Sperm production is negatively associated with muscle and sperm telomere length in a species subjected to strong sperm competition.

Life-history theory suggests that ageing is one of the costs of reproduction. Accordingly, a higher reproductive allocation is expected to increase the deterioration of both the somatic and the germinal lines through enhanced telomere attrition. In most species, males' reproductive allocation mainly regards traits that increase mating and fertilization success, that is sexually selected traits. In this study, we tested the hypothesis that a higher investment in sexually selected traits is associated with a reduced relative telomere length (RTL) in the guppy (Poecilia reticulata), an ectotherm species characterized by strong pre- and postcopulatory sexual selection. We first measured telomere length in both the soma and the sperm over guppies' lifespan to see whether there was any variation in telomere length associated with age. Second, we investigated whether a greater investment in pre- and postcopulatory sexually selected traits is linked to shorter telomere length in both the somatic and the sperm germinal lines, and in young and old males. We found that telomeres lengthened with age in the somatic tissue, but there was no age-dependent variation in telomere length in the sperm cells. Telomere length in guppies was significantly and negatively correlated with sperm production in both tissues and life stages considered in this study. Our findings indicate that telomere length in male guppies is strongly associated with their reproductive investment (sperm production), suggesting that a trade-off between reproduction and maintenance is occurring at each stage of males' life in this species.

Potential of the zebrafish model for the forensic toxicology screening of NPS: A comparative study of the effects of APINAC and methiopropamine on the behavior of zebrafish larvae and mice.

The increased diffusion of the so-called novel psychoactive substances (NPS) and their continuous change in structure andconceivably activity has led to the need of a rapid screening method to detect their biological effects as early as possible after their appearance in the market. This problem is very felt in forensic pathology and toxicology, so the preclinical study is fundamental in the approach to clinical and autopsy cases of difficult interpretation intoxication. Zebrafish is a high-throughput suitable model to rapidly hypothesize potential aversive or beneficial effects of novel molecules. In the present study, we measured and compared the behavioral responses to two novel neuroactive drugs, namely APINAC, a new cannabimimetic drug, and methiopropamine (MPA), a methamphetamine-like compound, on zebrafish larvae (ZL) and adult mice. By using an innovative statistical approach (general additive models), it was found that the spontaneous locomotor activity was impaired by the two drugs in both species: the disruption extent varied in a dose-dependent and time-dependent manner. Sensorimotor function was also altered: i) the visual object response was reduced in mice treated with APINAC, whereas it was not after exposure to MPA; ii) the visual placing responses were reduced after treatment with both NPS in mice. Furthermore, the visual motor response detected in ZL showed a reduction after treatment with APINAC during light-dark and dark-light transition. The same pattern was found in the MPA exposed groups only at the dark-light transition, while at the transition from light to dark, the individuals showed an increased response. In conclusion, the present study highlighted the impairment of spontaneous motor and sensorimotor behavior induced by MPA and APINAC administration in both species, thus confirming the usefulness of ZL as a model for a rapid behavioural-based drug screening.

Dietary stress increases the total opportunity for sexual selection and modifies selection on condition-dependent traits.

Although it is often expected that adverse environmental conditions depress the expression of condition-dependent sexually selected traits, the full consequences of environmental change for the action of sexual selection, in terms of the opportunity for total sexual selection and patterns of phenotypic selection, are unknown. Here we show that dietary stress in guppies, Poecilia reticulata, reduces the expression of several sexually selected traits and increases the opportunity for total sexual selection (standardized variance in reproductive success) in males. Furthermore, our results show that dietary stress modulates the relative importance of precopulatory (mating success) and postcopulatory (relative fertilization success) sexual selection, and that the form of multivariate sexual selection (linear vs. nonlinear) depends on dietary regime. Overall, our results are consistent with a pattern of heightened directional selection on condition-dependent sexually selected traits under environmental stress, and underscore the importance of sexual selection in shaping adaptation in a changing world.

Feeding Entrainment of the Zebrafish Circadian Clock Is Regulated by the Glucocorticoid Receptor.

Glucocorticoids (GCs) are steroid hormones mainly acting as key regulators of body homeostasis and stress responses. Their activities are primarily based on the binding to the GC receptor (GR), a member of the nuclear receptor family, that regulates tissue-specific sets of genes. GCs secretion follows a circadian rhythmicity with a peak linked to the animal's activity phase. In mammals, GCs are also implicated in feeding entrainment mechanisms as internal zeitgeber. Here, we investigated, by means of behavioural and molecular approaches, the circadian clock and its regulation by light and food in wild-type (WT) and null glucocorticoid receptor (gr-/-) zebrafish larvae, juveniles and adults. In both WT and gr-/- larvae and adults, behavioural activity and clock gene expression were entrained to the light-dark (LD) cycle and rhythmic in constant conditions. Differences in the pattern of clock genes' expression indicated a modulatory role of GCs. A significant role of Gr was detected in the feeding entrainment which was absent or markedly dampened in mutants. Furthermore, the expression of two clock-regulated genes involved in glucidic and lipidic metabolism was altered, highlighting the participation of GCs in metabolic processes also in fish. Taken together, our results confirmed the role of GC-mediated Gr signaling in the feeding entrainment in a non-mammalian species, the zebrafish.