The costs and trade-offs of optimal foraging in marine fish larvae.

In a warming world, both the metabolic rates of ectotherm predators and the phenology of their prey organisms is subject to change. Knowledge on how intrinsic and extrinsic factors govern predator-prey interactions is essential in order to understand how the environment regulates the vital rates of consumers. Controlled experiments, however, simultaneously testing behavioural and growth responses of the larvae of fish and other ectotherm organisms in different feeding regimes are scarce. Prey size (PS) selection was determined for young Atlantic herring Clupea harengus L. larvae offered 100- to 850-µm copepods Acartia tonsa at five different concentrations. In separate, 4- (13°C) or 7-day (7°C) trials, the effect of prey size on larval foraging behaviour, specific growth rate (SGR) and biochemical condition (RNA:DNA, RD, a proxy for individual instantaneous growth) was tested. Preferred (selected) PS was similar at all prey concentrations but increased from 3% to 5% predator length with increasing larval size. At various temperatures, dome-shaped relationships existed between PS and larval RD (and accordingly SGR). Compensatory changes in foraging behaviour (pause and feeding strike frequencies) existed but were not adequate to maintain positive SGR when available prey were substantially smaller than those preferred by larvae. A physiology-based model predicted that larvae depended more heavily on optimal prey sizes at the colder versus warmer temperature to grow well and that the profitable prey niche breadth (the range in prey sizes in which growth was positive) increased at warmer temperatures. Seemingly subtle match-mismatch dynamics between ectotherm predators and their preferred prey size can have large, temperature-dependent consequences for rates of growth and likely survival of the predator. To the best knowledge, this was the first study to directly quantify the "costs and trade-offs" of optimal foraging in marine fish larvae.

It is Not (Always) the Mismatch That Beats You-On the Relationship Between Interaction of Early and Recent Life Stress and Emotion Regulation, an fMRI Study.

Stress may impact the ability to effectively regulate emotions. To study the impact of stressful experiences in early and recent life on emotion regulation, we examined the relationship between early life stress, recent stress, and brain activation during cognitive reappraisal. We investigated two regulation goals: the decrease and increase of emotional response to both negative and positive stimuli. Furthermore, two models of stress consequences were examined: the cumulative and match/mismatch models. A total of 83 participants (Mage = 21.66) took part in the study. There was an interaction between cumulative stress and stimuli valence in the cuneus, superior lateral occipital cortex, superior parietal lobule, supramarginal gyrus extending to superior temporal gyrus, and precentral gyrus extending to supplementary motor area. Interaction between mismatched stress index and stimuli valence was found in the left hippocampus, left insula extending to the orbitofrontal cortex and amygdala, and in a cluster including the anterior cingulate cortex, superior frontal gyrus, and frontal pole. Furthermore, there were differences between the effects of cumulative and mismatched stress indices on brain activation during reappraisal of positive but not negative stimuli. Results indicate that cumulative stress and match/mismatch approaches are both useful for explaining brain activation during reappraisal. This finding is important for our understanding of the multifaceted impact of stress on emotion regulation.

Early-season brown trout (Salmo trutta) migrants grow and survive better at sea.

The timing of seaward migration is a key life-history trait for many anadromous fish species, with growth and survival at sea depending on a match/mismatch scenario between the timing of the sea entry and optimal conditions. Based on a 25-year study with 15,226 individually tagged brown trout (Salmo trutta) in a Norwegian river, we analysed how the within-season timing of sea migration impacted growth and survival. In both first-time and veteran migrants, marine growth was highest for early migrating individuals, large individuals, and those with a low condition factor when entering the sea. Survival was highest for individuals entering the sea early in the season. In first-time migrants, survival increased with body length. Survival also increased with the number of other smolts migrating simultaneously. As the early smolts were the most successful, it may seem strange that many smolts migrate later in the season. We suggest that late-migrating smolts may not be of a size and/or physiological state suitable for early marine conditions, and may make the best of a bad situation.

syn-Selective Epoxidation of Chiral Terminal Allylic Alcohols with a Titanium Salalen Catalyst and Hydrogen Peroxide.

In the Sharpless asymmetric epoxidation of chiral secondary allylic alcohols, one substrate enantiomer is predominantly converted to the anti-epoxy alcohol. We herein report the first highly syn-selective epoxidation of terminal allylic alcohols using a titanium salalen complex as catalyst, at room temperature, and aqueous hydrogen peroxide as oxidant. With enantiopure terminal allylic alcohols as substrates, the epoxy alcohols were obtained with up to 98 % yield and up to >99 : 1 dr (syn). Catalyst loadings as low as 1 mol % can be applied without eroding the syn-diastereoselectivity. Modification of the allylic alcohol to an ether does not affect the diastereoselectivity either [>99 : 1 dr (syn)]. Inverting the catalyst configuration leads to the anti-product, albeit at lower dr (ca. 20 : 1). The synthetic potential is demonstrated by a short, gram-scale preparation of a tetrahydrofuran building block with three stereocenters, involving two titanium salalen catalyzed epoxidation steps.

Population dynamic regulators in an empirical predator-prey system.

Capelin (Mallotus villosus) is a short-lived (1-4 years) fish species, that plays a crucial role by dominating the intermediate trophic level in the Barents Sea. Several episodes of extreme biomass decline (collapse) have been observed during the last three decades. We postulate that these collapses might be regulated by food availability (bottom-up effect) and/or by time discrepancy between capelin feeding and abundance of its prey (match-mismatch hypothesis). This paper investigates our postulate using a model consisting of a set of coupled differential equations to describe the predator-prey system, with a single delay term, τ, in description of the predator dynamics. We derive theoretical conditions on τ, as well as determine how changes in these conditions define different stability regimes of the system. Unconstrained optimization is used to calculate optimal model parameters by fitting the predator-prey model to empirical data. The optimization results are combined with those from the theoretical analysis, to make inference about the empirical system stability. Our results show that Hopf bifurcation occurs in the predatory-prey system when τ exceeds a theoretically derived value τ∗>0. This value represents the critical time for prey availability in advance of the optimal predator growth period.Set into an ecological context, our findings provide mathematical evidence for validity of the match-mismatch hypothesis and a bottom-up effect for capelin.

No evidence for fitness signatures consistent with increasing trophic mismatch over 30 years in a population of European shag Phalacrocorax aristotelis.

As temperatures rise, timing of reproduction is changing at different rates across trophic levels, potentially resulting in asynchrony between consumers and their resources. The match-mismatch hypothesis (MMH) suggests that trophic asynchrony will have negative impacts on average productivity of consumers. It is also thought to lead to selection on timing of breeding, as the most asynchronous individuals will show the greatest reductions in fitness. Using a 30-year individual-level dataset of breeding phenology and success from a population of European shags on the Isle of May, Scotland, we tested a series of predictions consistent with the hypothesis that fitness impacts of trophic asynchrony are increasing. These predictions quantified changes in average annual breeding success and strength of selection on timing of breeding, over time and in relation to rising sea surface temperature (SST) and diet composition. Annual average (population) breeding success was negatively correlated with average lay date yet showed no trend over time, or in relation to increasing SST or the proportion of principal prey in the diet, as would be expected if trophic mismatch was increasing. At the individual level, we found evidence for stabilising selection and directional selection for earlier breeding, although the earliest birds were not the most productive. However, selection for earlier laying did not strengthen over time, or in relation to SST or slope of the seasonal shift in diet from principal to secondary prey. We found that the optimum lay date advanced by almost 4 weeks during the study, and that the population mean lay date tracked this shift. Our results indicate that average performance correlates with absolute timing of breeding of the population, and there is selection for earlier laying at the individual level. However, we found no fitness signatures of a change in the impact of climate-induced trophic mismatch, and evidence that shags are tracking long-term shifts in optimum timing. This suggests that if asynchrony is present in this system, breeding success is not impacted. Our approach highlights the advantages of examining variation at both population and individual levels when assessing evidence for fitness impacts of trophic asynchrony.

Direct and maternal reduced balanced protein diet influences the liver transcriptome in chickens.

The objective of this study was to evaluate, by means of RNA sequencing, the direct and transgenerational effect of a reduced balanced protein (RP) diet on broiler breeder metabolism. Chickens of the F0 generation were fed a control (C) or RP diet, and their F1 progeny was fed a C or RP diet as well, resulting in four groups of chickens: C/C, C/RP, RP/C and RP/RP. While both direct and maternal effects were seen on body weight, breast muscle weight and abdominal fat weight in the F1 generation, the direct effect was the most dominant one. The liver transcriptome in the F1 generation showed that amino acid metabolism was up-regulated in chickens that received the control feed when compared with their respective contemporaries that received the reduced protein diet. Interestingly, chickens hatched from control-fed hens but reared on the reduced protein diet (C/RP group) activated a fatty acid metabolism, expressing more fatty acid desaturase 1 gene, fatty acid desaturase 2 gene and elongation of very long-chain fatty acids protein 2 gene, when compared with control-fed chickens hatched from control-fed hens (C/C group), while chickens hatched from reduced protein-fed hens that received themselves the same reduced protein diet (RP/RP group) triggered their glucose metabolism more, showing elevated levels of phosphofructokinase gene, 6-phosphofructo-2-kinase/fructose-2,6-biphospatase 4 and fructose-biphosphate aldolase C mRNA compared with the chickens hatched from reduced protein-fed hens but reared on a control diet (RP/C group). This suggests that the maternal protein diet has an impact on the metabolism of broilers when they are reared on a RP diet.

Comparing two measures of phenological synchrony in a predator-prey interaction: Simpler works better.

Global climate change has sparked a vast research effort into the demographic and evolutionary consequences of mismatches between consumer and resource phenology. Many studies have used the difference in peak dates to quantify phenological synchrony (match in dates, MD), but this approach has been suggested to be inconclusive, since it does not incorporate the temporal overlap between the phenological distributions (match in overlap, MO). We used 24 years of detailed data on the phenology of a predator-prey system, the great tit (Parus major) and the main food for its nestlings, caterpillars, to estimate MD and MO at the population and brood levels. We compared the performance of both metrics on two key demographic parameters: offspring recruitment probability and selection on the timing of reproduction. Although MD and MO correlated quadratically as expected, MD was a better predictor for both offspring recruitment and selection on timing than MO. We argue-and verify through simulations-that this is because quantifying MO has to be based on nontrivial, difficult-to-verify assumptions that likely render MO too inaccurate as a proxy for food availability in practice. Our results have important implications for the allocation of research efforts in long-term population studies in highly seasonal environments.

Shells of the bivalve Astarte moerchi give new evidence of a strong pelagic-benthic coupling shift occurring since the late 1970s in the North Water polynya.

Climate changes in the Arctic may weaken the currently tight pelagic-benthic coupling. In response to decreasing sea ice cover, arctic marine systems are expected to shift from a 'sea-ice algae-benthos' to a 'phytoplankton-zooplankton' dominance. We used mollusc shells as bioarchives and fatty acid trophic markers to estimate the effects of the reduction of sea ice cover on the food exported to the seafloor. Bathyal bivalve Astarte moerchi living at 600 m depth in northern Baffin Bay reveals a clear shift in growth variations and Ba/Ca ratios since the late 1970s, which we relate to a change in food availability. Tissue fatty acid compositions show that this species feeds mainly on microalgae exported from the euphotic zone to the seabed. We, therefore, suggest that changes in pelagic-benthic coupling are likely due either to local changes in sea ice dynamics, mediated through bottom-up regulation exerted by sea ice on phytoplankton production, or to a mismatch between phytoplankton bloom and zooplankton grazing due to phenological change. Both possibilities allow a more regular and increased transfer of food to the seabed. This article is part of the theme issue 'The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.

Effects of climate and demography on reproductive phenology of a harvested marine fish population.

Shifts in phenology are a well-documented ecological response to changes in climate, which may or may not be adaptive for a species depending on the climate sensitivity of other ecosystem processes. Furthermore, phenology may be affected by factors in addition to climate, which may accentuate or dampen climate-driven phenological responses. In this study, we investigate how climate and population demographic structure jointly affect spawning phenology of a fish species of major commercial importance: walleye pollock (Gadus chalcogrammus). We use 32 years of data from ichthyoplankton surveys to reconstruct timing of pollock reproduction in the Gulf of Alaska and find that the mean date of spawning has varied by over 3 weeks throughout the last >3 decades. Climate clearly drives variation in spawn timing, with warmer temperatures leading to an earlier and more protracted spawning period, consistent with expectations of advanced spring phenology under warming. However, the effects of temperature were nonlinear, such that additional warming above a threshold value had no additional effect on phenology. Population demographics were equally as important as temperature: An older and more age-diverse spawning stock tended to spawn earlier and over a longer duration than a younger stock. Our models suggest that demographic shifts associated with sustainable harvest rates could shift the mean spawning date 7 days later and shorten the spawning season by 9 days relative to an unfished population, independent of thermal conditions. Projections under climate change suggest that spawn timing will become more stable for walleye pollock in the future, but it is unknown what the consequences of this stabilization will be for the synchrony of first-feeding larvae with production of zooplankton prey in spring. With ongoing warming in the world's oceans, knowledge of the mechanisms underlying reproductive phenology can improve our ability to monitor and manage species under changing climate conditions.

The phenology of migration in an unpredictable world.

In Focus: Freshwater, C., Trudel, M., Beacham, T. D., Gauthier, S., Johnson, S. C., Neville, C. & Juanes, F. (2016) Individual variation, population-specific migration behaviours and stochastic processes shape marine migration phenologies. Journal of Animal Ecology, 88, 67-78. https://doi.org/10.1111/1365-2656.12852 Pacific salmon undertake arduous and risky migrations from their freshwater nursery grounds to the coastal ocean, northwards to their feeding grounds, and then back to their freshwater natal habitats to spawn. Understanding the phenology of such migrations has largely been viewed through the lens of microevolution producing optimal strategies that reflect local selection pressures; less emphasis has been placed on quantifying how variation in migration patterns can spread the risks associated with life in variable and unpredictable ecosystems. In this issue, Freshwater et al. use the information contained in ear stones (otoliths) and DNA of migrating juvenile sockeye salmon from the Fraser River of western Canada to quantify variation in the timing of their marine migrations. Not only were there population-specific differences in migration phenology of fish from the same river, but there was substantial variation among individuals from specific populations. These patterns also varied from year to year. Data like these emphasize the risks involved in such migrations and suggest that variation in key migration traits are maintained because of the inherent unpredictability of ecosystems. Management and conservation efforts would be well-served to consider actions that maintain such ecological variation to facilitate meta-population persistence in a rapidly changing world.

The relevance of food peak architecture in trophic interactions.

Phenological shifts and associated changes in the temporal match between trophic levels have been a major focus of the study of ecological consequences of climate change. Previously, the food peak has been thought to respond as an entity to warming temperatures. However, food peak architecture, that is, timings and abundances of prey species and the level of synchrony between them, determines the timing and shape of the food peak. We demonstrate this with a case example of three passerine prey species and their predator. We explored temporal trends in the timing, height, width, and peakedness of prey availabilities and explained their variation with food peak architecture and ambient temperatures of prebreeding and breeding seasons. We found a temporal match between the predator's breeding schedule and food availability. Temporal trends in the timing of the food peak or in the synchrony between the prey species were not found. However, the food peak has become wider and more peaked over time. With more peaked food availabilities, predator's breeding success will depend more on the temporal match between its breeding schedule and the food peak, ultimately affecting the timing of breeding in the predator population. The height and width of the food peak depended on the abundances and breeding season lengths of individual prey species and their reciprocal synchronies. Peakednesses of separate prey species' availability distributions alone explained the peakedness of the food peak. Timing and quantity of food production were associated with temperatures of various time periods with variable relevance in different prey species. Alternating abundances of early and late breeding prey species caused high annual fluctuation in the timing of the food peak. Interestingly, the food peak may become later even when prey species' schedules are advanced. Climate warming can thus produce unexpected changes in the food availabilities, intervening in trophic interactions.

Maternal separation followed by isolation-housing differentially affects prepulse inhibition of the acoustic startle response in C57BL/6 mice.

Exposure to chronic stress is associated with an increased incidence of neuropsychiatric dysfunction. The current study evaluated two competing hypotheses, the cumulative stress and the match/mismatch hypothesis of neuropsychiatric dysfunction, using two paradigms relating to exposure to "stress": pre-weaning maternal separation and post-weaning isolation-housing. C57BL/6 offspring were reared under four conditions: typical animal facility rearing (AFR, control), early handling (EH, daily 15 min separation from dam), maternal separation (MS, daily 4 hr separation from dam), and maternal and peer separation (MPS, daily 4 hr separation from dam and from littermates). After weaning, mice were either housed socially (2-3/cage) or in isolation (1/cage) and then tested for prepulse inhibition in adulthood. Isolation-housed MPS subjects displayed greater deficits in prepulse inhibition relative to socially-housed MPS subjects while socially-housed AFR subjects displayed greater deficits in prepulse inhibition relative to isolation-housed AFR subjects. The results indicate that these treatment conditions represent a potentially valuable model for evaluating the match/mismatch hypothesis in regards to neuropsychiatric dysfunction.

Challenges in Using the Randomized Trial Design to Examine the Influence of Treatment Preferences.

The overall purpose of this methodological study was to investigate the strengths and limitations of the randomized clinical trial design in examining the influence of treatment preferences on outcomes. The study was a secondary analysis of data obtained in two randomized clinical trials that evaluated behavioral therapies for insomnia. In both trials, the same design and methods were used to assess participants' treatment preferences and outcomes, however, the treatments differed. The results illustrated the challenges encountered in using the randomized clinical trial design. The challenges were related to the unbalanced distribution of participants with preferences for the study treatments, non-comparability of the subgroups with treatments matched or mismatched to their preferences, differential attrition, which compromised the sample size and composition of the subgroups and limited the use of the planned statistical analyses. Whether these challenges occur in trials of other types of treatments and target populations should be explored in future research. Some strategies were proposed and should be evaluated for their utility in addressing these challenges.

Temperature seasonality during fry out-migration influences the survival of hatchery-reared chum salmon Oncorhynchus keta.

Among years, fry-to-adult survival of hatchery-reared chum salmon Oncorhynchus keta was positively correlated with the length (in days) of the fry out-migration period with temperatures suitable for migration. Furthermore, survival decreased with increasing difference in mean temperature between May and June. Thus, prolonged out-migration periods increased the probability of survival from fry to adult, lending support to the hypothesis that long migration periods decrease the risk of mortality (bet-hedging), and increase the probability of migration when environmental conditions in fresh water and the ocean are suitable (match-mismatch).

The interaction between maternal and post-hatch n-3 fatty acid supplementation in broiler diets.

This study investigated whether offspring from n-3-supplemented breeders have an enhanced performance and immune organ weight when fed a post-hatch n-3-enriched diet in comparison with their control-fed counterparts and the importance of timing of omega-3 supplementation. Therefore, 480 Ross-308 broiler breeder hens were fed one of four different diets (120/treatment). The control diet (CON) was a basal diet, rich in n-6 fatty acids (FA). The three other diets were enriched in n-3 FA, formulated to obtain a different EPA/DHA ratio of 1/1 (EPA = DHA), 1/2 (DHA) or 2/1 (EPA). At 33 weeks of age, eggs were incubated to obtain 1440 offspring. They were set up according to their maternal diet and sex in 48 pens of 30 chicks each (12 pens per maternal treatment: six male and six female). Half of the offspring were given a post-hatch control diet, whereas to other half received an n-3-supplemented diet. Zootechnical performance was followed for starter, grower and finisher phase, and at the end of each phase two, chicks per pen were sacrificed to determine the weight of the immune organs. No interaction was found between maternal and post-hatch n-3 treatment for zootechnical performance. An interaction arose between the maternal and post-hatch n-3 supplementation for proportional bursa weight at day 1 and day 14 and proportional liver weight at day 14, but effects on immune organ weight were rather limited. Offspring post-hatch n-3 supplementation did not enhance maternal n-3 supplementation.

Effects of maize development and phenology on the field infestation dynamics of the European corn borer (Lepidoptera: Crambidae).

Phenological match/mismatch between cultivated plants and their pest could impact pest infestation dynamics in the field. To explore how such match/mismatch of plant and pest phenologies may interact with plant defense dynamics, we studied the infestation dynamics of maize by one of its main pests in Europe, the European Corn Borer (Ostrinia nubilalis; Lepidoptera: Crambidae). A two-year field experiment was carried out on a collection of 23 maize inbred lines contrasted for their earliness. Each inbred line was sown at three different dates in order to expose different developmental stages of maize to natural European corn borer infestation. The effect of the sowing date depended on the inbred line, the pest generation, and the year. In 2021, the final pest incidence ranged from 36% to 91% depending on inbred lines and sowing date. In 2022, it ranged from 2% to 77%. This variability in final pest incidence can be related to variations in plant development during plant exposure to pest infestation. However, this relationship was not straightforward. Indeed, the shape and intensity of the relationship depended on the timing of the onset of the pest infestation. When infestation occurred while plants were in a vegetative stage, a nonlinear relationship between development and pest incidence was observed with the least and most developed plants being the most infested. When infestation occurred when all plants were in the mature phase, the most developed plants were the least infested. Our results highlight the effect of plant-pest phenological match/mismatch on pest infestation dynamics and underline the importance of taking plant-pest interactions into account to propose relevant control strategies.

The role of vowel and consonant onsets in neural tracking of natural speech.

Objective. To investigate how the auditory system processes natural speech, models have been created to relate the electroencephalography (EEG) signal of a person listening to speech to various representations of the speech. Mainly the speech envelope has been used, but also phonetic representations. We investigated to which degree of granularity phonetic representations can be related to the EEG signal.Approach. We used recorded EEG signals from 105 subjects while they listened to fairy tale stories. We utilized speech representations, including onset of any phone, vowel-consonant onsets, broad phonetic class (BPC) onsets, and narrow phonetic class onsets, and related them to EEG using forward modeling and match-mismatch tasks. In forward modeling, we used a linear model to predict EEG from speech representations. In the match-mismatch task, we trained a long short term memory based model to determine which of two candidate speech segments matches with a given EEG segment.Main results. Our results show that vowel-consonant onsets outperform onsets of any phone in both tasks, which suggests that neural tracking of the vowel vs. consonant exists in the EEG to some degree. We also observed that vowel (syllable nucleus) onsets exhibit a more consistent representation in EEG compared to syllable onsets.Significance. Finally, our findings suggest that neural tracking previously thought to be associated with BPCs might actually originate from vowel-consonant onsets rather than the differentiation between different phonetic classes.

Is the speed of adjusting to environmental change condition dependent? An experiment with house mice (Mus musculus).

Environmental conditions change constantly either by anthropogenic perturbation or naturally across space and time. Often, a change in behavior is the first response to changing conditions. Behavioral flexibility can potentially improve an organism's chances to survive and reproduce. Currently, we lack an understanding on the time-scale such behavioral adjustments need, how they actually affect reproduction and survival and whether behavioral adjustments are sufficient in keeping up with changing conditions. We used house mice (Mus musculus) to test whether personality and life-history traits can adjust to an experimentally induced food-switch flexibly in adulthood or by intergenerational plasticity, that is, adjustments only becoming visible in the offspring generation. Mice lived in 6 experimental populations of semi-natural environments either on high or standard quality food for 4 generations. We showed previously that high-quality food induced better conditions and a less risk-prone personality. Here, we tested whether the speed and/ or magnitude of adjustment shows condition-dependency and whether adjustments incur fitness effects. Life-history but not personality traits reacted flexibly to a food-switch, primarily by a direct reduction of reproduction and slowed-down growth. Offspring whose parents received a food-switch developed a more active stress-coping personality and gained weight at a slower rate compared with their respective controls. Furthermore, the modulation of most traits was condition-dependent, with animals previously fed with high-quality food showing stronger responses. Our study highlights that life-history and personality traits adjust at different speed toward environmental change, thus, highlighting the importance of the environment and the mode of response for evolutionary models.

Quantitative analysis of aortic Na[18F]F uptake in macrocalcifications and microcalcifications in PET/CT scans.

BACKGROUND: Currently, computed tomography (CT) is used for risk profiling of (asymptomatic) individuals by calculating coronary artery calcium scores. Although this score is a strong predictor of major adverse cardiovascular events, this method has limitations. Sodium [18F]fluoride (Na[18F]F) positron emission tomography (PET) has shown promise as an early marker for atherosclerotic progression. However, evidence on Na[18F]F as a marker for high-risk plaques is limited, particularly on its presentation in clinical PET/CT. Besides, the relationship between microcalcifications visualized by Na[18F]F PET and macrocalcifications detectable on CT is unknown. PURPOSE: To establish a match/mismatch score in the aorta between macrocalcified plaque content on CT and microcalcification Na[18F]F PET uptake. METHODS: Na[18F]F-PET/CT scans acquired in our centre in 2019-2020 were retrospectively collected. The aorta of each low-dose CT was manually segmented. Background measurements were placed in the superior vena cava. The vertebrae were automatically segmented using an open-source convolutional neural network, dilated with 10 mm, and subtracted from the aortic mask. Per patient, calcium and Na[18F]F-hotspot masks were retrieved using an in-house developed algorithm. Three match/mismatch analyses were performed: a population analysis, a per slice analysis, and an overlap score. To generate a population image of calcium and Na[18F]F hotspot distribution, all aortic masks were aligned. Then, a heatmap of calcium HU and Na[18F]F-uptake on the surface was obtained by outward projection of HU and uptake values from the centerline. In each slice of the aortic wall of each patient, the calcium mass score and target-to-bloodpool ratios (TBR) were calculated within the calcium masks, in the aortic wall except the calcium masks, and in the aortic wall in slices without calcium. For the overlap score, three volumes were identified in the calcium and Na[18F]F masks: volume of PET (PET+/CT-), volume of CT (PET-/CT+), and overlapping volumes (PET+/CT+). A Spearman's correlation analysis with Bonferroni correction was performed on the population image, assessing the correlation between all HU and Na[18F]F vertex values. In the per slice analysis, a paired Wilcoxon signed-rank test was used to compare TBR values within each slice, while an ANOVA with post-hoc Kruskal-Wallis test was employed to compare TBR values between slices. p-values < 0.05 were considered significant. RESULTS: In total, 186 Na[18F]F-PET/CT scans were included. A moderate positive exponential correlation was observed between total aortic calcium mass and total aortic TBR (r = 0.68, p < 0.001). A strong positive correlation (r = 0.77, p < 0.0001) was observed between CT values and Na[18F]F values on the population image. Significantly higher TBR values were found outside calcium masks than inside calcium masks (p < 0.0001). TBR values in slices where no calcium was present, were significantly lower compared with outside calcium and inside calcium (both p < 0.0001). On average, only 3.7% of the mask volumes were overlapping. CONCLUSIONS: Na[18F]F-uptake in the aorta behaves similarly to macrocalcification detectable on CT. Na[18F]F-uptake values are also moderately correlated to calcium mass scores (match). Higher uptake values were found just outside macrocalcification masks instead of inside the macrocalcification masks (mismatch). Also, only a small percentage of the Na[18F]F-uptake volumes overlapped with the calcium volumes (mismatch).