Ostrich chick humoral immune responses and growth rate are predicted by parental immune responses and paternal colouration

The Immune Regulatory Effect of Boron on Ostrich Chick Splenic Lymphocytes

Boron is a trace element which plays important roles in immune response. The relationship between boron and splenic lymphocyte proliferation, apoptosis, secretion of cytokines, and genes potentially related to immune response in ostrich chicks were investigated in the present study. Different concentrations of boron (0, 0.01, 0.1, 0.5, 1, 5, 10, 25, 50, and 100 mmol/L) were applied to splenic lymphocytes of African ostrich, respectively. The effect of boron on lymphocyte proliferation was checked by the CCK-8 method. Flow cytometry was used to detect the effect of boron on apoptosis. The secretion levels of IL-6 and IFN-α were determined by ELISA. Splenic lymphocyte gene expression profiles of ostrich chicks treated with boron (0, 0.1, 100 mmol/L) were studied using RNA-seq technology. The results showed that cell proliferation increased with 0.01-10 mmol/L boron, when it was 25-100 mmol/L, the cell proliferation gradually decreased as the boron concentration increased. Apoptosis ratio in ostrich splenic lymphocytes was closely related to boron concentrations. 0.01- and 0.1-mmol/L boron inhibited apoptosis in splenic lymphocytes, whereas 1, 10, 50, and 100-mmol/L boron promoted apoptosis. As the concentration of boron increased, the secretion of IL-6 gradually decreased; IFN-α was initially increased and then decreased with boron concentrations increased, reaching the maximum level with 1 mmol/L boron. In terms of the RNA-Seq data, there was no differentially expressed gene between the 0- and 0.1-mmol/L boron-treated samples; 21 differentially expressed genes were found between the 0- and 100-mmol/L boron-treated samples; 43 differentially expressed genes were found between the 0.1- and 100-mmol/L boron-treated samples. Functional analysis of the differentially expressed genes by Gene Ontology verified multiple functions associated with immune response. Pathway analysis showed that systemic lupus erythematosus, alcoholism, viral carcinogenesis, and necroptosis pathway were the major enriched pathways, and BIRC2-3, FTH1, and IL-1β genes showed differential expression in necroptosis pathway. These results demonstrated that low concentrations (0.01-0.1 mmol/L) of boron may promote the proliferation and the secretion of cytokines, inhibit cell apoptosis of ostrich splenic lymphocytes by enhancing the function of the cell membrane and the activity of intracellular catalytic enzymes, whereas high-concentration (25-100 mmol/L) boron had opposite effects on cells. The necroptosis pathway might play a pivotal role in regulating the immune response of boron-treated splenic lymphocytes in ostrich chicks.

Sexual selection favours good or bad genes for pathogen resistance depending on males' pathogen exposure

Resistance to pathogens is often invoked as an indirect benefit of female choice, but experimental evidence for links between father's sexual success and offspring resistance is scarce and equivocal. Two proposed mechanisms might generate such links. Under the first, heritable resistance to diverse pathogens depends on general immunocompetence; owing to shared condition dependence, male sexual traits indicate immunocompetence independently of the male's pathogen exposure. By contrast, other hypotheses (e.g. Hamilton-Zuk) assume that sexual traits only reveal heritable resistance if the males have been exposed to the pathogen. The distinction between the two mechanisms has been neglected by experimental studies. We show that Drosophila melanogaster males that are successful in mating contests (one female with two males) sire sons that are substantially more resistant to the intestinal pathogen Pseudomonas entomophila-but only if the males have themselves been exposed to the pathogen before the mating contest. By contrast, sons of males sexually successful in the absence of pathogen exposure are less resistant than sons of unsuccessful males. We detected no differences in daughters' resistance. Thus, while sexual selection may have considerable consequences for offspring resistance, these consequences may be sex-specific. Furthermore, contrary to the 'general immunocompetence' hypothesis, these consequences can be positive or negative depending on the epidemiological context under which sexual selection operates.

Sexual selection reveals a cost of pathogen resistance undetected in life-history assays

Mechanisms of resistance to pathogens and parasites are thought to be costly and thus to lead to evolutionary trade‐offs between resistance and life‐history traits expressed in the absence of the infective agents. On the other hand, sexually selected traits are often proposed to indicate “good genes” for resistance, which implies a positive genetic correlation between resistance and success in sexual selection. Here I show that experimental evolution of improved resistance to the intestinal pathogen Pseudomonas entomophila in Drosophila melanogaster was associated with a reduction in male sexual success. Males from four resistant populations achieved lower paternity than males from four susceptible control populations in competition with males from a competitor strain, indicating an evolutionary cost of resistance in terms of mating success and/or sperm competition. In contrast, no costs were found in larval viability, larval competitive ability and population productivity assayed under nutritional limitation; together with earlier studies this suggests that the costs of P. entomophila resistance for nonsexual fitness components are negligible. Thus, rather than indicating heritable pathogen resistance, sexually selected traits expressed in the absence of pathogens may be sensitive to costs of resistance, even if no such costs are detected in other fitness traits.

Transcriptional Study Revealed That Boron Supplementation May Alter the Immune-Related Genes Through MAPK Signaling in Ostrich Chick Thymus

The objective of this study is to construct a digital gene expression tag profile to identify genes potentially related to immune response in the ostrich. Exposure to boron leads to an immune response in the ostrich, although the underlying mechanism remains obscure. Thus, a dire need of biological resource in the form of transcriptomic data for ostriches arises to key out genes and to gain insights into the function of boron on the immune response of thymus. For this purpose, RNA-Seq analysis was performed using the Illumina technique to investigate differentially expressed genes in ostrich thymuses treated with different boric acid concentrations (0, 80, and 640 mg/L). Compared with the control group, we identified 309 upregulated and 593 downregulated genes in the 80 mg/L treated sample and 228 upregulated and 1816 downregulated genes in 640 mg/L treated sample, respectively. Trend analysis of these differentially expressed genes uncovers three statistically significant trends. Functional annotation analysis of the differentially expressed genes verifies multiple functions associated with immune response. When ostrich thymuses were treated with boron, expression changes were observed in genes predominantly associated with MAPK and calcium signaling pathways. The results of this study provide all-inclusive information on gene expression at the transcriptional level that further enhances our apprehension for the molecular mechanisms of boron on the ostrich immune system. The calcium and MAPK signaling pathways might play a pivotal role in regulating the immune response of boron-treated ostriches.

Boron Affects the Development of the Kidney Through Modulation of Apoptosis, Antioxidant Capacity, and Nrf2 Pathway in the African Ostrich Chicks

The nuclear-related factor 2 (Nrf2) pathway is the most important mechanism in antioxidant capacity, which regulates the cell's redox homeostasis. In addition, Nrf2 pathway also can inhibit cell apoptosis. The mechanism of boron actions on various organs is well documented. But, it is not known whether boron can also regulate the Nrf2 pathway in the kidneys. Therefore, in this research, the actions of boron on the kidneys of ostrich chicks, especially the antioxidant effects, have been studied. The ostrich chicks were divided into six groups and supplemented with boric acid (BA) (source of boron) in the drinking water (0, 40, 80, 160, 320, 640 mg respectively) to examine apoptotic, antioxidant, biochemical, and histochemical alterations induced by boron administration in the ostrich chick's kidney. The cellular apoptosis was assessed by terminal deoxynucleotidyl transferase dUTP Nick-End Labeling (TUNEL) assay. The relative antioxidant enzymes (T-AOC, MDA, GSH-Px, SOD, GR, CAT) and biochemical indices (ALT, AST, ALP, CK, LDH, BUN, CREA, UA) in the kidney were determined by spectrophotometric method. The expression of three important genes in the antioxidant pathway (Nrf2, HO-1, GCLc) was measured by quantitative real-time PCR (qPCR), and the localization of key regulator Nrf2 was examined by immunohistochemistry (IHC) method. Western blotting was also performed to further validate our results. Our results revealed that low doses of boron (up to 160 mg) had positive effect, while high doses (especially 640 mg) caused negative effect on the development of the kidney. The cellular apoptosis was in a biphasic manner by altering the boron quantities. The low doses regulate the oxidative and enzyme activity in the kidney. The IHC and western blot showed maximum localization of Nrf2 in 80 mg/L BA dose group. Furthermore, supplementation of boron at low doses upregulated the expression of genes involved in the antioxidant pathway. Taken together, the study demonstrated that low levels of boron (up to 160 mg) inhibited the cell apoptosis, regulate the enzyme activity, and improved the antioxidant system, thus may encourage the development of the ostrich chick's kidney, while a high amount of boron especially 640 mg/L promoted cell apoptosis and reduced the antioxidant capacity, thus caused negative effect to the ostrich chick's kidney.

Effects of Boron Supplementation on Expression of Hsp70 in the Spleen of African Ostrich

Increased synthesis of heat shock protein 70 (Hsp70) occurs in prokaryotes and eukaryotes in response to physiological, environmental, and chemical exposures, thus allowing the cell survival from fatal conditions. Hsp70 cytoprotective properties may be clarified by its anti-apoptotic function. Boron has been reported to play an essential role in various organ developments and metabolisms. However, it is not known if boron is also able to modulate the Hsp70. In the present study, the actions of boron on ostrich spleen and expression level of Hsp70 were investigated. Thirty healthy ostrich chicks were randomly assigned to six groups: groups I, II, III, IV, V, and VI and fed the basal diet spiked with 0-, 40-, 80-, 160-, 320-, and 640-mg boric acid (BA)/L, respectively, in drinking water. The histomorphological examination in the spleen was done by hematoxylin and eosin (HE) staining. The expression level of Hsp70 was analyzed by immunohistochemistry (IHC) and western blotting, and mRNA expression of Hsp70 was investigated by quantitative real-time PCR (qPCR). In order to investigate apoptosis, TUNEL assay reaction in all treatment groups was analyzed. Our results showed that the histological structure of spleen up to 160 mg/L BA supplementation groups well developed. The Hsp70 expression level first induced at low-dose groups (up to group IV) and then inhibited dramatically in high-dose groups (V and VI) while comparing with the group I (0 mg BA). The TUNEL assay reaction revealed that the cell apoptosis amount was decreased in group IV, but in group V and especially in group VI, it was significantly increased (P < 0.01). Taken altogether, proper dietary boron treatment might stimulate ostrich chick spleen development by promoting the Hsp70 expression level and inhibiting apoptosis, while a high amount of boron supplementation would impair the ostrich spleen structure by inhibiting Hsp70 expression level and promoting cell apoptosis.

Effect of Boric Acid Supplementation on the Expression of BDNF in African Ostrich Chick Brain

The degree of brain development can be expressed by the levels of brain brain-derived neurotrophic factor (BDNF). BDNF plays an irreplaceable role in the process of neuronal development, protection, and restoration. The aim of the present study was to evaluate the effects of boric acid supplementation in water on the ostrich chick neuronal development. One-day-old healthy animals were supplemented with boron in drinking water at various concentrations, and the potential effects of boric acid on brain development were tested by a series of experiments. The histological changes in brain were observed by hematoxylin and eosin (HE) staining and Nissl staining. Expression of BDNF was analyzed by immunohistochemistry, quantitative real-time PCR (QRT-PCR), and enzyme linked immunosorbent assay (ELISA). Apoptosis was evaluated with Dutp-biotin nick end labeling (TUNEL) reaction, and caspase-3 was detected with QRT-PCR. The results were as follows: (1) under the light microscope, the neuron structure was well developed with abundance of neurites and intact cell morphology when animals were fed with less than 160 mg/L of boric acid (groups II, III, IV). Adversely, when boric acid doses were higher than 320 mg/L(groups V, VI), the high-dose boric acid neuron structure was damaged with less neurites, particularly at 640 mg/L; (2) the quantity of BDNF expression in groups II, III, and IV was increased while it was decreased in groups V and VI when compared with that in group I; (3) TUNEL reaction and the caspase-3 mRNA level showed that the amount of cell apoptosis in group II, group III, and group IV were decreased, but increased in group V and group VI significantly. These results indicated that appropriate supplementation of boric acid, especially at 160 mg/L, could promote ostrich chicks' brain development by promoting the BDNF expression and reducing cell apoptosis. Conversely, high dose of boric acid particularly in 640 mg/L would damage the neuron structure of ostrich chick brain by inhibiting the BDNF expression and increasing cell apoptosis. Taken together, the 160 mg/L boric acid supplementation may be the optimal dose for the brain development of ostrich chicks.

Relationships among plumage coloration, blood selenium concentrations, and immune responses of adult and nestling tree swallows

In a number of taxa, males and females both display ornaments that may be associated with individual quality and could be reliable signals to potential mates or rivals. We examined the iridescent blue/green back and white breast of adult tree swallows (Tachycineta bicolor) to determine if plumage reflectance was related to adult or offspring immune responses. We simultaneously addressed the influence of blood selenium levels and the interaction between blood selenium and plumage coloration on adult and nestling immunity. Selenium is a well-known antioxidant necessary for mounting a robust immune response but its importance in wild birds remains poorly understood. In females, the brightness of white breast coloration was positively associated with bactericidal capacity, but there was no association with blood selenium. In contrast, male bactericidal capacity was associated with an interactive effect between dorsal plumage coloration and blood selenium concentrations. Males with bluer hues and greater blue chroma showed increased bactericidal capacity as blood selenium concentrations increased, while bactericidal capacity declined in greener males at higher blood selenium concentrations. In nestlings, bactericidal capacity was positively associated with nestling blood selenium concentrations and white brightness of both social parents. These results suggest that white plumage reflectance is indicative of quality in tree swallows and that greater attention should be paid to the reflectance of large white plumage patches. Additionally, the role of micronutrients, such as selenium, in mediating relationships between physiology and signals of quality, should be explored further.

Genetic and environmental variation in condition, cutaneous immunity, and haematocrit in house wrens

BACKGROUND

Life-history studies of wild bird populations often focus on the relationship between an individual's condition and its capacity to mount an immune response, as measured by a commonly-employed assay of cutaneous immunity, the PHA skin test. In addition, haematocrit, the packed cell volume in relation to total blood volume, is often measured as an indicator of physiological performance. A multi-year study of a wild population of house wrens has recently revealed that those exhibiting the highest condition and strongest PHA responses as nestlings are most likely to be recruited to the breeding population and to breed through two years of age; in contrast, intermediate haematocrit values result in the highest recruitment to the population. Selection theory would predict, therefore, that most of the underlying genetic variation in these traits should be exhausted resulting in low heritability, although such traits may also exhibit low heritability because of increased residual variance. Here, we examine the genetic and environmental variation in condition, cutaneous immunity, and haematocrit using an animal model based on a pedigree of approximately 2,800 house wrens.

RESULTS

Environmental effects played a paramount role in shaping the expression of the fitness-related traits measured in this wild population, but two of them, condition and haematocrit, retained significant heritable variation. Condition was also positively correlated with both the PHA response and haematocrit, but in the absence of any significant genetic correlations, it appears that this covariance arises through parallel effects of the environment acting on this suite of traits.

CONCLUSIONS

The maintenance of genetic variation in different measures of condition appears to be a pervasive feature of wild bird populations, in contradiction of conventional selection theory. A major challenge in future studies will be to explain how such variation persists in the face of the directional selection acting on condition in house wrens and other species.