Sensitivity to psychosocial influences at age 3 predicts mental health in middle childhood.

Children vary in how sensitive they are to experiences, with consequences for their developmental outcomes. In the current study, we investigated how behavioral sensitivity at age 3 years predicts mental health in middle childhood. Using a novel repeated measures design, we calculated child sensitivity to multiple psychological and social influences: parent praise, parent stress, child mood, and child sleep. We conceptualized sensitivity as the strength and direction of the relationship between psychosocial influences and child behavior, operationalized as toothbrushing time, at age 3 years. When children were 5-7 years old (n = 60), parents reported on children's internalizing and externalizing problems. Children who were more sensitive to their parents' praise at age 3 had fewer internalizing (r = -0.37, p = 0.016, pFDR = 0.042) and externalizing (r = -0.35, p = 0.021, pFDR = 0.042) problems in middle childhood. Higher average parent praise also marginally predicted fewer externalizing problems (r = -0.33, p = 0.006, pFDR = 0.057). Child sensitivity to mood predicted fewer internalizing (r = -0.32, p = 0.013, pFDR = 0.042) and externalizing (r = -0.38, p = 0.003, pFDR = 0.026) problems. By capturing variability in how children respond to daily fluctuations in their environment, we can contribute to the early prediction of mental health problems and improve access to early intervention services for children and families who need them most. RESEARCH HIGHLIGHTS: Children differ in how strongly their behavior depends on psychosocial factors including parent praise, child mood, child sleep, and parent stress. Children who are more sensitive to their parents' praise at age 3 have fewer internalizing and externalizing problems at age 5-7 years. Child sensitivity to mood also predicts fewer internalizing and externalizing problems.

Examining the role of social vulnerability, neighborhood characteristics, and geospatial patterns of firearm-related injuries and clinical outcomes in Milwaukee county.

BACKGROUND: Previous work has shown socioenvironmental factors can influence firearm injury. Milwaukee County, Wisconsin is a diverse midwestern county with historic disinvestment in marginalized communities yielding stark segregation along racial and ethnic lines. It is also one of the many U.S. counties burdened by surging firearm injuries. The differences among communities within Milwaukee County provides a unique opportunity to explore the intersection of socioenvironmental factors that may affect clinical outcomes and geospatial patterns of firearm injury. METHODS: The trauma registry from the regional adult level 1 trauma center was queried for patients who sustained a firearm-related injury from 2015 to 2022 (N = 2402). The Social Vulnerability Index (SVI) ranking was derived using patient residence addresses to evaluate its association with traumatic injury clinical outcomes (i.e., in-hospital mortality, length of hospital stay, ICU or ventilator treatment, or injury severity score) and risk screening results for alcohol use disorder (AUD), posttraumatic stress disorder (PTSD), and depression. We evaluated hotspots of firearm injury density over time for patient residences and injury locations and distances between locations. A spatially lagged regression model tested the association between firearm injury density and SVI domains, alcohol outlet types, and park coverage. RESULTS: Most firearm injury patients were younger, male, racial or ethnic minorities from disadvantaged neighborhoods (SVI total; M = 0.86, SD = 0.15). SVI was not associated with any clinical outcomes. Of those screened, 12.9% screened positive for AUD and 44.5% screened at risk for PTSD, depression, or both. Hotspot analysis indicated consistent concentrations of firearm injury density. There were no differences in clinical outcomes between those injured inside or outside the home. Census tracts with lower socioeconomic status, greater off-premises and lower on-premises alcohol outlet density were associated with greater firearm injury density. CONCLUSIONS: In Milwaukee County, firearm injury patients are injured in and often return to the same disadvantaged neighborhoods that may hamper recovery. Results replicate and expand previous work and implicate specific socioenvironmental factors for intervention and prevention of firearm injury.

Selection of positive controls and their impact on anti-drug antibody assay performance.

Development of assays to reliably identify and characterize anti-drug antibodies (ADAs) depends on positive control anti-idiotype (anti-id) reagents, which are used to demonstrate that the standards recommended by regulatory authorities are met. This work employs a set of therapeutic antibodies under clinical development and their corresponding anti-ids to investigate how different positive control reagent properties impact ADA assay development. Positive controls exhibited different response profiles and apparent assay analytical sensitivity values depending on assay format. Neither anti-id affinity for drug, nor sensitivity in direct immunoassays related to sensitivity in ADA assays. Anti-ids were differentially able to detect damage to drug conjugates used in bridging assays and were differentially drug tolerant. These parameters also failed to relate to assay sensitivity, further complicating selection of anti-ids for use in ADA assay development based on functional characteristics. Given this variability among anti-ids, alternative controls that could be employed across multiple antibody drugs were investigated as a more uniform means to define ADA detection sensitivity across drug products and assay protocols, which could help better relate assay results to clinical risks of ADA responses. Overall, this study highlights the importance of positive control selection to reliable detection and clinical interpretation of the presence and magnitude of ADA responses.

Surgical Resident Education and Performance in Extended Focused Abdominal Sonography for Trauma.

Extended focused assessment with sonography for trauma (eFAST) is a rapid triage tool aiding the detection of life-threatening injuries. In academic settings, residents perform most eFAST; however, the ACGME has no recommendations for eFAST training standards. We surveyed general surgery programs (GSPs) regarding eFAST training and established a baseline for sensitivity, specificity, and positive and negative predictive values for resident-performed eFAST. US GSP eFAST surveys were conducted by email and phone. We prospectively collected patient variables and evaluated resident performance from May to September 2022 and 2023 at an academic level I trauma center. A total of 60/339 general surgery residency programs (GSRPs) responded: Ten use Advanced Trauma Life Support (ATLS) only, n = 7 group training, n = 8 on-the-job only, and n = 33 several methods. Resident-performed eFAST had accuracy = 85.6%, sensitivity = 35.6%, specificity = 97.2%, PPV = 75%, and NPV = 87%. General surgery residency program training in eFAST is non-standardized. Sensitivity was considerably lower than the literature suggests. Positive resident-performed eFAST is generally accurate. We recommend a standardized approach to resident training in eFAST.

The Indirect Effects of Proximal Stressors Associated with Posttraumatic Stress Symptoms Severity among Sexually Victimized Sexual Minority Women: A Cross-Sectional Path Analysis.

Sexual minority women (SMW) are at risk for sexual victimization and stressors specifically related to their minority identity (e.g., discrimination). However, SMW experience posttraumatic stress disorder (PTSD) at rates beyond what may be explained by elevated risk for sexual victimization alone. This study aimed to examine the impact of stigma on PTSD symptoms among SMW survivors of sexual victimization. Results indicate that in relation to minority-specific distal stressors (i.e., heterosexist experiences), both minority-specific and general proximal stressors (i.e., internalized heterosexism, negative posttraumatic cognitions) indirectly affected PTSD symptom severity among this cross-sectional sample of sexually victimized SMW.

Multilayer network associations between the exposome and childhood brain development.

Growing up in a high poverty neighborhood is associated with elevated risk for academic challenges and health problems. Here, we take a data-driven approach to exploring how measures of children's environments relate to the development of their brain structure and function in a community sample of children between the ages of 4 and 10 years. We constructed exposomes including measures of family socioeconomic status, children's exposure to adversity, and geocoded measures of neighborhood socioeconomic status, crime, and environmental toxins. We connected the exposome to two structural measures (cortical thickness and surface area, n = 170) and two functional measures (participation coefficient and clustering coefficient, n = 130). We found dense connections within exposome and brain layers and sparse connections between exposome and brain layers. Lower family income was associated with thinner visual cortex, consistent with the theory that accelerated development is detectable in early-developing regions. Greater neighborhood incidence of high blood lead levels was associated with greater segregation of the default mode network, consistent with evidence that toxins are deposited into the brain along the midline. Our study demonstrates the utility of multilayer network analysis to bridge environmental and neural explanatory levels to better understand the complexity of child development.

Exploring an Unknown Corner of a Well-Known Topic: HIIE Influence on Renal Health and Filtration in Healthy Individuals Free of Cardiometabolic Diseases.

Aerobic exercise, specifically high-intensity interval exercise (HIIE), and its effects on renal health and filtration (RHF) are not well understood. Several studies support incorporating contemporary biomarkers serum cystatin C (CyC) and urine epidermal growth factor (uEGF) to combat the volatility of serum creatinine (sCr). Using these biomarkers, we examined the acute influences HIIE has on RHF to determine if there is a ceiling effect in healthy populations. The purpose was to determine the influence of an acute bout of HIIE on RHF. Thirty-six participants (n = 22 males; n = 14 females; age 37.6 ± 12.4 years.; BF% 19.2 ± 7.1%; VO2max 41.8 + 7.4 mL/kg/min) completed 30 min of HIIE on a treadmill (80% and 40% of VO2reserve in 3:2 min ratio). Blood and urine samples were obtained under standardized conditions before, 1 h, and 24 h post-exercise. CyC, sCR, uEGF, urine creatinine (uCr), uCr/uEGF ratio, and multiple estimates of glomerular filtration rate (eGFR) Modification of Diet in Renal Disease (MDRD) and CKD-EPI equations were used. The analysis employed paired sample t-tests and repeated measures ANOVAs. CyC, uEGF, uCr, and uCr/uEGF ratio concentrations were not altered between timepoints. sCr increased 1 h post-exercise (p > 0.002) but not at 24 h post-exercise. eGFR decreased in the MDRD and CKD-EPI equations at 1 h (p > 0.012) with no changes at 24 h post-exercise. CyC and sCr/CyC demonstrated no significant changes. CyC and uEGF are not altered by acute HIIE. The results demonstrate a potential ceiling effect in contemporary and traditional biomarkers of RHF, indicating improvements in RHF may be isolated to populations with reduced kidney function.

Developmental Correlates of Accelerated Molar Eruption in Early Childhood.

Background: Adversity has been linked to accelerated maturation. Molar eruption is a simple and scalable way to identify early maturation, but its developmental correlates remain unexplored. Thus, we examined whether accelerated maturation as indexed by molar eruption is associated with children's mental health or cognitive skills. Methods: Molar eruption was evaluated from T2-weighted magnetic resonance imaging in 117 children (63 female; ages 4-7 years). Parents reported on child mental health with the Child Behavior Checklist. Children completed standardized assessments of fluid reasoning, working memory, processing speed, crystallized knowledge, and math performance. Relationships between molar eruption and developmental outcomes were examined using linear models, with age, gender, and stress risk as covariates. Results: Earlier molar eruption was positively associated with children's externalizing symptoms (false discovery rate-corrected p [pFDR] = .027) but not internalizing symptoms, and the relationship with externalizing symptoms did not hold when controlling for stress risk. Earlier molar eruption was negatively associated with fluid reasoning (pFDR < .001), working memory (pFDR = .033), and crystallized knowledge (pFDR = .001). The association between molar eruption and both reasoning and crystallized knowledge held when controlling for stress risk. Molar eruption also partially mediated associations between stress risk and both reasoning (proportion mediated = 0.273, p = .004) and crystallized knowledge (proportion mediated = 0.126, p = .016). Conclusions: Accelerated maturation, as reflected in early molar eruption, may have consequences for cognitive development, perhaps because it constrains brain plasticity. Knowing the pace of a child's maturation may provide insight into the impact of a child's stress history on their cognitive development.

A systematic review of interventions to ameliorate the impact of adversity on brain development.

Adversity, including abuse, neglect, and poverty, impacts child brain development. However, the developing brain is highly plastic, and some of the impacts of childhood adversity may be mitigated by psychosocial interventions. The purpose of this review is to synthesize literature on neural outcomes of childhood interventions among individuals exposed to adversity. A systematic literature search identified 36 reports of 13 interventions. Overall, these studies provide evidence for experience-dependent plasticity in the developing brain. We synthesize studies in light of three themes. First, there was mixed evidence for a benefit of a younger age at intervention. Second, interventions tended to accelerate functional brain development, but the impact of interventions on the pace of structural brain development was less clear. Third, individual differences in intervention response were difficult to predict, in part due to small samples. However, there was significant variability in intervention type and timing, neuroimaging outcomes, and follow-up timing. Together, the studies reviewed here hold promise for the role of psychosocial interventions in ameliorating the neurodevelopmental consequences of childhood adversity.

De novo genome assembly and comparative genomics for the colonial ascidian Botrylloides violaceus.

Ascidians have the potential to reveal fundamental biological insights related to coloniality, regeneration, immune function, and the evolution of these traits. This study implements a hybrid assembly technique to produce a genome assembly and annotation for the botryllid ascidian, Botrylloides violaceus. A hybrid genome assembly was produced using Illumina, Inc. short and Oxford Nanopore Technologies long-read sequencing technologies. The resulting assembly is comprised of 831 contigs, has a total length of 121 Mbp, N50 of 1 Mbp, and a BUSCO score of 96.1%. Genome annotation identified 13 K protein-coding genes. Comparative genomic analysis with other tunicates reveals patterns of conservation and divergence within orthologous gene families even among closely related species. Characterization of the Wnt gene family, encoding signaling ligands involved in development and regeneration, reveals conserved patterns of subfamily presence and gene copy number among botryllids. This supports the use of genomic data from nonmodel organisms in the investigation of biological phenomena.

Infarctive Apoplexy of Previously Healthy Pituitary Glands: A Small Case Series and Literature Review.

Introduction We present two cases of suspected pituitary apoplexy found instead to be infarcted pituitary glands without histopathologic evidence of neoplastic cells, likely resulting from spontaneous infarction of previously healthy pituitary glands. Case Presentations The first case is a 55-year-old man who presented with a pulsating headache, nausea, and several months of decreased libido, polyuria, and polydipsia. Magnetic resonance imaging (MRI) revealed a rim-enhancing sellar/suprasellar mass with evidence of recent hemorrhage on the right. Testosterone, follicle-stimulating hormone, and luteinizing hormone levels were suppressed. Analysis of the resected specimen showed fibrocollagenous tissue with evidence of old hemorrhage and microscopic focus of necrotic tissue. The second case is a 56-year-old man who presented with a throbbing headache, associated nausea, and 6 weeks of polyuria and polydipsia. Testosterone levels were found to be low, and 8-hour water deprivation test showed evidence for partial diabetes insipidus. MRI revealed a mass on the right side of the pituitary gland, with evidence of likely hemorrhage on the left. Analysis of the resected specimen showed necrotic tissue without neoplastic cells. Conclusion When evaluating small pituitary lesions in patients presenting with indolent onset of pituitary insufficiency, there should be a high degree of suspicion for an infarcted pituitary gland.

Pre-Learning Stress That Is Temporally Removed from Acquisition Impairs Fear Learning.

Few studies have examined the time-dependent effects of stress on fear learning. Previously, we found that stress immediately before fear conditioning enhanced fear learning. Here, we aimed to extend these findings by assessing the effects of stress 30 min prior to fear conditioning on fear learning and fear generalization. Two hundred and twenty-one healthy adults underwent stress (socially evaluated cold pressor test) or a control manipulation 30 min before completing differential fear conditioning in a fear-potentiated startle paradigm. One visual stimulus (CS+), but not another (CS-), was associated with an aversive airblast to the throat (US) during acquisition. The next day, participants were tested for their fear responses to the CS+, CS-, and several generalization stimuli. Stress impaired the acquisition of fear on Day 1 but had no significant impact on fear generalization. The stress-induced impairment of fear learning was particularly evident in participants who exhibited a robust cortisol response to the stressor. These findings are consistent with the notion that stress administered 30 min before learning impairs memory formation via corticosteroid-related mechanisms and may help us understand how fear memories are altered in stress-related psychological disorders.

Individual differences in T1w/T2w ratio development during childhood.

Myelination is a key developmental process that promotes rapid and efficient information transfer. Myelin also stabilizes existing brain networks and thus may constrain neuroplasticity, defined here as the brain's potential to change in response to experiences rather than the canonical definition as the process of change. Characterizing individual differences in neuroplasticity may shed light on mechanisms by which early experiences shape learning, brain and body development, and response to interventions. The T1-weighted/T2-weighted (T1w/T2w) MRI signal ratio is a proxy measure of cortical microstructure and thus neuroplasticity. Here, in pre-registered analyses, we investigated individual differences in T1w/T2w ratios in children (ages 4-10, n = 157). T1w/T2w ratios were positively associated with age within early-developing sensorimotor and attention regions. We also tested whether socioeconomic status, cognition (crystallized knowledge or fluid reasoning), and biological age (as measured with molar eruption) were related to T1w/T2w signal but found no significant effects. Associations among T1w/T2w ratios, early experiences, and cognition may emerge later in adolescence and may not be strong enough to detect in moderate sample sizes.

To Proceed Via Telehealth or Not? Considerations for Pediatric Anxiety and Related Disorders Beyond COVID-19.

The COVID-19 pandemic accelerated a widespread shift to telehealth among mental health professionals to prioritize both providers' and clients' safety. Telehealth is likely here to stay; however, there is limited practical guidance for clinicians about how to make decisions regarding who should proceed with care via telehealth versus in-person. There also is virtually no data on the effectiveness of hybrid approaches to care; yet this can be an attractive option with potential clinical benefit. This paper provides practice-informed guidance to support shared clinical decision-making between clinicians and families to decide whether to engage in therapy services in-person or via telehealth. We specifically focus on decision-making guidance relevant for youth with anxiety or related disorders, given the unique implications of telehealth for these youth. Guided by the three-legged stool of evidence-based practice, we discuss how clinicians can use principles of shared decision-making to inform clinical recommendations about treatment modality.

Evaluating Measures of Externalizing Personality Pathology Traits in Black and White American Adolescents in a Program for at-Risk Youths.

Adolescent personality assessment measures can aid in the identification of traits that are associated with various types of maladjustment. Externalizing personality pathology traits (e.g., antisocial, borderline, and narcissistic personality disorder features) are particularly relevant for many problematic outcomes, yet measures that assess these traits have not been validated extensively in diverse samples. The present study aimed to examine the properties of measures of externalizing personality pathology traits in a sample of White (n = 184) and Black (n = 99) adolescents participating in a residential program for at-risk youth. The fit of the proposed structure for these measures was tested in the sample as a whole and in each racial group separately. Associations between these measures and the count of disciplinary infractions received while in the program were also tested. Measures were found to have less than optimal fit in this sample, especially among Black adolescents. Suggestions for future research and clinical use of these measures are discussed.

The Age of Reason: Functional Brain Network Development during Childhood.

Human childhood is characterized by dramatic changes in the mind and brain. However, little is known about the large-scale intrinsic cortical network changes that occur during childhood because of methodological challenges in scanning young children. Here, we overcome this barrier by using sophisticated acquisition and analysis tools to investigate functional network development in children between the ages of 4 and 10 years ([Formula: see text]; 50 female, 42 male). At multiple spatial scales, age is positively associated with brain network segregation. At the system level, age was associated with segregation of systems involved in attention from those involved in abstract cognition, and with integration among attentional and perceptual systems. Associations between age and functional connectivity are most pronounced in visual and medial prefrontal cortex, the two ends of a gradient from perceptual, externally oriented cortex to abstract, internally oriented cortex. These findings suggest that both ends of the sensory-association gradient may develop early, in contrast to the classical theories that cortical maturation proceeds from back to front, with sensory areas developing first and association areas developing last. More mature patterns of brain network architecture, controlling for age, were associated with better visuospatial reasoning abilities. Our results suggest that as cortical architecture becomes more specialized, children become more able to reason about the world and their place in it.SIGNIFICANCE STATEMENT Anthropologists have called the transition from early to middle childhood the "age of reason", when children across cultures become more independent. We employ cutting-edge neuroimaging acquisition and analysis approaches to investigate associations between age and functional brain architecture in childhood. Age was positively associated with segregation between cortical systems that process the external world and those that process abstract phenomena like the past, future, and minds of others. Surprisingly, we observed pronounced development at both ends of the sensory-association gradient, challenging the theory that sensory areas develop first and association areas develop last. Our results open new directions for research into how brains reorganize to support rapid gains in cognitive and socioemotional skills as children reach the age of reason.

Early stressful experiences are associated with reduced neural responses to naturalistic emotional and social content in children.

How do children's experiences relate to their naturalistic emotional and social processing? Because children can struggle with tasks in the scanner, we collected fMRI data while 4-to-11-year-olds watched a short film with positive and negative emotional events, and rich parent-child interactions (n = 70). We captured broad, normative stressful experiences by examining socioeconomic status (SES) and stressful life events, as well as children's more proximal experiences with their parents. For a sub-sample (n = 30), parenting behaviors were measured during a parent-child interaction, consisting of a picture book, a challenging puzzle, and free play with novel toys. We characterized positive parenting behaviors (e.g., warmth, praise) and negative parenting behaviors (e.g., harsh tone, physical control). We found that higher SES was related to greater activity in medial orbitofrontal cortex during parent-child interaction movie events. Negative parenting behaviors were associated with less activation of the ventral tegmental area and cerebellum during positive emotional events. In a region-of-interest analysis, we found that stressful life events and negative parenting behaviors were associated with less activation of the amygdala during positive emotional events. These exploratory results demonstrate the promise of using movie fMRI to study how early experiences may shape emotional, social, and motivational processes.

Functional outcomes from psychotherapy for people with posttraumatic stress disorder: A meta-analysis.

People with posttraumatic stress disorder (PTSD) experience a wide array of symptoms, often accompanied by significant functional and quality of life impairments. Evidence-based psychotherapies are effective for alleviating symptoms in this group, but functional outcomes following psychotherapy are understudied. This study aimed to synthesize existing work on functional outcomes of psychotherapy to conduct a meta-analytic investigation examining whether people with PTSD experience significant improvements in functioning and quality of life following a course of psychotherapy. A literature search was conducted for studies reporting results of randomized clinical trials of psychotherapies for people diagnosed with PTSD that included a functional or quality of life outcome measured at pre- and post-intervention. Both between-groups and within-groups analyses were conducted using a random effects model. Fifty-six independent samples were included. Results suggest that, on average, people with PTSD experience significant, moderate improvement in functional outcomes after a course of psychotherapy. Taken together, this meta-analysis represents a substantial advance in our understanding of functional outcomes of psychotherapy for people with PTSD. Findings suggest that psychotherapy is one vehicle through which functional outcomes may be improved for this group, though notably to a lesser degree than symptom improvement.

Introductory patient communication training for medical physics graduate students: Pilot experience.

Despite medical physics becoming a more patient-facing part of the radiation oncology team, medical physics graduate students have no training in patient communication. An introductory patient communication training for medical physics graduate students is presented here. This training exposes participants to foundational concepts and effective communication skills through a lecture and it allows them to apply these concepts through realistic simulated patient interactions. The training was conducted virtually, and eight students participated. The impact of the training was evaluated based on changes in both confidence and competence of the participants' patient communication skills. Participants were asked to fill out a survey to assess their confidence on communicating with patients before and after the training. They also underwent a simulated patient interaction pre- and postlecture. Their performance during these was evaluated by both the simulated patient actors and the participants themselves using a rubric. Each data set was paired and analyzed for significance using a Wilcoxon rank-sum test with an alpha of 0.05. Participants reported significantly higher confidence in their feeling of preparedness to interact with patients (mean = 2.38 vs. 3.88, p = 0.008), comfort interacting independently (mean = 2.00 vs. 4.00, p = 0.002), comfort showing patients they are actively listening (mean = 3.50 vs. 4.50, p = 0.005), and confidence handling challenging patient interactions (mean = 1.88 vs. 3.38, p = 0.01), after the training. Their encounter scores, as evaluated by the simulated patient actors, significantly increased (mean = 77% vs. 91%, p = 0.022). Self-evaluation scores increased, but not significantly (mean = 62% vs. 68%, p = 0.184). The difference between the simulated patient and self-evaluation scores for the postinstruction encounter was statistically significant (p = 0.0014). This patient communication training for medical physics graduate students is effective at increasing both the confidence and the competence of the participants in the subject. We propose that similar trainings be incorporated into medical physics graduate training programs prior to students entering into residency.

Growth Resilience of Subarctic Rhodoliths (Lithothamnion glaciale, Rhodophyta) to Chronic Low Sea Temperature and irradiance.

Rhodolith beds are pervasive marine biological systems in the subarctic North Atlantic. Limited knowledge about effects of temperature and irradiance on rhodolith growth limits the ability to anticipate the response of rhodolith beds to this ocean's chronic low, yet changing sea temperature and irradiance regimes. We carried out a 149-d laboratory experiment with Newfoundland Lithothamnion glaciale rhodoliths to test the predictions that growth (i) is inhibited at temperatures of ~0.5°C and (ii) resumes as temperature increases above 0.5°C, albeit at a higher rate under high than low irradiances. Rhodoliths were grown in experimental tanks at near-zero (~0.7°C) seawater temperatures during the first 85 d and at temperatures increasing naturally to ~6°C for the remaining 64 d. Rhodoliths in those tanks were exposed to either low (0.02 mol photons·m-2 ·d-1 ) or high (0.78 mol photons·m-2 ·d-1 ) irradiances during the entire experiment. Rhodoliths grew at a linear rate of ~281 µm·year-1 (0.77 µm·d-1 ) throughout the experiment under both irradiance treatments despite daily seawater temperature variation of up to 3°C. Near-zero temperatures of ~0.5 to 1.0°C did not inhibit rhodolith growth. Model selection showed that PAR-day (a cumulative irradiance index) was a better predictor of growth variation than Degree-day (a cumulative thermal index). Our findings extend to ~0.5°C the lower limit of the known temperature range (~1 to at least 16°C) over which growth in L. glaciale rhodoliths remains unaffected, while suggesting that the growth-irradiance relationship in low-light environments at temperatures below 6°C is less irradiance-driven than recently proposed.