Browsing by Subject "Androgens"
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Item Aggression, space use, and dominance in a social cichlid fish(2021-12-03) Friesen, Caitlin Nicole; Hofmann, Hans (Hans A.); Ryan, Michael J. (Michael Joseph), 1953-; Alonzo, Suzanne; Gore, Andrea C.; Phelps, Steven M.How do individuals adjust their behavior across changing contexts to obtain resources needed to survive and reproduce? In group living animals, behavioral variation is regulated by the surrounding group and the underlying patterns of hormones and neural gene expression. We can often learn more by studying an individual in response to different challenging situations than in an undisturbed setting. For example, the challenge hypothesis has provided a useful framework across taxa to understand causal relationships between androgen hormones and aggressive behavior in response to reproductively motivated social challenges (reviewed in Chapter 1). In contrast, we still have much to learn about dynamic interactions across molecular, physiological, morphological, or behavioral traits that may be functionally linked (the “integrated phenotype”), or the effects of an individual response on others within the social group. There is a paucity of data focused on acute measures of dynamic space use, social behavior, and hormone levels in response to a challenge. To address this gap in our understanding, I conducted a series of experiments using the African cichlid fish, Astatotilapia burtoni. This species occurs in dynamic social groups, and males form dominance hierarchies where socially dominant males defend territories to gain exclusive access to reproductive opportunities. In chapter 2, I examined behavioral variation across dominant males in relation to space use, hormone levels, and gene expression in response to a perturbation to create an integrative metric of territorial behavior. My results show that an integrative analysis of behavioral variation can identify sub-types of dominant male and predict their response to perturbation. In chapter 3, I utilized this integrative metric to investigate how resident dominant males respond to a male intruder within the social group. I found that resident males exhibited distinct types of aggressive displays that differed depending on the outcome of intrusion. Finally, in chapter 4, I investigated whether traits involved in territorial behavior exhibited patterns of covariation by hormonally manipulating one dominant male within each social group. I found context-dependent associations between hormones, space use, and social behavior in dominant males. Taken together, my research highlights the importance of considering acute, dynamic measures of social behavior and space use along with physiological and neural mechanisms involved in individual responses to challenges within naturalistic social groups.Item Androgen modulation of vocal circuits in Alston’s singing mice, scotinomys teguina(2020-12-05) Zheng, Da-Jiang; Phelps, Steven Michael, 1970-; Gore, Andrea; Ryan, Mike; Zakon, HaroldSexual dimorphism in brain and behavior are often among the most conspicuous forms of intraspecific variation. Gonadal state often shape differences between the sexes. Steroids may directly lead to changes in most of levels of biological organization. In the vertebrate brain for example, expression of steroid receptors and its ligands may lead to direct consequences from the motor systems to the limbic system. The songs of Alston’s singing mouse (Scotinomys teguina) are sexually dimorphic and are composed of a series of rapidly repeated, broad-bandith, frequency-modulated notes. Males sing more often than females. Castration makes songs softer, shorter, and less common. This decrease in performance can be rescued by the application of dihydrotestosterone suggesting that androgen receptors play a critical role. In this dissertation, I seek to further understand the role of the androgen receptor in influencing the singing behavior of this species by three interconnected aims. First, we map the sites of androgen sensitivity along a pathway that spans from limbic structures to vocal control regions and quantify differences in nuclear androgen receptor-like labeling in male and female brains. Second, we use a transsynaptic virus to examine how the forebrain connects to the motor control of the jaw and larynx. Third, we manipulate the hormonal milieu by castrating and then implanting DHT to observe changes in both brain and behavior. Together we gained better insight into not only how androgen receptors mediate changes to vocalization but also how gonadal state lead to variation between the sexes.Item The effects of androgens on steroidogenesis in the ovary of Atlantic croaker (Micropogonias undulatus) : mechanism of action, the biochemical characterization of a membrane androgen receptor, and the chronic effects of exposure to an environmental antiandrogen(2002-05) Braun, Alyssa Maria, 1974-; Thomas, P. (Peter)This study focuses on the actions of androgens in the gonads of the Atlantic croaker (Micropogonias undulatus). Physiologically relevant concentrations of androgens are shown to inhibit in vitro ovarian production of estradiol through a rapid, nongenomic mechanism initiated at the cell surface, which is not reversed by co-incubation with antiandrogens. Experiments with steroid precursors suggest that the site of androgen action is distal to 17OH-progesterone in the steroidogenic pathway. Further investigation revealed the presence of a membrane androgen receptor (mAR) in the croaker ovary that may mediate this androgen action. This mAR demonstrates a high affinity and finite capacity for androgen binding, which vii is both tissue and steroid specific. The croaker ovarian mAR is relatively unique among androgen receptors, since it binds dihydrotestosterone, testosterone, and progesterone with high affinity. No other C21 or any C18 steroid tested binds with high affinity. Androgen association and dissociation from the mAR is rapid. Levels of mAR are highest in reproductively mature gonads, which suggests a role for this receptor in female reproduction. Finally, the effects of chronic in vivo exposure to p,p’-DDE or cyproterone acetate (CA), which have been shown to act as antiandrogens in mammals, on indicators of reproductive health in croaker are described. Although the results were not consistent at all doses and time points of sampling, exposure to p,p’-DDE in vivo significantly inhibited gonadal growth, circulating sex steroid levels, and in vitro gonadal steroidogenesis in both males and females. The effects were subtle and mostly observed in fish treated with the highest dose of p,p’-DDE (0.05 mg/100 g bw/day) for the longest time period (24 weeks). Effects of the antiandrogenCA on gonadal function differed from those of p,p’-DDE, so it is unclear whether the observed effects of p,p’-DDE were antiandrogenic. The finding that p,p’-DDE can affect gonadal growth and disrupt the reproductive endocrine system in female and male croaker suggests that this chemical could impair reproduction in fish and other wildlife species in severely contaminated sites.Item Ontogenetic and mechanistic explanations of within-sex behavioral variation in a lizard with temperature- dependent sex determination(2013-12) Huang, Victoria; Crews, DavidThe leopard gecko (Eublepharis macularius) is a reptile species in which embryonic temperature contributes both to sex determination and within- sex polymorphisms. Its life history makes the leopard gecko a model system for seeking ontogenic and proximate explanations for within-sex variation in sexually dimorphic behavior and neurophysiology, necessary attributes for reproductive success. For my dissertation I have incorporated the role of androgens that potentially modulate incubation temperature effects on behavioral and brain variation, which I approached using embryo and adult leopard geckos. First, I found that that the bias of same-sex clutch siblings is primarily incubation temperature- dependent and any maternal or genetic effects on same-sex clutch siblings are secondary. Second, I found that testosterone concentrations in the yolk-albumen were higher in eggs of late development than early development at 26 °C, a female-producing incubation temperature, but did not differ from eggs incubated at another female-biased temperature. This increase in testosterone concentrations during the temperature sensitive period in putative females is a finding opposite of reported trends in most other reptiles studied to date. Further, I found that the embryonic environment influences male sociosexual investigation in the absence of gonadal hormones. Lastly, in adult males of 32.5 °C, a male-biased incubation temperature, I found that the phosphoprotein DARPP-32 that is activated by the D1 dopamine receptor in limbic brain regions is correlated to this sociosexual investigatory behavior. Neurons immunopositive for phosphorylated DARPP-32 were not only less dense in the nucleus accumbens of males who spent more time with other males, but also more dense in the preoptic area of males who spent more time with females. The use of phosphorylated DARPP-32 as marker for sociosexual exposure is novel in a lizard species. Taken together, in support of previous studies, these results show that differences in embryonic environment stem primarily from incubation temperature, can explain behavioral differences in adulthood in the absence of hormones, and, in concert with hormonal manipulation, can influence neuronal marker sensitivity to sociosexual exposure.