in the dorsal root ganglia and spinal cord that leads to long-term sensitization and pain. This work characterizes the AYX1 dose-response profile in rats and the link to AYX1 pharmacokinetics and metabolism in the cerebrospinal fluid, dorsal root ganglia, and spinal cord. Results The effects of ascending dose-levels of AYX1 on mechanical hypersensitivity were measured in the spared nerve injury model of chronic pain and in a plantar incision model of acute post-surgical pain. AYX1 dose-response profile shows that efficacy rapidly increases from a minimum effective dose of ∼ 0.5 mg to a peak maximum effective dose of ∼ 1 mg. With further dose escalation, the efficacy paradoxically appears to decrease by ∼ 30% and then returns to full efficacy at the maximum feasible dose of ∼ 4 mg. The reduction of efficacy is associated to doses triggering a near-saturation of AYX1 metabolism by nucleases in the cerebrospinal fluid and a paradoxical reduction of AYX1 exposure during the period of early growth response protein 1 induction. This effect is overcome at higher doses that compensate for the effect of metabolism. Discussion AYX1 is a competitive antagonist of early growth response protein 1, which is consistent with the overall increased efficacy observed as dose-levels initially escalate. Chemically, AYX1 is unprotected against degradation by nucleases. The sensitivity to nucleases is reflected in a paradoxical reduction of efficacy in the dose-response curve. Conclusions These findings point to the importance of the nuclease environment of the cerebrospinal fluid to the research and development of AYX1 and other intrathecal nucleotide-based therapeutics.

Dissolved organic carbon modulates mercury concentrations in insect subsidies from streams to terrestrial consumers.

Mercury (Hg) concentrations in aquatic environments have increased globally, exposing consumers of aquatic organisms to high Hg levels. For both aquatic and terrestrial consumers, exposure to Hg depends on their food sources as well as environmental factors influencing Hg bioavailability. The majority of the research on the transfer of methylmercury (MeHg), a toxic and bioaccumulating form of Hg, between aquatic and terrestrial food webs has focused on terrestrial piscivores. However, a gap exists in our understanding of the factors regulating MeHg bioaccumulation by non-piscivorous terrestrial predators, specifically consumers of adult aquatic insects. Because dissolved organic carbon (DOC) binds tightly to MeHg, affecting its transport and availability in aquatic food webs, we hypothesized that DOC affects MeHg transfer from stream food webs to terrestrial predators feeding on emerging adult insects. We tested this hypothesis by collecting data over 2 years from 10 low-order streams spanning a broad DOC gradient in the Lake Sunapee watershed in New Hampshire, USA. We found that streamwater MeHg concentration increased linearly with DOC concentration. However, streams with the highest DOC concentrations had emerging stream prey and spiders with lower MeHg concentrations than streams with intermediate DOC concentrations; a pattern that is similar to fish and larval aquatic insects. Furthermore, high MeHg concentrations found in spiders show that MeHg transfer in adult aquatic insects is an overlooked but potentially significant pathway of MeHg bioaccumulation in terrestrial food webs. Our results suggest that although MeHg in water increases with DOC, MeHg concentrations in stream and terrestrial consumers did not consistently increase with increases in streamwater MeHg concentrations. In fact, there was a change from a positive to a negative relationship between aqueous exposure and bioaccumulation at streamwater MeHg concentrations associated with DOC above ~5 mg/L. Thus, our study highlights the importance of stream DOC for MeHg dynamics beyond stream boundaries, and shows that factors modulating MeHg bioavailability in aquatic systems can affect the transfer of MeHg to terrestrial predators via aquatic subsidies.

Combined in vivo optical and µCT imaging to monitor infection, inflammation, and bone anatomy in an orthopaedic implant infection in mice.

Multimodality imaging has emerged as a common technological approach used in both preclinical and clinical research. Advanced techniques that combine in vivo optical and µCT imaging allow the visualization of biological phenomena in an anatomical context. These imaging modalities may be especially useful to study conditions that impact bone. In particular, orthopaedic implant infections are an important problem in clinical orthopaedic surgery. These infections are difficult to treat because bacterial biofilms form on the foreign surgically implanted materials, leading to persistent inflammation, osteomyelitis and eventual osteolysis of the bone surrounding the implant, which ultimately results in implant loosening and failure. Here, a mouse model of an infected orthopaedic prosthetic implant was used that involved the surgical placement of a Kirschner-wire implant into an intramedullary canal in the femur in such a way that the end of the implant extended into the knee joint. In this model, LysEGFP mice, a mouse strain that has EGFP-fluorescent neutrophils, were employed in conjunction with a bioluminescent Staphylococcus aureus strain, which naturally emits light. The bacteria were inoculated into the knee joints of the mice prior to closing the surgical site. In vivo bioluminescent and fluorescent imaging was used to quantify the bacterial burden and neutrophil inflammatory response, respectively. In addition, µCT imaging was performed on the same mice so that the 3D location of the bioluminescent and fluorescent optical signals could be co-registered with the anatomical µCT images. To quantify the changes in the bone over time, the outer bone volume of the distal femurs were measured at specific time points using a semi-automated contour based segmentation process. Taken together, the combination of in vivo bioluminescent/fluorescent imaging with µCT imaging may be especially useful for the noninvasive monitoring of the infection, inflammatory response and anatomical changes in bone over time.

The Origin of Invasive Microorganisms Matters for Science, Policy, and Management: The Case of Didymosphenia geminata.

The value of distinguishing native from nonnative invasive species has recently been questioned. However, this dichotomy is important for understanding whether a species' successful dominance is caused by introductions, changing environmental conditions that facilitate an existing population, or both processes. We highlight the importance of knowing the origin of hard-to-detect invasive microorganisms for scientific research, management, and policy using a case study of recent algal blooms of the stalk-producing diatom Didymosphenia geminata. Nuisance blooms have been reported in rivers worldwide and have been hastily attributed to introductions. However, evidence indicates that blooms are probably not caused by introductions but, rather, by environmental conditions that promote excessive stalk production by this historically rare species. Effective responses to invasive microorganisms depend on knowing whether their proliferation is caused by being nonnative or is the result of changing environmental conditions that promote invasive characteristics of native species.