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Charles J Krebs - One of the best experts on this subject based on the ideXlab platform.
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physiology and behaviour of juvenile snowshoe hares at the start of the 10 year Cycle
Animal Behaviour, 2019Co-Authors: Sophia G. Lavergne, Charles J Krebs, K Smith, Alice J Kenney, Rupert Palme, Rudy BoonstraAbstract:Snowshoe hares, Lepus americanus, are the dominant prey species in the boreal forest and they undergo regular, predator-driven Population Cycles every 8–11 years. Previous research has found that hare stress physiology is highly sensitive to both within-year (seasonal/litter group) and across-year (Cycle phase) variation in predation risk and that maternal–offspring stress profiles are tightly correlated. Thus, both pre- and postnatal environments may interact to shape offspring physiological phenotype. If changes in the function and reactivity of the maternal stress axis are associated with variation in offspring behaviours that increase survival during periods of high predation risk, then the maternal effects on offspring physiology seen previously could represent a mechanistic route of adaptive maternal programming. To examine the relationship between physiology and behaviour in snowshoe hares, we monitored free-ranging adult and juvenile stress hormone levels in the first and second litters of the breeding season and assessed open field exploratory behaviour in weaning-age and independent juveniles in the southwestern Yukon (Canada) during 2013–2015, when predator density was low but increasing. Thus, our study spanned the late low phase (2013) and the early increase phase (2014–2015) of the hare Population Cycle. We found that increased concentrations of faecal cortisol metabolites (FCMs) were associated with aspects of risk avoidance in weaning-age hares. Juveniles with higher stress hormone levels spent more time under cover and were less active during open field trials, highlighting a potential mechanistic route to allow individuals to sensitively cope with a changing environment. Although average FCM levels of breeding females and juveniles were not correlated with one another and litter-based differences in physiology and behaviour were not present during these low-risk phases of the Cycle, the association between stress hormone levels and behaviour sets the stage for adaptive maternal effects on offspring behaviour and survival as the Cycle progresses and predation risk intensifies.
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Impact of high predation risk on genome-wide hippocampal gene expression in snowshoe hares
Oecologia, 2014Co-Authors: Sophia G. Lavergne, Charles J Krebs, Patrick O. Mcgowan, Rudy BoonstraAbstract:The Population dynamics of snowshoe hares ( Lepus americanus ) are fundamental to the ecosystem dynamics of Canada’s boreal forest. During the 8- to 11-year Population Cycle, hare densities can fluctuate up to 40-fold. Predators in this system (lynx, coyotes, great-horned owls) affect Population numbers not only through direct mortality but also through sublethal effects. The chronic stress hypothesis posits that high predation risk during the decline severely stresses hares, leading to greater stress responses, heightened ability to mobilize cortisol and energy, and a poorer body condition. These effects may result in, or be mediated by, differential gene expression. We used an oligonucleotide microarray designed for a closely-related species, the European rabbit ( Oryctolagus cuniculus ), to characterize differences in genome-wide hippocampal RNA transcript abundance in wild hares from the Yukon during peak and decline phases of a single Cycle. A total of 106 genes were differentially regulated between phases. Array results were validated with quantitative real-time PCR, and mammalian protein sequence similarity was used to infer gene function. In comparison to hares from the peak, decline phase hares showed increased expression of genes involved in metabolic processes and hormone response, and decreased expression of immune response and blood cell formation genes. We found evidence for predation risk effects on the expression of genes whose putative functions correspond with physiological impacts known to be induced by predation risk in snowshoe hares. This study shows, for the first time, a link between changes in demography and alterations in neural RNA transcript abundance in a natural Population.
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linking climate change to Population Cycles of hares and lynx
Global Change Biology, 2013Co-Authors: Chuan Yan, Charles J Krebs, Nils Chr Stenseth, Zhibin ZhangAbstract:The classic 10-year Population Cycle of snowshoe hares (Lepus americanus, Erxleben 1777) and Canada lynx (Lynx canadensis, Kerr 1792) in the boreal forests of North America has drawn much attention from both Population and community ecologists worldwide; however, the ecological mechanisms driving the 10-year cyclic dynamic pattern are not fully revealed yet. In this study, by the use of historic fur harvest data, we constructed a series of generalized additive models to study the effects of density dependence, predation, and climate (both global climate indices of North Atlantic Oscillation index (NAO), Southern Oscillation index (SOI) and northern hemispheric temperature (NHT) and local weather data including temperature, rainfall, and snow). We identified several key pathways from global and local climate to lynx with various time lags: rainfall shows a negative, and snow shows a positive effect on lynx; NHT and NAO negatively affect lynx through their positive effect on rainfall and negative effect on snow; SOI positively affects lynx through its negative effect on rainfall. Direct or delayed density dependency effects, the prey effect of hare on lynx and a 2-year delayed negative effect of lynx on hare (defined as asymmetric predation) were found. The simulated Population dynamics is well fitted to the observed long-term fluctuations of hare and lynx Populations. Through simulation, we find density dependency and asymmetric predation, only producing damped oscillation, are necessary but not sufficient factors in causing the observed 10-year Cycles; while extrinsic climate factors are important in producing and modifying the sustained Cycles. Two recent Population declines of lynx (1940–1955 and after 1980) were likely caused by ongoing climate warming indirectly. Our results provide an alternative explanation to the mechanism of the 10-year Cycles, and there is a need for further investigation on links between disappearance of Population Cycles and global warming in hare–lynx system.
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From process to pattern: how fluctuating predation risk impacts the stress axis of snowshoe hares during the 10-year Cycle
Oecologia, 2011Co-Authors: Michael J. Sheriff, Charles J Krebs, Rudy BoonstraAbstract:Predation is a central organizing process affecting Populations and communities. Traditionally, ecologists have focused on the direct effects of predation—the killing of prey. However, predators also have significant sublethal effects on prey Populations. We investigated how fluctuating predation risk affected the stress physiology of a cyclic Population of snowshoe hares ( Lepus americanus ) in the Yukon, finding that they are extremely sensitive to the fluctuating risk of predation. In years of high predator numbers, hares had greater plasma cortisol levels at capture, greater fecal cortisol metabolite levels, a greater plasma cortisol response to a hormone challenge, a greater ability to mobilize energy and poorer body condition. These indices of stress had the same pattern within years, during the winter and over the breeding season when the hare:lynx ratio was lowest and the food availability the worst. Previously we have shown that predator-induced maternal stress lowers reproduction and compromises offspring’s stress axis. We propose that predator-induced changes in hare stress physiology affect their demography through negative impacts on reproduction and that the low phase of cyclic Populations may be the result of predator-induced maternal stress reducing the fitness of progeny. The hare Population Cycle has far reaching ramifications on predators, alternate prey, and vegetation. Thus, predation is the predominant organizing process for much of the North American boreal forest community, with its indirect signature—stress in hares—producing a pattern of hormonal changes that provides a sensitive reflection of fluctuating predator pressure that may have long-term demographic consequences.
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Overwinter mass loss of snowshoe hares in the Yukon: starvation, stress, adaptation or artefact?
The Journal of animal ecology, 2006Co-Authors: Karen E. Hodges, Rudy Boonstra, Charles J KrebsAbstract:1. Overwinter mass loss can reduce energetic requirements in mammals (Dehnel's phenomenon). Alternatively, mass loss can result from food limitation or high predation risk. 2. We use data from fertilizer, food-supplementation and predator-exclusion experiments in the Yukon during a Population Cycle from 1986 to 1996 to test the causes of overwinter mass loss by snowshoe hares (Lepus americanus). In all years, some hares on control sites gained mass overwinter. During the increase phase the majority gained mass, but in all other phases the majority lost mass. 3. Snowshoe hares weighing 1800 g in autumn usually lost mass. 4. Snowshoe hares on the predator-exclosure + food site gained mass overwinter in all years. Hares on the food-supplementation sites lost mass during the decline but gained mass in all other phases. Fertilization had little effect on mass dynamics. 5. Snowshoe hares were more likely to lose mass during winters with low survival rates. Snowshoe hares on the predator-exclosure treatments were more likely to gain mass than were hares on control sites. 6. Overwinter mass loss was correlated with maximum snow depth. At equivalent snow depths, hares on food-supplemented areas lost 98 g (+/- 14.6 SE) less on average than hares on the controls and predator-exclosure treatment. 7. Bone-marrow fat was related to body mass and cause of death. Small hares had the lowest marrow fat. Hares killed by humans had higher marrow fat than those killed by predators; hares that simply died had the lowest marrow fat. Hares on food-supplemented sites had the highest kidney and marrow fat. 8. Overwinter-mass loss for snowshoe hares is explained interactively by winter conditions, food supply, predation risk and autumn mass. Some snowshoe hares lost mass overwinter in all years and on all treatments, suggesting that reducing body mass may facilitate survival, especially in cases where foraging costs are high energetically or increase predation risk.
Rudy Boonstra - One of the best experts on this subject based on the ideXlab platform.
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physiology and behaviour of juvenile snowshoe hares at the start of the 10 year Cycle
Animal Behaviour, 2019Co-Authors: Sophia G. Lavergne, Charles J Krebs, K Smith, Alice J Kenney, Rupert Palme, Rudy BoonstraAbstract:Snowshoe hares, Lepus americanus, are the dominant prey species in the boreal forest and they undergo regular, predator-driven Population Cycles every 8–11 years. Previous research has found that hare stress physiology is highly sensitive to both within-year (seasonal/litter group) and across-year (Cycle phase) variation in predation risk and that maternal–offspring stress profiles are tightly correlated. Thus, both pre- and postnatal environments may interact to shape offspring physiological phenotype. If changes in the function and reactivity of the maternal stress axis are associated with variation in offspring behaviours that increase survival during periods of high predation risk, then the maternal effects on offspring physiology seen previously could represent a mechanistic route of adaptive maternal programming. To examine the relationship between physiology and behaviour in snowshoe hares, we monitored free-ranging adult and juvenile stress hormone levels in the first and second litters of the breeding season and assessed open field exploratory behaviour in weaning-age and independent juveniles in the southwestern Yukon (Canada) during 2013–2015, when predator density was low but increasing. Thus, our study spanned the late low phase (2013) and the early increase phase (2014–2015) of the hare Population Cycle. We found that increased concentrations of faecal cortisol metabolites (FCMs) were associated with aspects of risk avoidance in weaning-age hares. Juveniles with higher stress hormone levels spent more time under cover and were less active during open field trials, highlighting a potential mechanistic route to allow individuals to sensitively cope with a changing environment. Although average FCM levels of breeding females and juveniles were not correlated with one another and litter-based differences in physiology and behaviour were not present during these low-risk phases of the Cycle, the association between stress hormone levels and behaviour sets the stage for adaptive maternal effects on offspring behaviour and survival as the Cycle progresses and predation risk intensifies.
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Impact of high predation risk on genome-wide hippocampal gene expression in snowshoe hares
Oecologia, 2014Co-Authors: Sophia G. Lavergne, Charles J Krebs, Patrick O. Mcgowan, Rudy BoonstraAbstract:The Population dynamics of snowshoe hares ( Lepus americanus ) are fundamental to the ecosystem dynamics of Canada’s boreal forest. During the 8- to 11-year Population Cycle, hare densities can fluctuate up to 40-fold. Predators in this system (lynx, coyotes, great-horned owls) affect Population numbers not only through direct mortality but also through sublethal effects. The chronic stress hypothesis posits that high predation risk during the decline severely stresses hares, leading to greater stress responses, heightened ability to mobilize cortisol and energy, and a poorer body condition. These effects may result in, or be mediated by, differential gene expression. We used an oligonucleotide microarray designed for a closely-related species, the European rabbit ( Oryctolagus cuniculus ), to characterize differences in genome-wide hippocampal RNA transcript abundance in wild hares from the Yukon during peak and decline phases of a single Cycle. A total of 106 genes were differentially regulated between phases. Array results were validated with quantitative real-time PCR, and mammalian protein sequence similarity was used to infer gene function. In comparison to hares from the peak, decline phase hares showed increased expression of genes involved in metabolic processes and hormone response, and decreased expression of immune response and blood cell formation genes. We found evidence for predation risk effects on the expression of genes whose putative functions correspond with physiological impacts known to be induced by predation risk in snowshoe hares. This study shows, for the first time, a link between changes in demography and alterations in neural RNA transcript abundance in a natural Population.
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From process to pattern: how fluctuating predation risk impacts the stress axis of snowshoe hares during the 10-year Cycle
Oecologia, 2011Co-Authors: Michael J. Sheriff, Charles J Krebs, Rudy BoonstraAbstract:Predation is a central organizing process affecting Populations and communities. Traditionally, ecologists have focused on the direct effects of predation—the killing of prey. However, predators also have significant sublethal effects on prey Populations. We investigated how fluctuating predation risk affected the stress physiology of a cyclic Population of snowshoe hares ( Lepus americanus ) in the Yukon, finding that they are extremely sensitive to the fluctuating risk of predation. In years of high predator numbers, hares had greater plasma cortisol levels at capture, greater fecal cortisol metabolite levels, a greater plasma cortisol response to a hormone challenge, a greater ability to mobilize energy and poorer body condition. These indices of stress had the same pattern within years, during the winter and over the breeding season when the hare:lynx ratio was lowest and the food availability the worst. Previously we have shown that predator-induced maternal stress lowers reproduction and compromises offspring’s stress axis. We propose that predator-induced changes in hare stress physiology affect their demography through negative impacts on reproduction and that the low phase of cyclic Populations may be the result of predator-induced maternal stress reducing the fitness of progeny. The hare Population Cycle has far reaching ramifications on predators, alternate prey, and vegetation. Thus, predation is the predominant organizing process for much of the North American boreal forest community, with its indirect signature—stress in hares—producing a pattern of hormonal changes that provides a sensitive reflection of fluctuating predator pressure that may have long-term demographic consequences.
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Overwinter mass loss of snowshoe hares in the Yukon: starvation, stress, adaptation or artefact?
The Journal of animal ecology, 2006Co-Authors: Karen E. Hodges, Rudy Boonstra, Charles J KrebsAbstract:1. Overwinter mass loss can reduce energetic requirements in mammals (Dehnel's phenomenon). Alternatively, mass loss can result from food limitation or high predation risk. 2. We use data from fertilizer, food-supplementation and predator-exclusion experiments in the Yukon during a Population Cycle from 1986 to 1996 to test the causes of overwinter mass loss by snowshoe hares (Lepus americanus). In all years, some hares on control sites gained mass overwinter. During the increase phase the majority gained mass, but in all other phases the majority lost mass. 3. Snowshoe hares weighing 1800 g in autumn usually lost mass. 4. Snowshoe hares on the predator-exclosure + food site gained mass overwinter in all years. Hares on the food-supplementation sites lost mass during the decline but gained mass in all other phases. Fertilization had little effect on mass dynamics. 5. Snowshoe hares were more likely to lose mass during winters with low survival rates. Snowshoe hares on the predator-exclosure treatments were more likely to gain mass than were hares on control sites. 6. Overwinter mass loss was correlated with maximum snow depth. At equivalent snow depths, hares on food-supplemented areas lost 98 g (+/- 14.6 SE) less on average than hares on the controls and predator-exclosure treatment. 7. Bone-marrow fat was related to body mass and cause of death. Small hares had the lowest marrow fat. Hares killed by humans had higher marrow fat than those killed by predators; hares that simply died had the lowest marrow fat. Hares on food-supplemented sites had the highest kidney and marrow fat. 8. Overwinter-mass loss for snowshoe hares is explained interactively by winter conditions, food supply, predation risk and autumn mass. Some snowshoe hares lost mass overwinter in all years and on all treatments, suggesting that reducing body mass may facilitate survival, especially in cases where foraging costs are high energetically or increase predation risk.
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Population declines in the snowshoe hare and the role of stress.
General and Comparative Endocrinology, 1993Co-Authors: Rudy Boonstra, Grant R. SingletonAbstract:Abstract Every 10 years snowshoe hare Populations across the boreal forest of North America go through a Population Cycle, culminating in a decline lasting 4 or more years. We tested the hypothesis that snowshoe hares during the decline are in poor condition and less able to respond to challenges in their environment by examining the stress response of male hares. Three groups from February and May, 1991 (the second year of the hare decline in the Yukon), were compared: baseline hares were collected to obtain resting hormone levels; control hares were wild animals caught at randomly placed sites: and fed hares were wild animals caught on supplementary fed areas. The latter two groups were sequentially bled to examine their response to dexamethasone (DEX) followed by adrenocorticotropic hormone (ACTH). Trapping and handling were stressful to the experimental hares as the initial blood levels of total and free cortisol levels were higher (especially in controls), testosterone levels were lower, and glucose levels were higher in experimental hares than in baseline hares. Control and fed hares showed similar total and free cortisol responses, falling to low levels after the DEX injection and increasing rapidly in response to the ACTH injection. However, control hares were in worse condition than fed hares as indicated by the higher free cortisol levels and lower maximum corticosteroid-binding capacity (MCBC) in control hares. In addition, though testosterone levels fell in both groups in response to DEX, only the fed hares showed a large, transitory increase 30 min after the ACTH injection. An unexpected finding was a dramatic increase in MCBC levels 30 min after the ACTH injection in both experimental groups, but it was more pronounced in the fed group. We conclude that the pituitary-adrenocortical feedback system in hares from declining Populations is operating normally anti that they should be able to cope with acute, short-term stressors, but that they are in poor condition and are exposed to higher levels of free cortisol than fed hares in good condition.
Elizabeth L. Chaney - One of the best experts on this subject based on the ideXlab platform.
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Pubic lice (Pthirus pubis): history, biology and treatment vs. knowledge and beliefs of US college students.
International journal of environmental research and public health, 2009Co-Authors: Alice L. Anderson, Elizabeth L. ChaneyAbstract:Pubic lice (Pthirus pubis) maintain a worldwide parasitic Population infesting two to over 10 percent of human Populations, continuing a presence that has been constant since early evidence 10,000 years ago. Outbreaks in the 1970s have been recorded, but incomplete records preclude description of a definitive Population Cycle. Current levels of infestation in a US college student Population were investigated in this study. Knowledge and opinions of students were also recorded in an online survey administered to college students taking a basic health course at a mid-sized East Coast University. In a group of 817 students, 35 reported experience with pubic lice or other STD infection. Knowledge, beliefs, and treatment attitudes were examined for the 782 students who did not have experience with either pubic lice or STD infection. These students deemed antibiotics as a viable treatment for pubic lice infestation. They also indicated negative attitudes toward the use of pesticide cremes, which are the most useful prescription. Symptoms and transmission myths in student answers are described.
Alice L. Anderson - One of the best experts on this subject based on the ideXlab platform.
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OPEN ACCESS
2015Co-Authors: Alice L. Anderson, Elizabeth ChaneyAbstract:Abstract: Pubic lice (Pthirus pubis) maintain a worldwide parasitic Population infesting two to over 10 percent of human Populations, continuing a presence that has been constant since early evidence 10,000 years ago. Outbreaks in the 1970s have been recorded, but incomplete records preclude description of a definitive Population Cycle. Current levels of infestation in a US college student Population were investigated in this study. Knowledge and opinions of students were also recorded in an online survey administered to college students taking a basic health course at a mid-sized East Coast University. In a group of 817 students, 35 reported experience with pubic lice or other STD infection. Knowledge, beliefs, and treatment attitudes were examined for the 782 students who did not have experience with either pubic lice or STD infection. These students deemed antibiotics as a viable treatment for pubic lice infestation. They also indicated negative attitudes toward the use of pesticide crèmes, which are the most useful prescription. Symptoms and transmission myths in student answers are described
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Pubic lice (Pthirus pubis): history, biology and treatment vs. knowledge and beliefs of US college students.
International journal of environmental research and public health, 2009Co-Authors: Alice L. Anderson, Elizabeth L. ChaneyAbstract:Pubic lice (Pthirus pubis) maintain a worldwide parasitic Population infesting two to over 10 percent of human Populations, continuing a presence that has been constant since early evidence 10,000 years ago. Outbreaks in the 1970s have been recorded, but incomplete records preclude description of a definitive Population Cycle. Current levels of infestation in a US college student Population were investigated in this study. Knowledge and opinions of students were also recorded in an online survey administered to college students taking a basic health course at a mid-sized East Coast University. In a group of 817 students, 35 reported experience with pubic lice or other STD infection. Knowledge, beliefs, and treatment attitudes were examined for the 782 students who did not have experience with either pubic lice or STD infection. These students deemed antibiotics as a viable treatment for pubic lice infestation. They also indicated negative attitudes toward the use of pesticide cremes, which are the most useful prescription. Symptoms and transmission myths in student answers are described.
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Pubic Lice (Pthirus pubis): History, Biology and Treatment vs. Knowledge and Beliefs of US College Students
MDPI AG, 2009Co-Authors: Elizabeth Chaney, Alice L. AndersonAbstract:Pubic lice (Pthirus pubis) maintain a worldwide parasitic Population infesting two to over 10 percent of human Populations, continuing a presence that has been constant since early evidence 10,000 years ago. Outbreaks in the 1970s have been recorded, but incomplete records preclude description of a definitive Population Cycle. Current levels of infestation in a US college student Population were investigated in this study. Knowledge and opinions of students were also recorded in an online survey administered to college students taking a basic health course at a mid-sized East Coast University. In a group of 817 students, 35 reported experience with pubic lice or other STD infection. Knowledge, beliefs, and treatment attitudes were examined for the 782 students who did not have experience with either pubic lice or STD infection. These students deemed antibiotics as a viable treatment for pubic lice infestation. They also indicated negative attitudes toward the use of pesticide crèmes, which are the most useful prescription. Symptoms and transmission myths in student answers are described
Siw Turid Killengreen - One of the best experts on this subject based on the ideXlab platform.
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Rodent Population Cycle as a determinant of gastrointestinal nematode abundance in a low-arctic Population of the red fox.
International journal for parasitology. Parasites and wildlife, 2019Co-Authors: Torill Mørk, Rolf A. Ims, Siw Turid KillengreenAbstract:Abstract We analyzed an 11-year time series (2005–2015) of parasite abundance for three intestinal nematode species in the red fox (Vulpes vulpes) as a function of the multi-annual rodent Population Cycle in low-arctic Norway, while correcting for other potential covariates that could influence prevalence and abundance. Rodents are paratenic and facultative intermediate hosts for the two Ascarididae species Toxascaris leonina and Toxocara canis, respectively and key prey for the red fox. Still the relative importance of indirect transmission through rodents and direct transmission through free-living stages is unclear. Abundance of these Ascarididae species in individual red foxes (N = 612) exhibited strongly cyclic dynamics that closely mirrored the 4-year rodent Cycle. Negative binomial models provided evidence for a direct proportional increase in Ascarididae abundance with rodent density suggesting that predator functional response to rodent prey is the key transmission mechanism. In contrast, no Cycles and constantly very low abundance were apparent for Uncinaria stenocephala – a third nematode species recorded without paratenic or intermediate stages.