The Experts below are selected from a list of 2004 Experts worldwide ranked by ideXlab platform
Peter J Hudson - One of the best experts on this subject based on the ideXlab platform.
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Parasites and climate synchronize Red Grouse populations.
Nature, 2005Co-Authors: Isabella M. Cattadori, Daniel T. Haydon, Peter J HudsonAbstract:There is circumstantial evidence that correlated climatic conditions can drive animal populations into synchronous fluctuations in abundance. However, it is unclear whether climate directly affects the survival and fecundity of individuals, or indirectly, by influencing food and natural enemies. Here we propose that climate affects trophic interactions and could be an important mechanism for synchronizing spatially distributed populations. We show that in specific years the size of Red Grouse populations in northern England either increases or decreases in synchrony. In these years, widespread and correlated climatic conditions during May and July affect populations regionally and influence the density-dependent transmission of the gastrointestinal nematode Trichostrongylus tenuis, a parasite that Reduces Grouse fecundity. This in turn forces Grouse populations into synchrony. We conclude that specific climatic events may lead to outbreaks of infectious diseases or pests that may cause dramatic, synchronized changes in the abundance of their hosts.
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Ticks need not bite their Red Grouse hosts to infect them with louping ill virus.
Proceedings of the Royal Society of London. Series B: Biological Sciences, 2004Co-Authors: Lucy Gilbert, Hugh W. Reid, Linda D. Jones, M. Karen Laurenson, E. A. Gould, Peter J HudsonAbstract:For pathogens transmitted by biting vectors, one of the fundamental assumptions is often that vector bites are the sole or main route of host infection. Here, we demonstrate experimentally a transmission route whereby hosts (Red Grouse, Lagopus lagopus scoticus) became infected with a member of the tick-borne encephalitis virus complex, louping ill virus, after eating the infected tick vector. Furthermore, we estimated from field observations that this mode of infection could account for 73-98% of all virus infections in wild Red Grouse in their first season. This has potential implications for the understanding of other biting vector-borne pathogens where hosts may ingest vectors through foraging or grooming.
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faecal egg counts provide a reliable measure of trichostrongylus tenuis intensities in free living Red Grouse lagopus lagopus scoticus
Journal of Helminthology, 2004Co-Authors: Linzi Seivwright, Stephen M Redpath, Francois Mougeot, L Watt, Peter J HudsonAbstract:The reliability of different egg counting methods for estimating the intensity of Trichostrongylus tenuis infections in Red Grouse, Lagopus lagopus scoticus, was investigated in the autumn, when Grouse may harbour high parasite intensities. Possible limitations to the use of these methods were also examined. Faecal egg counts were found to accurately estimate T. tenuis worm intensities, at least up to an observed maximum of c. 8000 worms. Two egg counting methods (smear and McMaster) gave consistent results, although the exact relationship with worm intensity diffeRed according to the method used. Faecal egg counts significantly decreased with increasing length of sample storage time, but egg counts were reliable for estimating worm intensity for three weeks. The concentration of eggs in the caecum was also found to reliably estimate worm intensity. However, egg counts from frozen gut samples cannot be used to estimate worm intensities. These results conclude that, despite some limitations, faecal and caecum egg counts provide useful and reliable ways of measuring T. tenuis intensities in Red Grouse.
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The shape of Red Grouse cycles
Journal of Animal Ecology, 2004Co-Authors: Darren J. Shaw, Peter J Hudson, Daniel T. Haydon, Isabella M. Cattadori, Simon J. ThirgoodAbstract:Summary 1. We examined 223 time-series of Red Grouse ( Lagopus lagopus scoticus ) numbers compiled from shooting bag-records from Grouse moors located across England, Scotland and Wales for evidence of non-time-reversibility, asymmetry in cycle shape and non-linearity. 2. We found 44% of time-series to be non-time-reversible. Over 80% of time-series spent more time increasing than decreasing (but only 32% did so significantly). 3. Non-linearity was detected in 44% of time-series examined, and these non-linear time-series were 1·7 times more likely to be non-time-reversible compaRed to the linear time-series. 4. The occurrence of non-linear and non-time-reversible series was not related to location, number of days with rain, temperature, moor area or population growth rate. The pRedominance of symmetrical peaks increased with easting but was not related to number of days with rain, temperature, northing or moor area. 5. There were no significant relationships between time-reversibility or non-linearity status and either tendency to cycle or cycle periodicity. However, populations that cycled with longer periods exhibited slower rates of increase and more equal lengths of time increasing and decreasing in numbers. 6. Our results provide little evidence that Grouse cycles observed in different parts of the species range in the United Kingdom arise from fundamentally different processes.
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Rising burden of immature sheep ticks (Ixodes ricinus) on Red Grouse (Lagopus lagopus scoticus) chicks in the Scottish uplands.
Medical and Veterinary Entomology, 2004Co-Authors: A. D. Kirby, A. A. Smith, Tim G. Benton, Peter J HudsonAbstract:The sheep tick Ixodes ricinus (L.) (Acari: Ixodidae) is an ectoparasite of major economic and pathogenic importance in Scotland. Its distribution in the Scottish uplands is assumed to be governed by the abundance and distribution of its definitive hosts (deer and sheep) and climatic variables such as temperature and rainfall. As the numbers of its major host in Scotland, Red deer, have increased dramatically and climatic conditions have become more favourable, the level of parasitism could have been expected to rise. We use data gatheRed from tick counts on over 4000 Red Grouse chicks Lagopus lagopus scoticus Latham (Galliformes: Tetraonidae) in various experiments over the past 19 years to ascertain whether the intensity and prevalence of parasitism has been increasing. From 1985 to 2003 the average tick burden of a parasitized Red Grouse chick has grown from 2.60 � 1.12 ticks per chick to 12.71 � 1.44. Over this period the percentage of chicks of a given brood parasitized has also increased from 4 � 2% to 92 � 3%. The possible implications of this increase in parasitism for Red Grouse production are discussed.
Francois Mougeot - One of the best experts on this subject based on the ideXlab platform.
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Appendix C. Parameter estimates of treatments in Red Grouse survival.
2016Co-Authors: J. Martínez-padilla, Francois Mougeot, L. Pérez-rodríguez, S. C. Ludwig, Stephen M RedpathAbstract:Parameter estimates of treatments in Red Grouse survival
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Insights into population ecology from long-term studies of Red Grouse Lagopus lagopus scoticus.
Journal of Animal Ecology, 2013Co-Authors: Jesús Martínez-padilla, Stephen M Redpath, Mohammed Zeineddine, Francois MougeotAbstract:Summary Long-term studies have been the backbone of population ecology. The Red Grouse Lagopus lagopus scoticus is one species that has contributed widely to this field since the 1950s. This paper reviews the trajectory and profound impact that these studies have had. Red Grouse research has combined long-term studies of marked individuals with demographic studies over wide geographical areas and replicated individual- and population-level manipulations. A main focus has been on understanding the causes of population cycles in Red Grouse, and in particular the relative importance of intrinsic (behaviour) and extrinsic (climate, food limitation and parasite) mechanisms. Separate studies conducted in different regions initially proposed either the nematode parasite Trichostrongylus tenuis or changes in male aggressiveness in autumn as drivers of population cycles. More recent experiments suggest that parasites are not a necessary cause for cycles and have highlighted that behavioural and parasite-mediated mechanisms are interrelated. Long-term experiments show that parasites and aggressiveness interact. Two outstanding questions remain to be tested experimentally. First, what intrinsic mechanism causes temporal variation in patterns of male aggressiveness? The current favouRed mechanism is related to patterns of kin structuring although there are alternative hypotheses. Second, how do the dual, interacting mechanisms, affect population dynamics? Red Grouse studies have had an important impact on the field of population ecology, in particular through highlighting: (1) the impact of parasites on populations; (2) the role of intrinsic mechanisms in cyclic dynamics and (3) the need to consider multiple, interacting mechanisms.
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Transcriptomic response of Red Grouse to gastro-intestinal nematode parasites and testosterone: implications for population dynamics.
Molecular Ecology, 2010Co-Authors: Lucy M. I. Webster, Francois Mougeot, Jesús Martínez-padilla, Steve Paterson, Stuart B. PiertneyAbstract:A central issue in ecology is in understanding the relative influences of intrinsic and extrinsic effects on population regulation. Previous studies on the cyclic population dynamics of Red Grouse (Lagopus lagopus scoticus) have emphasized the destabilizing effects of either nematode parasites or territorial behaviour and aggression. The potential interacting effects of these processes, mediated through density-dependent, environmentally induced alterations of host immunocompetence influencing susceptibility to parasites have not been consideRed. Male Red Grouse at high density are more aggressive, associated with increased testosterone, which potentially could lead to Reduced immunocompetence at a stage when parasites are most prevalent. This could depress individual condition, breeding performance and survival and thus drive or contribute to overall Reductions in population size. Here, we characterize the transcriptomic response of Grouse to nematode parasite infection and investigate how this is subsequently affected by testosterone, using a microarray approach contrasting Red Grouse with high and low parasite load at both high and low testosterone titre. A suite of 52 transcripts showed a significant level of up-regulation to either chronic parasite load or experimental parasite infection. Of these, 51 (98%) showed a Reduced level of expression under conditions of high parasite load and high testosterone. The genes up-regulated by parasites and then down-regulated at high testosterone titre were not necessarily associated with immune response, as might be intuitively expected. The results are discussed in relation to the fitness and condition of individual Red Grouse and factors influencing the regulation of abundance in natural populations.
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Ornamental comb colour pRedicts T-cell-mediated immunity in male Red Grouse Lagopus lagopus scoticus.
Naturwissenschaften, 2007Co-Authors: Francois MougeotAbstract:Sexual ornaments might reliably indicate the ability to cope with parasites and diseases, and a better ability to mount a primary inflammatory response to a novel challenge. Carotenoid-based ornaments are amongst the commonest sexual signals of birds and often influence mate choice. Because carotenoids are immuno-stimulants, signallers may trade-off allocating these to ornamental colouration or using them for immune responses, so carotenoid-based ornaments might be particularly useful as honest indicators of immuno-compentence. Tetraonid birds, such as the Red Grouse Lagopus lagopus scoticus, exhibit supra-orbital yellow–Red combs, a conspicuous ornament which functions in intra- and inter-sexual selection. The colour of combs is due to epidermal pigmentation by carotenoids, while their size is testosterone-dependent. In this study, I investigated whether comb characteristics, and in particular, comb colour, indicated immuno-competence in free-living male Red Grouse. I assessed T-cell-mediated immunity using a standardised challenge with phytohaemagglutinin. Red Grouse combs reflect in the Red and in the ultraviolet spectrum of light, which is not visible to humans but that Grouse most likely see, so I measuRed comb colour across the whole bird visible spectrum (300–700 nm) using a reflectance spectrometer. I found that males with bigger and Redder combs, but with less ultraviolet reflectance, had greater T-cell-mediated immune response. Comb colour pRedicted T-cell-mediated immune response better than comb size, indicating that the carotenoid-based colouration of this ornament might reliably signal this aspect of male quality.
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Nematode parasites Reduce carotenoid-based signalling in male Red Grouse
Biology Letters, 2007Co-Authors: Jesús Martínez-padilla, Francois Mougeot, Lorenzo Pérez-rodríguez, Gary R. BortolottiAbstract:Carotenoids determine the yellow–Red colours of many ornaments, which often function as signals of quality. Carotenoid-based signalling may reliably advertise health and should be particularly sensitive to parasite infections. Nematodes are among the commonest parasites of vertebrates, with well-documented negative effects on their hosts. However, to date, little is known about the effects that these parasites may have on carotenoid-based signalling. Tetraonid birds (Grouse) exhibit supra-orbital combs, which are bright integumentary ornaments pigmented by carotenoids. We tested the effect of the nematode parasite Trichostrongylus tenuis on signalling in free-living male Red Grouse Lagopus lagopus scoticus. We show that experimentally Reduced nematode infection increases plasma carotenoid concentration and comb Redness, demonstrating for the first time that nematodes can influence carotenoid-based signals.
Stuart B. Piertney - One of the best experts on this subject based on the ideXlab platform.
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Adaptive and neutral genetic differentiation among Scottish and endangeRed Irish Red Grouse (Lagopus lagopus scotica)
Conservation Genetics, 2016Co-Authors: Yvonne Meyer-lucht, Marianne C. James, Stuart B. Piertney, Kevin P. Mulder, Barry J. Mcmahon, Kieran Buckley, Jacob HöglundAbstract:Studying patterns of intra-specific genetic variation among populations allows for a better understanding of population structure and local adaptation. However, those patterns may differ according to the genetic markers applied, as neutral genetic markers reflect demographic processes and random genetic drift, whereas adaptive markers also carry the footprint of selection. In combination, neutral and adaptive genetic markers permit to assess the relative roles of drift and selection in shaping population structure. Among the best understood adaptive genetic loci are the genes of the major histocompatibility complex (MHC). We here study variation and differentiation at neutral SNP markers and MHC class II genes in Red Grouse (Lagopus lagopus scotica) from Ireland and Scotland. Irish Red Grouse populations are fragmented and drastically declining, but Red Grouse are abundant in Scotland. We find evidence for positive selection acting on the MHC genes and variation in MHC gene copy numbers among Irish individuals. Furthermore, there was significant population differentiation among Red Grouse from Ireland and Scotland at the neutral SNP markers (FST = 0.084) and the MHC-BLB genes (FST: BLB1 = 0.116, BLB2 = 0.090, BLB3 = 0.104). Differentiation at the MHC-BLB1 was significantly higher than at the neutral SNP markers, suggesting that selection plays an important role in shaping MHC variation, in addition to genetic drift. We speculate that the observed differentiation pattern might be due to local adaptation to different parasite regimes. These findings have strong conservation implications and we advise against the introduction of Scottish Red Grouse to supplement Irish populations.
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Genotype data for 231 Red Grouse individuals
2016Co-Authors: Marius A. Wenzel, Alex Douglas, Marianne C. James, Steve M. Redpath, Stuart B. PiertneyAbstract:Genotype data for 231 Red Grouse individual
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Sampling-related and phenotypic data for 231 Red Grouse individuals
2016Co-Authors: Marius A. Wenzel, Alex Douglas, Marianne C. James, Steve M. Redpath, Stuart B. PiertneyAbstract:Sampling-related and phenotypic data for 231 Red Grouse individual
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Identification and characterisation of 17 polymorphic candidate genes for response to parasitic nematode (Trichostrongylus tenuis) infection in Red Grouse (Lagopus lagopus scotica)
Conservation Genetics Resources, 2015Co-Authors: Marius A. Wenzel, Lucy M. I. Webster, Steve Paterson, Stuart B. PiertneyAbstract:The Red Grouse ( Lagopus lagopus scotica ) is an economically important game bird species endemic to the upland heather moors of the British Isles, where its conservation status is “amber” due to long-term declines in breeding populations. One major driver of Grouse population ecology is chronic infection by the highly prevalent, gastrointestinal parasitic nematode Trichostrongylus tenuis . Here, we outline the identification and characterisation of 17 candidate genes for the physiological response of Red Grouse to parasite infection, developed de novo from functional and genetic analysis of Grouse transcriptomic and genomic resources. These genes capture broad physiological functions, including immune system processes, xenobiotics detoxification, oxidative balance, metabolism and cell cycle regulation. All genes were polymorphic at the landscape scale in north-east Scotland, indicating great utility for characterising the causes and consequences of spatio-temporal genetic variation in relation to parasite-mediated eco-evolutionary processes in Red Grouse populations.
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Genetic variation among endangeRed Irish Red Grouse (Lagopus lagopus hibernicus) populations: implications for conservation and management
Conservation Genetics, 2012Co-Authors: Barry J. Mcmahon, Stuart B. Piertney, Kieran Buckley, Magnus P. Johansson, Jacob HöglundAbstract:Extant populations of Irish Red Grouse ( Lagopus lagopus hibernicus ) are both small and fragmented, and as such may have an increased risk of extinction through the effects of inbreeding depression and compromised adaptive potential. Here we used 19 microsatellite markers to assay genetic diversity across 89 georeferenced samples from putatively semi-isolated areas throughout the Republic of Ireland and we also genotyped 27 Red Grouse from Scotland using the same markers. The genetic variation within Ireland was low in comparison to previously published data from Britain and the sample of Scottish Red Grouse, and comparable to threatened European Grouse populations of related species. Irish and Scottish Grouse were significantly genetically differentiated (F_ST = 0.07, 95% CI = 0.04–0.10). There was evidence for weak population structure within Ireland with indications of four distinct genetic clusters. These correspond approximately to Grouse populations inhabiting suitable habitat patches in the North West, Wicklow Mountains, Munster and Cork, respectively, although some admixture was detected. Pair-wise F_ST values among these populations ranged from 0.02 to 0.04 and the overall mean allelic richness was 5.5. Effective population size in the Munster area was estimated to be 62 individuals (95% CI = 33.6–248.8). Wicklow was the most variable population with an AR value of 5.4 alleles/locus. Local (Munster) neighbourhood size was estimated to 31 individuals corresponding to an average dispersal distance of 31 km. In order to manage and preserve Irish Grouse we recommend that further fragmentation and destruction of habitats need to be prevented in conjunction with population management, including protection of the integrity of the existing population by refraining from augmenting it with individuals from mainland Britain to maximise population size.
Andrew P Dobson - One of the best experts on this subject based on the ideXlab platform.
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Harvesting unstable populations: Red Grouse Lagopus lagopus scoticus (Lath.) in the United Kingdom
Wildlife Biology, 2001Co-Authors: Peter J Hudson, Andrew P DobsonAbstract:The optimal harvesting strategies for unstable populations are exploRed using first discrete time models and second a continuous time model specifically applied to the destabilising effects of the caecal nematode Trichostrongylus tenuis on the dynamics of Red Grouse Lagopus lagopus scoticus. In discrete time models, with overcompensation generating either cyclic or chaotic fluctuations in abundance harvesting can act as both a stabilising and a destabilising process. Maximum yields occur at the harvesting rate that coincides with the point where the harvesting stabilises the overcompensation. Optimal harvesting rates increase with the degree of overcompensation although these are more vulnerable to overharvesting. Harvesting in the continuous time model provides similar results, although observed hunting records do not appear to be stabilised by harvesting. Empirical data on the mortality caused by other natural enemies of Red Grouse, the hen harrier Circus cyaenus and the louping ill virus, show that the...
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regulation and stability of a free living host parasite system trichostrongylus tenuis in Red Grouse i monitoring and parasite Reduction experiments
Journal of Animal Ecology, 1992Co-Authors: Peter J Hudson, David Newborn, Andrew P DobsonAbstract:Intensive population studies were conducted for 10 years on Red Grouse (Lagopus lagopus scoticus) and the parasitic nematode, Trichostrongylus tenuis, in northern England. Winter loss was the key factor determining changes in Grouse numbers, although breeding losses were also important. T. tenuis had an aggregated distribution within the adult Grouse population, even though the degree of aggregation was relatively low compaRed with other parasite systems
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regulation and stability of a free living host parasite system trichostrongylus tenuis in Red Grouse ii population models
Journal of Animal Ecology, 1992Co-Authors: Andrew P Dobson, Peter J HudsonAbstract:The population dynamics of Red Grouse, Lagopus lagopus scoticus and the parasitic nematode, Trichostrongylus tenuis were exploRed to determine whether interactions between the parasite and host were sufficient to generate cycles in Grouse abundance. Two alternative models were used that explicitly consider the dynamics of either the free-living, or arrested larval stages of the parasite. Providing that the life expectancy of the free-living larvae is more than 2-4 weeks, the parasite can readily establish in gousse populations
Stephen M Redpath - One of the best experts on this subject based on the ideXlab platform.
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Appendix C. Parameter estimates of treatments in Red Grouse survival.
2016Co-Authors: J. Martínez-padilla, Francois Mougeot, L. Pérez-rodríguez, S. C. Ludwig, Stephen M RedpathAbstract:Parameter estimates of treatments in Red Grouse survival
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Insights into population ecology from long-term studies of Red Grouse Lagopus lagopus scoticus.
Journal of Animal Ecology, 2013Co-Authors: Jesús Martínez-padilla, Stephen M Redpath, Mohammed Zeineddine, Francois MougeotAbstract:Summary Long-term studies have been the backbone of population ecology. The Red Grouse Lagopus lagopus scoticus is one species that has contributed widely to this field since the 1950s. This paper reviews the trajectory and profound impact that these studies have had. Red Grouse research has combined long-term studies of marked individuals with demographic studies over wide geographical areas and replicated individual- and population-level manipulations. A main focus has been on understanding the causes of population cycles in Red Grouse, and in particular the relative importance of intrinsic (behaviour) and extrinsic (climate, food limitation and parasite) mechanisms. Separate studies conducted in different regions initially proposed either the nematode parasite Trichostrongylus tenuis or changes in male aggressiveness in autumn as drivers of population cycles. More recent experiments suggest that parasites are not a necessary cause for cycles and have highlighted that behavioural and parasite-mediated mechanisms are interrelated. Long-term experiments show that parasites and aggressiveness interact. Two outstanding questions remain to be tested experimentally. First, what intrinsic mechanism causes temporal variation in patterns of male aggressiveness? The current favouRed mechanism is related to patterns of kin structuring although there are alternative hypotheses. Second, how do the dual, interacting mechanisms, affect population dynamics? Red Grouse studies have had an important impact on the field of population ecology, in particular through highlighting: (1) the impact of parasites on populations; (2) the role of intrinsic mechanisms in cyclic dynamics and (3) the need to consider multiple, interacting mechanisms.
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Hen harriers and Red Grouse: moving towards consensus?
Journal of Applied Ecology, 2009Co-Authors: Stephen M Redpath, Simon J. ThirgoodAbstract:Summary 1. The presence of pRedators may lead to conflict between different stakeholders. Finding ways to resolve such conflicts is a challenge to all involved. 2. Within the UK a long and, at times, acrimonious conflict has developed around the conservation of hen harriers Circus cyaneus on moorland managed for Red Grouse Lagopus lagopus scoticus. This paper follows our original forum article and the replies from colleagues in the Royal Society for the Protection of Birds (RSPB) and the Game and Wildlife Conservation Trust (GWCT). 3. Whilst differences of opinion remain, there are encouraging signs that both sides are striving for consensus. There is broad agreement that evidence is requiRed on three fronts to address: (1) the ecological, economic and social consequences of alternative forms of land management in the uplands; (2) the efficacy of diversionary feeding of hen harriers; and (3) the utility of a brood management scheme to improve harrier conservation status and Reduce the extent of the conflict. 4. Synthesis and applications: The conflict between hen harrier conservation and Red Grouse management has existed for decades with little sign of progress. For the first time, stakeholders, researchers and policy advisors are engaged in effective dialogue and are striving for solutions. There are encouraging signs that all sides are now willing to listen to alternative viewpoints and appear prepaRed to seriously consider compromises. It is to be hoped that a solution to the harrier–Grouse conflict can be found as this will have considerable positive ramifications for management of heather moorlands in the UK and wider implications for the conservation of pRedators around the world.
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Fitting Models of Multiple Hypotheses to Partial Population Data: Investigating the Causes of Cycles in Red Grouse
The American Naturalist, 2009Co-Authors: Leslie New, Stephen M Redpath, Jason Matthiopoulos, Stephen T. BucklandAbstract:There are two postulated causes for the observed periodic fluctuations (cycles) in Red Grouse (Lagopus lagopus scoticus). The first involves interaction with the parasitic nematode Trichostrongylus tenuis. The second invokes delayed regulation through the effect of male aggressiveness on territoriality. Empirical evidence exists to sup- port both hypotheses, and each hypothesis has been modeled de- terministically. However, little effort has gone into looking at the combined effects of the two mechanisms or formally fitting the cor- responding models to field data. Here we present a model for Red Grouse dynamics that includes both parasites and territoriality. To explore the single and combined hypotheses, we specify three versions of this model and fit them to data using Bayesian state-space mod- eling, a method that allows statistical inference to be performed on mechanistic models such as ours. Output from the three models is then examined to determine their goodness of fit and the biological plausibility of the parameter values requiRed by each to fit the pop- ulation data. While all three models are capable of emulating the observed cyclic dynamics, only the model including both aggression and parasites does so under consistently realistic parameter values, providing theoretical support for the idea that both mechanisms shape Red Grouse cycles.
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Elevated spring testosterone increases parasite intensity in male Red Grouse
Behavioral Ecology, 2005Co-Authors: Francois Mougeot, Stephen M Redpath, Stuart B. PiertneyAbstract:The expression of testosterone-dependent sexual traits might signal the ability of their bearers to cope with parasite infections. According to the immunocompetence handicap hypothesis (IHH), such signals would be honest because physiological costs of testosterone, such as a Reduced ability to control parasite infections, would prevent cheating. We tested whether testosterone would affect the outcome of a standardized parasite challenge in Red Grouse, using a main parasite of the species, the nematode Trichostrongylus tenuis. We caught males in spring, removed their nematode parasites, and implanted them with testosterone or empty implants, as controls. After 1 month, they were reinfected with a standard dose of infective T. tenuis parasites. When challenged, testosterone males had relatively less globulin relative to albumin plasma proteins than control males, an indication that they had experienced increased physiological stress. Testosterone-treated males had significantly more T. tenuis parasites than controls in the next autumn and also had more coccidia and lost more weight than controls. Testosterone-treated males nevertheless benefited from their elevated spring testosterone: they had bigger sexual ornaments than controls both in spring and autumn, and they tended to have a higher pairing and breeding success than controls. Our results supported the IHH in showing that elevated testosterone impaiRed the ability of males to cope with a standardized challenge by a dominant parasite. Testosterone thus plays a key role in mediating trade-offs between reproductive activities and parasite defense, and testosterone-dependent comb size might honestly signal the ability of Red Grouse to control T. tenuis infection. Copyright 2006.
