Search

The discovery by Schwabl that maternal steroid hormones are transferred to the egg yolk and have effects on the phenotype of offspring revealed a new pathway for non-genetic maternal effects. The initial model relied on passive transfer. The thinking was that steroids passively entered the lipophillic yolk during yolk deposition and then were deposited in the yolk until they were passively delivered to the embryo as the yolk was used. Subsequent studies revealed that the system is much more dynamic than that. Here, we explore questions about how dynamic the system really is and look at questions like: Is transfer of maternal steroids to the yolk passive or is it actively regulated? At what stages of the maternal reproductive cycle are steroids transferred? During reproduction, how dynamic are the levels of yolk steroids? Especially in the case of potentially deleterious steroids (e.g., androgens in female offspring; glucocorticoids), once deposited can they come out of the yolk over time? Can they be metabolized by the yolk or by the embryo? During incubation, how much do steroid levels in the yolk change? Can steroids diffuse from the yolk to the embryo prior to yolk utilization? Does the embryo contribute to yolk steroid levels as it develops? We believe that comprehensive answers to questions like these will eventually allow us to generate a much more accurate and complete model of the transfer and utilization of yolk steroids and that this model will be much more dynamic and active than the one initially proposed.

The mechanisms by which testosterone regulates aggression are unclear and may involve changes that alter the activity levels of one or more brain nuclei. We estimate neural activity by counting immunopositive cells against phosphorylated cyclic AMP response element binding protein (pCREB). We demonstrate increased pCREB immunoreactivity within the dorsolateral subdivision of the ventromedial hypothalamus (VMHdl) following an aggressive encounter in male tree lizards Urosaurus ornatus. This immunoreactivity is induced both by exposure to and performance of aggressive behaviors. This dual activation of the VMHdl suggests its possible role as an integration center for assessment and expression of aggressive behavior. Furthermore, pCREB induction was greater in encounters involving higher frequency and intensity of aggressive display, demonstrating a direct relationship between neural activation and behavior. The VMHdl is also rich in steroid receptors. In a second experiment involving hormone manipulations, testosterone treatment increased aggression levels, though it did not increase the number of pCREB positive cells within the VMHdl. This lack of an effect of testosterone on pCREB induction within the VMHdl may be due to induction arising from the behaviors of conspecifics (especially in low-testosterone, low-aggression individuals), variation in aggression mediated by other variables, or regulation of aggression by circuits outside of the VMHdl. Together, these findings support a notion of the VMHdl as a nucleus involved in integrating afferent and efferent information within the neural aggression-control circuit.

The neuropeptide arginine vasotocin (AVT) and its mammalian homologue arginine vasopressin (AVP) are neuromodulators known to be steroid sensitive and associated with social behaviors in a number of vertebrate taxa. However, the role of AVT/P in the regulation of aggression remains unclear and contrasting effects of this peptide on aggression are seen in differing species and contexts. In this study, we used immunohistochemistry to examine the effects of testosterone on the AVT system in male and female tree lizards, Urosaurus ornatus, and to determine whether AVT is related to territorial aggression in this species. Tree lizards are a free-living species that exhibit natural hormonal fluctuations across breeding seasons. We detected a male-biased sexual dimorphism in centrally projecting AVT fibers within the limbic system. Furthermore, changes with season, reproductive state, and hormonal treatment suggest that testosterone regulates AVT immunoreactivity in limbic brain regions, especially in the bed nucleus of the stria terminalis. Testosterone also affects AVT immunoreactivity in peripherally projecting cell clusters, as well as the size of AVT cell bodies in the paraventricular nucleus. Although higher testosterone levels alter AVT immunoreactivity, and are known to increase the frequency and intensity of male-male aggression in this species, no individual correlations between AVT immunoreactivity and aggression were detected.

SUMMARYPhysiological trade-offs arise because multiple processes compete for the same limiting resources. While competition for resources has been demonstrated between reproduction and immune function, the regulation of this competition remains unclear. Corticosterone (CORT) is a likely mediator due to its dual role in mobilizing energy stores throughout the body and regulating physiological responses to stressors. We manipulated CORT concentrations and resources in pre-reproductive and reproductive female tree lizards(Urosaurus ornatus) to test the hypothesis that CORT regulates the distribution of limiting resources between the reproductive and immune systems. To manipulate circulating concentrations of CORT we utilized a novel method of hormone implantation, in which a polymeric compound is mixed with hormone and injected in liquid form into the animal. After injection, the liquid quickly gels in situ forming a slow release hormone implant. This method of hormone delivery eliminated the need for substantial wounds to the animal or repeated handling required by other methods. In this study, the hormone-treated animals had plasma CORT concentrations comparable to high physiological concentrations. We found that CORT treatment suppressed immune function, but only when animals were energetically compromised. We assessed immune function by measuring the healing rate of a cutaneous biopsy. Healing was suppressed in all CORT-treated reproductive animals and in all CORT-treated animals (pre-reproductive and reproductive) undergoing food restriction, but CORT had no effect in ad libitum non-reproductive females. The context-dependent action of CORT renders its response adjustable to changing environmental conditions and may allow for the suppression of specific functions depending on resource availability.

The neural mechanisms by which steroid hormones regulate aggression are unclear. Although testosterone and its metabolites are involved in both the regulation of aggression and the maintenance of neural morphology, it is unknown whether these changes are functionally related. We addressed the hypothesis that parallel changes in steroid levels and brain volumes are involved in the regulation of adult aggression. We examined the relationships between seasonal hormone changes, aggressive behavior, and the volumes of limbic brain regions in free-living male and female tree lizards (Urosaurus ornatus). The brain nuclei that we examined included the lateral septum (LS), preoptic area (POA), amygdala (AMY), and ventromedial hypothalamus (VMH). We showed that the volumes of the POA and AMY in males and the POA in females vary with season. However, reproductive state (and thus hormonal state) was incompletely predictive of these seasonal changes in males and completely unrelated to changes in females. We also detected male-biased dimorphisms in volume of the POA, AMY, and a dorsolateral subnucleus of the VMH but did not detect a dimorphism between alternate male morphological phenotypes. Finally, we showed that circulating testosterone levels were higher in males exhibiting higher frequency and intensity of aggressive display to a conspecific, though brain nucleus volumes were unrelated to behavior. Our findings fail to support our hypothesis and suggest instead that plasma testosterone level covaries with aggression level and in a limited capacity with brain nucleus volumes but that these are largely unrelated relationships.

Exposure to stress can affect an organism's partitioning of resources among immune function and other organismal functions. However, measuring immune function is often difficult. Recent studies show that the rate of cutaneous wound healing in laboratory rodents is a simple, integrated measure of stress-sensitive immune function. We investigated the use of this technique in tree lizards to test the hypotheses (1) that stress compromises wound healing and (2) that this effect is at least partially mediated by corticosterone. Laboratory-housed male tree lizards randomly assigned to the experimental and control treatment groups received a 3.5 mm cutaneous biopsy on the dorsal surface of the pelvis. Experimental group males were restrained in cloth bags for 60 min every day for 21 days during the healing profile, whereas control males were left in their cages. Wound sizes were measured every other day by image analysis. Control animals healed faster than stressed animals. The difference in wound surface area between the groups was most pronounced early in the healing profile. Stressed animals also had higher corticosterone levels and corticosterone was negatively correlated with healing rate in the stressed animals. These observations support both hypotheses that stress compromises healing and that corticosterone may act to mediate the effects of stress.

Testosterone is usually thought to be the major sex steroid regulating adult male territorial aggression in vertebrates. However, recent evidence has suggested a role for progesterone, as well as testosterone, in the organization of the two male reproductive phenotypes of tree lizards (Urosaurus ornatus), which differ in adult levels of territorial behavior. In the present experiment we tested whether progesterone and testosterone could also play an activational role in the expression of adult aggressive behavior. We subjected post-reproductive male tree lizards to the following treatments: sham surgery, castration, castration with progesterone supplementation, and castration with testosterone supplementation. We measured several different dimensions of aggressive behavior. Overall in these post-reproductive animals, the level of aggression from lowest to highest was: castrates, shams, progesterone-treated, and testosterone-treated. Although testosterone appears to be the more potent regulator of aggressive behavior, progesterone enhanced several measures of aggression suggesting that it could play a role in natural regulation of aggressive behavior. This initial study used very high levels of progesterone (similar to or above those experienced by hatchlings) to maximize the probability of detecting an effect. Further studies are needed to determine if natural adult progesterone levels are sufficiently high to influence aggressive behavior.

During development, sex steroids are important in establishing differences between males and females. However, sex steroids also are involved in the development and maintenance of individual differences in morphology and behavior within each sex. As adults, male tree lizards (Urosaurus ornatus) exhibit alternative reproductive tactics correlated with dewlap (throat fan) coloration. Males with orange-blue dewlaps are aggressive and territorial, whereas males with orange dewlaps are less aggressive and employ a satellite strategy. Dewlap coloration develops within the first 90 days after hatching and remains fixed throughout life. Recent work demonstrates that individual males differ in progesterone and testosterone secretion during development, suggesting that these hormones regulate the development of alternative male phenotypes. The current work uses in vitro incubation of adrenal and gonadal tissues to identify the source of progesterone and testosterone during the period of male differentiation and to follow ontogenetic changes in hormone release. The results indicate that, in all developmental stages sampled, adrenal incubations primarily contain progesterone and corticosterone whereas gonadal incubations contain primarily testosterone. These data indicate that the hatchling adrenal is the primary source of progesterone during early post-hatching development. Since progesterone has been demonstrated to play a role in the establishment of individual differences in morphology and behavior in male tree lizards, our results suggest that the hatchling adrenal gland plays an important role in post-hatching development of alternative male phenotypes.

Dominant and subordinate males respond differently to the stress of social interaction. After an hour of social interaction, subordinate male Anolis carolinensis have elevated serotonergic activity in hippocampus, but dominant males do not. In other species, and using other stressors, the activation of hippocampal serotonergic activity is much more rapid than one hour. To elucidate early stress responsiveness, adult male A. carolinensis were divided into four groups: isolated controls, and pairs of males sampled after 10, 20 or 40 minutes of aggressive interaction. Development of dominant-subordinate relationships was determined by behavior and by the celerity of eyespot darkening. Serotonergic activity in the hippocampus, nucleus accumbens and amygdala was elevated rapidly and equally in both dominant and subordinate males, as were plasma corticosterone concentrations. Serotonergic activity remained elevated through 40 minutes in hippocampus and nucleus accumbens. Only subordinate males had elevated corticosterone levels at 40 minutes. Social status does not impede socially induced stress responses. Rather, rapid regulation of serotonergic stress responses appears to be a mediating factor in determining both behavioral output and social status. Temporal expressions of monoaminergic and endocrine stress responses are distinctive between males of dominant and subordinate social status. Such temporal patterns of transmitter and glucocorticoid activity may reflect neurocircuitry adaptations that result in behavior modified to fit social status.

Understanding the relationship between energy metabolism and signals that regulate reproduction may provide insight into the coordination of the energetically costly behavioral and physiological events that occur during reproduction. Significant changes in the utilization of stored lipids may occur during reproduction and the patterns of utilization observed often differ between females and males. Changes in levels of stored lipid reserves have been described extensively in animals from many taxa, but detailed biochemical analyses of alterations in the enzymes and substrates regulating lipid metabolism during periods of active reproductive effort rarely have been performed. In addition, few studies have compared males and females from the same population during the same reproductive season. In this study we examined lipid metabolism in free-living female and male tree lizards across a single reproductive season. We measured lipid stores, circulating lipid substrates, and the activities of enzymes regulating lipid storage and release in both liver and adipose tissue. Overall, females and males showed significant variation in abdominal fat body mass, liver total lipid, the activity of an enzyme regulating fat storage (DGAT) in both of these tissues, and circulating free fatty acids across the reproductive season. In females, total fat body mass, adipose DGAT, liver lipid, and liver DGAT significantly varied across reproductive stage, with vitellogenic and Gravid females often at opposite extremes. In males, fat body mass and liver fat varied across reproductive stage (without significant variation in DGAT in either tissue), as did circulating glycerol and free fatty acids. Correlations among sex steroid hormone levels and lipid metabolism variables suggested a role for these hormones in producing the patterns observed in each sex and in the observed sex differences lipid metabolism.

The magnitude of the glucocorticoid response to a stressor can depend on both environmental and physiological context. One factor that has not been examined is whether females of different reproductive states have different responses to a stressor. We examined whether corticosterone (CORT) increased after a 10 min handling stress in oviparous female tree lizards (Urosaurus ornatus) that were vitellogenic (yolking follicles) or gravid (post-ovulatory). We found that stressed vitellogenic females had a large increase in plasma CORT whereas gravid females did not. Baseline levels of CORT in gravid females were relatively high and similar to those in stressed vitellogenic females. The lack of a stress response in gravid females may be due to an inability to secrete higher levels of CORT or a suppression of the stress response. In addition, within vitellogenic females, CORT was positively correlated with ovarian weight, suggesting that CORT may function in some aspect of ovarian development during vitellogenesis.

We investigated maternal-fetal hormone transfer in the mountain spiny lizard, Sceloporus jarrovi, a viviparous species with a simple chorioallantoic placenta. In one experiment, we examined the effect of elevated maternal progesterone on fetal and yolk hormone levels. Progesterone implants increased maternal progesterone nearly 100-fold; however, the resulting increase in fetal and yolk progesterone was only about 2% of that seen in mothers, providing evidence that the placenta buffers hormone diffusion. In addition, some effects of progesterone treatment differed between male and female fetuses, suggesting that this buffering may differ between the sexes. In a second experiment, we examined the relationship between maternal and fetal hormone levels in viviparous versus oviparous species. We measured endogenous progesterone, testosterone, estradiol, and corticosterone levels in pregnant S. jarrovi and their fetuses and neonates, and in gravid S. graciosus (an oviparous congener) and their fetuses and hatchlings. No clear relationship was identified between maternal and fetal or hatchling S. graciosus hormone levels. However, the data for S. jarrovi suggest that maternal hormones may inhibit perinatal hormone secretion. These findings indicate that, despite the relatively recent evolutionary origin and simple structure of the S. jarrovi placenta, mechanisms for placental mediation of the maternal-fetal endocrine relationship have evolved. Although the placenta appears to buffer hormone transport, maternal hormones can affect fetal and yolk hormone levels, suggesting that disruption of endocrine regulation could be a physiological cost of the evolution of viviparity.

Although female aggression is found in many species and in a variety of contexts, little is known about its physiological bases. To compare neuroendocrine responses to aggression in females and males, we staged aggressive interactions between free-living territorial mountain spiny lizards and same-sex intruders and measured brain monoamines, plasma steroid hormone levels, and plasma glucose levels. Both females and males that had participated in a staged aggressive interaction had similar changes in serotonin (5-HT) activity in telencephalic tissue punches as indicated by a lowered ratio of forebrain:brainstem 5-HT concentrations. In addition, both females and males had elevated plasma corticosterone (B) after an aggressive interaction when compared to controls. The only difference detected between males and females was that females had a higher ratio of forebrain:brainstem norepinephrine (NE) concentrations throughout the brain compared to males. Together, these data indicate that acute neural and hormonal responses that accompany aggressive interactions in females are similar to those in males.

The potential of mitotane (ortho, para′-DDD, commonly used to treat adrenal carcinomas in humans and dogs) was investigated as an alternative to surgical adrenalectomy in birds, salamanders, and lizards. House sparrows ( Passer domesticus ) were injected twice daily with vehicle or one of two doses of mitotane (225 or 450 mg/kg), and basal and stress-induced levels of corticosterone (CORT) were measured 3 and 5 days after injections. Mitotane reduced basal CORT levels to nondetectable and abolished stress-induced CORT increases by the 3rd day of treatment. In another study, a single injection of mitotane was effective in lowering endogenous CORT levels 36 h later, but levels had apparently recovered by 10 days after the injection. Mitotane did not effect testicular weights and had no detectable effect on testosterone levels. In contrast to its effects on house sparrows, mitotane did not lower endogenous CORT levels in either tiger salamanders ( Ambystoma tigrinum ) or tree lizards ( Urosaurus ornatus ), even at doses much higher than those used in house sparrows.

In certain species, females are highly aggressive. For example, female mountain spiny lizards, Sceloporus jarrovi, express aggressive behaviours when defending their territories. Despite the occurrence of female aggression, relatively little is known about its underlying hormonal mediation. As a first step in understanding neuroendocrine mechanisms of female aggression, this study documented seasonal changes in territorial aggression, plasma steroid hormone levels, and reproductive condition in free-living female mountain spiny lizards. We determined how seasonal patterns of testosterone (T), oestradiol (E), dihydrotestosterone (DHT) and corticosterone (B) corresponded to seasonal patterns of aggression. At times of the year when females were most aggressive, plasma levels of T and E were elevated. At times of the year when females were least aggressive, plasma B was elevated. Furthermore, when levels of T were elevated, females were more aggressive, and when levels of B were elevated, females were less aggressive. Plasma levels of DHT were not associated with aggression. These seasonal patterns are consistent with the hypotheses that T, and perhaps E, promote female aggression, while B suppresses female aggression. Despite these associations of hormones and aggression, no hormone was associated with aggression in a one-to-one fashion. This suggests that if steroid hormones contribute to the expression of female aggression, they must interact with each other or with other factors (for example, other hormones, receptor levels, environmental factors) to mediate fully the expression of aggression. Copyright 1999 The Association for the Study of Animal Behaviour.

Abstract —The mechanisms of sodium-induced myocardial hypertrophy and vascular hypertrophy are poorly understood. We tested the hypothesis that a high sodium concentration can directly induce cellular hypertrophy. Neonatal rat myocardial myoblasts (MMbs) and vascular smooth muscle cells (VSMCs) were cultured in a 50:50 mixture of DMEM and M199 supplemented with 10% fetal bovine serum. When the monolayers reached ≈80% confluence, normal sodium medium (146 mmol/L) was replaced with high sodium media (152 mmol/L, 160 mmol/L, and 182 mmol/L) for up to 5 days. Increasing sodium from a baseline concentration of 146 mmol/L to the higher concentrations for 5 days caused dose-related increases in cell mean diameter, cell volume, and cellular protein content in both MMbs and VSMCs. Increasing the sodium concentration by only 4% (from 146 mmol/L to 152 mmol/L) caused the following respective changes in MMbs and VSMCs: 8.5% and 8.7% increase in cell mean diameter, 27.6% and 27.0% increase in cell volume, and 55.7% and 46.7% increase in cellular protein content. The rate of protein synthesis, expressed as [ 3 H]leucine incorporation, increased by 87% and 99% in MMbs after exposure to 152 mmol/L and 160 mmol/L sodium, respectively, compared with the 146-mmol/L sodium control group. Exposure of MMbs to medium with a sodium concentration of 10% above normal, ie, 160 mmol/L, caused a significant decrease (range, 26% to 44%) in the rate of protein degradation at multiple time points over a 48-hour period compared with normal sodium control cells. The increase in cellular protein content caused by 160 mmol/L sodium returned to normal within 3 days after MMbs were returned to a normal sodium medium. These findings support the hypothesis that sodium has a direct effect to induce cellular hypertrophy and may therefore be an important determinant in causing myocardial and/or vascular hypertrophy in subjects with increased sodium concentration in the extracellular fluid.

Changes in circulating glucocorticoid and androgen levels mediate agonistic behaviors in many vertebrates. Individual variation in the magnitude of the glucocorticoid response to stressful stimuli, the negative effects of elevated glucocorticoid levels on androgen levels, or both could mediate individual differences in subsequent agonistic behavior. In a series of previous studies, we found that both alternative male reproductive morphs in the tree lizard, Urosaurus ornatus, can exhibit elevated levels of plasma corticosterone following male–male encounters, but that the territorial morph appears less likely to exhibit coincident decreases in plasma testosterone. Two studies tested the hypothesis that the two morphs differ in the degree to which testosterone levels are influenced by elevated corticosterone levels. In the first study, physically restraining males elicited endogenous elevations of circulating corticosterone levels. Testosterone levels were significantly negatively correlated with corticosterone levels in the nonterritorial morph, but there was no correlation between levels of the two steroids in territorial males. In the second study, corticosterone levels were artificially elevated in free-living male tree lizards using a noninvasive dermal patch. This exogenous elevation of corticosterone significantly depressed testosterone levels in both morphs, but it produced a significantly greater depression in the nonterritorial morph. Nonterritorial males appear to be more sensitive than territorial males to the testosterone-suppressing effects of elevated circulating levels of corticosterone. This difference between the morphs in the effects of a stress hormone on the reproductive axis may be a fundamental part of the mechanism (1) underlying behavioral tactic switching within the nonterritorial morph or (2) contributing to behavioral differences between the morphs.

The spadefoot toad, Scaphiopus couchii, is an explosively breeding, desert dwelling amphibian that shows two characteristics hypothesized to select for a dissociated breeding pattern: it lives in a harsh environment and it has a very short, but predictable breeding period. We tested the hypothesis that these factors select for a dissociated breeding cycle by measuring plasma steroid hormones and the gametogenic cycles in a free-living population of S. couchii. Blood and tissue samples were obtained from prebreeding, calling (males only), amplexed, and postbreeding toads. In males, plasma testosterone (T), dihydrotestosterone (DHT), and corticosterone (B) differed significantly among reproductive groups, with calling and amplexing toads having the highest levels of each of these steroids. In females, plasma T, DHT, B, progesterone (P), and estradiol (E2) were measured; all steroids except B changed significantly among mating groups. Plasma T and E2 were greatest in prebreeding and amplexed females, while P and DHT were highest only in amplexed females. Primary spermatogonia (SPG I), secondary spermatogonia (SPG II), spermatocytes, spermatids (SPT), and spermatozoa embedded in Sertoli cells (SPS) all changed significantly among male breeding groups. Although all stages were present in all breeding groups, early stages of spermatozoa (SPG I and SPG II) were greatest in postbreeding males, while late stages (SPT and SPS) were highest in prebreeding, calling, and amplexing males. In females, oocyte stages I, II, III, V, and VI and atretic follicles also differed significantly among mating groups. Prebreeding female ovaries were dominated by late-stage (V and VI) oocytes which were subsequently ovulated during amplexus. In postbreeding females, oogenesis was well under way as indicated by the rising numbers of stage II and III oocytes. These results indicate that aspects of gametogenesis occur during and after breeding in both sexes. Although the results demonstrate that gonadal activity was high during the period of sexual activity, suggesting that S. couchii most closely fits an associated pattern of reproduction as defined by Crews (1984, Horm. Behav. 18, 22-28), we also found that gonadal activity continued past the breeding season. For this reason, S. couchii does not completely conform to an associated pattern.

Few studies have examined the role of steroid hormones in mediating tactic-associated differences in male agonistic behaviour. Long-term (24 h) steroid hormone responses to winning staged male–male encounters in different morphs of free-living male tree lizards,Urosaurus ornatus, were studied. Males belong to either an aggressive, territorial (type) morph or to a less aggressive, non-territorial morph. On the day after winning a staged male–male encounter, males of the less aggressive morph showed elevated plasma levels of the stress hormone corticosterone and depressed levels of the sex steroid testosterone compared with controls of the same morph not subjected to an encounter. In contrast, males of the more aggressive, territorial morph that engaged in an encounter had levels of both hormones similar to controls. This morph difference in hormonal response is the first endocrine difference between adult males of the two tree lizard morphs detected to date; previous field and laboratory studies showed no morph difference in resting hormone levels or in hormonal responses 30 min following male–male encounters. The consequences of these morph differences in hormone responses to male–male interactions are unknown, but the hormonal changes in the less aggressive morph may (1) influence spontaneous agonistic behaviour, (2) influence agonistic behaviour in subsequent male–male interactions or (3) reflect morph differences in physiological capabilities related to energy expenditure during male–male interactions.

Male tree lizards (Urosaurus ornatus) exhibit permanent adult differences in color and size that are functionally linked with behavioral differences: males with a central blue throat patch are territorial, more aggressive, and smaller than males lacking the patch, who are nomads or satellites foregoing territory defense. Gonadectomy or long-lasting hormone implants in hatchlings affect the development of these permanent adult differences, but similar manipulations in adults are ineffective. Analogous early hormone actions in vertebrate sexual differentiation typically must occur during a critical period. Whether there is a critical period for early hormone actions affecting development of male types in tree lizards is unclear. We followed a protocol identical to our previous experiments on hatchlings, but we manipulated testosterone (T) in later-aged juveniles to determine if they remained sensitive to such hormone manipulations. Testosterone implants given at 60 days posthatching (day 60) did not alter adult throat color, indicating that sensitivity of throat color to T declines by day 60. This contrasts to our earlier work where adult color was affected by T manipulations on day 30. However, size and throat color responded differently to exogenous T, as juveniles given T implants at day 60 grew less than control-implanted males.

Fitness tradeoffs are difficult to examine because many fitness variables are correlated and vary in the same direction. Phenotypic manipulation circumvents many of these difficulties, and here we used this technique to examine mechanisms for tradeoffs between increased aggression (territorial defense) and survivorship. The behavioral phenotype of male mountain spiny lizards (Sceloporus jarrovi) was manipulated with testosterone to increase territorial defense, a sexually selected trait. We previously demonstrated that increased territorial defense results in a decrease in survival caused by a lower ratio of energy intake to energy expenditure. Here we measured energy consumption of increased territorial aggression using the doubly labeled water technique in the field and compared males with and without testosterone implants (Fig. 1). In a supplementary study we measured standard metabolic rate using captive lizards given similar testosterone implants to examine if an increase in energy expenditure was a result of only an increase in standard metabolic rate (Fig. 3). Our results indicated that a primary contribution to tradeoffs between increased territorial defense and survivorship could be made by a 31% increase in energy expenditure in the field that is not due to an increase in standard metabolic rate.

Males of many species exhibit strongly dimorphic reproductive behavior and morphology associated with alternative reproductive tactics. Little is known about the physiological control of these individual differences. The relative plasticity hypothesis proposes that such within-sex differences arise from either organizational or activational actions of sex steroid hormones depending on whether adults can switch tactics or not. This hypothesis predicts that differences between individuals in a species where adults cannot switch between tactics (are "fixed") should be organized by early actions of hormones. Three experiments explored the possible organizational role of testosterone (T) on the development of male alternatives in the tree lizard (Urosaurus ornatus), which has two fixed male morphs. Orange (O) males have a mostly orange throat fan (dewlap), are non-territorial nomads, and are larger than orange-blue (OB) males which have an orange dewlap with a central blue patch and are territorial. In the first experiment intact males on the day of hatching were (1) sham-operated and implanted with empty capsules, (2) castrated, or (3) testosterone-implanted. As adults, the castration group had more O males than the control and the T-implanted group had more OB males than the control. Adult body size in castrated and T-implanted groups paralleled naturally occurring morph differences but both were smaller than controls. A second experiment with a lower dose yielded similar results for dewlap type and growth. In a third experiment, intact males were given an empty capsule or a T-implant at 30 days posthatching. Again, the frequency of OB males in the T-implanted group was significantly greater than that in the empty implant group, indicating that either the critical period extends past Day 30 or there is no well-defined critical period. Together, these results support the hypothesis that the organizational action of T or one of its metabolites contributes to the differentiation of these within-sex differences.

To examine the reciprocal interactions among gonadal and adrenal steroid secretion, male tree lizards (Urosaurus ornatus) were subjected to two forms of stress. They were subjected either to the acute stress of being held in collecting bags for up to 4 hr or to the chronic stress of being maintained in individual cages in the laboratory for up to 3 weeks. In both cases, levels in stressed animals were compared to levels in free-living animals as controls. Under both conditions plasma levels of corticosterone increased and plasma levels of testosterone decreased compared to free-living controls. The response to the acute stress was much greater for both hormones than to the chronic stress, although in both cases testosterone levels changed less in response to stress than corticosterone levels. The corticosterone response to acute stress was extremely rapid with levels increasing over six-fold in the first 10 min. Plasma levels of corticosterone and testosterone were negatively correlated among individuals in the chronic stress experiment, but not in the acute stress experiment. This correlational evidence is consistent with the hypothesis of a direct effect of corticosterone levels on testosterone levels and suggests that these may only be expressed under some conditions.

KABELIK, D., Weiss S. L. AND MOORE M. C. Steroid hormones alter neuroanatomy and aggression independently in the tree lizard. PHYSIOL BEHAV 00(0) 000-000, 0000. –Steroid hormones affect changes in both neuroanatomy and aggressive behavior in animals of various taxa. However, whether changes in neuroanatomy directly underlie changes in aggression is unknown. We investigate this relationship among steroid hormones, neuroanatomy, and aggression in a free-living vertebrate with a relatively simple nervous system, the tree lizard (Urosaurus ornatus). Weiss and Moore [1] manipulated testosterone and progesterone levels in adult male tree lizards and found that both hormones facilitated aggressive behavior toward a conspecific. In this study, we examined the brains of a subset of these animals to determine whether changes in limbic morphology were associated with hormone-induced changes in aggressive behavior. Specifically, we tested the hypothesis that testosterone and/or progesterone cause changes in neural morphology that are necessary for the expression of testosterone’s effects on aggressive behavior. We found that both hormones increased aggression; however, only testosterone induced changes in neuroanatomy. Testosterone increased the size of both the amygdala and nucleus sphericus. However, we could detect no individual correlations between neuroanatomy and aggression levels suggesting that the observed large-scale changes in neuroanatomy are not precisely reflective of changes in mechanisms underlying aggression.

The regulation of hatching in oviparous animals is important for successful reproduction and survival, but is poorly understood. We unexpectedly found that RU-486, a progesterone and glucocorticoid antagonist, interferes with hatching of viable tree lizard (Urosaurus ornatus) embryos in a dose-dependent manner and hypothesized that embryonic glucocorticoids regulate hatching. To test this hypothesis, we treated eggs with corticosterone (CORT) or vehicle on Day 30 (85%) of incubation, left other eggs untreated, and observed relative hatch order and hatch time. In one study, the CORT egg hatched first in 9 of 11 clutches. In a second study, the CORT egg hatched first in 9 of 12 clutches, before vehicle-treated eggs in 10 of 12 clutches, and before untreated eggs in 7 of 9 clutches. On average, CORT eggs hatched 18.2 h before vehicle-treated eggs and 11.6 h before untreated eggs. Thus, CORT accelerates hatching of near-term embryos and RU-486 appears to block this effect. CORT may mobilize energy substrates that fuel hatching and/or accelerate lung development, and may provide a mechanism by which stressed embryos escape environmental stressors.

The placenta provides a maternal-fetal exchange interface that maximizes the diffusion of gases, nutrients, and wastes. However, the placenta also may permit diffusion of lipid-soluble steroid hormones that influence processes such as sex-specific fetal development and maternal pregnancy maintenance. In mammals, placental steroid metabolism contributes to regulation of maternal and fetal hormone levels. Such mechanisms may be less highly developed in species that have recently evolved placentation, such as many reptiles. We therefore chose to investigate placental metabolism of steroids in the viviparous lizard Sceloporus jarrovi. In vitro tissue incubations tested the abilities of the chorioallantoic placenta to clear progesterone and corticosterone by converting them to other metabolites and to synthesize progesterone. Placental tissue rapidly cleared progesterone and corticosterone added to the incubation media, indicating that the tissue had converted the steroids to other products. Placental tissue also synthesized substantial concentrations of progesterone from the prohormone pregnenolone. Thus, even in a species with a simple, recently evolved placenta, steroid metabolism appears to be highly developed and could be critical for regulation of maternal and fetal hormone levels. This finding suggests that placental hormone metabolism may be critical to the successful evolution of placentation.

In most species, plasma levels of baseline glucocorticoids such as corticosterone (B) have a circadian rhythm. This rhythm can be entrained by both photoperiod and food intake and is related to aspects of energy intake and metabolism. Marine iguanas (Amblyrhynchus cristatus) offer a unique opportunity to better understand the relative importance of the light:dark cycle versus food intake in influencing the rhythm in baseline B in a natural system. Compared to other species, food intake is not as strictly determined by the phase of the light:dark cycle. Animals feed in the intertidal zone so feeding activity is heavily influenced by the tidal cycle. We measured baseline plasma B levels in free-living iguanas over several 24-h periods that varied in the timing of low tide/foraging activity. We found that baseline B levels were higher during the day relative to night. However, when low tide occurred during the day, baseline B levels dropped coincident with the timing of low tide. Whether the baseline B rhythm (including the drop during foraging) is an endogenous rhythm with a circatidal component, or is simply a result of feeding and associated physiological changes needs to be tested. Together, these data suggest that the baseline B rhythm in marine iguanas is influenced by the tidal cycle/food intake as well as the light:dark cycle.

Long-term captivity can result in abnormal behavior and physiology in many vertebrates. Here, we examine whether semi-natural, outdoor captive environments can offer a compromise, allowing much of the experimental control afforded by captivity, while providing the environmental conditions essential for normal behavior and physiology. We first determined plasma concentration of the sex steroid hormones progesterone, testosterone, and estradiol of free-ranging female striped plateau lizards (Sceloporus virgatus) throughout the reproductive season, and second, compared the results to those from conspecific females maintained in semi-natural outdoor enclosures. Among free-ranging females, levels of progesterone and estradiol were elevated during vitellogenesis, with an apparent surge in progesterone and testosterone occurring in association with ovulation. Following ovulation, estradiol fell to non-reproductive levels while progesterone remained elevated during the month-long period of gravidity. Long-term captivity in outdoor enclosures did not significantly affect progesterone or estradiol levels at any stage of the reproductive cycle, and did not affect testosterone levels during normal ovarian development and gravidity. However, (1) females with delayed oviposition in captivity had lower testosterone levels than free-ranging females with normal oviposition, and (2) when all females sampled were post-reproductive, captive females continued to have lower testosterone levels than free-ranging females. Thus, the endocrine response to captivity may be greater among post-reproductive females than among reproductive females. Our results are in marked contrast to many studies that show captivity can dramatically impair reproduction of female vertebrates.

Although estradiol (E2) mediates many behaviors in females, relatively little is known about its role in female aggression. Previous studies in female mountain spiny lizards indicated that female aggression is modulated by ovariectomy and sex steroid hormone replacement and that expression of aggressive behavior is accompanied by changes in serotonin activity. This study examines if E2 modulates the activity of serotonin and other central monoamines. Free-living females were caught and housed in the laboratory and received one of 3 treatments: sham surgery (SHAM), ovariectomy plus empty implant (OVEX), or sham surgery plus a long lasting E2 implant (E2-IMP). After 3 weeks of treatment, selected brain areas were examined for levels of monoamines and their metabolites. Changes in monoamine activity were most pronounced in the septum where levels of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), and norepinephrine (NE) were higher in E2-IMP females relative to SHAM, and levels of 5-HIAA were higher in OVEX females relative to SHAM. Changes in dopamine (DA) activity were also found, with increased DA concentration and decreased ratio of forebrain:brainstem HVA concentrations in E2-IMP relative to SHAM females. These results suggest that the actions of E2 on aggression might be mediated, in part, by dose-dependent effects on 5-HT activity in the septum.

Plasma steroid-binding globulins, for example, corticosteroid-binding globulin and sex hormone-binding globulin (SHBG), have been identified in a number of vertebrates. One possible function of these proteins is to regulate the amount of steroid delivery to target tissues, as only free steroids are believed to diffuse from the circulation to target cells. Male tree lizards, Urosaurus ornatus, exhibit alternative male reproductive tactics correlated with dewlap (throat-fan) coloration. Males with orange-blue dewlaps are aggressive and territorial, whereas males with orange dewlaps are less aggressive and employ a satellite strategy. The two types of males have similar basal levels of total plasma corticosterone and testosterone. However, testosterone levels of nonterritorial males are more sensitive than those of territorial males to negative regulation by stress-induced increases in corticosterone. We tested the hypothesis that this difference in corticosterone feedback on testosterone could be mediated, in part, by differences in binding globulin levels between the two types of males. We have identified two steroid-binding globulins in male tree lizards. The first binds androgens and estradiol with high affinity (10(-9) M) and is similar to previously described sex hormone-binding globulins. The second binds both androgens and C(21) steroids, such as progesterone and corticosterone, with higher specificity than estradiol and is best described as an androgen-glucocorticoid-binding globulin (AGBG). In both types of males, the capacity of AGBG is much higher than SHBG. In addition, AGBG capacity is significantly greater in territorial than nonterritorial males, whereas the capacity of SHBG does not differ between the two types of males. Calculations of free steroid levels based on the affinity and capacity measures suggest that although most testosterone circulates bound to binding globulins, binding capacity is high enough that binding globulins are also able to bind to other steroids such as corticosterone. Thus, differences in binding capacity between the two types of males could result in higher levels of free corticosterone in nonterritorial males than in territorial males, especially during stress-induced increases in corticosterone, and may explain why testosterone levels of nonterritorial males are more sensitive to negative feedback by corticosterone.

We tested whether increased endogenous adenosine produced by the adenosine kinase inhibitor GP-515 (Metabasis Therapeutics) can induce vascular endothelial growth factor (VEGF) expression in cultured rat myocardial myoblasts (RMMs). RMMs were cultured for 18 h in the absence (control) and presence of GP-515, adenosine (Ado), adenosine deaminase (ADA), or GP-515 + ADA. GP-515 (0.2–200 μM) caused a dose-related increase in VEGF protein expression (1.99–2.84 ng/mg total cell protein); control VEGF was 1.84 ± 0.05 ng/mg. GP-515 at 2 and 20 μM also increased VEGF mRNA by 1.67- and 1.82-fold, respectively. ADA (10 U/ml) decreased baseline VEGF protein levels by 60% and completely blocked GP-515 induction of VEGF. Ado (20 μM) and GP-515 (20 μM) caused a 59 and 39% increase in VEGF protein expression and a 98 and 33% increase in human umbilical vein endothelial cell proliferation, respectively, after 24 h of exposure. GP-515 (20 μM) had no effect on VEGF protein expression during severe hypoxia (1% O2) but increased VEGF by an additional 27% during mild hypoxia (10% O2). These results indicate that raising endogenous levels of Ado through inhibition of adenosine kinase can increase the expression of VEGF and stimulate endothelial cell proliferation during normoxic and hypoxic conditions.

We tested whether adenosine has differential effects on vascular endothelial growth factor (VEGF) expression under normoxic and hypoxic conditions, and whether A1or A2receptors (A1R; A2R) mediate these effects. Myocardial vascular smooth muscle cells (MVSMCs) from dog coronary artery were exposed to hypoxia (1% O2) or normoxia (20% O2) in the absence and presence of adenosine agonists or antagonists for 18 h. VEGF protein levels were measured in media with ELISA. VEGF mRNA expression was determined with Northern blot analysis. Under normoxic conditions, the adenosine A1R agonists, N6-cyclopentyladenosine and R(-)- N6-(2-phenylisopropyl)adenosine did not increase VEGF protein levels at A1R stimulatory concentrations. However, adenosine (5 μM) and the adenosine A2R agonist N6-[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)]ethyl adenosine (DPMA; 100 nM) increased VEGF protein levels by 51 and 132% and increased VEGF mRNA expression by 44 and 90%, respectively, in cultured MVSMCs under normoxic conditions. Hypoxia caused an approximately fourfold increase in VEGF protein and mRNA expression, which could not be augmented with exogenous adenosine, A2R agonist (DPMA), or A1R agonist [1,3-diethyl-8-phenylxanthine (DPX)]. The A2R antagonist 8-(3-chlorostyryl)-caffeine completely blocked adenosine-induced VEGF protein and mRNA expression and decreased baseline VEGF protein levels by up to ∼60% under normoxic conditions but only by ∼25% under hypoxic conditions. The A1R antagonist DPX had no effect. These results are consistent with the hypothesis that 1) adenosine increases VEGF protein and mRNA expression by way of A2R. 2) Adenosine plays a major role as an autocrine factor regulating VEGF expression during normoxic conditions but has a relatively minor role during hypoxic conditions. 3) Endogenous adenosine can account for the majority of basal VEGF secretion by MVSMCs under normoxic conditions and could therefore be a maintenance factor for the vasculature.

Females are aggressive in many species but relatively little is known about the hormonal basis of female aggression, especially in free-living animals. Female mountain spiny lizards aggressively defend territories from other females. Previously, we showed that plasma levels of testosterone (T) and estradiol (E) are positively associated with levels of female aggression. Here, we manipulated hormone levels in free-living females and examined aggression expressed by females returned to their natural territories. Females received one of the following: (1) ovariectomy + empty implant (OVEX), (2) ovariectomy + T implant (T-IMP), or (3) sham surgery + empty implant (SHAM). OVEX females had reduced plasma levels of E but not T relative to SHAM females. T-IMP females had elevated plasma levels of T. Levels of display and aggression in OVEX females were reduced relative to SHAM females. T-IMP females had restored levels of display behavior although, unlike SHAM, no T-IMP females expressed the overt aggressive behavior of charging. These data are most consistent with the hypothesis that an ovarian factor such as E promotes female aggression, since ovariectomy reduced both plasma E and aggression but had no effect on plasma T. The results from the T-IMP females are also consistent with this hypothesis if we assume that the effects of T are due to aromatization to E in target tissues. The data do not rule out a role for T in promoting female aggression since T-implants resulted in elevated plasma T and restored display behaviors. This study represents one of the first studies examining the hormonal basis of female aggression in free-living females.

MATT, K. S., M. C. MOORE, R. KNAPP AND I. T. MOORE. Sympathetic Mediation of Stress and Aggressive Competition: Plasma Catecholamines in Free-living Male Tree Lizards. PHYSIOL BEHAV 61 (5) 639–647, 1997.—The sympathetic nervous system and adrenal catecholaminergic tissue act to prepare an animal for “fight or flight” by release of catecholamines into synapses and plasma. However, few studies have measured plasma catecholamines in nonmammalian vertebrates and none have measured them in free-living animals. We report plasma levels of norepinephrine (NE), epinephrine (EPI) and dopamine (DA) in free-living tree lizards ( Urosaurus ornatus ) bled in the field: 1) immediately after capture, 2) after 10 minutes of restraint, 3) immediately after a staged territorial encounter and 4) four minutes after the end of a staged territorial encounter. Time to capture and time to bleed after capture were also recorded for each sample. Time to capture had little effect on plasma catecholamines suggesting that plasma catecholamines do not rise during the brief pursuit by the investigator necessary to capture the lizards in the field. In contrast, plasma NE and EPI increased during blood collection. However, this response was very consistent allowing comparisons to be made using analysis of covariance to control for time to bleed. Results indicate that restraint stress caused a large increase in plasma levels of NE, E and DA. Plasma levels of NE and E, but not plasma DA, were also significantly elevated both immediately and 4 minutes after aggressive encounters, although less so than following restraint stress. These studies show that stress and aggression activate the sympatho-adrenal system. This activation could be involved in behavioral changes during aggression, meeting metabolic demands of the encounter, or both.

Hormonal responses to male-male interactions have been detected in some studies of vertebrates but not others. One hypothesis that may partially explain these discrepancies is that differences in the duration of male-male interactions cause different hormonal responses. In social systems based on dominance-subordinance hierarchies interactions often last longer than if exclusive territories are maintained. Tests of the hypothesis that encounter duration explains discrepancies in hormonal responses would be facilitated by a species that shows elements of both types of social systems, such as species in which males practice alternative reproductive tactics. We compared plasma levels of corticosterone and testosterone in males of the territorial morph of the tree lizard (Urosaurus ornatus) subjected either to short (15 min) male-male encounters or to long (7 days) dominance interactions. In the long interactions, dominant males had lower levels of corticosterone than did subordinate males over the first day, but this difference subsequently disappeared. In sharp contrast, winners of short-term encounters had elevated plasma corticosterone levels which peaked the day after the encounter. Thus, males isolated after a short encounter experienced an increase in corticosterone that was apparently inhibited in males who continued interacting with other males. The delayed increase in corticosterone after a short encounter may facilitate metabolic recovery from the encounter, mobilize metabolic substrates useful in subsequent encounters, or may alter subsequent behavior. The response does not appear to be simply recovery from exercise because in a second experiment males exercised for 15 min did not show a similar delayed increase in corticosterone the following day. Testosterone levels were also monitored and did not change in any of these treatments. These results demonstrate that the duration and the outcome of male-male interactions may each independently influence hormone levels.

Vertebrates species vary in the degree to which the sexes differ in their expression of secondary sex characters, which can be expressed in one sex but not the other, fully expressed in both sexes, or expressed to different degrees in the two sexes. Sex steroid hormones contribute to the development of sex differences, either through action early in life (organization), following sexual maturation (activation), or both. However, relatively little is known about the contributions of sex steroid hormones to species-level variation in sexual dimorphism. We began to address this by assessing in tree lizards, Urosaurus ornatus, the effects of testosterone (T) and dihydrotestosterone (DHT) on expression of the male-typical traits: femoral pore secretions, accessory sex tissues, patches of ventrolateral blue, intensity and hue of throat color, and body size. We administered long-lasting hormone implants of these androgens to intact or ovariectomized adult females, intact hatchling females, and intact hatchling males to determine the relative contribution of organizational and activational influences of androgens on sexual differentiation of these traits. Waxy femoral pore secretions and full intensity of the orange background color of the throat fan (dewlap) required only activation and both androgens were equally effective. Both androgens caused hypertrophy of accessory tissues associated with the hemipenes, but only in hatchling males. Full expression of ventrolateral blue patches required organization by DHT. Androgens had complex organizational actions on growth. In the doses used in the experiment, DHT inhibited body-length growth but not mass growth of hatchling males. Only T inhibited the growth (length and mass) of hatchling females. Because earlier work found that castration also reduced the growth of hatchling males, the organizational effects of androgen on growth might be dose-related. Results for hormonal control of dewlap type were complex. In this population dewlap color is solid orange in females, but polymorphic in males with 50% expressing solid orange (O) and 50% orange-blue (orange with a central blue patch, OB). These color morphs represent permanent male alternatives: OB males are territorial and more aggressive than O males who do not defend territories. Results of the hormone manipulations are most consistent with the interpretation that dewlap morph type requires both organization and activation by androgen. T appears to be more important in organizing morph differences, whereas DHT appears to be more important in activating expression of underlying morph differences. Females only expressed male-typical OB dewlaps when given DHT, and only about 50% did so.

The lizard genus Cnemidophorus consists of both sexual species and unisexual, all-female species. We characterized changes in circulating levels of gonadal sex steroid hormones in males and females in one of the sexual species, C. inornatus, to compare them to previously measured levels in a unisexual, parthenogenetic species, C. uniparens. Reproductively active male C. inornatus have high levels of dihydrotestosterone and somewhat lower levels of testosterone. These levels are highest immediately after females become sexually receptive and decrease later at the onset of testicular regression. Female C. inornatus have high levels of estradiol and low levels of progesterone during the previtellogenic and vitellogenic phases of the ovarian cycle. During the postovulatory phase, they have low levels of estradiol and high levels of progesterone. We could not detect circulating levels of androgen at any phase of the ovarian cycle. The patterns of hormone secretion in the female C. inornatus are virtually identical to those of its direct evolutionary descendant, C. uniparens. This confirms our previous conclusion that the evolution of the parthenogenetic mode of reproduction and expression of male-like pseudosexual behavior that are characteristic of the unisexual C. uniparens has not been accomplished by evolutionary modifications in the pattern of sex steroid hormone secretion. Rather it is the response to this pattern of secretion that has been modified.

Two models of the mechanism that measures daylength in the photoperiodic testicular response in Passer domesticus have been proposed. Both explain adequately the "ultra-short-day" response of this species, which appears to be unique among avian photoperiodic species. However, the models differ in their predictions of the response to very long days and to continuous light. Because of this we have examined experimentally the responses of this species thereto and have compared them with those of Zonotrichia leucophrys gambelii, which does not respond to "ultra-short days." We measured testicular growth rates and plasma levels of luteinizing hormone (LH), both of which increased with increasing daylength up to about 18L 6D and were maximal for all photoregimes from 20L 4D through LL. The results are consistent with the predictions of the simplest form of external-coincidence model, but not with those of the internal-coincidence model of Dolnik or the class of simple models that involve coincidence in phase of...

Circulating levels of testosterone in male white-crowned sparrows increase when their mates are sexually receptive. Two experiments were conducted to test the hypothesis that this increase in circulating levels of testosterone results in an increase in the intensity of male territorial defense. The first experiment demonstrated that males with sexually receptive females are more aggressive than males with nonreceptive females under laboratory conditions. The second experiment, conducted in the field, confirmed the laboratory finding and also demonstrated that experimental elevation of plasma levels of testosterone results in increased territorial defense. Thus, male territorial behavior in white-crowned sparrows appears to be regulated by changes in circulating levels of testosterone. The fact that this results in males being most aggressive when their mates are sexually receptive suggests that this response functions as mate-guarding behavior.

In many vertebrates, seasonal activation of sexual and territorial behaviors coincides with seasonal gonadal activation and is caused by the increase in sex steroid hormones. Both male and female Sceloporus jarrovi are territorial, but in this species territorial behavior is seasonally activated in late April, months before seasonal gonadal maturation, which occurs in August prior to the fall mating season. Measurements of seasonal changes in circulating levels of the sex steroid hormones testosterone, progesterone, and estradiol indicated that testosterone levels in both sexes are elevated when territorial behavior is expressed, even during the period of nonbreeding-season territoriality during the summer. This suggests that a nonbreeding season behavior is activated by a sex steroid hormone in this species.

We examined the hypothesis that increased aggression results in decreased survivorship. We tested this hypothesis by increasing aggression of free-living male lizards Sceloporus jarrovi with testosterone implants and evaluating the effects on survivorship. A previous study showed that testosterone-implanted males were more aggressive than controls, suggesting a greater degree of success in male-male competition. Results of the present study show that the same testosterone-implanted lizards experienced greater mortality. Testosterone-treated males were also seen more frequently and more conspicuous ones were less likely to survive. Testosterone-treated males lost more weight over the summer. In controls, survivorship was negatively correlated with the body weight index. These data suggest that conspicuousness and energetic demands interact in their influence on survivorship. Thus, the natural plasma level of testosterone may be at an optimal level balancing any potential selection pressures for a higher level of testosterone through sexual selection with selection pressures for a lower level through a decrease in survivorship.

The testes of male white-crowned sparrows, Zonotrichia leucophrys gambelii, subjected to a photoregimen of 12-h days (12L 12D) undergo quasiannual cycles of repeated growth and regression. These cycles decrease successively in period and amplitude and are not accompanied by postnuptial molts. This suggests that they are not physiologically equivalent to those of birds subjected to natural photocycles. Our results demonstrate that transfer of white-crowned sparrows undergoing testicular regression on 12L 12D to long days (20L 4D) induces both testicular growth and increases in plasma levels of luteinizing hormone at normal rates for 20L 4D. These data indicate that testicular regression on 12L 12D must be induced by mechanisms other than the development of photorefractoriness, which is the normal cause of regression on natural photocycles. This suggests very strongly that daylength functions as a driver of the independent components of the annual cycle rather than, as in some other species, a Zeitgeber for...

In free-living male white-crowned sparrows (Zonotrichia leucophrys), plasma levels of testosterone, 5α-dihydrotestosterone (DHT), and luteinizing hormone (LH) decrease precipitously at onset of incubation. The hypothesis that this decrease is a response to the simultaneous cessation of estradiol-dependent solicitation displays by females was tested in an experiment on free-living pairs. Solicitation displays were prolonged by implanting females with subcutaneous estradiol capsules and releasing them. Subsequent capture and blood sampling of the mates of these females showed that they had significantly higher plasma levels of testosterone and DHT than did control males, but results for LH were equivocal. Nevertheless, these results support the above hypothesis and suggest that hormone-behavior interactions are important even in free-living animals exposed to the entire spectrum of environmental information.

Previous experiments have shown that expression of mounting behavior in sexually inexperienced, adult male white-crowned sparrows does not require elevated plasma levels of androgen; adult males maintained on nonstimulatory short days mount sexually receptive females. The experiments reported here demonstrate that (1) sexually inexperienced, prepubertal males maintained on nonstimulatory short days show very low mounting rates in response to female sexual displays; (2) these males exhibit high mounting rates when exposed to stimulatory long days but androgen treatment on short days is ineffective in stimulating high mounting rates; and (3) prepubertal castration has no effect on the expression of mounting behavior by photostimulated adult males. Thus, there is no evidence that mounting behavior of adult male white-crowned sparrows depends on androgen.

Seasonal changes in testosterone levels in male mountain spiny lizards (Sceloporus jarrovi) are correlated tightly with seasonal changes in intensity of aggressive territorial defense. Testosterone levels are lowest in the winter when males aggregate, are moderately elevated during the summer when males show low-intensity territorial defense, and are highest during the fall breeding season when males show high-intensity territorial defense. In this study, we tested the hypothesis that changes in testosterone levels cause these seasonal changes in territorial behavior. We experimentally increased and decreased circulating testosterone levels in free-living males during the summer, when they display non-breeding season territoriality. Artificially increasing testosterone levels to levels equivalent to the breeding season significantly increased some, but not all, measures of territorial aggression. Levels of aggression attained, however, were still well below those typical of breeding season males. This implies that the transition to full breeding season levels of aggression is caused only partly by an increase in testosterone levels. Castration of males during the summer had no effect on several measures of territorial aggression. Thus the activation of nonbreeding season territoriality, which precedes testicular recrudescence by several months, is relatively unaffected by testosterone levels. Taken together these results suggest that the same behavior, in this case territorial aggression, may be controlled by different mechanisms in different seasons.

Cnemidophorus uniparens is a unisexual lizard that reproduces by parthenogenesis. Individuals of this species display male-like and female-like copulatory behaviors during different phases of the ovarian cycle suggesting that these pseudocopulatory behaviors are hormonally activated. To learn more about both the endocrinology of parthenogenesis and the possible hormonal activation of male-like copulatory behavior in female individuals, we (1) characterized changes in plasma levels of the sex steroid hormones progesterone, 5 alpha-dihydrotestosterone, testosterone, and 17 beta-estradiol during the ovarian cycle in both free-living and captive individuals, and (2) measured sex steroid hormones in plasma collected from captive individuals immediately after they expressed male-like or female-like copulatory behavior. In general, the pattern of secretion of ovarian hormones in C. uniparens appears to be similar to that of other oviparous vertebrates with similar reproductive cycles. Estradiol is elevated only during the preovulatory phase, whereas progesterone increases slightly during vitellogenesis and then increases dramatically following ovulation. Circulating levels of androgen are very low and are generally below the sensitivity of our radioimmunoassay at all stages of the ovarian cycle. The hormonal correlates of female-like copulatory behavior suggest that, as in other vertebrates, female receptivity is activated by a synergism of estradiol and progesterone. There is no evidence that the hormonal cycle has been altered to produce elevated levels of androgens during the phase of the cycle when male-like behavior is expressed. Rather it seems more likely that the central nervous system has evolved a novel response to a typical pattern of ovarian steroid hormone secretion. At present, the best hormonal correlate of male-like behavior is that changes in plasma levels of progesterone closely parallel changes in probability of expressing male-like behavior.

Two aspects of hormonal control of aggressive territorial behavior in male mountain spiny lizards Sceloporus jarrovi were studied. First, testosterone (T) implants were given to free-living castrated males during the breeding season. These implants fully restored breeding season levels of aggressive and sexual behavior. Earlier studies showed that identical implants given to free-living males during the nonbreeding season did not induce full breeding season levels of aggression. The full effectiveness of these implants during the breeding season indicates that the lack of effectiveness in the nonbreeding season was not due (1) to the need to replace additional gonadal factors or (2) to ineffectiveness of tonic delivery by the implants. It is more likely that males are less sensitive to T during the nonbreeding season or that other cues present in the breeding season environment synergize with T to induce full levels of aggression. Thus, seasonal changes in aggressive behavior in male S. jarrovi cannot be explained simply as a direct response to changes in circulating levels of T; other environmental factors play a necessary role as well. In the second phase of the study, changes in aggressive behavior of free-living T-implanted castrates were monitored following staged encounters with other males. Despite their inability to alter secretion rates of T, the T-implanted castrates still showed a rapid postencounter increase in aggressive displays that was identical to controls. Previous results showed that this dramatic postencounter increase in aggressive behavior is not accompanied by simultaneous changes in circulating T. Together, these results now allow the hypothesis that this rapid behavioral change in aggressive behavior is caused by simultaneous changes in circulating T levels to be confidently rejected.