Interspecific variation in egg testosterone levels: implications for the evolution of bird song

Although interspecific variation in maternal effects via testosterone levels can be mediated by natural selection, little is known about the evolutionary consequences of egg testosterone for sexual selection. However, two nonexclusive evolutionary hypotheses predict an interspecific relationship between egg testosterone levels and the elaboration of sexual traits. First, maternal investment may be particularly enhanced in sexually selected species, which should generate a positive relationship. Secondly, high prenatal testosterone levels may constrain the development of sexual characters, which should result in a negative relationship. Here we investigated these hypotheses by exploring the relationship between yolk testosterone levels and features of song in a phylogenetic study of 36 passerine species. We found that song duration and syllable repertoire size were significantly negatively related to testosterone levels in the egg, even if potentially confounding factors were held constant. These relationships imply that high testosterone levels during early development of songs may be detrimental, thus supporting the developmental constraints hypothesis. By contrast, we found significant evidence that song-post exposure relative to the height of the vegetation is positively related to egg testosterone levels. These results support the hypothesis that high levels of maternal testosterone have evolved in species with intense sexual selection acting on the location of song-posts. We found nonsignificant effects for intersong interval and song type repertoire size, which may suggest that none of the above hypothesis apply to these traits, or they act simultaneously and have opposing effects.     

Dynamics of biochemical components, lipid classes and energy values on gonadal development of R. philippinarum associated with the temperature and ingestion rate

This study evaluates the effect of temperature, coupled with ingestion rate, on the dynamics of biochemical components and lipid classes in R. philippinarum. The data are discussed with regard to sexual development and energy balance. Experimental protocol developed in the present study used two groups of the clam R. philippinarum: L (temperatures of 14 degrees C and 18 degrees C) and H (temperatures of 18 degrees C and 22 degrees C). The intra-group ingestion level was similar, although the ingestion level of the clams in the group H was 2.4 times higher than group L. We observed that R. philippinarum conditioned at 18 degrees C (18L) shows higher protein content, furthermore an important loss of organic weight was observed after 48 days. In such a situation, the clams use their own reserves (carbohydrates and glycogen) for sexual development while in situations without food stress (positive energy balance) and low temperature (14 degrees C) an accumulation of reserves is produced. Strikingly dissimilar behaviour in biochemical composition was observed for the 18H and 22H treatments, both with a positive energy balance. Despite similar protein content, the highest levels of carbohydrates were observed at the lower temperature (18 degrees C). Glycogen was also higher for the 18 degrees C treatment, although the differences were significant only in the males. Although the total lipids in R. philippinarum showed no significant differences in any treatment, they became apparent and related to sex when considering the individual lipid classes. There was no variation in lipid classes in the males between the 14L and 22H treatments despite the large disparity in the degree of sexual development. However, in the females significant differences in lipid classes (phospholipids, triglycerides) were observed. The results of this study show that a positive energy balance permits R. philippinarum gonadal development and accumulation of reserves both in low and high temperature conditions. In low temperature situations, gonadal development is slower and the energy reserves are accumulated in the form of carbohydrates. When the clams are conditioned at high temperatures, gonadal development is fast and complete, carbohydrates are consumed and lipids are accumulated.     

Social cues elicit sexual behavior in subordinate Damaraland mole-rats independent of gonadal status

Damaraland mole-rats (Fukomys damarensis) are among a small number of eusocial mammals. Eusociality is a social system where only a few individuals within a colony engage in direct reproduction, while remaining subordinate members are non-breeders and support reproductive efforts of breeding individuals. Inbreeding avoidance precludes mating between subordinate siblings and between offspring and parents. Interestingly, non-breeders readily attempt to mate with unrelated opposite-sex individuals. This is unusual since the non-breeding females do not attain puberty while in their natal colony. Based on this finding, the present study investigated the role of the gonads in the regulation of mating behaviors in this species and identified the mechanism of inbreeding avoidance. Gonadal-intact and gonadectomized non-breeders from different colonies were removed from their colonies and tested for the expression of sexual behavior. Results indicated that gonadal status had only minor effects on the expression of sexual behavior in either males or females. In a second experiment, sexual behaviors were absent between opposite-sex siblings so long as they had frequent contact with each other; however, following 5 weeks of separation, sexual behavior between these siblings was robustly expressed. Thus, Damaraland mole-rats avoid establishing mating relationships with familiar individuals but will readily mate with unfamiliar individuals of the opposite sex, with genetic relatedness apparently playing little role. The initiation of sexual behavior in Damaraland mole-rats does not require the presence of the gonads, but does require that the members of the pair have not been in contact with one another for at least several weeks.     

Differential responsiveness of prostatic acid phosphatase and prostate-specific antigen mRNA to androgen in prostate cancer cells

Androgens regulate the expression of both human prostatic acid phosphatase (PAcP) and prostate-specific antigen (PSA), two major prostate epithelium-specific differentiation antigens. Due to the important role of these two enzymes as prostate epithelium differentiation markers, we investigated their regulation of expression at the mRNA level in LNCaP human prostate carcinoma cells. Interestingly, phenol red, a pH indicator in the culture medium, promoted cell growth. To eliminate this non-specific effect, a phenol red-free, steroid-reduced medium was utilized. When high-density cells were grown in that medium, 5alpha-dihydrotestosterone (DHT) suppressed PAcP but stimulated PSA. However, tumor promoter phorbol ester 12-o-tetradecanoyl phorbol-13-acetate (TPA) functioned as a potent inhibitor of both PAcP and PSA expression. Prolonged treatment with DHT as well as TPA resulted in a similar down-regulation of protein kinase C and cellular PAcP activities. Thus, the levels of PAcP and PSA mRNA are differentially regulated by androgens in LNCaP cells.     

Gonadectomy reveals sex differences in circadian rhythms and suprachiasmatic nucleus androgen receptors in mice

In mammals, it is well established that circadian rhythms in physiology and behavior, including the rhythmic secretion of hormones, are regulated by a brain clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus. While SCN regulation of gonadal hormone secretion has been amply studied, the mechanisms whereby steroid hormones affect circadian functions are less well known. This is surprising considering substantial evidence that sex hormones affect many aspects of circadian responses, and that there are significant sex differences in rhythmicity. Our previous finding that "core" and "shell" regions of the SCN differ in their expression of clock genes prompted us to examine the possibility that steroid receptors are localized to a specific compartment of the brain clock, with the discovery that the androgen receptor (AR) is concentrated in the SCN core in male mice. In the present study, we compare AR expression in female and male mice using Western blots and immunochemistry. Both of these methods indicate that ARs are more highly expressed in males than in females; gonadectomy eliminates and androgen treatment restores these sex differences. At the behavioral level, gonadectomy produces a dramatic loss of the evening activity onset bout in males, but has no such effect in females. Treatment with testosterone, or with the non-aromatizable androgen dihydrotestosterone, restores male locomotor activity and eliminates sex differences in the behavioral response. The results indicate that androgenic hormones regulate circadian responses, and suggest an SCN site of action.     

蓝太阳鱼第一次性周期性腺发育的组织学

蓝太阳鱼(Lepomis cyanellus)是广东省于1997年从北美引进的小型淡水鱼类,本文采用组织切片技术对蓝太阳鱼的性腺发育进行了研究。蓝太阳鱼的性腺发育程序可以分为5个时期。在1月龄,卵巢和精巢处于第Ⅰ期;2~3月龄时,卵巢和精巢发育到第Ⅱ期;4月龄时发育到第Ⅲ期;5~6月龄时发育到第Ⅳ期;7~8月龄时达到性成熟第Ⅴ期。过冬时,卵巢退化到第Ⅱ~Ⅲ期,而精巢仍停留在第Ⅴ期。成熟卵巢的成熟系数为2.80%~8.10%,成熟精巢的成熟系数为1.45%~3.45%。精巢和卵巢发育都为不完全同步型,且精巢发育比卵巢稍快。蓝太阳鱼的繁殖期在广州地区为3~11月,为多次产卵类型。本文从生殖和生长的关系上对蓝太阳鱼生长缓慢的原因进行了初步探讨,并将蓝太阳鱼作为一种鱼类实验动物的可行性进行了分析。     

南方鲶性腺分化的组织学观察

用芳香化酶抑制剂(Fadrozole)、雌激素受体拮抗剂(Tamoxifen)对人工孵化的南方鲶(Silurus meridionalis)幼鱼进行雄性化诱导处理(口服),获得雄鱼。对孵化后第5—130d的南方鲶幼鱼性腺进行组织学观察,结果表明,在实验条件下,南方鲶性腺分化发生在孵化后7d左右,雌雄性分化过程差异明显。雌鱼卵巢腔在孵化后12d左右形成,生殖细胞在孵化后35d左右快速增殖,成熟分裂最早发生在孵化后55d左右;雄鱼生殖细胞在孵化后130d左右快速增殖,成熟分裂最早发生在孵化后130d左右。雌性性腺分化早于雄性。     

Effect of paired encounters on plasma androgens and behaviour in males and females of the spiny damselfish Acanthochromis polyacanthus

Sexually mature male and female spiny damselfish, Acanthochromis polyacanthus (Pomacentridae) were introduced to resident fish of both sexes in paired encounter trials and the effect on activity, agonistic behaviour and plasma levels of testosterone (T) and 11-ketotestosterone (11-KT) in males, and T and 17β-estradiol (E₂) in females, and cortisol in both sexes was determined. Introduced males showed suppressed levels of T in the presence of both resident males and females, whereas resident males showed elevated T in response to introduced males but not females. Plasma 11-KT levels were unchanged in either resident or introduced males. Resident males showed increased activity in the presence of males but not females. Resident females showed an increase in activity when paired with introduced females and greater aggressive behaviour towards females than males. There were no differences in plasma hormone levels in either resident or introduced female fish. Plasma cortisol levels were low in all fish and stress effects did not appear to account for differences in T levels in males. The results of the present study show that elevations in plasma T levels in resident male spiny damselfish are associated only with male presence but that suppression of T in introduced fish occurs irrespective of the sex of the resident. In contrast resident females, which show stronger evidence of aggressive behaviour do not show changes in plasma androgen levels. This suggests that aggressive behaviour in male and female fishes may be mediated by different endocrine pathways.     

Within-clutch patterns of yolk testosterone vary with the onset of incubation in black-headed gulls

Hatching asynchrony in birds produces an age and size hierarchyamong siblings. Later-hatching chicks have a competitive disadvantage,and brood reduction may occur when food availability is insufficientto raise all chicks. When early-hatched chicks fail to surviveor if the circumstances allow raising all chicks, mothers shouldreverse the disadvantage to later-hatched chicks. Increasingdeposition of maternal androgens with the laying sequence hasbeen suggested to compensate for detrimental effects of hatchingasynchrony, allowing a more precise adjustment of the survivalprobabilities of each chick. Here, we show for black-headedgulls that the increase in yolk testosterone with each successiveegg is greater when the mother incubates longer before clutchcompletion, which is the major determinant of the degree ofhatching asynchrony. This finding supports the idea that yolktestosterone has a compensatory function in the context of hatchingasynchrony. Our data further show that if the time needed tocomplete a clutch is lengthened, the developmental differencesdue to incubation between the first- and the last-laid eggsincrease. In addition, the onset of incubation before clutchcompletion occurs sooner as the breeding season progresses.Both long inter-egg intervals and the seasonal shift in incubationbehavior enhance the necessity of compensation for later-hatchingchicks. Indeed, yolk levels of testosterone increased more steeplyover the laying order, if the duration of the egg-laying periodwas extended and in later-laid clutches. We suggest that prolactinplays a key role in the adjustment of testosterone allocationto the incubation pattern.