Widespread alterations to hypothalamic-pituitary-gonadal (HPG) axis signaling underlie high temperature reproductive inhibition in the eurythermal sheepshead minnow (Cyprinodon variegatus)

Influence of water pH and temperature on breeding and embryo development of Indian spiny loach (Lepidocephalichthys thermalis)

The Indian spiny loach (Lepidocephalichthys thermalis), a member of the Cobitidae family and small indigenous species (SIS), is an emerging candidate species for diversification in the Indian aquaculture sector due to its ecological adaptability and culture potential. However, the captive breeding and seed production protocols for commercial seed production of loach fish remain unexplored. Therefore, the present experiment was aimed at studying the effects of water pH and temperature manipulation on the natural spawning and embryonic development of L. thermalis. The study carried out two different experiments and in the first experiment, fish was released in three different pH regimes such as 6.0-6.5 (T1), 7.0-7.5 (T2), and 8.0-8.5 (T3) for a period of 60 days. A total of 9 experimental troughs (water holding capacity - 48 L) were used to stock the loach fish (average length - 5.77 ± 0.11 cm, average weight - 0.78 ± 0.06 g) at 1:2 sex ratio (female: male). Out of these three pH treatments, significantly higher (P < 0.05) spawning rate (1047.0 ± 71.33 eggs/g of female), fertilization rate (86.66 ± 6.42 %) and hatching rate (79.86 ± 5.57 %) were obtained in T2 treatment group which indicated better breeding performance of fish in that group. Further, the loach fish embryonic development was also recorded in T2 treatment group bred fish. In the thermal stimulation experiment, loach fish was kept at a constant water temperature of 26 °C and the fish were exposed to four different water temperatures such as T1 (25 °C), T2 (24 °C), T3 (23 °C) and T4 (22 °C) on 15th and 30th days. During this trial, no sign of breeding activity was recorded in different treatment exposed fish. However, the histological analysis of oocytes documented five different oocyte maturity stages such as chromatin nucleus stage (CNS), perinucleus stage (PS), vitellogenic stage (VS), ripening egg (RE), and hydrated oocytes (HYO) during the thermal stimulation experiment. Further, the study found significantly higher (63.24 ± 4.26 %) and lower (27.05 ± 2.14 %) final gamete maturation rates in T4 and T2 groups exposed fish, respectively. Based on the above results, it can be concluded that the pH of 7.0-7.5 is more suitable for successful captive spawning of loach fish. On the other side, temperature manipulation (sudden reduction of water temperature from 26 °C to 22 °C) had significantly improved the final gamete maturation of L. thermalis fish under captivity. These findings provide valuable insights for its inclusion in India's aquaculture diversification strategies through captive seed production and also provide a promising solution for this species conservation at wild conditions.

Temperature change and male infertility prevalence: an ecological study

BACKGROUND

Although the effects of climate change on human health are widely recognized, its potential role in male infertility prevalence has not been thoroughly examined. This study seeks to explore the association between changes in ambient temperature and the prevalence of male infertility.

METHODS

This ecological study encompassed 174 countries and regions. We utilized data from 2000 to 2019 on the age-standardized prevalence rate (ASPR) of male infertility and ambient temperature to assess their potential association. The analysis accounted for several covariates, including the Sociodemographic Index (SDI), continent, smoking prevalence, alcohol consumption per capita (APC), nitrogen dioxide (NO₂), and ozone (O₃). Annual temperature values were derived by averaging monthly temperatures, and the deviance percentage of temperature (DPT) was computed based on the 20-year mean temperature. To examine spatial and nonlinear relationships between temperature and male infertility ASPR, we applied the geographic detector approach and Restricted Cubic Spline (RCS) curves. Furthermore, linear mixed-effects models were employed to quantify the association between DPT and male infertility ASPR, and adjusted models were subsequently used to forecast changes in ASPR under projected temperature scenarios for 2020-2030.

RESULTS

From 2000 to 2019, a spatial association was identified between temperature and the ASPR of male infertility. Additionally, a U-shaped correlation emerged, indicating the lowest ASPR at 15.7 °C. Higher DPT were linked to elevated male infertility ASPR, with an adjusted β estimate of 38.770 (95% CI: 8.392, 69.162). Projections suggest that ongoing temperature increases may continue to drive up male infertility ASPR.

CONCLUSION

Temperature change may be associated with an increased male infertility prevalence.

Temperature modulates 17β-estradiol regulation of oogenesis protein expression in the liver of the eurythermal pupfish Cyprinodon nevadensis

Female fish experiencing atypically high or prolonged elevations in temperature during oogenesis can suffer impaired oocyte development with fewer or smaller eggs, eggs with reduced yolk content or thinner envelopes, and lower egg viability. These changes in oocyte quality and quantity are in part caused by diminished liver synthesis of egg yolk (vitellogenin, Vtg) and egg envelope (choriogenin) proteins at anomalously high temperatures. Those declines in liver Vtg and choriogenin production are commonly paralleled by reduced blood concentrations of 17β-estradiol (E2). However, it is unclear whether declines in liver vitellogenin and choriogenin production at elevated temperatures result solely from lower circulating E2 or if other aspects of E2 signaling are also altered to diminish liver synthesis of oogenesis proteins. In this study, adult female Amargosa River pupfish (Cyprinodon nevadensis amargosae), a species with asynchronous follicular development, were maintained at 20 °C, 28 °C, or 36 °C and then administered E2 or vehicle solution. Ovarian gonadosomatic index (GSI) values and plasma E2 were lower in females at 36 °C compared to those at cooler temperatures. Females at 36 °C also had reduced plasma Vtg protein, lower liver abundances for mRNAs encoding vitellogenin genes (vtgAa, vtgAb, vtgc), choriogenin genes (cgh, cghm, cgl), and estrogen receptor α (esr1). Supplemental E2 increased plasma E2 in females at all temperatures, but only upregulated liver vitellogenin and choriogenin mRNAs at 36 °C, despite E2 upregulation of hepatic esr1 receptor transcripts at all temperatures. Females at 36 °C also exhibited higher liver mRNA abundances for sex hormone-binding globulin (shbg) and cytochrome P450 family 1 subfamily A member 1 (cyp1a1), an estrogen-metabolizing monooxygenase enzyme that converts E2 to 2-hydroxyestradiol. Together, these findings indicate elevated temperatures diminish E2 stimulation of liver Vtg and choriogenin expression in pupfish via effects on several aspects of E2 signaling including circulating E2 concentrations and liver esr1 expression as well as shbg and cyp1a1 expression, which may result in changes to free:bound E2 and the rate of hepatic E2 inactivation. These results also demonstrate that E2 replacement can help compensate for high temperature-induced declines in hepatic oogenesis gene expression in female pupfish.

Elevated temperature impairs gonadal development by suppressing the expression of the genes for kisspeptin, GnRH1 and GTH subunits in Nile tilapia Oreochromis niloticus

Temperature is a preeminent factor in the regulation of fish reproduction and hinders gonadal development beyond a specific threshold. To comprehend the molecular mechanism responsible for reproductive suppression at different temperature, expression of the genes encoding kisspeptin (kiss2), gonadotropin-releasing hormone (gnrh1) and their receptors (gpr54, gnrh1r) in the brain, and the gonadotropin (GTH) subunits (fshb and lhb) in the pituitary were studied in juvenile Nile tilapia (Oreochromis niloticus) along with gonadal histology. Fish were acclimatized to three distinct temperatures, including 31 °C, 34 °C and 37 °C for 14 days. The mRNA levels of kiss2, gpr54, gnrh1, and gnrh1r were significantly decreased at 37 °C compared to 31 °C and 34 °C in the both sexes. In parallel, the expression level of fshb in the both sexes and lhb in the female were significantly lower at 37 °C in the pituitary. Histologically, the gonads of both sexes had normal growth of gametes at control temperature (31 °C), whereas the spermatogenesis and oocyte maturation were slowed down and atretic oocytes were found in the ovary at 37 °C acclimation temperature. Taken together, the results imply that elevated temperature beyond the specific threshold may have a negative impact on reproduction by suppressing the gene expressions of kisspeptin/GnRH1/GTH system and eventually restrains normal growth and maturation of gametes in the both sexes of Nile tilapia.

Melatonin treatment during the breeding season increases testosterone in male green anole lizards (Anolis carolinensis)

Melatonin is a natural hormone that regulates seasonal behaviors in vertebrates by binding to its receptors (MT1 and MT2). Specifically, high levels of melatonin are associated with short photoperiods, often coinciding with the non-breeding season, meaning that melatonin may inhibit seasonal reproduction. Green anole lizards (Anolis carolinensis), have large, active gonads, increased levels of testosterone and estradiol, and increased reproductive behaviors during the breeding season. Previous studies have examined the role of melatonin in seasonal reproduction in this species, but it is unclear how melatonin receptors change seasonally or if melatonin treatment during the early breeding season influences reproduction. In Experiment 1, we measured MT1 and MT2 mRNA expression in the brains and gonads of unmanipulated anoles between breeding and non-breeding seasons. MT1 mRNA expression was significantly higher in the male brain during the breeding season compared to the non-breeding season, and MT1 mRNA levels were generally higher compared to MT2. This suggests that melatonin may regulate seasonal reproduction through MT1 in the brain, and higher levels during the breeding season may compensate for low seasonal levels of melatonin. In Experiment 2, anoles were treated with melatonin or a blank control for 10 weeks during the breeding season. In males, melatonin treatment increased testosterone levels. This suggests that rather than inhibiting reproduction, continuous high doses of melatonin may increase reproductive hormones during the breeding season. Our findings support the role of melatonin in modulating seasonal reproduction, but the exact mechanisms behind melatonin's stimulatory effect is unclear.

Divergent perspectives on the synergistic impacts of thermal-chemical stress on aquatic biota within the framework of climate change scenarios

Climate change, including global warming, leads to rising temperatures in aquatic ecosystems, which is one of the numerous repercussions it brings. Furthermore, water warming can indirectly impact aquatic organisms by modifying the toxicity levels of pollutants. Nevertheless, numerous studies have explored the potential impacts of chemical stress on aquatic biota, but little is known about how such chemicals and toxins interact with climate change factors, especially elevated temperatures. As such, this review paper focuses on exploring the potential effects of thermochemical stress on a wide sector of aquatic organisms, including aquatic vertebrates and invertebrates, in various aquatic ecosystems (freshwater and marine systems). Herein, the objective of this study is to explore the most up-to-date the impact of water warming (without chemical stress) and thermochemical stress on various biochemical and physiological processes in aquatic fauna and how this greatly affects biodiversity and sustainability. Therefore, there is a growing need to understand and evaluate this synergistic mechanism and its potential hazardous impacts. However, we need further investigations and scientific reports to address this serious environmental issue in order to confront anthropogenic pollutants regarding climate change and chemical pollution risks in the near future and subsequently find sustainable solutions for them.

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.

Impact of stress phenotype, elevated temperature, and bacterin exposure on male Atlantic salmon (Salmo salar) growth, stress, and immune biomarker gene expression

In this study, postsmolt male Atlantic salmon, previously identified as low responders (LRs) or high responders (HRs) based on poststress cortisol levels, had their head kidney and liver sampled at 12°C and 20°C before injection (time 0) and after injection (i.e., at 12- and 24-h postinjection, respectively) with either Forte Micro (a multivalent vaccine containing bacterin, to capture peak antibacterial responses) or an equal volume of PBS. Quantitative real-time PCR (qPCR) was then used to measure the expression of 15 biomarker genes in the head kidney and 12 genes in the liver at each temperature/sampling point. Target transcripts were chosen that were related to growth, stress, and innate antibacterial immune responses. Many temperature, phenotype, and injection effects were found for individual genes within these three broad categories, and multivariate statistical analyses (i.e., principal component analysis and permutational multivariate analysis of variance) were used to look for overall patterns in transcript expression. These analyses revealed that HR salmon at 20°C mounted a more robust response (P < 0.05) for the 10 head kidney immune-related transcripts when injected with Forte Micro than LR salmon. In contrast, the seven liver stress-related transcripts displayed a greater response (P = 0.057) in LR versus HR fish with Forte Micro at 12°C. Overall, although this research did find some differences between LR and HR fish, it does not provide strong (conclusive) evidence that the selection of a particular phenotype would have major implications for the health of salmon over the temperature range examined.NEW & NOTEWORTHY This is the first paper to describe the impact of both temperature and bacterial stimulation on head kidney and liver transcript expression in Atlantic salmon characterized as LRs versus HRs. Notably, we found that HR salmon at 20°C mounted a more robust innate antibacterial immune response than LR salmon. In addition, LR fish at 12°C may (P = 0.057) exhibit higher expression of stress-related transcripts in response to vaccine injection relative to HR fish.

A simulated marine heatwave impacts European sea bass sperm quantity, but not quality

Rapid environmental changes will be the major challenge that most biota will have to deal with in the near future. Extreme events, such as marine heatwaves, are becoming more frequent and could be spatially uniform at a regional scale for a relatively long period of time. To date, most research studies on heatwaves have focused on sessile organisms, but these extreme events can also impact mobile species. Here, a 3-week marine heatwave was simulated to investigate its effects on the male reproductive performance of a Mediterranean Sea emblematic species, the European sea bass Dicentrarchus labrax. Males from the control condition (c. 13°C) produced significantly more sperm than those exposed to a relatively warm thermal treatment (c. 16°C). Nonetheless, neither the percentage of motile spermatozoa nor most of the other sperm motility parameters were significantly affected by the rearing temperature over the whole period. Overall, the results of this study suggest only moderated effects of a potential winter heatwave on the reproductive performance of male European sea bass.

Effect of PACAP/PAC1R on Follicle Development of Djungarian Hamster (Phodopus sungorus) with the Variation of Ambient Temperatures

In Phodopus sungorus, the relationship between pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptor (PAC1R), follicle-stimulating hormone (FSH), and follicle development remains unclear. In this study, we found that the development of growing follicles and antral follicles were inhibited at low (8 °C, 14 °C) and high (29 °C) temperatures. Meanwhile, PACAP/PAC1R expression and follicle-stimulating hormone (FSH) serum concentration significantly decreased during ambient temperatures of 8 °C, 14 °C and 29 °C compared to 21 °C. Thus, ambient temperature may influence the expression of PACAP/PAC1R and the synthesis of FSH for involvement in follicle development. Moreover, PACAP/PAC1R had major functional elements including PKA/PKG and PKC phosphorylation sites, which may involve in the pathway of FSH synthesis through cAMP-PKA and its downstream signal pathway. Moreover, there was a significant positive correlation between the expression levels of PACAP/PAC1R and the number of the growing and antral follicles, as well as the serum FSH concentration and the number of antral follicles. However, there was no significant correlation between the expression levels of PACAP/PAC1R and the serum FSH concentration, indicating a complicated pathway between PACAP/PAC1R and FSH. In conclusion, ambient temperature affects the expression of PACAP/PAC1R and the serum FSH concentration. The expression of PACAP/PAC1R and the serum FSH concentration are correlated with follicle development, which implies that they are involved in follicle development, which will ultimately influence the reproduction of Phodopus sungorus. This study can lay the foundation for future investigation on the regulation mechanism of reproduction in Phodopus sungorus.

Accustomed to the heat: Temperature and thyroid hormone influences on oogenesis and gonadal steroidogenesis pathways vary among populations of Amargosa pupfish (Cyprinodon nevadensis amargosae)

Many fish experience diminished reproductive performance under atypically high or prolonged elevations of temperature. Such high temperature inhibition of reproduction comes about in part from altered stimulation of gametogenesis by the hypothalamic-pituitary-gonadal (HPG) endocrine axis. Elevated temperatures have also been shown to affect thyroid hormone (TH) signaling, and altered TH status under high temperatures may impact gametogenesis via crosstalk with HPG axis pathways. Here, we examined effects of temperature and 3'-triiodo-_L-thyronine (T₃) on pathways for gonadal steroidogenesis and gametogenesis in Amargosa pupfish (Cyprinodon nevadensis amargosae) from two allopatric populations: 1) the Amargosa River - a highly variable temperature habitat, and 2) Tecopa Bore - an invariably warm groundwater-fed marsh. These populations were previously shown to differ in TH signaling profiles both in the wild and under common laboratory conditions. Sexually-mature pupfish from each population were maintained at 24 °C or 34 °C for 88 days, after which a subset of fish was treated with T₃ for 18-24 h. In both populations, mRNA abundances for follicle-stimulating hormone receptor and luteinizing hormone receptor were higher in the ovary and testis at 24 °C compared to 34 °C. Females from Tecopa Bore - but not from the Amargosa River - also had greater ovarian transcript abundances for steroidogenic enzymes cytochrome P450 aromatase, 3β-hydroxysteroid dehydrogenase, and 17β-hydroxysteroid dehydrogenase at 24 °C compared to 34 °C, as well as higher liver mRNA levels of vitellogenins and choriogenins at cooler temperature. Transcript abundances for estrogen receptors esr1, esr2a, and esr2b were reduced at 34 °C in Amargosa River females, but not in Tecopa Bore females. T₃ augmented gonadal gene transcript levels for steroid acute regulatory protein (StAR) transporter in both sexes and populations. T₃ also downregulated liver estrogen receptor mRNAs in females from the warmer Tecopa Bore habitat only, suggesting T₃ modulation of liver E₂ sensitivity as a possible mechanism whereby temperature-induced changes in TH status may contribute to shifts in thermal sensitivity for oogenesis.

Anomalous Temperature Interdicts the Reproductive Activity in Fish: Neuroendocrine Mechanisms of Reproductive Function in Response to Water Temperature

Fish are poikilotherm and small changes in water temperature can greatly affect physiological processes including reproduction, which is regulated by complex neuroendocrine mechanisms that respond to climatic events. This review provides evidence that anomalous high and low temperature may directly affect reproduction in fish by suppressing the expression of genes in the reproductive neuroendocrine system. The grass puffer, Takifugu alboplumbeus, is an excellent animal model for studying the thermal regulation of reproduction, for they exhibit periodic spawning activities, which are synchronized with seasonal, lunar and daily cycles. In the grass puffer, the expression of the genes encoding gonadotropin-releasing hormone (GnRH) 1, kisspeptin, gonadotropin-inhibitory hormone (GnIH) and their receptors were markedly suppressed in the diencephalon of fish exposed to high temperature (28°C) when compared to normal temperature (21°C), followed by the decrease in the pituitary mRNA levels for follicle-stimulating hormone (FSH), luteinizing hormone (LH) and growth hormone (GH). On the other hand, the exposure to low temperature (14°C) also inhibited the expression of gnrh1, kiss2, gnih and their receptor genes in the brain and fshb, lhb, gh and prl in the pituitary. Taken together, it is plausible that anomalous high and low temperature may be a proximate driver of termination of reproduction by suppressing the activity of the reproductive GnRH/kisspeptin/GnIH system, possibly through direct action of temperature signals at transcription level.