and Discussion
Diapause treatment extended lifespan (Figure 1A), reducing
the hazard of death by approximately 65% compared to
controls (Cox Proportional Hazards model; Hazard Ratio
[HR] = 0.35, 95% CI: 0.26–0.49; Wald test,
p = 5×10−9).
This was also reflected in the median survival determined by
Kaplan-Meier analysis which was 30 days (95% CI: 28–32
days) for the diapause group (n=71), versus 22 days (95%
CI: 22–23 days) for controls (n=101).
From 715,987 CpG sites classified as methylated (SI
Dataset S1), the generalized linear model (12) identified 7,950
CpGs with significant age-related differential methylation (SI
Dataset S2). We further prioritized 289 of these sites that
were strongly correlated with chronological age (Pearson’s
|r|≥0.3, uncorrected p≤0.05) as input features for an
Elastic Net regression model (SI Dataset S3). The final
optimised model (mixing parameter α= 0.5; regularization
λ= 1.84207, determined by 10-fold repeated cross-validation
[3 repeats] minimizing Root Mean Squared Error [RMSE])
utilized a concise panel of 27 CpGs to estimate epigenetic
age (SI Dataset S4).
Our resulting epigenetic clock accurately predicted chrono-
logical age in control samples, explaining 91.7% of the variance
(cross-validatedR2; RMSE = 2.44 days). Importantly, the
clock also performed robustly when applied to diapause
samples, accounting for 78.0% of chronological age variance
(R2; RMSE = 3.98 days), demonstrating its potential
applicability across distinct physiological conditions.
Curiously, at day 6 post-eclosion, diapaused adults were
epigenetically older than age-matched controls by an esti-
mated 2.8 days (diapaused: 11.32 days vs. control: 8.53
days, t = -3.22, d.f. = 36, p = 0.0027,
emmeans post
hoc). One possible explanation is that epigenetic ageing
occurs during the diapause period, albeit at a markedly
reduced rate compared to adult ageing. Alternatively, the
observed overshoot may reflect transient remodelling of DNA
methylation during emergence from diapause. Distinguishing
between these scenarios will require direct measurement of
methylation dynamics during diapause itself.
Despite this initial increase in epigenetic age, diapaused
adults subsequently age epigenetically 29% more slowly than
controls (Figure 1B; control slope = 0.78812, diapause slope
= 0.55828; linear model interaction of day and treatment: t
= -3.903, d.f. = 36, p = 0.000399). By day 18, both groups
converge on an epigenetic age of approximately 18 days.
However, by day 30, diapaused individuals are epigenetically
2.7 days younger than controls (24.71 days vs. 27.44 days;
emmeans post hoc: t = 3.152, d.f. = 36, p = 0.0033).
This striking deceleration mirrors the observed extension in
lifespan and 65% reduction in mortality hazard in diapaused
individuals. Together, these results suggest that the molecular
changes captured by the epigenetic clock are closely aligned
with the physiological mechanisms that promote survival
post-diapause.
Our findings place diapause-induced epigenetic decelera-
tion within the broader context of early life programming,
where environmental cues can reshape long-term molecular
and physiological trajectories. The direction and magnitude
of changes in the epigenome largely depend on early life
environmental conditions (14). This is not unexpected, as the
epigenome is highly plastic during early development. Such
plasticity may be adaptive, allowing early life environments to
reconfigure the epigenome in ways that enhance future fitness,
2 — www.pnas.org/cgi/doi/10.1073/pnas.XXXXXXXXXX Foley et al.
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consistent with the predictive adaptive response hypothesis
(15). In this framework, insect larval diapause would serve as
a predictive adaptive response: an overwintering strategy that
anticipates a more challenging adult environment. Adults
that have passed through diapause may be under selection
to survive longer, facilitating reproductive success in harsher
post-winter conditions. In Nasonia, our data suggest that
this is mirrored at the molecular level by a long-term slowing
of the epigenetic clock.
Epigenetic clocks across diverse species consistently high-
light key developmental gene sets as predictors of biological
age (16). The CpGs comprising our Nasonia epigenetic clock
are significantly enriched for gene ontology terms related
to conserved developmental and nutrient-sensing pathways,
including mTOR and insulin/IGF signaling (SI Dataset S5).
These pathways are central regulators of growth, metabolism,
and lifespan. Theoretical links between development and
ageing have a long history in evolutionary biology ( 17), and
experimental studies, particularly in invertebrates such as
C. elegans, have shown that developmental alterations, such as
entry into the dauer stage, can dramatically extend lifespan.
Our findings align with recent work in Drosophila, where
Kang et al. (18) demonstrated that delayed development in
prothoracicotropic hormone (PTTH)-null mutants extends
lifespan and postpones the onset of age-related transcriptional
changes. In Nasonia, we observe a similar phenomenon,
larval diapause, a naturally induced developmental delay,
slows the progression of the epigenetic ageing clock. Notably,
PTTH suppression has been implicated in diapause induction
across diverse insect species ( 19). Together, these findings
point to a conserved endocrine-epigenetic axis through which
developmental timing modulates ageing trajectories.
Epigenetic ageing is influenced by inflammation, cell
division, metabolic state, and early-life environment ( 3).
With its compact genome, short lifespan, and functional
methylation system, Nasonia enables experimental dissection
of these processes in vivo ( 6). Our findings demonstrate
that epigenetic ageing in this model is not only measurable,
but developmentally modifiable. This positions Nasonia to
address a fundamental translational question: can targeted
reductions in epigenetic age improve long-term health and
resilience?
ACKNOWLEDGMENTS. EBF was supported by a BBSRC
MIBTP DTP studentships. CT was funded by a Leverhulme Trust
award RPG-2020-363. EM was funded by a BBSRC Pioneer Award
APP3335. For the purpose of open access, the author has applied
a Creative Commons Attribution (CC BY) licence to any Author
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was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
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1
Supporting Information for2
Larval diapause slows adult epigenetic ageing in an insect model, Nasonia vitripennis3
Erin B. Foley, Charalambos P. Kyriacou, Christian L. Thomas & Eamonn B. Mallon4
Eamonn B. Mallon.5
E-mail:
[email protected]
This PDF file includes:7
Supporting text8
Legends for Dataset S1 to S59
SI References10
Other supporting materials for this manuscript include the following:11
Datasets S1 to S512
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was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
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Supporting Information Text13
Methods14
Rearing. Nasonia vitripennis used in this study were from the Leicester strain, a laboratory colony maintained at the University15
of Leicester for over nine years. This strain derives from AsymC, originally isolated in 1989 and subsequently cured ofWolbachia16
via heat shock treatment (1,2).17
To generate diapaused offspring, virgin females were housed at 20°C under a 16:8 h dark:light photoperiod. Host pupae18
were collected from Day 10 post-oviposition onwards to ensure recovery of diapaused larvae. These larvae developed to the19
fourth instar before being transferred to continuous darkness at 4°C for three months. After the diapause period, larvae were20
returned to standard rearing conditions and allowed to complete development to adulthood.21
Lifespan Experiments.Diapaused and non-diapaused virgin maleNasonia were collected in batches within 24 hours of adult22
emergence (Day 0) and housed individually in plastic tubes. All individuals were maintained at 25°C and 40% relative humidity23
under a 12:12 h light:dark cycle. Each wasp received a daily feeding of 20µL of 20% sucrose solution on filter paper, and24
mortality was recorded daily. Lifespan was defined as the number of days from adult emergence to death.25
Kaplan–Meier survival analyses were performed using the survival package (v3.7) (3) and visualized with the survminer26
package (v0.4.9) (4). Cox proportional hazards models were fitted using the survival package. All analyses were conducted in27
R v4.4.1 (5).28
Lifespan data were used to select sampling time points for whole-genome bisulfite sequencing (WGBS). Diapaused and29
non-diapaused virgin males were sampled at Days 6, 12, 18, 24, and 30, always at the same time of day. Upon collection,30
individuals were snap-frozen in liquid nitrogen and stored at –80°C until DNA extraction.31
DNA Extraction.DNA was extracted using an adapted protocol based on the AllPrep® DNA/RNA Micro Kit (Qiagen). Each32
sample consisted of ten whole-body adult virgin maleNasonia. Four biological replicates were processed per time point (Days33
6, 12, 18, 24, and 30).34
DNA quality and concentration were assessed using a NanoDrop 2000 spectrophotometer (Thermo Fisher Scientific), a35
QubitTM dsDNA BR Assay Kit (Thermo Fisher Scientific), and electrophoresis on a 1% agarose gel run for 40 minutes at36
100V. Samples were sent to Novogene (Beijing) for whole-genome bisulfite sequencing (WGBS). A 1% unmethylated lambda37
DNA spike-in was included in each sample to assess bisulfite conversion efficiency.38
Whole-Genome Bisulfite Sequencing and Bioinformatic Processing. Raw sequencing data were provided in FASTQ format39
(submitted to Sequence Read Archive (SRA)). For samples sequenced across multiple lanes, read files were concatenated using40
the Unix cat command. Read quality was assessed using FastQC v0.12.1 (6).41
A custom Snakemake pipeline (Snakemake v7.32.4; Python v3.12.1) (7) was used for preprocessing. Adapter sequences were42
trimmed and the first 10 bases removed from each read using Cutadapt v4.4 (8). Paired-end reads were aligned to theNasonia43
vitripennis reference genome (Nvit_PSR1.1) (9) using Bowtie2 v2.5.1 with default parameters (10). Reads were also aligned to44
the unmethylated lambda genome (RefSeq accession: GCF_000840245.1) to assess bisulfite conversion efficiency.45
Aligned reads were deduplicated and cytosine methylation calls extracted using Bismark v0.22.3 (11). Strand ambiguity was46
resolved using thecoverage2cytosine utility in Bismark to generate destranded coverage files, which were used for downstream47
analyses.48
Methylation Analysis.All downstream analyses were performed in R v4.4.1 (5). Destranded CpG coverage files were imported49
into the MethylKit package v1.30.0 (12) using themethRead() function. CpG sites with less than 10× coverage or coverage50
above the 99th percentile were filtered out. A binomial test was applied to each sample using the lambda genome conversion51
rate as the null probability of success, with a false discovery rate (FDR) threshold ofp < 0.05 (SI Dataset S5). Only CpG sites52
showing significant methylation in at least one sample were retained. Percentage methylation at each site was calculated using53
the percMethylation() function.54
Differential Methylation Analysis.Differential methylation analysis was performed using theDSS package v2.52.0 (13), which55
models methylation proportions using a beta-binomial generalized linear model (GLM) with an arcsine link function. A design56
matrix was constructed incorporating time point and treatment (diapause vs. non-diapause) as experimental factors. Linear57
models were fitted using theDMLfit() function to evaluate main effects and interactions. Differentially methylated loci (DMLs)58
and regions (DMRs) were identified accordingly.59
Genomic features were assigned to CpG sites using a custom annotation file (GFF format) generated by Dr. Hollie Marshall60
using AGAT v0.10.0 (14).61
Epigenetic Clock Construction.An elastic net regression model was trained to predict chronological age from DNA methylation62
levels across CpG sites, using data from virgin maleNasonia vitripennis sampled at five time points (Days 6, 12, 18, 24, and63
30). Methylation data (percentage values) were filtered to retain CpG sites previously identified as differentially methylated64
across time usingDSS (13).65
To enhance model sparsity and robustness, CpG sites were pre-selected based on univariate Pearson correlation with age in66
the non-diapaused (control) group. Sites with absolute correlation≥ 0.3 and uncorrectedp-value≤ 0.05 were retained. CpG67
features were then centered and scaled.68
2 of 4 Erin B. Foley, Charalambos P. Kyriacou, Christian L. Thomas & Eamonn B. Mallon
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was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
The copyright holder for this preprint (whichthis version posted May 23, 2025. ; https://doi.org/10.1101/2025.05.22.655466doi: bioRxiv preprint
The final model was implemented using theglmnet algorithm with elastic net regularization (α = 0.5), as part of thecaret69
framework (15). Ten-fold cross-validation with three repeats was used for model tuning and performance estimation. The70
treatment group (diapause vs. control) was included as a categorical predictor, encoded as a dummy variable, and entered71
alongside the CpG methylation features. The optimal model was selected based on minimum root mean squared error (RMSE).72
Predictions were generated for all samples, and model performance was assessed using RMSE andR2, stratified by treatment73
group.74
Post-hoc analysis of predicted age trajectories was conducted using linear models with interaction terms, and estimated75
marginal means were compared between treatment groups at multiple time points using theemmeans package (16).76
Gene Ontology Enrichment Analysis.Gene Ontology (GO) enrichment analysis was performed to assess the functional signifi-77
cance of genes associated with CpG sites included in the final epigenetic clock model. The 27 clock CpGs (SI Dataset S4)78
were mapped to nearby genes, which were then tested for enrichment against a background set comprising all genes associated79
with differentially methylated loci across time (SI Dataset S1). GO annotations were derived fromNasonia vitripennis and80
formatted for compatibility withGOstats (17).81
The gene list was tested for overrepresentation of GO terms in the Biological Process (BP), Cellular Component (CC), and82
Molecular Function (MF) ontologies using a conditional hypergeometric test. Analyses were performed using theGOstats and83
GSEABase packages. For each ontology, both over- and under-representation were tested, and GO terms with an adjusted84
FDR of< 0.05 (Benjamini-Hochberg) were considered significant.85
To visualise and summarise redundant GO terms, semantic similarity clustering was performed using therrvgo package (18).86
Pairwise GO term similarities were calculated using theorg.Dm.eg.db annotation database and the “Rel” semantic similarity87
measure. Representative GO terms were identified by reducing the similarity matrix with a similarity threshold of 0.7. Enriched88
terms were visualised using treemaps, heatmaps, and scatter plots. Final results were exported in tabular form (SI Dataset S5).89
All scripts used are available athttps://tinyurl.com/5n6vcvsk90
SI Dataset S1 (SI_Datasets.xlsx/S1_Methylated_CpGs)91
CpG sites classified as methylated using a binomial test with the lambda genome conversion rate as the null probability of92
success. Sites passing a false discovery rate (FDR) threshold ofp< 0.05 and significantly methylated in at least one sample93
were retained.94
SI Dataset S2 (SI_Datasets.xlsx/S2_Age_DMPs)95
7,950 CpG sites showing significant age-associated differential methylation.96
SI Dataset S3 (SI_Datasets.xlsx/S3_Age_Correlated)97
289 age-associated CpG sites with strong correlation to chronological age (Pearson’s|r|≥ 0.3, uncorrectedp≤ 0.05).98
SI Dataset S4 (SI_Datasets.xlsx/S4_Clock_Coefficients)99
Elastic net model coefficients for the 27 CpG sites and intercept used to estimate epigenetic age.100
SI Dataset S5 (SI_Datasets.xlsx/S5_GO_terms)101
Enriched gene ontology terms associated with the 27 CpG sites comprising the epigenetic clock.102
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