Ellen Ketterson

Publications

• Hormones and the evolution of behavior and other complex phenotypes

  E. D. Ketterson, J. W. Atwell, J. W. McGlothlin

  01/2012;
• 2.18

  Impact points

  Maintenance of MHC Class IIB diversity in a recently established songbird population

  Danielle J. Whittaker, Amy L. Dapper, Mark P. Peterson, Jonathan W. Atwell, Ellen D. Ketterson

  Journal of Avian Biology. 01/2012; in press.
• 2.41

  Impact points

  Role of testosterone in stimulating seasonal changes in a potential avian chemosignal.

  Danielle J Whittaker, Helena A Soini, Nicole M Gerlach, Amanda L Posto, Milos V Novotny, Ellen D Ketterson

  Journal of chemical ecology. 12/2011; 37(12):1349-57.

  Songbird preen oil contains volatile and semivolatile compounds that may contain information about species, sex, individual identity, and season. We examined the relationship between testosterone (T) and the amounts of preen oil volatile and semivolatile compounds in wild and captive dark-eyed junco... [more] Songbird preen oil contains volatile and semivolatile compounds that may contain information about species, sex, individual identity, and season. We examined the relationship between testosterone (T) and the amounts of preen oil volatile and semivolatile compounds in wild and captive dark-eyed juncos (Junco hyemalis). In wild males and females, we observed an increase in volatile compound relative concentration early in the breeding season. This increase mirrored previously described seasonal elevation in T levels in wild males and females, suggesting a positive relationship between hormone levels and preen gland secretions, and a possible role for these secretions in signaling receptivity. In females, the greatest relative concentrations of most compounds were observed close to egg laying, a time when steroid hormones are high and also the only time that females respond to an injection of gonadotropin-releasing hormone with a short-term increase in T. In a study of captive juncos held on short days, we asked whether the seasonal increases observed in the wild could be induced with experimental elevation of T alone. We found that exogenous T stimulated the production of some volatile compounds in non-breeding individuals of both sexes. However, of the 15 compounds known to increase during the breeding season, only four showed an increase in relative concentration in birds that received T implants. Our results suggest that testosterone levels likely interact with other seasonally induced physiological changes to affect volatile compound amounts in preen oil.
• 4.80

  Impact points

  Deciphering information encoded in birdsong: male songbirds with fertile mates respond most strongly to complex, low-amplitude songs used in courtship.

  Dustin G Reichard, Rebecca J Rice, Carla C Vanderbilt, Ellen D Ketterson

  The American naturalist. 10/2011; 178(4):478-87.

  Research on the function of acoustic signals has focused on high-amplitude long-range songs (LRS) and largely ignored low-amplitude songs produced by many species during close-proximity, conspecific interactions. Low-amplitude songs can be structurally identical to LRS (soft LRS), or they can be wid... [more] Research on the function of acoustic signals has focused on high-amplitude long-range songs (LRS) and largely ignored low-amplitude songs produced by many species during close-proximity, conspecific interactions. Low-amplitude songs can be structurally identical to LRS (soft LRS), or they can be widely divergent, sharing few spectral and temporal attributes with LRS (short-range song [SRS]). SRS is often more complex than LRS and is frequently sung by males during courtship. To assess function, we performed two playback experiments on males of a socially monogamous songbird. We compared responses of males whose mates were fertile or nonfertile with differences in song structure (SRS vs. LRS and soft LRS), amplitude (SRS and soft LRS vs. LRS), and tempo (slow SRS vs. fast SRS). Males responded more strongly to SRS than to LRS or soft LRS, indicating that song structure had a greater effect on response than song amplitude. SRS tempo did not detectably affect male response. Importantly, males responded more strongly to SRS when their mates were fertile, presumably because hearing SRS can indicate that a male's mate is being courted by an intruding male and a strong response can deter extrapair competitors. We conclude that low-amplitude songs can function in both inter- and intrasexual communication and should receive greater attention in future studies of mate choice and male-male competition.
• 2.02

  Impact points

  Two sides of the same coin? Consistency in aggression to conspecifics and predators in a female songbird.

  K E Cain, M S Rich, K Ainsworth, E D Ketterson

  Ethology : formerly Zeitschrift fur Tierpsychologie. 09/2011; 117(9):786-795.

  Different forms of aggression have traditionally been treated separately according to function or context (e.g. aggression towards a conspecific versus a predator). However, recent work on individual consistency in behavior predicts that different forms of aggression may be correlated across context... [more] Different forms of aggression have traditionally been treated separately according to function or context (e.g. aggression towards a conspecific versus a predator). However, recent work on individual consistency in behavior predicts that different forms of aggression may be correlated across contexts, suggesting a lack of independence. For nesting birds, aggression towards both conspecifics and nest predators can affect reproductive success, yet the relationship between these behaviors, especially in females, is not known. Here we examine free-living female dark-eyed juncos (Junco hyemalis) and compare their aggressive responses towards three types of simulated intruders near the nest: a same-sex conspecific, an opposite-sex conspecific, and a nest predator. We also examine differences in the strength of response that might relate to the immediacy of the perceived threat the intruder poses for the female or her offspring. We found greater aggression directed towards a predator than a same-sex intruder, and towards a same-sex than an opposite-sex intruder, consistent with a predator being a more immediate threat than a same-sex intruder, followed by an opposite-sex intruder. We also found positive relationships across individuals between responses to a same-sex intruder and a simulated predator, and between responses to a same-sex and an opposite-sex intruder, indicating that individual females are consistent in their relative level of aggression across contexts. If correlated behaviors are mediated by related mechanisms, then different forms of aggression may be expressions of the same behavioral tendency and constrained from evolving independently.
• 4.11

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  Promiscuous mating produces offspring with higher lifetime fitness.

  Nicole M Gerlach, Joel W McGlothlin, Patricia G Parker, Ellen D Ketterson

  Proceedings. Biological sciences / The Royal Society. 08/2011; 279(1730):860-6.

  In many species, each female pairs with a single male for the purpose of rearing offspring, but may also engage in extra-pair copulations. Despite the prevalence of such promiscuity, whether and how multiple mating benefits females remains an open question. Multiple mating is typically thought to be... [more] In many species, each female pairs with a single male for the purpose of rearing offspring, but may also engage in extra-pair copulations. Despite the prevalence of such promiscuity, whether and how multiple mating benefits females remains an open question. Multiple mating is typically thought to be favoured primarily through indirect benefits (i.e. heritable effects on the fitness of offspring). This prediction has been repeatedly tested in a variety of species, but the evidence has been equivocal, perhaps because such studies have focused on pre-reproductive survival rather than lifetime fitness of offspring. Here, we show that in a songbird, the dark-eyed junco (Junco hyemalis), both male and female offspring produced by extra-pair fertilizations have higher lifetime reproductive success than do offspring sired within the social pair. Furthermore, adult male offspring sired via extra-pair matings are more likely to sire extra-pair offspring (EPO) themselves, suggesting that fitness benefits to males accrue primarily through enhanced mating success. By contrast, female EPO benefited primarily through enhanced fecundity. Our results provide strong support for the hypothesis that the evolution of extra-pair mating by females is favoured by indirect benefits and shows that such benefits accrue much later in the offspring's life than previously documented.
• 3.30

  Impact points

  The effect of winter sex ratio on immune function and condition in a differential migrant.

  Dawn M O'Neal, Ryan P Kiley, Ellen D Ketterson

  Physiology & behavior. 03/2011; 102(3-4):406-13.

  The dark-eyed junco (Junco h. hyemalis) is a differential migrant in which females migrate farther south in winter than males. Hypotheses to explain this difference in migratory behavior have given limited consideration to physiological differences between the sexes, particularly with respect to imm... [more] The dark-eyed junco (Junco h. hyemalis) is a differential migrant in which females migrate farther south in winter than males. Hypotheses to explain this difference in migratory behavior have given limited consideration to physiological differences between the sexes, particularly with respect to immune function. We hypothesized that female migratory behavior could either be directly dependent on climate if migratory distance traveled is a product of interactions between climate and inherent sex differences in physiology, or indirectly dependent on climate owing to interactions between climate and aggressive encounters with males which are known to be behaviorally dominant to females and restrict their access to food. We tested the latter of these two hypotheses by measuring condition in females held in two sex ratio regimes in a common winter environment. Holding density constant in 28 replicate populations, we compared flocks composed of 100% female to mixed-sex flocks composed of 20% female. We assessed condition by measuring immune function via complement activity and response to a foreign antigen, keyhole limpet hemocyanin, as well as by indices of mass, fat, and pectoral muscle. Unexpectedly, females in mixed-sex flocks did not differ in condition from females housed only with females, despite increased aggressive interactions in mixed flocked cages. Combined, our results suggest that overwintering with males has no significant effect on female winter condition. Differential migration in the junco may be mediated by sex differences in ability to withstand harsh northern climate, as has been demonstrated in several mammalian systems, rather than dominance interactions.
• 2.98

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  Intraspecific preen oil odor preferences in dark-eyed juncos (Junco hyemalis)

  Danielle J. Whittaker, Kaitlin M. Richmond, Allison K. Miller, Ryan Kiley, Christine Bergeon Burns, Jonathan W. Atwell, Ellen D. Ketterson

  Behavioral Ecology. 01/2011; 22(1256):1263.
• 4.80

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  Natural selection on testosterone production in a wild songbird population.

  Joel W McGlothlin, Danielle J Whittaker, Sara E Schrock, Nicole M Gerlach, Jodie M Jawor, Eric A Snajdr, Ellen D Ketterson

  The American naturalist. 06/2010; 175(6):687-701.

  Because of their role in mediating life-history trade-offs, hormones are expected to be strongly associated with components of fitness; however, few studies have examined how natural selection acts on hormonal variation in the wild. In a songbird, the dark-eyed junco (Junco hyemalis), field experime... [more] Because of their role in mediating life-history trade-offs, hormones are expected to be strongly associated with components of fitness; however, few studies have examined how natural selection acts on hormonal variation in the wild. In a songbird, the dark-eyed junco (Junco hyemalis), field experiments have shown that exogenous testosterone alters individuals' resolution of the survival-reproduction trade-off, enhancing reproduction at the expense of survival. Here we used standardized injections of gonadotropin-releasing hormone (GnRH) to assay variation in the testosterone production of males. Using measurements of annual survival and reproduction, we found evidence of strong natural selection acting on GnRH-induced increases in testosterone. Opposite to what would be predicted from the survival-reproduction trade-off, patterns of selection via survival and reproduction were remarkably similar. Males with GnRH-induced testosterone production levels that were slightly above the population mean were more likely to survive and also produced more offspring, leading to strong stabilizing selection. Partitioning reproduction into separate components revealed positive directional selection via within-pair siring success and stabilizing selection via extrapair mating success. Our data represent the most complete demonstration of natural selection on hormones via multiple fitness components, and they complement previous experiments to illuminate testosterone's role in the evolution of life-history trade-offs.
• 2.98

  Impact points

  Songbird chemosignals: volatile compounds in preen gland secretions vary among individuals, sexes, and populations.

  Danielle J Whittaker, Helena A Soini, Jonathan W Atwell, Craig Hollars, Milos V Novotny, Ellen D Ketterson

  Behavioral ecology : official journal of the International Society for Behavioral Ecology. 01/2010; 21(3):608-614.

  Chemical signaling has been documented in many animals, but its potential importance in avian species, particularly songbirds, has received far less attention. We tested whether volatile compounds in the preen oil of a songbird (Junco hyemalis) contain reliable information about individual identity,... [more] Chemical signaling has been documented in many animals, but its potential importance in avian species, particularly songbirds, has received far less attention. We tested whether volatile compounds in the preen oil of a songbird (Junco hyemalis) contain reliable information about individual identity, sex, or population of origin by repeated sampling from captive male and female juncos originating from 2 recently diverged junco populations in southern California. One of the populations recently colonized an urban environment; the other resides in a species-typical montane environment. The birds were field-caught as juveniles, housed under identical conditions, and fed the same diet for 10 months prior to sampling. We used capillary gas chromatography-mass spectrometry to quantify the relative abundance of 19 volatile compounds previously shown to vary seasonally in this species. We found individual repeatability as well as significant sex and population differences in volatile profiles. The persistence of population differences in a common environment suggests that preen oil chemistry likely has a genetic basis and may thus evolve rapidly in response to environmental change. These finding suggest that songbird preen oil odors have the potential to function as chemosignals associated with mate recognition or reproductive isolation.

• Songbird chemosignals: volatile compounds in preen gland secretions vary among individuals, sexes, and populations

  Danielle J Whittaker, Helena A Soini, Jonathan W. Atwell, Craig Hollars, Milos V Novotny, Ellen D Ketterson

  Oxford University Press for the International Society for Behavioral Ecology, Behavioral Ecology. 01/2010; 21(3):608-614.

  Chemical signaling has been documented in many animals, but its potential importance in avian species, particularly songbirds, has received far less attention. We tested whether volatile compounds in the preen oil of a songbird (Junco hyemalis) contain reliable information about individual identity,... [more] Chemical signaling has been documented in many animals, but its potential importance in avian species, particularly songbirds, has received far less attention. We tested whether volatile compounds in the preen oil of a songbird (Junco hyemalis) contain reliable information about individual identity, sex, or population of origin by repeated sampling from captive male and female juncos originating from 2 recently diverged junco populations in southern California. One of the populations recently colonized an urban environment; the other resides in a species-typical montane environment. The birds were field-caught as juveniles, housed under identical conditions, and fed the same diet for 10 months prior to sampling. We used capillary gas chromatography--mass spectrometry to quantify the relative abundance of 19 volatile compounds previously shown to vary seasonally in this species. We found individual repeatability as well as significant sex and population differences in volatile profiles. The persistence of population differences in a common environment suggests that preen oil chemistry likely has a genetic basis and may thus evolve rapidly in response to environmental change. These finding suggest that songbird preen oil odors have the potential to function as chemosignals associated with mate recognition or reproductive isolation. Copyright 2010, Oxford University Press.
• 1.98

  Impact points

  Phenotypic integration and independence: Hormones, performance, and response to environmental change.

  Ellen D Ketterson, Jonathan W Atwell, Joel W McGlothlin

  Integrative and comparative biology. 10/2009; 49(4):365-79.

  Hormones coordinate the co-expression of behavioral, physiological, and morphological traits, giving rise to correlations among traits and organisms whose parts work well together. This article considers the implications of these hormonal correlations with respect to the evolution of hormone-mediate... [more] Hormones coordinate the co-expression of behavioral, physiological, and morphological traits, giving rise to correlations among traits and organisms whose parts work well together. This article considers the implications of these hormonal correlations with respect to the evolution of hormone-mediated traits. Such traits can evolve owing to changes in hormone secretion, hormonal affinity for carrier proteins, rates of degradation and conversion, and interaction with target tissues to name a few. Critically, however, we know very little about whether these changes occur independently or in tandem, and thus whether hormones promote the evolution of tight phenotypic integration or readily allow the parts of the phenotype to evolve independently. For example, when selection favors a change in expression of hormonally mediated characters, is that alteration likely to come about through changes in hormone secretion (signal strength), changes in response to a fixed level of secretion (sensitivity of target tissues), or both? At one extreme, if the phenotype is tightly integrated and only the signal responds via selection's action on one or more hormonally mediated traits, adaptive modification may be constrained by past selection for phenotypic integration. Alternatively, response to selection may be facilitated if multivariate selection favors new combinations that can be easily achieved by a change in signal strength. On the other hand, if individual target tissues readily "unplug" from a hormone signal in response to selection, then the phenotype may be seen as a loose confederation that responds on a trait-by-trait basis, easily allowing adaptive modification, although perhaps more slowly than if signal variation were the primary mode of evolutionary response. Studies reviewed here and questions for future research address the relative importance of integration and independence by comparing sexes, individuals, and populations. Most attention is devoted to the hormone testosterone (T) and a songbird species, the dark-eyed junco (Junco hyemalis).
• 3.77

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  Neural activation in the orbitofrontal cortex in response to male faces increases during the follicular phase.

  Heather A Rupp, Thomas W James, Ellen D Ketterson, Dale R Sengelaub, Erick Janssen, Julia R Heiman

  Hormones and behavior. 04/2009;

  Women's sexual interest changes with hormonal fluctuations across the menstrual cycle. It is unclear how hormones modify women's sexual behavior and desire, but one possibility is that they alter women's positive appraisals of stimuli and thus their sexual interest. Using 3 T fMRI, we me... [more] Women's sexual interest changes with hormonal fluctuations across the menstrual cycle. It is unclear how hormones modify women's sexual behavior and desire, but one possibility is that they alter women's positive appraisals of stimuli and thus their sexual interest. Using 3 T fMRI, we measured neural activation in women at two time points in their menstrual cycle (late follicular, luteal) while they evaluated photos of men presented as potential sexual partners. Participants were ten heterosexual women aged 23-28 none of who was using hormonal contraceptives or in a committed relationship. In an event-related design, the women were presented with as series of photos of male faces and asked questions to assess their degree of sexual interest in the men depicted. Results demonstrate an overall effect of menstrual cycle phase on neural activation. During their follicular versus luteal phase, women demonstrated increased activation in the right medial orbitofrontal cortex (OFC), suggesting increased positive appraisal. Activation in the OFC was positively correlated with women's estradiol to progesterone ratios. There were no areas that demonstrated increased activation during the luteal versus follicular phase. The observed increase in activation in the OFC during the follicular phase may reflect a hormonally mediated increase in appetitive motivation and may prime women towards increased sexual interest and behavior around ovulation.
• 1.60

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  Partner Status Influences Women's Interest in the Opposite Sex.

  Heather Rupp, Giliah R Librach, Nick C Feipel, Ellen D Ketterson, Dale R Sengelaub, Julia R Heiman

  Human nature (Hawthorne, N.Y.). 03/2009; 20(1):93-104.

  Previous research has demonstrated that hormones, relationship goals, and social context influence interest in the opposite sex. It has not been previously reported, however, whether having a current sexual partner also influences interest in members of the opposite sex. To test this, we obtained ex... [more] Previous research has demonstrated that hormones, relationship goals, and social context influence interest in the opposite sex. It has not been previously reported, however, whether having a current sexual partner also influences interest in members of the opposite sex. To test this, we obtained explicit and implicit measures of interest by measuring men's and women's subjective ratings and response times while they evaluated photos of opposite-sex faces. Fifty-nine men and 56 women rated 510 photos of opposite-sex faces for realism, masculinity, attractiveness, or affect. We found that these subjective ratings were not influenced by partner status in either men or women. However, women who did not report having a current sexual partner spent more time evaluating the photos than women who did have partners, demonstrating greater interest in the photos. Sexual partner status did not predict men's response times. These findings may reveal that relationship commitment in women suppresses interest in alternative partners.

• Song types, song performance, and the use of repertoires in dark-eyed juncos (Junco hyemalis)

  Gon�alo C. Cardoso, Jonathan W. Atwell, Ellen D Ketterson, Trevor D. Price

  Oxford University Press for the International Society for Behavioral Ecology, Behavioral Ecology. 01/2009; 20(4):901-907.

  Song performance encompasses the idea of how physiologically demanding different songs are to sing, and this is thought to reflect the singing ability of individual birds. In the dark-eyed junco (Junco hyemalis), each male has a repertoire of song types, some of which are shared with other males in ... [more] Song performance encompasses the idea of how physiologically demanding different songs are to sing, and this is thought to reflect the singing ability of individual birds. In the dark-eyed junco (Junco hyemalis), each male has a repertoire of song types, some of which are shared with other males in the population. We used 4 measures of performance, based on trade-offs between song traits, to test if song performance is consistent among the song types making up the repertoire of individual males. We also tested if song types differ consistently in performance regardless of which males sing them. We found low but significant correlations of performance measures among the song types of individual males. This contrasts with highly consistent differences in performance among song types, regardless of which males sing them. We conclude that performance of single song types, as evaluated by trade-off--based measures of performance, gives little information about male singing ability. As song types differ in performance, we asked if males use the song types in their repertoires differently. We found that juncos use higher performance song types during bouts of more motivated singing, as evaluated by the length of songs, suggesting that song types may be preferentially used in different contexts depending on their performance. Copyright 2009, Oxford University Press.
• 2.18

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  Behavioral responses of nesting female dark-eyed juncos Junco hyemalis to hetero- and conspecific passerine preen oils

  Danielle J. Whittaker, Dustin G. Reichard, Amy L. Dapper, Ellen D. Ketterson

  Journal of Avian Biology. 01/2009; 40(579):583.
• 3.59

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  Neural Activation in Women in Response to Masculinized Male Faces: Mediation by Hormones and Psychosexual Factors.

  Heather A Rupp, Thomas W James, Ellen D Ketterson, Dale R Sengelaub, Erick Janssen, Julia R Heiman

  Evolution and human behavior : official journal of the Human Behavior and Evolution Society. 01/2009; 30(1):1-10.

  Women's preference for masculine faces varies with hormonal state, sociosexuality, and relationship status, but the underlying mechanisms are poorly understood. We hypothesized that hormones and psychosexual factors (sociosexuality, sexual inhibition/excitation) mediate the perception and evalua... [more] Women's preference for masculine faces varies with hormonal state, sociosexuality, and relationship status, but the underlying mechanisms are poorly understood. We hypothesized that hormones and psychosexual factors (sociosexuality, sexual inhibition/excitation) mediate the perception and evaluation of male faces thereby influencing women's preferences. We used fMRI to measure brain activity in twelve women as they evaluated pictures of male faces (half 30% masculinized, half 30% feminized). Participants were heterosexual women, age 23-28, who were not in a committed relationship and not using hormonal contraception. Women were tested during both the follicular and luteal phase of their menstrual cycle. We found five brain regions related to face and risk processing that responded more to the masculinized than to the feminized faces, including the superior temporal gyrus, precentral gyrus, posterior cingulate cortex, inferior parietal lobule, and anterior cingulate cortex. Increased activation in the anterior cingulate cortex, specifically, may indicate that women perceive masculinized faces to be both more risky and more attractive. We did not see any areas that were more strongly activated by feminized faces. Levels of activation were influenced by hormonal and psychosexual factors. The patterns of hormonally and psychosexually mediated neural activation observed may offer insight into the cognitive processes underlying women's partner preferences.
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  The role of the anterior cingulate cortex in women's sexual decision making.

  Heather A Rupp, Thomas W James, Ellen D Ketterson, Dale R Sengelaub, Erick Janssen, Julia R Heiman

  Neuroscience letters. 11/2008;

  Women's sexual decision making is a complex process balancing the potential rewards of conception and pleasure against the risks of possible low paternal care or sexually transmitted infection. Although neural processes underlying social decision making are suggested to overlap with those involv... [more] Women's sexual decision making is a complex process balancing the potential rewards of conception and pleasure against the risks of possible low paternal care or sexually transmitted infection. Although neural processes underlying social decision making are suggested to overlap with those involved in economic decision making, the neural systems associated with women's sexual decision making are unknown. Using fMRI, we measured the brain activation of 12 women while they viewed photos of men's faces. Face stimuli were accompanied by information regarding each man's potential risk as a sexual partner, indicated by a written description of the man's number of previous sexual partners and frequency of condom use. Participants were asked to evaluate how likely they would be to have sex with the man depicted. Women reported that they would be more likely to have sex with low compared to high risk men. Stimuli depicting low risk men also elicited stronger activation in the anterior cingulate cortex (ACC), midbrain, and intraparietal sulcus, possibly reflecting an influence of sexual risk on women's attraction, arousal, and attention during their sexual decision making. Activation in the ACC was positively correlated with women's subjective evaluations of sex likelihood and response times during their evaluations of high, but not low risk men. These findings provide evidence that neural systems involved in sexual decision making in women overlap with those described previously to underlie nonsexual decision making.
• 3.77

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  Experimentally-elevated testosterone, female parental care, and reproductive success in a songbird, the Dark-eyed Junco (Junco hyemalis).

  Dawn M O'Neal, Dustin G Reichard, Katie Pavilis, Ellen D Ketterson

  Hormones and behavior. 07/2008;

  In male dark-eyed juncos (Junco hyemalis), experimentally elevated testosterone (T) decreases male parental care and offspring survival, but results in higher overall fitness through greater mating success. To help address the ensuing question of what prevents selection from favoring higher levels o... [more] In male dark-eyed juncos (Junco hyemalis), experimentally elevated testosterone (T) decreases male parental care and offspring survival, but results in higher overall fitness through greater mating success. To help address the ensuing question of what prevents selection from favoring higher levels of T in male juncos, we manipulated T in female juncos. A previous study demonstrated no effect of experimentally elevated T on female incubation behavior, suggesting that female parental behavior might be insensitive to T. In this study we asked whether experimentally elevated T mediates other female parental behaviors and whether variation in T-mediated parental behavior might influence reproductive success. We videotaped free-living control- and T-females during nesting to quantify brooding behavior when young were 3 days old and provisioning behavior when young were 6 days old. Nest defense was measured by quantifying responses to a mounted predator placed near the nest. Reproductive success was assessed via fecundity, nestling quality, and nest survival. T-females spent less time than control females brooding but did not differ in provisioning rate. T-females performed fewer dives at the predator mount and, unlike controls, failed to increase defense as nesting progressed. T-females also had lower daily nest survival and lower nest success (odds of producing at least one fledgling). We conclude that some aspects of female parental behavior are sensitive to experimentally elevated T while others are not and consider the implications for the evolution of T-mediated characters in both sexes.
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  Changes in adrenal capacity contribute to a decline in the stress response with age in a long-lived seabird.

  Britt J Heidinger, Ian C T Nisbet, Ellen D Ketterson

  General and comparative endocrinology. 06/2008; 156(3):564-8.

  In response to stressors, most vertebrates elevate secretion of glucocorticoids (CORT) to produce a 'stress response' that enhances survival, but simultaneously inhibits reproduction. Circumstances in which the value of current reproduction is high relative to the value of future reproductio... [more] In response to stressors, most vertebrates elevate secretion of glucocorticoids (CORT) to produce a 'stress response' that enhances survival, but simultaneously inhibits reproduction. Circumstances in which the value of current reproduction is high relative to the value of future reproduction and survival, often lead to suppression of the stress response thus ensuring that critical resources are not diverted away from reproduction. Consistent with this expectation, we have previously reported that the magnitude of the stress response (maximum levels of CORT) declines with age in breeding adults of a long-lived seabird, the common tern (Sterna hirundo). While age-related changes in the stress response may be common in vertebrates, the mechanisms that underlie them are poorly understood. The glucocorticoid stress response is regulated by the hypothalamic-pituitary-adrenal (HPA) axis, and one mechanism that may contribute to an age-related decline in the stress response is changes in adrenal capacity (adrenal sensitivity to ACTH and/or an ability to secrete CORT in response to ACTH). To test this hypothesis, we captured and injected 92 known-aged adult common terns (Sterna hirundo) ranging in age from 3 to 29 years with either a control saline or an experimental adrenocorticotropin (ACTH) solution and measured the effects on stress-induced CORT after 30 min of restraint. In both treatment groups, stress-induced CORT significantly declined with age, suggesting that a decrease in adrenal capacity contributes to a reduction in the stress response in older adults.