Urbanization of animal habitats has the potential to affect the natural communication systems of any species able to survive in the changed environment. Urban animals such as squirrels use multiple signal channels to ...Urbanization of animal habitats has the potential to affect the natural communication systems of any species able to survive in the changed environment. Urban animals such as squirrels use multiple signal channels to communicate, but it is un- known how ttrbanization has affected these behaviors. Multimodal commtmication, involving more than one sensory modality, can be studied by use of biomimetic mechanical animal models that are designed to simulate the multimodal signals and be pre- sented to animal subjects in the field. In this way the responses to the various signal components can be compared and contrasted to determine whether the multimodal signal is made up of redundant or nonredundant components. In this study, we presented wild gray squirrels in relatively urban and relatively rural habitats in Western Massachusetts with a biomimetic squirrel model that produced tail flags and alarm barks in a variety of combinations. We found that the squirrels responded to each unimodal component on its own, the bark and tail flag, but they responded most to the complete multimodal signal, containing both the acoustic and the moving visual components, providing evidence that in this context the signal components are redundant and that their combination elicits multimodal enhancement. We expanded on the results of Partan et al. （2009） by providing data on sig- naling behavior in the presence and absence of conspecifics, suggesting that alarm signaling is more likely if conspecifics are present. We found that the squirrels were more active in the urban habitats and that they responded more to tail flagging in the urban habitats as compared to the rural ones, suggesting the interesting possibility of a multimodal shift from reliance on audio to visual signals in noisier more crowded urban habitats [Current Zoology 56 （3）： 313-326, 2010].展开更多
Glucocorticoids(GCs)are involved in the regulation of an animal's energetic state.Under stressful situations,they are part of the neuroendocrine response to cope with environmental challenges.Animals react to aver...Glucocorticoids(GCs)are involved in the regulation of an animal's energetic state.Under stressful situations,they are part of the neuroendocrine response to cope with environmental challenges.Animals react to aversive stimuli also through behavioral responses,defined as coping styles.Both in captive and wild populations,individuals differ in their behavior along a proactive-reactive continuum.Proactive animals exhibit a bold,active explorative and social personality,whereas reactive ones areshy,less active-explorative and less social.Here,we test the hypothesis that personality traits and physiological responses to stressors covary,with more proactive individuals having a less pronounced GC stress response.In wild populations of invasive gray squirrels Sciurus carolinensis,we measuredfecal glucocorticoid metabolites(FGMs),an integrated measure of circulating GCs,and 3 personality traits(activity,sociability,and exploration)derived from open field test(OFT)and mirror image stimulation(MIS)test.Gray squirrels had higher FGMs in Autumn than in Winter and males with scrotal testes had higher FGMs than nonbreeding males.Personality varied with body mass and population density.Squirrels expressed more activity exploration at higher than at lower density and heavier squirrels had higher scores for activity exploration than animals that weighed less.Variation in FGM concentrations was not correlated with the expression of the 3 personality traits.Hence,our results do not support a strong association between the behavioral and physiological stress responses but show that in wild populations,where animals experience varying environmental conditions,the GC endocrine response and the expression of personality are uncorrelated traits among individuals.展开更多
In polymorphic mammalian species that display multiple color forms, those with dark, or melanic pelage would be prone to overheating, especially if they live in warm climates, because their fur absorbs solar energy at...In polymorphic mammalian species that display multiple color forms, those with dark, or melanic pelage would be prone to overheating, especially if they live in warm climates, because their fur absorbs solar energy at a higher rate. However, experimental studies indicate that certain physical properties of fur of dark individuals appear to prevent, or minimize heat stress, although it is not clear what properties do so. Here, we tested the possibility that black-furred individuals simply have shorter or thinner hair fibers, which would create a lighter （in terms of weight） coat or one that allows greater air flow for evaporative coo- ling. We examined museum specimens of eastern fox squirrels Sciurus niger, a species native to the United States and one that displays brown, grey or all-black pelage color, and used image analysis procedures to quantify hairs from the dorsal surface and tail. From examination of 43 specimens （19 brown, 9 black and 15 grey）, and 1,720 hairs, we found no significant difference in hair lengths across color morphs, but significant differences in hair fiber widths. Black squirrels had thinner body hairs than other forms （7% thinner）, but thicker tail hairs （9% thicker） than the others. Given that the dorsal surface would be directly exposed to solar radiation, we interpret this to be an adaptation to prevent heat stress during the day. The thicker tail hairs may be an adapta- tion for nighttime thermoregulation, since squirrels sleep with their tails wrapped around their bodies. These results add to a growing literature body of the functional significance of mammalian pelage [Current Zoology 57 （6）： 731-736, 2011].展开更多
Short-term elevation of glucocorticoids(GCs)is one of the major physiological mechanisms by which vertebrates cope with challenging environmental or social factors(stressors).However,when exposure to stressors occurs ...Short-term elevation of glucocorticoids(GCs)is one of the major physiological mechanisms by which vertebrates cope with challenging environmental or social factors(stressors).However,when exposure to stressors occurs repeatedly or over a prolonged period of time,animals may experience chronic elevation of GCs,which reduces the immune response efficiency and can lead to higher intensity of parasitic infection.Here,we used invasive gray squirrels Sciurus carolinensis in troduced in Norther n Italy and their 2 most prevale nt gastrointesti nal parasites,the n ematode Strongyloides robustus and coccidia of the genus Eimeria,as a model to investigate relati on ships among macroparasite infection and concentrations of fecal glucocorticoid metabolites(FGMs),an integrated measure of circulating GCs.Our results revealed an association of FGMs with infection by St.robustus,but not with coccidia.Individuals with higher FGMs appear to be responsible for the greatest St.robustus egg shedding within gray squirrel populations,thus possibly acting as superspreaders.However,FGMs were negatively associated with adult St.robustus,suggesting that the abundance of adults of this nematode species does not induce elevation in FGMs,but is only affected by it through immun e-mediated effects on its fecun dity.Fin ally,the relati on ship betwee n St.robustus(both eggs and adult parasites)and FGMs was not linear,suggesting that only high levels of physiological stress in fluence parasite inf ection.Our fin dings highlight that the direction and magnitude of the stress-infection relationship may depend not only on the specific hostparasite system,but also on the different life stages of the same parasite.展开更多
Scatterhoarding rodents often place caches in the open where pilferage rates are reduced,suggesting that they tradeoff higher risks of predation for more secure cache sites.We tested this hypothesis in two study syste...Scatterhoarding rodents often place caches in the open where pilferage rates are reduced,suggesting that they tradeoff higher risks of predation for more secure cache sites.We tested this hypothesis in two study systems by measuring predation risks inferred from measures of giving-up densities(GUDs)at known cache sites and other sites for comparison.Rodent GUDs were measured with small trays containing 3 L of fine sand mixed with sunflower seeds.In the first experiment,we relied on a 2-year seed dispersal study in a natural forest to identify caches of eastern gray squirrels(Sciurus carolinensis)and then measured GUDs at:(i)these caches;(ii)comparable points along logs and rocks where rodent activity was assumed highest;and(iii)a set of random points.We found that GUDs and,presumably,predation risks,were higher at both cache and random points than those with cover.At the second site,we measured GUDs of eastern gray squirrels in an open park system and found that GUDs were consistently lowest at the base of the tree compared to more open sites,where previous studies show caching by squirrels to be highest and pilferage rates by naïve competitors to be lowest.These results confirm that predation risks can influence scatterhoarding decisions but that they are also highly context dependent,and that the landscape of fear,now so well documented in the literature,could potentially shape the temporal and spatial patterns of seedling establishment and forest regeneration in systems where scatterhoarding is common.展开更多
Habitats are characterized by different local environmental conditions that influence both behavior and morphology of species,which can result in habitat-dependent phenotypic differences among animals living in heterog...Habitats are characterized by different local environmental conditions that influence both behavior and morphology of species,which can result in habitat-dependent phenotypic differences among animals living in heterogeneous environments.We studied 3 alpine populations of Eurasian red squirrels(Sciurus vulgaris),1 living in a marginal high-elevation habitat at the edge of the species’altitudinal distribution,and 2 occurring in higher-quality habitats.Here,we investigated whether squirrels living in the marginal area differed in 2 morphological parameters(body size and body mass)and/or in the expression of 4 personality traits estimated with an openfield test and a mirror image stimulation test(activity,exploration,activity-exploration,and social tendency).Furthermore,we tested whether within-individual variance of the traits(behavioral plasticity)was higher in the edge habitat.Male squirrels in the edge habitat were smaller and weighed less than in the other study areas,while among females,size–habitat relationships were less marked.These sex-specific patterns were explained by a strong association between body mass and reproductive success in female squirrels.Squirrels in the marginal habitat were more active,explorative,and had a more social personality than in the other habitats.However,in contrast to our predictions,behavioral plasticity was smaller in the marginal habitat,but only for the trait exploration.Our results suggest that animals choose the habitat that bestfits their personality,and that habitat-related differences in selective pressures may shape animals’morphology.展开更多
文摘Urbanization of animal habitats has the potential to affect the natural communication systems of any species able to survive in the changed environment. Urban animals such as squirrels use multiple signal channels to communicate, but it is un- known how ttrbanization has affected these behaviors. Multimodal commtmication, involving more than one sensory modality, can be studied by use of biomimetic mechanical animal models that are designed to simulate the multimodal signals and be pre- sented to animal subjects in the field. In this way the responses to the various signal components can be compared and contrasted to determine whether the multimodal signal is made up of redundant or nonredundant components. In this study, we presented wild gray squirrels in relatively urban and relatively rural habitats in Western Massachusetts with a biomimetic squirrel model that produced tail flags and alarm barks in a variety of combinations. We found that the squirrels responded to each unimodal component on its own, the bark and tail flag, but they responded most to the complete multimodal signal, containing both the acoustic and the moving visual components, providing evidence that in this context the signal components are redundant and that their combination elicits multimodal enhancement. We expanded on the results of Partan et al. （2009） by providing data on sig- naling behavior in the presence and absence of conspecifics, suggesting that alarm signaling is more likely if conspecifics are present. We found that the squirrels were more active in the urban habitats and that they responded more to tail flagging in the urban habitats as compared to the rural ones, suggesting the interesting possibility of a multimodal shift from reliance on audio to visual signals in noisier more crowded urban habitats [Current Zoology 56 （3）： 313-326, 2010].
文摘Glucocorticoids(GCs)are involved in the regulation of an animal's energetic state.Under stressful situations,they are part of the neuroendocrine response to cope with environmental challenges.Animals react to aversive stimuli also through behavioral responses,defined as coping styles.Both in captive and wild populations,individuals differ in their behavior along a proactive-reactive continuum.Proactive animals exhibit a bold,active explorative and social personality,whereas reactive ones areshy,less active-explorative and less social.Here,we test the hypothesis that personality traits and physiological responses to stressors covary,with more proactive individuals having a less pronounced GC stress response.In wild populations of invasive gray squirrels Sciurus carolinensis,we measuredfecal glucocorticoid metabolites(FGMs),an integrated measure of circulating GCs,and 3 personality traits(activity,sociability,and exploration)derived from open field test(OFT)and mirror image stimulation(MIS)test.Gray squirrels had higher FGMs in Autumn than in Winter and males with scrotal testes had higher FGMs than nonbreeding males.Personality varied with body mass and population density.Squirrels expressed more activity exploration at higher than at lower density and heavier squirrels had higher scores for activity exploration than animals that weighed less.Variation in FGM concentrations was not correlated with the expression of the 3 personality traits.Hence,our results do not support a strong association between the behavioral and physiological stress responses but show that in wild populations,where animals experience varying environmental conditions,the GC endocrine response and the expression of personality are uncorrelated traits among individuals.
文摘In polymorphic mammalian species that display multiple color forms, those with dark, or melanic pelage would be prone to overheating, especially if they live in warm climates, because their fur absorbs solar energy at a higher rate. However, experimental studies indicate that certain physical properties of fur of dark individuals appear to prevent, or minimize heat stress, although it is not clear what properties do so. Here, we tested the possibility that black-furred individuals simply have shorter or thinner hair fibers, which would create a lighter （in terms of weight） coat or one that allows greater air flow for evaporative coo- ling. We examined museum specimens of eastern fox squirrels Sciurus niger, a species native to the United States and one that displays brown, grey or all-black pelage color, and used image analysis procedures to quantify hairs from the dorsal surface and tail. From examination of 43 specimens （19 brown, 9 black and 15 grey）, and 1,720 hairs, we found no significant difference in hair lengths across color morphs, but significant differences in hair fiber widths. Black squirrels had thinner body hairs than other forms （7% thinner）, but thicker tail hairs （9% thicker） than the others. Given that the dorsal surface would be directly exposed to solar radiation, we interpret this to be an adaptation to prevent heat stress during the day. The thicker tail hairs may be an adapta- tion for nighttime thermoregulation, since squirrels sleep with their tails wrapped around their bodies. These results add to a growing literature body of the functional significance of mammalian pelage [Current Zoology 57 （6）： 731-736, 2011].
基金Thanks to Zainab Almusawi and Teera Losch for helping in laboratory analysis,Candice Gagnaison,Laure Vanlauwe,and Mattia Panzeri for assistance with the fieldwork.We are grateful to the private land owners for access to their estates.Three anonymous reviewers provided constructive comments that helped us to improve the article.
文摘Short-term elevation of glucocorticoids(GCs)is one of the major physiological mechanisms by which vertebrates cope with challenging environmental or social factors(stressors).However,when exposure to stressors occurs repeatedly or over a prolonged period of time,animals may experience chronic elevation of GCs,which reduces the immune response efficiency and can lead to higher intensity of parasitic infection.Here,we used invasive gray squirrels Sciurus carolinensis in troduced in Norther n Italy and their 2 most prevale nt gastrointesti nal parasites,the n ematode Strongyloides robustus and coccidia of the genus Eimeria,as a model to investigate relati on ships among macroparasite infection and concentrations of fecal glucocorticoid metabolites(FGMs),an integrated measure of circulating GCs.Our results revealed an association of FGMs with infection by St.robustus,but not with coccidia.Individuals with higher FGMs appear to be responsible for the greatest St.robustus egg shedding within gray squirrel populations,thus possibly acting as superspreaders.However,FGMs were negatively associated with adult St.robustus,suggesting that the abundance of adults of this nematode species does not induce elevation in FGMs,but is only affected by it through immun e-mediated effects on its fecun dity.Fin ally,the relati on ship betwee n St.robustus(both eggs and adult parasites)and FGMs was not linear,suggesting that only high levels of physiological stress in fluence parasite inf ection.Our fin dings highlight that the direction and magnitude of the stress-infection relationship may depend not only on the specific hostparasite system,but also on the different life stages of the same parasite.
基金We thank J.Healey and P.Lello for assistance with fieldwork and N.Lichti,R.K.Swihart and S.Agosta for earlier discussions on the potential for predators to impact patterns of cache placement by scatterhoarders and,in turn,the seed dispersal process.This study was in part supported by a Bullard Fellowship from Harvard Forest,Harvard University(to MAS),Wilkes University mentoring Fund,the U.S.National Science Foundation(DEB-12540642594)to MAS and the Howard Hughes Medical Institute to Wilkes University.
文摘Scatterhoarding rodents often place caches in the open where pilferage rates are reduced,suggesting that they tradeoff higher risks of predation for more secure cache sites.We tested this hypothesis in two study systems by measuring predation risks inferred from measures of giving-up densities(GUDs)at known cache sites and other sites for comparison.Rodent GUDs were measured with small trays containing 3 L of fine sand mixed with sunflower seeds.In the first experiment,we relied on a 2-year seed dispersal study in a natural forest to identify caches of eastern gray squirrels(Sciurus carolinensis)and then measured GUDs at:(i)these caches;(ii)comparable points along logs and rocks where rodent activity was assumed highest;and(iii)a set of random points.We found that GUDs and,presumably,predation risks,were higher at both cache and random points than those with cover.At the second site,we measured GUDs of eastern gray squirrels in an open park system and found that GUDs were consistently lowest at the base of the tree compared to more open sites,where previous studies show caching by squirrels to be highest and pilferage rates by naïve competitors to be lowest.These results confirm that predation risks can influence scatterhoarding decisions but that they are also highly context dependent,and that the landscape of fear,now so well documented in the literature,could potentially shape the temporal and spatial patterns of seedling establishment and forest regeneration in systems where scatterhoarding is common.
文摘Habitats are characterized by different local environmental conditions that influence both behavior and morphology of species,which can result in habitat-dependent phenotypic differences among animals living in heterogeneous environments.We studied 3 alpine populations of Eurasian red squirrels(Sciurus vulgaris),1 living in a marginal high-elevation habitat at the edge of the species’altitudinal distribution,and 2 occurring in higher-quality habitats.Here,we investigated whether squirrels living in the marginal area differed in 2 morphological parameters(body size and body mass)and/or in the expression of 4 personality traits estimated with an openfield test and a mirror image stimulation test(activity,exploration,activity-exploration,and social tendency).Furthermore,we tested whether within-individual variance of the traits(behavioral plasticity)was higher in the edge habitat.Male squirrels in the edge habitat were smaller and weighed less than in the other study areas,while among females,size–habitat relationships were less marked.These sex-specific patterns were explained by a strong association between body mass and reproductive success in female squirrels.Squirrels in the marginal habitat were more active,explorative,and had a more social personality than in the other habitats.However,in contrast to our predictions,behavioral plasticity was smaller in the marginal habitat,but only for the trait exploration.Our results suggest that animals choose the habitat that bestfits their personality,and that habitat-related differences in selective pressures may shape animals’morphology.
