No correlative evidence of costs of infection or immunity on leucocyte telomere length in a wild population of Soay sheep.

Telomere length (TL) is a biomarker hypothesized to capture evolutionarily and ecologically important physiological costs of reproduction, infection and immunity. Few studies have estimated the relationships among infection status, immunity, TL and fitness in natural systems. The hypothesis that short telomeres predict reduced survival because they reflect costly consequences of infection and immune investment remains largely untested. Using longitudinal data from a free-living Soay sheep population, we tested whether leucocyte TL was predicted by infection with nematode parasites and antibody levels against those parasites. Helminth parasite burdens were positively associated with leucocyte TL in both lambs and adults, which is not consistent with TL reflecting infection costs. We found no association between TL and helminth-specific IgG levels in either young or old individuals which suggests TL does not reflect costs of an activated immune response or immunosenescence. Furthermore, we found no support for TL acting as a mediator of trade-offs between infection, immunity and subsequent survival in the wild. Our results suggest that while variation in TL could reflect short-term variation in resource investment or environmental conditions, it does not capture costs of infection and immunity, nor does it behave like a marker of an individual's helminth-specific antibody immune response.

Heritable variation in telomere length predicts mortality in Soay sheep.

Telomere length (TL) is considered an important biomarker of whole-organism health and aging. Across humans and other vertebrates, short telomeres are associated with increased subsequent mortality risk, but the processes responsible for this correlation remain uncertain. A key unanswered question is whether TL-mortality associations arise due to positive effects of genes or early-life environment on both an individual's average lifetime TL and their longevity, or due to more immediate effects of environmental stressors on within-individual TL loss and increased mortality risk. Addressing this question requires longitudinal TL and life history data across the entire lifetimes of many individuals, which are difficult to obtain for long-lived species like humans. Using longitudinal data and samples collected over nearly two decades, as part of a long-term study of wild Soay sheep, we dissected an observed positive association between TL and subsequent survival using multivariate quantitative genetic models. We found no evidence that telomere attrition was associated with increased mortality risk, suggesting that TL is not an important marker of biological aging or exposure to environmental stress in our study system. Instead, we find that among-individual differences in average TL are associated with increased lifespan. Our analyses suggest that this correlation between an individual's average TL and lifespan has a genetic basis. This demonstrates that TL has the potential to evolve under natural conditions, and suggests an important role of genetics underlying the widespread observation that short telomeres predict mortality.

Anionic lipid vesicles have differential effects on the aggregation of early onset-associated α-synuclein missense mutants.

α-synuclein (αS) is the key component of synucleinopathies such as Parkinson's disease (PD), dementia with Lewy bodies, and multiple system atrophy. αS was first linked to PD through the identification of point mutations in the SNCA gene, causing single amino acid substitutions within αS and familial autosomal dominant forms of PD that profoundly accelerated disease onset by up to several decades. At least eight single-point mutations linked to familial PD (A30G/P, E46K, H50Q, G51D, and A53T/E/V) are located in proximity of the region preceding the non-ß amyloid component (preNAC) region, strongly implicating its pathogenic role in αS-mediated cytotoxicity. Furthermore, lipids are known to be important for native αS function, where they play a key role in the regulation of synaptic vesicle docking to presynaptic membranes and dopamine transmission. However, the role of lipids in the function of mutant αS is unclear. Here, we studied αS aggregation properties of WT αS and five of the most predominant single-point missense mutants associated with early onset PD in the presence of anionic 1,2-dimyristoyl-sn-glycero-3-phospho-l-serine lipid vesicles. Our results highlight significant differences between aggregation rates, the number of aggregates produced, and overall fibril morphologies of WT αS and the A30P, E46K, H50Q, G51D, and A53T missense mutants in the presence of lipid vesicles. These findings have important implications regarding the interplay between the lipids required for αS function and the individual point mutations known to accelerate PD and related diseases.

Associations between MHC class II variation and phenotypic traits in a free-living sheep population.

Pathogen-mediated selection (PMS) is thought to maintain the high level of allelic diversity observed in the major histocompatibility complex (MHC) class II genes. A comprehensive way to demonstrate contemporary selection is to examine associations between MHC variation and individual fitness. As individual fitness is hard to measure, many studies examine associations between MHC variation and phenotypic traits, including direct or indirect measures of adaptive immunity thought to contribute to fitness. Here, we tested associations between MHC class II variation and five phenotypic traits measured in free-living sheep captured in August: weight, strongyle faecal egg count, and plasma IgA, IgE and IgG immunoglobulin titres against the gastrointestinal nematode parasite Teladorsagia circumcincta. We found no association between MHC class II variation and weight or strongyle faecal egg count. We did, however, find associations between MHC class II variation and immunoglobulin levels which varied with isotype, age and sex. Our results suggest associations between MHC and phenotypic traits are more likely to be found for traits more closely associated with pathogen defence than integrative traits such as bodyweight and highlight the association between MHC variation and antibodies in wild populations.

The association between female reproductive performance and leukocyte telomere length in wild Soay sheep.

Telomere length (TL), typically measured across a sample of blood cells, has emerged as an exciting potential marker of physiological state and of the costs of investment in growth and reproduction within evolutionary ecology. While there is mounting evidence from studies of wild vertebrates that short TL predicts raised subsequent mortality risk, the relationship between reproductive investment and TL is less clear cut, and previous studies report both negative and positive associations. In this study, we examined the relationship between TL and different aspects of maternal reproductive performance in a free-living population of Soay sheep. We find evidence for shorter TL in females that bred, and thus paid any costs of gestation, compared to females that did not breed. However, we found no evidence for any association between TL and litter size. Furthermore, females that invested in gestation and lactation actually had longer TL than females who only invested in gestation because their offspring died shortly after birth. We used multivariate models to decompose these associations into among- and within-individual effects, and discovered that within-individual effects were driving both the negative association between TL and gestation, and the positive association between TL and lactation. This suggests that telomere dynamics may reflect recent physiologically costly investment or variation in physiological condition, depending on the aspect of reproduction being investigated. Our results highlight the physiological complexity of vertebrate reproduction, and the need to better understand how and why different aspects of physiological variation underpinning life histories impact blood cell TL.

The genetic architecture of helminth-specific immune responses in a wild population of Soay sheep (Ovis aries).

Much of our knowledge of the drivers of immune variation, and how these responses vary over time, comes from humans, domesticated livestock or laboratory organisms. While the genetic basis of variation in immune responses have been investigated in these systems, there is a poor understanding of how genetic variation influences immunity in natural, untreated populations living in complex environments. Here, we examine the genetic architecture of variation in immune traits in the Soay sheep of St Kilda, an unmanaged population of sheep infected with strongyle gastrointestinal nematodes. We assayed IgA, IgE and IgG antibodies against the prevalent nematode Teladorsagia circumcincta in the blood plasma of > 3,000 sheep collected over 26 years. Antibody levels were significantly heritable (h2 = 0.21 to 0.57) and highly stable over an individual's lifespan. IgA levels were strongly associated with a region on chromosome 24 explaining 21.1% and 24.5% of heritable variation in lambs and adults, respectively. This region was adjacent to two candidate loci, Class II Major Histocompatibility Complex Transactivator (CIITA) and C-Type Lectin Domain Containing 16A (CLEC16A). Lamb IgA levels were also associated with the immunoglobulin heavy constant loci (IGH) complex, and adult IgE levels and lamb IgA and IgG levels were associated with the major histocompatibility complex (MHC). This study provides evidence of high heritability of a complex immunological trait under natural conditions and provides the first evidence from a genome-wide study that large effect genes located outside the MHC region exist for immune traits in the wild.

The role of maternally transferred antibodies in maternal performance in red deer.

Maternal effects are ubiquitous. Yet, the pathways through which maternal effects occur in wild mammals remain largely unknown. We hypothesise that maternal immune transfer is a key mechanism by which mothers can affect their offspring fitness, and that individual variation in maternally derived antibodies mainly depends on a mother's characteristics and the environmental conditions she experiences. To test this, we assayed six colostrum-derived antibodies in the plasma of 1447 neonates in a wild red deer population. Neonatal antibody levels were mainly affected by maternal genes, environmental variation and costs of prior reproductive investment. We found consistent heterogeneity in maternal performance across traits, with mothers producing the heaviest calves also having calves with more antibodies. Unexpectedly, antibody levels were not associated with calf survival. We provide a unique example of how evolutionary theory on maternal effects can be used to gain insight into the causes of maternal effects in wild populations.

Maternally derived anti-helminth antibodies predict offspring survival in a wild mammal.

The transfer of antibodies from mother to offspring provides crucial protection against infection to offspring during early life in humans and domestic and laboratory animals. However, few studies have tested the consequences of variation in maternal antibody transfer for offspring fitness in the wild. Further, separating the immunoprotective effects of antibodies from their association with nutritional resources provided by mothers is difficult. Here, we measured plasma levels of total and parasite-specific antibodies in neonatal (less than 10 days old) wild Soay sheep over 25 years to quantify variation in maternal antibody transfer and test its association with offspring survival. Maternal antibody transfer was predicted by maternal age and previous antibody responses, and was consistent within mothers across years. Neonatal total IgG antibody levels were positively related to early growth, suggesting they reflected nutritional transfer. Neonatal parasite-specific IgG levels positively predicted first-year survival, independent of lamb weight, total IgG levels and subsequent lamb parasite-specific antibody levels. This relationship was partly mediated via an indirect negative association with parasite burden. We show that among-female variation in maternal antibody transfer can have long-term effects on offspring growth, parasite burden and fitness in the wild, and is likely to impact naturally occurring host-parasite dynamics.

Natural Selection on Antihelminth Antibodies in a Wild Mammal Population.

An effective immune response is expected to confer fitness benefits through improved resistance to parasites but also incur energetic costs that negatively impact fitness-related traits, such as reproduction. The fitness costs and benefits of an immune response are likely to depend on host age, sex, and levels of parasite exposure. Few studies have examined the full extent to which patterns of natural selection on immune phenotypes vary across demographic groups and environments in the wild. Here, we assessed natural selection on plasma levels of three functionally distinct isotypes (IgA, IgE, and IgG) of antibodies against a prevalent nematode parasite measured in a wild Soay sheep population over 26 years. We found little support for environment-dependent selection or reproductive costs. However, antibody levels were negatively associated with parasite egg counts and positively associated with subsequent survival, albeit in a highly age- and isotype-dependent manner. Raised levels of antiparasite IgA best predicted reduced egg counts, but this did not predict survival in lambs. In adults increased antiparasite IgG predicted reduced egg counts, and in adult females IgG levels also positively predicted overwinter survival. Our results highlight the potential importance of age- and sex-dependent selection on immune phenotypes in nature and show that patterns of selection can vary even among functionally related immune markers.

Joint associations of blood plasma proteins with overwinter survival of a large mammal.

In many wild animal populations, hosts are at risk of parasites and malnutrition and resource costs of defence may be difficult to afford. We postulate that proteins, important in homeostasis and immunity, play a complex but central role in condition dependence and resource costs of mammalian immune defence. To test this, we measured plasma concentrations of albumin, total proteins. Self-reactive antibodies and parasite-specific IgG in female Soay sheep. Using a principal component analysis, we found a new metric of condition reflecting individual variation in acquisition, assimilation and/or recycling of plasma proteins that predicted overwinter survival. Controlling for this metric, an age-dependent trade-off between antibody titres and protein reserves emerged, indicating costs of mounting an antibody response: younger individuals survived best when prioritising immunity while older individuals fared better when maintaining high-protein nutritional plane. These findings suggest fascinating roles for protein acquisition and allocation in influencing survival in wild animal populations.

Sex differences in leucocyte telomere length in a free-living mammal.

Mounting evidence suggests that average telomere length reflects previous stress and predicts subsequent survival across vertebrate species. In humans, leucocyte telomere length (LTL) is consistently shorter during adulthood in males than in females, although the causes of this sex difference and its generality to other mammals remain unknown. Here, we measured LTL in a cross-sectional sample of free-living Soay sheep and found shorter telomeres in males than in females in later adulthood (>3 years of age), but not in early life. This observation was not related to sex differences in growth or parasite burden, but we did find evidence for reduced LTL associated with increased horn growth in early life in males. Variation in LTL was independent of variation in the proportions of different leucocyte cell types, which are known to differ in telomere length. Our results provide the first evidence of sex differences in LTL from a wild mammal, but longitudinal studies are now required to determine whether telomere attrition rates or selective disappearance are responsible for these observed differences.

Natural selection on individual variation in tolerance of gastrointestinal nematode infection.

Hosts may mitigate the impact of parasites by two broad strategies: resistance, which limits parasite burden, and tolerance, which limits the fitness or health cost of increasing parasite burden. The degree and causes of variation in both resistance and tolerance are expected to influence host-parasite evolutionary and epidemiological dynamics and inform disease management, yet very little empirical work has addressed tolerance in wild vertebrates. Here, we applied random regression models to longitudinal data from an unmanaged population of Soay sheep to estimate individual tolerance, defined as the rate of decline in body weight with increasing burden of highly prevalent gastrointestinal nematode parasites. On average, individuals lost weight as parasite burden increased, but whereas some lost weight slowly as burden increased (exhibiting high tolerance), other individuals lost weight significantly more rapidly (exhibiting low tolerance). We then investigated associations between tolerance and fitness using selection gradients that accounted for selection on correlated traits, including body weight. We found evidence for positive phenotypic selection on tolerance: on average, individuals who lost weight more slowly with increasing parasite burden had higher lifetime breeding success. This variation did not have an additive genetic basis. These results reveal that selection on tolerance operates under natural conditions. They also support theoretical predictions for the erosion of additive genetic variance of traits under strong directional selection and fixation of genes conferring tolerance. Our findings provide the first evidence of selection on individual tolerance of infection in animals and suggest practical applications in animal and human disease management in the face of highly prevalent parasites.

Marker-dependent associations among oxidative stress, growth and survival during early life in a wild mammal.

Oxidative stress (OS) is hypothesized to be a key physiological mechanism mediating life-history trade-offs, but evidence from wild populations experiencing natural environmental variation is limited. We tested the hypotheses that increased early life growth rate increases OS, and that increased OS reduces first-winter survival, in wild Soay sheep (Ovis aries) lambs. We measured growth rate and first-winter survival for four consecutive cohorts, and measured two markers of oxidative damage (malondialdehyde (MDA), protein carbonyls (PC)) and two markers of antioxidant (AOX) protection (total AOX capacity (TAC), superoxide dismutase (SOD)) from blood samples. Faster lamb growth was weakly associated with increased MDA, but not associated with variation in the other three markers. Lambs with higher SOD activity were more likely to survive their first winter, as were male but not female lambs with lower PC concentrations. Survival did not vary with MDA or total TAC. Key predictions relating OS to growth and survival were therefore supported in some OS markers, but not others. This suggests that different markers capture different aspects of the complex relationships between individual oxidative state, physiology and fitness, and that overarching hypotheses relating OS to life-history variation cannot be supported or refuted by studying individual markers.

Heritable, heterogeneous, and costly resistance of sheep against nematodes and potential feedbacks to epidemiological dynamics.

Infected hosts may preserve fitness by resisting parasites (reducing parasite burden) and/or tolerating them (preventing or repairing infection-induced damage). Theory predicts that these individual-level defense strategies generate divergent population-level feedbacks that would maintain genetic heterogeneity for resistance but purge heterogeneity for tolerance. Because resistance reduces parasite abundance, selection for costly resistance traits will weaken as resistance becomes common. Such negative frequency-dependent selection contrasts with predictions for tolerance, which maintains parasite abundance and so is expected to generate positive frequency-dependent selection, unless, for example, tolerance trades off with resistance. Thus far, there have been few tests of this theory in natural systems. Here, we begin testing the predictions in a mammalian field system, using data on individual gastrointestinal nematode burdens, nematode-specific antibody titers (as a resistance metric), the slope of body weight on parasite burden (as a tolerance metric), and fitness from an unmanaged population of Soay sheep. We find that nematode resistance is costly to fitness and underpinned by genetic heterogeneity, and that resistance is independent of tolerance. Drawing upon empirical metrics such as developed here, future work will elucidate how resistance and tolerance feedbacks interact to generate population-scale patterns in the Soay sheep and other field systems.

Multivariate immune defences and fitness in the wild: complex but ecologically important associations among plasma antibodies, health and survival.

Despite our rapidly advancing mechanistic understanding of vertebrate immunity under controlled laboratory conditions, the links between immunity, infection and fitness under natural conditions remain poorly understood. Antibodies are central to acquired immune responses, and antibody levels circulating in vivo reflect a composite of constitutive and induced functional variants of diverse specificities (e.g. binding antigens from prevalent parasites, self tissues or novel non-self sources). Here, we measured plasma concentrations of 11 different antibody types in adult females from an unmanaged population of Soay sheep on St Kilda. Correlations among antibody measures were generally positive but weak, and eight of the measures independently predicted body mass, strongyle parasite egg count or survival over the subsequent winter. These independent and, in some cases, antagonistic relationships point to important multivariate immunological heterogeneities affecting organismal health and fitness in natural systems. Notably, we identified a strong positive association between anti-nematode immunoglobulin (Ig) G antibodies in summer and subsequent over-winter survival, providing rare evidence for a fitness benefit of helminth-specific immunity under natural conditions. Our results highlight both the evolutionary and ecological importance and the complex nature of the immune phenotype in the wild.

Whole of government approaches to accelerate adolescent success: efficiency and financing considerations.

The multiple domains of development covered by the Sustainable Development Goals (SDGs) present a practical challenge for governments. This is particularly acute in highly resource-constrained settings which use a sector-by-sector approach to structure financing and prioritization. One potentially under-prioritized solution is to implement interventions with the potential to simultaneously improve multiple outcomes across sectors, what United Nations Development Programme refer to as development 'accelerators'. An increasing number of accelerators are being identified in the literature. There are, however, challenges associated with the evaluation and implementation of accelerators. First, as accelerators have multiple benefits, possibly in different sectors, they will be undervalued if the priority setting is conducted sector-by-sector. Second, even if their value is recognized, accelerators may not be adopted if doing so clashes with any of the multiple competing interests policymakers consider, of which efficiency/social desirability is but one. To illustrate the first challenge, and outline a possible solution, we conduct a cost-effectiveness analysis comparing the implementation of three sector-specific interventions to an accelerator, first using a sector-by-sector planning perspective, then a whole of government approach. The case study demonstrates how evaluating the cost-effectiveness of interventions sector-by-sector can lead to suboptimal efficiency rankings and overlook interventions that are efficient from a whole of government perspective. We then examine why recommendations based on a whole of government approach to evaluation are unlikely to be heeded. To overcome this second challenge, we outline a menu of existing and novel financing mechanisms that aim to address the mismatch between political incentives and logistical constraints in the priority setting and the economic evaluation evidence for cost-effective accelerators. These approaches to financing accelerators have the potential to improve efficiency, and in doing so, progress towards the SDGs, by aligning political incentives more closely with recommendations based on efficiency rankings.

Does perceived caregiver HIV stigma and depression increase adolescent neuro-behavioral difficulties? A mediation analysis in the Asenze Cohort.

People living with HIV (PLWH) often experience HIV related stigma that is, in turn, associated with several negative health outcomes including depression, harmful drinking, and intimate partner violence. Despite knowledge of these proximal impacts of HIV stigma on PLWH, less is known about the impact that Caregivers living with HIV's perception of stigma has on the health and behavior of adolescents in their care. Utilizing data from adolescents and their primary caregivers from the population-based Asenze cohort study in KwaZulu-Natal, South Africa, we conducted a path analysis to determine if caregiver depression [operationalized as mental health functioning] is a mediator of the hypothesized association between caregiver HIV stigma and adolescent neurodevelopmental behavior including internalizing and externalizing behaviors. Results suggest good model fit and a statistically significant relationship between caregiver HIV stigma and caregiver mental health functioning. However, neither the direct nor indirect (including potential mediator caregiver mental health functioning) effect of HIV stigma on adolescent behavioral difficulties was statistically significant. This paper builds on previous research demonstrating the relationship between HIV stigma and depression, highlighting the need for continued study of underlying mechanisms that impact the stigma and health of PLWH and others important to them such as their children.

The impact of family support and organization on adolescents during school closure under Covid-19 lockdown regulations in an area of South Africa.

The Covid-19 pandemic and resultant disruptions to schooling presented significant challenges for many families. Well organised families have been shown to have a protective effect on adolescent wellbeing in periods of shock. At the onset of the Covid-19 pandemic, Asenze, a population-based cohort study, was conducting a third wave of data collection in peri-urban South Africa, examining risk and protective factors during adolescence. By March 2020, n = 272 adolescents and their caregivers (n = 241) in the cohort had been assessed when in-person data collection was halted by lockdown measures countrywide. During this cessation we undertook a brief telephonic qualitative sub-study to explore whether families enrolled in the cohort were able to cohabit cohesively and undertake distance learning during lockdown. A purposeful sample of 20 families (caregivers n = 20, adolescents n = 24) recently assessed in the Wave 3 of the main study, participated in semi-structured interviews. Quantitative data from Waves 1-3 of the main study was used to measure family function, adolescent cognitive function, and profile adolescent and caregivers. The quantitative and qualitative data were integrated to illustrate the dynamics of the participants' lives before and during lockdown. We found that families classified as well-organized before lockdown, were more likely to report co-operation during lockdown. Adolescents who were self-motivated, had access to smartphones or the internet, and were supported by both family and educators, were well-placed to continue their education without much disruption. However, few schools instituted distance learning. Of the adolescents who were not assisted- some studied on their own or with peers, but others did no schoolwork, hindered by a lack of digital connectivity, and poor service delivery. The experience of adolescence and caregivers in the Asenze Cohort during lockdown highlight the importance of family functioning for adolescent wellbeing in crisis, as well as the need for access to health, mental health, and social services, communication upgrades, and enhancements to the education system during peaceful times, to make a difference to young lives in times of crisis.

Development of a hydroxyflavone-labelled 4554W peptide probe for monitoring αS aggregation.

Parkinson's is the second most common neurodegenerative disease, with the number of individuals susceptible due to increase as a result of increasing life expectancy and a growing worldwide population. However, despite the number of individuals affected, all current treatments for PD are symptomatic-they alleviate symptoms, but do not slow disease progression. A major reason for the lack of disease-modifying treatments is that there are currently no methods to diagnose individuals during the earliest stages of the disease, nor are there any methods to monitor disease progression at a biochemical level. Herein, we have designed and evaluated a peptide-based probe to monitor αS aggregation, with a particular focus on the earliest stages of the aggregation process and the formation of oligomers. We have identified the peptide-probe K1 as being suitable for further development to be applied to number of applications including: inhibition of αS aggregation; as a probe to monitor αS aggregation, particularly at the earliest stages before Thioflavin-T is active; and a method to detect early-oligomers. With further development and in vivo validation, we anticipate this probe could be used for the early diagnosis of PD, a method to evaluate the effectiveness of potential therapeutics, and as a tool to help in the understanding of the onset and development of PD.

A mixed-model approach for estimating drivers of microbiota community composition and differential taxonomic abundance.

Next-generation sequencing (NGS) and metabarcoding approaches are increasingly applied to wild animal populations, but there is a disconnect between the widely applied generalized linear mixed model (GLMM) approaches commonly used to study phenotypic variation and the statistical toolkit from community ecology typically applied to metabarcoding data. Here, we describe the suitability of a novel GLMM-based approach for analyzing the taxon-specific sequence read counts derived from standard metabarcoding data. This approach allows decomposition of the contribution of different drivers to variation in community composition (e.g., age, season, individual) via interaction terms in the model random-effects structure. We provide guidance to implementing this approach and show how these models can identify how responsible specific taxonomic groups are for the effects attributed to different drivers. We applied this approach to two cross-sectional data sets from the Soay sheep population of St. Kilda. GLMMs showed agreement with dissimilarity-based approaches highlighting the substantial contribution of age and minimal contribution of season to microbiota community compositions, and simultaneously estimated the contribution of other technical and biological factors. We further used model predictions to show that age effects were principally due to increases in taxa of the phylum Bacteroidetes and declines in taxa of the phylum Firmicutes. This approach offers a powerful means for understanding the influence of drivers of community structure derived from metabarcoding data. We discuss how our approach could be readily adapted to allow researchers to estimate contributions of additional factors such as host or microbe phylogeny to answer emerging questions surrounding the ecological and evolutionary roles of within-host communities. IMPORTANCE NGS and fecal metabarcoding methods have provided powerful opportunities to study the wild gut microbiome. A wealth of data is, therefore, amassing across wild systems, generating the need for analytical approaches that can appropriately investigate simultaneous factors at the host and environmental scale that determine the composition of these communities. Here, we describe a generalized linear mixed-effects model (GLMM) approach to analyze read count data from metabarcoding of the gut microbiota, allowing us to quantify the contributions of multiple host and environmental factors to within-host community structure. Our approach provides outputs that are familiar to a majority of field ecologists and can be run using any standard mixed-effects modeling packages. We illustrate this approach using two metabarcoding data sets from the Soay sheep population of St. Kilda investigating age and season effects as worked examples.