Differences In Testosterone Concentrations Research Articles

Age-Related Differences in Testosterone Concentration and Its Relation to Testicular Biometrics, Hemodynamics, and Fertility in Alpacas (Vicugna pacos).

The goal of this study was to investigate the age-related differences in testosterone concentration and its relation to testicular biometrics, testicular blood flow, and fertility in alpacas (Vicugna pacos). Fifteen alpaca males with different ages (young (YM; ~12-14 mo.), n = 5; intermediate (IM; ~24 mo.), n = 5; and old (OM; ≥36 mo.), n = 5) were enrolled in the study. Blood samples were taken from each alpaca male and the circulating plasmatic testosterone concentration (TC; ng/mL) was determined using ELISA analysis. The testicular traits related to bio-morphometric parameters (the length (L), width (W), area (A), and volume (TV)) were assessed using B-mode ultrasonography. Pulse-wave/power Doppler ultrasonography was used to obtain the circulatory dynamic values (testicular hemodynamics) before the beginning of natural service mating. Significant differences were observed in TC among the age groups, increasing as the age of the males increased (2.47 ± 0.31, 8.45 ± 1.53, and 22.66 ± 2.15 for YM, IM, and OM, respectively; p < 0.05); however, no differences were observed regarding the testicular B-mode ultrasonographic parameters (L, W, and A) (p > 0.05). Positive correlations were observed between TV and testicular L, W, and A (r = 0.96, r = 0.95, and r = 0.96, respectively; p ≤ 0.001). Pulse-wave-Doppler-derived parameters such as the pulsatility index (PI) and the resistive index (RI), as well as the total vascularity area (TVA) assessed by power Doppler, were similar in all of the age groups studied (p > 0.05). General linear model (GLM) analysis showed a relationship between TC and TV (OR = 0.95; p = 0.04), as well as between TC and TVA (OR = 0.99; p= 0.02). Finally, no differences were observed regarding the pregnancy rate among the different age groups (p > 0.05). In conclusion, TC increased as the age of the alpaca males increased. Although TC was related to TV and TVA, the pregnancy rates obtained from individuals belonging to the different age groups were similar, indicating that TC, TV, and TVA were not determining factors in assessing the potential age-related fertility differences in alpaca males.

CANNIBALISM PERFORMANCE OF ASIAN REDTAIL CATFISH (Hemibagrus nemurus) FED RATION SUPPLEMENTED WITH DIFFERENT DOSES OF 17α-METHYLTESTOSTERONE

One of the obstacles in Asian redtail catfish hatchery is the high cannibalism incidence. Cannibalism is associated with aggressive behavior caused by hormonal metabolism especially of testosterone. The purpose of this study was to evaluate the effect of testosterone administration on the cannibalism incidence in the Asian redtail catfish juveniles. The experiment was conducted by rearing fish with initial length of 4.09±0.19 cm in 16 of 20 L aquariums with a density of 2 fish L-1. The experiment was designed with a completely randomized design with 4 treatments which were different level of 17α-methyltestosterone supplementation in feed, i.e., 0 mg kg-1 feed (A) as control, 7.5 mg kg-1 feed (B), 15 mg kg-1 feed (C), and 30 mg kg-1 feed (D). Each treatment has 4 replications. Fish fed experimental diet (40% protein) 4 times a day to satiation for 30 days. The parameters observed were type and index of cannibalism, aggressive behavior, survival rate, normal mortality, growth performance, hormones concentrations (estradiol, testosterone, and cortisol), and water quality. The results showed that cannibalism type II (the fish eaten completely or missing) and cannibalism index increased with the increasing doses of testosterone administration in the feed with the highest cannibalism incidence was 40.63%. The highest survival rate was found in treatment B (73.75±2.50%) and was not significantly different from the control treatment (69.38±2.39%). No differences in testosterone concentration and in the growth performance among the treatments. However, there was a trend of decrease in the estradiol concentration of Asian redtail catfish juveniles fed ration supplemented with the increasing doses of 17α-methyltestosterone. Based on the results obtained in this research, estradiol changed in the body's plasma, it appears that there was a role for plasma estradiol concentration in controlling cannibalism of Asian redtail catfish juveniles. It concluded that the testosterone administration affected the cannibalism incidence in the Asian redtail Catfish.

Ethnic differences in serum testosterone concentration among Malay, Chinese and Indian men: A cross-sectional study.

To investigate non-urological patients with multiple comorbidities for factors contributing towards differences in testosterone concentration in multiethnic Malaysian men. An observational study. Sexually active men, ≥40 years, with no known urological problems, were recruited at the phlebotomy clinic at our centre. A brief history along with latest fasting lipid profile and plasma glucose levels were obtained. An Aging Male Symptoms questionnaire was administered; waist circumference (WC) and serum testosterone concentration were measured. Analysis of testosterone concentration between Malay, Indian and Chinese men was performed. Statistical tests such as analysis of variance, χ2 test, univariate and multivariable regression were performed. Any p < .05 was noted as statistically significant. Among the 604 participants analysed, mean testosterone concentration was significantly lower in Malays (15.1 ± 5.9 nmol/L) compared to the Chinese (17.0 ± 5.9 nmol/L) and Indian (16.1 ± 6.5 nmol/L) participants. The mean WC was also found to be higher among the Malays (96.1 ± 10.9 cm) compared to Chinese (92.6 ± 9.6 cm) and Indians (95.6 ± 9.9 cm). Testosterone concentration tended to be lower with higher age, but this was not statistically significant (p > .05). In the multivariable analysis only Malay ethnicity, WC ≥ 90 cm and low high-density lipoprotein (HDL) were associated with lower testosterone concentration. In this study, Malaysian men of Malay origin had lower testosterone concentration compared with Indian and Chinese men. WC and low HDL were also associated with lower testosterone concentrations.

Determining the Effects of Serial Injections of Pregnant Mare Serum Gonadotropin on Plasma Testosterone Concentrations, Testicular Dynamics, and Semen Production in Leopard Geckos (Eublepharis macularius).

Simple SummaryCurrent estimates have determined that one in five reptile species are already threatened with extinction. The aim of this study was to determine if pregnant mare serum gonadotropin could be used in leopard geckos (Eublepharis macularius) to stimulate the production of sperm and increase their testosterone concentrations. This information may aid in the development of breeding programs for endangered gecko species in the future that will be useful for conservation efforts. Our results demonstrated that this hormone did stimulate sperm production and increased testicular size in leopard geckos. However, it did not increase testosterone concentrations under the current conditions between October–December in the Northern hemisphere. Ultimately, future studies are needed to further characterize the annual reproductive cycle of leopard geckos.Reptiles are highly susceptible to anthropogenic activities as a result of their narrow geographical ranges and habitat specialization, making them a conservation concern. Geckos represent one of the mega-diverse reptile lineages under pressure; however, limited assisted reproductive technologies currently exist for these animals. Exogenous pregnant mare serum gonadotropin (PMSG) has been found to exhibit follicle stimulating hormone-like action and has been routinely used to alter reproductive hormones of vertebrates in assisted reproductive protocols. The purpose of this study was to determine the effects of serial injections of 20 IU and 50 IU PMSG on circulating testosterone concentrations, testicular dynamics, and semen production in a model species of gecko. Twenty-four captive-bred, adult, male leopard geckos (Eublepharis macularius) were divided into three treatment groups and administered a once-weekly injection of either PMSG or saline for a total of nine weeks. Ultrasonographic testicular measurements, electrostimulation for semen collection, and venipuncture were performed on days 0, 21, 42, and 63. Right unilateral orchidectomies and epididymectomies were performed in all animals on day 63; tissues were submitted for histopathology. PMSG treated geckos had significantly higher testicular volumes and weights, spermatozoa motility, and spermatozoa concentrations compared with controls. However, there were no significant differences in testosterone concentrations by treatment or time. Under the conditions outlined, PMSG is effective at stimulating spermatogenesis and increasing testicular size, but not effective at increasing testosterone concentrations in the leopard gecko between October–December in the Northern hemisphere.

EFECT OF INTENSIVE PHYSICAL LOADS ON TESTOSTERONE, CORTISOL AND INSULIN BLOOD CONCENTRATIONS IN ELITE ATHLETES

The aim of the work was to investigate the effect of intense physical activity on testosterone, cortisol and insulin blood concentration in elite athletes. The study was conducted with the participation of 26 elite athletes of endurance events. This study assessed the resting hormones concentration before exercise and acute response of hormones concentration after intensive physical loads. The influence of intensive physical loads with different direction (strength and speed vs incremental load to VO2 max achievement) was investigated.&#x0D; The average values of total testosterone in blood serum, measured at rest state before exercise were 28,2 nmol·l-1, 40 minutes after exercise – 19,2 nmol·l-1. The mean concentration of cortisol was 506,2 nmol·l-1, after physical activity – 518,1 nmol·l-1. The average value morning insulin concentration was 6,6 μIU·l-1, after loading 5,6 μIU·l-1. It was established a significant (p = 0.001) decrease of the total testosterone concentration after intensive physical loads; the registered changes in the blood cortisol and insulin concentrations were not statistically significant. A significant correlation was established (p ≤ 0.05) between the maximum oxygen consumption (VO2max, ml·min·kg-1) and testosterone concentration (r = 0.76 resting morning concentration, r = 0.87 after intensive physical loads), cortisol (r = 0.69) and insulin (r = 0.51) after exercising.&#x0D; It was established the differences in testosterone concentration due intensive physical loads with various direction (strength and speed vs incremental load to VO2 max achievement). The significant difference of cortisol and insulin concentration depending the physical test was not found in this study.

Can maintenance intake reduce production costs without compromising the reproductive performance in bucks?

Excessive intake of nutrients can result in decreases in the reproductive efficiency of goat bucks and increase production costs in goat e nterprises. In this study, the aim was to compare the reproductive features of young bucks fed diets for maintenance of growth or were fed ad libitum. Ten bucks were used (n = 5/group), with a completely randomized design. Blood and semen were collected from each animal every 2 weeks for nine collections. Semen was frozen and later analyzed using flow cytometry to compare reactive oxygen species, plasma membrane integrity, acrosome integrity, and membrane lipid peroxidation. Body condition score, sexual behavior, testicular biometry and histomorphometry of the testis, as well as oxidative enzymes and carbonylated proteins, were also evaluated. Animals fed ad libitum had a greater body condition score (3.32 + 0.08 × 2.88 + 0.05), sperm volume (0.68 + 0.04 × 0.52 + 0.03 mL), and testis circumference (25.2 + 0.21 × 24.5 + 0.24 cm) and volume (121 + 5.83 × 107 + 4.38 cm³, left testicle; 116 + 5.26 × 100 + 3.75 cm³, right testicle). Ejaculates of the bucks fed diets to maintain growth rate had a larger number of minor and total sperm morphology defects. There were no differences in testosterone concentrations and sexual behavior. In conclusion, there can be feeding for growth rate maintenance instead of ad libitum feeding, for the reduction in production costs of young bucks without compromising semen quality and reproductive functions.

Differences in the thermal sensitivity and seminal quality of distinct ovine genotypes raised in tropical conditions

For different ovine breeds to maximize their reproductive capacity in countries with tropical climate, it is important to evaluate their potential for thermal resilience and consequences on their reproductive traits. Therefore, the objective of this study was to evaluate the effect of thermal environment temperatures of climate seasons in a tropical climate region on the surface temperatures of the scrotum, testicular biometric characteristics, seminal quality and serum testosterone concentration of rams of different genotypes. Breeders of four different genotypes (Dorper, n = 8, Texel, n = 8, Santa Inês, n = 9 and Morada Nova, n = 8) were used throughout the four climate seasons. Higher thermal challenge was recorded in the spring and summer. In the summer increase in scrotal surface temperature was detected by infrared thermography (P < 0.05), mainly in the regions of the distal testicular pole and tail of the epididymis. The animals of the Texel genotype had higher rectal temperature in the summer. In spring, this genotype also had the highest testicular pole (32.2 ± 0.5 °C; P < 0.05) and distal (29.9 ± 0.4 °C; P < 0.05) temperatures and a higher mean testicular temperature (31.7 ± 0.4 °C; P < 0.05). The Morada Nova genotype showed a higher surface temperature gradient between testicular poles (2.96 ± 0.1 °C; P < 0.05), especially in spring. Genotype-dependent thermal sensitivity was detected for the thermal gradient between the testicular poles, reflecting the seminal quality. There was a positive correlation of the thermal gradient between testicular poles with sperm membrane integrity and negative correlation with total sperm defects. The Texel genotype showed less progressive motility and higher percentage of sperm defects. There was no difference in testosterone concentration between genotypes and in the different seasons (P > 0.05). Thus, the indigenous genotypes showed a greater capability to maintain the scrotum-testicular thermoregulation. Dorper animals resembled the indigenous sheep genotypes, in terms of seminal characteristics, unlike Texel animals, which showed lower adaptability and lower seminal quality.

Calcium chloride combined with dimethyl sulphoxide for the chemical sterilization of dogs.

The aim of this study was to evaluate the effect of intratesticular injection of calcium chloride (CaCl2 ) combined with dimethyl sulphoxide (DMSO) as a chemical sterilization in dogs. Twelve dogs were divided into two groups: the treated group (n=6), in which 15mg/kg of a 7.5% CaCl2 solution combined with 0.5% DMSO was injected into each testicle (volume range 1.0-4.76ml); and a control group (n=6) that received the same volume/kg of 0.9% sodium chloride solution (NaCl). Semen characteristics pre- and post-treatment were evaluated. Serum testosterone concentration was determined before the injection (D-1) and at 15 (D15), 30 (D30) and 60 (D60) days after intratesticular injection. Testicle sizes and local pain were evaluated for 7 consecutive days (D1 to D7) and at D15, D30 and D60 after injection. At D60, testicle histological evaluation was performed after orchiectomy. No pain was observed by testicular palpation, with the exception of one dog in the treated group; this dog then received analgesic therapy. An increase in testicular volume was evident within 24hr after treatment, followed by gradual reduction for 3weeks. Five of 6 dogs from the treated group presented azoospermia at D15; the remaining dog presented at D30. There was no significant difference in testosterone concentrations in the treated group during the experimental period. Histological evaluation showed testicular degenerative lesions, especially at the proximal and middle portions. The results indicated that one injection of 7.5% CaCl2 combined with 0.5% DMSO into each testis is a viable alternative for canine sterilization.

No relationship between autistic traits and salivary testosterone concentrations in men from the general population.

It is suggested that testosterone may play a part in the higher prevalence of Autism Spectrum Disorder (ASD) in males compared to females. Previous studies have reported elevated postnatal testosterone levels in children and women with ASD but not in men. We compared levels of salivary testosterone across 67 undergraduate males (Mage 19.5 yrs, SD 1.92) selected for low, mid-range and high levels of autistic traits assessed using the Autism-spectrum Quotient. Analyses revealed no significant differences in testosterone concentrations across the three groups. The current data add to the increasing evidence for the lack of relationship between autistic traits and postnatal levels of testosterone in men.

Pubertal changes in testicular parameters and secretion of testosterone in Najdi and Naemi ram lambs under desert conditions

The present work was conducted to elucidate the relationships between chronological age, testosterone concentration and testis size of Najdi and Naemi ram lambs under desert conditions to determine the reproductive capacity of the above two breeds. The postnatal development of the seminiferous epithelium of the testes was also monitored. A total of 90 (45 Najdi and 45 Naemi lambs) aged between one and nine months, with five lambs at each month of age for each breed were used. The results showed that the testosterone concentration increased dramatically and rapidly between five and six months, followed by a period of gradual growth where testicular size was increased from 3 to 6 months of age. There was a significant (P > 0.05) difference in testosterone concentration (TC) and testis size (TS) in ram lambs between different age groups, similarly there were significant differences between body weights and lamb age between one and nine months. A positive correlation between the increasing body weight and the size of the testicle was observed. The testicles of lambs at each age-group had a different histological appearance except those of Najdi lambs at 2, 3 and 4 months and Naemi lambs at 2, 3, 4 and 5 months, where few differences were apparent. Small quantities were of spermatozoa appeared at the eighth month of age and increased in the ninth month. In conclusion, the current findings indicate that puberty in Najdi and Naemi rams occurs at the 8th and 9th month of age, respectively.

Pubertal changes in testicular parameters and secretion of testosterone in Najdi and Naemi ram lambs under desert conditions

The present work was conducted to elucidate the relationships between chronological age, testosterone concentration and testis size of Najdi and Naemi ram lambs under desert conditions to determine the reproductive capacity of the above two breeds. The postnatal development of the seminiferous epithelium of the testes was also monitored. A total of 90 (45 Najdi and 45 Naemi lambs) aged between one and nine months, with five lambs at each month of age for each breed were used. The results showed that the testosterone concentration increased dramatically and rapidly between five and six months, followed by a period of gradual growth where testicular size was increased from 3 to 6 months of age. There was a significant (P &gt; 0.05) difference in testosterone concentration (TC) and testis size (TS) in ram lambs between different age groups, similarly there were significant differences between body weights and lamb age between one and nine months. A positive correlation between the increasing body weight and the size of the testicle was observed. The testicles of lambs at each age-group had a different histological appearance except those of Najdi lambs at 2, 3 and 4 months and Naemi lambs at 2, 3, 4 and 5 months, where few differences were apparent. Small quantities were of spermatozoa appeared at the eighth month of age and increased in the ninth month. In conclusion, the current findings indicate that puberty in Najdi and Naemi rams occurs at the 8th and 9th month of age, respectively.

Age-Related Variations in Comparative Testosterone Concentrations Between Boys with Autism Spectrum Disorder and their typically-Developing Peers: A Challenge to the ‘Extreme Male Brain’ Hypothesis of ASD

There is some disagreement in the literature regarding the presence of elevated testosterone concentrations in boys with Autism Spectrum Disorder (ASD). To explore that disagreement, the presence of significant differences in testosterone concentrations in young males with Autism Spectrum Disorder (ASD) and normally developing controls aged 6 yr. to 17 yr. was investigated. A total of 136 young males with ASD and 48 age-matched non-ASD males contributed samples of saliva at a set time and these were assayed for testosterone concentrations. There was no significant difference in testosterone concentrations between the two entire samples. When examined at two-yearly intervals, ASD participants had significantly lower testosterone concentrations at age 12 yr. to 13 yr. and also exhibited relatively homogeneous testosterone concentrations compared to non-ASD participants. These data challenge the ‘extreme male brain’ hypothesis for ASD and suggest that ASD young males were delayed in their pubertal development and that the developmental variability expected in the wider population was not present.

Comparing the Natural and Anthropogenic Sodium Channel Blockers Tetrodotoxin and Indoxacarb in Garter Snakes.

Synthetic chemicals, such as pesticides, are used in a variety of ways in the agricultural industry. Anthropogenic chemicals pose a unique challenge to organisms because of the lack of evolutionary history between the chemical and the organism. However, research has shown that some organisms have a resistance to these synthetic chemicals due to their evolved resistance to a natural compound with a similar structure or mode of action. Indoxacarb (INDOX) is a relatively new pesticide with a similar mode of action to that of tetrodotoxin (TTX). Tetrodotoxin is a naturally occurring toxin that is used as an antipredator defense in the rough-skinned newt (Taricha granulosa). Some populations of the common garter snake (Thamnophis sirtalis) have developed a resistance to tetrodotoxin. Here, we investigated the correlation between TTX and INDOX resistance in snakes. We hypothesized that INDOX would induce a much higher stress response than the naturally occurring TTX. We injected each snake with tetrodotoxin (1 mass-adjusted mouse unit). We did the same with mass-adjusted units of INDOX. We measured corticosterone, testosterone, and bactericidal ability. Our results show an acute stress response to INDOX, but not TTX through an elevate corticosterone and innate immune response, although there was no difference in testosterone concentration. These results suggest that, although INDOX may have a similar mechanism of action, garter snakes do not react in a similar manner as to TTX. This research gives a physiological perspective on the differences between naturally occurring compounds and synthetic compounds.

Circadian variations in peripheral levels of growth hormone and testosterone in male Murrah buffaloes

The aim of this study was to investigate the endocrine profiles of growth hormone (GH), testosterone and their interrelationship in prepubertal, pubertal and orchiectomised male Murrah buffaloes under starving conditions. The prepubertal and pubertal buffaloes were subjected to frequent blood sampling over 24 h at an interval of 1 h, whereas in orchiectomised buffaloes, the blood samples were collected over 18 h. Irrespective of group, the GH concentrations fluctuated in an episodic manner over 24 h and the fluctuations did not exhibit a consistent pattern between the animals of each group. The mean basal and peak concentrations of GH did not differ significantly (p > 0.05) among the groups. A significant (p > 0.0001) difference in testosterone concentrations was observed between prepubertal and pubertal groups. The differences in mean basal and peak testosterone concentrations between the prepubertal and pubertal groups were also significant (p < 0.01). The associations between testosterone and GH levels in both prepubertal (r = 0.15; p > 0.05) and pubertal (r = −0.37; p > 0.05) buffaloes were non-significant. The possible reasons for erratic episodic pattern of GH secretion will be discussed.

Individual Differences in Testosterone Predict Persistence in Men

Persistence is an important predictor of future successes. The present research addresses the relationship between testosterone and persistence in men. One hundred eighteen men were randomly assigned to win or lose a competitive number tracing task against a confederate or complete the task alone in a non–competitive control condition. Saliva samples were collected prior to and after the competition or control conditions. Participants were then given a maximum time of 30 min to spend attempting to solve unsolvable puzzles, with the option to quit at any time. In contrast to our prediction, changes in testosterone concentrations in response to the competitive interaction did not predict persistence behaviour. However, individual differences in testosterone concentrations (pre–competition/non–competition) were positively correlated with persistence. These findings are the first to examine associations between neuroendocrine function and persistence behaviour in people and suggest that testosterone should also be considered when predicting persistence–related outcomes. Copyright © 2014 European Association of Personality Psychology

The order effect of combined endurance and strength loadings on force and hormone responses: effects of prolonged training

To examine acute responses and recovery of force and serum hormones to combined endurance and strength loadings utilizing different orders of exercises before and after training. Physically active men were matched to an order sequence of endurance followed by strength (E + S, n = 12) or strength followed by endurance (S + E, n = 17). The subjects performed one experimental loading consisting of steady-state cycling and a leg press protocol before and after 24 weeks of order-specific combined training. No between-group difference in acute reductions of force was observed at week 0 (E + S -23 %, p < 0.001; S + E -22 %, p < 0.01) and 24 (E + S -25 %, p < 0.001; S + E -27 %, p < 0.001) and recovery in force was completed after 24 h in both groups at week 0 and 24. Concentrations of growth hormone (22-kDa) increased post-acute loading at week 0 (E + S, +57 fold, p < 0.05; S + E, +300 fold, p < 0.001; between-groups p < 0.001) and 24 (E + S, +80 fold, p < 0.01; S + E, +340 fold, p < 0.05; between-groups p < 0.05). No significant acute responses in concentrations of testosterone were observed at week 0 or 24. However, at week 0 testosterone was reduced during recovery following the E + S loading only (24 h -23 %, p < 0.01; 48 h -21 %, p < 0.001; between-groups at 24 and 48 h, p < 0.05), but was no longer observed after training. 1RM strength improved similarly in E + S (13 %, p < 0.001) and S + E (17 %, p < 0.001). This study showed an order effect (E + S vs. S + E) in concentrations of testosterone during 2 days of recovery at week 0, which was diminished after 24 weeks of training. The initial difference in testosterone concentrations during recovery did not seem to be associated with strength development.

Testosterone concentrations in young healthy us versus Chinese men

Previous small studies examining differences in testosterone concentrations by ethnicity found mixed results for Caucasians and Chinese men, which might be confounded by age differences and living standards. The aim of the present study is to examine the differences in total, free, and bioavailable testosterone concentrations between healthy young men from the United States (US) and from the most economically developed part of China, i.e., Hong Kong (HK). Cross-sectional analysis based on 365 young men from the Third National Health and Nutrition examination Survey (NHANES III) in the US and 299 Chinese men recruited from university students. All participants were aged from 18 to 29 years. Main outcome measures were total testosterone (TT) and calculated bioavailable testosterone (Bio T) and free testosterone (FT). In both US and Chinese men, TT, FT, and Bio T concentration peaked at 20-24 years of age, at 23.19, 0.49, and 12.23 nmol/l in US men, and 20.72, 0.48 and 12.59 nmol/l in Chinese men, respectively. Among those aged 18-24 years, after adjusting for age, US men had higher TT (mean, 95% confidence interval: 21.64, 21.31-21.99 versus 20.20, 20.12-20.28 nmol/l), but not FT (0.47, 0.47-0.48 versus 0.47, 0.47-0.47 nmol/l) or Bio T (11.90, 11.83-11.97 versus 12.39, 12.35-12.42 nmol/l) than Chinese men. TT, but not FT or Bio T concentrations are lower in young healthy Chinese men than US men. These differences apparent in young men may be important in understanding different patterns of diseases between Western and Asian populations.

Does heterosexual experience matter for bucks' homosexual mating behavior?

Abstract Our aim was to compare bucks' homosexual mating behavior after mixing 2 groups of bucks, one that was reared in permanent contact and another in complete isolation from female goats, and determine if this behavior was related with testosterone concentration. Two groups of 1-year-old Saanen bucks were reared in permanent contact with 4 adult females until 1 week before the experiment (n = 8; group RF) or isolated from females (n = 9; group RI). When bucks were 1 year old, both groups were mixed (day 0), and mount attempts and matings were recorded on days 1, 3, 6, and 9. Testosterone concentrations were determined by radioimmnoassay from blood samples collected twice daily on days −7, 0, 1, 3, 6, and 9. Each RI male attempted to mate more RF than RI males (31.9 ± 5.1% vs. 16.7 ± 3.6%, respectively; P = 0.01), but there was no difference on the frequency in which RF males attempted to mate RI (19.4 ± 0.1%) or RF (11.1 ± 0.1%) males ( P = 0.24). Similarly, RI males mated more RF than RI males (12.5 ± 2.9% vs. 5.6 ± 0.02%, respectively; P = 0.04). Furthermore, there was no difference on the frequency in which RF males mated RI (10.7 ± 8.9%) or RF (3.6 ± 0.02%) males ( P = 0.23). Testosterone concentrations tended to be greater in RF than RI ( P = 0.054), but no interaction between time and group was observed ( P = 0.13). We propose that as RI bucks never had contact with females, they directed their sexual behavior toward other males that had the stimulating effect of the novelty. On the other hand, for RF bucks, although the novelty effect of the new bucks existed, the previous knowledge of females determined that other bucks were not considered as highly sexual attractive. This difference was not related to the differences in testosterone concentration.

Experimental induction of social instability during early breeding does not alter testosterone levels in male black redstarts, a socially monogamous songbird

Testosterone plays an important role in territorial behavior of many male vertebrates and the Challenge Hypothesis has been suggested to explain differences in testosterone concentrations between males. For socially monogamous birds, the challenge hypothesis predicts that testosterone should increase during male–male interactions. To test this, simulated territorial intrusion (STI) experiments have been conducted, but only about a third of all bird species investigated so far show the expected increase in testosterone. Previous studies have shown that male black redstarts (Phoenicurus ochruros) do not increase testosterone during STIs or short-term male–male challenges. The aim of this study was to evaluate whether black redstarts modulate testosterone in an experimentally induced longer-term unstable social situation. We created social instability by removing males from their territories and compared the behavior and testosterone concentrations of replacement males and neighbors with those of control areas. Testosterone levels did not differ among replacement males, neighbors and control males. Injections with GnRH resulted in elevation of testosterone in all groups, suggesting that all males were capable of increasing testosterone. We found no difference in the behavioral response to STIs between control and replacement males. Furthermore, there was no difference in testosterone levels between replacement males that had expanded their territory and new-coming males. In combination with prior work these data suggest that testosterone is not modulated by male–male interactions in black redstarts and that testosterone plays only a minor role in territorial behavior. We suggest that territorial behavior in species that are territorial throughout most of their annual life-cycle may be decoupled from testosterone.

Testosterone and year-round territoriality in tropical and non-tropical songbirds

Past studies have suggested a fundamental difference in testosterone concentrations between tropical and northern latitude male birds, with the convention being that males in the tropics express much lower levels of testosterone. However, recent comparative studies have shown that tropical males with a short and synchronous breeding season (i.e. a breeding season typical of northern species) express maximum testosterone levels similar to those of northern latitude birds. Here, we ask the converse: do northern latitude songbirds that express a defining life-history characteristic typical of the tropics, i.e. year-round territoriality, have an annual testosterone profile similar to that of tropical songbirds? For the few year-round territorial species for which data are available, we found that seasonal testosterone profiles and seasonal maxima in plasma testosterone were similar between males of tropical and non-tropical species. For example, males of both groups expressed seasonal maxima during the period when females were fertile, and testosterone levels at this time were similar. In contrast, this and other studies show that species with seasonal territories typically express maximum testosterone levels earlier in the breeding cycle, when territories are first being established. Taken together, we suggest that specific life-history traits may play a more important role in determining testosterone profiles of tropical and non-tropical birds than breeding latitude and encourage further studies to allow for more formal comparisons.