H2O2-induced oxidative stress impairs meat quality by inducing apoptosis and autophagy via ROS/NF-κB signaling pathway in broiler thigh muscle

Effects of Se-enriched yeast on the amelioration of atrazine-induced meat quality degradation

Atrazine (ATR) is herbicide that causes serious harm to the environment and threatens human food safety. Se-enriched yeast is the best organic selenium source for protecting cells from damage caused by poisonous substances. To explore mechanism of ATR on meat quality degradation and potential protective effects of Se-enriched yeast on ATR-induced muscle injury, quails were treated with ATR and/or Se-enriched yeast for 28 days. The results found ATR disrupted muscle fiber structure and decreased pH, tenderness, water-holding capacity, essential amino acid content and polyunsaturated fatty acid content. ATR aggravated oxidative stress and inflammation by inhibiting Nrf2 pathway and activating NF-κB pathway, ultimately causing apoptosis. However, Se-enriched yeast alleviated ATR-induced alterations in muscle chemical and physical properties by inhibiting oxidative stress and inflammation. Taken together, these results revealed that ATR exposure caused meat quality degradation and Se-enriched yeast had the potential to counteract ATR-induced myotoxicity by inhibiting oxidative stress and inflammation.

Polystyrene microplastics exposure reduces meat quality and disturbs skeletal muscle angiogenesis via thrombospondin 1

Microplastics (MPs) pose a significant threat to livestock health. Yet, the roles of polystyrene MPs (PS-MPs) on meat quality and skeletal muscle development in pigs have not been fully determined. To investigate the effect of PS-MPs on skeletal muscle, piglets were given diets supplementation with 0 mg/kg (CON group), 75 mg/kg (75 mg/kg PS-MPs group), and 150 mg/kg PS-MPs (150 mg/kg PS-MPs group), respectively. The results indicated that the average daily gain (ADG) of piglets in the 150 mg/kg PS-MPs group was significantly lower than that in the CON group. No significant differences were observed in the final body weight and ADG between the CON group and the 75 mg/kg PS-MPs group. Piglets in the 150 mg/kg PS-MPs group exhibited decreased meat redness index and type I muscle fiber density. Metabolomic analysis revealed that the contents of meat flavor compounds carnosine, beta-alanine, palmitic acid, and niacinamide in muscle were lower in the 150 mg/kg PS-MPs group than in the CON group. Additionally, piglets subjected to 150 mg/kg PS-MPs exhibited impaired muscle angiogenesis. Further analysis indicated that PS-MPs exposure up-regulated thrombospondin 1 (THBS1) expression by inhibiting THBS1 mRNA and protein degradation, thereby disrupting skeletal muscle angiogenesis. These findings indicate that PS-MPs exposure adversely affects meat quality and hinders skeletal muscle angiogenesis in pigs, providing deeper insights into the detrimental effects of PS-MPs on meat quality and skeletal muscle development.

Selenomethionine Inhibited HADV-Induced Apoptosis Mediated by ROS through the JAK-STAT3 Signaling Pathway

Adenovirus (HAdV) can cause severe respiratory infections in children and immunocompromised patients. There is a lack of specific therapeutic drugs for HAdV infection, and the study of anti-adenoviral drugs has far-reaching clinical implications. Elemental selenium can play a specific role as an antioxidant in the human immune cycle by non-specifically binding to the amino acid methionine in body proteins. Methods: The antiviral mechanism of selenomethionine was explored by measuring cell membrane status, intracellular DNA status, cytokine secretion, mitochondrial membrane potential, and ROS production. Conclusions: Selenomethionine improved the regulation of ROS-mediated apoptosis by modulating the expression of Jak1/2, STAT3, and BCL-XL, which led to the inhibition of apoptosis. It is anticipated that selenomethionine will offer a new anti-adenoviral therapeutic alternative.

Comparison of the effects of chlorogenic acid isomers and their compounds on alleviating oxidative stress injury in broilers

The development of large-scale and intensive breeding models has led to increasingly prominent oxidative stress issues in animal husbandry production. Chlorogenic acid (CGA) is an important extract with a variety of biological activities. It is an effective antioxidant drug and shows different antioxidant capacities due to its different chemical structures. Therefore, it is a new research target to determine the proportion of chlorogenic acid isomers with high antioxidant activity to resist the damage caused by oxidative stress. In this experiment, the antioxidant activities of the chlorogenic acid monomer and its compounds were compared by a series of in vitro antioxidant indexes. Based on the above experiments, it was found that LB and LC have superior antioxidant abilities (P < 0.05). Subsequently, 300 healthy 1-day-old Arbor Acres (AA) male broilers with no significant difference in body weight (about 44 g) were randomly selected and randomly divided into 5 groups with 6 replicates in each group and 10 chickens in each replicate. One group was the control group, 1 group was the model group, and the remaining 3 groups were the experimental groups. At 37 d of age, animals in the control group were injected with normal saline, and animals in the other 4 groups were injected with 1 mL/kg 5% hydrogen peroxide (H2O2) through the chest muscle before the supplementation. The control group (control) and the model group (PC) were fed a standard diet. The remaining 3 groups included the CGA group, LB group (CIB), and LC group (CIC). In these groups, 50 g/t chlorogenic acid, LB compound, or LC compound were added to the basal diet, respectively, and the other feeding conditions remained consistent. The addition of the LB complex to the diet could significantly improve the growth performance and antioxidant performance of broilers (P < 0.05), upregulate the expression of Nuclear factor erythroid 2-related factor 2 (Nrf2) pathway-related genes in liver and jejunum (P < 0.05), regulate the disordered intestinal flora, and alleviate the damage caused by oxidative stress. These results suggested for the first time that the LB complex exhibited superior effects in vitro and vivo.

Arzanol, a natural phloroglucinol α-pyrone, protects HaCaT keratinocytes against H2O2-induced oxidative stress, counteracting cytotoxicity, reactive oxygen species generation, apoptosis, and mitochondrial depolarization

Skin oxidative stress results in structural damage, leading to premature senescence, and pathological conditions such as inflammation and cancer. The plant-derived prenylated pyrone-phloroglucinol heterodimer arzanol, isolated from Helichrysum italicum ssp. microphyllum (Willd.) Nyman aerial parts, exhibits anti-inflammatory, anticancer, antimicrobial, and antioxidant activities. This study explored the arzanol protection against hydrogen peroxide (H2O2) induced oxidative damage in HaCaT human keratinocytes in terms of its ability to counteract cytotoxicity, reactive oxygen species (ROS) generation, apoptosis, and mitochondrial membrane depolarization. Arzanol safety on HaCaT cells was preliminarily examined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and microscopic observation. The arzanol pre-incubation (5-100 μM, for 24 h) did not induce cytotoxicity and morphological alterations. The phloroglucinol, at 50 μM, significantly protected keratinocytes against cytotoxicity induced by 2 h-incubation with 2.5 and 5 mM H2O2, decreased cell ROS production induced by 1 h-exposure to all tested H2O2 concentrations (0.5-5 mM), as determined by the 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA) assay, and lipid peroxidation (thiobarbituric acid reactive substances [TBARS] method). The 2-h incubation of keratinocytes with H2O2 determined a significant increase of apoptotic cells versus control cells, evaluated by NucView® 488 assay, from the dose of 2.5 mM. Moreover, an evident mitochondrial membrane potential depolarization, monitored by fluorescent mitochondrial dye MitoView™ 633, was assessed at 5 mM H2O2. Arzanol pre-treatment (50 μM) exerted a strong significant protective effect against apoptosis, preserving the mitochondrial membrane potential of HaCaT cells at the highest H2O2 concentrations. Our results validate arzanol as an antioxidant agent for the prevention/treatment of skin oxidative-related disorders, qualifying its potential use for cosmeceutical and pharmaceutical applications.

Resveratrol improves meat quality traits by activating the lncRNAs-KEAP1-NRF2 axis in pigs

This research aims at uncovering the effects and investigating the molecular mechanisms of dietary resveratrol (RES) supplementation on antioxidant capacity and meat quality of pigs. In this study, 20 μM RES could activate the KEAP1-NRF2 antioxidant defense pathway in response to oxidative stress in porcine skeletal muscle satellite cells was firstly found. Then, twenty-four healthy crossbred castrated boars were allocated to 4 treatments that were fed with a basal diet (control) and a basal diet supplemented with 200 mg, 400 mg or 600 mg RES per Kilogram (kg) of feed for 41 days, respectively. 400 and 600 mg/kg RES-supplemented diet can effectively improve the meat quality traits and activities of antioxidizing enzymes via the KEAP1-NRF2 signaling pathway of pigs. The molecular dynamic simulation further revealed that RES could directly binding to KEAP1 to reduce the tightness of KEAP1-NRF2 protein-protein interaction. More importantly, dietary supplementation of RES also improves antioxidant capacity through a series of KEAP1-NRF2 pathway-related lncRNAs were found by RNA sequencing (RNA-seq). Altogether, this study demonstrated that RES improves meat quality traits by effectively increasing antioxidant levels via the lncRNA-KEAP1-NRF2 axis in vivo and/or in vitro. These results provide new insights into the molecular mechanisms by which RES, as a nutritional agent, regulates antioxidant capacity and improves meat quality in pigs.

Insights into the mechanism of L-malic acid on drip loss of chicken meat under commercial conditions

BACKGROUND

A deterioration in the meat quality of broilers has attracted much more attention in recent years. L-malic acid (MA) is evidenced to decrease meat drip loss in broilers, but the underlying molecular mechanisms are still unclear. It's also not sure whether the outputs obtained under experimental conditions can be obtained in a commercial condition. Here, we investigated the effects and mechanisms of dietary MA supplementation on chicken meat drip loss at large-scale rearing.

RESULTS

Results showed that the growth performance and drip loss were improved by MA supplementation. Meat metabolome revealed that L-2-aminoadipic acid, β-aminoisobutyric acid, eicosapentaenoic acid, and nicotinamide, as well as amino acid metabolism pathways connected to the improvements of meat quality by MA addition. The transcriptome analysis further indicated that the effect of MA on drip loss was also related to the proper immune response, evidenced by the enhanced B cell receptor signaling pathway, NF-κB signaling pathway, TNF signaling pathway, and IL-17 signaling pathway.

CONCLUSIONS

We provided evidence that MA decreased chicken meat drip loss under commercial conditions. Metabolome and transcriptome revealed a comprehensive understanding of the underlying mechanisms. Together, MA could be used as a promising dietary supplement for enhancing the water-holding capacity of chicken meat.

Green tea catechin prevents oxidative stress-regulated autophagy and apoptosis signaling, and inhibits tenderness in postmortem bovine longissimus thoracis et lumborum muscle

Although green tea catechin has been reported to be an antioxidant and preservative in meat, the extent to which it affects the tenderization of bovine muscle remains largely unknown. This study seeks to evaluate the effect of catechin on the interplay between apoptosis and autophagy, and subsequently, the development of bovine muscle tenderness. The results indicate that catechin significantly alleviated oxidative stress. A concomitant reduction of autophagic markers LC3-II/LC3-I ratio, Beclin-1, and Atg7 levels were caused by catechin. Besides, aforementioned autophagy inhibition was further augmented by PI3K/Akt/mTOR activation. Additionally, catechin protected against mitochondrial dysfunction and inhibited mitochondria-dependent caspase apoptosis pathway. Furthermore, there was a reciprocal inhibition between autophagy and apoptosis. Ultimately, tenderness at 24 and 120 h, an increase in the gap between muscle fiber bundles, and disintegration of myofibrillar architectures were all inhibited by catechin. Therefore, despite alleviating oxidative stress, catechin may hamper tenderization pattern of postmortem bovine muscle.

MicroRNA-129-1-3p attenuates autophagy-dependent cell death by targeting MCU in granulosa cells of laying hens under H2O2-induced oxidative stress

The present study aimed to investigate the mechanism of microRNA-129-1-3p (miR-129-1-3p) in regulating hydrogen peroxide (H2O2)-induced autophagic death of chicken granulosa cell by targeting mitochondrial calcium uniporter (MCU). The results indicated that the exposure of hens' ovaries to H2O2 resulted in a significant elevation in reactive oxygen species (ROS) levels, as well as the apoptosis of granulosa cells and follicular atresia. This was accompanied by an upregulation of glucose-regulated protein 75 (GRP75), voltage-dependent anion-selective channel 1 (VDAC1), MCU, mitochondria fission factor (MFF), microtubule-associated protein 1 light chain 3 (LC3) I, and LC3II expression, and a downregulation of peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) and mitofusin-2 (MFN2) expression. In hens' granulosa cells, a luciferase reporter assay confirmed that miR-129-1-3p directly regulates MCU. The induction of oxidative stress through H2O2 resulted in the activation of the permeability transition pore, an overload of calcium, depolarization of the mitochondrial membrane potential, dysfunction of mitochondria-associated endoplasmic reticulum membranes (MAMs), and ultimately, autophagic cell death. The overexpression of miR-129-1-3p effectively mitigated these H2O2-induced changes. Furthermore, miR-129-1-3p overexpression in granulosa cells prevented the alterations induced by H2O2 in the expression of key proteins that play crucial roles in maintaining the integrity of MAMs and regulating autophagy, such as GRP75, VDAC1, MFN2, PTEN-induced kinase 1 (Pink1), and parkin RBR E3 ubiquitin-protein ligase (Parkin). Together, these in vitro- and in vivo-based experiments suggest that miR-129-1-3p protects granulosa cells from oxidative stress-induced autophagic cell death by downregulating the MCU-mediated mitochondrial autophagy. miR-129-1-3p/MCU calcium signaling pathway may act as a new target to alleviate follicular atresia caused by oxidative stress in laying hens.

Potential roles for lncRNA Mirg/Foxp1 in an ARHL model created using C57BL/6J mice

Age-related hearing loss (ARHL) is associated with hair cell apoptosis, but the underlying mechanism of hair cell apoptosis remains unclear. Here, we investigated the expression profiles of long noncoding RNAs (lncRNAs) and mRNAs in an ARHL model created with C57BL/6 J mice using RNA sequencing and found that the expression of several lncRNAs was significantly correlated with apoptosis-associated mRNAs in the cochlear tissues of old mice compared to young mice. We found that lncRNA Mirg was upregulated in the cochlear tissues of old mice compared to young mice and its overexpression promoted apoptosis in House Ear Institute-Organ of Corti 1 (HEI-OC1). H2O2-induced oxidative stress increased HEI-OC1 cell apoptosis by upregulating lncRNA Mirg. Furthermore, the expression of lncRNA Mirg and Foxp1 showed the highest correlation coefficient in the cochlear tissues of old mice, and lncRNA Mirg promoted HEI-OC1 cell apoptosis by increasing Foxp1 expression. In conclusion, our findings suggest that lncRNA Mirg expression correlates with cell apoptosis-associated mRNAs in the ARHL model created using C57BL/6 J mice and that oxidative stress-induced lncRNA Mirg promotes HEI-OC1 cell apoptosis by increasing Foxp1 expression. These data suggest the potential therapeutic significance of targeting lncRNA Mirg/Foxp1 signaling in ARHL.

Selenium deficiency induced inflammation and apoptosis via NF-κB and MAPKs pathways in muscle of common carp (Cyprinus carpio L.)

Selenium (Se), one of the essential trace elements of fish, regulates immune system function and maintains immune homeostasis. Muscle is the important tissue that generate movement and maintain posture. At present, there are few studies on the effects of Se deficiency on carp muscle. In this experiment, carps were fed with dietary with different Se content to successfully establish a Se deficiency model. Low-Se dietary led to the decrease of Se content in muscle. Histological analysis showed that Se deficiency resulted in muscle fiber fragmentation, dissolution, disarrangement and increased myocyte apoptosis. Transcriptome revealed a total of 367 differentially expressed genes (DEGs) were screened, including 213 up-regulated DEGs and 154 down-regulated DEGs. Bioinformatics analysis showed that DEGs were concentrated in oxidation-reduction process, inflammation and apoptosis, and were related to NF-κB and MAPKs pathways. Further exploration of the mechanism showed that Se deficiency led to excessive accumulation of ROS, decreased the activity of antioxidant enzymes, and also resulted in increased expression of the NF-κB and MAPKs pathways. In addition, Se deficiency significantly increased the expressions of TNF-α, IL-1β and IL-6, and the pro-apoptotic factors BAX, p53, caspase-7 and caspase-3, while decreased the expressions of anti-apoptotic factors Bcl-2 and Bcl-xl. In conclusion, Se deficiency reduced the activities of antioxidant enzymes and led to excessive accumulation of ROS, which caused oxidative stress and affected the immune function of carp, leading to muscle inflammation and apoptosis.

Protective Effect of Phloretin against Hydrogen Peroxide-Induced Oxidative Damage by Enhancing Autophagic Flux in DF-1 Cells

Phloretin (PHL) is a dihydrochalcone flavonoid isolated from the peel and root bark of apples, strawberries, and other plants with antioxidative characteristic. In this study, we aimed to investigate the protective effect and the potential mechanism of PHL on hydrogen peroxide (H₂O₂)-induced oxidative damage in DF-1 cells. The results showed that PHL exhibited no cytotoxic effect on DF-1 cells at concentration below 20 μM. PHL markedly increased H₂O₂-reduced cell viability, decreased H₂O₂-induced apoptosis, as evidenced by reduced apoptosis rate, the upregulation of gene and protein level of Bcl-2, and the downregulation of gene and protein level of Bax and Cleaved caspase3. In addition, PHL reduced H₂O₂-induced reactive oxygen species (ROS) production and restored antioxidant enzymes activities as well as mitochondrial membrane potential in a dose-dependent manner. Moreover, PHL prior to H₂O₂ further increased LC3-II level, promoted p62 turnover and improved lysosomal function. Importantly, autophagy inhibitor chloroquine (CQ) reversed the protective effect of PHL, and increased H₂O₂-induced apoptosis. Furthermore, PHL inhibited the phosphorylation levels of ERK, p38, and JNK. Collectively, these results indicate that PHL could attenuate H₂O₂-induced oxidative injury and apoptosis by maintaining lysosomal function and promoting autophagic flux, and MAPKs pathway may be involved in this process. Our study provides evidence that PHL could as a new strategy to against oxidative damage in poultry industry.

Effects of dietary supplementation with quercetagetin on nutrient digestibility, intestinal morphology, immunity, and antioxidant capacity of broilers

Quercetagetin (QG) is gaining increased attention as a potential alternative to in-feed antioxidants due to its antioxidant activity. This experiment was conducted to investigate the effects of dietary supplementation with QG on nutrient digestibility, intestinal morphology, immunity, and antioxidant capacity of broilers. Four hundred 1-day-old Ross 308 broilers were randomly assigned into 4 groups with 10 replicates in each group and 10 broilers in each replicate. The four dietary treatments included the basal diet supplemented with 0, 3.2, 4.8, or 6.4 mg/kg QG. The results showed that dietary supplementation with QG significantly promoted the broilers' apparent digestibility of phosphorus (P < 0.05), increased the villus height in jejunum and ileum, and reduced the crypt depth in jejunum and ileum, which significantly increased the ratio of villus height to crypt depth in the jejunum and ileum (P < 0.05). The dietary supplementation with QG also significantly enhanced the immunoglobulin G (IgG) and complement 4 (C4) levels in the blood (P < 0.05), the activity of total antioxidant capacity (T-AOC) in serum, jejunum mucosa, and ileum mucosa, the activity of superoxide dismutase (SOD) in the serum and liver (P < 0.05), and significantly up-regulated the kelch-like ECH-associated protein 1 (Keap1), nuclear factor E2 related factor 2 (Nrf2), heme oxygenase-1 (HO-1), NAD(P)H: quinone oxidoreductase 1 (NQO-1), glutathione peroxidase (GSH-Px) and superoxide dismutase 1 (SOD1) mRNA expression levels in the jejunum mucosa, ileum mucosa, and liver tissues of broilers. Therefore, supplementing broilers' diets with QG can enhance the apparent digestibility of phosphorus, improve the structure and morphology of jejunum and ileum, promote immunity, and increase the activity of antioxidant enzymes and the antioxidantive capacity through the Nrf2/antioxidant response element (ARE) signaling pathway mediated by Keap1.

H2O2-induced oxidative stress improves meat tenderness by accelerating glycolysis via hypoxia-inducible factor-1α signaling pathway in postmortem bovine muscle

Reactive oxygen species (ROS) affect meat quality through multiple biochemical pathways. To investigate the effect of ROS on postmortem glycolysis and tenderness of bovine muscle, ROS content, glycolytic potential, glycolysis rate-limiting enzyme activities, expression of hypoxia-inducible factor-1α (HIF-1α), phosphatidylinositol 3-kinase (PI3K), serine-threonine kinase (AKT), phosphorylated AKT (p-AKT), and tenderness were determined in the H₂O₂ group and control group. Results showed that the H₂O₂ group exhibited significantly higher ROS content within 48 h, coupled with increased glycolytic potential, pH decline, hexokinase (HK), and phosphofructokinase activities (PFK) early postmortem. These were attributed to ROS-induced PI3K/AKT signaling pathway activation and resultant HIF-1α accumulation. Moreover, shear force in the H₂O₂ group reached the peak 12 h earlier and decreased obviously after 24 h, accompanied by a significantly higher myofibril fragmentation index (MFI). These findings suggested that ROS drive HIF-1α accumulation by activating PI3K/AKT signaling pathway, thereby accelerating glycolysis and tenderization of postmortem bovine muscle.

Effects of dietary supplementation with selenium yeast and jujube powder on mitochondrial oxidative damage and apoptosis of chicken

The main objective of this study was to explore the effects of dietary selenium yeast and jujube powder on mitochondrial oxidative damage and cell apoptosis of broilers during postmortem aging, chicken breasts of broilers fed diets supplemented with different concentrations of selenium yeast and jujube powder were used as research subjects. With the prolongation of postmortem aging time, the levels of reactive oxygen species (ROS), carbonyl content, mitochondrial permeability transition pore (MPTP) openness, and mitochondrial membrane permeability increased significantly (P < 0.05). The contents of the sulfhydryl, mitochondrial membrane potential, shear force, and cytochrome C (Cyt-c) reduction level decreased significantly (P < 0.05). The activity of Caspase-3 and Caspase-9 increased from 0 to 24 h postmortem but fell from 24 to 72 h postmortem. Compared with the control group, dietary selenium yeast and jujube powder significantly reduced mitochondrial oxidative damage. They greatly increased the shear force, mitochondrial membrane potential, and Cyt-c reduction levels (P < 0.05). Among them, the combination group of high-dose selenium yeast and jujube powder had more significant effects on ROS scavenging, reducing cell membrane permeability, protecting cell membrane integrity, and increasing Cyt-c reduction level (P < 0.05). In conclusion, cell apoptosis intensifies during the chicken breast's aging time, and muscle tenderness continues. Still, different doses of dietary selenium yeast and jujube powder can inhibit mitochondrial oxidation to various degrees. The combined group of selenium yeast and jujube powder with 0.6 mg·kg⁻¹ has the best effect. This study is of great significance for applying natural antioxidant ingredients such as selenium yeast and jujube powder in the development and utilization of poultry feed.

Untargeted Metabolomics Reveals the Effect of Selective Breeding on the Quality of Chicken Meat

The selection for improved body weight is an effective approach in animal breeding. Guangxi Partridge chickens have differentiated into two lines under selective breeding, which include line S and line D that have shown statistically significant differences in body weight. However, the meat quality analysis in our study indicated that the quality of breast and thigh muscles in line S chickens changed, which included increased values of L*, b*, and drip loss and decreased a* value, pH, and shear force in skeletal muscles. To illuminate the effect of selection on skeletal muscles, LC-MS/MS metabolomics was performed to explore differentiated metabolites in divergent tissues from the two chicken lines. The results of principal component analysis and orthogonal projection to latent structures discriminant analysis suggested that metabolites of different groups were separated, which suggested that selective breeding certainly affected metabolism of skeletal muscles. KEGG analysis identified that valine, leucine, and isoleucine biosynthesis, glycerophospholipid metabolism, and glutathione metabolism noteworthily changed in breast muscle. Amino sugars and nucleotide sugar metabolism, ascorbate and aldarate metabolism, the pentose phosphate pathway, pentose and glucuronate interconversions, fructose and mannose metabolism, and glycerophospholipid metabolism were remarkedly identified in thigh muscle. These screened pathways suggested oxidative stress in breast and thigh muscles, which corresponded with our previous results. Therefore, this study determined that glycerophospholipid metabolism conservatively functioned in muscle flavor and development but exhibited different anti-oxidative patterns in different skeletal muscles. Overall, the present study identified several differentiated metabolites and pathways for exploring differences in meat quality between different broiler populations.