Using epigenetic clocks to investigate changes in the age structure of critically endangered Māui dolphins

The age of an individual is an essential demographic parameter but is difficult to estimate without long-term monitoring or invasive sampling. Epigenetic approaches are increasingly used to age organisms, including nonmodel organisms such as cetaceans. Māui dolphins (Cephalorhynchus hectori maui) are a critically endangered subspecies endemic to Aotearoa New Zealand, and the age structure of this population is important for informing conservation. Here we present an epigenetic clock for aging Māui and Hector's dolphins (C. h. hectori) developed from methylation data using DNA from tooth aged individuals (n = 48). Based on this training data set, the optimal model required only eight methylation sites, provided an age correlation of .95, and had a median absolute age error of 1.54 years. A leave-one-out cross-validation analysis with the same parameters resulted in an age correlation of .87 and median absolute age error of 2.09 years. To improve age estimation, we included previously published beluga whale (Delphinapterus leucas) data to develop a joint beluga/dolphin clock, resulting in a clock with comparable performance and improved estimation of older individuals. Application of the models to DNA from skin biopsy samples of living Māui dolphins revealed a shift from a median age of 8-9 years to a younger population aged 7-8 years 10 years later. These models could be applied to other dolphin species and demonstrate the ability to construct a clock even when the number of known age samples is limited, removing this impediment to estimating demographic parameters vital to the conservation of critically endangered species.

Universal DNA methylation age across mammalian tissues

Aging, often considered a result of random cellular damage, can be accurately estimated using DNA methylation profiles, the foundation of pan-tissue epigenetic clocks. Here, we demonstrate the development of universal pan-mammalian clocks, using 11,754 methylation arrays from our Mammalian Methylation Consortium, which encompass 59 tissue types across 185 mammalian species. These predictive models estimate mammalian tissue age with high accuracy (r > 0.96). Age deviations correlate with human mortality risk, mouse somatotropic axis mutations and caloric restriction. We identified specific cytosines with methylation levels that change with age across numerous species. These sites, highly enriched in polycomb repressive complex 2-binding locations, are near genes implicated in mammalian development, cancer, obesity and longevity. Our findings offer new evidence suggesting that aging is evolutionarily conserved and intertwined with developmental processes across all mammals.

DNA methylation networks underlying mammalian traits

Using DNA methylation profiles (n = 15,456) from 348 mammalian species, we constructed phyloepigenetic trees that bear marked similarities to traditional phylogenetic ones. Using unsupervised clustering across all samples, we identified 55 distinct cytosine modules, of which 30 are related to traits such as maximum life span, adult weight, age, sex, and human mortality risk. Maximum life span is associated with methylation levels in HOXL subclass homeobox genes and developmental processes and is potentially regulated by pluripotency transcription factors. The methylation state of some modules responds to perturbations such as caloric restriction, ablation of growth hormone receptors, consumption of high-fat diets, and expression of Yamanaka factors. This study reveals an intertwined evolution of the genome and epigenome that mediates the biological characteristics and traits of different mammalian species.

An epigenetic clock to estimate the age of living beluga whales

DNA methylation data facilitate the development of accurate molecular estimators of chronological age or "epigenetic clocks." We present a robust epigenetic clock for the beluga whale, Delphinapterus leucas, developed for an endangered population in Cook Inlet, Alaska, USA. We used a custom methylation array to measure methylation levels at 37,491 cytosine-guanine sites (CpGs) from skin samples of dead whales (n = 67) whose chronological ages were estimated based on tooth growth layer groups. Using these calibration data, a penalized regression model selected 23 CpGs, providing an R 2 = 0.92 for the training data; and an R 2 = 0.74 and median absolute age error = 2.9 years for the leave one out cross-validation. We applied the epigenetic clock to an independent dataset of 38 skin samples collected with a biopsy dart from living whales between 2016 and 2018. Age estimates ranged from 11 to 27 years. We also report sex correlations in CpG data and describe an approach of identifying the sex of an animal using DNA methylation. The epigenetic estimators of age and sex presented here have broad applications for conservation and management of Cook Inlet beluga whales and potentially other cetaceans.

Population genomics of rapidly invading lionfish in the Caribbean reveals signals of range expansion in the absence of spatial population structure

Range expansions driven by global change and species invasions may have significant genomic, evolutionary, and ecological implications. During range expansions, strong genetic drift characterized by repeated founder events can result in decreased genetic diversity with increased distance from the center of the historic range, or the point of invasion. The invasion of the Indo-Pacific lionfish, Pterois volitans, into waters off the US East Coast, Gulf of Mexico, and Caribbean Sea provides a natural system to study rapid range expansion in an invasive marine fish with high dispersal capabilities. We report results from 12,759 single nucleotide polymorphism loci sequenced by restriction enzyme-associated DNA sequencing for nine P. volitans sampling areas in the invaded range, including Florida and other sites throughout the Caribbean, as well as mitochondrial control region D-loop data. Analyses revealed low to no spatially explicit metapopulation genetic structure, which is partly consistent with previous finding of little structure within ocean basins, but partly divergent from initial reports of between-basin structure. Genetic diversity, however, was not homogeneous across all sampled sites. Patterns of genetic diversity correlate with invasion pathway. Observed heterozygosity, averaged across all loci within a population, decreases with distance from Florida while expected heterozygosity is mostly constant in sampled populations, indicating population genetic disequilibrium correlated with distance from the point of invasion. Using an F ST outlier analysis and a Bayesian environmental correlation analysis, we identified 256 and 616 loci, respectively, that could be experiencing selection or genetic drift. Of these, 24 loci were shared between the two methods.

Patterns of deep-sea genetic connectivity in the New Zealand region: implications for management of benthic ecosystems

Patterns of genetic connectivity are increasingly considered in the design of marine protected areas (MPAs) in both shallow and deep water. In the New Zealand Exclusive Economic Zone (EEZ), deep-sea communities at upper bathyal depths (<2000 m) are vulnerable to anthropogenic disturbance from fishing and potential mining operations. Currently, patterns of genetic connectivity among deep-sea populations throughout New Zealand’s EEZ are not well understood. Using the mitochondrial Cytochrome Oxidase I and 16S rRNA genes as genetic markers, this study aimed to elucidate patterns of genetic connectivity among populations of two common benthic invertebrates with contrasting life history strategies. Populations of the squat lobster Munida gracilis and the polychaete Hyalinoecia longibranchiata were sampled from continental slope, seamount, and offshore rise habitats on the Chatham Rise, Hikurangi Margin, and Challenger Plateau. For the polychaete, significant population structure was detected among distinct populations on the Chatham Rise, the Hikurangi Margin, and the Challenger Plateau. Significant genetic differences existed between slope and seamount populations on the Hikurangi Margin, as did evidence of population differentiation between the northeast and southwest parts of the Chatham Rise. In contrast, no significant population structure was detected across the study area for the squat lobster. Patterns of genetic connectivity in Hyalinoecia longibranchiata are likely influenced by a number of factors including current regimes that operate on varying spatial and temporal scales to produce potential barriers to dispersal. The striking difference in population structure between species can be attributed to differences in life history strategies. The results of this study are discussed in the context of existing conservation areas that are intended to manage anthropogenic threats to deep-sea benthic communities in the New Zealand region.

Characterization of the Carcinus maenas neuropeptidome by mass spectrometry and functional genomics

Carcinus maenas, commonly known as the European green crab, is one of the best-known and most successful marine invasive species. While a variety of natural and anthropogenic mechanisms are responsible for the geographic spread of this crab, its ability to adapt physiologically to a broad range of salinities, temperatures and other environmental factors has enabled its successful establishment in new habitats. To extend our understanding of hormonal control in C. maenas, including factors that allow for its extreme adaptability, we have undertaken a mass spectral/functional genomics investigation of the neuropeptides used by this organism. Via a strategy combining MALDI-based high resolution mass profiling, biochemical derivatization, and nanoscale separation coupled to tandem mass spectrometric sequencing, 122 peptide paracrines/hormones were identified from the C. maenas central nervous system and neuroendocrine organs. These peptides include 31 previously described Carcinus neuropeptides (e.g. NSELINSILGLPKVMNDAamide [beta-pigment dispersing hormone] and PFCNAFTGCamide [crustacean cardioactive peptide]), 49 peptides only described in species other than the green crab (e.g. pQTFQYSRGWTNamide [Arg(7)-corazonin]), and 42 new peptides de novo sequenced here for the first time (e.g. the pyrokinins TSFAFSPRLamide and DTGFAFSPRLamide). Of particular note are large collections of FMRFamide-like peptides (25, including nine new isoforms sequenced de novo) and A-type allatostatin peptides (25, including 10 new sequences reported here for the first time) in this study. Also of interest is the identification of two SIFamide isoforms, GYRKPPFNGSIFamide and VYRKPPFNGSIFamide, the latter peptide known previously only from members of the astacidean genus Homarus. Using transcriptome analyses, 15 additional peptides were characterized, including an isoform of bursicon beta and a neuroparsin-like peptide. Collectively, the data presented in this study not only greatly expand the number of identified C. maenas neuropeptides, but also provide a framework for future investigations of the physiological roles played by these molecules in this highly adaptable species.

Mass spectral characterization of peptide transmitters/hormones in the nervous system and neuroendocrine organs of the American lobster Homarus americanus

The American lobster Homarus americanus is a decapod crustacean with both high economic and scientific importance. To facilitate physiological investigations of peptide transmitter/hormone function in this species, we have used matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and nanoscale liquid chromatography coupled to electrospray ionization quadrupole time-of-flight tandem mass spectrometry (nanoLC-ESI-Q-TOF MS/MS) to elucidate the peptidome present in its nervous system and neuroendocrine organs. In total, 84 peptides were identified, including 27 previously known H. americanus peptides (e.g., VYRKPPFNGSIFamide [Val(1)-SIFamide]), 23 peptides characterized previously from other decapods, but new to the American lobster (e.g., pQTFQYSRGWTNamide [Arg(7)-corazonin]), and 34 new peptides de novo sequenced/detected for the first time in this study. Of particular note are a novel B-type allatostatin (TNWNKFQGSWamide) and several novel FMRFamide-related peptides, including an unsulfated analog of sulfakinin (GGGEYDDYGHLRFamide), two myosuppressins (QDLDHVFLRFamide and pQDLDHVFLRFamide), and a collection of short neuropeptide F isoforms (e.g., DTSTPALRLRFamide and FEPSLRLRFamide). Our data also include the first detection of multiple tachykinin-related peptides in a non-brachyuran decapod, as well as the identification of potential individual-specific variants of orcokinin and orcomyotropin-related peptide. Taken collectively, our results not only expand greatly the number of known H. americanus neuropeptides, but also provide a framework for future studies on the physiological roles played by these molecules in this commercially and scientifically important species.