Partial Clonality Expands the Opportunity for Spatial Adaptation.

AbstractReproductive mode may strongly impact adaptation in spatially varying populations linked by dispersal, especially when sexual and clonal offspring differ in dispersal. We determined how spatial structure affects adaptation in populations with mixed clonal and sexual reproduction. In a source-sink quantitative genetic deterministic model (with stabilizing selection around different optima), greater clonal reproduction or parent-offspring association (a measure of the part of the parent's phenotype other than the additive genetic component inherited by clonal offspring) increased the selective difference (difference between phenotypic optima) allowing sink populations to adapt. Given dispersal differences between clonally and sexually produced juveniles, adaptation increased with an increasing fraction of clonal dispersers. When considering migrational meltdown, partially clonal reproduction reduced cases where dispersal caused habitat loss. Stochastic individual-based simulations support these results, although the effect of differential dispersal was reversed, with decreased clonal dispersal allowing greater adaptation. These results parallel earlier findings that for an instantaneous shift in phenotypic optimum, increasing clonality allowed population persistence for a greater shift; here, selective change is spatial rather than temporal. These results may help explain the success of many partially clonal organisms in invading new habitats, complementing traditional explanations based on avoiding Allee effects.

Periprocedural P2Y12 inhibitors improve perioperative outcomes after carotid stenting by primarily decreasing strokes.

OBJECTIVE: The continuation of antiplatelet agents in the periprocedural period around carotid stenting (CAS) procedures is felt to be mandatory to minimize the risk of periprocedural stroke. However, the optimal antiplatelet regimen is unclear, with some advocating dual antiplatelet therapy, and others supporting the use of P2Y12 inhibitors alone. The objective of this study was to evaluate the periprocedural effect of P2Y12 inhibitors for CAS. METHODS: The Vascular Quality Initiative was used from years 2007 to 2020. All transcarotid artery revascularization (TCAR) and transfemoral carotid artery stenting (TF-CAS) procedures were included. Patients were stratified based on perioperative use of P2Y12 inhibitors as well as symptomatic status. Primary end points were perioperative neurological events (strokes and transient ischemic attacks). Secondary end points were mortality and myocardial infarction. RESULTS: A total of 31,036 CAS procedures were included for analysis, with 49.8% TCAR and 50.2% TF-CAS cases; 63.8% of patients were male and 82.3% of patients were on a P2Y12 inhibitor. P2Y12 inhibitor use was more common in males, asymptomatic patients, those older than 70 years, and concurrent statin use. P2Y12 inhibitors were more likely to be used in TCAR cases than in TF-CAS cases (87.3% vs 76.8%; P < .001). The rate of periprocedural neurological events in the whole cohort was 2.6%. Patients on P2Y12 inhibitors were significantly less likely to experience a periprocedural neurological event (2.3% vs 3.9%; P < .001) and mortality (0.6% vs 2.1%; P < .001) than those who were not on a P2Y12 inhibitor. There was no effect on the rates of myocardial infarction. On multivariate analysis, both symptomatic and asymptomatic patients on P2Y12 inhibitors were significantly less likely to develop perioperative neurological events. Additionally, the use of P2Y12 inhibitors demonstrated an independent significant effect in reducing of the rate of perioperative stroke (odds ratio, 0.29; 95% confidence interval, 0.25-0.33). Finally, additional analysis of the types of P2Y12 inhibitors used revealed that all seemed to be equally effective in decreasing the periprocedural neurological event rate. CONCLUSIONS: The use of perioperative P2Y12 inhibitors seems to markedly decrease the perioperative neurological event rate with TCAR and TF-CAS in both symptomatic and asymptomatic patients and should be strongly considered. Patients with contraindications to P2Y12 inhibitors may not be appropriate candidates for any CAS procedure. Additionally, alternative types of P2Y12 inhibitors seem to be equally effective as clopidogrel. Finally, an analysis of the Vascular Quality Initiative demonstrates that, even for TCAR cases, only 87.3% of patients seem to be on P2Y12 inhibitors in the periprocedural period, leaving room for significant improvement.

The interplay of movement and spatiotemporal variation in transmission degrades pandemic control.

Successful public health regimes for COVID-19 push below unity long-term regional Rt -the average number of secondary cases caused by an infectious individual. We use a susceptible-infectious-recovered (SIR) model for two coupled populations to make the conceptual point that asynchronous, variable local control, together with movement between populations, elevates long-term regional Rt , and cumulative cases, and may even prevent disease eradication that is otherwise possible. For effective pandemic mitigation strategies, it is critical that models encompass both spatiotemporal heterogeneity in transmission and movement.

The Effect of Predator Population Dynamics on Batesian Mimicry Complexes.

AbstractUnderstanding Batesian mimicry is a classic problem in evolutionary biology. In Batesian mimicry, a defended species (the model) is mimicked by an undefended species (the mimic). Prior theories have emphasized the role of predator behavior and learning as well as evolution in model-mimic complexes but have not examined the role of population dynamics in potentially governing the relative abundances and even persistence of model-mimic systems. Here, we examined the effect of the population dynamics of predators and alternative prey on the prevalence of warning-signaling prey composed of models and mimics. Using optimal foraging theory and signal detection theory, we found that the inclusion of predator and alternative prey population dynamics could reverse traditional theoretical predictions: as alternative prey increase in numbers, mimics suffer because larger populations of predators are maintained, resulting in apparent competition. Under some circumstances, apparent competition affects model populations as well, although not as severely as it affects mimics. Our results bear on the intriguing puzzle that in nature warning signals are relatively scarce, yet experiments suggest that such signals can be highly advantageous. The availability of alternative prey and numerical responses by predators can overwhelm advantages observed in experiments to keep warning signals in model-mimic systems relatively scarce.

Litter, Plant Competition, and Ecosystem Dynamics: A Theoretical Perspective.

AbstractCommunity structure depends jointly on species' responses to, and effects on, environmental factors. Many such factors, including detritus, are studied in ecosystem ecology. Detritus in terrestrial ecosystems is dominated by plant litter (nonliving organic material), which, in addition to its role in material cycling, can act as a niche factor modulating interactions among plants. Litter thus links traditional community and ecosystem processes, which are often studied separately. We explore this connection using population dynamics models of two plant species and a litter pool. We first find conditions determining the outcome of interactions between these species, highlighting the role that litter plays and the role of broader ecosystem parameters, such as decomposition rate. Species trade-offs in tolerance to direct competition and litter-based interference competition allow for coexistence, provided the litter-tolerant species produces more litter at the population level; otherwise, priority effects may result. When species coexist, litter-mediated interactions between plants disrupt the traditional relationship between biomass accumulation and decomposition. Increasing decomposition rate may have no effect on standing litter density and, in some cases, may even increase litter load. These results illustrate how ecosystem variables can influence community outcomes that then feed back to influence the ecosystem.

Risk Factors for and Intraoperative Management of Intolerance to Flow Reversal in TCAR.

BACKGROUND: In patients deemed high risk for carotid endarterectomy (CEA) who are indicated for treatment of carotid artery stenosis (CAS), transcarotid artery revascularization (TCAR) has been demonstrated as a safe and effective alternative to trans-femoral carotid artery stenting (TF-CAS). Compared to CEA, where approx. 12% of patients undergoing awake intervention do not tolerate internal carotid artery (ICA) clamping, only 1-2% of patients were observed to have intolerance to flow reversal during TCAR based on data from the ROADSTER1/2 trials. This study reviewed awake interventions from those trials to assess factors associated with intolerance to flow reversal and review how those cases were managed. METHODS: This is a retrospective review of prospectively collected data from Reverse Flow Used During Carotid Artery Stenting Procedure (ROADSTER) multicenter trial along with the subsequent post-approval (ROADSTER-2) trial. The subset of patients from both trials undergoing awake TCAR was analyzed to compare demographics, procedural details, and anatomic factors between patients who did and did not experience intolerance to reversal of flow to assess for predisposing factors. Patients were deemed intolerant to flow reversal at the discretion of the operator, often related to changes in completion of neurologic tasks, hemodynamic stability, or patient reported symptoms. RESULTS: A total of 103 patients from ROADSTER and 194 patients from ROADSTER-2 underwent TCAR under local/regional anesthesia. Of these, 8 patients had intolerance to flow reversal, though all cases were successfully completed. While intraoperative hemodynamic data was only available for 5 of the 8 intolerant patients, none experienced hypotension. 4 cases were completed under low flow reversal, 3 cases were successfully weaned from low to high flow over several minutes, and 1 case required general anesthesia. No significant association was found between intolerance to flow reversal and comorbidities including diabetes mellitus (DM), hypertension (HTN), hyperlipidemia (HLD), congestive heart failure (CHF), prior MI or angina, pre-op CAS-related symptoms, prior stroke, prior CAS or CEA, prior neck radiation, tandem stenosis, high cervical stenosis, or hostile neck. A trend towards significance was seen with chronic obstructive pulmonary disease (COPD) and contralateral carotid artery occlusion (P = 0.086 and 0.139, respectively). CONCLUSIONS: Despite intolerance to flow reversal, TCAR cases were successfully completed by adjusting reversal-of-flow rate and do not typically require conversion to GETA. While factors contributing to intolerance of flow reversal during TCAR remain poorly understood, this study identified a trend towards significance with an association of preexisting COPD and contralateral carotid artery occlusion. Given the low number of patients who experienced this issue, a larger sample size is required to better elucidate these trends.

Mannitol Use is Renal Protective in Patients with Chronic Kidney Disease Requiring Suprarenal Aortic Clamping.

BACKGROUND: Mannitol is often administered during open juxtarenal or suprarenal aortic surgery to prevent ischemic injury to the kidneys. Prior evidence evaluating the benefits of intraoperative mannitol in reducing ischemia/reperfusion injury is conflicting and largely based on small, retrospective series. The aim of this study was to evaluate the effect of mannitol in preventing postoperative hemodialysis in patients undergoing open abdominal aortic aneurysm (AAA) repair where proximal control involved temporary renal ischemia. METHODS: The Society for Vascular Surgery Quality Initiative database was queried for all patients undergoing elective open AAA repair between 2003 and 2020. Patients were included in the current analysis if the proximal aortic clamp was placed above at least one renal artery. Chronic kidney disease (CKD) was defined as Cr > 1.8 mg/dL. Primary end points were 30-day major morbidity (myocardial infarction, respiratory complications, lower extremity or intestinal ischemia, and the need for temporary or permanent hemodialysis) and mortality. Comparisons were made between the mannitol and nonmannitol cohorts and stratified by the presence of preexisting CKD. RESULTS: During the study period, 4,156 patients underwent elective open AAA repair requiring clamp placement more than one (32.7%) or both (67.3%) renal arteries; 182 patients (4.4%) had preexisting CKD. Overall, 69.8% of patients received mannitol during their surgery. Mannitol was more frequently used in cases involving clamp placement above both renal arteries (70.3%) than one renal artery (61.5%). While prolonged ischemia time (more than 40 min) was associated with a higher risk of postoperative dialysis in patients without CKD, it was not significant in patients with baseline CKD. On a univariate analysis, mannitol use in patients with CKD was associated with a lower risk of postoperative dialysis (P = 0.005). This remained significant on a multivariate analysis (P = 0.008). Mannitol use did not appear to confer renal protective effects in patients without baseline CKD. CONCLUSIONS: Mannitol use was associated with a decreased risk of need for postoperative hemodialysis in patients with CKD undergoing suprarenal aortic clamping for open aneurysm repair. In appropriately selected patients, particularly those with underlying renal insufficiency, mannitol may confer a renal protective effect in open repair of pararenal AAA requiring suprarenal clamping.

Anticoagulation Therapy is Associated with Increased Access-related Wound Infections after Hemodialysis Access Creation.

BACKGROUND: The effect of anticoagulation therapy (AC) on hemodialysis access patency and related complications is not well defined. Patients on long-term or chronic AC due to their underlying comorbid conditions may be particularly susceptible to access-related bleeding and complications from repetitive cannulation. Our goal is to assess the effect of anticoagulation therapy on outcomes after access creation. METHODS: The Vascular Quality Initiative (VQI) database was queried for patients undergoing arteriovenous fistula (AVF) or graft (AVG) placement, from 2011 to 2019. Only patients with data on post-procedural AC status were included. Anticoagulation use was defined as patients on warfarin, dabigatran, or rivaroxaban after access creation at postoperative follow up. Demographic and procedural details were analyzed. Wound infection and patency rates at six months were assessed. Binomial logistic regression analysis was performed to assess the association of anticoagulation use with these outcomes. RESULTS: A total of 27,757 patients underwent access creation, with the majority undergoing AVF creation (78.8%). The average age was 61.4 years and 55.3% were male. 12.9% of patients were on postoperative AC. The wound infection rate was 2.3- 3.8% in the no AC and AC cohorts, respectively (P < 0.001). At six months follow-up, patency was 85.7- 84.3% in the no AC and AC cohorts, respectively (P = 0.044). Expectedly, grafts had lower patency rates compared to AVF; those within the no AC cohort had a patency of 83.0% compared to 81.2 % in those on AC (P = 0.106). On multivariable analysis, anticoagulation use was associated with a higher risk of wound infections (odds ratio [OR] 1.513, 95% confidence interval [CI] 1.160-1.973, P = 0.002). AC use did not significantly affect access patency. CONCLUSION: Anticoagulation therapy was associated with a higher rate of wound infections but did not affect short-term access patency within six-months. These patients warrant close surveillance of their access for signs of infection. Furthermore, long-term implications of anticoagulation needs further evaluation.

Tropical forests can maintain hyperdiversity because of enemies.

Explaining the maintenance of tropical forest diversity under the countervailing forces of drift and competition poses a major challenge to ecological theory. Janzen-Connell effects, in which host-specific natural enemies restrict the recruitment of juveniles near conspecific adults, provide a potential mechanism. Janzen-Connell is strongly supported empirically, but existing theory does not address the stable coexistence of hundreds of species. Here we use high-performance computing and analytical models to demonstrate that tropical forest diversity can be maintained nearly indefinitely in a prolonged state of transient dynamics due to distance-responsive natural enemies. Further, we show that Janzen-Connell effects lead to community regulation of diversity by imposing a diversity-dependent cost to commonness and benefit to rarity. The resulting species-area and rank-abundance relationships are consistent with empirical results. Diversity maintenance over long time spans does not require dispersal from an external metacommunity, speciation, or resource niche partitioning, only a small zone around conspecific adults in which saplings fail to recruit. We conclude that the Janzen-Connell mechanism can explain the maintenance of tropical tree diversity while not precluding the operation of other niche-based mechanisms such as resource partitioning.

Revisiting the Role of Hyperparasitism in the Evolution of Virulence.

AbstractHyperparasitism denotes the natural phenomenon where a parasite infecting a host is in turn infected by its own parasite. Hyperparasites can shape the dynamics of host-parasite interactions and often have a deleterious impact on pathogens, an important class of parasites, causing a reduction in their virulence and transmission rate. Hyperparasitism thus could be an important tool of biological control. However, host-parasite-hyperparasite systems have so far been outside the mainstream of modeling studies, especially those dealing with eco-evolutionary aspects of species interactions. Here, we theoretically explore the evolution of life-history traits in a generic host-parasite-hyperparasite system, focusing on parasite virulence and the positive impact that hyperparasitism has on the host population. We also explore the coevolution of life-history traits of the parasite and hyperparasite, using adaptive dynamics and quantitative genetics frameworks to identify evolutionarily singular strategies. We find that in the presence of hyperparasites, the evolutionarily optimal pathogen virulence generally shifts toward more virulent strains. However, even in this case the use of hyperparasites in biocontrol could be justified, since overall host mortality decreases. An intriguing possible outcome of the evolution of the hyperparasite can be its evolutionary suicide.

Low-frequency avoidable errors during transcarotid artery revascularization.

OBJECTIVE: Transcarotid artery revascularization (TCAR) seems to be a safe and effective alternative to carotid endarterectomy (CEA) and transfemoral carotid artery stenting (TF-CAS). The TCAR system represents a paradigm shift in the management of carotid artery stenosis with potential for a significant decrease in periprocedural morbidity. However, as with CEA or TF-CAS, TCAR is associated with infrequent complications related to user technical error, most of which are preventable. Our goal is to describe these low-frequency events, and to provide guidelines for avoiding them. METHODS: The U.S. Food and Drug Administration (FDA) requires that all medical device manufacturers create a system for receiving, reviewing, and evaluating complaints (Code 21 of Federal Regulations 820.198). Silk Road Medical, Inc (Sunnyvale, Calif), has established a process by which all feedback, including complaints that may not meet FDA criteria, is captured and stored in a database for detailed analysis. More than 13,300 cases have been performed; submitted complaints were reviewed for incidents of serious injury and periprocedural complications, above and beyond the device-related events that must be reported to the FDA. RESULTS: A total of 13,334 patients have undergone TCAR worldwide between early 2011 and December 2019 using the SilkRoad device. Reported complications included 173 dissections (1.4% overall rate) of the common carotid artery at the access point, of which 22.5% were managed without intervention or with medical therapy alone and 24.3% were converted to CEA (considered failing safely). Errors in the location of stent deployment occurred in 16 cases (0.13%), with the most common site being the external carotid artery (75%). One wrong side carotid artery stent was placed in a patient with a high midline pattern of the bovine arch. Cranial nerve injury was reported in 11 cases (0.08%), only one of which persisted beyond 3 months. There have been three reported pneumothoraces and one reported chylothorax. Many of these errors can be recognized and prevented with careful attention to detail. CONCLUSIONS: In high-risk patients requiring treatment for carotid artery stenosis, TCAR has been proven as an alternative to TF-CAS with an excellent safety profile. As with CEA or TF-CAS, this procedure has the potential for infrequent complications, often as a result of user technical error. Although significant, these events can be avoided through a review of the collective experience to date and recognition of potential pitfalls, as we have described.

Closed incision negative pressure wound therapy may decrease wound complications in major lower extremity amputations.

OBJECTIVE: Wound complications after major lower extremity amputations (LEAs) are a cause of significant morbidity in vascular surgery patients. Recent publications have demonstrated the efficacy of the closed incision negative pressure dressing at preventing surgical site infections (SSIs); however, there are few data on its use in major LEAs. This study sought to assess if closed incision negative pressure wound therapy (NPWT) would decrease the risk of complications as compared with a standard dressing in patients with peripheral vascular disease undergoing major LEA. METHODS: Fifty-four consecutive patient limbs with a history of peripheral arterial disease underwent below-knee or above-knee amputations. This was a retrospective review of a prospectively maintained database from January 2018 to December 2019, and it included 23 amputations in the NPWT group and 31 amputations in the standard dressing group. NPWT using the PREVENA system was applied intraoperatively at the discretion of the operating surgeon and removed 5 to 7 days postoperatively. The standard group received a nonadherent dressing with an overlying compression dressing. Amputation incisions were assessed and wound complications were recorded. Student's t-test and two-sample proportion z-test were used for statistical analysis. A P value of less than .05 was considered statistically significant. RESULTS: For comorbidities, there was a higher incidence of tobacco use in the NPWT as compared with the standard group (44% vs 13%; P = .011), as well as trends toward increased prior amputations, anemia, hyperlipidemia, and chronic obstructive pulmonary disorder in the NPWT group. For risk factors, there were more dirty wounds in the NPWT as compared with the standard group (52% vs 26%; P = .046). For outcomes, there were fewer wound complications in the NPWT as compared with the standard group (13% vs 39%; P = .037). The types of wound-related complications in the NPWT group included one wound dehiscence with a deep SSI, one superficial SSI, and one incision line necrosis. In the standard group, there were four wound dehiscences with deep SSI, three superficial SSIs, four incision line necroses, and one stump hematoma. The rates of perioperative mortality and amputation revision did not differ significantly between the NPWT and the standard groups (3% vs 4% and 4.3% vs 10%, respectively). CONCLUSIONS: Closed incision NPWT may decrease the incidence of wound complications in vascular patients undergoing major LEA. This held true even among a population that was potentially at higher risk. This therapy may be considered for use in lower extremity major amputations.

Endovascular treatment of popliteal artery aneurysms has comparable long-term outcomes to open repair with shorter lengths of stay.

OBJECTIVE: During the past two decades, the treatment of popliteal artery aneurysms (PAAs) has undergone a transformation. Although open surgical repair (OR) has remained the reference standard for treatment, endovascular repair (ER) has become an attractive alternative for select patient populations. The objective of the present study was to compare the outcomes of OR vs ER of PAAs at a single institution. METHODS: We performed a retrospective review of the medical records for all patients who had undergone repair for PAAs from 1998 to 2017. The baseline patient, anatomic, and operative characteristics and outcomes were compared between the OR and ER cohorts. Intervention and treatment were at the discretion of the surgeon. RESULTS: From 1998 to 2017, 64 patients had undergone repair of 73 PAAs at our tertiary care center. Of the 69 patients (73 PAAs), 29 (33 PAAs) had undergone OR and 35 (40 PAAs) had undergone ER. When comparing the two cohorts, no statistically significant differences were found in the demographic characteristics such as age, gender, or number of runoff vessels. Significantly more patients in the ER group (n = 21; 53%) than in the OR group (n = 7; 21%) had had hyperlipidemia (P = .008) and a previous carotid intervention (6% vs 0%; P = .029). Overall, the presence of symptoms was similar between the two groups. However, the OR group had a significantly higher number of patients who had presented with acute ischemia (P = .01). The length of stay was significantly shorter for the ER cohort (mean, 1.8 days; range, 1-11 days) than for the OR group (mean, 5.4 days; range, 2-13 days; P < .0001). No significant difference was found in the primary or secondary patency rates between the two groups. In the ER group, good runoff (two or more vessels) was a positive predictor for primary patency at 1 year (odds ratio, 3.36; 95% confidence interval, 1.0-11.25). However, it was not in the OR group. Postoperative single and/or dual antiplatelet therapy did not affect primary patency in either cohort. CONCLUSIONS: The results of our study have demonstrated that ER of PAAs is a safe and durable option with patency rates comparable to those with OR and a decreased length of stay, with good runoff a positive predictor for primary patency in the ER cohort.

Environmental fluctuations dampen the effects of clonal reproduction on evolutionary rescue.

Evolutionary rescue occurs when genetic change allows a population to persist in response to an environmental change that would otherwise have led to extinction. Most studies of evolutionary rescue assume that species have either fully clonal or fully sexual reproduction; however, many species have partially clonal reproductive strategies in which they reproduce both clonally and sexually. Furthermore, the few evolutionary rescue studies that have evaluated partially clonal reproduction did not consider fluctuations in the environment, which are nearly ubiquitous in nature. Here, we use individual-based simulations to investigate how environmental fluctuations (either uncorrelated or positively autocorrelated) influence the effect of clonality on evolutionary rescue. We show that, for moderate magnitudes of environmental fluctuations, as was found in the absence of fluctuations, increasing the degree of clonality increases the probability of population persistence in response to an abrupt environmental change, but decreases persistence in response to a continuous, directional environmental change. However, with large magnitudes of fluctuations, both the benefits of clonality following a step change and the detrimental effects of clonality following a continuous, directional change are generally reduced; in fact, in the latter scenario, increasing clonality can even become beneficial if environmental fluctuations are autocorrelated. We also show that increased generational overlap dampens the effects of environmental fluctuations. Overall, we demonstrate that understanding the evolutionary rescue of partially clonal organisms requires not only knowledge of the species life history and the type of environmental change, but also an understanding of the magnitude and autocorrelation of environmental fluctuations.

Adjunctive false lumen intervention for chronic aortic dissections is safe but offers unclear benefit.

OBJECTIVE: Adjunctive false lumen embolization (FLE) with thoracic endovascular aortic repair (TEVAR) in patients with chronic aortic dissection is thought to induce FL thrombosis and favorable aortic remodeling. However, these data are derived from small single-institution experiences and the potential benefit of FLE remains unproven. In this study, we examined perioperative and midterm outcomes of patients with aortic dissection undergoing concomitant TEVAR and FLE.* METHODS: : Patients 18 or older who underwent TEVAR for chronic aortic dissection with known FLE status in the Society for Vascular Surgery Vascular Quality Initiative database between January 2010 and February 2020 were included. Ruptured patients and emergent procedures were excluded. Patient characteristics, operative details and outcomes were analyzed by group: TEVAR with or without FLE. Primary outcomes were in-hospital post-operative complications and all-cause mortality. Secondary outcomes included follow-up mean maximum aortic diameter change, rates of false lumen thrombosis, re-intervention rates, and mortality. RESULTS: 884 patients were included: 46 had TEVAR/FLE and 838 had TEVAR alone. There was no significant difference between groups in terms of age, gender, comorbidities, prior aortic interventions, mean maximum pre-operative aortic diameter (5.1cm vs. 5.0cm, P=0.43), presentation symptomatology, or intervention indication. FLE was associated with significantly longer procedural times (178min vs. 146min, P=0.0002), increased contrast use (134mL vs. 113mL, P=0.02), and prolonged fluoroscopy time (34min vs. 21min, P<0.0001). However, FLE was not associated with a significant difference in post-operative complications (17.4% vs. 13.8%, P=0.51), length of stay (6.5 vs. 5.7 days, P=0.18), or in-hospital all-cause mortality (0% vs. 1.3%, P=1). In mid-term follow-up (median 15.5months, IQR 2.2-36.2 months), all-cause mortality trended lower, but was not significant (2.2% vs. 7.8%); and Kaplan-Meier analysis demonstrated no difference in overall survival between groups (P=0.23). By Cox regression analysis, post-operative complications had the strongest independent association with all-cause mortality (HR 2.65, 95% CI 1.56-4.5, P<0.001). In patients with available follow-up imaging and re-intervention status, mean aortic diameter change (n=337, -0.71cm vs. -0.69cm, P=0.64) and re-intervention rates (n=487, 10% vs. 11.4%, P=1) were similar. CONCLUSIONS: Adjunctive FLE, despite increased procedural times, can be performed safely for patients with chronic dissection without significantly higher overall perioperative morbidity or mortality. TEVAR/FLE demonstrates trends for improved survival and increased rates of FL thrombosis in the treated thoracic segment; however, given the lack of evidence to suggest a significant reduction in re-intervention rates or induction of more favorable aortic remodeling compared to TEVAR alone, the overall utility of this technique in practice remains unclear. Further investigation is needed to determine the most appropriate role for FLE in managing chronic aortic dissections.

Environmental fluctuations can promote evolutionary rescue in high-extinction-risk scenarios.

Substantial environmental change can force a population onto a path towards extinction, but under some conditions, adaptation by natural selection can rescue the population and allow it to persist. This process, known as evolutionary rescue, is believed to be less likely to occur with greater magnitudes of random environmental fluctuations because environmental variation decreases expected population size, increases variance in population size and increases evolutionary lag. However, previous studies of evolutionary rescue in fluctuating environments have only considered scenarios in which evolutionary rescue was likely to occur. We extend these studies to assess how baseline extinction risk (which we manipulated via changes in the initial population size, degree of environmental change or mutation rate) influences the effects of environmental variation on evolutionary rescue following an abrupt environmental change. Using a combination of analytical models and stochastic simulations, we show that autocorrelated environmental variation hinders evolutionary rescue in low-extinction-risk scenarios but facilitates rescue in high-risk scenarios. In these high-risk cases, the chance of a run of good years counteracts the otherwise negative effects of environmental variation on evolutionary demography. These findings can inform the development of effective conservation practices that consider evolutionary responses to abrupt environmental changes.

Towards a unified framework for connectivity that disentangles movement and mortality in space and time.

Predicting connectivity, or how landscapes alter movement, is essential for understanding the scope for species persistence with environmental change. Although it is well known that movement is risky, connectivity modelling often conflates behavioural responses to the matrix through which animals disperse with mortality risk. We derive new connectivity models using random walk theory, based on the concept of spatial absorbing Markov chains. These models decompose the role of matrix on movement behaviour and mortality risk, can incorporate species distribution to predict the amount of flow, and provide both short- and long-term analytical solutions for multiple connectivity metrics. We validate the framework using data on movement of an insect herbivore in 15 experimental landscapes. Our results demonstrate that disentangling the roles of movement behaviour and mortality risk is fundamental to accurately interpreting landscape connectivity, and that spatial absorbing Markov chains provide a generalisable and powerful framework with which to do so.

Pulsed Immigration Events Can Facilitate Adaptation to Harsh Sink Environments.

In nature, rates of dispersal vary greatly over time, yet most theoretical explorations of ecological and evolutionary dynamics to date have assumed constant movement rates. Here we examine how a particular pattern of temporal variation-periodic pulses of immigration-influences adaptation to a harsh environment, in which a species experiences conditions outside its niche requirements. Using both deterministic models and stochastic individual-based simulations, we show that for many ecological and genetic scenarios, temporally spacing out immigration events increases the probability that local adaptation is sufficient for persistence (i.e., niche evolution). When immigration events are too frequent, gene flow can hamper local adaptation in sexual species, but sufficiently infrequent pulses of immigration allow for repeated opportunities for adaptation with temporary escapes from gene flow during which local selection is unleashed. We develop versions of our models with and without density dependence for three different assumptions about the genetics underlying fitness (haploid, diploid, and quantitative genetic variation) so that our results may be applicable to a wide range of natural systems. Our study adds to a growing body of literature showing that temporal variation in migration rates can have significant effects on local adaptation and is among the first to show how such variation affects niche evolution.

The interplay of nested biotic interactions and the abiotic environment regulates populations of a hypersymbiont.

The role of biotic interactions in shaping the distribution and abundance of species should be particularly pronounced in symbionts. Indeed, symbionts have a dual niche composed of traits of their individual hosts and the abiotic environment external to the host, and often combine active dispersal at finer scales with host-mediated dispersal at broader scales. The biotic complexity in the determinants of species distribution and abundance should be even more pronounced for hyper symbionts (symbionts of other symbionts). We use a chain of symbiosis to explore the relative influence of nested biotic interactions and the abiotic environment on occupancy and abundance of a hypersymbiont. Our empirical system is the epibiont ciliate Lagenophrys discoidea, which attaches to an ostracod that is itself ectosymbiotic on crayfish (the basal host). We applied multimodel selection and variance partitioning for GLMM to assess the relative importance of (a) traits of symbiotic hosts (ostracod sex and abundance), (b) traits of basal hosts (crayfish body weight, abundance and intermoult stage), (c) the abiotic environment (water chemistry and climate) and (d) geospatial autocorrelation patterns (capturing potential effects of crayfish dispersal among localities). Our models explained about half of the variation in prevalence and abundance of the hypersymbiont. Variation in prevalence was partly explained, in decreasing order of importance (18%-4%) by shared effects of symbiotic host traits and the abiotic environment, pure fixed effects of symbiotic hosts, abiotic environment and geospatial patterns (traits of basal hosts were not relevant). Hypersymbiont abundance was most strongly explained by random effects of host traits (mainly the symbiotic host), in addition to weaker fixed effects (mostly abiotic environment). Our results highlight the major role of the interplay between abundance of symbiotic hosts and water physico-chemistry in regulating populations of a hypersymbiotic ciliate, which is likely critical for dispersal dynamics, availability of attachment resources and suitability of on-host living conditions for the ciliate. We also found moderate signal of regulation by the basal host, for which we propose three mechanisms: (a) modulation of microhabitat suitability (crayfish-created water currents); (b) concentration of symbiotic hosts within crayfish; and (c) dispersal mediated by crayfish.

Evolutionary Rescue in a Linearly Changing Environment: Limits on Predictability.

Populations subject to substantial environmental change that decreases absolute fitness (expected number of offspring per individual) to less than one must adapt to persist. The probability of adaptive evolutionary rescue may be influenced by factors intrinsic to the organism itself, or by features specific to the individual population and its environment. An important question (given the increasing prevalence of environmental change) is the predictability of evolutionary rescue. We used an individual-based simulation model and a related analytic model to examine population persistence, given a continuously changing environment that leads to a linear change in the optimum for a phenotypic trait under selection. Population persistence was not well predicted by the population genetics at the start of environmental change, which contrasts strongly with the results shown in prior work for persistence after a sudden environmental change. Larger populations, which had a greater scope for the generation and maintenance of beneficial genetic variation, showed a clear advantage, but increasing the rate of environmental change always decreased the probability of persistence. Extinctions occurred throughout the period of continuous change, and populations that went extinct showed little sign of their eventual fate until shortly before extinction. Partially clonal populations showed less predictability and greater vulnerability to extinction when impacted by continuous change than did fully sexual populations-any advantage gained by the initial transmission of well-adapted phenotypes via clonal reproduction is lost as the phenotypic optimum continues to shift and the generation of novel variation is required for continuous adaptation.