A tradeoff between immunocompetence and sexual ornamentation in domestic fowl.
Females often select their mates on the basis of the size or intensity of sexual ornaments, and it is thought that such traits are reliable indicators of male quality because the costliness of these traits prevents cheating. The immunocompetence handicap hypothesis is a recently proposed mechanistic explanation of these costs and states that males carry ornaments at the expense of their resistance to disease and parasites. The tradeoff between immunocompetence and sexual ornamentation was hypothesized to arise as a consequence of the dual effect of androgens on ornamentation (+) and immune function (-). To test this hypothesis, we compared comb size between male domestic chickens Gallus domesticus of lines divergently selected for antibody responses to sheep erythrocytes (three lines: selected for low response or high response and a control line). The importance of comb size in inter- and intrasexual selection is well established, and comb size is strongly dependent on testosterone level. Comb size was larger in the males of the low line than in the high line, and comb size of control males was intermediate, indicating a tradeoff between ornamentation and immunocompetence. Testosterone (T) levels varied in a similar fashion (TLow > TControl > THigh), suggesting that this hormone could mediate the tradeoff between ornamentation and immunocompetence. These results support the idea that a tradeoff with immune function may constrain the expression of secondary sexual ornaments. (+info)
Inter-ocular interference and circadian regulation of the chick electroretinogram.
Illumination of a chick's eye allows light to pass through to the retina of the contralateral eye. Electroretinographic (ERG) recording employing the scalp or comb as a reference results in shorter implicit time, higher amplitude and lower sensitivity during the day than during the night in a light:dark (LD) cycle and in constant darkness (DD). ERG recordings employing the contralateral eye as reference abolishes rhythmicity or reverses the phase angle (higher amplitudes at night). This is probably due to light transmission through the eyes to elicit visual responses in the reference. The contralateral eye is a poor choice for reference in birds and obscures physiological analyses of clock control of vision. (+info)
Central effects of clonidine 2-(2,6-dichlorophenylamino)-2-imidazoline hydrochloride in fowls.
1 The effects of clonidine infused into the IIIrd cerebral ventricle, the hypothalamus or intravenously were studied on behaviour, electrocortical activity, body, comb and leg temperatures, respiration and carbon dioxide elimination in adult and young fowls (Gallus domesticus). 2 Behavioural and electrocortical slow wave sleep were induced by clonidine infused into IIIrd cerebral ventricle, the hypothalamus or intravenously. Suprisingly, sleep elicited by intravenous clonidine was much longer-lasting than that induced by an identical dose given intraventricularly. 3 Body temperature was lowered by clonidine given intraventricularly or infused into the hypothalamus. Depending on initial comb temperature and ambient temperature, comb temperature was elevated, unaffected or lowered as body temperature fell; temperature of the unfeathered legs also rose as body temperature declined after clonidine. 4 Following clonidine, but before any considerable decline of body temperature, tachypnoea and wing abduction developed; during recovery of body temperature, the wings were lowered and applied closely to the trunk and the feathers partly erected. 5 CO2 elimination fell more swiftly than body temperature following intrahypothalamic clonidine in young chicks; initial recovery developed sooner than that of body temperature, but eventual recovery was delayed compared to that for body temperature. The effects of clonidine were much more marked in young chicks studied at an ambient temperature below thermoneutrality as compared to thermoneutrality. 6 The soporific effects of clonidine were attenuated by intraventricular phentolamine; its hypothermic effects were prevented by phenoxybenzamine and prevented or attenuated by phentolamine. Intraventricular atropine, haloperidol, methysergide and propranolol were ineffective. 7 Larger doses of intraventricular phentolamine elicited shivering, tachypnoea and wing abduction; body temperature was elevated, to the extent even of lethal hyperthermia. Intraventricular atropine also elevated body temperature. 8 Clonidine infused intravenously, intraventricularly or into the hypothalamus, replaced the behavioural and electrocortical arousal evoked with dexamphetamine, by sleep associated with slow wave electrocortical activity. (+info)
Effects of bisphenol-A on the growth of comb and testes of male chicken.
Bisphenol-A (BPA) has been reported to have some xenoestrogenic effects on the reproductive system of male animals. In this study, we examined the growth of combs and testes of the male chickens exposed to BPA. White leghorn male chicks were administered 200 mg BPA orally every week from 2 wk of age. The combs and testes were examined at 16 wk of age. The body growth showed no significant difference between BPA-administered and control birds. However, the weight of the combs and testes were lower in the BPA-treated birds. Histologically, testes of the control birds were well matured; the seminiferous tubuli were filled with sperm. In contrast, the testes of most of the BPA-treated birds showed an immature appearance with smaller seminiferous tubuli and limited spermatogenesis. These findings suggest that the xenoestrogenic property of BPA might disturb the growth of the comb and testes of male chickens by a possible endocrine disrupting mechanism. (+info)
In vivo requirement for silicon in articular cartilage and connective tissue formation in the chick.
Studies were undertaken to determine further effects of silicon deficiency in the chick. The diet and experimental conditions were the same as those used in previous studies to demonstrate the essentiality of silicon for growth and development. Skeletal and other abnormalities involving glycosaminoglycans in formation of articular cartilage and comb connective tissue were found to be associated with silicon deficiency. The bones of 1 day-old deutectomized cockerels fed a silicon supplemented diet and killed at 4 weeks of age had significantly greater amounts of articular cartilage and water as compared with the silicon deficient group and also a greater proportion of hexosamine in the cartilage. The greater water content in bones of the silicon supplemented chicks coincided with a larger content of glycosaminoglycans in the articular cartilage. A similar relationship was obtained in cockerel comb. In addition to larger amounts of connective tissue and of total hexosamine in combs of the supplemented group, a higher percentage of hexosamine and a higher silicon content was found. These findings provide the first evidence for a requirement for silicon in articular cartilage and connective tissue formation and that the site of action of silicon is in the glycosaminoglycan-protein complexes of the ground substance. (+info)
Defective reproductive organ morphology and function in domestic rooster embryonically exposed to o,p'-DDT or ethynylestradiol.
Environmental pollutants with estrogenic activity have a potential to disrupt estrogen-dependent developmental processes. The objective of this study was to investigate if embryonic exposure to the environmental estrogens o,p'-DDT (1-(2-chlorophenyl)-1-(4-chlorophenyl)-2,2,2-trichloroethane; 37, 75, 150 or 300 microg/g egg) and EE2 (17alpha-ethynyl estradiol; 60 ng/g egg) affects the reproductive system in domestic roosters. Following egg injection on Embryonic Day 4, the newly hatched chicks were sexed by cloacal inspection. A skewed phenotypic sex ratio with overrepresentation of chicks deemed as females was observed in the groups exposed to the three highest doses of o,p'-DDT but not in the EE2-exposed group. Normal sex ratios were observed in all groups at adulthood. However, a cloacal deformation seemed to remain in the adult roosters, causing an abnormal semen flow upon semen collection. Semen yield was significantly reduced in both o,p'-DDT-exposed and EE2- exposed birds, whereas semen quality was unaffected. When killed, deformations of the left testis were found in all treatment groups. Image analysis revealed a reduced seminiferous tubular area in the roosters exposed to the two highest doses of o,p'-DDT. Embryonic exposure to o,p'-DDT caused decreased comb weight and right-spur diameter, while EE2 only affected right-spur diameter. In conclusion, this study shows that embryonic exposure to estrogenic compounds can induce permanent effects in male birds. The effects of the two studied compounds were partly similar but o,p'-DDT also induced alterations not seen in the EE2-treated birds. (+info)
Effect of a natural extract of chicken combs with a high content of hyaluronic acid (Hyal-Joint) on pain relief and quality of life in subjects with knee osteoarthritis: a pilot randomized double-blind placebo-controlled trial.