I am overwhelmed by the number of people to whom I owe credit and thanks for the opportunities I ... more I am overwhelmed by the number of people to whom I owe credit and thanks for the opportunities I have been given while at the University of Memphis. Above all, I must thank my dissertation advisor Dr. Stephan Schoech for his patience. Dr. Schoech went beyond expectations in his role as an advisor and has taught me more about science, writing, and life than I ever thought possible in such a short time span. I'm honored to be able to call him my mentor and friend. A huge "thank you" as well to Drs. Dave Freeman, Joel Bumgardner, Yonghong Xu, and Michael Ferkin for being excellent committee members, sounding boards, and coffee mates. Thank you to Drs. Travis Wilcoxen and Michelle Rensel (co-member of Team Awesome) who guided me in my first years in the Schoech lab and taught me how to navigate the sometimes treacherous waters of graduate school and food in the field. Michelle, your zest for life, strong determination, and the laughter we shared have brought me through more than you know. Thank you for showing me the true definition of strength. Thank you to Dr. Eli Bridge, the genius behind our SmartFeeders and power tool wielder extraordinaire. Many thanks to the current Schoech lab members; Emily Elderbrock, Sara Bebus, and Blake Jones for putting up with me during field seasons and always making the best of any situation. Special thanks to Dr. Tom Small for his help and humor. For struggling through it all with me, thanks especially to Sara Carter, Jared Henson, Shane Hanlon, and all of the other graduate students and faculty at the University of Memphis. Special thanks iv also to the staff of the Department of Biological Sciences at the University of Memphis, especially Ms. Donna Haskins, for providing constant support.
A growing body of evidence from across taxa suggests that exposure to elevated levels of glucocor... more A growing body of evidence from across taxa suggests that exposure to elevated levels of glucocorticoids during early development can have long-term effects upon physiological and behavioral phenotypes. Additionally, there is some, though limited, evidence that similar early exposure can also negatively impact cognitive ability. Following pioneering mammalian studies, several avian studies have revealed that the responsiveness of the hypothalamo-pituitary-adrenal (HPA) axis as an adult can be explained by levels of corticosterone, the avian glucocorticoid, the individual experienced as a nestling or even as an embryo via yolk exposure. Studies also suggest that perinatal exposure to corticosterone can have effects upon avian ‘personalities’ or coping styles, and findings from mammalian studies suggest that these long-term effects are mediated epigenetically via altered expression of relevant DNA sequences. Although a consistent pattern across-species has yet to emerge, recent work i...
Until recently, the use of olfactory signals in birds has been largely ignored, despite the fact ... more Until recently, the use of olfactory signals in birds has been largely ignored, despite the fact that birds do possess a fully functioning olfactory system and have been shown to use odours in social and foraging tasks, predator detection and orientation. The present study investigates whether carrion crows (Corvus corone corone), a bird species living in complex social societies, respond behaviourally to olfactory cues of conspecifics. During our experiment, carrion crows were observed less often close to the conspecific scent compared to a control side. Because conspecific scent was extracted during handling, a stressful procedure for birds, we interpreted the general avoidance of the 'scent' side as disfavour against a stressed conspecific. However, males, unlike females, showed less avoidance towards the scent of a familiar individual compared to an unfamiliar one, which might reflect a stronger interest in the information conveyed and/or willingness to provide social support.
Reproduction is energetically demanding, and how much an individual is able to invest in reproduc... more Reproduction is energetically demanding, and how much an individual is able to invest in reproduction is often a function of its health state. An understanding of the relationship between oxidative balance and reproductive decisions, especially in free-living species, is still very limited. We evaluated the relationship between oxidative health and reproductive effort in a free-living population of the cooperatively breeding Florida scrub jay Aphelocoma coerulescens. Specifically, we assessed whether prebreeding oxidative damage levels predicted reproductive effort and subsequently whether postbreeding oxidative damage levels reflected reproductive effort. Prebreeding oxidative damage levels were negatively correlated with reproductive effort in males. In males, postbreeding levels of oxidative damage were significantly greater than prebreeding levels. Given that females exhibited no such patterns, our results suggest that in this species, males bear the brunt of the oxidative costs associated with reproduction.
Journal of Experimental Zoology Part A: Ecological Genetics and Physiology, 2011
Antioxidants play key roles in preventing free radical damage to various molecules, cells, and ti... more Antioxidants play key roles in preventing free radical damage to various molecules, cells, and tissues, but it is not well understood how variation in antioxidant levels may relate to the reproductive success or health of wild animals. We explored the relationship between circulating antioxidant concentrations and both body condition and timing of reproduction in male and female Florida Scrub-Jays (Aphelocoma coerulescens), a cooperatively breeding passerine bird. We examined whether levels of uric acid, vitamin E, and carotenoids (all potentially important antioxidants) were linked to body condition and timing of reproduction, two measures that are directly related to reproductive success. Antioxidant concentrations were not correlated with body condition, but they were related to timing of first clutch initiation, though not always in the predicted direction. Elevated circulating levels of carotenoids were associated with delayed clutch initiation in female breeders. Relatively higher vitamin E levels in control birds were associated with earlier clutch initiation, whereas male breeders that received long-term food supplementation had elevated levels of vitamin E and delayed reproduction. Several potential explanations for the link between elevated levels of antioxidants and delayed clutch initiation are discussed. Separate explanations for each sex include, but are not limited to, oxidative stress as a result of territory defense efforts in males, different dietary regimes due to supplementation, and mobilized plasma antioxidants in females that were coping with a stressor.
In urbanized areas, many adult birds find sufficient foods to survive, but the anthropogenic food... more In urbanized areas, many adult birds find sufficient foods to survive, but the anthropogenic foods that are abundant there may be detrimental to nestling growth. In fact, American Crow (Corvus brachyrhynchos) nestlings are smaller in suburban than rural areas, possibly because of nutrient limitation. Here, we seek to identify possible causes of size differences by comparing both size and blood chemistry measures in rural and suburban crow nestlings. We quantified land use in known crow territories and distinguished three distinct environments: suburban-residential, suburban-managed (e.g., golf courses), and rural. We measured nestlings near fledging age in each environment and bled them for determination of unbound plasma calcium, total protein, and corticosterone. We supplemented a subset of broods in suburban-residential and rural areas with a food high in protein and calcium. Rural nestlings were significantly larger than suburban-residential crows and had higher total serum protein. Nestlings in suburban-managed areas were intermediate in size and serum protein but had the lowest plasma calcium levels. Nestling corticosterone levels did not differ significantly among habitats, indicating that, although suburban nestlings may be food-limited, they were not starving. Supplemented nestlings in suburban-residential areas were significantly larger in some growth measures than their unsupplemented counterparts. Unexpectedly, supplemented rural nestlings were significantly smaller than unsupplemented rural ones, suggesting that parents use easily accessible food even when it is nutritionally suboptimal. Our results indicate that nestlings in suburban areas are nutrient restricted, rather than calorie restricted.
The relationship between individual fitness and antioxidants and oxidative stress has come under ... more The relationship between individual fitness and antioxidants and oxidative stress has come under increasing scrutiny of late. In particular, associations between oxidative balance indicators and reproductive success in the wild have been inconsistent in the limited prior work on this topic. Studies spanning multiple seasons and antioxidant types are particularly lacking. Here, we examined associations between reproductive success over two breeding seasons and several metrics of circulating antioxidants (antioxidant capacity, uric acid, carotenoids, and vitamin E, measured in the intervening nonbreeding season) in Florida Scrub-Jays (Aphelocoma coerulescens (Bosc, 1795)). We found that carotenoid levels in the nonbreeding season were negatively associated with reproductive success in the preceding breeding season but unassociated with that in the subsequent breeding season. This correlation may be driven by the cost of reproduction (i.e., carotenoid depletion while breeding) or some other unmeasured and intercorrelated variable such as diet. Antioxidant capacity, uric acid, and vitamin E were not associated with reproductive success. These data are consistent with an emerging theme in physiological ecology: that antioxidants and oxidative stress are but one part of a suite of integrative physiological systems that interact and trade-off in complex ways, making full understanding of their ecological roles challenging.
A growing body of evidence from across taxa suggests that exposure to elevated levels of glucocor... more A growing body of evidence from across taxa suggests that exposure to elevated levels of glucocorticoids during early development can have long-term effects upon physiological and behavioral phenotypes. Additionally, there is some, though limited, evidence that similar early exposure can also negatively impact cognitive ability. Following pioneering mammalian studies, several avian studies have revealed that the responsiveness of the hypothalamo-pituitary-adrenal (HPA) axis as an adult can be explained by levels of corticosterone, the avian glucocorticoid, the individual experienced as a nestling or even as an embryo via yolk exposure. Studies also suggest that perinatal exposure to corticosterone can have effects upon avian 'personalities' or coping styles, and findings from mammalian studies suggest that these long-term effects are mediated epigenetically via altered expression of relevant DNA sequences. Although a consistent pattern across-species has yet to emerge, recent work in Florida scrub-jays Aphelocoma coerulescens found that baseline corticosterone levels in 11-day-old nestlings explained 84% of the variation in 'personality' (bold vs. timid) when those individuals were tested approximately seven months later. Nestlings with elevated corticosterone levels were more timid than those individuals that as nestlings experienced relatively low corticosterone levels. Some researchers have suggested that parents might use such mechanisms to 'program' their offsprings' phenotype to best fit prevailing environmental conditions. This review will visit what is known about the links between stressful developmental conditions that result in exposure to elevated corticosterone and the short-and long-term effects of this steroid hormone upon central nervous system function and whether alterations thereof are beneficial, deleterious, or neutral. It will concentrate on examples from birds, although critical supporting studies from the mammalian literature will be included as appropriate [Current Zoology 57 (4): 514-530, 2011].
I am overwhelmed by the number of people to whom I owe credit and thanks for the opportunities I ... more I am overwhelmed by the number of people to whom I owe credit and thanks for the opportunities I have been given while at the University of Memphis. Above all, I must thank my dissertation advisor Dr. Stephan Schoech for his patience. Dr. Schoech went beyond expectations in his role as an advisor and has taught me more about science, writing, and life than I ever thought possible in such a short time span. I'm honored to be able to call him my mentor and friend. A huge "thank you" as well to Drs. Dave Freeman, Joel Bumgardner, Yonghong Xu, and Michael Ferkin for being excellent committee members, sounding boards, and coffee mates. Thank you to Drs. Travis Wilcoxen and Michelle Rensel (co-member of Team Awesome) who guided me in my first years in the Schoech lab and taught me how to navigate the sometimes treacherous waters of graduate school and food in the field. Michelle, your zest for life, strong determination, and the laughter we shared have brought me through more than you know. Thank you for showing me the true definition of strength. Thank you to Dr. Eli Bridge, the genius behind our SmartFeeders and power tool wielder extraordinaire. Many thanks to the current Schoech lab members; Emily Elderbrock, Sara Bebus, and Blake Jones for putting up with me during field seasons and always making the best of any situation. Special thanks to Dr. Tom Small for his help and humor. For struggling through it all with me, thanks especially to Sara Carter, Jared Henson, Shane Hanlon, and all of the other graduate students and faculty at the University of Memphis. Special thanks iv also to the staff of the Department of Biological Sciences at the University of Memphis, especially Ms. Donna Haskins, for providing constant support.
A growing body of evidence from across taxa suggests that exposure to elevated levels of glucocor... more A growing body of evidence from across taxa suggests that exposure to elevated levels of glucocorticoids during early development can have long-term effects upon physiological and behavioral phenotypes. Additionally, there is some, though limited, evidence that similar early exposure can also negatively impact cognitive ability. Following pioneering mammalian studies, several avian studies have revealed that the responsiveness of the hypothalamo-pituitary-adrenal (HPA) axis as an adult can be explained by levels of corticosterone, the avian glucocorticoid, the individual experienced as a nestling or even as an embryo via yolk exposure. Studies also suggest that perinatal exposure to corticosterone can have effects upon avian ‘personalities’ or coping styles, and findings from mammalian studies suggest that these long-term effects are mediated epigenetically via altered expression of relevant DNA sequences. Although a consistent pattern across-species has yet to emerge, recent work i...
Until recently, the use of olfactory signals in birds has been largely ignored, despite the fact ... more Until recently, the use of olfactory signals in birds has been largely ignored, despite the fact that birds do possess a fully functioning olfactory system and have been shown to use odours in social and foraging tasks, predator detection and orientation. The present study investigates whether carrion crows (Corvus corone corone), a bird species living in complex social societies, respond behaviourally to olfactory cues of conspecifics. During our experiment, carrion crows were observed less often close to the conspecific scent compared to a control side. Because conspecific scent was extracted during handling, a stressful procedure for birds, we interpreted the general avoidance of the 'scent' side as disfavour against a stressed conspecific. However, males, unlike females, showed less avoidance towards the scent of a familiar individual compared to an unfamiliar one, which might reflect a stronger interest in the information conveyed and/or willingness to provide social support.
Reproduction is energetically demanding, and how much an individual is able to invest in reproduc... more Reproduction is energetically demanding, and how much an individual is able to invest in reproduction is often a function of its health state. An understanding of the relationship between oxidative balance and reproductive decisions, especially in free-living species, is still very limited. We evaluated the relationship between oxidative health and reproductive effort in a free-living population of the cooperatively breeding Florida scrub jay Aphelocoma coerulescens. Specifically, we assessed whether prebreeding oxidative damage levels predicted reproductive effort and subsequently whether postbreeding oxidative damage levels reflected reproductive effort. Prebreeding oxidative damage levels were negatively correlated with reproductive effort in males. In males, postbreeding levels of oxidative damage were significantly greater than prebreeding levels. Given that females exhibited no such patterns, our results suggest that in this species, males bear the brunt of the oxidative costs associated with reproduction.
Journal of Experimental Zoology Part A: Ecological Genetics and Physiology, 2011
Antioxidants play key roles in preventing free radical damage to various molecules, cells, and ti... more Antioxidants play key roles in preventing free radical damage to various molecules, cells, and tissues, but it is not well understood how variation in antioxidant levels may relate to the reproductive success or health of wild animals. We explored the relationship between circulating antioxidant concentrations and both body condition and timing of reproduction in male and female Florida Scrub-Jays (Aphelocoma coerulescens), a cooperatively breeding passerine bird. We examined whether levels of uric acid, vitamin E, and carotenoids (all potentially important antioxidants) were linked to body condition and timing of reproduction, two measures that are directly related to reproductive success. Antioxidant concentrations were not correlated with body condition, but they were related to timing of first clutch initiation, though not always in the predicted direction. Elevated circulating levels of carotenoids were associated with delayed clutch initiation in female breeders. Relatively higher vitamin E levels in control birds were associated with earlier clutch initiation, whereas male breeders that received long-term food supplementation had elevated levels of vitamin E and delayed reproduction. Several potential explanations for the link between elevated levels of antioxidants and delayed clutch initiation are discussed. Separate explanations for each sex include, but are not limited to, oxidative stress as a result of territory defense efforts in males, different dietary regimes due to supplementation, and mobilized plasma antioxidants in females that were coping with a stressor.
In urbanized areas, many adult birds find sufficient foods to survive, but the anthropogenic food... more In urbanized areas, many adult birds find sufficient foods to survive, but the anthropogenic foods that are abundant there may be detrimental to nestling growth. In fact, American Crow (Corvus brachyrhynchos) nestlings are smaller in suburban than rural areas, possibly because of nutrient limitation. Here, we seek to identify possible causes of size differences by comparing both size and blood chemistry measures in rural and suburban crow nestlings. We quantified land use in known crow territories and distinguished three distinct environments: suburban-residential, suburban-managed (e.g., golf courses), and rural. We measured nestlings near fledging age in each environment and bled them for determination of unbound plasma calcium, total protein, and corticosterone. We supplemented a subset of broods in suburban-residential and rural areas with a food high in protein and calcium. Rural nestlings were significantly larger than suburban-residential crows and had higher total serum protein. Nestlings in suburban-managed areas were intermediate in size and serum protein but had the lowest plasma calcium levels. Nestling corticosterone levels did not differ significantly among habitats, indicating that, although suburban nestlings may be food-limited, they were not starving. Supplemented nestlings in suburban-residential areas were significantly larger in some growth measures than their unsupplemented counterparts. Unexpectedly, supplemented rural nestlings were significantly smaller than unsupplemented rural ones, suggesting that parents use easily accessible food even when it is nutritionally suboptimal. Our results indicate that nestlings in suburban areas are nutrient restricted, rather than calorie restricted.
The relationship between individual fitness and antioxidants and oxidative stress has come under ... more The relationship between individual fitness and antioxidants and oxidative stress has come under increasing scrutiny of late. In particular, associations between oxidative balance indicators and reproductive success in the wild have been inconsistent in the limited prior work on this topic. Studies spanning multiple seasons and antioxidant types are particularly lacking. Here, we examined associations between reproductive success over two breeding seasons and several metrics of circulating antioxidants (antioxidant capacity, uric acid, carotenoids, and vitamin E, measured in the intervening nonbreeding season) in Florida Scrub-Jays (Aphelocoma coerulescens (Bosc, 1795)). We found that carotenoid levels in the nonbreeding season were negatively associated with reproductive success in the preceding breeding season but unassociated with that in the subsequent breeding season. This correlation may be driven by the cost of reproduction (i.e., carotenoid depletion while breeding) or some other unmeasured and intercorrelated variable such as diet. Antioxidant capacity, uric acid, and vitamin E were not associated with reproductive success. These data are consistent with an emerging theme in physiological ecology: that antioxidants and oxidative stress are but one part of a suite of integrative physiological systems that interact and trade-off in complex ways, making full understanding of their ecological roles challenging.
A growing body of evidence from across taxa suggests that exposure to elevated levels of glucocor... more A growing body of evidence from across taxa suggests that exposure to elevated levels of glucocorticoids during early development can have long-term effects upon physiological and behavioral phenotypes. Additionally, there is some, though limited, evidence that similar early exposure can also negatively impact cognitive ability. Following pioneering mammalian studies, several avian studies have revealed that the responsiveness of the hypothalamo-pituitary-adrenal (HPA) axis as an adult can be explained by levels of corticosterone, the avian glucocorticoid, the individual experienced as a nestling or even as an embryo via yolk exposure. Studies also suggest that perinatal exposure to corticosterone can have effects upon avian 'personalities' or coping styles, and findings from mammalian studies suggest that these long-term effects are mediated epigenetically via altered expression of relevant DNA sequences. Although a consistent pattern across-species has yet to emerge, recent work in Florida scrub-jays Aphelocoma coerulescens found that baseline corticosterone levels in 11-day-old nestlings explained 84% of the variation in 'personality' (bold vs. timid) when those individuals were tested approximately seven months later. Nestlings with elevated corticosterone levels were more timid than those individuals that as nestlings experienced relatively low corticosterone levels. Some researchers have suggested that parents might use such mechanisms to 'program' their offsprings' phenotype to best fit prevailing environmental conditions. This review will visit what is known about the links between stressful developmental conditions that result in exposure to elevated corticosterone and the short-and long-term effects of this steroid hormone upon central nervous system function and whether alterations thereof are beneficial, deleterious, or neutral. It will concentrate on examples from birds, although critical supporting studies from the mammalian literature will be included as appropriate [Current Zoology 57 (4): 514-530, 2011].
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Papers by Rebecca Heiss