Biology subjects

Stockin, K. A.

Publications and source records attributed to Stockin, K. A..

7 recordsLinked to original sources

bioRxiv2026

Epigenetic age acceleration is associated with contaminant exposure in common dolphins (Delphinus delphis)

Metals and per- and polyfluoroalkyl substances (PFAS) represent a significant environmental concern, yet their association with epigenetic age acceleration (EAA) remain largely understudied in marine mammals. Here, associations between EAA in common dolphins (Delphinus delphis) and life history (sex and sexual maturity), trace metals, and PFAS were investigated. EAA was calculated as the residual in the regression of epigenetic age vs chronological age, hence providing a direct measure of the deviation of the epigenetic age of an organism (positive or negative) by comparison with expectation, given their actual chronological age. Sixteen trace elements were quantified in hepatic and renal tissues (n = 53). In addition, 28 PFAS were quantified in hepatic tissue (n = 58). Associations between EAA and explanatory variables were assessed using regression-based and multivariate modelling approaches (linear models and canonical analysis of principal coordinates). No effect of sex was observed, although sexual maturity did significantly increase EAA. Exposure to metals was significantly associated with EAA, explaining 55.4% of the variation, with hepatic metals (Se, Zn, Cu, Al, Mn) driving this relationship. Although EAA was not significantly related to the total PFAS exposure overall, a subset of PFAS variables (PFBA, PFDA, PFHxS-B, PFNA) showed significant association with EAA after adjusting for sex and sexual maturity. Together, these subsets of metal and PFAS variables, in addition to the selenium-to-mercury (Se:Hg) molar ratio, explained 66.7% of the variation in EAA. Our results identify sexual maturity and specific contaminant mixtures as key potential drivers of EAA in common dolphins, highlighting the possible use of EAA as a biomarker of environmental and physiological stress in marine mammals.

zoology↗

bioRxiv2026

PFAS exposure is associated with accelerated epigenetic ageing in a wild marine mammal

Chronic contaminant exposure may impose hidden physiological costs long before obvious demographic or health effects become detectable in wildlife populations. Epigenetic clocks quantify biological ageing and may provide sensitive biomarkers of cumulative toxicological stress. Per-and polyfluoroalkyl substances (PFAS) are persistent contaminants that bioaccumulate in marine food webs, yet their long-term physiological consequences for wildlife remain poorly understood. Here, we tested whether PFAS exposure is associated with accelerated biological ageing in common dolphins (Delphinus delphis). We analysed liver PFAS concentrations and skin DNA methylation profiles from 30 stranded or bycaught dolphins from New Zealand waters. Epigenetic age was estimated using a recently developed species-specific epigenetic clock, and age acceleration was calculated as the residual deviation between epigenetic and chronological age. Using an information-theoretic modelling framework, we assessed the effects of total PFAS burden, sex, and their interactions on epigenetic age acceleration. Total PFAS concentrations were positively associated with epigenetic age acceleration, indicating that dolphins with higher PFAS burdens were biologically older than expected for their chronological age. Each 1 ng g{square}{superscript 1} increase in total PFAS was associated with an average increase of 0.031 years in biological age. Sex did not significantly influence age acceleration, suggesting that PFAS-associated ageing effects occur across both sexes. Although modest, this effect is consistent with PFAS acting as a chronic physiological stressor influencing molecular ageing processes. Our findings provide the first evidence linking PFAS exposure to accelerated biological ageing in a wild mammal, highlighting epigenetic ageing as an integrative biomarker of long-term contaminant effects in wildlife.

ecology↗

bioRxiv2026

Radiographic assessment of bone maturation as a tool for age estimation in common dolphins (Delphinus delphis)

We present the first radiographic ageing framework for common dolphins (Delphinus delphis), based on ossification and epiphyseal fusion patterns in the pectoral flipper, demonstrating higher reliability for chronological age estimation than currently available epigenetic approaches for this species. Using individuals of known dental age, we calibrated two modelling approaches to predict dental age from radiographic bone scores: 1) a univariate polynomial regression using a total bone score (sum of 16 scores across all assessed flipper bones), and 2) a multivariate canonical analysis of principal coordinates (CAP) incorporating 16 individual bone-score variables. Both approaches successfully predicted dental age from skeletal ossification patterns. For an age range of 0 to 24 years, polynomial regression demonstrated high predictive accuracy with median absolute errors (MAEs) of 1.25 years in females (Spearmans {rho} = 0.93, R{superscript 2} = 0.90) and 1.08 years in males ({rho} = 0.95, R{superscript 2} = 0.86). The CAP model yielded MAEs of 1.35 years in females ({rho} = 0.90, R{superscript 2} = 0.85) and 1.80 years in males ({rho} = 0.94, R{superscript 2} = 0.84). Notably, both radiographic bone ageing models achieved equal or lower median absolute errors and higher coefficients of determination than a recently developed epigenetic clock for common dolphins derived from the same population (MAE = 1.80, Pearsons correlation (r) = 0.91, R{superscript 2} = 0.82). When applying the bone ageing models to individuals of unknown dental age, both models produced age estimates consistent with expected life-history stages (foetus, neonate, juvenile, subadult, adult), although accuracy declined in dolphins above 20 years, likely as a consequence of subtle age-related variation in skeletal changes in this species. Radiographic ageing provides an accurate non-invasive tool for demographic assessment to support conservation management of common dolphins.

zoology↗

bioRxiv2026

Global patterns and predictors of PFAS contamination in odontocetes

Per- and polyfluoroalkyl substances (PFAS) are globally recognised as emerging contaminants of concern due to their persistence, toxicity, endocrine-disrupting and immunosuppressive effects. Because of their extensive industrial use, PFAS are now widespread across ecosystems and accumulate in marine environments. Despite their ubiquity, the extent and drivers of PFAS contamination remain poorly characterised, particularly in marine systems. Odontocetes (toothed whales) are effective bioindicators of marine pollution, integrating contamination across regions, time, and trophic levels. Here, we present the first global assessment of factors influencing PFAS contamination in marine ecosystems by analysing standardised PFAS concentrations of PFNA, PFDA, PFUnDA, PFDoDA and PFOS reported for 713 liver samples across 33 odontocete species spanning 13 countries from 2000 to 2023. Using generalised linear mixed models, we evaluated the effects of genus, location, sex, life stage, and sampling year on PFAS concentrations, combining published datasets with new samples from Australia. Genus and location were the strongest predictors, suggesting that interspecific ecological and physiological traits likely contribute to PFAS accumulation. Concentrations were highest in males and younger individuals, consistent with maternal offloading and possible age-related dilution. Spatio-temporal trends indicate that PFAS contamination is widespread and increasing globally, with highest concentrations reported in the Pacific. This study provides a critical baseline for understanding global PFAS exposure in marine mammals, which underscores the need for coordinated monitoring and further research to address regional data gaps and potential unrecognised biological effects. HighlightsO_LIHigh genus-specific and spatial differences in PFAS contamination across odontocetes globally. C_LIO_LIIncreased contamination in younger/smaller individuals. C_LIO_LISex-specific trends, including higher PFAS levels in male odontocetes. C_LIO_LISpatio-temporal trends suggesting increased PFAS concentration despite global regulatory efforts, with highest concentrations in the Pacific Ocean. C_LI

pharmacology and toxicology↗

bioRxiv2025

Dental aging offers new insights to the first epigenetic clock for common dolphins (Delphinus delphis)

Determining exact age in wild odontocetes is essential for understanding population dynamics, survival, and reproduction, yet remains logistically challenging. While epigenetic aging is emerging as a valuable approach, only nine species-specific clocks currently exist. Most have been calibrated using captive known-age animals or well-studied wild populations. Only two previous studies have used dental ages from stranded or bycaught individuals. This is due to concerns that dental age inaccuracies, especially in older animals, may affect epigenetic clock performance. To explore this, we developed the first species-specific epigenetic clock for common dolphins (Delphinus delphis), analysing DNA methylation at 37,492 cytosine-phosphate-guanine sites in skin samples from stranded and bycaught dolphins with estimated dental ages. Elastic net models with Leave-One-Out Cross-Validation were applied to three subsets: the relaxed subset (all individuals; n = 75, median absolute error (MAE) = 2.02, r = 0.81, R2 = 0.66), the strict subset (excluding individuals with minimum dental age estimates only; n = 73, MAE = 2.29, r = 0.81, R2 = 0.66), and the restricted subset (excluding outliers with prediction errors > 6 years; n = 63, MAE = 1.80, r = 0.91, R2 = 0.82) to compare performance. Our models consistently underestimated the age of dolphins >16 years, even when minimum dental ages were applied, suggesting absolute errors between dental and epigenetic estimates unlikely reflect dental aging error. Additionally, post-mortem decomposition condition code (DCC 1 to 3) did not affect age prediction, signalling promise for future epigenetic clocks calibrated with strandings and bycaught individuals.

genetics↗

bioRxiv2024

A CONTRIBUTION TO THE ANATOMY OF TWO RARE CETACEAN SPECIES: THE HOURGLASS DOLPHIN (Lagenorhynchus cruciger) AND THE SPECTACLED PORPOISE (Phocoena dioptrica)

The anatomical description of the hourglass dolphin (Lagenorhynchus cruciger) and the spectacled porpoise (Phocoena dioptrica) remains largely unexplored, due to limited specimen availability and preservation challenges. This study employed digital imaging techniques, conventional histology and computed tomography to provide visualisation of anatomical structures for a detailed analysis. We present a comprehensive analysis of the gross macroscopical and microscopical morphology of two hourglass dolphins and four spectacled porpoises. The hourglass dolphins were characterised by their distinctive black and white pigmentation and a hooked dorsal fin, while the spectacled porpoises were defined by their large dorsal fin, lack of a visible rostrum and unique eye markings. Morphometric measurements and skeletal characteristics aligned with the literature, while internal anatomy (organs and systems) were similar to other odontocetes. Although precise lung measurements were challenging, qualitative assessments indicated relatively large lungs for their body size, supporting the "short dive, big lung" hypothesis and suggesting that these species are not deep divers. The spectacled porpoise dorsal fin was uniquely large with a well-developed blood supply; this is hypothesised to act as a thermoregulatory window, helping to manage body heat. Overall, this study provides new data on the anatomy of the hourglass dolphin and spectacled porpoise, contributing insights that may influence future research on these rare species. The findings highlight the importance of anatomical studies in explaining evolutionary relationships within cetaceans and their ecological roles in the Southern Ocean ecosystems.

evolutionary biology↗

bioRxiv2024

A High-quality Oxford Nanopore Assembly of the Hourglass Dolphin (Sagmatias cruciger) Genome

The hourglass dolphin (Lagenorhynchus cruciger) is a small cetacean species of the Southern Ocean, with significance to iwi M[a]ori (M[a]ori tribes) of Aotearoa New Zealand as taonga (treasured/valued). Due to the remoteness and difficulty of surveying Antarctic waters, it remains one of the least-studied dolphin species. A recent stranding of an hourglass dolphin represented a rare opportunity to generate a genome assembly as a resource for future study into the conservation and evolutionary biology of this species. In this study, we present a high-quality genome assembly of an hourglass dolphin individual using a single sequencing platform, Oxford Nanopore Technologies, coupled with computationally efficient assembly methods. Our assembly strategy yielded a genome of high contiguity (N50 of 8.07 Mbp) and quality (98.3% BUSCO completeness). Compared to other Delphinoidea reference genomes, this assembly has fewer missing BUSCOs than any except Orcinus orca, more single-copy complete BUSCOs than any except Phocoena sinus, and 20% fewer duplicated BUSCOs than the average Delphinoidea reference genome. This suggests that it is one of the most complete and accurate marine mammal genomes to date. This study showcases the feasibility of a cost-effective mammalian genome assembly method, allowing for genomic data generation outside the traditional confines of academia and/or resource-rich genome assembly hubs, and facilitating the ability to uphold Indigenous data sovereignty. In the future the genome assembly presented here will allow valuable insights into the past population size changes, adaptation, vulnerability to future climate change of the hourglass dolphin and related species.

genomics↗