Purifying and balancing selection on embryonic semi-lethal haplotypes in a wild mammal.

Embryonic lethal mutations are arguably the earliest and most severe manifestation of inbreeding depression, but their impact on wild populations is not well understood. Here, we combined genomic, fitness, and life-history data from 5,925 wild Soay sheep sampled over nearly three decades to explore the impact of embryonic lethal mutations and their evolutionary dynamics. We searched for haplotypes that in their homozygous state are unusually rare in the offspring of known carrier parents and found three putatively semi-lethal haplotypes with 27%-46% fewer homozygous offspring than expected. Two of these haplotypes are decreasing in frequency, and gene-dropping simulations through the pedigree suggest that this is partially due to purifying selection. In contrast, the frequency of the third semi-lethal haplotype remains relatively stable over time. We show that the haplotype could be maintained by balancing selection because it is also associated with increased postnatal survival and body weight and because its cumulative frequency change is lower than in most drift-only simulations. Our study highlights embryonic mutations as a largely neglected contributor to inbreeding depression and provides a rare example of how harmful genetic variation can be maintained through balancing selection in a wild mammal population.

A compassion-based treatment for couples with the female partner suffering from current depressive disorder: A randomized-controlled trial.

BACKGROUND: Studies have shown that depression and interpersonal relationships are interdependently connected and that including the intimate partner in treatment for depression has beneficial effects. Given evidence that compassion is both an interpersonal quality and a promising treatment target, the goal of this study was to examine the effects of a compassion-based, contemplative treatment for couples employing a multi-method approach for evaluation. METHODS: In a pre-post-follow-up design, n = 53 different-sex couples including women with current depression were randomly assigned to a 10-week-long CBCT®-fC (Cognitively-Based Compassion Training/intervention for couples) or treatment-as-usual (TAU) condition. Multi-level linear regression models and post-hoc contrasts were calculated to determine changes in depressive symptoms, mindfulness and self-compassion, interpersonal functioning and neuroendocrine markers collected during a partnership appreciation task (PAT) in the laboratory before and after CBCT-fC treatment. RESULTS: While CBCT-fC led to a comparable decrease of depressive symptoms as TAU, the training specifically increased self-compassion and mindfulness versus TAU. Interestingly, interpersonal functioning did not improve, which was also reflected in participants' preferred self-focus in-between-session practices, instead of practices with interpersonal focus. There were no group-specific changes in psychobiological stress-marker reactivity. CONCLUSIONS: CBCT-fC was effective in decreasing current depressive symptomatology and increasing mindfulness, and self-compassion. Especially the motivation to participate, such as improving interpersonal functioning, should be addressed and intrinsic motives of the partners to be involved. In highly burdened individuals, self-regulation may need to be improved before co-regulation can be addressed, which would requiring longer treatments. Facilitating factors for engaging in the practice between-sessions seem meaningful.

Associations of SLC6A4 methylation with salivary cortisol, salivary alpha-amylase, and subjective stress in everyday life.

Dysregulations of the hypothalamic-pituitary-adrenal (HPA) and sympatho-adrenal medullary (SAM) axis are associated with mental and somatic illness. However, there is lack of knowledge regarding the molecular mechanisms underlying these effects. Epigenetic states in the serotonin transporter gene (SLC6A4) were shown to be associated with stress in various forms. We hypothesized that levels of DNA methylation (DNAm) of SLC6A4 would be associated with altered SAM- and HPA regulation in daily life. N = 74 healthy persons participated in the study. An ecological momentary assessment (EMA) approach was used to assess indicators of stress in daily life. Each day included six concurrent assessments of saliva, to quantify cortisol (sCort; HPA axis) and alpha-amylase (sAA; SAM axis), and to assess self-reports on subjective stress. To assess SLC6A4 DNAm, peripheral blood was drawn and analyzed via bisulfite pyrosequencing. All data were assessed in two waves three months apart, each including two days of EMA and the assessment of SLC6A4 DNAm. Data were analyzed using multilevel models. On the between-person level, higher average levels of SLC6A4 DNAm were associated with higher average levels of sAA, but not with average levels of sCort. On the within-person level, higher levels of SLC6A4 DNAm were associated with lower levels of sAA and sCort. There were no associations of subjective stress with SLC6A4 DNAm. The results help to clarify the association between environmental stress and stress axes regulation, pointing towards an important role of differential within- and between-person effects of SLC6A4 DNAm, which might shape this association.

Conservation management strategy impacts inbreeding and mutation load in scimitar-horned oryx.

In an age of habitat loss and overexploitation, small populations, both captive and wild, are increasingly facing the effects of isolation and inbreeding. Genetic management has therefore become a vital tool for ensuring population viability. However, little is known about how the type and intensity of intervention shape the genomic landscape of inbreeding and mutation load. We address this using whole-genome sequence data of the scimitar-horned oryx (Oryx dammah), an iconic antelope that has been subject to contrasting management strategies since it was declared extinct in the wild. We show that unmanaged populations are enriched for long runs of homozygosity (ROH) and have significantly higher inbreeding coefficients than managed populations. Additionally, despite the total number of deleterious alleles being similar across management strategies, the burden of homozygous deleterious genotypes was consistently higher in unmanaged groups. These findings emphasize the risks associated with deleterious mutations through multiple generations of inbreeding. As wildlife management strategies continue to diversify, our study reinforces the importance of maintaining genome-wide variation in vulnerable populations and has direct implications for one of the largest reintroduction attempts in the world.

Effects of mental contrasting on sleep and associations with stress: A randomized controlled trial.

Mental contrasting with implementation intentions (MCII) has been successfully applied to improve health-related behaviors (e.g. exercise). We explored its effectiveness to improve sleep outcomes beyond effects of sleep hygiene (SH) information, and investigated associations with stress. Eighty university employees (mean age: 29.6, SD = 4.5) were randomized to either a MCII + SH or a SH-only condition. During a baseline-week and a post-intervention week, sleep duration (Fitbit Alta and self-report), sleep quality, and stress were assessed daily and saliva was collected to assess the cortisol awakening response (CAR). In total, self-reported sleep quality and duration increased, but there was no meaningful condition*week interaction for sleep parameters or CAR. Higher average stress was associated with shorter sleep duration and lower sleep quality. Within-person, days with higher stress were followed by nights with lower sleep quality. Despite overall improvements, effects of MCII were not confirmed. MCII might be less effective to improve behaviors which are less controllable.

Selection, recombination and population history effects on runs of homozygosity (ROH) in wild red deer (Cervus elaphus).

The distribution of runs of homozygosity (ROH) may be shaped by a number of interacting processes such as selection, recombination and population history, but little is known about the importance of these mechanisms in shaping ROH in wild populations. We combined an empirical dataset of >3000 red deer genotyped at >35,000 genome-wide autosomal SNPs and evolutionary simulations to investigate the influence of each of these factors on ROH. We assessed ROH in a focal and comparison population to investigate the effect of population history. We investigated the role of recombination using both a physical map and a genetic linkage map to search for ROH. We found differences in ROH distribution between both populations and map types indicating that population history and local recombination rate have an effect on ROH. Finally, we ran forward genetic simulations with varying population histories, recombination rates and levels of selection, allowing us to further interpret our empirical data. These simulations showed that population history has a greater effect on ROH distribution than either recombination or selection. We further show that selection can cause genomic regions where ROH is common, only when the effective population size (Ne) is large or selection is particularly strong. In populations having undergone a population bottleneck, genetic drift can outweigh the effect of selection. Overall, we conclude that in this population, genetic drift resulting from a historical population bottleneck is most likely to have resulted in the observed ROH distribution, with selection possibly playing a minor role.

Characteristics of salivary cortisol and alpha-amylase as psychobiological study outcomes in palliative care research.

BACKGROUND: Psychosocial interventions are rapidly emerging in palliative care. However, randomized trials often fail to provide evidence for their effectiveness with regard to patient-reported outcomes. Stress biomarkers could complement self-report data, but little is known about their feasibility, acceptance, and interpretability. METHODS: Therefore, we designed a randomized crossover trial in which 42 patients in a palliative care unit participated in both a brief mindfulness intervention (MI) and a resting state control condition (CC) on two consecutive afternoons. On each day, we collected four saliva samples in 20-min intervals using Salivettes© to determine salivary cortisol (sCort) and alpha-amylase (sAA) concentration levels. At all measurement points, self-rated well-being and stress as well as cardiovascular markers were assessed. Baseline measurements further included self-rated quality of life and clinician-rated functional status. RESULTS: 78.6% of the patients provided the maximum number of 8 saliva samples and 62.2% reported no subjective difficulties with the sampling procedures. 66.6% (sCort) and 69.6% (sAA) of all possible samples were finally included in the analysis. Xerostomia and nausea were the main reasons for missing data. Higher sCort levels were associated with higher heart rate and lower quality of life, functional status, and heart rate variability. Corticosteroid and sedative medication as well as time since last meal were identified as potential confounders. Regarding reactivity to the MI, we found an overall decrease in sCort levels over time (b = -.03, p = .01), but this effect did not differ significantly between the study conditions (b = .03, p = .21). sAA levels were higher in men than in women. Trajectories over time did not significantly differ between the two conditions (b = -.02, p = .80) and associations with other stress and health-related constructs were weak. CONCLUSIONS: Findings indicate that sCort might serve as a psychobiological outcome in future palliative care trials. However, future research should refine the exact measurement and conceptualization strategies for sCort in palliative care research. High attrition rates should be expected in patients with xerostomia or nausea. TRIAL REGISTRATION: Registered at the German Clinical Trials Registry (DRKS00013135) at 04/12/2017.

Inbreeding depression and the probability of racing in the Thoroughbred horse.

Small effective population sizes and active inbreeding can lead to inbreeding depression due to deleterious recessive mutations exposed in the homozygous state. The Thoroughbred racehorse has low levels of population genetic diversity, but the effects of genomic inbreeding in the population are unknown. Here, we quantified inbreeding based on runs of homozygosity (ROH) using 297 K SNP genotypes from 6128 horses born in Europe and Australia, of which 13.2% were unraced. We show that a 10% increase in inbreeding (FROH) is associated with a 7% lower probability of ever racing. Moreover, a ROH-based genome-wide association study identified a haplotype on ECA14 which, in its homozygous state, is linked to a 32.1% lower predicted probability of ever racing, independent of FROH. The haplotype overlaps a candidate gene, EFNA5, that is highly expressed in cartilage tissue, which when damaged is one of the most common causes of catastrophic musculoskeletal injury in racehorses. Genomics-informed breeding aiming to reduce inbreeding depression and avoid damaging haplotype carrier matings will improve population health and racehorse welfare.

Psychoneuroendocrinological effects of music therapy versus mindfulness in palliative care: results from the 'Song of Life' randomized controlled trial.

PURPOSE: Although research on psychosocial interventions in palliative care provided evidence for their effectiveness regarding patient-reported outcomes, few studies have examined their psychobiological effects yet. Therefore, the purpose of the present work as part of an overarching study was to investigate differential effects of music therapy versus mindfulness on subjective distress and both neuroendocrine and autonomic stress biomarkers. METHODS: A total of 104 patients from two palliative care units were randomly assigned to three sessions of either music therapy or mindfulness. Before and after the second session (completed by 89 patients), participants rated their momentary distress and provided three saliva samples for cortisol and α-amylase analysis. Furthermore, photoplethysmography recordings were continuously assessed to calculate mean heart rate and heart rate variability. Data were analyzed using multilevel modeling of all available data and sensitivity analysis with multiply imputed data. RESULTS: Between 67 and 75% of the maximally available data points were included in the primary analyses of psychobiological outcomes. Results showed a significant time*treatment effect on distress (b = - 0.83, p = .02) indicating a greater reduction in the music therapy group. No interaction effects were found in psychobiological outcomes (all p > .05), but multilevel models revealed a significant reduction in cortisol (b = - 0.06, p = .01) and mean heart rate (b = - 7.89, p = .05) over time following either intervention. CONCLUSION: Findings suggest a beneficial effect music therapy on distress while no differential psychobiological treatment effects were found. Future studies should continue to investigate optimal stress biomarkers for psychosocial palliative care research. TRIAL REGISTRATION: German Clinical Trials Register (DRKS)-DRKS00015308 (date of registration: September 7, 2018).

How to assess and interpret everyday life salivary cortisol measures: A tutorial on practical and statistical considerations.

Salivary cortisol has been the central marker in psychoneuroendocrinological stress research for three decades. Given the technological possibilities to assess data in ecologically valid circumstances, many studies have implemented longitudinal assessments of salivary cortisol in study participants' everyday life. Such studies bear the potential to understand real-life associations of cortisol with psychological traits, states, and health variables. Furthermore, changes in the neuroendocrine regulation and in cortisol reactivity can be used to evaluate the effects of behavioral interventions in real-life circumstances. While standardized paradigms have been developed to measure cortisol in laboratory settings, there is high heterogeneity in the assessment, statistical processing, and interpretation of everyday life cortisol measures. This methodological tutorial aims at summarizing important knowledge which had been accumulated during the past two decades and which could be used to set up an ambulatory assessment study focusing on salivary cortisol in everyday life. Practical advice for possible strategies at all stages of the research process is outlined in detail. Additionally, an example on how to statistically process cortisol data in a multilevel framework (including syntax) is provided. In these analyses, we investigate within- and between-person research questions regarding the association between stress and cortisol in daily life. Thus, the present work (a) can be used as tutorial for setting up everyday life studies focusing on the assessment of salivary cortisol, and (b) can be useful to avoid inconsistencies in study planning, data assessment and data processing in future studies.

Effects of a mindfulness-based intervention on mindfulness, stress, salivary alpha-amylase and cortisol in everyday life.

A large body of literature has shown the effectiveness of mindfulness-based interventions (MBI) on stress-reduction. However, little is known about their effects on psychobiological stress-markers in daily life through an ecological momentary assessment approach. Our study examines the effects of MBI on state mindfulness, perceived stress, and indicators of sympathetic-nervous-system (saliva alpha-amylase, sAA) and hypothalamic-pituitary-adrenal-axis (saliva cortisol, sCort) activation in daily life. Twenty-eight individuals participated in a three-month MBI (IG) and were compared to 46 controls (CG). An ecological momentary assessment (EMA) was used to assess mindfulness, stress, sAA and sCort at six measurements per day on two days each before and after the MBI. Multilevel-modeling was used to analyze the data on a moment-to-moment and averaged day-level. The IG showed decreased sAA levels (AUCg) from pre to post, while the CG showed increases. Furthermore, diurnal decreases in sCort (AUCi) were pronounced in the IG compared to the CG. On a momentary basis, mindfulness was associated with lower stress and sAA levels, but not sCort. As such, we show that MBI can reduce sympathetic and to a lesser extent hypothalamic-pituitary-adrenal activation in daily life. Increased mindfulness can momentarily decrease stress and stress-related autonomic activation with implications for health. Our results emphasize the importance of brief interventions that can be easily integrated into everyday life.

Covariation of psychobiological stress regulation with valence and quantity of social interactions in everyday life: disentangling intra- and interindividual sources of variation.

While the overall effects of social relationships on stress and health have extensively been described, it remains unclear how the experience of social interactions covaries with the activity of psychobiological stress in everyday life. We hypothesized that the valence as well as quantitative characteristics of social interactions in everyday life would attenuate psychobiological stress. Sixty healthy participants provided data for the analyses. Using an ecological momentary assessment design, participants received 6 prompts on their smartphone for 4 days. At each prompt, they reported on social interactions since the last prompt (any occurrence, frequency, duration, quality, and perceived social support), current subjective stress, and provided one saliva sample for the analyses of cortisol (sCort) and alpha-amylase (sAA). Experiencing any contact within days as well as higher daily levels of contact quality and perceived social support were associated with reduced levels of sCort. Furthermore, on a daily level, experiencing at least one contact in-between prompts more often as well as having more contacts on average attenuated the sAA output. Perceived social support and contact quality as well as higher daily contact durations were associated with lower subjective stress. For sCort, daily levels of stress moderated the effects of experiencing any contact within days while daily perceived social support moderated the effects of subjective stress. For sAA, experiencing at least one contact in-between prompts more often on a daily level moderated the effects of subjective stress. There were no between-person effects throughout all analyses. The results show ecologically valid evidence for direct attenuating effects of social interactions on psychobiological stress as well as for the stress-buffering hypothesis in everyday life. Increasing the quantity and improving the valence of social interactions on an intrapersonal level can possibly reduce psychobiological stress and prevent its consequences.

Mutation load decreases with haplotype age in wild Soay sheep.

Runs of homozygosity (ROH) are pervasive in diploid genomes and expose the effects of deleterious recessive mutations, but how exactly these regions contribute to variation in fitness remains unclear. Here, we combined empirical analyses and simulations to explore the deleterious effects of ROH with varying genetic map lengths in wild Soay sheep. Using a long-term dataset of 4879 individuals genotyped at 417K SNPs, we found that inbreeding depression increases with ROH length. A 1% genomic increase in long ROH (>12.5 cM) reduced the odds of first-year survival by 12.4% compared to only 7.7% for medium ROH (1.56-12.5 cM), whereas short ROH (<1.56 cM) had no effect on survival. We show by forward genetic simulations that this is predicted: compared to shorter ROH, long ROH will have higher densities of deleterious alleles, with larger average effects on fitness and lower population frequencies. Taken together, our results are consistent with the idea that the mutation load decreases in older haplotypes underlying shorter ROH, where purifying selection has had more time to purge deleterious mutations. Finally, our study demonstrates that strong inbreeding depression can persist despite ongoing purging in a historically small population.

partR2: partitioning R2 in generalized linear mixed models.

The coefficient of determination R 2 quantifies the amount of variance explained by regression coefficients in a linear model. It can be seen as the fixed-effects complement to the repeatability R (intra-class correlation) for the variance explained by random effects and thus as a tool for variance decomposition. The R 2 of a model can be further partitioned into the variance explained by a particular predictor or a combination of predictors using semi-partial (part) R 2 and structure coefficients, but this is rarely done due to a lack of software implementing these statistics. Here, we introduce partR2, an R package that quantifies part R 2 for fixed effect predictors based on (generalized) linear mixed-effect model fits. The package iteratively removes predictors of interest from the model and monitors the change in the variance of the linear predictor. The difference to the full model gives a measure of the amount of variance explained uniquely by a particular predictor or a set of predictors. partR2 also estimates structure coefficients as the correlation between a predictor and fitted values, which provide an estimate of the total contribution of a fixed effect to the overall prediction, independent of other predictors. Structure coefficients can be converted to the total variance explained by a predictor, here called 'inclusive' R 2, as the square of the structure coefficients times total R 2. Furthermore, the package reports beta weights (standardized regression coefficients). Finally, partR2 implements parametric bootstrapping to quantify confidence intervals for each estimate. We illustrate the use of partR2 with real example datasets for Gaussian and binomial GLMMs and discuss interactions, which pose a specific challenge for partitioning the explained variance among predictors.

Psychological structure and neuroendocrine patterns of daily stress appraisals.

Threat and challenge are two fundamental appraisal concepts of psychological stress theories, determined by the mismatch between demands and resources. Previous research has predominantly investigated the neuroendocrine correlates of stress appraisal in laboratory contexts during acute demanding situations. We tested whether the psychoneuroendocrinology of stress appraisals can also be investigated in naturalistic trans-contextual everyday life settings. Forty-two participants produced five daily saliva samples and provided concurrent questionnaire data on subjective stress, demands, resources, and the threat-challenge continuum over the course of five days (69% female; mean age = 22.8, range = 18-30 years). Momentary salivary cortisol and alpha amylase were predicted with three-level autoregressive linear mixed models. We found that both momentary cortisol and alpha amylase were elevated during higher subjective stress. In contrast, cortisol was not significantly related to a bipolar threat-challenge indicator. Moreover within-person response surface analyses showed no effect of the mismatch between demands and resources on either physiological stress indicator, but confirmed theoretically proposed effects on subjective threat-challenge, which was replicated in another intensive longitudinal (N = 61) and a large cross-sectional sample (N = 1194). In sum, our study (a) suggests robust relations between subjective stress and HPA/SAM axis activity on a moment-to-moment basis and (b) confirms theoretical predictions concerning stress appraisal and the mismatch between demands and resources on a psychological level. In contrast, no neuroendocrine patterns of threat-challenge were found, suggesting that neuroendocrine patterns might be context-specific and do not apply to a general demand-resource imbalance in everyday life.

Chemical patterns of colony membership and mother-offspring similarity in Antarctic fur seals are reproducible.

Replication studies are essential for evaluating the validity of previous research findings. However, it has proven challenging to reproduce the results of ecological and evolutionary studies, partly because of the complexity and lability of many of the phenomena being investigated, but also due to small sample sizes, low statistical power and publication bias. Additionally, replication is often considered too difficult in field settings where many factors are beyond the investigator's control and where spatial and temporal dependencies may be strong. We investigated the feasibility of reproducing original research findings in the field of chemical ecology by performing an exact replication of a previous study of Antarctic fur seals (Arctocephalus gazella). In the original study, skin swabs from 41 mother-offspring pairs from two adjacent breeding colonies on Bird Island, South Georgia, were analyzed using gas chromatography-mass spectrometry. Seals from the two colonies differed significantly in their chemical fingerprints, suggesting that colony membership may be chemically encoded, and mothers were also chemically similar to their pups, hinting at the possible involvement of phenotype matching in mother-offspring recognition. In the current study, we generated and analyzed chemical data from a non-overlapping sample of 50 mother-offspring pairs from the same two colonies 5 years later. The original results were corroborated in both hypothesis testing and estimation contexts, with p-values remaining highly significant and effect sizes, standardized between studies by bootstrapping the chemical data over individuals, being of comparable magnitude. However, exact replication studies are only capable of showing whether a given effect can be replicated in a specific setting. We therefore investigated whether chemical signatures are colony-specific in general by expanding the geographic coverage of our study to include pups from a total of six colonies around Bird Island. We detected significant chemical differences in all but a handful of pairwise comparisons between colonies. This finding adds weight to our original conclusion that colony membership is chemically encoded, and suggests that chemical patterns of colony membership not only persist over time but can also be generalized over space. Our study systematically confirms and extends our previous findings, while also implying more broadly that spatial and temporal heterogeneity need not necessarily negate the reproduction and generalization of ecological research findings.

Instructed Partnership Appreciation in Depression: Effects on Mood, Momentary Relationship Satisfaction, and Psychobiological Arousal.

BACKGROUND: Depressive disorders are associated with attentional bias and social anhedonia. There is evidence supporting the hypothesis that depressed individuals participate less in potentially rewarding social situations and exhibit alterations in stress reactivity. With the present study, we aimed at investigating the affective and psychobiological response of couples with a depressed (female) partner in an instructed partnership appreciation task (PAT) that included positive and appreciative communication. METHODS: In a quasi-experimental repeated-measures design, depressive couples (DCs)-i.e., the female partner being diagnosed with a depressive disorder-were compared to non-depressive couples (NDCs). Study outcomes were the PAT-induced changes in state mood, momentary relationship satisfaction, salivary cortisol, and salivary alpha-amylase. Additionally, we assessed psychometric baseline data on depression, relationship quality, social support, and chronic stress. Data was analyzed using multilevel modeling. RESULTS: A total of 184 individuals from N = 47 DCs and N = 45 NDCs were included. DCs were characterized by higher depressiveness, lower relationship quality, less actually received social support from the partner, and higher chronic stress than NDCs. Manipulation checks led to the additional exclusion of two couples. Regarding mood, depressed women showed lower baseline scores and no significant differences in mood increase compared to non-depressed women (p = 0.107). Increases in relationship satisfaction were significantly stronger in the depressed group (p = 0.035). In addition, we found a significantly stronger cortisol increase in depressed women, but only if relationship duration was taken into account as a moderating factor (p = 0.022). No significant group differences were found for women's amylase trajectories or for sex-dependent interaction effects on the couple level (all p > 0.05). CONCLUSIONS: Instructed engagement in positive couple interaction may require high effort and increased psychobiological arousal, but may finally result in emotional and social benefits in depressed women. While these findings encourage speculations about the therapeutic application of instructed partnership appreciation, more research is needed on the effectiveness of such interventions and on the moderating role of relationship duration in depression and couple functioning.

Publisher Correction: The genetic legacy of extreme exploitation in a polar vertebrate.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The genetic legacy of extreme exploitation in a polar vertebrate.

Understanding the effects of human exploitation on the genetic composition of wild populations is important for predicting species persistence and adaptive potential. We therefore investigated the genetic legacy of large-scale commercial harvesting by reconstructing, on a global scale, the recent demographic history of the Antarctic fur seal (Arctocephalus gazella), a species that was hunted to the brink of extinction by 18th and 19th century sealers. Molecular genetic data from over 2,000 individuals sampled from all eight major breeding locations across the species' circumpolar geographic distribution, show that at least four relict populations around Antarctica survived commercial hunting. Coalescent simulations suggest that all of these populations experienced severe bottlenecks down to effective population sizes of around 150-200. Nevertheless, comparably high levels of neutral genetic variability were retained as these declines are unlikely to have been strong enough to deplete allelic richness by more than around 15%. These findings suggest that even dramatic short-term declines need not necessarily result in major losses of diversity, and explain the apparent contradiction between the high genetic diversity of this species and its extreme exploitation history.

Early sexual dimorphism in the developing gut microbiome of northern elephant seals.

The gut microbiome is an integral part of a species' ecology, but we know little about how host characteristics impact its development in wild populations. Here, we explored the role of such intrinsic factors in shaping the gut microbiome of northern elephant seals (Mirounga angustirostris) during a critical developmental window of 6 weeks after weaning, when the pups stay ashore without feeding. We found substantial sex differences in the early-life gut microbiome, even though males and females could not yet be distinguished morphologically. Sex and age both explained around 15% of the variation in gut microbial beta diversity, while microbial communities sampled from the same individual showed high levels of similarity across time, explaining another 40% of the variation. Only a small proportion of the variation in beta diversity was explained by health status, assessed by full blood counts, but clinically healthy individuals had a greater microbial alpha diversity than their clinically abnormal peers. Across the post-weaning period, the northern elephant seal gut microbiome was highly dynamic. We found evidence for several colonization and extinction events as well as a decline in Bacteroides and an increase in Prevotella, a pattern that has previously been associated with the transition from nursing to solid food. Lastly, we show that genetic relatedness was correlated with gut microbiome similarity in males but not females, again reflecting early sex differences. Our study represents a naturally diet-controlled and longitudinal investigation of how intrinsic factors shape the early gut microbiome in a species with extreme sex differences in morphology and life history.