A Rare Anastomosis Between the Internal and the External Jugular Veins: A Case Report.

Usually, the external jugular vein (EJV) is located superficially over the sternocleidomastoid muscle and joins the subclavian vein or the venous angle. The internal jugular vein (IJV) lies deeply in close relation with the common carotid artery and vagus nerve, enveloped by the carotid sheath. Normally, there is no direct connection between those vessels. During a routine neck dissection, we found a rare anastomosis between IJV and EJV. The anastomosis was localized on the level of the cricoid cartilage. It was approximately 1 cm long, with the diameter of the lumen being 0.3 cm. There was no obstruction along the length of the vessel. The direction was oblique and followed the blood flow from IJV to EJV. The observed variation has high clinical importance related to numerous procedures executed in the neck region, such as placement of hemodialysis catheter in patients with renal failure, insertion of central venous line in the care of critically ill patients, and radical neck dissections.

Preanalytical Errors in Clinical Laboratory Testing at a Glance: Source and Control Measures.

The accuracy of diagnostic results in clinical laboratory testing is paramount for informed healthcare decisions and effective patient care. While the focus has traditionally been on the analytical phase, attention has shifted towards optimizing the preanalytical phase due to its significant contribution to total laboratory errors. This review highlights preanalytical errors, their sources, and control measures to improve the quality of laboratory testing. Blood sample quality is a critical concern, with factors such as hemolysis, lipemia, and icterus leading to erroneous results. Sources of preanalytical errors encompass inappropriate test requests, patient preparation lapses, and errors during sample collection, handling, and transportation. Mitigating these errors includes harmonization efforts, education and training programs, automated methods for sample quality assessment, and quality monitoring. Collaboration between laboratory personnel and healthcare professionals is crucial for implementing and sustaining these measures to enhance the accuracy and reliability of diagnostic results, ultimately improving patient care.

Complete mitochondrial genomes of the black corals Alternatipathesmirabilis Opresko & Molodtsova, 2021 and Parantipatheslarix (Esper, 1788) (Cnidaria, Anthozoa, Hexacorallia, Antipatharia, Schizopathidae).

We describe the complete mitogenomes of the black corals Alternatipathesmirabilis Opresko & Molodtsova, 2021 and Parantipatheslarix (Esper, 1790) (Cnidaria, Anthozoa, Hexacorallia, Antipatharia, Schizopathidae). The analysed specimens include the holotype of Alternatipathesmirabilis, collected from Derickson Seamount (North Pacific Ocean; Gulf of Alaska) at 4,685 m depth and a potential topotype of Parantipatheslarix, collected from Secca dei Candelieri (Mediterranean Sea; Tyrrhenian Sea; Salerno Gulf; Italy) at 131 m depth. We also assemble, annotate and make available nine additional black coral mitogenomes that were included in a recent phylogeny (Quattrini et al. 2023b), but not made easily accessible on GenBank. This is the first study to present and compare two mitogenomes from the same species of black coral (Stauropathesarctica (Lütken, 1871)) and, thus, place minimum boundaries on the expected level of intraspecific variation at the mitogenome level. We also compare interspecific variation at the mitogenome-level across five different specimens of Parantipathes Brook, 1889 (representing at least two different species) from the NE Atlantic and Mediterranean Sea.

Accessory Extensor Pollicis Longus Spanning the Fourth Dorsal Compartment of the Wrist: A Case Report.

Introduction: Variations of the extensor pollicis longus (EPL) tendon of the hand are not uncommon. Yet, this anatomic structure exhibits the least variations among the extensors of the upper extremity. Case Report: This article highlights the presence of an accessory EPL tendon in the fourth dorsal compartment, which was presented as an incidental finding during an elective wrist arthrodesis in a woman in her 40s. Conclusion: Knowledge of this anatomic variation can guide surgical planning and mitigate iatrogenic injury by anticipating potential challenges.

Plasticity-led and mutation-led evolutions are different modes of the same developmental gene regulatory network.

The standard theory of evolution proposes that mutations cause heritable variations, which are naturally selected, leading to evolution. However, this mutation-led evolution (MLE) is being questioned by an alternative theory called plasticity-led evolution (PLE). PLE suggests that an environmental change induces adaptive phenotypes, which are later genetically accommodated. According to PLE, developmental systems should be able to respond to environmental changes adaptively. However, developmental systems are known to be robust against environmental and mutational perturbations. Thus, we expect a transition from a robust state to a plastic one. To test this hypothesis, we constructed a gene regulatory network (GRN) model that integrates developmental processes, hierarchical regulation, and environmental cues. We then simulated its evolution over different magnitudes of environmental changes. Our findings indicate that this GRN model exhibits PLE under large environmental changes and MLE under small environmental changes. Furthermore, we observed that the GRN model is susceptible to environmental or genetic fluctuations under large environmental changes but is robust under small environmental changes. This indicates a breakdown of robustness due to large environmental changes. Before the breakdown of robustness, the distribution of phenotypes is biased and aligned to the environmental changes, which would facilitate rapid adaptation should a large environmental change occur. These observations suggest that the evolutionary transition from mutation-led to plasticity-led evolution is due to a developmental transition from robust to susceptible regimes over increasing magnitudes of environmental change. Thus, the GRN model can reconcile these conflicting theories of evolution.

Multiple variation of right renal and gonadal vascularization: report of two cases.

We present two cases of multiple anatomical variations of the renal and gonadal vessels. The first case presented duplication of the renal vein and the presence of an accessory renal artery. However, the most interesting fact, in this case, was that the right gonadal vein emptied into the inferior right renal vein instead of ending in the inferior vena cava as would typically be the case. In the second case, we also found an accessory renal artery and the right gonadal vein emptied at the exact junction between the right renal vein and the inferior vena cava. Clinicians and surgeons should be familiar with anatomical variations to provide an accurate diagnosis during preoperative studies and to avoid surprises in abdominal surgical procedures.

Este estudo apresenta dois casos de variação anatômica múltipla de vasos renais e gonadais. O primeiro caso apresentou uma duplicação da veia renal e a presença de uma artéria renal acessória. Porém, o fato mais interessante nesse caso foi a veia gonadal direita desembocar na veia renal direita inferior em vez de terminar na veia cava inferior, como seria o normal. No segundo caso, além de também encontrarmos uma artéria renal acessória, a veia gonadal direita desembocava no exato ponto de junção entre a veia renal direita e a veia cava inferior. Clínicos e cirurgiões devem estar familiarizados com a presença de possíveis variações dos vasos renais e gonadais, sendo um conhecimento imprescindível para obter um diagnóstico mais preciso e para evitar surpresas em procedimentos cirúrgicos abdominais.

Variation coefficient of stone density and renal cortical thickness: the parameters evaluating non-contrast computed tomography imaging for predict extracorporeal shock wave lithotripsy success.

The stone density (SD) is not the same in all parts of the stone due to the heterogeneous nature of the stone and the shock wave (SW) passes through tissues of many different densities until it reaches the stone. These factors affect the success of Extracorporeal Shock Wave Lithotripsy (ESWL). We aimed to evaluate the effect of the Variation Coefficient of Stone Density (VCSD) and Renal Cortical Tickness (RCT) on the success of ESWL. Between 2020 and 2023, 510 patients who underwent ESWL were divided into 2 groups treatment success (n:304) and treatment failure (n:206). Non-Contrast Computed Tomography (NCCT) imaging values of hydronephrosis degree of the kidney, stone location, stone volume (SV), stone-skin distance (SSD), SD, Standard deviation of Stone Density (SDSD), VCSD, RCT, Soft-Tissue Thickness (STT), Muscle Thickness (MT) were analyzed. VCSD value was obtained by dividing SDSD by SD. Along the SW, tissues were divided into three components: kidney (renal cortex), muscle and other soft tissues. RCT, MT and SSD were measured at three different angles (0°, 45°, and 90°) and these 3 lengths were averaged. In univariate analysis, Body Mass Index (BMI), SV, SD, VCSD, SSD, RCT and STT were demonstrated to affect ESWL success. In multivariate analysis, low BMI, SV, SD, RCT and large VCSD were significant independent predictors of ESWL success. Among these parameters, VCSD had the highest prediction accuracy, followed by SD, SV, RCT and BMI, respectively. This study demonstrated that VCSD value and RCT are predictive parameters in determining the treatment of patients with urinary calculi and selecting suitable ESWL candidates.

MC4R variants modulate α-MSH and setmelanotide induced cellular signaling at multiple levels.

CONTEXT: Melanocortin-4 receptor (MC4R) plays an important role in body weight regulation. Pathogenic MC4R variants are the most common cause of monogenic obesity. OBJECTIVE: We have identified 17 MC4R variants in adult and pediatric patients with obesity. Here, we aimed to functionally characterize these variants by analyzing four different aspects of MC4R signaling. In addition, we aimed to analyze the effect of setmelanotide, a potent MC4R agonist, on these MC4R variants. MATERIALS AND METHODS: Cell surface expression and α-MSH- or setmelanotide-induced cAMP response, ß-arrestin-2 recruitment, and ERK activation were measured in cells expressing either wild type (WT) or variant MC4R. RESULTS: We found a large heterogeneity in the function of these variants. We identified variants with a loss of response for all studied MC4R signaling, variants with no cAMP accumulation or ERK activation but normal ß-arrestin-2 recruitment, and variants with normal cAMP accumulation and ERK activation but decreased ß-arrestin-2 recruitment, indicating disrupted desensitization and signaling mechanisms. Setmelanotide displayed a greater potency and similar efficacy as α-MSH, and induced significantly increased maximal cAMP responses of several variants compared to α-MSH. Despite the heterogeneity in functional response, there was no apparent difference in the obesity phenotype in our patients. DISCUSSION: We show that these obesity-associated MC4R variants affect MC4R signaling differently, yet leading to a comparable clinical phenotype. Our results demonstrate the clinical importance of assessing the effect of MC4R variants on a range of molecular signaling mechanisms to determine their association with obesity, which may aid in improving personalized treatment.

Type 1 fimbrial phase variation in multidrug-resistant asymptomatic uropathogenic Escherichia coli clinical isolates upon adherence to HTB-4 cells.

The adherence of bladder uroepithelial cells, subsequent expression, and regulation of type 1 fimbrial genes (key mediator of attachment) in clinical multidrug-resistant uropathogenic Escherichia coli (MDR-UPECs) isolated from individuals with asymptomatic bacteriuria (ABU) remain unexplored till date. Therefore, this study aimed to investigate the underlying molecular mechanisms associated with the adherence of clinical MDR-ABU-UPECs to human a uroepithelial cell line (HTB-4), both in the absence and presence of D-Mannose. These investigations focused on phase variation, expression, and regulation of type 1 fimbriae and were compared to a prototype ABU-strain (E. coli 83972) and symptomatic MDR-UPECs. Discordant to the ABU prototype strain, MDR-ABU-UPECs exhibited remarkable adhesive capacity that was significantly reduced after D-mannose exposure, fairly like the MDR symptomatic UPECs. The type 1 fimbrial phase variation, determined by the fim switch analysis, asserted the statistically significant incidence of "both OFF and ON" orientation among the adherent MDR-ABU-UPECs with a significant reduction in phase-ON colonies post-D-mannose exposure, akin to the symptomatic ones. This was indicative of an operative and alternating type 1 fimbrial phase switch. The q-PCR assay revealed a coordinated action of the regulatory factors; H-NS, IHF, and Lrp on the expression of FimB and FimE recombinases, which further controlled the function of fimH and fimA genes in ABU-UPECs, similar to symptomatic strains. Therefore, this study is the first of its kind to provide an insight into the regulatory crosstalk of different cellular factors guiding the adhesion of ABU-UPECs to the host. Additionally, it also advocated for the need to accurately characterize ABU-UPECs.

Coexistence of a retroesophageal right subclavian artery with a left maxillary artery medial to the mandibular nerve.

This case report describes the coexistence of a retroesophageal right subclavian artery and left maxillary artery which passed deep to the mandibular nerve. An 88-year-old woman died of acute heart failure, and the postmortem revealed that the right subclavian artery originated from the aortic arch as the last branch at the level of the fourth thoracic vertebra, then passed between the esophagus and the vertebral column. The artery then ascended right superiorly and passed behind the anterior scalene muscle. The right vertebral artery arose from the retroesophageal right subclavian artery and entered the transverse foramen of the sixth cervical vertebra. The left maxillary artery branched at the common trunk of the posterior deep temporal and the inferior alveolar arteries. The maxillary artery then turned anteromedially and branched to give the middle meningeal artery. The mandibular nerve gave off the buccal nerve, deep temporal nerve and a thick nerve just below the foramen ovale. The auriculotemporal nerve that branched from the thick nerve ran deep to the maxillary artery. The maxillary artery turned anteriorly, passing deep to the branches. The artery then split to give the buccal artery and the anterior deep temporal artery. In the pterygopalatine section, the maxillary artery branched off to form the common trunk of the infraorbital and sphenopalatine arteries and the posterior superior alveolar artery. It may be necessary to pay attention to the course of the maxillary artery and its relationship to the mandibular nerve branches, when a retroesophageal right subclavian artery is seen.

Functional characterization of archaic-specific variants in mitonuclear genes: insights from comparative analysis in S. cerevisiae.

Neanderthal and Denisovan hybridisation with modern humans has generated a non-random genomic distribution of introgressed regions, the result of drift and selection dynamics. Cross-species genomic incompatibility and more efficient removal of slightly deleterious archaic variants have been proposed as selection-based processes involved in the post-hybridisation purge of archaic introgressed regions. Both scenarios require the presence of functionally different alleles across Homo species onto which selection operated differently according to which populations hosted them, but only a few of these variants have been pinpointed so far. In order to identify functionally divergent archaic variants removed in humans, we focused on mitonuclear genes, which are underrepresented in the genomic landscape of archaic humans. We searched for non-synonymous, fixed, archaic-derived variants present in mitonuclear genes, rare or absent in human populations. We then compared the functional impact of archaic and human variants in the model organism Saccharomyces cerevisiae. Notably, a variant within the mitochondrial tyrosyl-tRNA synthetase 2 (YARS2) gene exhibited a significant decrease in respiratory activity and a substantial reduction of Cox2 levels, a proxy for mitochondrial protein biosynthesis, coupled with the accumulation of the YARS2 protein precursor and a lower amount of mature enzyme. Our work suggests that this variant is associated with mitochondrial functionality impairment, thus contributing to the purging of archaic introgression in YARS2. While different molecular mechanisms may have impacted other mitonuclear genes, our approach can be extended to the functional screening of mitonuclear genetic variants present across species and populations.

Helicobacter pylori glycan biosynthesis modulates host immune cell recognition and response.

Introduction: The pathogenic bacterium Helicobacter pylori has evolved glycan-mediated mechanisms to evade host immune defenses. This study tests the hypothesis that genetic disruption of H. pylori glycan biosynthesis alters immune recognition and response by human gastric epithelial cells and monocyte-derived dendritic cells. Methods: To test this hypothesis, human cell lines were challenged with wildtype H. pylori alongside an array of H. pylori glycosylation mutants. The relative levels of immune response were measured via immature dendritic cell maturation and cytokine secretion. Results: Our findings indicate that disruption of lipopolysaccharide biosynthesis diminishes gastric cytokine production, without disrupting dendritic cell recognition and activation. In contrast, variable immune responses were observed in protein glycosylation mutants which prompted us to test the hypothesis that phase variation plays a role in regulating bacterial cell surface glycosylation and subsequent immune recognition. Lewis antigen presentation does not correlate with extent of immune response, while the extent of lipopolysaccharide O-antigen elaboration does. Discussion: The outcomes of this study demonstrate that H. pylori glycans modulate the host immune response. This work provides a foundation to pursue immune-based tailoring of bacterial glycans towards modulating immunogenicity of microbial pathogens.

The genetic landscape of autism spectrum disorder in the Middle Eastern population.

Introduction: Autism spectrum disorder (ASD) is characterized by aberrations in social interaction and communication associated with repetitive behaviors and interests, with strong clinical heterogeneity. Genetic factors play an important role in ASD, but about 75% of ASD cases have an undetermined genetic risk. Methods: We extensively investigated an ASD cohort made of 102 families from the Middle Eastern population of Qatar. First, we investigated the copy number variations (CNV) contribution using genome-wide SNP arrays. Next, we employed Next Generation Sequencing (NGS) to identify de novo or inherited variants contributing to the ASD etiology and its associated comorbid conditions in families with complete trios (affected child and the parents). Results: Our analysis revealed 16 CNV regions located in genomic regions implicated in ASD. The analysis of the 88 ASD cases identified 41 genes in 39 ASD subjects with de novo (n = 24) or inherited variants (n = 22). We identified three novel de novo variants in new candidate genes for ASD (DTX4, ARMC6, and B3GNT3). Also, we have identified 15 de novo variants in genes that were previously implicated in ASD or related neurodevelopmental disorders (PHF21A, WASF1, TCF20, DEAF1, MED13, CREBBP, KDM6B, SMURF1, ADNP, CACNA1G, MYT1L, KIF13B, GRIA2, CHM, and KCNK9). Additionally, we defined eight novel recessive variants (RYR2, DNAH3, TSPYL2, UPF3B KDM5C, LYST, and WNK3), four of which were X-linked. Conclusion: Despite the ASD multifactorial etiology that hinders ASD genetic risk discovery, the number of identified novel or known putative ASD genetic variants was appreciable. Nevertheless, this study represents the first comprehensive characterization of ASD genetic risk in Qatar's Middle Eastern population.

Intraday and interday variations of milk fatty acids in dairy cows in early and late lactation.

The composition of milk fatty acid (FA) was determined using Fourier-transform mid-infrared spectroscopy, which enables the rapid measurement of many samples. Milk FA is one indicator supporting the management of dairy cows and herds. This study aimed to determine an appropriate sampling method for milk FA in a practical farm condition based on intraday and interday variations in milk FA composition during early and late lactation stages. Milk samples were collected in the morning (07:00-08:00 h) and afternoon (16:30-17:30 h) for five consecutive days during early and late lactation. Within the day, de novo FA as the total FA basis was higher in the morning than in the afternoon, whereas preformed FA as the total FA basis was lower in the morning than in the afternoon. The weighted averages of milk FA composition according to milk yield collected in the morning and afternoon were significantly different between cows in early and late lactation; however, these were not significantly different among the consecutive five sampling days in each period. It was concluded that milk samples collected in the morning and afternoon for 1 day are suitable for milk FA determination. These results provide basic data for determining precise sampling methods for practical farms.

Diffuse large B-cell lymphoma with DNA copy number changes in a Japanese black calf.

A 2-month-old Japanese Black calf exhibited mandibular and superficial cervical lymph node swelling. Fine needle aspiration cytology of the superficial cervical lymph node revealed large lymphoblast-like cells with mitoses. Hematological examination revealed remarkable lymphocytosis with atypical lymphocytes. Increased activities of serum total lactate dehydrogenase and thymidine kinase were detected. At necropsy, generalized swelling of lymph nodes was observed. Histopathological analysis revealed diffuse proliferation of medium-sized round centroblastic neoplastic cells that were positive for CD20, CD79α, PAX5, and BLA-36, and negative for CD3, CD5, CD10, and CD34. The calf was diagnosed with centroblastic diffuse large B-cell lymphoma (DLBCL) based on these findings. Analysis of DNA copy number variation revealed an increased copy number for the GIMAP family relative to that in healthy cattle. Moreover, decreases in copy numbers of GBP-1, MIR3141, OR5P1E, and PTPRG relative to those in healthy cattle were also observed. Because DNA copy number variation represent a major contribution to the somatic mutation landscapes in human tumors, these findings suggest that DNA copy number changes might have contributed to the onset of DLBCL in the present case.

The drivers of intraspecific trait variation and their implications for future tree productivity and survival.

Forests are facing unprecedented levels of stress from pest and disease outbreaks, disturbance, fragmentation, development, and a changing climate. These selective agents act to alter forest composition from regional to cellular levels. Thus, a central challenge for understanding how forests will be impacted by future change is how to integrate across scales of biology. Phenotype, or an observable trait, is the product of an individual's genes (G) and the environment in which an organism lives (E). To date, researchers have detailed how environment drives variation in tree phenotypes over long time periods (e.g., long-term ecological research sites [LTERs]) and across large spatial scales (e.g., flux network). In parallel, researchers have discovered the genes and pathways that govern phenotypes, finding high degrees of genetic control and signatures of local adaptation in many plant traits. However, the research in these two areas remain largely independent of each other, hindering our ability to generate accurate predictions of plant response to environment, an increasingly urgent need given threats to forest systems. I present the importance of both genes and environment in determining tree responses to climate stress. I highlight why the difference between G versus E in driving variation is critical for our understanding of climate responses, then propose means of accelerating research that examines G and E simultaneously by leveraging existing long-term, large-scale phenotypic data sets from ecological networks and adding newly affordable sequence (-omics) data to both drill down to find the genes and alleles influencing phenotypes and scale up to find how patterns of demography and local adaptation may influence future response to change.

Shaping immunity: The influence of natural selection on population immune diversity.

Humans exhibit considerable variability in their immune responses to the same immune challenges. Such variation is widespread and affects individual and population-level susceptibility to infectious diseases and immune disorders. Although the factors influencing immune response diversity are partially understood, what mechanisms lead to the wide range of immune traits in healthy individuals remain largely unexplained. Here, we discuss the role that natural selection has played in driving phenotypic differences in immune responses across populations and present-day susceptibility to immune-related disorders. Further, we touch on future directions in the field of immunogenomics, highlighting the value of expanding this work to human populations globally, the utility of modeling the immune response as a dynamic process, and the importance of considering the potential polygenic nature of natural selection. Identifying loci acted upon by evolution may further pinpoint variants critically involved in disease etiology, and designing studies to capture these effects will enrich our understanding of the genetic contributions to immunity and immune dysregulation.

Morphologic and mechanical adaptive variations in Saiga tatarica calcaneus: A model for interpreting the bone functional adaptation of wild artiodactyl in captivity.

Background and Aim: Captivity alters the locomotor behavior of wild artiodactyls and affects the mechanical loading of the calcaneus; however, the resulting adaptive changes in calcaneus morphology have not been sufficiently studied to date. This study aimed to investigate the morphological and mechanical adaptive variations in the calcaneus of Saiga tatarica to understand further the functional adaptation of the calcaneus in wild artiodactyl to captivity. Materials and Methods: Paired calcanei from autopsy samples of six captive wild artiodactyls (S. tatarica) and six domesticated artiodactyls (Ovis aries) were divided into skeletally immature and mature groups using X-ray evaluation of growth plate closure. High-resolution microcomputed tomography revealed a calcaneal diaphyseal cross-section. The mechanical and nanomorphological characteristics of the trabecular bone were determined by atomic force microscopy. Results: The percent cortical bone area (%CA), cortical thickness ratio (CTR), and Young's modulus (E) differed between species in the immature groups but not in the mature groups. S. tatarica had significantly higher growth rates for %CA, CTR, and E in the mid-shaft than O. aries (p < 0.05). Conclusion: The calcaneus morphology of S. tatarica converges with that of domesticated O. aries during ontogeny. These results indicate that the calcaneus of wild artiodactyls can undergo potentially transitional changes during the short-term adaptation to captivity. The above parameters can be preliminarily identified as morphological signs of functional bone adaptation in artiodactyls.

Predictors of germline genetic testing referral and completion in ovarian cancer patients at a Comprehensive Cancer Center.

OBJECTIVES: To identify predictors of referral and completion of germline genetic testing among newly diagnosed ovarian cancer patients, with a focus on geographic social deprivation, oncologist-level practices, and time between diagnosis and completion of testing. METHODS: Clinical and sociodemographic data were abstracted from medical records of patients newly diagnosed with ovarian cancer between 2014 and 2019 in the University of North Carolina Health System. Factors associated with referral for genetic counseling, completion of germline testing, and time between diagnosis and test results were identified using multivariable regression. RESULTS: 307/459 (67%) patients were referred for genetic counseling and 285/459 (62%) completed testing. The predicted probability of test completion was 0.83 (95% CI: 0.77-0.88) for patients with a referral compared to 0.27 (95% CI: 0.18-0.35) for patients without a referral. The predicted probability of referral was 0.75 (95% CI: 0.69-0.82) for patients at the 25th percentile of ZIP code-level Social Deprivation Index (SDI) and 0.67 (0.60-0.74) for patients at the 75th percentile of SDI. Referral varied by oncologist, with predicted probabilities ranging from 0.47 (95% CI: 0.32-0.62) to 0.93 (95% CI: 0.85-1.00) across oncologists. The median time between diagnosis and test results was 137 days (IQR: 55-248 days). This interval decreased by a predicted 24.46 days per year (95% CI: 37.75-11.16). CONCLUSIONS: We report relatively high germline testing and a promising trend in time from diagnosis to results, with variation by oncologist and patient factors. Automated referral, remote genetic counseling and sample collection, reduced out-of-pocket costs, and educational interventions should be explored.

Recruitment dynamics of juvenile salmonids: Comparisons among populations and with classic case studies.

Understanding recruitment, the process by which individuals are added to a population or to a fishery, is critical for understanding population dynamics and facilitating sustainable fisheries management. Important variation in recruitment dynamics is observed among populations, wherein some populations exhibit asymptotic productivity and others exhibit overcompensation (i.e., compensatory density-dependence in recruitment). Our ability to understand this interpopulation variability in recruitment patterns is limited by a poor understanding of the underlying mechanisms, such as the complex interactions between density dependence, recruitment, and environment. Furthermore, most studies on recruitment are conducted using an observational design with long time series that are seldom replicated across populations in an experimentally controlled fashion. Without proper replication, extrapolations between populations are tenuous, and the underlying environmental trends are challenging to quantify. To address these issues, we conducted a field experiment manipulating stocking densities of juvenile brook trout Salvelinus fontinalis in three wild populations to show that these neighboring populations-which exhibit divergent patterns of density dependence due to environmental conditions-also have important differences in recruitment dynamics. Testing against four stock-recruitment models (density independent, linear, Beverton-Holt, and Ricker), populations exhibited ~twofold variation in asymptotic productivity, with no overcompensation following a Beverton-Holt model. Although environmental variables (e.g., temperature, pH, depth, substrate) correlated with population differences in recruitment, they did not improve the predictive power in individual populations. Comparing our patterns of recruitment with classic salmonid case studies revealed that despite differences in the shape and parameters of the curves (i.e., Ricker vs. Beverton-Holt), a maximum stocking density of about five YOY fish/m2 emerged. Higher densities resulted in very marginal increases in recruitment (Beverton-Holt) or reduced recruitment due to overcompensation (Ricker).