Milan Vrtílek

Senescence is age-related decline that may carry over to subsequent generations. Advanced parental age can both improve or reduce offspring fitness, however. Identification of mechanisms of parental effects senescence thus proved challenging so far. We investigated the effects of old parental age on offspring performance in a laboratory short-lived fish, Nothobranchius furzeri (Cyprinodontiformes). We followed age-related changes in parents and then focused on the effect of parental age on key offspring life-history traits (embryonic survival, hatching rate, and juvenile growth). We employed telomere length as a senescence marker and a potential route for transmitting senescence effects from parents to the offspring. As parents aged, their body condition, reproductive output, and telomere length declined. Offspring of older parents showed lower survival and hatching rate. In contrast, old parental age did not compromise juvenile growth and telomere length of the successfully hatched offspring. This, among other things, resulted in decoupling of parent–offspring telomere length. Our study highlights the sensitivity of the early life-stages to old parental age in contrast to offspring post-hatching performance.

Parental ageing can influence offspring through non-genetic mechanisms. The contribution of epigenetic inheritance parental effects still remains poorly understood. DNA methylation is a widespread regulator of gene expression that changes during development and ageing and can also act as a mediator of intergenerational effects. We tested whether age-related changes in parental DNA methylation are transmitted to offspring in the short-lived turquoise killifish ( Nothobranchius furzeri , Cyprinodontiformes). Using reduced-representation sequencing, we quantified genome-wide DNA methylation and examined methylation dynamics at individual loci. The overall proportion of methylated CpG sites increased during early ageing but declined at later ages, revealing a non-linear trajectory with substantial among-individual variation. Despite these age-related changes, we found no evidence that parental methylation patterns were transmitted to offspring, either at the genome-wide level or at individual loci. Our findings indicate that although DNA methylation undergoes pronounced age-dependent remodelling in adult killifish, these changes are not detectably inherited by the next generation. We discuss these results in the context of epigenetic inheritance and ageing in vertebrate model systems.

Our understanding of the vertebrate immune system is dominated by a few model organisms such as mice. This use of a few model systems is reasonable if major features of the immune systems evolve slowly and are conserved across most vertebrates, but may be problematic if there is substantial macroevolutionary change in immune responses. Here, we present a test of the macroevolutionary stability, across 14 species of ray-finned fishes, of the transcriptomic response to a standardized immune challenge. Intraperitoneal injection of an immune adjuvant (alum) induces a fibrosis response in nearly all jawed fishes, which in some species contributes to anti-helminth protection. Despite this conserved phenotypic response, the underlying transcriptomic response is highly inconsistent across species. Although many gene orthogroups exhibit differential expression between saline versus alum-injected fish in at least one species, few orthogroups exhibit consistent differential expression across species. This result suggests that although the phenotypic response to alum (fibrosis) is highly conserved, the underlying gene regulatory architecture is very flexible and cannot readily be extrapolated from any one species to fishes (or vertebrates) more broadly. The vertebrate immune response is remarkably changeable over macroevolutionary time, requiring a diversity of model organisms to describe effectively.

Diet standardization of model organisms is crucial for experimental consistency and repeatability in laboratory research, yet laboratory fish often lack species‐specific, open‐formula standardized diets. This study aims to address this gap by testing the effect of macronutrient content on the performance of Nothobranchius furzeri , an intensively studied research model in biogerontology, and providing the basal formula of the purified diet for further development to support the good and consistent performance of this species in laboratory research. After 5 months of feeding, growth, body condition, reproduction and feed efficiency were compared among treatments of individually housed fish fed by one of the two purified diets, (1) high protein (~66% protein, 9% lipid) and (2) low protein (34% protein, 22% lipid), and control bloodworm‐fed fish. Survival on both purified diets and male growth on the high‐protein diet were comparable to that of the control. The absolute protein intake regulated fish growth irrespective of the total caloric intake. Only the low‐protein diet with 22% lipids supported a comparable fertilization rate to the control group. Female performance exhibited greater diet dependency than that of males. This suggests that a female‐specific formula should be developed in the future, as males would perform well on a wider variety of diets. This study provides the first data on the performance of N. furzeri fed with a purified diet and establishes a baseline diet formula for further refinement of a standardized laboratory diet for N. furzeri .

Senescence is a multifactorial and individualised process of age-related physiological decline. Cellular markers, such as telomere length and DNA methylation, can reveal subtle changes associated with chronological age or expected lifespan. In this study, we evaluated the utility of fin tissue as a surrogate for assessing telomere length and proportion of DNA methylation in the gonads of a small, short-lived laboratory fish, the turquoise killifish ( Nothobranchius furzeri ). We collected fin and gonadal tissues from both females and males at three different ages. We extracted DNA to measure telomere length via terminal restriction fragment (TRF) analysis and global DNA methylation levels using double-digest restriction-associated DNA sequencing (ddRADseq). Our results show a notable correspondence between telomere length and DNA methylation patterns in fin and gonadal tissues. These findings support the use of fin biopsies as a non-lethal method for assessing ageing biomarkers in the gonads of small freshwater fish.

Senescence is a multifactorial and individualised process of age-related physiological decline. Cellular markers, such as telomere length and DNA methylation, can reveal subtle changes associated with chronological age or expected lifespan. In this study, we evaluated the utility of fin tissue as a surrogate for assessing telomere length and proportion of DNA methylation in the gonads of a small, short-lived laboratory fish, the turquoise killifish ( Nothobranchius furzeri ). We collected fin and gonadal tissues from both females and males at three different ages, and extracted DNA to measure telomere length via terminal restriction fragment (TRF) analysis and global DNA methylation levels using double-digest restriction-associated DNA sequencing (ddRADseq). Our results show a notable correspondence between telomere length and DNA methylation patterns in fin and gonadal tissues. These findings support the use of fin biopsies as a non-lethal method for assessing ageing biomarkers in the gonads of small freshwater fish.

Our understanding of the vertebrate immune system is dominated by a few model organisms such as mice. This use of a few model systems is reasonable if major features of the immune systems evolve slowly and are conserved across most vertebrates, but may be problematic if there is substantial macroevolutionary change in immune responses. Here, we present a test of the macroevolutionary stability, across 15 species of jawed fishes, of the transcriptomic response to a standardized immune challenge. Intraperitoneal injection of an immune adjuvant (alum) induces a fibrosis response in nearly all jawed fishes, which in some species contributes to anti-helminth resistance. Despite this conserved phenotypic response, the underlying transcriptomic response is highly inconsistent across species. Although many gene orthogroups exhibit differential expression between saline versus alum-injected fish in at least one species, few orthogroups exhibit consistent differential expression across species. This result suggests that although the phenotypic response to alum (fibrosis) is highly conserved, the underlying gene regulatory architecture is very flexible and cannot readily be extrapolated from any one species to fishes (or vertebrates) more broadly. The vertebrate immune response is remarkably changeable over macroevolutionary time, requiring a diversity of model organisms to describe effectively.

Repeated, independent emergence of the same trait within different phylogenetic lineages is termed parallel evolution. It typically occurs as a result of similar selective pressures. Annual killifish have adapted to survive in the extreme habitat of temporary pools on three continents and present an especially amenable system for studying fundamental principles of evolutionary parallelism. When the pools dry, annual killifish embryos survive through the dry phase in the bottom substrate in a stage of dormancy—a diapause. The diapause is a complex set of three different developmental stages, none of which is obligate, thus leading to a multitude of potential developmental trajectories. While the intricacy of the killifishes' embryonic development has been thoroughly studied in the laboratory, information on their natural development is virtually absent. We hypothesised that the natural development of annual killifishes is largely synchronised and governed by ambient conditions as shown in the lineage of the African genus Nothobranchius. We sampled wild embryo banks of the South American genus Austrolebias, which evolved its diapause independently of the African lineage. We sampled during two consecutive dry seasons, using both longitudinal and snapshot monitoring, and conducted transplant experiments to determine the extent of the evolutionary parallelism and role of the environment in Austrolebias spp. embryo development. Main habitat phases were characterised by largely synchronised embryo banks. Different inter‐seasonal or local environmental conditions were reflected in a different developmental profile of the embryo banks, suggesting a high degree of environmental control. We found striking similarity in the habitat phase–embryo stage associations between the two lineages. The diapause in the two annual killifish lineages represents a unique example of evolutionary parallelism, with the analogy manifested in very close detail. We highlight the similarity of the selective forces in the two genera despite the different geographic origins, climate zones and reversed seasonality. The repeatedly occurring strict association of the same developmental stages with the same habitat conditions suggests a limited array of developmental settings that can be applied to cope with the given environmental challenges.

The origin, incidence, and consequences of reproductive senescence vary greatly across the tree of life. In vertebrates, research on reproductive senescence has been mainly focused on mammals and birds, demonstrating that its variation is largely linked to critical life history traits, such as growth patterns, juvenile, and adult mortality, and reproductive strategy. Fishes represent half of the vertebrate taxonomic diversity and display remarkable variation in life history. Based on a thorough literature review, we summarize current evidence on reproductive senescence in ray-finned fishes (Actinopterygii). While survival and physiological senescence are acknowledged in fish, their potential age-related reproductive decline has often been disregarded due to the prevalence of indeterminate growth. We demonstrate that age-related reproductive decline is reported across fish phylogeny, environments, and traits. An important point of our review is that the incidence of reproductive senescence in a species depends on both the number of studies for that species and the coverage of its maximum lifespan by the study. Reproductive senescence was documented for one-third of the studied fish species, with females suffering an age-related decline in reproductive traits less often than males or both parents combined. Neither parental care nor migratory strategy corresponded with the occurrence of reproductive senescence in fish. The traits that were affected by reproductive senescence most often were sex-specific, with pre-mating and mating categories of traits declining in females and sperm quality and quantity in males. We also demonstrate that reproductive senescence can be buffered by indeterminate growth. We provide rich evidence of reproductive senescence across ray-finned fishes, but we highlight the need for better data on age-related reproduction in fishes.

Antagonistic interactions between hosts and parasites may drive the evolution of novel host defenses, or new parasite strategies. Host immunity is therefore one of the fastest evolving traits. But where do the novel immune traits come from? Here, we test for phylogenetic conservation in a rapidly evolving immune trait—peritoneal fibrosis. Peritoneal fibrosis is a costly defense against a specialist tapeworm, Schistocephalus solidus (Cestoda), expressed in some freshwater populations of threespine stickleback fish (Gasterosteus aculeatus, Perciformes). We asked whether stickleback fibrosis is a derived species-specific trait or an ancestral immune response that was widely distributed across ray-finned fish (Actinopterygii) only to be employed by threespine stickleback against the specialist parasite. We combined literature review on peritoneal fibrosis with a comparative experiment using either parasite-specific, or nonspecific, immune challenge in deliberately selected species across fish tree of life. We show that ray-finned fish are broadly, but not universally, able to induce peritoneal fibrosis when challenged with a generic stimulus (Alum adjuvant). The experimental species were, however, largely indifferent to the tapeworm antigen homogenate. Peritoneal fibrosis, thus, appears to be a common and deeply conserved fish immune response that was co-opted by stickleback to adapt to a new selective challenge.