Many migratory songbirds follow circuitous migratory routes instead of taking the shortest path between overwintering and breeding areas. Here, we study the migration patterns in Swainson's thrush (Catharus ustulatus), a neartic–neotropical migrant songbird, using molecular genetic approaches. This species is presently separated into genetically distinct coastal and continental populations that diverged during the Late Pleistocene (as indicated by molecular dating), yet appear to have retained ancestral patterns of migration. Low nucleotide diversity, a star–like haplotype phylogeny and unimodal mismatch distributions all support the hypothesis that both the coastal and the continental populations have undergone recent demographic expansions. Nearctic–neotropical banding and genetic data show nearly complete segregation of migratory routes and of overwintering locations: coastal populations migrate along the Pacific Coast to overwintering sites in Central America and Mexico, whereas continental populations migrate along an eastern route to overwintering sites in Panama and South America. Nearctic–neotropical banding data also show that continental birds north, northwest and east of this migratory divide fly thousands of miles east before turning south. We conclude that circuitous migration in the Swainson's thrush is an artefact of a Late Pleistocene range expansion.
{"title":"Not as the crow flies: a historical explanation for circuitous migration in Swainson's thrush (Catharus ustulatus)","authors":"K. Ruegg, T. Smith","doi":"10.1098/rspb.2002.2032","DOIUrl":"https://doi.org/10.1098/rspb.2002.2032","url":null,"abstract":"Many migratory songbirds follow circuitous migratory routes instead of taking the shortest path between overwintering and breeding areas. Here, we study the migration patterns in Swainson's thrush (Catharus ustulatus), a neartic–neotropical migrant songbird, using molecular genetic approaches. This species is presently separated into genetically distinct coastal and continental populations that diverged during the Late Pleistocene (as indicated by molecular dating), yet appear to have retained ancestral patterns of migration. Low nucleotide diversity, a star–like haplotype phylogeny and unimodal mismatch distributions all support the hypothesis that both the coastal and the continental populations have undergone recent demographic expansions. Nearctic–neotropical banding and genetic data show nearly complete segregation of migratory routes and of overwintering locations: coastal populations migrate along the Pacific Coast to overwintering sites in Central America and Mexico, whereas continental populations migrate along an eastern route to overwintering sites in Panama and South America. Nearctic–neotropical banding data also show that continental birds north, northwest and east of this migratory divide fly thousands of miles east before turning south. We conclude that circuitous migration in the Swainson's thrush is an artefact of a Late Pleistocene range expansion.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81311837","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}
C. Berticat, F. Rousset, M. Raymond, A. Berthomieu, M. Weill
Wolbachia symbionts are responsible for various alterations in host reproduction. The effects of the host genome on endosymbiont levels have often been suggested, but rarely described. Here, we show that Wolbachia density is strongly modified by the presence of insecticide–resistant genes in the common house mosquito, Culex pipiens. The Wolbachia density was estimated using a real–time quantitative PCR assay. Strains harbouring different genes conferring resistance were more infected than a susceptible strain with the same genetic background. We show that this interaction also operates in natural populations. We propose that mosquitoes may control Wolbachia density less efficiently when they carry an insecticide–resistant gene, i.e. when they suffer from a physiological resistance cost.
{"title":"High Wolbachia density in insecticide–resistant mosquitoes","authors":"C. Berticat, F. Rousset, M. Raymond, A. Berthomieu, M. Weill","doi":"10.1098/rspb.2002.2022","DOIUrl":"https://doi.org/10.1098/rspb.2002.2022","url":null,"abstract":"Wolbachia symbionts are responsible for various alterations in host reproduction. The effects of the host genome on endosymbiont levels have often been suggested, but rarely described. Here, we show that Wolbachia density is strongly modified by the presence of insecticide–resistant genes in the common house mosquito, Culex pipiens. The Wolbachia density was estimated using a real–time quantitative PCR assay. Strains harbouring different genes conferring resistance were more infected than a susceptible strain with the same genetic background. We show that this interaction also operates in natural populations. We propose that mosquitoes may control Wolbachia density less efficiently when they carry an insecticide–resistant gene, i.e. when they suffer from a physiological resistance cost.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73851312","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}
Comparisons across bird species have indicated that those more exposed to parasites and pathogens invest more in immunological defence, as measured by spleen size. We investigated how spleen volume varied with colony size, parasite load and an individual's colony–size history in the cliff swallow, Petrochelidon pyrrhonota, a colonial passerine bird of North America. We used a sample of over 1700 birds that had all died during a period of inclement weather in 1996. We experimentally manipulated ectoparasitism by fumigating nests in some colonies prior to the bad weather. Birds from parasite–free colonies had significantly smaller spleens than those from naturally infested sites; spleen volume did not differ between the sexes and did not vary with age. Mean spleen volume increased significantly with the colony size at a site prior to the bad weather in 1996 and at the site in 1995, both measures of colony size being indices of ectoparasitism at a site. An individual's history of breeding–colony size (defined as the average colony size it had occupied in years prior to 1996) had no association with its spleen size. The results are consistent with parasite–induced splenomegaly whenever birds are exposed to large numbers of ectoparasites. The results do not support spleen size as being a signal of differential life–history investment in immunological defence among individuals and thus run counter to interpretations from recent cross–species comparisons.
{"title":"Spleen volume varies with colony size and parasite load in a colonial bird","authors":"C. Brown, M. Brown","doi":"10.1098/rspb.2002.2036","DOIUrl":"https://doi.org/10.1098/rspb.2002.2036","url":null,"abstract":"Comparisons across bird species have indicated that those more exposed to parasites and pathogens invest more in immunological defence, as measured by spleen size. We investigated how spleen volume varied with colony size, parasite load and an individual's colony–size history in the cliff swallow, Petrochelidon pyrrhonota, a colonial passerine bird of North America. We used a sample of over 1700 birds that had all died during a period of inclement weather in 1996. We experimentally manipulated ectoparasitism by fumigating nests in some colonies prior to the bad weather. Birds from parasite–free colonies had significantly smaller spleens than those from naturally infested sites; spleen volume did not differ between the sexes and did not vary with age. Mean spleen volume increased significantly with the colony size at a site prior to the bad weather in 1996 and at the site in 1995, both measures of colony size being indices of ectoparasitism at a site. An individual's history of breeding–colony size (defined as the average colony size it had occupied in years prior to 1996) had no association with its spleen size. The results are consistent with parasite–induced splenomegaly whenever birds are exposed to large numbers of ectoparasites. The results do not support spleen size as being a signal of differential life–history investment in immunological defence among individuals and thus run counter to interpretations from recent cross–species comparisons.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80298230","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}
A new method for detecting site–specific variation of evolutionary rate (the so–called covarion process) from protein sequence data is proposed. It involves comparing the maximum–likelihood estimates of the replacement rate of an amino acid site in distinct subtrees of a large tree. This approach allows detection of covarion at the gene or the amino acid levels. The method is applied to mammalian–mitochondrial–protein sequences. Significant covarion–like evolution is found in the (simian) primate lineage: some amino acid positions are fast–evolving (i.e. unconstrained) in non–primate mammals but slow–evolving (i.e. highly constrained) in primates, and some show the opposite pattern. Our results indicate that the mitochondrial genome of primates reached a new peak of the adaptive landscape through positive selection.
{"title":"A covarion-based method for detecting molecular adaptation: application to the evolution of primate mitochondrial genomes","authors":"T. Pupko, N. Galtier","doi":"10.1098/rspb.2002.2025","DOIUrl":"https://doi.org/10.1098/rspb.2002.2025","url":null,"abstract":"A new method for detecting site–specific variation of evolutionary rate (the so–called covarion process) from protein sequence data is proposed. It involves comparing the maximum–likelihood estimates of the replacement rate of an amino acid site in distinct subtrees of a large tree. This approach allows detection of covarion at the gene or the amino acid levels. The method is applied to mammalian–mitochondrial–protein sequences. Significant covarion–like evolution is found in the (simian) primate lineage: some amino acid positions are fast–evolving (i.e. unconstrained) in non–primate mammals but slow–evolving (i.e. highly constrained) in primates, and some show the opposite pattern. Our results indicate that the mitochondrial genome of primates reached a new peak of the adaptive landscape through positive selection.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82815080","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}
Do birds show a different pattern of insular evolution from mammals? Mammals follow the ‘island rule’, with large–bodied species getting smaller on islands and small–bodied species getting bigger. By contrast, the traditional view on birds is that they follow no general island rule for body size, but that there is an insular trend for large bills. Insular shifts in feeding ecology are, therefore, widely assumed to be the primary cause of divergence in island birds. We use a comparative approach to test these ideas. Contrary to the traditional view, we find no evidence for increased bill size in insular populations. Instead, changes in both bill size and body size obey the ‘island rule’. The differences between our results and the traditional view arise because previous analyses were based largely on passerines. We also investigate some ecological factors that are thought to influence island evolution. As predicted by the traditional view, shifts in bill size are associated with feeding ecology. By contrast, shifts in body size are associated with the potential for intraspecific competition and thermal ecology. All these results remain qualitatively unchanged when we use different methods to score the ecological factors and restrict our analyses to taxa showing pronounced morphological divergence. Because of strong covariation between ecological factors, however, we cannot estimate the relative importance of each ecological factor. Overall, our results show that the island rule is valid for both body size and bill length in birds and that, in addition to feeding ecology, insular shifts in the level of intraspecific competition and the abiotic environment also have a role.
{"title":"The ‘island rule’ in birds: medium body size and its ecological explanation","authors":"S. Clegg, Ian P. F. Owens","doi":"10.1098/rspb.2002.2024","DOIUrl":"https://doi.org/10.1098/rspb.2002.2024","url":null,"abstract":"Do birds show a different pattern of insular evolution from mammals? Mammals follow the ‘island rule’, with large–bodied species getting smaller on islands and small–bodied species getting bigger. By contrast, the traditional view on birds is that they follow no general island rule for body size, but that there is an insular trend for large bills. Insular shifts in feeding ecology are, therefore, widely assumed to be the primary cause of divergence in island birds. We use a comparative approach to test these ideas. Contrary to the traditional view, we find no evidence for increased bill size in insular populations. Instead, changes in both bill size and body size obey the ‘island rule’. The differences between our results and the traditional view arise because previous analyses were based largely on passerines. We also investigate some ecological factors that are thought to influence island evolution. As predicted by the traditional view, shifts in bill size are associated with feeding ecology. By contrast, shifts in body size are associated with the potential for intraspecific competition and thermal ecology. All these results remain qualitatively unchanged when we use different methods to score the ecological factors and restrict our analyses to taxa showing pronounced morphological divergence. Because of strong covariation between ecological factors, however, we cannot estimate the relative importance of each ecological factor. Overall, our results show that the island rule is valid for both body size and bill length in birds and that, in addition to feeding ecology, insular shifts in the level of intraspecific competition and the abiotic environment also have a role.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78636176","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}
L. Gigord, M. Macnair, M. Stritesky, M. Stritesky, A. Smithson
More than one–third of orchid species do not provide their pollinators with either pollen or nectar rewards. Floral mimicry could explain the maintenance of these rewardless orchid species, but most rewardless orchids do not appear to have a rewarding plant that they mimic specifically. We tested the hypothesis that floral mimicry can occur through similarity based on corolla colour alone, using naive bumble–bees foraging on arrays of plants with one rewarding model species, and one rewardless putative mimic species (Dactylorhiza sambucina) which had two colour morphs. We found that when bees were inexperienced, they visited both rewardless morphs randomly. However, after bees had gained experience with the rewarding model, and it was removed from the experiment, bees resampled preferentially the rewardless morph most similar to it in corolla colour. This is the first clear evidence, to our knowledge, that pollinators could select for floral mimicry. We suggest that floral mimicry can be a selective force acting on rewardless orchids, but only under some ecological conditions. In particular, we argue that selection on early–flowering rewardless orchids that receive visits from a large pool of naive pollinators will be weakly influenced by mimicry.
{"title":"The potential for floral mimicry in rewardless orchids: an experimental study","authors":"L. Gigord, M. Macnair, M. Stritesky, M. Stritesky, A. Smithson","doi":"10.1098/rspb.2002.2018","DOIUrl":"https://doi.org/10.1098/rspb.2002.2018","url":null,"abstract":"More than one–third of orchid species do not provide their pollinators with either pollen or nectar rewards. Floral mimicry could explain the maintenance of these rewardless orchid species, but most rewardless orchids do not appear to have a rewarding plant that they mimic specifically. We tested the hypothesis that floral mimicry can occur through similarity based on corolla colour alone, using naive bumble–bees foraging on arrays of plants with one rewarding model species, and one rewardless putative mimic species (Dactylorhiza sambucina) which had two colour morphs. We found that when bees were inexperienced, they visited both rewardless morphs randomly. However, after bees had gained experience with the rewarding model, and it was removed from the experiment, bees resampled preferentially the rewardless morph most similar to it in corolla colour. This is the first clear evidence, to our knowledge, that pollinators could select for floral mimicry. We suggest that floral mimicry can be a selective force acting on rewardless orchids, but only under some ecological conditions. In particular, we argue that selection on early–flowering rewardless orchids that receive visits from a large pool of naive pollinators will be weakly influenced by mimicry.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78411780","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}
Organisms are expected to be sensitive to cues of genetic relatedness when making decisions about social behaviour. Relatedness can be assessed in several ways, one of which is phenotype matching: the assessment of similarity between others' traits and either one's own traits or those of known relatives. One candidate cue of relatedness in humans is facial resemblance. Here, I report the effects of an experimental manipulation of facial resemblance in a two–person sequential trust game. Subjects were shown faces of ostensible playing partners manipulated to resemble either themselves or an unknown person. Resemblance to the subject's own face raised the incidence of trusting a partner, but had no effect on the incidence of selfish betrayals of the partner's trust. Control subjects playing with identical pictures failed to show such an effect. In a second experiment, resemblance of the playing partner to a familiar (famous) person had no effect on either trusting or betrayals of trust.
{"title":"Facial resemblance enhances trust","authors":"L. DeBruine","doi":"10.1098/rspb.2002.2034","DOIUrl":"https://doi.org/10.1098/rspb.2002.2034","url":null,"abstract":"Organisms are expected to be sensitive to cues of genetic relatedness when making decisions about social behaviour. Relatedness can be assessed in several ways, one of which is phenotype matching: the assessment of similarity between others' traits and either one's own traits or those of known relatives. One candidate cue of relatedness in humans is facial resemblance. Here, I report the effects of an experimental manipulation of facial resemblance in a two–person sequential trust game. Subjects were shown faces of ostensible playing partners manipulated to resemble either themselves or an unknown person. Resemblance to the subject's own face raised the incidence of trusting a partner, but had no effect on the incidence of selfish betrayals of the partner's trust. Control subjects playing with identical pictures failed to show such an effect. In a second experiment, resemblance of the playing partner to a familiar (famous) person had no effect on either trusting or betrayals of trust.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84106790","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}
Trait evolution via sexual selection has traditionally been viewed as isolated from life–history constraints. Recent theoretical treatments, however, predict that costly sexually selected characters should be mediated by the same allocational trade–offs that apply to more conventional aspects of reproductive investment. Participation in risky competitive behaviours, for example male–male combat, should therefore increase as the opportunity for future reproduction declines. However, the demonstration of such trade–offs has proven to be elusive due to concomitant age–based variation in the physical determinants of fighting ‘ability’. Here, I exploit the unique nature of a butterfly contest system to provide compelling evidence for lifetime partitioning of risky and aggressive sexually selected behaviours. I show that male Hypolimnas bolina become more willing to persist in contests over mating territories, and more generally accepting of injury risks, as they age. Contest persistence in this species is not mediated simply by physical condition, and I experimentally isolate the effect of ageing per se from resource ownership and previous contest experience. These results demonstrate how sexually selected behaviours can be ultimately mediated by a shifting trade–off between contemporary reproductive effort and future opportunities.
{"title":"Sexual selection constrained by life history in a butterfly","authors":"D. Kemp","doi":"10.1098/rspb.2002.2000","DOIUrl":"https://doi.org/10.1098/rspb.2002.2000","url":null,"abstract":"Trait evolution via sexual selection has traditionally been viewed as isolated from life–history constraints. Recent theoretical treatments, however, predict that costly sexually selected characters should be mediated by the same allocational trade–offs that apply to more conventional aspects of reproductive investment. Participation in risky competitive behaviours, for example male–male combat, should therefore increase as the opportunity for future reproduction declines. However, the demonstration of such trade–offs has proven to be elusive due to concomitant age–based variation in the physical determinants of fighting ‘ability’. Here, I exploit the unique nature of a butterfly contest system to provide compelling evidence for lifetime partitioning of risky and aggressive sexually selected behaviours. I show that male Hypolimnas bolina become more willing to persist in contests over mating territories, and more generally accepting of injury risks, as they age. Contest persistence in this species is not mediated simply by physical condition, and I experimentally isolate the effect of ageing per se from resource ownership and previous contest experience. These results demonstrate how sexually selected behaviours can be ultimately mediated by a shifting trade–off between contemporary reproductive effort and future opportunities.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88673440","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}
Smallpox causes roughly 20% mortality whereas chickenpox causes less than 0.1%. Most ‘verbal’ (i.e. non–mathematical) discussions using a mortality definition of virulence would therefore label smallpox as more virulent. Indeed, the virulence of many diseases is measured using such case mortalities, &b.chi;, or related measures such as expected host lifespan, T, or lethal dose, LDx. But &b.chi;, T and LDx are only indirectly related to parasite–induced instantaneous mortality rate, α, which is the mortality measure used in much of the theory developed to explain virulence evolution. Here I point out that relatively deadly pathogens can actually have lower values of α than benign pathogens, demonstrating that α does not, by itself, reflect the extent to which a parasite causes host mortality. I present mathematical relationships between α and &b.chi;, T and LDx, and use these to demonstrate that predictions about virulence evolution can be qualitatively altered depending upon which measure is used as the definition of virulence. Two simple examples are presented to illustrate this point, one of which demonstrates that the well–cited prediction that virulence should evolve to be higher when disease–independent host mortality increases need not hold. This prediction has been made in terms of parasite–induced instantaneous mortality, α, but if virulence is measured using case mortality (or T or LDx) then this prediction can easily be reversed. Theoretical and empirical researchers must use compatible mortality measures before a productive exchange between the two can take place, and it is suggested that case mortality (or lethal dose) is best suited as a single (mortality) measure of parasite virulence.
{"title":"On the evolution of virulence and the relationship between various measures of mortality","authors":"T. Day","doi":"10.1098/rspb.2002.2021","DOIUrl":"https://doi.org/10.1098/rspb.2002.2021","url":null,"abstract":"Smallpox causes roughly 20% mortality whereas chickenpox causes less than 0.1%. Most ‘verbal’ (i.e. non–mathematical) discussions using a mortality definition of virulence would therefore label smallpox as more virulent. Indeed, the virulence of many diseases is measured using such case mortalities, &b.chi;, or related measures such as expected host lifespan, T, or lethal dose, LDx. But &b.chi;, T and LDx are only indirectly related to parasite–induced instantaneous mortality rate, α, which is the mortality measure used in much of the theory developed to explain virulence evolution. Here I point out that relatively deadly pathogens can actually have lower values of α than benign pathogens, demonstrating that α does not, by itself, reflect the extent to which a parasite causes host mortality. I present mathematical relationships between α and &b.chi;, T and LDx, and use these to demonstrate that predictions about virulence evolution can be qualitatively altered depending upon which measure is used as the definition of virulence. Two simple examples are presented to illustrate this point, one of which demonstrates that the well–cited prediction that virulence should evolve to be higher when disease–independent host mortality increases need not hold. This prediction has been made in terms of parasite–induced instantaneous mortality, α, but if virulence is measured using case mortality (or T or LDx) then this prediction can easily be reversed. Theoretical and empirical researchers must use compatible mortality measures before a productive exchange between the two can take place, and it is suggested that case mortality (or lethal dose) is best suited as a single (mortality) measure of parasite virulence.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85409926","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}
In some taxa of Hymenoptera, fungi, red algae and mistletoe, parasites and their hosts are either sibling species or at least closely related (Emery's rule). Three evolutionary mechanisms have been proposed for this phenomenon: (i) intraspecific parasitism is followed by sympatric speciation; (ii) allopatric speciation is followed by secondary sympatry and the subsequent parasitism of one sibling species by the other; and (iii) allopatric speciation of a species with intraspecific parasitism is followed by secondary sympatry, in which one species becomes an obligate parasite of the other. Mechanisms (i) and (ii) are problematic, while mechanism (iii) has not, to our knowledge, been analysed quantitatively. In this paper, we develop a model for single- and two-species evolutionary stable strategies (ESSs) to examine the basis for Emery's rule and to determine whether mechanism (iii) is consistent with ESS reasoning. In secondary sympatry after allopatric speciation, the system's evolution depends on the relative abundances of the two sibling species and on the proportional damage wrought by parasites of each species on non-parasitic members of the other. Depending on these interspecific effects, either the rarer or the commoner species may become the parasite and the levels of within-species parasitism need not determine which evolves to obligate parasitism.
{"title":"The evolution of parasites from their hosts: intra– and interspecific parasitism and Emery's rule","authors":"R. M. Lowe, S. A. Ward, R. Crozier","doi":"10.1098/rspb.2002.2008","DOIUrl":"https://doi.org/10.1098/rspb.2002.2008","url":null,"abstract":"In some taxa of Hymenoptera, fungi, red algae and mistletoe, parasites and their hosts are either sibling species or at least closely related (Emery's rule). Three evolutionary mechanisms have been proposed for this phenomenon: (i) intraspecific parasitism is followed by sympatric speciation; (ii) allopatric speciation is followed by secondary sympatry and the subsequent parasitism of one sibling species by the other; and (iii) allopatric speciation of a species with intraspecific parasitism is followed by secondary sympatry, in which one species becomes an obligate parasite of the other. Mechanisms (i) and (ii) are problematic, while mechanism (iii) has not, to our knowledge, been analysed quantitatively. In this paper, we develop a model for single- and two-species evolutionary stable strategies (ESSs) to examine the basis for Emery's rule and to determine whether mechanism (iii) is consistent with ESS reasoning. In secondary sympatry after allopatric speciation, the system's evolution depends on the relative abundances of the two sibling species and on the proportional damage wrought by parasites of each species on non-parasitic members of the other. Depending on these interspecific effects, either the rarer or the commoner species may become the parasite and the levels of within-species parasitism need not determine which evolves to obligate parasitism.","PeriodicalId":20585,"journal":{"name":"Proceedings of the Royal Society of London. Series B. Biological Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88667045","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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