Telomeres and telomerase: active but complex players in life-history decisions

Studies on human telomeres have established that telomeres exert a significant influence on lifespan and health of organisms. However, recent research has indicated that the original idea that telomeres affect lifespan in a universal and central manner across all eukaryotic species is an oversimplification. Indeed, findings from a variety of animal species revealed that the role of telomere biology in aging is more subtle and intricate than previously recognized. Here, we show how telomere biology varies depending on the taxon. We also show how telomere biology corresponds to basic life history traits and affects the life table of a species and investments in growth, body size, reproduction, and lifespan; telomeres are hypothesized to shape evolutionary perspectives for species in an active but complex manner. Our evaluation is based on telomere biology data from many examples from throughout the animal kingdom that vary according to the degree of organismal complexity and life history strategies.

Manganese Exacerbates Seasonal Health Declines in a Suicidally Breeding Mammal

Reproductive costs must be balanced with survival to maximize lifetime reproductive rates; however, some organisms invest in a single, suicidal bout of breeding known as semelparity. The northern quoll (Dasyurus hallucatus) is an endangered marsupial in which males, but not females, are semelparous. Northern quolls living near mining sites on Groote Eylandt, Northern Territory, Australia, accumulate manganese (Mn) in their brains, testes, and hair, and elevated Mn impacts motor performance. Whether Mn is associated with other health declines is yet unknown. In the present study we show that male and female northern quolls with higher Mn accumulation had a 20% reduction in immune function and a trend toward reduced cortisol concentrations in hair. The telomere lengths of male quolls did not change pre- to postbreeding, but those with higher Mn levels had longer telomeres; in contrast, the telomeres of females shortened during the breeding season but recovered between the first year and second year of breeding. In addition, the telomeres of quolls that were recaptured declined at significantly higher rates in quolls with higher Mn between prebreeding, breeding, and/or postbreeding seasons. Future research should determine whether changes in cortisol, immune function, or telomere length affect reproductive output or survival-particularly for semelparous males. Environ Toxicol Chem 2024;43:74-86. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

The evolution of early-life telomere length, pace-of-life and telomere-chromosome length dynamics in birds

Telomeres, the short DNA sequences that protect chromosome ends, are an ancient molecular structure, which is highly conserved across most eukaryotes. Species differ in their telomere lengths, but the causes of this variation are not well understood. Here, we demonstrate that mean early-life telomere length is an evolutionary labile trait across 57 bird species (representing 35 families in 12 orders) with the greatest trait diversity found among passerines. Among these species, telomeres are significantly shorter in fast-lived than in slow-lived species, suggesting that telomere length may have evolved to mediate trade-offs between physiological requirements underlying the diversity of pace-of-life strategies in birds. This association was attenuated when excluding studies that may include interstitial telomeres in the estimation of mean telomere length. Curiously, within some species, larger individual chromosome size predicts longer telomere lengths on that chromosome, leading to the hypothesis that telomere length also covaries with chromosome length across species. We show that longer mean chromosome length or genome size tends to be associated with longer mean early-life telomere length (measured across all chromosomes) within a phylogenetic framework constituting up to 31 bird species. These associations were strengthened when excluding highly influential outliers. However, sensitivity analyses suggested that they were susceptible to sample size effects and not robust to the exclusion of studies that may include interstitial telomeres. Combined, our analyses generalize patterns previously found within a few species and provide potential adaptive explanations for the 10-fold variation in telomere lengths observed among birds.

Chromosomal Instability in Genome Evolution: From Cancer to Macroevolution

The integrity of the genome is crucial for the survival of all living organisms. However, genomes need to adapt to survive certain pressures, and for this purpose use several mechanisms to diversify. Chromosomal instability (CIN) is one of the main mechanisms leading to the creation of genomic heterogeneity by altering the number of chromosomes and changing their structures. In this review, we will discuss the different chromosomal patterns and changes observed in speciation, in evolutional biology as well as during tumor progression. By nature, the human genome shows an induction of diversity during gametogenesis but as well during tumorigenesis that can conclude in drastic changes such as the whole genome doubling to more discrete changes as the complex chromosomal rearrangement chromothripsis. More importantly, changes observed during speciation are strikingly similar to the genomic evolution observed during tumor progression and resistance to therapy. The different origins of CIN will be treated as the importance of double-strand breaks (DSBs) or the consequences of micronuclei. We will also explain the mechanisms behind the controlled DSBs, and recombination of homologous chromosomes observed during meiosis, to explain how errors lead to similar patterns observed during tumorigenesis. Then, we will also list several diseases associated with CIN, resulting in fertility issues, miscarriage, rare genetic diseases, and cancer. Understanding better chromosomal instability as a whole is primordial for the understanding of mechanisms leading to tumor progression.

Telomeres in ecology and evolution: A review and classification of hypotheses

Research on telomeres in the fields of ecology and evolution has been rapidly expanding over the last two decades. This has resulted in the formulation of a multitude of, often name-given, hypotheses related to the associations between telomeres and life-history traits or fitness-facilitating processes (and the mechanisms underlying them). However, the differences (or similarities) between the various hypotheses, which can originate from different research fields, are often not obvious. Our aim here is therefore to give an overview of the hypotheses that are of interest in ecology and evolution and to provide two frameworks that help discriminate among them. We group the hypotheses (i) based on their association with different research questions, and (ii) using a hierarchical approach that builds on the assumptions they make, such as about causality of telomere length/shortening and/or the proposed functional consequences of telomere shortening on organism performance. Both our frameworks show that there exist parallel lines of thoughts in different research fields. Moreover, they also clearly illustrate that there are in many cases competing hypotheses within clusters, and that some of these even have contradictory assumptions and/or predictions. We also touch upon two topics in telomere research that would benefit from further conceptualization. This review should help researchers, both those familiar with and those new to the subject, to identify future avenues of research.

Fanconi anemia and dyskeratosis congenita/telomere biology disorders: Two inherited bone marrow failure syndromes with genomic instability

Inherited bone marrow failure syndromes (IBMFS) are a complex and heterogeneous group of genetic diseases. To date, at least 13 IBMFS have been characterized. Their pathophysiology is associated with germline pathogenic variants in genes that affect hematopoiesis. A couple of these diseases also have genomic instability, Fanconi anemia due to DNA damage repair deficiency and dyskeratosis congenita/telomere biology disorders as a result of an alteration in telomere maintenance. Patients can have extramedullary manifestations, including cancer and functional or structural physical abnormalities. Furthermore, the phenotypic spectrum varies from cryptic features to patients with significantly evident manifestations. These diseases require a high index of suspicion and should be considered in any patient with abnormal hematopoiesis, even if extramedullary manifestations are not evident. This review describes the disrupted cellular processes that lead to the affected maintenance of the genome structure, contrasting the dysmorphological and oncological phenotypes of Fanconi anemia and dyskeratosis congenita/telomere biology disorders. Through a dysmorphological analysis, we describe the phenotypic features that allow to make the differential diagnosis and the early identification of patients, even before the onset of hematological or oncological manifestations. From the oncological perspective, we analyzed the spectrum and risks of cancers in patients and carriers.

Strategies for meiotic sex chromosome dynamics and telomeric elongation in Marsupials

During meiotic prophase I, homologous chromosomes pair, synapse and recombine in a tightly regulated process that ensures the generation of genetically variable haploid gametes. Although the mechanisms underlying meiotic cell division have been well studied in model species, our understanding of the dynamics of meiotic prophase I in non-traditional model mammals remains in its infancy. Here, we reveal key meiotic features in previously uncharacterised marsupial species (the tammar wallaby and the fat-tailed dunnart), plus the fat-tailed mouse opossum, with a focus on sex chromosome pairing strategies, recombination and meiotic telomere homeostasis. We uncovered differences between phylogroups with important functional and evolutionary implications. First, sex chromosomes, which lack a pseudo-autosomal region in marsupials, had species specific pairing and silencing strategies, with implications for sex chromosome evolution. Second, we detected two waves of γH2AX accumulation during prophase I. The first wave was accompanied by low γH2AX levels on autosomes, which correlated with the low recombination rates that distinguish marsupials from eutherian mammals. In the second wave, γH2AX was restricted to sex chromosomes in all three species, which correlated with transcription from the X in tammar wallaby. This suggests non-canonical functions of γH2AX on meiotic sex chromosomes. Finally, we uncover evidence for telomere elongation in primary spermatocytes of the fat-tailed dunnart, a unique strategy within mammals. Our results provide new insights into meiotic progression and telomere homeostasis in marsupials, highlighting the importance of capturing the diversity of meiotic strategies within mammals.

The generation of haploid gametes is a hallmark of sexual reproduction. And this is accomplished by a complex, albeit tightly regulated, reductional cell division called meiosis. Although meiosis has been extensively studied in eutherian mammal model species, our understanding of the mechanisms regulating chromosome synapsis, recombination and segregation during meiosis progression is still incomplete especially in non-eutherian mammals. To fill this gap and capture the diversity of meiotic strategies among mammals, we study previously uncharacterised representative marsupial species, an evolutionary assemblage that last shared a common ancestry more than 80 million years ago. We uncover novel, hence non-canonical, strategies for sex chromosome pairing, DNA repair, recombination and transcription. Most importantly, we reveal the uniqueness of marsupial meiosis, which includes the unprecedented detection of alternative mechanism (ALT) for the paternal control of telomere length during prophase I. Our findings suggest that ALT (previously only associated to cancer cells) could play a role in telomere homeostasis in mammalian germ cells.

Anthropogenic activities are associated with shorter telomeres in chicks of Adélie penguin (Pygoscelis adeliae)

Defining the impact of anthropogenic stressors on Antarctic wildlife is an active aim for investigators. Telomeres represent a promising molecular tool to investigate the fitness of wild populations, as their length may predict longevity and survival. We examined the relationship between telomere length and human exposure in Adélie penguin chicks (Pygoscelis adeliae) from East Antarctica. Telomere length was compared between chicks from areas with sustained human activity and on neighboring protected islands with little or no human presence. Adélie penguin chicks from sites exposed to human activity had significantly shorter telomeres than chicks from unexposed sites in nearby protected areas, with exposed chicks having on average 3.5% shorter telomeres than unexposed chicks. While sampling limitations preclude our ability to draw more sweeping conclusions at this time, our analysis nonetheless provides important insights into measures of colony vulnerability. More data are needed both to understand the proximate causes (e.g., stress, feeding events) leading to shorter telomeres in chicks from human exposed areas, as well as the fitness consequences of reduced telomere length. We suggest to further test the use of telomere length analysis as an eco-indicator of stress in wildlife among anthropized sites throughout Antarctica.

Contrasting associations between nestling telomere length and pre and postnatal helpers' presence in a cooperatively breeding bird

Studies on cooperative breeders have addressed the effects of non-breeding 'helpers' on reproduction and parental care, but the consequences for offspring physiology and long-term survival are less understood. Helpers are expected to benefit offspring, but their presence can also lead to decreased pre- or post-natal parental reproductive effort. To examine whether prenatal and postnatal helpers influence offspring condition, we conducted a whole-clutch cross-fostering experiment in sociable weavers (Philetairus socius) that altered the nestlings' social environment (presence/absence of helpers). We tested whether relative telomere length (rTL), an indicator of somatic maintenance, was influenced by prenatal and/or postnatal presence of helpers 9 and 17 days after hatching, and whether rTL predicted long-term survival. Nine days after hatching, we found an overall positive effect of postnatal helpers on rTL: for nestlings with prenatal helpers, a reduction in the number of helpers post-hatch was associated with shorter telomeres, while nestlings swapped from nests without helpers to nests with helpers had a larger rTL. However, when prenatal helpers were present, an increased number of helpers after hatching led to shorter telomeres. Nine-day old chicks with longer rTL tended to be more likely to survive over the 5 years following hatching. However, close to fledging, there was no detectable effect of the experiment on rTL and no link between rTL and survival. This experimental study of a wild cooperative breeder, therefore, presents partial support for the importance of the presence of helpers for offspring rTL and the link between early-life telomere length and long-term survival.

First Record on Sex Chromosomes in a Species of the Family Cynodontidae: Cynodon gibbus (Agassiz, 1829)

The fish family Cynodontidae belongs to the superfamily Curimatoidea, together with the Hemiodontidae, Serrasalmidae, Parodontidae, Prochilodontidae, Chilodontidae, Curimatidae, and Anostomidae. The majority of the species of this superfamily that have been analyzed to date have a diploid chromosome number of 2n = 54. Differentiated sex chromosomes (with female heterogamety) have been observed only in the Prochilodontidae, Parodontidae, and Anostomidae. The present study provides the first description of differentiated sex chromosomes in the cynodontid species Cynodon gibbus, which has a ZZ/ZW system, and shows that repetitive DNA has played a fundamental role in the differentiation of these sex chromosomes.

Temperature and telomeres: thermal treatment influences telomere dynamics through a complex interplay of cellular processes in a cold-climate skink

Telomere dynamics vary fundamentally between endothermic populations and species as a result of differences in life history, yet we know little about these patterns in ectotherms. In ectotherms, the relationships between climate, metabolism and life history suggest that telomere attrition should be higher at relatively high environmental temperatures compared to relatively low environmental temperatures, but these effects may vary between populations due to local adaptation. To address this hypothesis, we sampled reactive oxygen species (ROS) and telomere length of lizards from warm lowland and cool highland populations of a climatically widespread lizard species that we exposed to hot or cold basking treatments. The hot treatment increased relative telomere length compared to the cold treatment independent of climatic origin or ROS levels. Lizards from the cool highland region had lower ROS levels than those from the warm lowland region. Within the highland lizards, ROS increased more in the cold basking treatment than the hot basking treatment. These results are in the opposite direction to those predicted, suggesting that the relationships between temperature, metabolism, ROS and telomere dynamics are not straightforward. Future work incorporating detailed understanding of the thermal reaction norms of these and other linked traits is needed to fully understand these processes.

Ectothermic telomeres: it's time they came in from the cold

We review the evolutionary ecology and genetics of telomeres in taxa that cannot elevate their body temperature to a preferred level through metabolism but do so by basking or seeking out a warm environment. This group of organisms contains all living things on earth, apart from birds and mammals. One reason for our interest in this synthetic group is the argument that high, stable body temperature increases the risk of malignant tumours if long, telomerase-restored telomeres make cells 'live forever'. If this holds true, ectotherms should have significantly lower cancer frequencies. We discuss to what degree there is support for this 'anti-cancer' hypothesis in the current literature. Importantly, we suggest that ectothermic taxa, with variation in somatic telomerase expression across tissue and taxa, may hold the key to understanding ongoing selection and evolution of telomerase dynamics in the wild. We further review endotherm-specific effects of growth on telomeres, effects of autotomy ('tail dropping') on telomere attrition, and costs of maintaining sexual displays measured in telomere attrition. Finally, we cover plant ectotherm telomeres and life histories in a separate 'mini review'.This article is part of the theme issue 'Understanding diversity in telomere dynamics'.

The methylation and telomere landscape in two families of marsupials with different rates of chromosome evolution

Two marsupial families exemplify divergent rates of karyotypic change. The Dasyurid family has an extremely conserved karyotype. In contrast, there is significant chromosomal variation within the Macropodidae family, best exemplified by members of the genus Petrogale (rock-wallabies). Both families are also distinguished by their telomere landscape (length and epigenetics), with the dasyurids having a unique telomere length dimorphism not observed in other marsupials and hypothesised to be regulated in a parent-of-origin fashion. Previous work has shown that proximal ends of chromosomes are enriched in cytosine methylation in dasyurids, but that the chromosomes of a macropod, the tammar wallaby, have DNA methylation enrichment of pericentric regions. Using a combination of telomere and 5-methylcytosine immunofluorescence staining, we investigated the telomere landscape of four dasyurid and three Petrogale species. As part of this study, we also further examined the parent-of-origin hypothesis for the regulation of telomere length dimorphism in dasyurids, using epigenetic modifications known to differentiate the active maternal X chromosome, including 5-methylcytosine methylation and histone modifications H3K4me2, H3K9ac and H4Kac. Our results give further support to the parent-of-origin hypothesis for the regulation of telomere length dimorphism in dasyurids, where the paternally derived X chromosome in females was associated with long telomeres and the maternally derived with short telomeres. In contrast to the tammar wallaby, rock-wallabies demonstrated a similar 5-methylcytosine staining pattern across all chromosomes to that of dasyurids, suggesting that DNA methylation of telomeric regions is not responsible for differences in the rates of chromosome evolution between these two families.

Cytogenetics in Arctica islandica (Bivalvia, Arctidae): the Longest Lived Non-Colonial Metazoan

Due to its extraordinary longevity and wide distribution, the ocean quahog Arctica islandica has become an important species model in both aging and environmental change research. Notwithstanding that, most genetic studies on ocean quahogs have been focused on fishery related, phylogeographic and phylogenetic aspects but nothing is known about their chromosomes. In this work, the chromosomes of the ocean quahog Arctica islandica were analysed by means of 4′,6-diamidino-2-phenylindole (DAPI)/propidium iodide (PI) staining and fluorescent in situ hybridization (FISH) with rDNA, histone gene and telomeric probes. Whilst both 5S rDNA and 45S rDNA were clustered at single subcentromeric locations on the long arms of chromosome pairs 2 and 12, respectively, histone gene clusters located on the short arms of chromosome pairs 7, 10 and 17. As happens with most bivalves, the location of the vertebrate type telomeric sequence clusters was restricted to chromosome ends. The knowledge of the karyotype can facilitate the anchoring of genomic sequences to specific chromosome pairs in this species.

Chromosome Evolution in Marsupials

Marsupials typically possess very large, distinctive chromosomes that make them excellent subjects for cytogenetic analysis, and the high level of conservation makes it relatively easy to track chromosome evolution. There are two speciose marsupial families with contrasting rates of karyotypic evolution that could provide insight into the mechanisms driving genome reshuffling and speciation. The family Dasyuridae displays exceptional karyotype conservation with all karyotyped species possessing a 2n = 14 karyotype similar to that predicted for the ancestral marsupial. In contrast, the family Macropodidae has experienced a higher rate of genomic rearrangement and one genus of macropods, the rock-wallabies (Petrogale), has experienced extensive reshuffling. For at least some recently diverged Petrogale species, there is still gene flow despite hybrid fertility issues, making this species group an exceptional model for studying speciation. This review highlights the unique chromosome features of marsupial chromosomes, particularly for these two contrasting families, and the value that a combined cytogenetics, genomics, and epigenomics approach will have for testing models of genome evolution and speciation.