Dawn O'Neal

Publications

• 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.
• 3.77

  Impact points

  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.
• 3.77

  Impact points

  Consequences of elevating plasma testosterone in females of a socially monogamous songbird: evidence of constraints on male evolution?

  Ethan D Clotfelter, Dawn M O'Neal, Jacqueline M Gaudioso, Joseph M Casto, Ian M Parker-Renga, Eric A Snajdr, Deborah L Duffy, Val Nolan, Ellen D Ketterson

  Hormones and behavior. 09/2004; 46(2):171-8.

  To explore whether selection for testosterone-mediated traits in males might be constrained by costs of higher testosterone to females, we examined the effects of experimental elevation of plasma testosterone on physiological, reproductive, and behavioral parameters in a female songbird, the dark-ey... [more] To explore whether selection for testosterone-mediated traits in males might be constrained by costs of higher testosterone to females, we examined the effects of experimental elevation of plasma testosterone on physiological, reproductive, and behavioral parameters in a female songbird, the dark-eyed junco (Junco hyemalis). We used subcutaneous implants to elevate testosterone (T) in captive and free-living female juncos. In captive birds, we measured the effects of high T on body mass, feather molt, and brood patch formation. In the field, we monitored its effects on the timing of egg laying, clutch size, egg size, egg steroid levels, incubation, and nest-defense behavior. Females implanted with testosterone (T-females) had significantly higher circulating levels of testosterone than did control females (C-females). Captive T-females had lower body mass, were less likely to develop brood patches, and delayed feather molt relative to C-females. Among free-living females, the interval between nest completion and appearance of the first egg was longer for T-females than for C-females and egg yolk concentrations of testosterone were higher, but there were no significant differences in estradiol levels, clutch size, or egg size. Incubation and nest defense behavior were also similar between T- and C-females. Our results suggest that selection on males for higher testosterone might initially lead to a correlated response in females producing changes in body mass and feather molt, both of which could be detrimental. Other possible female responses would be delayed onset of reproduction, which might reduce reproductive success, and higher yolk testosterone, which might have either positive or negative effects on offspring development. We found no reason to expect reduced parental behavior by females as a negative fitness consequence of selection for higher testosterone in males.

• 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.

  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.