The role of steroid hormones in protogynous sex change in the Blackeye goby, Coryphopterus nicholsii (Teleostei: Gobiidae).

To detect and describe correlations between steroid concentrations and sexual function in the protogynous Coryphopterus nicholsii, we examined whole-body concentrations of the gonadal steroids testosterone (T), 11-ketotestosterone (11-KT), and 17beta-estradiol (17beta-E2). Our results show that T, 11-KT, and 17beta-E2 are naturally occurring steroids in both female and male C. nicholsii. Further, mean whole-body concentrations of T and 11-KT in males were approximately twice those in females, whereas mean whole-body concentration of 17beta-E2 in females was almost twice that in males. Second, we tested hypotheses on the causation of sex change arising from these correlations between steroid concentrations and sexual function. We examined the effects of administration of 11-KT, 11-KA, 17alpha-methyltestosterone, and an aromatase inhibitor (Fadrozole) on gonadal structures of mature females. Complete sex change was induced by 11-KT, 11-KA, and Fadrozole. Our results strongly suggest that an increase in 11-KT concentration and perhaps also a decrease in 17beta-E2 concentration are involved in mediating natural sex change in C. nicholsii.

PCPA increases aggression in male firemouth cichlids.

We observed the effect of the 5-hydroxytryptamine synthesis inhibitor p-chlorophenylalanine on aggression in male firemouth cichlids (Cichlasoma meeki). p-Chlorophenylalanine-treated firemouths showed a significantly greater number of mirror-directed bites as compared with saline-injected controls. This finding is consistent with the effects of this drug on social aggression in mammals and birds and supplements previous reports that 5-hydroxytryptamine inhibits aggression in fish.

Effect of dominance status on sex hormone levels in laboratory and wild-spawning male trout.

We investigated the relationship between male social status and hormone levels in salmonids spawning under laboratory and field conditions. In small groups of rainbow trout (Onchorhynchus mykiss) spawning in the laboratory, dominant males had higher plasma levels of testosterone (T) and 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17,20 beta-P) compared with subordinates. Steroid levels increased in subordinate males that became dominant after dominant males were experimentally removed; higher steroid levels in dominant males appears to be a result rather than a cause of their social status. In free-ranging brown trout (Salmo trutta) sampled in the field, we found higher levels of 11-ketotestosterone (11KT) but not T in dominant males. No significant differences in levels of either androgen were found between dominant and subordinate male brook trout (Salvelinus fontinalis) sampled at the same field location. Furthermore, in marked contrast with the laboratory fish, there were no significant differences in plasma 17,20 beta-P between dominant and subordinate males in either species of fish in the wild. The different findings in the laboratory and field may indicate species differences in behavioral endocrinology among brook, brown, and rainbow trout. Alternatively, the greater differential in hormonal profile of dominant and subordinate males in the laboratory may reflect the relative uniformity of the laboratory environment; this simple environment may allow competitively superior males to more completely dominate less competitive tank-mates and to exclude them from female sexual cues. In any case, these results suggest that the relationship between steroid hormones and spawning behavior in male salmonids is likely more complex than suggested by experiments conducted solely on laboratory-held rainbow trout.

Stimulation of spawning behavior in castrated rainbow trout (Oncorhynchus mykiss) by 17 alpha,20 beta-dihydroxy-4-pregnen-3-one, but not by 11-ketoandrostenedione.

The onset of spawning behavior in male salmonids can be closely correlated to circulating levels of the progestin 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (20-P). However, evidence that 20-P plays a causal role in the development and maintenance of spawning behavior in male salmonids is largely lacking. The purpose of this study was to investigate the effect of 20-P implants on the spawning behavior in castrated rainbow trout in the presence of a sexually active female. Mature rainbow trout were placed in five experimental groups: sham-operated and castrated implanted with either Silastic capsules containing 20-P, 11-ketoandrostenedione (11-KA), 11-KA + 20-P or empty capsules. Five to 6 weeks after implantation, all males were tested individually in a stream channel in the presence of a nesting ovulated female. Following behavioral observations, blood samples were taken from all tested males. Implants of 20-P and 11-KA resulted in increased plasma levels of 20-P and 11-ketotestosterone, respectively. Sham males exhibited the strongest behavioral response, both in the frequency of quiver bouts and attention toward the female. Castrated controls and 11-KA males showed no quiver response and reduced attention toward the female, while the behavioral responses shown by the 20-P and 20-P/11-KA males were intermediate. The results indicate that 20-P, but not 11-androgens, plays a significant role in the stimulation of spawning behavior in male rainbow trout.

Endocrine changes associated with spawning behavior in male kokanee salmon (Oncorhynchus nerka) and the effects of anosmia.

This study examines the relationship between social status, behavioral activity, and hormone levels through the spawning cycle in male kokanee salmon (Oncorhynchus nerka). Shortly after arrival at the spawning grounds, male kokanee undergo dramatic changes in morphological and physiological condition: there is an increase in body depth, a bright silvery appearance is replaced by an intense red coloration, and spermiation commences. Males become associated with nesting females which they defend against other males. The androgens, testosterone and 11-ketotestosterone, decline slowly over the spawning period from high levels observed in the silvery males; gonadotropin (GtH II) and 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one increase as males approach final maturation. Androgen and GtH levels in males placed in pens with females over the spawning bed were higher than those in males penned without females. Among males competing for females, amounts of milt and plasma concentrations of GtH were higher in those males that were successful in gaining access to nesting females. A marked reduction in milt and plasma hormones following cauterization of the olfactory nares indicates that olfactory stimuli play a role in mediating endocrine and spermiation responses to the nesting females. Anosmic males were less vigorous and persistent in their courtship, suggesting that, either a female pheromone and/or high levels of hormone are necessary to maintain full reproductive behavior in male kokanee. The role of socially induced hormone changes in modulating reproductive behavior is discussed.

The significance of olfaction and social cues in milt availability, sexual hormone status, and spawning behavior of male rainbow trout (Oncorhynchus mykiss).

Male rainbow trout orientate to a "releaser" pheromone emitted by an ovulated female. This chemical signal is not necessary for the completion of spawning behavior: anosmic males spawned as readily as intact males when paired with ovulated females. The amount of "strippable" milt and plasma concentrations of testosterone (T) and 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta-P) were greater in males paired for 3 hr with ovulated females than in isolated males, or males placed with nonvitellogenic adult females or in all male groups. Milt and plasma T, 17,20 beta-P, and 11-ketotestosterone (11-KT) were reduced in anosmic males paired with ovulated females, indicating the existence of a priming pheromone. Milt, T, 11-KT, and 17,20 beta-P increased in intact males within 4 hr after injection of salmon gonadotrophin-releasing hormone analogue, lyophilized salmon pituitary extract, or homogenized fresh rainbow trout pituitary material. The results indicate that the priming pheromone acts through the hypothalamus-pituitary-gonad axis.

Androgen control of social status in males of a wild population of stoplight parrotfish, Sparisoma viride (Scaridae).

In the protogynous stoplight parrotfish (Sparisoma viride), large males defend territories that encompass the home-ranges of several mature females. However, high-quality habitat is in short supply, such that smaller, competitively inferior males do not defend territories. We investigated the role of 11-ketotestosterone (11KT) and testosterone (T) in the regulation of territorial behavior in a wild population of a protogynous reef fish, the stoplight parrotfish, at Glover's Reef, Belize. Radioimmunoassay of plasma samples from individuals of known social status revealed that nonterritorial males have lower levels of T and 11KT than territorial males. Nonterritorial males allowed access to vacant territories underwent pronounced increases in T and 11KT. When sampled 1 week after territory acquisition, levels of T and 11KT in new territorial males were significantly higher than the levels in established territorial males, but by 3 weeks after territory acquisition, there was no significant difference. We further investigated the hypothesis that such short-term increases in androgen levels are a response to intense male-male interactions during territory establishment. Simulated territorial intrusion promoted increased plasma levels of both T and 11KT while access to vacant territories without neighboring territorial males did not. These findings suggest that the endocrine system plays a role in fine-tuning the levels of territorial aggression exhibited by male stoplight parrotfish. We discuss these results in light of recent theory in behavioral endocrinology.

Hormonal control of sex and color change in the stoplight parrotfish, Sparisoma viride.

The stoplight parrotfish, Sparisoma viride, changes sex from female to male. In most cases, sex change is accompanied by dramatic change in coloration, from the female-like "initial phase" coloration to "terminal phase" coloration that is associated with males. However, some males do not change color at the same time they change sex, becoming female-mimic males (termed initial phase males). Using radioimmunoassays validated here for use with plasma from S. viride, we examined the hormonal profile of stoplight parrotfish undergoing sex change. As predicted, females were characterized by undetectable levels of 11-ketotestosterone (11KT), moderate levels of testosterone, and high levels of 17 beta-estradiol (E2). Fish that were found histologically to be undergoing sex change had elevated levels of 11KT and decreased levels of E2. Testosterone appeared to be unaffected. Males had the highest levels of 11KT and testosterone and low levels of E2. Because initial phase males eventually change color, we were able to take blood samples from males (sex confirmed histologically) before, during, or after color change. Thus, we also examined the hormonal correlates of color phase change. Initial phase males, like females, had undetectable levels of 11KT, moderate levels of testosterone, and significantly higher levels of E2 than either terminal phase males or males with transitional coloration. During color transition, 11KT levels rose sharply and levels of E2 declined. Males with terminal phase coloration had the highest levels of 11KT and testosterone and low levels of E2. Finally, administration of 11KT induced precocious sex change and color change in functional adult females. These findings suggest that 11KT plays a key role in instigating natural sex and color change, but that once sex change is complete, 11KT is not necessary for spermatogenesis or spawning behavior.

Endocrine changes associated with spawning behavior and social stimuli in a wild population of rainbow trout (Salmo gairdneri). I. Males.

Rainbow trout (Salmo gairdneri) were collected from a natural spawning population at Pennask Lake, B.C. Blood samples were taken from male trout at different stages of spawning and assayed by radioimmunoassay for gonadotropin (GtH), testosterone (T). 11-ketotestosterone (11-KT), and 17 alpha-hydroxy-20 beta-dihydroprogesterone (17,20-P). Testosterone and 11-KT were detected in the plasma of males in spawning condition: 11-KT was at a higher concentration than T and declined to undetectable levels in postspawning fish. There were striking increases in plasma GtH and 17,20-P in males actively courting nest building females. The increase in 17,20-P was evidently not dependent upon an elevation of the pituitary hormone: 17,20-P remained low in males placed with sexually inactive, unovulated females even though GtH levels rose above levels measured in males isolated from females. The significance of the social control of hormone levels is not clear. There is some evidence that 17,20-P and/or GtH may cause an increase in quantity of the milt, and thus the endocrine response to a sexually active female may serve to synchronize maximum male fertility with oviposition readiness in the female.

Endocrine changes associated with spawning behavior and social stimuli in a wild population of rainbow trout (Salmo gairdneri). II. Females.

Rainbow trout (Salmo gairdneri) were collected from a natural spawning population at Pennask Lake, B.C. Blood samples taken from female trout at different stages of spawning were assayed by radioimmunoassay for gonadotropin (GtH), estradiol-17 beta (E2), androgens, including testosterone (T), and 17 alpha-hydroxy-20 beta-dihydroprogesterone (17,20-P). Plasma levels of androgen and estradiol were highest in females sampled shortly before ovulation ("green" females) and declined in ovulated and sexually active females, reaching lowest levels in postspawning fish. Concentrations of 17,20-P rose markedly in ovulated females allowed to dig nests and interact with sexually active males. Plasma GtH levels were similar in green unovulated females and ovulated fish prevented from spawning, but showed a marked increase in actively nest building ovulated fish. The results demonstrate that social stimuli affect plasma levels of 17,20-P and perhaps GtH. The functional significance of the endocrine responses to social factors is not clear, but it is suggested that increased hormone levels may contribute to an acceleration or synchronization of breeding, or be responsible for causing and maintaining more vigorous sexual activity.

The effects of early and late androgen treatments on the behavior of Sarotherodon mossambicus (Pisces: Cichlidae).

Groups of Sarotherodon mossambicus were treated with androgen by immersion or oral treatment at various stages of development. Fish were allowed to mature and the effects of treatment on gonadal and behavioral differentiation were examined. The effects of treatment on gonadal differentiation were assessed by determining the sex ratio for each group. Three treatments resulted in sex ratios significantly different from the 1:1 sex ratio obtained in untreated fish. Behavioral differences were detected between groups of males in three measures of territorial defense and aggression, and differences were detected between groups of females in two measures of male-female courtship interaction. A second experiment determined that early-treated females were more sensitive to a second androgen treatment later in life than females not exposed to androgen during development. A number of sex-reversed genetic females functioning as males were detected in two treatment groups with predominantly male sex ratios. There were no differences in the behavior of sex-reversed and non-sex-reversed male fish from the same treatment group. This study establishes that hormone treatments administered during development influence behavioral differentiation in a teleost.

The effects of photoperiod on androgen-induced reproductive behavior in male ring doves, Streptopelia risoria.

The effect of photoperiod on reproductive behavior in male ring doves (Streptopelia risoria) was studied in androgen-injected castrates maintained under long (16L:8D) or short (86:16D) photoperiods. Behavioral recordings were made over a 2-week period during which each male was paired with a female for 6.5 hr/day. There was some indication that males held on long days display higher levels of courtship activity during the initial period following pairing, but the evidence was not conclusive. Day length had no effect upon copulatory behavior. Long-day males exhibited consistently higher levels of nest building than short-day males, indicating that photoperiod affects building through some mechanism other than changes in endogenous androgen levels.

The role of estrogen and progesterone in the regulation of reproductive behaviour in female ring doves(Streptopelia risoria) under long vs. short photoperiods.

PIP: The role of estrogen and progesterone in the regulation of reproductive behavior was studied in female ring doves (Streptopelia risoria) under long vs. short photoperiods. The doves held under long (16 hours/day) or short (8 hours/day) photoperiods were treated for 15 days with saline, estrogen, or progesterone, alone or in combination. 7 days after the start of hormone therapy, the doves were placed with reproductively active males for 4 hours/day for 9 days. No difference was seen in egg-laying, courtship or nest-building by control birds under the 2 photo regimes. Ovarian follicles remained small in all doves receiving hormone treatment. Oviducts of doves receiving progesterone alone remained small in the short-photoperiod group but at long photoperiods the oviducts became enlarged. Estrogen stimulated oviduct growth at both photoperiods wheras the combined hormone treatment resulted in greater oviduct development than estrogen alone (p less than .02). Female soliciting and nest-building activity remained low in progesterone-treated doves under short photoperiod but increased rapidly under long photoperiod. Doves treated with estrogen and estrogen plus progesterone performed considerable soliciting and nest-building. No marked tendency was seen for doves under long-photoperiod conditions to be more active in nest-oriented behavior. Copulatory behavior by the female occurred infrequently in all hormone-treated doves.^ieng