Environmental control and control of the environment: the basis of longevity in bivalves

Health and wellbeing status of the long-lived individuals of the Spanish LONGECYL cross-sectional study

BACKGROUND

The increase in life expectancy and long-lived individuals is a challenge for public health and provides an opportunity to understand the determinants of longevity. However, few studies have addressed the factors associated with the health status and quality of life in a long-lived individual population. We described the perceived health, clinical status, quality of life, and dependency for activities of daily living in a representative population in Castile and Leon, Spain.

METHODS

A sample of 759 long-lived individuals aged 95 years and older was studied by the Health Sentinel Network of Castile and Leon (Spain) through a health examination and a structured questionnaire covering quality of life (EQ-5D-3), lifestyle habits, diet, working life and family health. A blood sample was taken for the study of biological and genetic markers. Chi Square and logistic regression OR with 95% confidence intervals were used to analyze the determinants of the long-lived individuals' health status. The significant level for the bivariate analysis was established at 0.05.

RESULTS

Perceived health was good, very good or excellent in 64.2%, while only 46.0% had a quality-of-life index above 0.5 (ranging from 0 to 1) and 44.1% maintained acceptable independence for activities of daily living. Quality-of-life index was higher in the oldest, (OR 7.98 [2,32-27.41]) above 100 years compared to those under 98, and men had better values for independence than women (OR 2.43 [1.40-4.29]). Cardiovascular diseases were the most prevalent (85.5%), but neurological and mental diseases and vision problems had the highest impact on quality of life and independence.

CONCLUSION

The long-lived individuals of Castile and Leon have a relatively well-preserved health status, although the perception of health is higher than that describing their quality of life and dependence. The quality of life was higher in the oldest age group and showed differences according to sex, with a better quality of life in men. Public health policies and programs should take in account the differences by sex and age as well as the prevention and control of the main conditions related with poor quality of life or dependence. Future research must include the interaction among genetic, socioeconomic, environmental, and other clinical factors in the quality of life and disability of long-lived individuals.

Presence of male mitochondria in somatic tissues and their functional importance at the whole animal level in the marine bivalve Arctica islandica

Metazoans normally possess a single lineage of mitochondria inherited from the mother (♀-type mitochondria) while paternal mitochondria are absent or eliminated in fertilized eggs. In doubly uniparental inheritance (DUI), which is specific to the bivalve clade including the ocean quahog, Arctica islandica, ♂-type mitochondria are retained in male gonads and, in a few species, small proportions of ♂-type mitochondria co-exist with ♀-type in somatic tissues. To the best of our knowledge, we report, for the first time in metazoan, the natural occurrence of male and female individuals with exclusively ♂-type mitochondria in somatic tissues of the bivalve A. islandica. Mitochondrial genomes differ by ~5.5% at DNA sequence level. Exclusive presence of ♂-type mitochondria affects mitochondrial complexes partially encoded by mitochondrial genes and leads to a sharp drop in respiratory capacity. Through a combination of whole mitochondrial genome sequencing and molecular assays (gene presence and expression), we demonstrate that 1) 11% of individuals of an Icelandic population appear homoplasmic for ♂-type mitochondria in somatic tissues, 2) ♂-type mitochondrial genes are transcribed and 3) individuals with ♂-type mitochondria in somatic cells lose 30% of their wild-type respiratory capacity. This mitochondrial pattern in A. islandica is a special case of DUI, highlighted in individuals from both sexes with functional consequences at cellular and conceivably whole animal level.

Long-Lived Species of Bivalves Exhibit Low MT-DNA Substitution Rates

Bivalves represent valuable taxonomic group for aging studies given their wide variation in longevity (from 1–2 to >500 years). It is well known that aging is associated to the maintenance of Reactive Oxygen Species homeostasis and that mitochondria phenotype and genotype dysfunctions accumulation is a hallmark of these processes. Previous studies have shown that mitochondrial DNA mutation rates are linked to lifespan in vertebrate species, but no study has explored this in invertebrates. To this end, we performed a Bayesian Phylogenetic Covariance model of evolution analysis using 12 mitochondrial protein-coding genes of 76 bivalve species. Three life history traits (maximum longevity, generation time and mean temperature tolerance) were tested against 1) synonymous substitution rates (dS), 2) conservative amino acid replacement rates (Kc) and 3) ratios of radical over conservative amino acid replacement rates (Kr/Kc). Our results confirm the already known correlation between longevity and generation time and show, for the first time in an invertebrate class, a significant negative correlation between dS and longevity. This correlation was not as strong when generation time and mean temperature tolerance variations were also considered in our model (marginal correlation), suggesting a confounding effect of these traits on the relationship between longevity and mtDNA substitution rate. By confirming the negative correlation between dS and longevity previously documented in birds and mammals, our results provide support for a general pattern in substitution rates.

Biochemical adaptations of the stout razor clam (Tagelus plebeius) to changes in oxygen availability: resilience in a changing world?

Climate change is producing sea level rise and deoxygenation of the ocean, altering estuaries and coastal areas. Changes in oxygen availability are expected to have consequences on the physiological fitness of intertidal species. In this work we analyze the coping response of the intertidal stout razor clam (Tagelus plebeius (Lightfoot, 1786)) to extreme environmental changes in oxygen concentration. Their biochemical responses to normoxia, hypoxia, and hyperoxia transition at different intertidal level (low–high) were measured through an in situ transplant experiment. The high intertidal level negatively affected the analyzed traits of the T. plebeius populations. The differences in reactive oxygen species production, total oxyradical scavenger capacities, and catalase activity also suggested more stressful conditions at the high level where long-term hypoxia periods occur. Both hypoxia and re-oxygenation provoked re-adjustments in the antioxidant responses and higher lipid oxidative damage (normoxia < hypoxia < re-oxygenation). The observed responses in transplanted clams at the opposite intertidal level suggested the potential acclimation of T. plebeius to cope with new environmental conditions. These findings are discussed within a global changing context where both increasing deoxygenation conditions and sea level rise are predicted to be exacerbated in the area driven by climate change.

Integration of Biochemical, Cellular, and Genetic Indicators for Understanding the Aging Process in a Bivalve Mollusk Chlamys farreri

The major causal factors for the irreversible decline in physical vitality during organismal aging are postulated to be a chronic state of cellular redox imbalance, metabolic toxicity, and impaired energy homeostasis. We assessed whether the relevant enzyme activity, oxidative stress, and intracellular ATP might be causally involved in the aging of short-lived Chlamys farreri (life span 4~5 years). A total of eight related biochemical and cellular indicators were chosen for the subsequent analysis. All the indicators were measured in seven different tissues from scallops aged one to four years, and our data support that the aging of C. farreri is associated with attenuated tissue enzyme activity as well as a decreased metabolic rate. Through principal component analysis, we developed an integrated vigor index for each tissue for comprehensive age-related fitness evaluation. Remarkably, all tissue-integrated vigor indexes significantly declined with age, and the kidney was observed to be the most representative tissue. Further transcriptional profiling of the enzymatic genes provided additional detail on the molecular responses that may underlie the corresponding biochemical results. Moreover, these critical molecular responses may be attributed to the conserved hierarchical regulators, e.g., FOXO, AMPKs, mTOR, and IGF1R, which were identified as potentially novel markers for chronic fitness decline with age in bivalves. The present study provides a systematic approach that could potentially benefit the global assessment of the aging process in C. farreri and provide detailed evaluation of the biochemical, cellular, and genetic indicators that might be involved. This information may assist in a better understanding of bivalve adaptability and life span.

Drivers of shell growth of the bivalve, Callista chione (L. 1758) - Combined environmental and biological factors

Seasonal shell growth patterns were analyzed using the stable oxygen and carbon isotope values of live-collected specimens of the bivalve Callista chione from two sites in the Adriatic Sea (Pag and Cetina, Croatia). Micromilling was performed on the shell surface of three shells per site and shell oxygen isotopes of the powder samples were measured. The timing and rate of seasonal shell growth was determined by aligning the δ¹⁸O_shell-derived temperatures so that the best fit was achieved with the instrumental temperature curve. According to the data, shells grew only at very low rates or not at all during the winter months, i.e., between January and March. Shell growth slowdown/shutdown temperatures varied among sites, i.e., 13.6 °C at Pag and 16.6 °C at Cetina, indicating that temperature was not the only driver of shell growth. Likely, seasonal differences in seawater temperature and food supply were the major component explaining contrasting growth rates of C. chione at two study sites. Decreasing shell growth rates were also associated with the onset of gametogenesis suggesting a major energy reallocation toward reproduction rather than growth. These results highlight the need to combine sclerochronological analyses with ecological studies to understand life history traits of bivalves as archives of environmental variables.

Inducing the Alternative Oxidase Forms Part of the Molecular Strategy of Anoxic Survival in Freshwater Bivalves

Hypoxia in freshwater ecosystems is spreading as a consequence of global change, including pollution and eutrophication. In the Patagonian Andes, a decline in precipitation causes reduced lake water volumes and stagnant conditions that limit oxygen transport and exacerbate hypoxia below the upper mixed layer. We analyzed the molecular and biochemical response of the North Patagonian bivalve Diplodon chilensis after 10 days of experimental anoxia (<0.2 mg O₂/L), hypoxia (2 mg O₂/L), and normoxia (9 mg O₂/L). Specifically, we investigated the expression of an alternative oxidase (AOX) pathway assumed to shortcut the regular mitochondrial electron transport system (ETS) during metabolic rate depression (MRD) in hypoxia-tolerant invertebrates. Whereas, the AOX system was strongly upregulated during anoxia in gills, ETS activities and energy mobilization decreased [less transcription of glycogen phosphorylase (GlyP) and succinate dehydrogenase (SDH) in gills and mantle]. Accumulation of succinate and induction of malate dehydrogenase (MDH) activity could indicate activation of anaerobic mitochondrial pathways to support anoxic survival in D. chilensis. Oxidative stress [protein carbonylation, glutathione peroxidase (GPx) expression] and apoptotic intensity (caspase 3/7 activity) decreased, whereas an unfolded protein response (HSP90) was induced under anoxia. This is the first clear evidence of the concerted regulation of the AOX and ETS genes in a hypoxia-tolerant freshwater bivalve and yet another example that exposure to hypoxia and anoxia is not necessarily accompanied by oxidative stress in hypoxia-tolerant mollusks.

What modulates animal longevity? Fast and slow aging in bivalves as a model for the study of lifespan

Delineating the physiological and biochemical causes of aging process in the animal kingdom is a highly active area of research not only because of potential benefits for human health but also because aging process is related to life history strategies (growth and reproduction) and to responses of organisms to environmental conditions and stress. In this synthesis, we advocate studying bivalve species as models for revealing the determinants of species divergences in maximal longevity. This taxonomic group includes the longest living metazoan on earth (Arctica islandica), which insures the widest range of maximum life span when shorter living species are also included in the comparative model. This model can also be useful for uncovering factors modulating the pace of aging in given species by taking advantages of the wide disparity of lifespan among different populations of the same species. For example, maximal lifespan in different populations of A islandica range from approximately 36 years to over 500 years. In the last 15 years, research has revealed that either regulation or tolerance to oxidative stress is tightly correlated to longevity in this group which support further investigations on this taxon to unveil putative mechanistic links between Reactive Oxygen Species and aging process.

A Distinct Mitochondrial Genome with DUI-Like Inheritance in the Ocean Quahog Arctica islandica

Mitochondrial DNA (mtDNA) is strictly maternally inherited in metazoans. The major exception to this rule has been found in many bivalve species which allow the presence of different sex-linked mtDNA molecules. This mechanism, named doubly uniparental inheritance (DUI), is characterized by the presence of two mtDNAs: The female mtDNA is found in somatic tissue and female gonads, whereas the male mtDNA is usually found in male gonads and sperm. In this study we highlight the existence of two divergent mitochondrial haplotypes with a low genetic difference around 6–8% in Arctica islandica, a long-lived clam belonging to the Arcticidae, a sister group to the Veneridae in which DUI has been found. Phylogenetic analysis on cytochrome b and 16S sequences from somatic and gonadic tissues of clams belonging to different populations reveals the presence of the “divergent” type in male gonads only and the “normal” type in somatic tissues and female gonads. This peculiar segregation of divergent mtDNA types speaks for the occurrence of the DUI mechanism in A. islandica. This example also highlights the difficulties to assess the presence of such particular mitochondrial inheritance system and underlines the possible misinterpretations in phylogeographic and phylogenetic studies of bivalve species linked to the presence of two poorly differentiated mitochondrial genomes.

Telomere-independent ageing in the longest-lived non-colonial animal, Arctica islandica

The shortening of telomeres as a causative factor in ageing is a widely discussed hypothesis in ageing research. The study of telomere length and its regenerating enzyme telomerase in the longest-lived non-colonial animal on earth, Arctica islandica, should inform whether the maintenance of telomere length plays a role in reaching the extreme maximum lifespan (MLSP) of >500years in this species. Since longitudinal measurements on living animals cannot be achieved, a cross-sectional analysis of a short-lived (MLSP 40years from the Baltic Sea) and a long-lived population (MLSP 226years Northeast of Iceland) and in different tissues of young and old animals from the Irish Sea was performed. A high heterogeneity of telomere length was observed in investigated A. islandica over a wide age range (10-36years for the Baltic Sea, 11-194years for Irish Sea, 6-226years for Iceland). Constant telomerase activity and telomere lengths were detected at any age and in different tissues; neither correlated with age or population habitat. Stable telomere maintenance might contribute to the long lifespan of A. islandica. Telomere dynamics are no explanation for the distinct MLSPs of the examined populations and thus the cause of it remains to be investigated.

The mitochondrial genome of Arctica islandica; Phylogeny and variation

Arctica islandica is known as the longest-lived non-colonial metazoan species on earth and is therefore increasingly being investigated as a new model in aging research. As the mitochondrial genome is associated with the process of aging in many species and bivalves are known to possess a peculiar mechanism of mitochondrial genome inheritance including doubly uniparental inheritance (DUI), we aimed to assess the genomic variability of the A. islandica mitochondrial DNA (mtDNA). We sequenced the complete mitochondrial genomes of A. islandica specimens from three different sites in the Western Palaearctic (Iceland, North Sea, Baltic Sea). We found the A. islandica mtDNA to fall within the normal size range (18 kb) and exhibit similar coding capacity as other animal mtDNAs. The concatenated protein sequences of all currently known Veneroidea mtDNAs were used to robustly place A. islandica in a phylogenetic framework. Analysis of the observed single nucleotide polymorphism (SNP) patterns on further specimen revealed two prevailing haplotypes. Populations in the Baltic and the North Sea are very homogenous, whereas the Icelandic population, from which exceptionally old individuals have been collected, is the most diverse one. Homogeneity in Baltic and North Sea populations point to either stronger environmental constraints or more recent colonization of the habitat. Our analysis lays the foundation for further studies on A. islandica population structures, age research with this organism, and for phylogenetic studies. Accessions for the mitochondrial genome sequences: KC197241 Iceland; KF363951 Baltic Sea; KF363952 North Sea; KF465708 to KF465758 individual amplified regions from different speciemen.