Effects of exogenous gonadotropic and steroid hormones on the social behaviour and gonadal maturation of male domestic ducklings Anas platyrhynchos L.

Male domestic ducklings were injected during their first month of life with mammalian gonadotrophins (ovine LH or FSH, HMG) or gonadal steroids (testosterone or oestradiol). LH and testosterone stimulated sexual behaviour while oestradiol inhibited the increase of aggression observed in control birds during the experiment. The mammalian gonadotrophins did not increase plasma testosterone but nevertheless they all stimulated the testis growth. Several hypotheses which could explain this finding (stimulation of spermatogenesis without any apparent effect on testosterone) are discussed and the possibility of a direct action of LH on the sexual behaviour is analysed. Social displays were only moderately stimulated by testosterone and not at all by gonadotrophins. The hormonal controls of these behaviour patterns remains thus largely unknown.     

Ontogeny of deep-body cold sensitivity in Pekin ducklings Anas platyrhynchos

The ontogeny of deep-body cold sensitivity was studied in 1 to 12 days old Pekin ducklings Anas platyrhynchos. Deep-body cold sensitivity was determined by means of thermodes implanted in the abdominal cavity. The thermodes were perfused with cold water for 15-min periods to lower the core temperature. Cooling of the body core elicited increases in metabolic rate and vasoconstrictions in the legs of all the ducklings. From the changes induced in metabolic rate and core temperature, deep-body cold sensitivity values of between −5.17 and −6.36 W · kg⁻¹ · °C⁻¹, were estimated. These values, which are in the range of those reported previously for adult Pekin ducks, did not change with age, and it is concluded that deep-body cold sensitivity is fully developed at hatching. Our next aim was to investigate whether the autonomic responses elicited by exposure of ducklings to cold ambient conditions could be explained by temperature changes within the body core. During cold exposure, the increase in metabolic rate was not accompanied by a concomitant decrease in core temperature. On the contrary, deep-body temperature increased slightly during the initial phase of cold exposure. The ducklings attained a metabolic rate amounting to 85–90% of their peak metabolic rate before the core temperature fell below the regulated level measured at thermoneutrality. Thus, despite the findings that Pekin ducklings have a highly-developed deep-body cold sensitivity, their metabolic cold defence under natural conditions seems to be mediated primarily by peripheral thermoreceptors. Accepted: 7 January 1997     

Behavioural and morphological effects of testosterone and gonadotropins in the young male domestic duck (Anas platyrhynchos L.)

Young male domestic ducks 20–72 days old were successively injected with two hormonal preparations. The first hormone treatment included males injected with testosterone propionate (TP), human chorionic gonadotropin (HCG), pregnant mare serum (PMS), control oil injected males (C) and males injected with TP and submitted at the same time to a permanent intense light. During the second hormonal treatment all males except controls were injected with TP.Almost no behavioural effects were observed in any group of males following the first treatment. The second one, however, induced intense social display and sexual behaviour in the four TP-injected groups. Some qualitative and quantitative differences were found between groups according to the first hormone treatment to which they had been submitted. This suggests a possible role of gonadotropic hormones in the control of social behaviour in ducks. Experimental data supporting this hypothesis are briefly reviewed and discussed.     

Directional bias as a component of social behaviour with special reference to the Mallard, Anas platyrhynchos

Three types of "shake", given by male Mallards, Anas platyrhynchos, during Social Display, exhibit a crious "directional bias" in that the first sideways turn of the head tends to be made towards one of the females present. An investigation of the phenomenon by means of film suggests that directional bias reliably reflects a male's "interest" in a particular female. Evolutionary implications and the possible role of directional bias in social communication are briefly discussed.     

Survival of Mallard ducklings Anas platyrhynchos and competition with fish for invertebrates on a flooded gravel quarry in England

The survival of Mallard Anas platyrhynchos ducklings was studied on a complex of flooded gravel quarries in England and their weight changes in response to invertebrate predation by fish were studied by experiment. The majority of duckling loss occurred during the first 12 days after hatching but those feeding on the river where fish were scarce survived better than those feeding on lakes where fish density was high. Duckling mortality was higher in broods with large home ranges. In the experimental trials an increase in fish density was related to a reduction in both the number of emerging invertebrates and the biomass of aquatic macrophytes. Ducklings feeding in these ponds travelled further and gained less weight than on the pond with a low fish density where the number of emerging invertebrates was higher.     

Effects of intracranial implants of testosterone propionate on intermale aggression in the castrated male mouse

Three experiments were conducted in order to assess the effects of intracranial implants of testosterone propionate (TP) on intermale aggression in the castrate male CF-1 mouse. In Experiment 1, seven groups received bilateral implants containing a total of 27 μg crystalline TP into the septum, neocortex, lateral ventricles, preoptic-anterior hypothalamus, hippocampus, medial reticular formation, and subcutaneously, and were tested 2 and 4 days after treatment. An eighth group received blank pellets in the brain. Animals receiving septal or lateral ventricle implants fought significantly more than other groups on trial 1. This difference had disappeared by trial 2, indicating diffusion of the hormone. The diffusion was corroborated by significant seminal vesicle growth. In Experiment 2 animals received bilateral implants of a total of 4.5 μg TP in paraffin or a blank pellet into the septum, preoptic-anterior hypothalamus, cortex, amygdala, olfactory bulbs, medial reticular formation, or subcutaneously. None of these treatments proved effective for activating aggression. Experiment 3 explored the activational effects of 10 μg of TP implanted bilaterally into the same areas as in Experiment 2, excluding the olfactory bulbs and cortex. Implants into the septum were followed by significantly increased fighting. Implants into the preoptic area were only marginally effective whereas the remaining two areas were not responsive to hormone treatment and did not differ from control animals. No seminal vesicle growth was detected as a result of the hormone treatments. These results would indicate that the septum is important in the control of androgen-dependent, intermale aggression in the male CF-1 mouse.     

Effects of testosterone propionate, prolactin and photoperiod on feeding behaviours of Indian male weaver birds.

Testosterone propionate (TP) is not associated with the total food consumption of the male weaver bird. Reproductively active birds maintained under long daylength eat continuously however under short daylength they eat in 2-3 peaks and are also reproductively quiescent. Results show that total food consumption is independent of length of photoperiod/reproductive states of the bird, perhaps associated with the caloric demand of the bird. Prolactin (PRL) stimulates the testicular development of the bird. PRL induced weight loss does not involve decrease food intake as there is no change in the total food consumption of the bird and therefore, reflects the improper utilization of the food. This hormone alters the feeding behaviour from cyclic (2-3 peaks) to continuous pattern.     

Daily variations of behavioural activities and of plasma testosterone levels in the domestic duck Anas platyrhynchos

The daily variation of various behavioural activities and of plasma testosterone levels have been studied simultaneously in two groups of five domestic ducks. The social displays and sexual behaviour are essentially exhibited by the birds during the early morning (and to a lesser extent in the late afternoon for major displays). The morning corresponds precisely with the highest testosterone levels observed in the blood. As testosterone propionate injections are known to elicit social displays and sexual behaviours in ducks, it is suggested that the correlation observed between the variations of testosterone levels and of behaviour could be due to a direct effect of the variations of hormone levels on behaviour. The theoretical possibility of such a short-term hormonal effect is briefly discussed.     

Serum estradiol, testosterone and dihydrotestosterone in male monkeys treated with testosterone propionate.

Serum estradiol (E2), testosterone (T) and dihydrotestosterone (DHT) were measured in juvenile (pre-pubertal) male rhesus monkeys injected with either 8 mg or 80 mg of testosterone propionate (TP). After one week, the three steroids were elevated and remained essentially unchanged for the duration of the study. There was little difference in serum E2 or DHT when comparing the two groups of steroid-treated monkeys. In contrast, T levels were consistently greater in the animals given the high dosage of TP.     

Effect of implanting bull calves with testosterone propionate, dihydrotestosterone propionate or oestradiol-17 beta prepubertally on the pituitary-testicular axis and on postpubertal social and sexual behaviour.

Twelve non-implanted crossbred bull calves served as controls and 30 crossbred bull calves (10/treatment) were implanted for 82 days, beginning at 34 days of age, to determine the influence of testosterone propionate (TP), dihydrotestosterone propionate (DHTP) and oestradiol-17 beta (E2) on prepubertal and pubertal pituitary-testicular function and on postpubertal social and sexual behaviour. Compared with control bulls, concentrations of serum luteinizing hormone (LH), follicle-stimulating hormone (FSH) and inhibin concentrations were suppressed (P less than 0.01) in all implanted bulls. Testosterone (T) concentration increased (P less than 0.001) in TP-implanted, but decreased (P less than 0.01) in DHTP and E2 bulls during the implant period. LH response to gonadotrophin-releasing hormone (GnRH) challenge during the implant period (2.5 months of age) was less (P less than 0.01) in TP, E2 and DHTP bulls than in controls. A small but significant T response to GnRH occurred in control bulls at 2.5 months of age. LH and T responses to GnRH challenge at 7 months of age (100 days after implant removal) was similar (P greater than 0.20) in control and implanted bulls. Steroid implants administered prepubertally had no effect (P greater than 0.10) on postpubertal social and sexual behaviours, including number of flehmen responses, abortive mounts, services and competitive order score. Body weight did not differ (P greater than 0.10) between treatment groups, but testis size was reduced (P less than 0.01) during the implant period and up to 10 months of age in treated bulls compared with controls. Testes remained smaller in E2-treated bulls up to the end of the study (23 months of age), but daily sperm production and epididymal weight did not differ (P greater than 0.10) between treatment groups at slaughter. Control bulls reached puberty earlier (P less than 0.01; 270 +/- 11 days of age) than did TP (302 +/- 11 days), DHTP (309 +/- 11 days) or E2 (327 +/- 11 days) bulls. Although puberty was delayed in all implant groups, there was no difference in scrotal circumference at puberty (average 28.4 +/- 0.4 cm) between treatment groups. Our findings indicate that TP, DHTP and E2 implants administered prepubertally result in acute suppression of serum LH, FSH and inhibin during the implant period and in post-implant suppression of testis size and delayed puberty in bulls. The lack of treatment effect on behaviour suggests that steroidal programming of sexual behaviour occurs before 1 month of age in bulls.     

It's just ducky to be clean: the water repellency and water penetration resistance of swimming mallard Anas platyrhynchos ducklings

Ducklings reared by a hen swim with dry plumage a day or two after hatching, while incubator-hatched ducklings of the same age may sink and even drown when placed in water. The common interpretation is that wild-reared chicks receive preen oil from the parent, and this oil makes them more waterproof. Using mallard ducklings Anas platyrhynchos we tested the effect of preen and other oils, as well as hydrophilic or surfactant contaminants, on the water resistance of down. We found that the true cause for the difference between incubator and hen-reared ducklings is the presence of hydrophilic hatching fluid residues in the down of incubator-hatched ducklings. Once well rinsed and dried, incubator-hatched ducklings can swim for over an hour with essentially dry down. Other tests showed that clean down is quite water resistant, and that water resistance was not improved by preen or other oils. Small amounts of preen or other oils had no effect on water repellency or wetting during surface swimming. However, oil decreased the hydraulic pressure needed to penetrate down. Down lacks the stabilizing interlocking structure of adult contour feathers, and small amounts of oil apparently cause barbules to stick together and reduce the effective number of down fibers. Detergent decreases water repellency and increases water retention, and has a more severe effect on oiled down or when applied in combination with oil. The penetration pressure of a clean down coat, 866±154 Pa, could allow static immersion to ca. 8cm before water would saturate the down and increase thermal conductance. Thus, clean ducklings have a 2×–3× safety margin for surface swimming. Saturation increases the thermal conductance of the down coat from 14.3±1.38 W/m²-°C to 193±25 W/m²-°C. Thus, water pollution or down contamination causing wetting can significantly increase energy use and the frequency of hypothermia.     

Effects of ingested lead on antibody production in mallards (Anas platyrhynchos)

We examined the effects of lead ingestion on in vitro and in vivo indices of immune function in mallards (Anas platyrhynchos). Twenty-four mallard drakes were randomly divided into three groups (I, II, III), then assigned to treatment or control subgroups (n = 4). On day 0, all treatment birds were dosed orally with one number 4 lead shot (mean = 0.2 g). We challenged all individuals in each group with washed sheep red blood cells (SRBC) injected intraperitoneally on days 0 (Group I), 7 (Group II) or 14 (Group III), and collected blood for analyses 7 and 8 days after SRBC challenge. We measured and compared blood lead concentrations, in vitro lymphocyte transformation responses to phytohemagglutinin A and lipopolysaccharide, and hemagglutination titers to SRBC. Mean blood lead concentrations were elevated (P less than or equal to 0.04) in treatment birds at each sampling period. Large individual variability in lymphocyte stimulation responses precluded further analysis of those data. Hemagglutination titers to SRBC were lower (P less than 0.0001) in lead-poisoned ducks than in controls, suggesting that ingested lead may have immunosuppressive effects on mallards.     

Effects of testosterone propionate and dihydrotestosterone on penile morphology and sexual reflexes of spinal male rats

Testosterone propionate (TP) has a quantitative influence on sexual reflexes mediated at the spinal level in male rats. The possibility that this influence reflects the direct action of androgen on neural elements in the cord, rather than on sensory receptors in the penis was examined indirectly by the use of dihydrotestosterone (DHT). Spinal castrated male rats maintained initially on TP and then switched to DHT showed a significant decline in sexual reflexes paralleling the decline of another group of spinal rats receiving no hormone after initial TP treatment. Yet the number of penile papillae and weight of the penile shaft for the DHT subjects were not significantly different from these measures of penile morphology in a third group of subjects receiving continuous TP and in which reflexes did not decline. These and other observations are consistent with the hypothesis that neural elements within the spinal cord, related to the mediation of the ejaculatory pattern in intact male rats, are directly influenced by gonadal androgen.