3-Year Outcomes for Degenerative Mitral Regurgitation Repair in a Medicare Population.

OBJECTIVE: Mitral valve repair (MVr) has become the standard therapy for degenerative mitral regurgitation (DMR), but real-world late mortality, reintervention, and readmission data are lacking. This study estimates MVr outcomes for DMR to 3 years in the Medicare fee-for-service population. METHODS: There were 4,219 DMR patients older than 65 years undergoing MVr within the Medicare 100% standard analytic file from October 2015 to December 2018 who were evaluated. Outcomes were analyzed for isolated MVr patients (n = 2,433) and patients undergoing MVr with certain concomitant procedures: MVr + tricuspid valve surgery (TVS; n = 619), MVr + cardiac ablation (CA; n = 540), and MVr + left atrial appendage closure (n = 627). Outcomes over a 3-year period included all-cause mortality, reintervention, rehospitalization, and common complications. All outcomes were modeled with adjustments for patient demographics and comorbid conditions. RESULTS: The average age for all patients was 71.9 ± 5.2 years. Adjusted all-cause mortality and MV reintervention (surgery or transcatheter) at 3 years for the primary cohort of isolated MVr was 3.5% and 1.6%, respectively. Directionally higher mortality at 3 years was observed in patients with concomitant TVS or CA. All-cause readmission and cardiac readmission for isolated MVr was 37.0% and 14.1%, with the highest rates for those with concomitant TVS or CA. Acute kidney injury and stroke/transient ischemic attack were the most common adverse events over 3 years for all patients. CONCLUSIONS: The 3-year mortality and reintervention rates in Medicare patients undergoing degenerative MVr are low. Those undergoing concomitant TVS or CA had directionally higher mortality and cardiac readmission rates. These results help refine outcome benchmarks as new transcatheter MVr procedures continue to emerge.

Investigating the effect of host plant identity on instar number in fall webworm, a common generalist herbivore.

For herbivorous insects with a broad diet breadth, host plant identity can influence larval development by either accelerating or delaying growth. For some species of Lepidoptera, the number of larval instars varies depending on the host plant's identity. Fall webworm (Hyphantria cunea, Drury) is a polyphagous herbivore that feeds on over 450 host plants worldwide. Of the 2 morphotypes (red- and black-head) of fall webworm, the number of instars for the red-head fall webworms has not been characterized. Given its broad diet breadth, fall webworm developmental stages may vary with plant identity. We investigated whether host plant identity affected the number of instars observed during red-head fall webworm development. We measured the head capsules of over 6,000 fall webworm larvae reared on 6 different plants commonly eaten by fall webworms in Colorado. We modeled head capsule widths as Gaussian mixture models, with a Gaussian distribution that corresponded to each instar. We show that our red-head fall webworms varied in number of instars depending on the identity of their host plant upon which they fed. We found that red-head fall webworm exhibited 7 instars on 5 of the host plants and 8 instars on 1 host plant that we studied. Our results for the number of instars for red-head fall webworm are consistent with reports of the number of instars for black-head fall webworm. Our research provides insight into the influence of host plant identity on fall webworm development, which can be used to advance lab and field research of this species.

Does artificial light at night alter moth community composition?

Ecological studies investigating the effects of artificial light at night (ALAN) have primarily focused on single or a few species, and seldom on community-level dynamics. As ALAN is a potential cause of insect and biodiversity declines, community-level perspectives are essential. We empirically tested the hypothesis that moth species differentially respond to ALAN and that these responses can cause shifts in community composition. We sampled moths from prairie fragments in Colorado, USA. We tested whether local light sources, sky glow, site area and/or vegetation affected moth community diversity. We found that increased sky glow decreased moth abundance and species richness and shifted community composition. Increased sky glow shifted moth community composition when light and bait traps were combined; notably this result appears to be driven entirely by moths sampled at bait traps, which is an unbiased sampling technique. Our results show that ALAN has significant effects on moth communities and that local light sources have contrasting effects on moth community composition compared to sky glow. It is imperative that we better understand the contrasting effects of types of ALAN to comprehend the overall impacts of light pollution on biodiversity declines. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Outpatient visits before and after Lyme disease diagnosis in a Maryland employer-based health plan.

BACKGROUND: Insurance claims data have been used to inform an understanding of Lyme disease epidemiology and cost of care, however few such studies have incorporated post-treatment symptoms following diagnosis. Using longitudinal data from a private, employer-based health plan in an endemic US state, we compared outpatient care utilization pre- and post-Lyme disease diagnosis. We hypothesized that utilization would be higher in the post-diagnosis period, and that temporal trends would differ by age and gender. METHODS: Members with Lyme disease were required to have both a corresponding ICD-9 code and a fill of an antibiotic indicated for treatment of the infection within 30 days of diagnosis. A 2-year 'pre- diagnosis' period and a 2-year 'post-diagnosis period' were centered around the diagnosis month. Lyme disease-relevant outpatient care visits were defined as specific primary care, specialty care, or urgent care visits. Descriptive statistics examined visits during these pre- and post-diagnosis periods, and the association between these periods and the number of visits was explored using generalized linear mixed effects models adjusting for age, season of the year, and gender. RESULTS: The rate of outpatient visits increased 26% from the pre to the post-Lyme disease diagnosis periods among our 317-member sample (rate ratio = 1.26 [1.18, 1.36], p < 0.001). Descriptively, care utilization increases appeared to persist across months in the post-diagnosis period. Women's care utilization increased by 36% (1.36 [1.24, 1.50], p < 0.001), a significantly higher increase than the 14% increase found among men (1.14 [1.02, 1.27], p = 0.017). This gender difference was mainly driven by adult members. We found a borderline significant 17% increase in visits for children < 18 years, (1.17 [0.99, 1.38], p = 0.068), and a 31% increase for adults ≥ 18 years (1.31 [1.21, 1.42], p < 0.001). CONCLUSIONS: Although modest at the population level, the statistically significant increases in post-Lyme diagnosis outpatient care we observed were persistent and unevenly distributed across demographic and place of service categories. As Lyme disease cases continue to grow, so will the cumulative prevalence of persistent symptoms after treatment. Therefore, it will be important to confirm these findings and understand their significance for care utilization and cost, particularly against the backdrop of other post-acute infectious syndromes.

Cost and Clinical Outcomes Evaluation Between the Endoaortic Balloon and External Aortic Clamp in Cardiac Surgery.

OBJECTIVE: Endoaortic balloon occlusion facilitates cardioplegic arrest during minimally invasive surgery (MIS). Studies have shown endoclamping to be as safe as traditional aortic clamping. We compared outcomes and hospital costs of endoclamping versus external aortic occlusion in a large administrative database. METHODS: There were 52,882 adults undergoing eligible cardiac surgery (October 2015 to March 2020) identified in the Premier Healthcare Database. Endoclamp procedures (n = 419) were 1:3 propensity score matched to similar procedures using external aortic occlusion (n = 1,244). Generalized linear modeling measured differences in in-hospital complications (major adverse renal and cardiac events, including mortality, new-onset atrial fibrillation, acute kidney injury [AKI], myocardial infarction [MI], postcardiotomy syndrome, stroke/transient ischemic attack [TIA], and aortic dissection) and length of stay (LOS). RESULTS: The mean age was 63 years, and 53% were male (n = 882). The majority (93%, n = 1,543) were mitral valve procedures, and 17% of procedures (n = 285) were robot-assisted. Total hospitalization costs were not statistically significantly different between the 2 groups ($52,158 vs $49,839, P = 0.06). The median LOS was significantly shorter in the endoclamp group (incident rate ratio = 0.87, P < 0.001). Mortality, atrial fibrillation, AKI, and stroke/TIA were similar between the 2 groups. MI and postcardiotomy syndrome were lower in the endoclamp group (odds ratio [OR] = 0.14, P = 0.006, and OR = 0.27, P = 0.005). There were no aortic dissections in the endoclamp group. CONCLUSIONS: Aortic endoclamping in MIS was associated with similar costs, shorter LOS, no dissections, and comparably low mortality and stroke rates when compared with external clamping in this hospital billing dataset. These results demonstrate the clinical safety and efficacy of endoaortic balloon clamping in a real-world setting. Further studies are warranted.

In-Hospital Outcomes of Heart Failure Patients with Valvular Heart Disease: Insights from Real-World Claims Data.

Purpose: Heart failure (HF) is a serious public health burden that is rapidly increasing in the aging population. Valvular heart disease (VHD) is a known etiology of heart failure (HF); however, the impact of VHD on outcomes of patients with HF has not been well-studied in Japan. This study aimed to determine the rates of VHD in Japanese patients admitted for HF and explore associations of VHD with in-hospital outcomes through a claim-based analysis. Patients and methods: We analyzed claims data from 86,763 HF hospitalizations (January 2017 through December 2019) from the Medical Data Vision database. Common etiologies of HF were examined, then hospitalizations were categorized into those with VHD and those without. Covariate-adjusted models were used to explore the association of VHD with in-hospital mortality, length of stay, and medical cost. Results: Of 86,763 hospitalizations for HF, 13,183 had VHD and 73,580 did not. VHD was the second most frequent etiology of HF (15.2%). The most frequent type of VHD was mitral regurgitation (36.4% of all hospitalizations with VHD), followed by aortic stenosis (33.7%) and aortic regurgitation (16.4%). There was no significant difference in in-hospital mortality between hospitalizations with VHD vs those without (9.0% vs 8.9%; odds ratio [95% CI]: 1.01 [0.95-1.08]; p=0.723). Hospitalizations with VHD were associated with significantly longer length of stay (26.1 vs 24.8 days; incident rate ratio [95% CI]: 1.05 [1.03-1.07]; p<0.001) and higher medical costs (1536 vs 1195 thousand yen; rate ratio [95% CI]: 1.29 [1.25-1.32]; p<0.001). Conclusion: VHD was a frequent etiology of HF that was associated with significant medical resource use. Future studies are needed to investigate whether timely VHD treatment could reduce HF progression and its associated healthcare resource utilization.

Association of ACEI/ARB and statin prescribing patterns with mortality after Transcatheter Aortic Valve Replacement (TAVR): Findings from real-world claims data.

BACKGROUND: Transcatheter aortic valve replacement (TAVR) has become the standard of care for most patients with severe aortic stenosis (AS), but the impact of medical therapy prescribing patterns on post-TAVR patients has not been thoroughly investigated. METHODS: We analyzed Optum claims data from 9,012 adults who received TAVR for AS (January 2014-December 2018). Pharmacy claims data were used to identify patients who filled ACEI/ARB and/or statin prescriptions during the study's 90-day landmark period post-TAVR. Kaplan-Meier and adjusted Cox Proportional Hazards models were used to evaluate the association of prescribing patterns with mortality during the 3-year follow-up period. Subgroup analyses were performed to examine the impact of 11 potential confounders on the observed associations. RESULTS: A significantly lower adjusted 3-year mortality was observed for patients with post-TAVR prescription for ACEI/ARBs (hazard ratio [HR] = 0.82, 95% confidence interval [CI] 0.74-0.91, P = .0003) and statins (HR = 0.85, 95% CI 0.77-0.94, P = .0018) compared to patients who did not fill prescriptions for these medications post-TAVR. Subgroup analyses revealed that the survival benefit associated with ACEI/ARB prescription was not affected by any of the potential confounding variables, except preoperative ACEI/ARB prescription was associated with significantly lower risk of mortality vs postoperative prescription only. No other subgroup variables had significant interactions associated with survival benefits, including preoperative use of statins. CONCLUSIONS: In this large-scale, real-world analysis of patients undergoing TAVR, the prescription of ACEI/ARB and statins was associated with a significantly lower risk of mortality at 3-years, especially in those where the medications were initiated preoperatively.

Bottom-up and top-down pressures mediate competition between two generalist insects.

The effects of competition can have far-reaching consequences for individuals, populations, and communities and therefore we should strive toward a deeper understanding of competitive interactions. In some cases, dietary generalists may be predicted to experience weak competition effects because of their ability to use a wide range of host plants. However, competition between insects frequently occurs indirectly, which can hinder insects' abilities to avoid competitive interactions. Therefore, competition may be as strong among dietary generalists as among dietary specialists. Yet competition between insects that are dietary generalists is infrequently studied. We tested for evidence of competitive interactions between two common, temporally separated, generalist insects: the western tent caterpillar (Malacosoma californicum), which feeds early in the season, and the fall webworm (Hyphantria cunea), which feeds later in the season. Both species frequently use a common host plant species (chokecherry) as a preferred host at our field sites. We tested the relative strength of bottom-up effects resulting from competitive interactions between these two generalists with laboratory-rearing trials at the relevant time of year for each insect. We recorded three common fitness measures (development time, pupal mass, and survival) for caterpillars reared on chokecherry with no damage from either of our focal species, with tent caterpillar damage, and with fall webworm damage. To test the strength of top-down pressures on fall webworm larval fitness and any potential interactions with bottom-up effects, we reared larvae in the field either exposed to or protected from predators on host plants that either did or did not have tent caterpillars feeding on them earlier in the season. We found evidence of bottom-up fitness effects on tent caterpillars and top-down and bottom-up fitness effects on fall webworms confirming that tent caterpillars and fall webworms compete indirectly. Tent caterpillars had lower pupal mass when reared on leaves from shrubs damaged by fall webworms. Fall webworms had lower pupal mass and longer development time when reared on leaves from shrubs damaged by tent caterpillars. In field trials, fall webworms reared on shrubs damaged by tent caterpillars had a lower survival and pupal mass. We show evidence of indirect competition in temporally separated generalists through leaf quality (bottom-up effects) and natural enemies (top-down effects).

Species loss and nitrogen pollution alter litter decomposition dynamics in coastal salt marshes.

Litter decomposition is a central ecosystem function because dead plant biomass plays a critical role in carbon storage, the nitrogen (N) cycle, and as food/habitat for animals and microorganisms. In the face of global change, interactions between organisms that participate in litter decomposition are likely to change due to species loss and N pollution. To understand how these global change factors may interact to alter litter decomposition, we manipulated the detritivore community and N concentrations in a coastal salt marsh for 2 years. We chose to manipulate densities of a dominant, detritivorous snail (Melampus bidentatus) because its population size is expected to decline due to climate change, yet its impact on litter decomposition has not been tested in the field. We measured litter decomposition rates, detritivore densities, and the N concentrations of sediment and litter. We found that endogenous N enrichment (N added live plants before decomposition), exogenous N enrichment (N added to decomposing plants) and higher densities of Melampus increased litter decomposition rates. Linear mixed models further revealed that snails, other detritivores, and soil NH4+ were the best predictors of litter mass loss in the middle stages of decomposition. Notably, exogenous N added to litter already enriched with N further increased mass loss but did not increase litter %N. Our study reveals how global change in the form species loss and N pollution can have palpable impacts on carbon cycling and ecosystem function.

Impact of Managing Provider Type on Severe Aortic Stenosis Management and Mortality.

Background Many patients with symptomatic severe aortic stenosis do not undergo aortic valve replacement (AVR) despite clinical guidelines. This study analyzed the association of managing provider type with cardiac specialist follow-up, AVR, and mortality for patients with newly diagnosed severe aortic stenosis (sAS). Methods and Results We identified adults with newly diagnosed sAS per echocardiography performed between January 2017 and March 2019 using Optum electronic health record data. We then selected from those meeting all eligibility criteria patients managed by a primary care provider (n=1707 [25%]) or cardiac specialist (n=5039 [75%]). We evaluated the association of managing provider type with cardiac specialist follow-up, AVR, and mortality, as well as the independent association of cardiac specialist follow-up and AVR with mortality, within 1 year of echocardiography detecting sAS. A subgroup analysis was limited to patients with symptomatic sAS. Patient characteristics and comorbidities at baseline were used for covariate-adjusted cause-specific and multivariable Cox proportional hazard models assessing group differences in outcomes by managing provider type. An adjusted Cox proportional hazard model with additional time-dependent covariates for follow-up and AVR was used to assess these practices' association with mortality. Within 1 year of echocardiography detecting sAS, data revealed that primary care provider management was associated with lower rates of cardiac specialist follow-up (hazard ratio [HR], 0.47 [95% CI, 0.43-0.50], P<0.0001) and AVR (HR, 0.58 [95% CI, 0.53-0.64], P<0.0001) and with higher 1-year mortality (HR, 1.45 [95% CI, 1.26-1.66], P<0.0001). Cardiac specialist follow-up and AVR were independently associated with lower mortality (follow-up: HR, 0.55 [95% CI, 0.48-0.63], P<0.0001; AVR: HR, 0.70 [95% CI, 0.60-0.83], P<0.0001). Results were similar for patients with symptomatic sAS. All analyses were adjusted for baseline patient characteristics and comorbidities. Conclusions For patients newly diagnosed with sAS, we observed differences in rates of cardiac specialist follow-up and AVR and risk of mortality between primary care provider- versus cardiologist-managed patients with sAS. In addition, a lower likelihood of receiving follow-up and AVR was independently associated with higher mortality.

Genetic divergence among threespine stickleback that differ in nuptial coloration.

Sexual signals are shaped by their intended and unintended receivers as well as the signalling environment. This interplay between sexual and natural selection can lead to divergence in signals in heterogeneous environments. Yet, the extent to which gene flow is restricted when signalling phenotypes vary across environments and over what spatial scales remains an outstanding question. In this study, we quantify gene flow between two colour morphs, red and black, of freshwater threespine stickleback fish (Gasterosteus aculeatus). We capitalize on the very recent divergence of signalling phenotypes in this system to characterize within-species and among-morph genetic variation and to test for levels of gene flow between colour morphs in Oregon and Washington. Despite limited evidence for assortative mating between allopatric red and black populations, we found that black populations are genetically distinct from nearby red populations and that the black morph appears to have evolved independently at least twice in Oregon and Washington. Surprisingly, we uncovered a group of stickleback in one small coastal stream, Connor Creek, which is genetically and morphologically distinct from the red and black colour morphs and from marine stickleback. Historically, both colour morphs have coexisted in this location and sometimes hybridized, raising new questions about the origins and history of these fish, which were first described as anadromous-black hybrids >50 years ago. Understanding how genetic variation is currently partitioned within and among populations and colour morphs in this system should prompt future studies to assess the relative roles of habitat, ecological and pre- and post-reproductive barriers in the genetic divergence and phenotypic patterns we observe in nature.

Streetlights positively affect the presence of an invasive grass species.

Anthropogenic disturbances associated with urban ecosystems can create favorable conditions for populations of some invasive plant species. Light pollution is one of these disturbances, but how it affects the growth and establishment of invasive plant populations is unknown. Cheatgrass (Bromus tectorum) is a problematic invasive species where it has displaced native grassland communities in the United States, but to our knowledge, there have been no studies of the ecological factors that affect cheatgrass presence in urban ecosystems. We conducted field surveys in urban alleys in Denver, Colorado, to compare the presence of cheatgrass at sites with and without artificial light at night (hereafter artificial light) from streetlights. These streetlights are mounted on utility poles, which cause ground disturbance when installed in alleys; we were able to test the independent effect of poles on cheatgrass establishment because not all poles have streetlights on them. We found that cheatgrass was positively associated with the presence of streetlights and to a lesser extent poles. In addition to cheatgrass, we also found that other plants were positively associated with the presence of both poles and streetlights. Our results suggest that artificial light may benefit the occurrence of cheatgrass and other plant species in urban settings. While invasive populations of cheatgrass in wild habitats attract the most attention from managers, we suggest more consideration for this grass in urban environments where its growth and establishment benefit from anthropogenic changes.

Utilization of Medical Codes for Hypotension in Shock Patients: A Retrospective Analysis.

PURPOSE: To evaluate the utilization of hypotension diagnosis codes by shock type and year in known hypotensive patients. PATIENTS AND METHODS: Retrospective analysis of the Medicare fee-for-service claims database. Patients with a shock diagnosis code between 2011 and 2017 were identified using the International Classification of Diseases, Ninth and Tenth Revision, Clinical Modification (ICD-9-CM and ICD-10-CM). Based on specific ICD codes corresponding to each shock type, patients were classified into four mutually exclusive cohorts: cardiogenic shock, hypovolemic shock, septic shock, and other/unspecified shock. Annual proportion and counts of cases with at least one hypotension ICD code for each shock cohort were generated to produce 7-year medical code utilization trends. A Cochran-Armitage test for trend was performed to evaluate the statistical significance. RESULTS: A total of 2,200,275 shock patients were analyzed, 13.3% (n=292,192) of which received a hypotension code. Hypovolemic shock cases were the most likely to receive a hypotension code (18.02%, n=46,544), while septic shock cases had the lowest rate (11.48%, n=158,348). The proportion of patients with hypotension codes for other cohorts were 18.0% (n=46,544) for hypovolemic shock and 16.9% (n=32,024) for other/unspecified shock. The presence of hypotension codes decreased by 0.9% between 2011 and 2014, but significantly increased from 10.6% in 2014 to 17.9% in 2017 (p <0.0001, Z=-105.05). CONCLUSION: Hypotension codes are remarkably underutilized in known hypotensive patients. Patients, providers, and researchers are likely to benefit from improved hypotension coding practices.

Relation of Institutional Mitral Valve Surgical Volume to Surgical and Transcatheter Outcomes in Medicare Patients.

There are limited data to support proposed increases to the minimum institutional mitral valve (MV) surgery volume required to begin a transcatheter mitral valve repair (TMVr) program. The current study examined the association between institutional MV procedure volumes and outcomes. All 2017 Medicare fee-for-service patients who received a TMVr or MV surgery procedure were included and analyzed separately. The exposure was institutional MV surgery volume: low (1 to 24), medium (25 to 39) or high (40+). Outcomes were in-hospital mortality and 1-year postdischarge mortality and cardiovascular rehospitalization. For MV surgery patients, in-hospital mortality rates were 6.4% at low-volume, 8.7% at medium-volume and 9.8% at high-volume facilities. Rates were significantly higher for low-volume [OR = 1.50, 95% CI (1.23 to 1.84)] and medium-volume [OR = 1.33, 95% CI (1.06 to 1.67)] compared with high-volume facilities. There was no statistically significant relationship between institutional MV surgery volume and in-hospital mortality for TMVr patients, either at low-volume [OR = 1.52, 95% CI (0.56, 4.13)] or medium-volume [OR = 1.58, 95% CI (0.82, 3.02)] facilities, compared with high-volume facilities. Across all volume categories, in-hospital mortality rates for TMVr patients were relatively low (2.3% on average). For both cohorts, the rates of 1-year mortality and cardiovascular rehospitalizations were not significantly higher at low- or medium-volume MV surgery facilities, as compared with high-volume. In conclusion, among Medicare patients, there was a relation between institutional MV surgery volume and in-hospital mortality for MV surgery patients, but not for TMVr patients.

Global change in marine coastal habitats impacts insect populations and communities.

Salt marsh and mangrove coastal ecosystems provide critical ecosystem services, but are being lost at an alarming rate. Insect communities in these ecosystems are threatened by human impacts, including sea level rise, habitat loss, external inputs including nutrients, metals, and hydrocarbons, as well as weather events, such as hurricanes. While some disturbances are felt throughout the food web (e.g. hurricanes), others are mediated by impacts on the dominant plants (e.g. nutrient subsidies). The impacts of these disturbances on insects/spiders and their rate of recovery is dependent on trophic level, life history, and diet breadth. While we understand impacts of single disturbances relatively well, we have very little understanding of how multiple disturbances interact to affect insect communities.

Prey identity but not prey quality affects spider performance.

Increasing host plant quality affects higher trophic level predators, but whether such changes are simply a result of prey density or are also affected by changes in prey quality remain uncertain. Moreover, whether changes in prey quality affect measures of predator performance is understudied. Using a combination of field and greenhouse mesocosm experiments, we demonstrate that the survival and body size of a hunting spider (Pardosa littoralis Araneae: Lycosidae) is affected more by prey species identity than the trophic level of the prey. Furthermore, increasing host plant quality does not necessarily propagate through the food web by altering prey quality. While changes in plant quality affected spider body mass, they did so in opposite ways for spiders feeding on Prokelisia (Hemiptera: Delphacodes) herbivores relative to Tytthus (Hemiptera: Miridae) egg predators, and had no impact on spider body mass for two additional species of intraguild prey. These changes in body mass were important because greater body mass increased spider egg production. To examine the generality of this pattern, we reviewed the literature and found a consistent positive relationship between female body size and egg production for Pardosa species, indicating that body size is a reliable proxy for fitness. While many studies emphasize the importance of nitrogen to arthropod diets, this focus may be driven largely by our understanding of herbivore diets rather than predator diets. Thus, the positive impact of host plant quality on higher trophic level predators appears to be driven more by altering prey composition, density, and availability rather than simply providing predators with more nutritious prey.

Predator population size structure alters consumption of prey from epigeic and grazing food webs.

Numerous studies have found that predators can suppress prey densities and thereby impact important ecosystem processes such as plant productivity and decomposition. However, prey suppression by spiders can be highly variable. Unlike predators that feed on prey within a single energy channel, spiders often consume prey from asynchronous energy channels, such as grazing (live plant) and epigeic (soil surface) channels. Spiders undergo few life cycle changes and thus appear to be ideally suited to link energy channels, but ontogenetic diet shifts in spiders have received little attention. For example, spider use of different food channels may be highly specialized in different life stages and thus a species may be a multichannel omnivore only when we consider all life stages. Using stable isotopes, we investigated whether wolf spider (Pardosa littoralis, henceforth Pardosa) prey consumption is driven by changes in spider size. Small spiders obtained > 80% of their prey from the epigeic channel, whereas larger spiders used grazing and epigeic prey almost equally. Changes in prey consumption were not driven by changes in prey density, but by changes in prey use by different spider size classes. Thus, because the population size structure of Pardosa changes dramatically over the growing season, changes in spider size may have important implications for the strength of trophic cascades. Our research demonstrates that life history can be an important component of predator diet, which may in turn affect community- and ecosystem-level processes.

Geography is more important than host plant use for the population genetic structure of a generalist insect herbivore.

Population divergence can occur due to mechanisms associated with geographic isolation and/or due to selection associated with different ecological niches. Much of the evidence for selection-driven speciation has come from studies of specialist insect herbivores that use different host plant species; however, the influence of host plant use on population divergence of generalist herbivores remains poorly understood. We tested how diet breadth, host plant species and geographic distance influence population divergence of the fall webworm (Hyphantria cunea; FW). FW is a broadly distributed, extreme generalist herbivore consisting of two morphotypes that have been argued to represent two different species: black-headed and red-headed. We characterized the differentiation of FW populations at two geographic scales. We first analysed the influence of host plant and geographic distance on genetic divergence across a broad continental scale for both colour types. We further analysed the influence of host plant, diet breadth and geographic distance on divergence at a finer geographic scale focusing on red-headed FW in Colorado. We found clear genetic and morphological distinction between red- and black-headed FW, and Colorado FW formed a genetic cluster distinct from other locations. Although both geographic distance and host plant use were correlated with genetic distance, geographic distance accounted for up to 3× more variation in genetic distance than did host plant use. As a rare study investigating the genetic structure of a widespread generalist herbivore over a broad geographic range (up to 3,000 km), our study supports a strong role for geographic isolation in divergence in this system.