A criptosporidiose já foi descrita em várias espécies animais, incluindo várias espécies de aves. É considerada uma das principais infecções por protozoários em aves das ordens Anseriformes, Charadriformes, Columbiformes, Galliformes, Passeriformes, Psittaciformes e Struthioniformes. Três espécies de Cryptosporidium infectam aves: Cryptosporidium baileyi, Cryptosporidium galli e Cryptosporidium meleagridis, além de vários genótipos distintos geneticamente, como os genótipos I, II, III, IV e V de aves. Cryptosporidium galli e Cryptosporidium genótipo III de aves estão relacionados com infecções crônicas no proventrículo, de forma semelhante à infecção por Cryptosporidium serpentis, em serpentes. Vários métodos de diagnóstico são utilizados para detecção do parasito, mas somente aqueles com base em biologia molecular são capazes de determinar a espécie de Cryptosporidium. O projeto teve com objetivo o desenvolvimento da PCR duplex em tempo real, tendo como alvo o gene da subunidade 18S do rRNA, por meio de ensaio TaqMan, para detecção de DNA de C.galli e Cryptosporidium genótipo III de aves, e avaliar os atributos diagnósticos da PCR duplex em tempo real quando comparada à nested PCR, utilizando 1027 amostras fecais de aves das ordens Passeriformes e Psittaciformes. A PCR duplex em tempo real apresentou positividade em 580/1027 (56,47%) para C. galli, enquanto que a nested PCR resultou em positividade para Cryptosporidium spp. em 104/1027 (10,13%) amostras. Para Cryptosporidium genótipo III de aves, houve positividade em 21/1027 (2,04%). A PCR duplex em tempo real resultou em alta especificidade analítica quando foram utilizadas amostras de DNA de outras espécies e genótipos de Cryptosporidium. A única exceção foi a amplificação de DNA de C. serpentis, com a utilização de primers e sonda para detecção de Cryptosporidium genótipo III de aves, porém, com uma baixa eficiência de amplificação. Foram identificados novos hospedeiros aviários para ambas as espécies gástricas, assim como foi possível a identificação de C. baileyi e, pela primeira vez no Brasil, de Cryptosporidium genótipo V de aves. Conclui-se que a PCR duplex em tempo real desenvolvida neste estudo é um recurso que apresenta rapidez e confiabilidade para diagnóstico de criptosporidiose gástrica em aves / Cryptosporidiosis has been described in several animal species, including many species of birds, and is considered a major protozoan infection of the orders Anseriformes, Charadriformes, Columbiformes, Galliformes, Passeriformes, Psittaciformes and Struthioniformes. Three species of Cryptosporidium are valid in birds: Cryptosporidium baileyi, Cryptosporidium meleagridis and Cryptosporidium galli; beside these species, there are several genotypes genetically distinct, as avian genotypes I, II, III, IV and V. Cryptosporidium galli and Cryptosporidium avian genotype III are related to chronic infections in proventriculus, similar to Cryptosporidium serpentis infection in snakes. Several methods are used for cryptosporidiosis diagnosis, but only those based on molecular biology are able to determine the Cryptosporidium species and genotypes. The aim of this project was the development of a duplex real-time PCR targeting 18S subunit of rRNA gene, by TaqMan assay, to detect DNA of C. galli and Cryptosporidium avian genotype III, and to evaluate the diagnostic attributes of the duplex real-time PCR compared to nested PCR, using 1027 fecal samples from birds of the orders Passeriformes and Psittaciformes. The duplex real time PCR showed positivity in 580/1027 (56.47%) for C. galli, whereas nested PCR was positive for Cryptosporidium spp. in 104/1027 (10.13%) samples. For Cryptosporidium avian genotype III, there was positivity in 21/1027 (2.04%) samples. The duplex real time PCR resulted in high analytical specificity when tested using DNA samples from other Cryptosporidium species and genotypes. The only exception was the amplification of DNA from C. serpentis with primers and probe for the detection of Cryptosporidium avian genotype III, although with lower efficiency. New avian hosts were identified for both gastric species, as well as it was possible to identify C. baileyi and, for the first time in Brazil, Cryptosporidium avian genotype V. It was concluded that the duplex real time PCR developed in this study is a fast and reliable tool for diagnosis of gastric cryptosporidiosis in birds.

Columbiformes sinantrópicos podem ter um importante papel na epidemiologia de patógenos com potencial zoonótico ou de impacto econômico para a indústria avícola. Dentre eles destacam-se: Mycoplasma spp., Salmonella spp., paramixovírus aviário tipo 1 (APMV-1), inseridos no Programa Nacional de Sanidade Avícola (PNSA) e a Chlamydophila psittaci, agente de uma das principais zoonoses relacionada com aves silvestres. Dentro desse contexto, este trabalho objetivou pesquisar, sazonalmente, a ocorrência destes patógenos em pombos-domésticos (Columba livia) em dois entrepostos no Estado de São Paulo. Ao longo de um ano, mensalmente 10 pombos foram capturados em cada entreposto para a colheita de amostras de suabe cloacal e sangue. A técnica de soroaglutinação rápida em placa (SAR) foi utilizada para a detecção de anticorpos anti-M. synoviae, anti-M. gallisepticum e anti-S.Pullorum/Gallinarum; para a confirmação dos sororeagentes foram utilizadas a prova de inibição da hemaglutinação e soroaglutinação lenta, respectivamente. Para a detecção do DNA de C. psittaci e RNA de AMPV-1 foram utilizados métodos moleculares, PCR e RT-PCR. Para investigação de anticorpos anti-APMV-1 foi empregada a técnica de HI. Na SAR, 3,3% dos soros foram reagentes para M. synoviae; 2,5% para M. gallisepticum e 0,4% para S. Pullorum/Gallinarum. No entanto, essas amostras foram negativas nas técnicas confirmatórias. A ocorrência do APMV-1 não foi detectada. O DNA de C. psittaci foi detectado em 13,3% das amostras sendo 10,8% provenientes de aves capturadas na estação seca e 15,8% na estação chuvosa. Tais resultados são relevantes, pois demonstram que a C. psittaci ocorre em pombos presentes em áreas públicas frequentadas por um grande número de pessoas. Frente à escassez de pesquisas realizadas em Columbiformes no país, novos estudos são necessários para a determinação do real risco que pombos-domésticos podem representar quanto à transmissão de patógenos para aves comerciais e a influência da sazonalidade na disseminação desses microrganismos. / Columbiformes may play an important role in the epidemiology of pathogens with zoonotic potential or economic impact in the poultry industry. Among these pathogens there are Mycoplasma spp., Salmonella spp., Avian Paramyxovirus type 1 (APMV-1), included in the National Poultry Health Program (PNSA) and Chlamydophila psittaci, etiologic agent of an important zoonosis associated with wild birds. Thus, the aim of this study was to investigate, seasonally, the occurrence of the pathogens listed above in feral pigeons (Columba livia) in two warehouses in São Paulo State. During one year, 10 birds were captured monthly in each locality and cloacal swabs and blood samples were collected from each pigeon. The rapid seroagglutination test was performed for the detection of antibodies against M. synoviae, M. gallisepticum and Salmonella Pullorum/Gallinarum. Positive results were submitted to the hemagglutination inhibition and slow seroagglutination test, respectively. For the C. psittacis DNA and APMV-1s RNA diagnosis, molecular techniques PCR and RT-PCR were performed. Hemagglutination inhibition test was also performed in order to detect antibodies against APMV-1. From the serum samples analyzed by rapid seroagglutination test, 3.3% were positive for M. synoviae, 2.5% for M. gallisepticum and 0.4% for S. Pullorum/Gallinarum. However, none of these samples was positive on the confirmatory tests. APMV-1 was not detected in any of the laboratory tests used. C. psittacis DNA was detected in 13.3% of the samples being, 10.8% from pigeons captured during the dry season and 15.8% in the rainy season. These results are relevant since they indicate that C. psittaci occurs in birds living in public areas frequented by a large number of people. The occurrence of the other pathogens was not detected. Nevertheless, due to lack of information about the pigeons sanitary status in the country, additional researches are necessary to determine the risk that feral pigeons can pose in the transmission of pathogens for poultry and the influence of each season in the spread of these microorganisms.

What explains the geographic distribution of pathogens? Better understanding and characterising disease patterns will help scientists to identify areas likely to host future epidemics and epizootics and to prioritise surveillance and intervention. However, the use of disease surveillance data to assess the risk of transmission and generate risk maps raises conceptual and methodological issues. Indeed, pathogens and more particularly viruses aren't ”species” like others that live in the open environment and must be studied with methods and concepts of their own. Avian influenza (AI), a disease caused by a virus infecting bird populations, has been selected to study these issues. AI has a major economic impact on the poultry industry in many countries, raises concerns of livelihood in low and middle-income countries, and represents a major concern for human health. The aim of this PhD thesis was to improve the knowledge on the spatial epidemiology of AI in different settings and conditions (i). For this, recent epizootics caused by the subtypes A (H5N1) and A (H7N9) were selected as case studies. First, highly pathogenic subtypes of the A (H5N1) virus have been studied in poultry farms (ducks and chickens) at different spatial scales: at the continental scale and the regional scale in the Mekong (Cambodia, Laos, Vietnam, Thailand) and the Nile Delta in Egypt. All these cases occurred between 2003, the date on which the virus starts to spread outside China, and 2015; the HPAI A (H5N1) subtypes are still reported today in many countries. Human infections caused by the A (H7N9) virus in China from March 2013 to 2017 were also studied. Studied different AI subtypes at different spatial scales within different host species also allowed to develop a conceptual model of AI transmission and to discuss the issue of the transferability of results in epidemiology (ii). Lastly, this PhD thesis leads to a discussion about the transfer of methods and concepts from ecology to spatial epidemiology, with a particular emphasis on their possible limitations (iii). / Doctorat en Sciences agronomiques et ingénierie biologique / info:eu-repo/semantics/nonPublished

I established the phage antibody library platform for the identification of specific antibodies. In the first part of my study, I tried to identify antibody against SARS-CoV. Two fragments on the spike protein, which is responsible for inducing viral entry, was chosen as target for the selection of antibody. An antibody was identified which can selectively recognize the SARS-CoV infected cells, but not non-infected cells. Although this antibody was found to retain no neutralizing ability, this specific antibody may have potential to develop for diagnostic purpose. / I utilized the phage system-based cloning method as an attractive approach to screen and identify virus-specific antibodies that can be encoded by the human genome. Once a useful phage clone is identified, unlimited amounts of human monoclonal virus-specific antibodies can be manufactured, and potentially applied clinically for prophylactic and therapeutic uses. The study focuses on two of these new infections, both of which cause severe respiratory disease: SARS and avian influenza. / Identification of specific antibodies, either for diagnostic or therapeutic use, was successfully demonstrated in the two infectious disease models. The phage antibody platform offers a fast and cost-effective method to identify phage antibodies, which can easily be converted to human viral specific monoclonal antibodies for clinical use. / In the 21st century, a number of novel infectious diseases emerged suddenly and spread rapidly, endangering the lives and well-being of people around the world. Severe acute respiratory syndrome (SARS) is a life threatening form of atypical pneumonia that ravaged Hong Kong, Taiwan, China, Canada and many cities in 2003. In the same year, novel avian influenza viruses infected human beings on two continents. Both of these diseases originated in animals and crossed over into the human population. These emerging diseases pose significant public health threats while providing a chilling reminder that another influenza pandemic could occur at any time. Thus, the development of effective therapeutics to control the disease is of paramount importance. Although several vaccines against SARS and avian influenza are available nowadays, the poor clinical performance and frequent mutation of viral strains may limit the practical use and value of the vaccines. Moreover, there are no promising antiviral drugs available for the treatment. Therefore, I aimed to develop an immunotherapy as an alternative treatment option against these diseases. / In the second part of my study, the extracellular domain of matrix protein of avian influenza virus was chosen as target for the selection of antibody. I successfully identified an antibody which can neutralize the avian influenza virus infection. This promising result indicated this antibody has potential to develop for therapeutic use and these antibodies can be easily manufactured in unlimited amounts for clinical application. / Leung, Ka Man. / Adviser: Kwok Pui Fung. / Source: Dissertation Abstracts International, Volume: 71-01, Section: B, page: 0212. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 112-123). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese.

Columbiformes sinantrópicos podem ter um importante papel na epidemiologia de patógenos com potencial zoonótico ou de impacto econômico para a indústria avícola. Dentre eles destacam-se: Mycoplasma spp., Salmonella spp., paramixovírus aviário tipo 1 (APMV-1), inseridos no Programa Nacional de Sanidade Avícola (PNSA) e a Chlamydophila psittaci, agente de uma das principais zoonoses relacionada com aves silvestres. Dentro desse contexto, este trabalho objetivou pesquisar, sazonalmente, a ocorrência destes patógenos em pombos-domésticos (Columba livia) em dois entrepostos no Estado de São Paulo. Ao longo de um ano, mensalmente 10 pombos foram capturados em cada entreposto para a colheita de amostras de suabe cloacal e sangue. A técnica de soroaglutinação rápida em placa (SAR) foi utilizada para a detecção de anticorpos anti-M. synoviae, anti-M. gallisepticum e anti-S.Pullorum/Gallinarum; para a confirmação dos sororeagentes foram utilizadas a prova de inibição da hemaglutinação e soroaglutinação lenta, respectivamente. Para a detecção do DNA de C. psittaci e RNA de AMPV-1 foram utilizados métodos moleculares, PCR e RT-PCR. Para investigação de anticorpos anti-APMV-1 foi empregada a técnica de HI. Na SAR, 3,3% dos soros foram reagentes para M. synoviae; 2,5% para M. gallisepticum e 0,4% para S. Pullorum/Gallinarum. No entanto, essas amostras foram negativas nas técnicas confirmatórias. A ocorrência do APMV-1 não foi detectada. O DNA de C. psittaci foi detectado em 13,3% das amostras sendo 10,8% provenientes de aves capturadas na estação seca e 15,8% na estação chuvosa. Tais resultados são relevantes, pois demonstram que a C. psittaci ocorre em pombos presentes em áreas públicas frequentadas por um grande número de pessoas. Frente à escassez de pesquisas realizadas em Columbiformes no país, novos estudos são necessários para a determinação do real risco que pombos-domésticos podem representar quanto à transmissão de patógenos para aves comerciais e a influência da sazonalidade na disseminação desses microrganismos. / Columbiformes may play an important role in the epidemiology of pathogens with zoonotic potential or economic impact in the poultry industry. Among these pathogens there are Mycoplasma spp., Salmonella spp., Avian Paramyxovirus type 1 (APMV-1), included in the National Poultry Health Program (PNSA) and Chlamydophila psittaci, etiologic agent of an important zoonosis associated with wild birds. Thus, the aim of this study was to investigate, seasonally, the occurrence of the pathogens listed above in feral pigeons (Columba livia) in two warehouses in São Paulo State. During one year, 10 birds were captured monthly in each locality and cloacal swabs and blood samples were collected from each pigeon. The rapid seroagglutination test was performed for the detection of antibodies against M. synoviae, M. gallisepticum and Salmonella Pullorum/Gallinarum. Positive results were submitted to the hemagglutination inhibition and slow seroagglutination test, respectively. For the C. psittacis DNA and APMV-1s RNA diagnosis, molecular techniques PCR and RT-PCR were performed. Hemagglutination inhibition test was also performed in order to detect antibodies against APMV-1. From the serum samples analyzed by rapid seroagglutination test, 3.3% were positive for M. synoviae, 2.5% for M. gallisepticum and 0.4% for S. Pullorum/Gallinarum. However, none of these samples was positive on the confirmatory tests. APMV-1 was not detected in any of the laboratory tests used. C. psittacis DNA was detected in 13.3% of the samples being, 10.8% from pigeons captured during the dry season and 15.8% in the rainy season. These results are relevant since they indicate that C. psittaci occurs in birds living in public areas frequented by a large number of people. The occurrence of the other pathogens was not detected. Nevertheless, due to lack of information about the pigeons sanitary status in the country, additional researches are necessary to determine the risk that feral pigeons can pose in the transmission of pathogens for poultry and the influence of each season in the spread of these microorganisms.

The first aim of this research was to determine the prevalence of IBV in broilers within the Canterbury province, New Zealand, in late winter and to search for associations with management or environmental factors. The second aim was to study how ambient stressors affect the immune system in birds, their adaptive capacity to respond, and the price that they have to pay in order to return to homeostasis. In a case control study, binary logistic regression analyses were used to seek associations between the presence of IBV in broilers and various risk factors that had been linked in other studies to the presence of different avian pathogens: ambient ammonia, oxygen, carbon dioxide, humidity and litter humidity. Pairs of sheds were selected from ten large broiler farms in Canterbury. One shed (case) from each pair contained poultry that had a production or health alteration that suggested the presence of IBV and the other was a control shed. Overall, IBV was detected by RT-PCR in 50% of the farms. In 2 of the 5 positive farms (but none of the control sheds) where IBV was detected there were accompanying clinical signs that suggested infectious bronchitis (IB). Ambient humidity was the only risk factor that showed an association (inverse) with the prevalence of IBV (p = 0.05; OR = 0.92). It was concluded within the constraints of the totally enclosed management systems described, that humidity had an influence on the presence of IBV, but temperature, ammonia, carbon dioxide, oxygen or litter humidity had no effect. In another study environmental temperatures were changed in order to affect the biological function and adaptive capacity of chickens following infection with IBV. The 'affective states' of the animal were assessed by measuring levels of corticosterone (CORT) in plasma and tonic immobility (TI). It was found that low (10 +/- 2°C) and high (30 +/- 2°C) temperatures exacerbated the respiratory signs and lesions in birds infected with IBV as compared to those housed at moderate (20 +/- 2°C) temperatures. The chickens housed at high temperatures showed significantly decreased growth, a higher proportion of hepatic lesions (principally haemorrhages) and a longer tonic immobility period, but there was no significant alteration in the plasma levels of CORT. The birds housed at low temperatures developed a higher proportion of heart lesions (hydropericardium, ventricular hypertrophy) and had significantly higher levels of plasma CORT than birds housed under moderate and/or high temperatures. The specific antibody response to IBV decreased in birds housed under high temperatures. Interestingly the birds housed at high temperatures developed significantly higher levels of haemagglutinin antibodies to sheep red blood cells (SRBC) than those birds housed under low or moderated temperatures. Cell mediated immunity was not significantly affected by heat or cold stress in the first 13 days of treatment but at 20 days the levels of interferon gamma in the birds subjected to low temperatures were lower than in the high temperature group. In other trials, the exogenous administration of low physiological doses of oral CORT (as compared to high pharmacological doses typically used in such experiments) to birds resulted in suppression or enhancement of the immune response depending on duration of treatment and/or dose and nature of the antigen. To our knowledge, this is the first study to show that exogenous CORT can produce an enhancement in the immune response in chickens. iv In conclusion, environmental stressors such as high or low temperatures do affect the physiology of the fast-growing broiler. The adjustments the birds have to make to maintain homeostasis impacts on the course of common infectious diseases, such as IB, that normally is mild in the New Zealand poultry industry. The administration of exogenous CORT showed that this hormone may be part of the physiological stress response and acts as a messenger to prepare the immune system for potential challenges (e.g., infection).

<p>An influence at one trophic level can result in dynamic impacts also on other components of a food web. These dynamics are known as trophic cascades, and can be both top-down and bottom-up. After a near-collapse of the Baltic cod <i>Gadus morhua</i> stock in the 1980s, its main prey sprat <i>Sprattus sprattus</i> increased dramatically. The main food of sprat, marine copepods, decreased during the same time period, likely a combined effect of increased predation pressure from sprat and decreasing salinities. This shortage of food for sprat resulted in decreasing quality of sprat as a food source for common guillemots <i>Uria aalge</i>. However, a recent increase in fishing for sprat has again resulted in better feeding conditions for guillemots.</p><p>Human impacts on this simple food web can be complex. In the early 20th century, marine mammals were abundant and nutrient levels were low in the Baltic Sea. This thesis illustrate that this situation corresponded to lower fish biomass. A reduction of seals early in the century led to reduced top-down control, which resulted in increasing fish stocks. Later, in the 1950s, the largest inflow of salt water during the century mobilized accumulated phosphorus from the deep sediments, which stimulated nitrogen fixation. Combined with increasing anthropogenic nutrient loads, this led to increased primary production and a rapid change from an oligotrophic to a eutrophicated state. This change can be termed a regime shift, which also stimulated fish production. Subsequent over-fishing of cod likely caused a second regime shift, from a cod- to a clupeid- dominated state, which led to the described effects on the common guillemots.</p><p>Several factors affect the life-history of this long-lived seabird. Bycatches in gillnet fisheries is one factor directly affecting guillemot survival, and the proportion of bycatches increased during a period of increasing fishing effort. Surprisingly, avian cholera, a previously undocumented disease in common guillemots, was found at times to cause considerable adult mortality. Common guillemot life-history information can communicate the diversity of factors influencing marine ecosystems – hopefully this can increase our understanding of how complex even "simple" food webs are.</p>

<p>Males and females differ in morphology and behaviour, so that selection acts differently on the two sexes. This changes the relative reproductive success of males and females, and it is beneficial for parents to bias the sex ratio of their broods in favour of the sex with the best survival and breeding prospects. Differences between the sexes and brood sex ratio in Tengmalm’s owl (Aegolius funereus) in northern Sweden were investigated, using a molecular sexing technique based on PCRamplification of sex-linked CHD1 genes. Among owls caught during autumn migration, females were commoner than males, especially within juveniles. However, in contrast to earlier studies, it was shown that adult males sometimes undertake migratory movements indicatory of nomadism. Measurements of these owls revealed that sexual size dimorphism in Tengmalm’s owl is not as great as previously reported from studies carried out during the breeding season. Females were slightly larger (4% by mass) than males, probably owing to the different roles of males and females during breeding, when this dimorphism is greater. The size difference between male and female nestlings was found to be similar to that for adults in autumn, and to investigate whether this led to differential mortality, the effect of supplementary feeding on mortality of male and female nestlings was studied. Supplementary feeding reduced male mortality when vole abundance was low, and it was concluded that larger female nestlings out-competed their smaller brothers, who then suffered increased mortality when food was scarce. Recruitment of male nestlings into the breeding population declined with decreasing food supply at the time of fledging, a pattern not observed in females. Juvenile males were therefore more vulnerable to food shortage than females, both in the nest and after fledging. Mean brood sex ratio varied significantly among years characterized by different phases of the vole cycle and associated vole abundance. Broods were male-biased (63% males) in a year when the food supply was favourable during spring and summer, neutral (50%) in a year with an intermediate food supply, and female-biased (35% males) in a year when food was in short supply. Parents appeared to adaptively adjust the sex ratio of their broods according to the relative mortality risk and reproductive potential of sons and daughters.</p>

Males and females differ in morphology and behaviour, so that selection acts differently on the two sexes. This changes the relative reproductive success of males and females, and it is beneficial for parents to bias the sex ratio of their broods in favour of the sex with the best survival and breeding prospects. Differences between the sexes and brood sex ratio in Tengmalm’s owl (Aegolius funereus) in northern Sweden were investigated, using a molecular sexing technique based on PCRamplification of sex-linked CHD1 genes. Among owls caught during autumn migration, females were commoner than males, especially within juveniles. However, in contrast to earlier studies, it was shown that adult males sometimes undertake migratory movements indicatory of nomadism. Measurements of these owls revealed that sexual size dimorphism in Tengmalm’s owl is not as great as previously reported from studies carried out during the breeding season. Females were slightly larger (4% by mass) than males, probably owing to the different roles of males and females during breeding, when this dimorphism is greater. The size difference between male and female nestlings was found to be similar to that for adults in autumn, and to investigate whether this led to differential mortality, the effect of supplementary feeding on mortality of male and female nestlings was studied. Supplementary feeding reduced male mortality when vole abundance was low, and it was concluded that larger female nestlings out-competed their smaller brothers, who then suffered increased mortality when food was scarce. Recruitment of male nestlings into the breeding population declined with decreasing food supply at the time of fledging, a pattern not observed in females. Juvenile males were therefore more vulnerable to food shortage than females, both in the nest and after fledging. Mean brood sex ratio varied significantly among years characterized by different phases of the vole cycle and associated vole abundance. Broods were male-biased (63% males) in a year when the food supply was favourable during spring and summer, neutral (50%) in a year with an intermediate food supply, and female-biased (35% males) in a year when food was in short supply. Parents appeared to adaptively adjust the sex ratio of their broods according to the relative mortality risk and reproductive potential of sons and daughters.

An influence at one trophic level can result in dynamic impacts also on other components of a food web. These dynamics are known as trophic cascades, and can be both top-down and bottom-up. After a near-collapse of the Baltic cod Gadus morhua stock in the 1980s, its main prey sprat Sprattus sprattus increased dramatically. The main food of sprat, marine copepods, decreased during the same time period, likely a combined effect of increased predation pressure from sprat and decreasing salinities. This shortage of food for sprat resulted in decreasing quality of sprat as a food source for common guillemots Uria aalge. However, a recent increase in fishing for sprat has again resulted in better feeding conditions for guillemots. Human impacts on this simple food web can be complex. In the early 20th century, marine mammals were abundant and nutrient levels were low in the Baltic Sea. This thesis illustrate that this situation corresponded to lower fish biomass. A reduction of seals early in the century led to reduced top-down control, which resulted in increasing fish stocks. Later, in the 1950s, the largest inflow of salt water during the century mobilized accumulated phosphorus from the deep sediments, which stimulated nitrogen fixation. Combined with increasing anthropogenic nutrient loads, this led to increased primary production and a rapid change from an oligotrophic to a eutrophicated state. This change can be termed a regime shift, which also stimulated fish production. Subsequent over-fishing of cod likely caused a second regime shift, from a cod- to a clupeid- dominated state, which led to the described effects on the common guillemots. Several factors affect the life-history of this long-lived seabird. Bycatches in gillnet fisheries is one factor directly affecting guillemot survival, and the proportion of bycatches increased during a period of increasing fishing effort. Surprisingly, avian cholera, a previously undocumented disease in common guillemots, was found at times to cause considerable adult mortality. Common guillemot life-history information can communicate the diversity of factors influencing marine ecosystems – hopefully this can increase our understanding of how complex even "simple" food webs are.