Genome-wide association study identifies genetic variants underlying footrot in Portuguese Merino sheep.

BACKGROUND: Ovine footrot caused by Dichelobacter nodosus (D. nodosus) is a contagious disease with serious economic and welfare impacts in sheep production systems worldwide. A better understanding of the host genetic architecture regarding footrot resistance/susceptibility is crucial to develop disease control strategies that efficiently reduce infection and its severity. A genome-wide association study was performed using a customized SNP array (47,779 SNPs in total) to identify genetic variants associated to footrot resistance/susceptibility in two Portuguese native breeds, i.e. Merino Branco and Merino Preto, and a population of crossbred animals. A cohort of 1375 sheep sampled across 17 flocks, located in the Alentejo region (southern Portugal), was included in the analyses. RESULTS: Phenotypes were scored from 0 (healthy) to 5 (severe footrot) based on visual inspection of feet lesions, following the Modified Egerton System. Using a linear mixed model approach, three SNPs located on chromosome 24 reached genome-wide significance after a Bonferroni correction (p < 0.05). Additionally, six genome-wide suggestive SNPs were identified each on chromosomes 2, 4, 7, 8, 9 and 15. The annotation and KEGG pathway analyses showed that these SNPs are located within regions of candidate genes such as the nonsense mediated mRNA decay associated PI3K related kinase (SMG1) (chromosome 24) and the RALY RNA binding protein like (RALYL) (chromosome 9), both involved in immunity, and the heparan sulfate proteoglycan 2 (HSPG2) (chromosome 2) and the Thrombospodin 1 (THBS1) (chromosome 7) implicated in tissue repair and wound healing processes. CONCLUSION: This is the first attempt to identify molecular markers associated with footrot in Portuguese Merino sheep. These findings provide relevant information on a likely genetic association underlying footrot resistance/susceptibility and the potential candidate genes affecting this trait. Genetic selection strategies assisted on the information obtained from this study could enhance Merino sheep-breeding programs, in combination with farm management strategies, for a more effective and sustainable long-term solution for footrot control.

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.

Do sheep (Ovis aries) discriminate human emotional odors?

While sheep can detect and discriminate human emotions through visual and vocal cues, their reaction to human body odors remains unknown. The present study aimed to determine whether sheep (Ovis aries) can detect human odors, olfactorily discriminate stressed from non-stressed individuals, and behave accordingly based on the emotional valence of the odors. Axillary secretions from 34 students were collected following an oral examination (stress odor) or a regular class (non-stress odor). Fourteen female and 15 male lambs were then exposed to these odors through a habituation-dishabituation procedure. The habituation stimulus was presented four times for one minute, followed by the dishabituation stimulus presented once for one minute. Behavioral variables included spatiality relative to target odors, approach/withdrawal, ear positioning, sniffing, ingestion, and vocalization. Both female and male lambs more often positioned their ears backwards/forwards, and asymmetrically when exposed to the dishabituation stimulus, but regardless of their stress or non-stress value. They also changed their approach behavior when exposed to the dishabituation stimuli. Lambs displayed some behavioral signs of discrimination between the habituation and dishabituation odors, but regardless of their relation to stress or non-stress of human donors. In sum, this exploratory study suggests that young sheep respond negatively to the odor of unfamiliar humans, without showing any specific emotional contagion related to the stress odor. This exploratory study suggests young ovines can detect human body odor, a further step toward understanding the human-sheep relationship.

MFSD2A frameshift variant in Kerry Hill sheep with microcephaly.

Microcephaly is a rare neurodevelopmental disorder characterized by reduced skull circumference and brain volume that occurs sporadically in farm animals. We investigated an early-onset neurodegenerative disorder observed in seven lambs of purebred Kerry Hill sheep. Clinical signs included inability to stand or severe ataxia, convulsions, and early death. Diagnostic imaging and brain necropsy confirmed microcephaly. The pedigree of the lambs suggested monogenic autosomal recessive inheritance. We sequenced the genome of one affected lamb, and comparison with 115 control genomes revealed a single private protein-changing variant. This frameshift variant, MFSD2A: c.285dupA, p.(Asp96fs*9), represents a 1-bp duplication predicted to truncate 80% of the open reading frame. MFSD2A is a transmembrane protein that is essential for maintaining blood-brain barrier homeostasis and plays a key role in regulating brain lipogenesis. Human MFSD2A pathogenic variants are associated with a neurodevelopmental disorder with progressive microcephaly, spasticity, and brain imaging abnormalities (NEDMISBA, OMIM 616486). Here we present evidence for the occurrence of a recessively inherited form of microcephaly in sheep due to a loss-of-function variant in MFSD2A (OMIA 002371-9940). To the best of our knowledge, this is the first report of a spontaneous MFSD2A variant in domestic animals.

A single base pair duplication in the SLC33A1 gene is associated with fetal losses and neonatal lethality in Manech Tête Rousse dairy sheep.

We recently discovered that the Manech Tête Rousse (MTR) deficient homozygous haplotype 2 (MTRDHH2) probably carries a recessive lethal mutation in sheep. In this study, we fine-mapped this region through whole-genome sequencing of five MTRDHH2 heterozygous carriers and 95 non-carriers from various ovine breeds. We identified a single base pair duplication within the SLC33A1 gene, leading to a frameshift mutation and a premature stop codon (p.Arg246Alafs*3). SLC33A1 encodes a transmembrane transporter of acetyl-coenzyme A that is crucial for cellular metabolism. To investigate the lethality of this mutation in homozygous MTR sheep, we performed at-risk matings using artificial insemination (AI) between heterozygous SLC33A1 variant carriers (SLC33A1_dupG). Pregnancy was confirmed 15 days post-AI using a blood test measuring interferon Tau-stimulated MX1 gene expression. Ultrasonography between 45 and 60 days post-AI revealed a 12% reduction in AI success compared with safe matings, indicating embryonic/fetal loss. This was supported by the MX1 differential expression test suggesting fetal losses between 15 and 60 days of gestation. We also observed a 34.7% pre-weaning mortality rate in 49 lambs born from at-risk matings. Homozygous SLC33A1_dupG lambs accounted for 47% of this mortality, with deaths occurring mostly within the first 5 days without visible clinical signs. Therefore, appropriate management of SLC33A1_dupG with an allele frequency of 0.04 in the MTR selection scheme would help increase overall fertility and lamb survival.

Loss-of-function variant in the ovine TMCO6 gene in North Country Cheviot sheep with motor neuron disease.

In North Country Cheviot lambs with early-onset progressive ataxia and motor neuron degeneration, whole-genome sequencing identified a homozygous loss-of-function variant in the ovine transmembrane and coiled-coil domains (TMCO6) gene. The familial recessive form of motor neuron disease in sheep is due to a pathogenic 4 bp deletion leading to a 50% protein truncation that is assumed to result in the absence of a functional TMCO6. This uncharacterised protein is proposed to interact with ubiquilin 1 which is associated with Alzheimer's disease, whereas sporadic forms of amyotrophic lateral sclerosis are caused by variants in UBQLN2. Our findings provide a first spontaneous animal model for TMCO6, which could have implications in the studies of other comparative neurodegenerative diseases. In addition, these results will allow the design of a genetic test to prevent the occurrence of this fatal disease in the affected sheep population.

Amplification of Ovis aries papillomavirus type 2 DNA from an ovine cutaneous fibropapilloma.

Seven of 60 Perendale sheep within a flock developed single or multiple exophytic masses on their distal hind limbs. A mass was excised from one sheep and histological evaluation revealed epidermal and mesenchymal proliferation, papillomavirus-induced keratinocyte changes and marked keratohyalin clumping. Ovis aries papillomavirus type 2 DNA sequences were amplified using PCR.

Sept des 60 moutons Perendale d'un troupeau ont développé des masses exophytiques uniques ou multiples sur leurs membres postérieurs distaux. Une masse a été excisée sur un mouton et l'évaluation histologique a révélé une prolifération épidermique et mésenchymateuse, des modifications kératinocytaires induites par le papillomavirus et une agglutination marquée de kératohyaline. Les séquences d'ADN du papillomavirus Ovis aries de type 2 ont été amplifiées par PCR.

Sete de 60 ovelhas Perendale de um rebanho desenvolveram massas exofíticas na porção distal dos seus membros posteriores. Uma massa foi removida de uma ovelha e a avaliação histopatológica revelou proliferação mesenquimal e epidérmica, alterações queratinocíticas induzidas por papilomavírus e aglomeração queratohialina. Sequências de papilomavírus Ovis aries tipo 2 foram amplificadas utilizando PCR.

Siete de 60 ovejas Perendale dentro de un rebaño desarrollaron masas exofíticas únicas o múltiples en sus extremidades traseras distales. Se extirpó una masa de una oveja y la evaluación histológica reveló proliferación epidérmica y mesenquimal, cambios de queratinocitos inducidos por el virus del papiloma y marcada acumulación de queratohialina. Mediante PCR se amplificaron secuencias de DNA del virus del papiloma Ovis aries tipo 2.

Nutritional strategies, performance, digestibility, and carcass traits of Santa Ines and Rabo Largo breeds in a tropical climate.

The aim of this study was to compare the performance, intake, digestibility, ruminal parameters, carcass traits, and the yield of commercial cuts of Santa Ines (SI) and Rabo Largo (RL) breeds fed diets with high or low roughage-to-concentrate ratio (R:C) under a tropical climate. Twenty lambs from each breed were individually housed in covered pens and fed the experimental diets for 58 days. The diets were formulated to meet the growth requirements of lambs with a roughage-to-concentrate ratio of 70:30 and 30:70. Significant interactions of breed × diet for nutrient intake were observed (P < 0.05), with SI lambs fed low R:C diet showing higher intake of dry matter, organic matter, crude protein, and total carbohydrates compared to RL lambs fed the same diet. SI lambs fed high R:C diet had higher intake of neutral detergent fiber than RL lambs (P < 0.05). SI lambs displayed better average daily gain and feed efficiency, regardless of diet (P < 0.05). Carcass traits and gastrointestinal components were influenced by breed and diet (P < 0.05). SI lambs fed low R:C diet showed higher subcutaneous fat thickness and better carcass finishing compared to RL lambs (P < 0.05). SI breed lambs exhibited better growth performance, carcass traits, and gastrointestinal characteristics, even when fed diets with a high roughage-to-concentrate ratio.

Trait-dependent associations between early- and late-life reproduction in a wild mammal.

Early- versus late-life trade-offs are a central prediction of life-history theory that are expected to shape the evolution of ageing. While ageing is widely observed in wild vertebrates, evidence that early-late trade-offs influence ageing rates remains limited. Vertebrate reproduction is a complex, multi-stage process, yet few studies have examined how different aspects of early-life reproductive allocation shape late-life performance and ageing. Here, we use longitudinal data from a 36-year study of wild Soay sheep to show that early-life reproduction predicts late-life reproductive performance in a trait-dependent manner. Females that started breeding earlier showed more rapid declines in annual breeding probability with age, consistent with a trade-off. However, age-related declines in offspring first-year survival and birth weight were not associated with early-life reproduction. Selective disappearance was evident in all three late-life reproductive measures, with longer-lived females having higher average performance. Our results provide mixed support for early-late reproductive trade-offs and show that the way early-life reproduction shapes late-life performance and ageing can differ among reproductive traits.

The InDel variants of sheep IGF2BP1 gene are associated with growth traits.

Insulin-like growth factor 2 mRNA binding protein 1 (IGF2BP1) plays positive roles in the growth, proliferation of cells and early embryos development by binding mRNA targets. Recently, it had been shown that some polymorphic loci within IGF2BP1 gene were associated with growth traits in animals, especially in goats. Therefore, it has been hypothesized that some variants within IGF2BP1 gene may be also involved in growth traits of sheep. Nine insertion/deletion (InDel) mutations within IGF2BP1 were identified and three loci were polymorphic. Meanwhile, the association analyses between three InDels and growth traits were carried out in 745 sheep. The results showed that all InDels included 5 bp InDel in downstream region, 9 bp InDel in intron 4 and 15 bp InDel in intron 2 within IGF2BP1 were significantly associated with growth traits (p<.05). Furthermore, at 5 and 9 bp InDel loci, the individuals of heterozygous genotype (ID) had superior growing performance especially at body weight (BW). In all, three InDels were crucial variants correlated with growth traits and could be applied in marker-assisted selection (MAS) in sheep.

Whole-genome resequencing of Dorper and Hu sheep to reveal selection signatures associated with important traits.

Dorper and Hu sheep exhibit different characteristics in terms of reproduction, growth, and meat quality. Comparison of the genomes of two breeds help to reveal important genomic information. In this study, whole genome resequencing of 30 individuals (Dorper, DB and Hu sheep, HY) identified 15,108,125 single nucleotide polymorphisms (SNPs). Population differentiation (Fst) and cross population extended haplotype homozygosity (XP-EHH) were performed for selective signal analysis. In total, 106 and 515 overlapped genes were present in both the Fst results and XP-EHH results in HY vs DB and in DB vs HY, respectively. In HY vs DB, 106 genes were enriched in 12 GO terms and 83 KEGG pathways, such as ATP binding (GO:0005524) and PI3K-Akt signaling pathway (oas04151). In DB vs HY, 515 genes were enriched in 109 GO terms and 215 KEGG pathways, such as skeletal muscle cell differentiation (GO:0035914) and MAPK signaling pathway (oas04010). According to the annotation results, we identified a series of candidate genes associated with reproduction (UNC5C, BMPR1B, and GLIS1), meat quality (MECOM, MEF2C, and MYF6), and immunity (GMDS, GALK1, and ITGB4). Our investigation has uncovered genomic information for important traits in sheep and provided a basis for subsequent studies of related traits.

Adaptive dynamics of indigenous sheep in Canary Islands, Spain: A machine learning approach.

The objective of the study was to characterize the adaptive profile of Ibero-American sheep of the Canaria breed, evaluating the possible changes in thermoregulatory responses and coat characteristics to which the animals are exposed in the different seasons of the year. Data collected over a period of 12 months were analyzed, with information being observed in the interval of 15 days of each month, in 23 adult ewes kept in an intensive breeding system. The rectal temperature (RT) of Canaria ewes was higher (P < 0.001) in the summer and spring seasons. In contrast, the respiratory rate (RR) of the animals was higher in autumn. The surface temperature (ST) of the herd was lower during the spring. It was observed that the hair length (HL) and the hair density (NH) did not vary during the seasons. However, the hair diameter (HD) and the coat thickness (CT) varied, being in the spring, the season in which the animals had the highest HD and autumn, the season in which they had the lowest. The performance was similar throughout the seasons (P > 0.05). The morphological variables of the coat presented 63.8% of original cases grouped, which may characterize the morphological responses of the coat of these animals as an important trait of the adaptive profile of the breed, whereas the opposite occurred for thermoregulatory responses. The variables most used by the herd and that were most important were autumn (CT, NH, HD, HR, RT, and HL), summer (ST and RR), spring (RR, ST, and RT), and winter (RT, HD, HR, and RR). Sheep of the Canaria breed have an adaptive profile that dynamically uses thermoregulatory and morphological responses, molding themselves according to climate changes resulting from seasonal periods on the Island of Tenerife, Spain. The Canaria sheep stood out for the modification of the morphological characteristics of the coat, especially during autumn and spring, and can be considered an excellent genetic resource with excellent adaptive characteristics for arid environments such as those found in the Canary Islands.

Natural adaptation and human selection of northeast African sheep genomes.

African sheep manifest diverse but distinct physio-anatomical traits, which are the outcomes of natural- and human-driven selection. Here, we generated 34.8 million variants from 150 indigenous northeast African sheep genomes sequenced at an average depth of ∼54× for 130 samples (Ethiopia, Libya) and ∼20× for 20 samples (Sudan). These represented sheep from diverse environments, tail morphology and post-Neolithic introductions to Africa. Phylogenetic and model-based admixture analysis provided evidence of four genetic groups corresponding to altitudinal geographic origins, tail morphotypes and possible historical introduction and dispersal of the species into and across the continent. Running admixture at higher levels of K (6 ≤ K ≤ 25), revealed cryptic levels of genome intermixing as well as distinct genetic backgrounds in some populations. Comparative genomic analysis identified targets of selection that spanned conserved haplotype structures overlapping clusters of genes and gene families. These were related to hypoxia responses, ear morphology, caudal vertebrae and tail skeleton length, and tail fat-depot structures. Our findings provide novel insights underpinning morphological variation and response to human-driven selection and environmental adaptation in African indigenous sheep.

A genome-wide comparison between selected and unselected Valle del Belice sheep reveals differences in population structure and footprints of recent selection.

About three decades of breeding and selection in the Valle del Belìce sheep are expected to have left several genomic footprints related to milk production traits. In this study, we have assembled a dataset with 451 individuals of the Valle del Belìce sheep breed: 184 animals that underwent directional selection for milk production and 267 unselected animals, genotyped for 40,660 single-nucleotide polymorphisms (SNPs). Three different statistical approaches, both within (iHS and ROH) and between (Rsb) groups, were used to identify genomic regions potentially under selection. Population structure analyses separated all individuals according to their belonging to the two groups. A total of four genomic regions on two chromosomes were jointly identified by at least two statistical approaches. Several candidate genes for milk production were identified, corroborating the polygenic nature of this trait and which may provide clues to potential new selection targets. We also found candidate genes for growth and reproductive traits. Overall, the identified genes may explain the effect of selection to improve the performances related to milk production traits in the breed. Further studies using high-density array data, would be particularly relevant to refine and validate these results.

Thermal stress index for native sheep.

The first objective of this study was to develop a thermal stress index for sheep based on environmental and animal data collected in a climate chamber under various environmental conditions. The second objective was to compare published indices of thermal comfort and the proposed index, testing them with the data from this study, with the objective of pointing out the most adequate index to be used by breeders when choosing management procedures. A total of 3024 data were obtained for the physiological variables of the sheep exposed to the eight thermal conditions in the climatic chamber and in ambient condition, kept three days in each thermal condition. A principal component analysis summarized the measurements of physiological variables into only one variable (y1). Using SigmaPlot software, multiple regression of y1 with the environmental variables and their combinations produced a number of indices. The equation chosen was the heat stress index for sheep, TSI = 24.153 - (0.0523*AT) + (0.746*BGT) + (4.104*Vp), with R2 = 0.668. The correlations presented high values, where these correlation values were assumed to indicate the efficiency of each index as indicators of the animals' response to the environment. Thus, it was assumed that the TSI presents a high efficiency.

Environment rather than breed or body site shapes the skin bacterial community of healthy sheep as revealed by metabarcoding.

BACKGROUND: The skin is inhabited by a variety of micro-organisms, with bacteria representing the predominant taxon of the skin microbiome. In sheep, the skin bacterial community of healthy animals has been addressed in few studies, only with culture-based methods or sequencing of cloned amplicons. OBJECTIVES: The objectives of this study were to determine the sheep skin bacterial community composition by using metabarcoding for a detailed characterisation and to determine the effect of body part, breed and environment. MATERIALS AND METHODS: Overall, 267 samples were taken from 89 adult female sheep, belonging to three different breeds and kept on nine different farms in Switzerland. From every individual, one sample each was taken from belly, left ear and left leg and metabarcoding of the 16S rRNA V3-V4 hypervariable region was performed. RESULTS: The main phyla identified were Actinobacteriota, Firmicutes, Proteobacteria and Bacteriodota. The alpha diversity as determined by Shannon's diversity index was significantly different between sheep from different farms. Beta diversity analysis by principal coordinate analysis (PCoA) showed clustering of the samples by farm and body site, while breed had only a marginal influence. A sparse partial least squares discriminant analysis (sPLS-DA) revealed seven main groups of operational taxonomic units (OTUs) of which groups of OTUs were specific for some farms. CONCLUSIONS AND CLINICAL RELEVANCE: These findings indicate that environment has a larger influence on skin microbial variability than breed, although the sampled breeds, the most abundant ones in Switzerland, are phenotypically similar. Future studies on the sheep skin microbiome may lead to novel insights in skin diseases and prevention.

Genetic polymorphism in European and African sheep breeds reared in Hungary based on 48 SNPs associated with resistance to gastrointestinal parasite infection using KASP-PCR technique.

This pilot study used an alternative and economically efficient technique, the Kompetitive Allele-Specific Polymerase Chain Reaction (KASP-PCR) to examine 48 SNPs from 11 parasite-resistance genes found on 8 chromosomes in 110 animals from five sheep breeds reared in Hungary; Hungarian Tsigai, White Dorper, Dorper, Ile de France, and Hungarian Merino. Allele and genotype frequencies, fixation index, observed heterozygosity, expected heterozygosity, F statistic, and their relationship with the Hardy-Weinberg equilibrium (WHE) and the polymorphic information content (PIC) were determined, followed by principal component analysis (PCA). As much as 32 SNPs out of the 48 initially studied were successfully genotyped. A total of 9 SNPs, 4 SNPs in TLR5, 1 SNP in TLR8, and 4 SNPs in TLR2 genes, were polymorphic. The variable genotype and allele frequency of the TLRs gene indicated genetic variability among the studied sheep breeds, with the Hungarian Merino exhibiting the most polymorphisms, while Dorper was the population with the most SNPs departing from the HWE. According to the PIC value, the rs430457884-TLR2, rs55631273-TLR2, and rs416833129-TLR5 were found to be informative in detecting polymorphisms among individuals within the populations, whereas the rs429546187-TLR5 and rs424975389-TLR5 were found to have a significant influence in clustering the population studied. This study reported a moderate level of genetic variability and that a low to moderate within-breed diversity was maintained in the studied populations.

Single-Step Protocol for Isolating the Recombinant Extracellular Domain of the Luteinizing Hormone Receptor from the Ovis aries Testis.

The luteinizing hormone receptor (LHR) is a glycoprotein member of the G protein-coupled receptors superfamily. It participates in corpus luteum formation and ovulation in females and acts in testosterone synthesis and spermatogenesis in males. In this study, we extracted RNA from sheep testicles and synthetized the cDNA to amplify the gene lhr-bed. This gene consists of 762 bp and encodes 273 amino acids of the extracellular domain of LHR. The lhr-bed was cloned into pJET1.2/blunt, then subcloned into pCOLD II, and finally, transformed in E. coli BL21 (DE3) cells. Because the induced rLHR-Bed protein was found in the insoluble fraction, we followed a modified purification protocol involving induction at 25 °C, subjection to denaturing conditions, and on-column refolding to increase solubility. We confirmed rLHR-Bed expression by means of Western blot and mass spectrometry analysis. It is currently known that the structure stem-loop 5'UTR on pCOLD II vector is stable at 15 °C. We predicted and obtained RNAfold stability at 25 °C. We successfully obtained the recombinant LHR extracellular domain, with protein yields of 0.2 mg/L, and purity levels of approximately 90%, by means of a single chromatographic purification step. The method described here may be used to obtain large quantities of rLHR-Bed in the future.

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.

Long-term temporal trends in gastrointestinal parasite infection in wild Soay sheep.

Monitoring the prevalence and abundance of parasites over time is important for addressing their potential impact on host life histories, immunological profiles and their influence as a selective force. Only long-term ecological studies have the potential to shed light on both the temporal trends in infection prevalence and abundance and the drivers of such trends, because of their ability to dissect drivers that may be confounded over shorter time scales. Despite this, only a relatively small number of such studies exist. Here, we analysed changes in the prevalence and abundance of gastrointestinal parasites in the wild Soay sheep population of St. Kilda across 31 years. The host population density (PD) has increased across the study, and PD is known to increase parasite transmission, but we found that PD and year explained temporal variation in parasite prevalence and abundance independently. Prevalence of both strongyle nematodes and coccidian microparasites increased during the study, and this effect varied between lambs, yearlings and adults. Meanwhile, abundance of strongyles was more strongly linked to host PD than to temporal (yearly) dynamics, while abundance of coccidia showed a strong temporal trend without any influence of PD. Strikingly, coccidian abundance increased 3-fold across the course of the study in lambs, while increases in yearlings and adults were negligible. Our decades-long, intensive, individual-based study will enable the role of environmental change and selection pressures in driving these dynamics to be determined, potentially providing unparalleled insight into the drivers of temporal variation in parasite dynamics in the wild.