Fluctuating temperatures extend median lifespan, improve reproduction and reduce growth in turquoise killifish

Cycling temperature treatments affect estimates of digestive performance in prairie lizards (Sceloporus consobrinus)

In nature, many organisms experience a daily range of body temperatures. Thermal performance at stable temperatures is often extrapolated to predict function in cyclical environments. However, temperature order and cyclicity may influence physiological processes. The current study compared energy intake, digestive passage time and energy budgets at a stable temperature (33°C) and two temperature cycles in lizards (Sceloporus consobrinus), to determine (1) whether stable treatments adequately project performance in a cycling environment and (2) whether temperature order influences performance. Cycles had a mean temperature of 33°C, and rotated through 30°C, 33°C and 36°C daily, with equal durations of time at each temperature but differing temperature order, with warm days and cool nights in cycle 1 and cool days and warm nights in cycle 2. For analyses, performance in the stable treatment was compared with that during cycles. If temperature is the primary factor regulating performance, then performance from the stable treatment and cycles should compare favorably. However, physiological performance varied based on temperature treatment. Energy intake and budgets were similar between the stable trial and cycle 1 but not cycle 2. However, passage time did not differ. Notably, the two cycling regimes consistently varied in performance, indicating that temperature order plays a primary role in regulating performance. Physiological data collection requires careful consideration of effects of cycling versus stable temperature treatments. Stable temperatures do not consistently represent performance in cycling regimes and consideration should be paid not only to which temperatures animals experience but also to how temperature is experienced in nature.

Fluctuating and Stable High Temperatures Differentially Affect Reproductive Endocrinology of Female Pupfish

For many fishes, reproductive function is thermally constrained such that exposure to temperatures above some upper threshold has detrimental effects on gametic development and maturation, spawning frequency, and mating behavior. Such impairment of reproductive performance at elevated temperatures involves changes to hypothalamic-pituitary-gonadal (HPG) axis signaling and diminished gonadal steroidogenesis. However, how HPG pathways respond to consistently high versus temporally elevated temperatures is not clear. Here, sexually mature Amargosa River Pupfish (Cyprinodon nevadensis amargosae) were maintained under thermal regimes of either stable ∼25°C (low temperature), diurnal cycling temperatures between ∼27 and 35°C (fluctuating temperature), or stable ∼35°C (high temperature) conditions for 50 days to examine effects of these conditions on HPG endocrine signaling components in the pituitary gland and gonad, ovarian and testicular gametogenesis status, and liver gene expression relating to oogenesis. Female pupfish maintained under stable high and fluctuating temperature treatments showed reduced gonadosomatic index values as well as a lower proportion of oocytes in the lipid droplet and vitellogenic stages. Females in both fluctuating and stable 35°C conditions exhibited reduced ovarian mRNAs for steroid acute regulatory protein (star), cholesterol side chain-cleavage enzyme, P450scc (cyp11a1), and 3β-hydroxysteroid dehydrogenase (3bhsd), while ovarian transcripts encoding 11β-hydroxysteroid dehydrogenase (11bhsd) and sex hormone-binding globulin (shbg) were elevated in females at constant 35°C only. Ovarian aromatase (cyp19a1a) mRNA levels were unaffected, but circulating 17β-estradiol (E2) was lower in females at 35°C compared to the fluctuating temperature condition. In the liver, mRNA levels for choriogenins and vitellogenin were downregulated in both the fluctuating and 35°C conditions, while hepatic estrogen receptor 2a (esr2a) and shbg mRNAs were elevated in 35°C females. Taken together, these results demonstrate the potential for elevated temperatures to impair ovarian steroidogenesis and reduce egg envelope and vitellogenin protein production in female C. n. amargosae pupfish, while also shedding light on how thermal regimes that only intermittently reach the upper thermal range for reproduction have differential impacts on reproductive endocrine pathways than constantly warm conditions.

Detection of genetic variation in bovine CRY1 gene and its associations with carcass traits

The biological clock (also known as circadian clock) is closely related to growth and development, metabolism, and diseases in animals. As a part of the circadian clock, the cryptochrome circadian regulator 1 (CRY1) gene is involved in the regulation of biological processes such as osteogenesis, energy metabolism and cell proliferation, however, few studies have been reported on the relationship between this gene and animal carcass traits. Herein, a total of four insertion/deletion (InDel) loci within the CRY1 gene were detected in Shandong Black Cattle Genetic Resource (SDBCGR) population (n = 433). Among them, the P1-6-bp-del locus was polymorphic in population of interest. Moreover, the P1-6-bp-del locus showed two genotypes, with a higher insertion/insertion (II) genotype frequency (0.751) than insertion/deletion (ID) genotype frequency (0.249). Correlation analysis showed that the P1-6-bp-del locus polymorphisms were significantly associated with twenty carcass traits (e.g., slaughter weight, limb weight, and belly meat weight). Individuals with II genotype were significantly better than those with ID genotype for eighteen carcass traits. Therefore, the P1-6-bp-del locus of the CRY1 gene can be used as a molecular marker for beef cattle breeding.

Of telomeres and temperature: Measuring thermal effects on telomeres in ectothermic animals

Ectotherms are classic models for understanding life-history tradeoffs, including the reproduction-somatic maintenance tradeoffs that may be reflected in telomere length and their dynamics. Importantly, life-history traits of ectotherms are tightly linked to their thermal environment, with diverse or synergistic mechanistic explanations underpinning the variation. Telomere dynamics potentially provide a mechanistic link that can be used to monitor thermal effects on individuals in response to climatic perturbations. Growth rate, age and developmental stage are all affected by temperature, which interacts with telomere dynamics in complex and intriguing ways. The physiological processes underpinning telomere dynamics can be visualized and understood using thermal performance curves (TPCs). TPCs reflect the evolutionary history and the thermal environment during an individual's ontogeny. Telomere maintenance should be enhanced at or near the thermal performance optimum of a species, population and individual. The thermal sensitivity of telomere dynamics should reflect the interacting TPCs of the processes underlying them. The key processes directly underpinning telomere dynamics are mitochondrial function (reactive oxygen production), antioxidant activity, telomerase activity and telomere endcap protein status. We argue that identifying TPCs for these processes will significantly help design robust, repeatable experiments and field studies of telomere dynamics in ectotherms. Conceptually, TPCs are a valuable framework to predict and interpret taxon- and population-specific telomere dynamics across thermal regimes. The literature of thermal effects on telomeres in ectotherms is sparse and mostly limited to vertebrates, but our conclusions and recommendations are relevant across ectothermic animals.

Differential reproductive plasticity under thermal variability in a freshwater fish (Danio rerio)

Human-driven increases in global mean temperatures are associated with concomitant increases in thermal variability. Yet, few studies have explored the impacts of thermal variability on fitness-related traits, limiting our ability to predict how organisms will respond to dynamic thermal changes. Among the myriad organismal responses to thermal variability, one of the most proximate to fitness—and, thus, a population's ability to persist—is reproduction. Here, we examine how a model freshwater fish (Danio rerio) responds to diel thermal fluctuations that span the species's viable developmental range of temperatures. We specifically investigate reproductive performance metrics including spawning success, fecundity, egg provisioning and sperm concentration. Notably, we apply thermal variability treatments during two ontogenetic timepoints to disentangle the relative effects of developmental plasticity and reversible acclimation. We found evidence of direct, negative effects of thermal variability during later ontogenetic stages on reproductive performance metrics. We also found complex interactive effects of early and late-life exposure to thermal variability, with evidence of beneficial acclimation of spawning success and modification of the relationship between fecundity and egg provisioning. Our findings illuminate the plastic life-history modifications that fish may undergo as their thermal environments become increasingly variable.

Quantification of noradrenergic-, dopaminergic-, and tectal-neurons during aging in the short-lived killifish Nothobranchius furzeri

Parkinson's disease (PD) is characterized by phosphorylation and aggregation of the protein α-Synuclein and ensuing neuronal death progressing from the noradrenergic locus coeruleus to midbrain dopaminergic neurons. In 2019, Matsui and colleagues reported a spontaneous age-dependent degeneration of dopaminergic neurons and an even greater neurodegeneration of the noradrenergic neurons in the short-lived killifish Nothobranchius furzeri. Given the great possible relevance of a spontaneous model for PD, we assessed neurodegeneration of noradrenergic and dopaminergic neurons in two further laboratory strains of N. furzeri. We implemented, for the first time in N. furzeri, a whole-brain clarification technique and proceeded to entire 3D nuclei reconstruction to quantify total cell numbers in two different stains of N. furzeri. In both strains, we observed that age-dependent neurodegeneration is limited to the locus coeruleus and does not involve the posterior tuberculum. We also applied 3D counting to the optic tectum, an area of active adult neurogenesis, and detected an increase of neurons with age. Our results confirm age-dependent neurodegeneration of noradrenergic neurons, a condition reminiscent of the presymptomatic stage of PD indicating that N. furzeri could be used in the future to identify modifying factors for age-dependent neurodegeneration and open the intriguing possibility that natural genetic variation may influence the susceptibility of dopaminergic neurons.

Negative effects of fluctuating temperatures around the optimal temperature on reproduction and survival of the red flour beetle

Whereas the vast majority of animals in nature experience daily or seasonal thermal fluctuations, most laboratory experiments use constant temperatures. We examined the effect of fluctuating temperatures on reproduction and survival under starvation, two important components of fitness. We used the red flour beetle as a model organism, which is a significant pest in grain mills around the world. Fluctuations around the optimal temperature were always negative for the adult survival under starvation. The effect of thermal fluctuations on the number of offspring reaching adulthood was negative as well but increased with the extent of exposure. It was the strongest when the adult parents were kept and the offspring were raised under fluctuating temperatures. However, the later the offspring were exposed to fluctuations during their development, the weaker the effect of fluctuating temperatures was. Moreover, raising the parents under fluctuating temperatures but keeping them after pupation at constant temperatures fully alleviated the negative effects of fluctuations on the offspring. Finally, we demonstrate that keeping the parents a few days under fluctuating temperatures is required to induce negative effects on the number of offspring reaching adulthood. Our study disentangles between the effects of thermal fluctuations experienced during the parental and offspring stage thus contributing to the ongoing research of insects under fluctuating temperatures.

The sources of sex differences in aging in annual fishes

Inter-sexual differences in lifespan (age at death) and aging (increase in mortality risk associated with functional deterioration) are widespread among animals, from nematodes to humans. Males often live shorter than females, but there is substantial unexplained variation among species and populations. Despite extensive research, it is poorly understood how lifespan differences between the sexes are modulated by an interplay among genetic, environmental and social factors. The goal of our study was to test how sex differences in lifespan and ageing are modulated by social and environmental factors, and by intrinsic differences between males and females. To disentangle the complex basis of sex differences in lifespan and aging, we combined comparative data from sex ratios in 367 natural populations of four species of African annual killifish with experimental results on sex differences in lifespan and aging from eight laboratory populations tested in treatments that varied social and environmental conditions. In the wild, females consistently outlived males. In captivity, sex-specific mortality depended on social conditions. In social-housed experimental groups, male-biased mortality persisted in two aggressive species, but ceased in two placid species. When social and physical contacts were prevented by housing all fish individually, male-biased mortality ceased in all four species. This outcome held across benign and challenging environmental conditions. Fitting demographic survival models revealed that increased baseline mortality was primarily responsible for a shorter male lifespan in social-housing conditions. The timing and rate of aging were not different between the sexes. No marker of functional aging we recorded in our study (lipofuscin accumulation, proliferative changes in kidney and liver) differed between males and females, despite their previously confirmed association with functional aging in Nothobranchius killifish. We show that sex differences in lifespan and aging in killifish are driven by a combination of social and environmental conditions, rather than differential functional aging. They are primarily linked to sexual selection but precipitated through multiple processes (predation, social interference). This demonstrates how sex-specific mortality varies among species even within an ecologically and evolutionary discrete lineage and explains how external factors mediate this difference.

Sperm cryopreservation and in vitro fertilization techniques for the African turquoise killifish Nothobranchius furzeri

Over the last decade, the African turquoise killifish, Nothobranchius furzeri, has emerged as an important model system for the study of vertebrate biology and ageing. Propagation of laboratory inbred strains of Nothobranchius furzeri, such as GRZ, however, can pose challenges due to the short window of fertility, the efforts and space requirements involved in continuous strain maintenance, and the risks of further inbreeding. The current method for long term strain preservation relies on arrest of embryos in diapause. To create an alternative for long term maintenance, we developed a robust protocol to cryopreserve and revive sperm for in vitro fertilization (IVF). We tested a variety of extender and activator buffers for sperm IVF, as well as cryoprotectants to achieve practical long-term storage and fertilization conditions tailored to this species. Our protocol enabled sperm to be preserved in a cryogenic condition for months and to be revived with an average of 40% viability upon thawing. Thawed sperm were able to fertilize nearly the same number of eggs as natural fertilization, with an average of ~ 25% and peaks of ~ 55% fertilization. This technical advance will greatly facilitate the use of N. furzeri as a model organism.