Gene duplications have been common throughout vertebrate evolution, introducing paralogy and so complicating phylogenetic inference from nuclear genes. Reconciled trees are one method capable of dealing with paralogy, using the relationship between a gene phylogeny and the phylogeny of the organisms containing those genes to identify gene duplication events. This allows us to infer phylogenies from gene families containing both orthologous and paralogous copies. Vertebrate phylogeny is well understood from morphological and palaeontological data, but studies using mitochondrial sequence data have failed to reproduce this classical view. Reconciled tree analysis of a database of 118 vertebrate gene families supports a largely classical vertebrate phylogeny.
{"title":"Going nuclear: gene family evolution and vertebrate phylogeny reconciled","authors":"J. Cotton, R. Page","doi":"10.1098/rspb.2002.2074","DOIUrl":"https://doi.org/10.1098/rspb.2002.2074","url":null,"abstract":"Gene duplications have been common throughout vertebrate evolution, introducing paralogy and so complicating phylogenetic inference from nuclear genes. Reconciled trees are one method capable of dealing with paralogy, using the relationship between a gene phylogeny and the phylogeny of the organisms containing those genes to identify gene duplication events. This allows us to infer phylogenies from gene families containing both orthologous and paralogous copies. Vertebrate phylogeny is well understood from morphological and palaeontological data, but studies using mitochondrial sequence data have failed to reproduce this classical view. Reconciled tree analysis of a database of 118 vertebrate gene families supports a largely classical vertebrate phylogeny.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75482529","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The causes and magnitude of inbreeding depression are of considerable importance for a wide range of issues in evolutionary and conservation biology, but we have only a limited understanding of inbreeding depression in natural populations. Here, we present a study of inbreeding in a large wild population of collared flycatchers (Ficedula albicollis). Inbreeding was rare, to the extent that we detected only 1.04%of 2139 matings over 18 years that resulted in offspring with a non–zero inbreeding coefficient, f > 0. When it did occur, inbreeding caused a significant reduction in the egg–hatching rate, in fledgling skeletal size and in post–fledging juvenile survival, with the number of offspring being recruited to the breeding population from a nest of f = 0.25 being reduced by 94% relative to a non–inbred nest. A maximum–likelihood estimate of the number of lethal equivalents per gamete was very high at B = 7.47, indicating a substantial genetic load in this population. There was also a non–significant tendency for inbreeding depression to increase with the strength of selection on a trait. The probability of mating between close relatives f = 0.25) increased throughout the breeding season, possibly reflecting increased costs of inbreeding avoidance. Our results illustrate how severe inbreeding depression and considerable genetic load may exist in natural populations, but detecting them may require extensive long–term datasets.
{"title":"Severe inbreeding depression in collared flycatchers (Ficedula albicollis)","authors":"L. Kruuk, B. Sheldon, J. Merilä","doi":"10.1098/rspb.2002.2049","DOIUrl":"https://doi.org/10.1098/rspb.2002.2049","url":null,"abstract":"The causes and magnitude of inbreeding depression are of considerable importance for a wide range of issues in evolutionary and conservation biology, but we have only a limited understanding of inbreeding depression in natural populations. Here, we present a study of inbreeding in a large wild population of collared flycatchers (Ficedula albicollis). Inbreeding was rare, to the extent that we detected only 1.04%of 2139 matings over 18 years that resulted in offspring with a non–zero inbreeding coefficient, f > 0. When it did occur, inbreeding caused a significant reduction in the egg–hatching rate, in fledgling skeletal size and in post–fledging juvenile survival, with the number of offspring being recruited to the breeding population from a nest of f = 0.25 being reduced by 94% relative to a non–inbred nest. A maximum–likelihood estimate of the number of lethal equivalents per gamete was very high at B = 7.47, indicating a substantial genetic load in this population. There was also a non–significant tendency for inbreeding depression to increase with the strength of selection on a trait. The probability of mating between close relatives f = 0.25) increased throughout the breeding season, possibly reflecting increased costs of inbreeding avoidance. Our results illustrate how severe inbreeding depression and considerable genetic load may exist in natural populations, but detecting them may require extensive long–term datasets.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91052065","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We demonstrate how variable temperatures, mediated by host thermoregulation and behavioural fever, critically affect the interaction between a host (the desert locust, Schistocerca gregaria) and a pathogen (the fungus Metarhizium anisopliae var. acridum). By means of behavioural thermoregulation, infected locusts can raise their body temperatures to fever levels. The adaptive value of this behaviour was examined using three thermal regimes wherein maximum body temperatures achievable were: (i) below, or (ii) at normally preferred temperatures, or were (iii) unrestricted, allowing heightened fever temperatures. All infected locusts ultimately succumbed to disease, with median survival times of 8, 15 and 21 days post–infection, respectively. Crucially, only those locusts able to fever produced viable offspring. This represents, to our knowledge, the first demonstration of the adaptive value of behavioural fever following infection with a naturally occurring pathogen. By contrast, although normal host thermoregulation moderately reduced pathogen reproduction (by 35%), there was no additional negative effect of fever, resulting in an asymmetry in the fitness consequences of fever for the host and the pathogen. The dependency of the host–pathogen interaction upon external abiotic conditions has implications for how virulence and resistance are treated both theoretically and in the management of pests and diseases.
{"title":"Host–pathogen interactions in a varying environment: temperature, behavioural fever and fitness","authors":"S. Elliot, S. Blanford, M. Thomas","doi":"10.1098/rspb.2002.2067","DOIUrl":"https://doi.org/10.1098/rspb.2002.2067","url":null,"abstract":"We demonstrate how variable temperatures, mediated by host thermoregulation and behavioural fever, critically affect the interaction between a host (the desert locust, Schistocerca gregaria) and a pathogen (the fungus Metarhizium anisopliae var. acridum). By means of behavioural thermoregulation, infected locusts can raise their body temperatures to fever levels. The adaptive value of this behaviour was examined using three thermal regimes wherein maximum body temperatures achievable were: (i) below, or (ii) at normally preferred temperatures, or were (iii) unrestricted, allowing heightened fever temperatures. All infected locusts ultimately succumbed to disease, with median survival times of 8, 15 and 21 days post–infection, respectively. Crucially, only those locusts able to fever produced viable offspring. This represents, to our knowledge, the first demonstration of the adaptive value of behavioural fever following infection with a naturally occurring pathogen. By contrast, although normal host thermoregulation moderately reduced pathogen reproduction (by 35%), there was no additional negative effect of fever, resulting in an asymmetry in the fitness consequences of fever for the host and the pathogen. The dependency of the host–pathogen interaction upon external abiotic conditions has implications for how virulence and resistance are treated both theoretically and in the management of pests and diseases.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91507042","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Haydon, D. Shaw, I. Cattadori, P. Hudson, S. Thirgood
We develop a method for describing the periodicity of noisy ‘quasi–cyclic’ time–series based on integrals of their power spectra corresponding to different frequency intervals that we use to classify time–series as ‘strongly cycli’,‘weakly cycli’ or‘non–cycli’. We apply this analysis to over 300 time–series of shooting records of red grouse from 289 moors located in 20 regions of the UK. Time–series from 63 of these populations were not distinguishable from white noise, but significant evidence of cyclic behaviour in the 2–15 year range was detected in time–series from 183 other populations. Time–series from the remaining 43 populations, though distinguishable from white noise, did not exhibit consistently recognizable cyclic behaviour in the same period range. Cyclic populations exhibit an average periodicity of 8.3 years, but only 20% of these populations cycle with a period of four to six years. Geographically, grouse populations are remarkable more for their dynamic heterogeneity than for any observable regularity. The relationship between the location of populations and their dynamical behaviour is weak. The prevalence of cyclic time–series within a region did not significantly differ from the overall average value. Moor region explained 22% of the variation in periodicity, differing from the overall mean in three regions. Average periodicity increases significantly from 6.8 to 8.9 years from the most southerly to most northerly populations. However, latitude explains only 5.3% of the variation in periodicity of the cycles.
{"title":"Analysing noisy time–series: describing regional variation in the cyclic dynamics of red grouse","authors":"D. Haydon, D. Shaw, I. Cattadori, P. Hudson, S. Thirgood","doi":"10.1098/rspb.2002.2053","DOIUrl":"https://doi.org/10.1098/rspb.2002.2053","url":null,"abstract":"We develop a method for describing the periodicity of noisy ‘quasi–cyclic’ time–series based on integrals of their power spectra corresponding to different frequency intervals that we use to classify time–series as ‘strongly cycli’,‘weakly cycli’ or‘non–cycli’. We apply this analysis to over 300 time–series of shooting records of red grouse from 289 moors located in 20 regions of the UK. Time–series from 63 of these populations were not distinguishable from white noise, but significant evidence of cyclic behaviour in the 2–15 year range was detected in time–series from 183 other populations. Time–series from the remaining 43 populations, though distinguishable from white noise, did not exhibit consistently recognizable cyclic behaviour in the same period range. Cyclic populations exhibit an average periodicity of 8.3 years, but only 20% of these populations cycle with a period of four to six years. Geographically, grouse populations are remarkable more for their dynamic heterogeneity than for any observable regularity. The relationship between the location of populations and their dynamical behaviour is weak. The prevalence of cyclic time–series within a region did not significantly differ from the overall average value. Moor region explained 22% of the variation in periodicity, differing from the overall mean in three regions. Average periodicity increases significantly from 6.8 to 8.9 years from the most southerly to most northerly populations. However, latitude explains only 5.3% of the variation in periodicity of the cycles.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87942737","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jukka T. Forsman, Janne-Tuomas Seppänen, M. Mönkkönen
The coexistence of species sharing mutual resources is usually thought to be limited by negative processes such as interspecific competition. This is because an overlap in resource use leads to negative fitness consequences, and traits favouring avoidance of potential competitors, for example in habitat selection, are therefore selected for. However, species interactions are acknowledged to vary from negative (competition) to mutualism, although empirical evidence for positive interspecific interactions from natural communities of other than plants and sessile animals is scarce. Here, we experimentally examined the habitat selection and its fitness consequences of a migrant bird, the pied flycatcher (Ficedula hypoleuca), in relation to the presence of competitively superior birds, resident titmice (Parus spp.). Experiments were conducted on two spatial scales: landscape and nest–site scale. We demonstrate that pied flycatchers were attracted to and accrued fitness benefits from the presence of titmice. Flycatchers breeding in tight association with titmice initiated breeding earlier, had larger broods and heavier young than solitarily breeding flycatchers. This paradoxical result indicates that species interactions may switch from negative to positive and that the coexistence of species is not always restricted by negative costs caused by other species.
{"title":"Positive fitness consequences of interspecific interaction with a potential competitor","authors":"Jukka T. Forsman, Janne-Tuomas Seppänen, M. Mönkkönen","doi":"10.1098/rspb.2002.2065","DOIUrl":"https://doi.org/10.1098/rspb.2002.2065","url":null,"abstract":"The coexistence of species sharing mutual resources is usually thought to be limited by negative processes such as interspecific competition. This is because an overlap in resource use leads to negative fitness consequences, and traits favouring avoidance of potential competitors, for example in habitat selection, are therefore selected for. However, species interactions are acknowledged to vary from negative (competition) to mutualism, although empirical evidence for positive interspecific interactions from natural communities of other than plants and sessile animals is scarce. Here, we experimentally examined the habitat selection and its fitness consequences of a migrant bird, the pied flycatcher (Ficedula hypoleuca), in relation to the presence of competitively superior birds, resident titmice (Parus spp.). Experiments were conducted on two spatial scales: landscape and nest–site scale. We demonstrate that pied flycatchers were attracted to and accrued fitness benefits from the presence of titmice. Flycatchers breeding in tight association with titmice initiated breeding earlier, had larger broods and heavier young than solitarily breeding flycatchers. This paradoxical result indicates that species interactions may switch from negative to positive and that the coexistence of species is not always restricted by negative costs caused by other species.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82651651","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Game theory models of sperm competition predict that within species, males should increase their sperm expenditure when they have one competitor, but decrease expenditure with increasing numbers of competitors. So far, there have been few tests or support for this prediction. Here, we show that males of a freshwater fish, the European bitterling, Rhodeus sericeus, do indeed adjust their ejaculation rate to the number of male competitors by first increasing and then decreasing their ejaculation rates as the number of competitors increases. However, this occurred only under restricted conditions. Specifically, the prediction was upheld as long as no female had deposited eggs in the live mussels that are used as spawning sites. After one or more females had spawned, males did not decrease their ejaculation rates with the number of competitors, but instead they became more aggressive. This indicates that decreased ejaculation rate and increased aggression are alternative responses to increased risk of sperm competition.
{"title":"Adjustments of ejaculation rates in response to risk of sperm competition in a fish, the bitterling (Rhodeus sericeus)","authors":"U. Candolin, J. Reynolds","doi":"10.1098/rspb.2002.2055","DOIUrl":"https://doi.org/10.1098/rspb.2002.2055","url":null,"abstract":"Game theory models of sperm competition predict that within species, males should increase their sperm expenditure when they have one competitor, but decrease expenditure with increasing numbers of competitors. So far, there have been few tests or support for this prediction. Here, we show that males of a freshwater fish, the European bitterling, Rhodeus sericeus, do indeed adjust their ejaculation rate to the number of male competitors by first increasing and then decreasing their ejaculation rates as the number of competitors increases. However, this occurred only under restricted conditions. Specifically, the prediction was upheld as long as no female had deposited eggs in the live mussels that are used as spawning sites. After one or more females had spawned, males did not decrease their ejaculation rates with the number of competitors, but instead they became more aggressive. This indicates that decreased ejaculation rate and increased aggression are alternative responses to increased risk of sperm competition.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86637648","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Albon, A. Stien, R. Irvine, R. Langvatn, E. Ropstad, O. Halvorsen
Even though theoretical models show that parasites may regulate host population densities, few empirical studies have given support to this hypothesis. We present experimental and observational evidence for a host–parasite interaction where the parasite has sufficient impact on host population dynamics for regulation to occur. During a six year study of the Svalbard reindeer and its parasitic gastrointestinal nematode Ostertagia gruehneri we found that anthelminthic treatment in April–May increased the probability of a reindeer having a calf in the next year, compared with untreated controls. However, treatment did not influence the over–winter survival of the reindeer. The annual variation in the degree to which parasites depressed fecundity was positively related to the abundance of O. gruehneri infection the previous October, which in turn was related to host density two years earlier. In addition to the treatment effect, there was a strong negative effect of winter precipitation on the probability of female reindeer having a calf. A simple matrix model was parameterized using estimates from our experimental and observational data. This model shows that the parasite–mediated effect on fecundity was sufficient to regulate reindeer densities around observed host densities.
{"title":"The role of parasites in the dynamics of a reindeer population","authors":"S. Albon, A. Stien, R. Irvine, R. Langvatn, E. Ropstad, O. Halvorsen","doi":"10.1098/rspb.2002.2064","DOIUrl":"https://doi.org/10.1098/rspb.2002.2064","url":null,"abstract":"Even though theoretical models show that parasites may regulate host population densities, few empirical studies have given support to this hypothesis. We present experimental and observational evidence for a host–parasite interaction where the parasite has sufficient impact on host population dynamics for regulation to occur. During a six year study of the Svalbard reindeer and its parasitic gastrointestinal nematode Ostertagia gruehneri we found that anthelminthic treatment in April–May increased the probability of a reindeer having a calf in the next year, compared with untreated controls. However, treatment did not influence the over–winter survival of the reindeer. The annual variation in the degree to which parasites depressed fecundity was positively related to the abundance of O. gruehneri infection the previous October, which in turn was related to host density two years earlier. In addition to the treatment effect, there was a strong negative effect of winter precipitation on the probability of female reindeer having a calf. A simple matrix model was parameterized using estimates from our experimental and observational data. This model shows that the parasite–mediated effect on fecundity was sufficient to regulate reindeer densities around observed host densities.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83021530","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. C. Marshall, David W. Coltman, J. Pemberton, J. Slate, J. A. Spalton, F. Guinness, J. A. Smith, J. Pilkington, T. Clutton‐Brock
A previous review of inbreeding in natural populations suggested that close inbreeding (inbreeding coefficient f = 0.25) is generally rare in wild birds and mammals. However, the review did not assess rates of moderate inbreeding (f = 0.125), which may make a rather larger contribution to overall inbreeding in a population. Furthermore, previous studies may have underestimated the prevalence of inbreeding in wild populations with incomplete pedigrees. By categorizing inbreeding events by the relationship of the parental pair, we suggest a simple method for estimating rates of close and moderate inbreeding from incomplete pedigree data. We applied this method to three wild populations of ruminants: red deer on Rum, Scotland, Soay sheep on Hirta, Scotland and reintroduced Arabian oryx on the Jiddat–al–Harasis, Oman. Although paternal half–sib pairs were the most common category of inbreeding in all three populations, there was considerable variation among populations in the frequencies of the various categories of inbreeding. This variation may be largely explained by differences in population size and dynamics, in maternal and paternal sibship size and in the overlap of reproductive lifespan of consecutive generations. Close and moderate inbreeding appear to be a routine part of breeding behaviour in these ruminant populations.
{"title":"Estimating the prevalence of inbreeding from incomplete pedigrees","authors":"T. C. Marshall, David W. Coltman, J. Pemberton, J. Slate, J. A. Spalton, F. Guinness, J. A. Smith, J. Pilkington, T. Clutton‐Brock","doi":"10.1098/rspb.2002.2035","DOIUrl":"https://doi.org/10.1098/rspb.2002.2035","url":null,"abstract":"A previous review of inbreeding in natural populations suggested that close inbreeding (inbreeding coefficient f = 0.25) is generally rare in wild birds and mammals. However, the review did not assess rates of moderate inbreeding (f = 0.125), which may make a rather larger contribution to overall inbreeding in a population. Furthermore, previous studies may have underestimated the prevalence of inbreeding in wild populations with incomplete pedigrees. By categorizing inbreeding events by the relationship of the parental pair, we suggest a simple method for estimating rates of close and moderate inbreeding from incomplete pedigree data. We applied this method to three wild populations of ruminants: red deer on Rum, Scotland, Soay sheep on Hirta, Scotland and reintroduced Arabian oryx on the Jiddat–al–Harasis, Oman. Although paternal half–sib pairs were the most common category of inbreeding in all three populations, there was considerable variation among populations in the frequencies of the various categories of inbreeding. This variation may be largely explained by differences in population size and dynamics, in maternal and paternal sibship size and in the overlap of reproductive lifespan of consecutive generations. Close and moderate inbreeding appear to be a routine part of breeding behaviour in these ruminant populations.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88413749","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Cichoń, M. Chadzińska, A. Książek, M. Konarzewski
This study was undertaken to examine the trade–off between the cost of thermoregulation and immune function in laboratory mice. Mice were maintained either at 23°C or cold exposed at 5°C for 10 days. Then, they were immunized with sheep red blood cells. Thus, the cold–exposed mice had either experienced or not experienced cold stress prior to immunization. Cold stress elicited a substantial increase in food intake, accompanied by a significant reduction in food digestibility. An increase in mass of metabolically active internal organs (small intestines, heart and kidney) was observed in cold–exposed mice. These findings reassured us that costs of increased thermoregulation caused by cold stress were substantial. The immune response of mice exposed to long–lasting cold stress was significantly lower, but immune response was not affected in short–exposed mice. Differences in immune response between experimental groups accompanied changes in mass of immunocompetent organs (thymus and spleen). Our findings indicate that studies of trade–offs should account for the fact that resource reallocation in response to an environmental challenge may not be immediate. In fact, resource reallocation may be postponed until the new environmental state becomes permanent or until an organism attains physiological adaptation to the current conditions.
{"title":"Delayed effects of cold stress on immune response in laboratory mice","authors":"M. Cichoń, M. Chadzińska, A. Książek, M. Konarzewski","doi":"10.1098/rspb.2002.2054","DOIUrl":"https://doi.org/10.1098/rspb.2002.2054","url":null,"abstract":"This study was undertaken to examine the trade–off between the cost of thermoregulation and immune function in laboratory mice. Mice were maintained either at 23°C or cold exposed at 5°C for 10 days. Then, they were immunized with sheep red blood cells. Thus, the cold–exposed mice had either experienced or not experienced cold stress prior to immunization. Cold stress elicited a substantial increase in food intake, accompanied by a significant reduction in food digestibility. An increase in mass of metabolically active internal organs (small intestines, heart and kidney) was observed in cold–exposed mice. These findings reassured us that costs of increased thermoregulation caused by cold stress were substantial. The immune response of mice exposed to long–lasting cold stress was significantly lower, but immune response was not affected in short–exposed mice. Differences in immune response between experimental groups accompanied changes in mass of immunocompetent organs (thymus and spleen). Our findings indicate that studies of trade–offs should account for the fact that resource reallocation in response to an environmental challenge may not be immediate. In fact, resource reallocation may be postponed until the new environmental state becomes permanent or until an organism attains physiological adaptation to the current conditions.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76181967","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
It is widely supposed that things tend to look blurred when they are moving fast. Previous work has shown that this is true for sharp edges but, paradoxically, blurred edges look sharper when they are moving than when stationary. This is‘motion sharpenin’. We show that blurred edges also look up to 50% sharper when they are presented briefly (8–24 ms) than at longer durations (100–500 ms) without motion. This argues strongly against high–level models of sharpening based specifically on compensation for motion blur. It also argues against a recent, low–level, linear filter model that requires motion to produce sharpening. No linear filter model can explain our finding that sharpening was similar for sinusoidal and non–sinusoidal gratings, since linear filters can never distort sine waves. We also conclude that the idea of a ‘defaul’ assumption of sharpness is not supported by experimental evidence. A possible source of sharpening is a nonlinearity in the contrast response of early visual mechanisms to fast or transient temporal changes, perhaps based on the magnocellular (M–cell) pathway. Our finding that sharpening is not diminished at low contrast sets strong constraints on the nature of the nonlinearity.
{"title":"Seeing blur: ‘motion sharpenin’ without motion","authors":"M. Georgeson, S. Hammett","doi":"10.1098/rspb.2002.2029","DOIUrl":"https://doi.org/10.1098/rspb.2002.2029","url":null,"abstract":"It is widely supposed that things tend to look blurred when they are moving fast. Previous work has shown that this is true for sharp edges but, paradoxically, blurred edges look sharper when they are moving than when stationary. This is‘motion sharpenin’. We show that blurred edges also look up to 50% sharper when they are presented briefly (8–24 ms) than at longer durations (100–500 ms) without motion. This argues strongly against high–level models of sharpening based specifically on compensation for motion blur. It also argues against a recent, low–level, linear filter model that requires motion to produce sharpening. No linear filter model can explain our finding that sharpening was similar for sinusoidal and non–sinusoidal gratings, since linear filters can never distort sine waves. We also conclude that the idea of a ‘defaul’ assumption of sharpness is not supported by experimental evidence. A possible source of sharpening is a nonlinearity in the contrast response of early visual mechanisms to fast or transient temporal changes, perhaps based on the magnocellular (M–cell) pathway. Our finding that sharpening is not diminished at low contrast sets strong constraints on the nature of the nonlinearity.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77411567","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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