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John C. Wingfield - One of the best experts on this subject based on the ideXlab platform.
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seasonal differences of gene expression profiles in song sparrow melospiza melodia hypothalamus in relation to Territorial Aggression
PLOS ONE, 2009Co-Authors: Motoko Mukai, Douglas W Wacker, John C. Wingfield, Kirstin Replogle, Jenny Drnevich, Gang Wang, Mark Band, David F ClaytonAbstract:Background: Male song sparrows (Melospiza melodia) are Territorial year-round; however, neuroendocrine responses to simulated Territorial intrusion (STI) differ between breeding (spring) and non-breeding seasons (autumn). In spring, exposure to STI leads to increases in luteinizing hormone and testosterone, but not in autumn. These observations suggest that there are fundamental differences in the mechanisms driving neuroendocrine responses to STI between seasons. Microarrays, spotted with EST cDNA clones of zebra finch, were used to explore gene expression profiles in the hypothalamus after Territorial Aggression in two different seasons. Methodology/Principal Findings: Free-living Territorial male song sparrows were exposed to either conspecific or heterospecific (control) males in an STI in spring and autumn. Behavioral data were recorded, whole hypothalami were collected, and microarray hybridizations were performed. Quantitative PCR was performed for validation. Our results show 262 cDNAs were differentially expressed between spring and autumn in the control birds. There were 173 cDNAs significantly affected by STI in autumn; however, only 67 were significantly affected by STI in spring. There were 88 cDNAs that showed significant interactions in both season and STI. Conclusions/Significance: Results suggest that STI drives differential genomic responses in the hypothalamus in the spring vs. autumn. The number of cDNAs differentially expressed in relation to season was greater than in relation to social interactions, suggesting major underlying seasonal effects in the hypothalamus which may determine the differential response upon social interaction. Functional pathway analyses implicated genes that regulate thyroid hormone action and neuroplasticity as targets of this neuroendocrine regulation.
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The effects of combined aromatase inhibitor and anti-androgen on male Territorial Aggression in a tropical population of rufous-collared sparrows, Zonotrichia capensis.
General and comparative endocrinology, 2004Co-Authors: Ignacio T. Moore, Brian G. Walker, John C. WingfieldAbstract:Territorial Aggression, exhibited by male vertebrates in a reproductive context, is generally thought to be mediated by elevated levels of the gonadal steroid hormone testosterone. Rufous-collared sparrows from Papallacta, Ecuador are only aggressive during the breeding season when plasma testosterone concentrations are elevated. However, previous experiments have determined that during the breeding season testosterone does not increase in response to Territorial challenges and testosterone implants do not make males more aggressive. This relationship between testosterone and Aggression is different from closely related northern latitude species. We conducted another experiment investigating the role of testosterone in mediating Territorial Aggression, during the breeding season, in male rufous-collared sparrows. We predicted that blocking the actions of the testosterone would suppress Aggression in response to Territorial challenges. During the early breeding season males were captured using a simulated Territorial intrusion and there was no relationship between time to capture and plasma testosterone, dihydrotestosterone, and corticosterone concentrations. Individual males were then implanted with both the aromatase inhibitor ATD and the anti-androgen Flutamide or empty implants as a control. After one week, birds were challenged with a simulated Territorial intrusion and the aggressive responses measured. There were no differences in individual behavioral responses (number of songs, flights, closest approach, or time within 5 m) or overall Aggression between the two groups. Androgen levels were elevated, post-implant, in the experimental group suggesting that the treatment was successful by blocking the negative feedback system. We conclude that pharmacologically inhibiting testosterone during the breeding season does not affect Territorial Aggression in these birds.
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Territorial Aggression of a Tropical Passerine, Zonotrichia Capensis, in Response to a Variety of Conspecific Intruders
Behaviour, 2004Co-Authors: D. Shallin Busch, John C. WingfieldAbstract:[The expression of Territorial Aggression by reproductively active, resident birds varies between the sexes and in response to different intruder types. Previous studies have predicted that individuals should be more aggressive towards conspecific intruders of the same sex and tolerate intruders of the opposite sex and immature individuals. In this study, we investigated the behavioural responses of a tropical population of rufous-collared sparrows (Zonotrichia capensis) to a variety of caged intruder types: Singing Males, Silent Males, Females, and Juveniles. In this species, territories are used by the resident male and female and their young, and are also used by floaters — mature individuals that do not hold territories. Resident males responded similarly and aggressively to all adult intruders in terms of song number, closest approach to the intruder, time within 5 m of the intruder, and a composite Aggression score. There was no significant variation in the response of resident females to the different intruder types, although the strongest responses of the resident female were to female intruders. Neither resident males nor females behaved aggressively towards juvenile intruders. These results fail to support the observational predictions for males and females that individuals should be most aggressive towards members of the same sex, who pose the greatest threat in terms of cuckoldry and Territorial takeover., The expression of Territorial Aggression by reproductively active, resident birds varies between the sexes and in response to different intruder types. Previous studies have predicted that individuals should be more aggressive towards conspecific intruders of the same sex and tolerate intruders of the opposite sex and immature individuals. In this study, we investigated the behavioural responses of a tropical population of rufous-collared sparrows (Zonotrichia capensis) to a variety of caged intruder types: Singing Males, Silent Males, Females, and Juveniles. In this species, territories are used by the resident male and female and their young, and are also used by floaters — mature individuals that do not hold territories. Resident males responded similarly and aggressively to all adult intruders in terms of song number, closest approach to the intruder, time within 5 m of the intruder, and a composite Aggression score. There was no significant variation in the response of resident females to the different intruder types, although the strongest responses of the resident female were to female intruders. Neither resident males nor females behaved aggressively towards juvenile intruders. These results fail to support the observational predictions for males and females that individuals should be most aggressive towards members of the same sex, who pose the greatest threat in terms of cuckoldry and Territorial takeover.]
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steroid hormone interrelationships with Territorial Aggression in an arctic breeding songbird gambel s white crowned sparrow zonotrichia leucophrys gambelii
Hormones and Behavior, 2002Co-Authors: Simone Meddle, Ignacio T. Moore, Michael L Romero, L B Astheimer, William A Buttemer, John C. WingfieldAbstract:The breeding season is very brief for arctic-breeding passerines, and any interruptions of parental care by aggressive interactions over territory may reduce reproductive success. We tested both the “testosterone insensitivity” and “corticosterone insensitivity” hypotheses in the arctic-breeding Gambel's white-crowned sparrow, Zonotrichia leucophrys gambelii. Additionally, we tested whether simulated Territorial intrusions (STIs), known to stimulate increases in luteinizing hormone (LH) and testosterone (T) in mid-latitude breeding Z. l. pugetensis, would also be effective in either the early or late phases of the brief breeding season of Z. l. gambelii. Plasma levels of T and LH were high early in the breeding season and declined as egg laying began. Exposure of free-living males to 10 min of STI significantly increased LH but not T secretion. Nonetheless, the pituitary–gonadal axis is sensitive as jugular injection of gonadotrophin-releasing hormone increased plasma T at 10 min relative to saline-challenged controls. T implants failed to increase Territorial Aggression following STI during incubation. These data are consistent with the T insensitivity hypothesis and contrast sharply with the response of the southerly breeding subspecies, Z. l. pugetensis, in which the Territorial response to T administration is retained throughout its relatively long breeding season. However, corticosterone implants during the incubation period decreased Territorial Aggression during STI. This responsiveness to corticosterone is not consistent with the corticosterone insensitivity hypothesis of stress modulation. Z. l. gambelii retain sensitivity to corticosterone levels that may occur naturally in response to environmental perturbations resulting in suppression of Territorial behavior.
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dehydroepiandrosterone in songbird plasma seasonal regulation and relationship to Territorial Aggression
General and Comparative Endocrinology, 2001Co-Authors: Kiran K Soma, John C. WingfieldAbstract:Many male animals are Territorial in the breeding season, when plasma testosterone (T) levels are high, and nonTerritorial in the nonbreeding season, when plasma T levels are basal. In contrast to this common pattern, male song sparrows (Melospiza melodia morphna) are Territorial year-round, except briefly during molt. Song sparrows are highly aggressive in the nonbreeding season (autumn and winter), even though plasma T, 5 alpha-dihydrotestosterone, androstenedione (AE), and 17beta-estradiol levels are undetectable (
Michael C Moore - One of the best experts on this subject based on the ideXlab platform.
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arginine vasotocin avt immunoreactivity relates to testosterone but not Territorial Aggression in the tree lizard urosaurus ornatus
Brain Behavior and Evolution, 2008Co-Authors: David Kabelik, Stacey L Weiss, Michael C MooreAbstract: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.
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ovarian hormones influence Territorial Aggression in free living female mountain spiny lizards
Hormones and Behavior, 1999Co-Authors: Sarah K Woodley, Michael C MooreAbstract: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.
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female Territorial Aggression and steroid hormones in mountain spiny lizards
Animal Behaviour, 1999Co-Authors: Sarah K Woodley, Michael C MooreAbstract:Abstract 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.
Kiran K Soma - One of the best experts on this subject based on the ideXlab platform.
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Brain Aromatase and Territorial Aggression Across the Seasons
2016Co-Authors: In Male Song Sparrows, Sarah A. Heimovics, Bobby H. Fokidis, Kiran K SomaAbstract:Estrogens regulate a variety of social behaviors, including appetitive and consummatory sexual behavior, social affi liation, and Aggression. Much of our understanding of the roles of estrogens in social behavior comes from laboratory studies of domesticated mice and rats (Blumstein et al., 2010; Soma et al., 2008)
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year round Territorial Aggression is independent of plasma dhea in the european nuthatch sitta europaea
Hormones and Behavior, 2013Co-Authors: Mėta M Landys, Kiran K Soma, Wolfgang Goymann, Tore SlagsvoldAbstract:Plasma testosterone can play an important role in promoting aggressive behaviors relating to territory defense in breeding male birds. Some birds defend territories also during the non-breeding phase, when testosterone circulates at basal levels. In such species, plasma levels of the pro-hormone dehydroepiandrosterone (DHEA) may support non-breeding Territoriality by acting as a local substrate for sex steroids. To test this possible role of plasma DHEA, we examined the seasonal DHEA profile of male (and female) European nuthatches Sitta europaea: a male and female nuthatch pair will defend an all-purpose territory throughout the year. We hypothesized that plasma DHEA would be detectable in wintering nuthatches with a territory. However, only ca. half of the Territorial wintering males (and females) displayed detectable DHEA levels, suggesting that plasma DHEA is not a major sex steroid precursor during non-breeding. Further, among hatching-year birds, plasma DHEA was significantly lower in Territorial birds than in “floaters”, i.e., subordinate birds without a territory. To experimentally examine the role of DHEA in non-breeding Territoriality, we treated adult wintering males with DHEA and measured effects on aggressive responses to conspecific challenge. DHEA treatment elevated plasma levels of DHEA (and testosterone), but did not enhance Territorial behaviors or their persistence. Taken together, our data suggest that DHEA (and, indeed, sex steroids per se) do not regulate non-breeding Territoriality in the nuthatch. Given that Territorial Aggression in nuthatches is expressed year-round, a hormone for its activation may be redundant.
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Territorial Aggression and hormones during the non breeding season in a tropical bird
Hormones and Behavior, 2004Co-Authors: Michaela Hau, Steven T Stoddard, Kiran K SomaAbstract:The hormonal control of Territorial Aggression in male and female vertebrates outside the breeding season is still unresolved. Most vertebrates have regressed gonads when not breeding and do not secrete high levels of sex steroids. However, recent studies implicate estrogens in the regulation of non-breeding Territoriality in some bird species. One possible source of steroids during the non-breeding season could be the adrenal glands that are known to produce sex steroid precursors such as dehydroepiandrosterone (DHEA). We studied tropical, year-round Territorial spotted antbirds (Hylophylax n. naevioides) and asked (1). whether both males and females are aggressive in the non-breeding season and (2). whether DHEA is detectable in the plasma at that time. We conducted simulated Territorial intrusions (STIs) with live decoys to male and female free-living spotted antbirds in central Panama. Non-breeding males and females displayed robust aggressive responses to STIs, and responded more intensely to decoys of their own sex. In both sexes, plasma DHEA concentrations were detectable and higher than levels of testosterone (T) and 17beta-estradiol (E(2)). In males, plasma DHEA concentrations were positively correlated with STI duration. Next, we conducted STIs in captive non-breeding birds. Captive males and females displayed robust aggressive behavior. Plasma DHEA concentrations were detectable in both sexes, whereas T was non-detectable (E(2) was not measured). Plasma DHEA concentrations of males were positively correlated with aggressive vocalizations and appeared to increase with longer STI durations. We conclude that male and female spotted antbirds can produce DHEA during the non-breeding season and DHEA may serve as a precursor of sex steroids for the regulation of year-round Territorial behavior in both sexes.
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dehydroepiandrosterone in songbird plasma seasonal regulation and relationship to Territorial Aggression
General and Comparative Endocrinology, 2001Co-Authors: Kiran K Soma, John C. WingfieldAbstract:Many male animals are Territorial in the breeding season, when plasma testosterone (T) levels are high, and nonTerritorial in the nonbreeding season, when plasma T levels are basal. In contrast to this common pattern, male song sparrows (Melospiza melodia morphna) are Territorial year-round, except briefly during molt. Song sparrows are highly aggressive in the nonbreeding season (autumn and winter), even though plasma T, 5 alpha-dihydrotestosterone, androstenedione (AE), and 17beta-estradiol levels are undetectable (
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testosterone and year round Territorial Aggression in a tropical bird
General and Comparative Endocrinology, 2000Co-Authors: Michaela Hau, Kiran K Soma, Martin Wikelski, John C. WingfieldAbstract:Testosterone (T) regulates avian behaviors such as song and Aggression during the breeding season. However, the role of T in year-round Territorial birds is still enigmatic, especially in tropical birds. Spotted antbirds (Hylophylax n. naevioides) defend territories in the Panamanian rainforest year-round but have low plasma T levels (0.1–0.2 ng/ml), except during brief periods of social challenges. We manipulated T action in captive male Spotted antbirds to test whether this hormone is involved in the regulation of song and Aggression. T-implants increased plasma androgen levels (T and dihydrotestosterone) and enhanced song in nonbreeding males. During a staged male–male encounter, T-implanted males sang more and were more aggressive than controls. In a second experiment, we blocked the two known T actions: its binding to androgen receptors and its conversion into estradiol by the enzyme aromatase. For this, we administered the androgen receptor antagonist flutamide (Flut) in combination with the aromatase inhibitor 1-4-6 androstatrien-3,17-dione (ATD) to birds in breeding condition. ATD + Flut treatment significantly elevated plasma levels of luteinizing hormone, presumably via the lack of T feedback from its receptors. ATD + Flut-treated birds gave fewer spontaneous songs than control-implanted males. During staged male–male encounters, ATD + Flut-treated males did not sing at all and showed reduced aggressive behavior. Our data indicate that T can regulate aggressive behavior in these tropical birds. Although plasma T levels can be low year-round, Spotted antbirds may use T either by secreting it briefly during social challenges, by having a high sensitivity to T action, or by enzymatically converting circulating T precursors directly at the site of action. We hypothesize that plasma T levels are kept low in these year-round Territorial birds to avoid potentially detrimental effects of tonically elevated T. Future treatment of nonbreeding birds with ATD + Flut will reveal whether T is indeed involved year-round in regulating aggressive behavior.
Michaela Hau - One of the best experts on this subject based on the ideXlab platform.
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plastic endocrine regulation of year round Territorial Aggression in tropical male spotted antbirds
General and Comparative Endocrinology, 2011Co-Authors: Michaela Hau, Katherine BeebeAbstract:Studies investigating the hormonal regulation of Aggression often focus on the role of the steroid hormone testosterone (T). These studies have generally found an association in temperate zone species between T and male Aggression in a reproductive context. However, in most temperate zone species seasonal variation in reproductive context cannot easily be separated from concomitant seasonal changes in other variables, including territory location and partner presence. Therefore, we investigated the hormonal regulation of Territorial Aggression in a tropical bird that breeds seasonally, but remains mated and Territorial year-round. Free-living male spotted antbirds (Hylophylax n. naevioides) displayed similar aggressive behavior in the non-breeding, early, and middle breeding seasons when exposed to a simulated Territorial intrusion (STI). Plasma T concentrations after STIs were low and seasonally invariant, but plasma dehydroepiandrosterone (DHEA) was elevated during the non-breeding season. Simultaneous administration of pharmacological inhibitors of androgenic and estrogenic actions during the non-breeding season was less effective in reducing aggressive behavior of captive males compared with a previous study conducted during the breeding season. Hence, in male spotted antbirds endocrine mechanisms appear to vary with reproductive context, both in DHEA concentrations and in the importance of T for regulating aggressive behavior. Furthermore, combining the current data with previous findings suggests that short-term increases in T during aggressive interactions in this tropical species are dependent on the context and the intensity of aggressive stimuli, regardless of season.
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Territorial Aggression and hormones during the non breeding season in a tropical bird
Hormones and Behavior, 2004Co-Authors: Michaela Hau, Steven T Stoddard, Kiran K SomaAbstract:The hormonal control of Territorial Aggression in male and female vertebrates outside the breeding season is still unresolved. Most vertebrates have regressed gonads when not breeding and do not secrete high levels of sex steroids. However, recent studies implicate estrogens in the regulation of non-breeding Territoriality in some bird species. One possible source of steroids during the non-breeding season could be the adrenal glands that are known to produce sex steroid precursors such as dehydroepiandrosterone (DHEA). We studied tropical, year-round Territorial spotted antbirds (Hylophylax n. naevioides) and asked (1). whether both males and females are aggressive in the non-breeding season and (2). whether DHEA is detectable in the plasma at that time. We conducted simulated Territorial intrusions (STIs) with live decoys to male and female free-living spotted antbirds in central Panama. Non-breeding males and females displayed robust aggressive responses to STIs, and responded more intensely to decoys of their own sex. In both sexes, plasma DHEA concentrations were detectable and higher than levels of testosterone (T) and 17beta-estradiol (E(2)). In males, plasma DHEA concentrations were positively correlated with STI duration. Next, we conducted STIs in captive non-breeding birds. Captive males and females displayed robust aggressive behavior. Plasma DHEA concentrations were detectable in both sexes, whereas T was non-detectable (E(2) was not measured). Plasma DHEA concentrations of males were positively correlated with aggressive vocalizations and appeared to increase with longer STI durations. We conclude that male and female spotted antbirds can produce DHEA during the non-breeding season and DHEA may serve as a precursor of sex steroids for the regulation of year-round Territorial behavior in both sexes.
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testosterone and year round Territorial Aggression in a tropical bird
General and Comparative Endocrinology, 2000Co-Authors: Michaela Hau, Kiran K Soma, Martin Wikelski, John C. WingfieldAbstract:Testosterone (T) regulates avian behaviors such as song and Aggression during the breeding season. However, the role of T in year-round Territorial birds is still enigmatic, especially in tropical birds. Spotted antbirds (Hylophylax n. naevioides) defend territories in the Panamanian rainforest year-round but have low plasma T levels (0.1–0.2 ng/ml), except during brief periods of social challenges. We manipulated T action in captive male Spotted antbirds to test whether this hormone is involved in the regulation of song and Aggression. T-implants increased plasma androgen levels (T and dihydrotestosterone) and enhanced song in nonbreeding males. During a staged male–male encounter, T-implanted males sang more and were more aggressive than controls. In a second experiment, we blocked the two known T actions: its binding to androgen receptors and its conversion into estradiol by the enzyme aromatase. For this, we administered the androgen receptor antagonist flutamide (Flut) in combination with the aromatase inhibitor 1-4-6 androstatrien-3,17-dione (ATD) to birds in breeding condition. ATD + Flut treatment significantly elevated plasma levels of luteinizing hormone, presumably via the lack of T feedback from its receptors. ATD + Flut-treated birds gave fewer spontaneous songs than control-implanted males. During staged male–male encounters, ATD + Flut-treated males did not sing at all and showed reduced aggressive behavior. Our data indicate that T can regulate aggressive behavior in these tropical birds. Although plasma T levels can be low year-round, Spotted antbirds may use T either by secreting it briefly during social challenges, by having a high sensitivity to T action, or by enzymatically converting circulating T precursors directly at the site of action. We hypothesize that plasma T levels are kept low in these year-round Territorial birds to avoid potentially detrimental effects of tonically elevated T. Future treatment of nonbreeding birds with ATD + Flut will reveal whether T is indeed involved year-round in regulating aggressive behavior.
Kendra B Sewall - One of the best experts on this subject based on the ideXlab platform.
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urbanization alters the relationship between coloration and Territorial Aggression but not hormones in song sparrows
Animal Behaviour, 2018Co-Authors: Michelle L. Beck, Scott Davies, Kendra B SewallAbstract:Melanin-based coloration is associated with aspects of phenotype, including conspecific Aggression and hormone concentrations. These relationships could arise as a result of genetic and/or biochemical links between melanin production and other traits. Additionally, anthropogenic change, including urbanization, exposes animals to novel conditions that can alter pigmentation, behaviour or hormones, potentially disrupting relationships between coloration and other traits. We examined relationships among the extent and darkness of melanin spotting on the breast of male song sparrows, Melospiza melodia, Territorial behaviour, plasma testosterone and corticosterone concentrations to determine whether coloration was reliably associated with phenotype in this species. We conducted this study in urban and rural populations to determine whether relationships between coloration, behaviour and hormones varied between habitats. Males in urban habitat had more extensive brown spotting than rural males. The relationship between melanin coloration and Territoriality differed in urban and rural habitats. In rural sparrows, Territoriality was negatively correlated with spotting area, while in urban sparrows Territoriality was positively associated with spotting darkness. Regardless of habitat, males with more extensive spotting increased testosterone secretion more in response to gonadotropin-releasing hormone administration and males with darker spotting had greater handling restraint-induced release of corticosterone. This suggests that plumage coloration is associated with underlying physiology, but the relationship between coloration and behaviour may shift between habitats.
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Territorial Aggression in urban and rural Song Sparrows is correlated with corticosterone, but not testosterone.
Hormones and behavior, 2017Co-Authors: Scott Davies, Michelle L. Beck, Kendra B SewallAbstract:Abstract Urban songbirds of several species more vigorously defend their territories in response to conspecific song playback than do their rural counterparts, but the hormonal basis of this behavioral difference is unclear. It is well established in vertebrates that both testosterone and corticosterone affect the intensity of Territoriality. Previous studies have found no evidence that initial (i.e., immediately following Territorial challenge, but prior to restraint) plasma testosterone accounts for the elevated Territorial Aggression of urban birds. Determining if testosterone still contributes to urban-rural differences in Territoriality requires also assessing males' abilities to transiently increase plasma testosterone (in response to an injection of gonadotropin-releasing hormone). We tested whether these hormones are correlated with the Territorial response to conspecific song playback in urban and rural male Song Sparrows (Melospiza melodia) in Montgomery County, Virginia. We found that the elevated Territorial Aggression of urban sparrows was not related to variation in either initial plasma testosterone or the ability to transiently increase testosterone. In contrast, despite no overall habitat difference in initial corticosterone, levels of this hormone were positively correlated with Territoriality in urban and rural sparrows. Furthermore, for a given level of corticosterone, urban sparrows were more Territorially aggressive. Our findings suggest that initial corticosterone may either play a role in the regulation of persistent differences in Territorial behavior between free-ranging urban and rural male Song Sparrows or be affected by the intensity of behavioral response to Territorial challenge.
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Two Neural Measures Differ between Urban and Rural Song Sparrows after Conspecific Song Playback
Frontiers Media S.A., 2017Co-Authors: Kendra B Sewall, Scott DaviesAbstract:Urbanization is a critical form of environmental change that can affect the physiology and behavior of wild animals and, notably, birds. One behavioral difference between birds living in urban and rural habitats is that urban males show elevated boldness or Territorial Aggression in response to simulated social challenge. This pattern has been described in several populations of song sparrow, Melospiza melodia. Such behavioral differences must be underpinned by differences in the brain, yet little work has explored how urbanization and neural function may be interrelated. We explored the relationship between urbanization and neural activation within a network of brain regions, collectively called the social behavior network, which contributes to the regulation of Territorial Aggression. Specifically, we captured free-living, Territorial male song sparrows by playing them conspecific songs for 6–11 min, and then collected their brains. We estimated recent neural activation, as indicated by the immediate early gene FOS, and measured levels of a neuropeptide, arginine vasotocin (AVT), which is involved in the regulation of social behavior. Based on previous studies we expected urban males, which are generally more Territorially aggressive, to have lower FOS expression in a node of the social behavior network implicated in regulating Territoriality, the lateral septum (LS). Additionally, we expected urban males to have lower AVT expression in a brain region involved in the regulation of sociality, the medial bed nucleus of the stria terminalis (BSTm). We found that, compared to rural males, urban male song sparrows did have lower FOS expression in the LS. This pattern suggests that lower neural activation in the LS could contribute to behavioral adjustments to urbanization in male song sparrows. Additionally, counter to our predictions, urban male song sparrows had higher AVT-like immunoreactivity in the BSTm. Future work building upon these findings is needed to determine the causal role of such neural differences across rural and urban habitats. Understanding the mechanisms impacted by urbanization will inform our understanding of the reversibility and consequences of this form of habitat change
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agonistic urban birds elevated Territorial Aggression of urban song sparrows is individually consistent within a breeding period
Biology Letters, 2016Co-Authors: Scott Davies, Kendra B SewallAbstract:Urban birds often more vigorously defend their territories during simulated intrusions than do their rural counterparts, but the factors responsible remain unclear. To address this issue, we investigated whether the disparity in Territorial Aggression of urban and rural male song sparrows, Melospiza melodia , is individually consistent within a breeding period. Additionally, to better understand the physiological and ecological factors underlying this behavioural difference, we examined whether Territoriality was associated with plasma testosterone, a hormone that contributes to elevated Aggression in vertebrates, and/or conspecific density, a factor often positively related to Aggression. The urbanization-related difference in Territoriality was individually consistent within a breeding period. However, the elevated Territorial Aggression of urban birds was not associated with plasma testosterone and, counter to our predictions, conspecific density was lower in urban compared with rural areas. We suggest that other aspects of testosterone signalling and features of the socio-ecological environment, such as the availability of breeding sites, may underlie increased Territorial Aggression in urban birds.
