Effects of inbreeding on individual levels of immunocompetence within bottlenecked bird populations that have been exposed to introduced pathogens

近亲繁殖和遗传多样性的丧失被认为会降低自然种群科普疾病的能力，这对保护小型、单颈种群具有重要意义。这一预测已经在果蝇种群（近交系抗性降低）和家雀（遗传多样性个体表现出更强的免疫反应和较轻的感染）中得到了实验证明。然而，很少有研究确定近亲繁殖对自由生活人群免疫功能的影响。最近的一项研究表明，与其远交来源相比，一个严重颈缩的知更鸟种群的免疫能力降低。虽然几乎没有疑问，近亲繁殖的人群更容易受到疾病的影响，但仍然不清楚这种情况在人群中发生的地点，时间和程度。该项目将研究两种鸟类的免疫功能和近亲繁殖之间的相互作用，其中近亲繁殖的水平和已知的病原感染程度在个体之间存在差异。在鸟类田间研究中，鸟类的免疫功能最常使用植物血凝素（PHA）皮肤试验进行测量。PHA反应已被证明是显着减少，在一个严重的necked知更鸟种群和显着升高，在杂交与纯种长尾小鹦鹉。该技术最近在鸟类中得到了组织学验证。该项目将测量两种特有鸟类的免疫能力水平，在过去的25年里，这些鸟类的恢复种群一直受到密切监测。濒危的毛里求斯鹦鹉（Psittacula echo）和濒危的毛里求斯粉红鸽（Columba mayeri）在过去30年中都经历了严重的人口瓶颈。长期的管理产生了详细的系谱记录和完整的生活史以来的所有个人的瓶颈。这两个种群都感染了引入的病原体。毛里求斯鹦鹉最近爆发了鹦鹉喙和羽毛病毒（PBFV）。粉红鸽是两种血液病原体的宿主;鸡毛滴虫和马丘西白细胞虫，其流行情况已被密切监测。PBFV是由野生环颈长尾鹦鹉和T.鸡亚科毛里求斯的野生地鸠种群。遗传和系谱资料证实，在每一个濒危鸟类种群内，近亲繁殖存在相当大的变异。引进印度环颈长尾鹦鹉和禁止地面鸽子的同域种群将提供远交的“控制”种群。作为持续恢复方案的一部分，每年对每个居民进行密切监测。毛里求斯的野外鸟类饲养场将能够重复测量个体在繁殖和非繁殖季节的免疫能力，并提供免疫反应遗传力的估计。现有的研究假设免疫活性低，以反映对感染的抵抗力下降。然而，在毛里求斯，可以重新测量自由生活的受感染鸟类的免疫能力，以评估随着感染进展免疫功能的变化。该项目将使用已确认的谱系来确定个体近亲繁殖系数;验证已知近亲繁殖系数的免疫能力测量和观察到的自由生活人群中的感染水平，以确定近亲繁殖和免疫功能之间的相互作用。毛里求斯长尾小鹦鹉种群已经存在遗传学证实的谱系，鸽子谱系将使用存档样本进行证实。将使用PHA皮肤试验和溶血-血凝试验在来自四个种群的每一个的约180只鸡中测量免疫能力。PHA方法在用于自由生活种群之前将在圈养条件下进行校准。一般的线性模型将确定近亲繁殖对免疫活性的影响，从季节/生活史的影响近亲繁殖对免疫活性的影响。

Inbreeding and loss of genetic diversity are believed to reduce the ability of natural populations to cope with disease, presenting important implications for the conservation of small, bottlenecked populations. This prediction has been shown experimentally in Drosophila populations (reduced resistance in inbred lines) and in house finches (genetically-diverse individuals showed stronger immune responses and less severe infection). However, few studies have identified the effect of inbreeding on immune function in free-living populations. A recent study demonstrated reduced immunocompetence in a severely bottlenecked robin population in comparison to their out-bred source. Whilst there is little doubt that inbred populations are more likely to be susceptible to disease, it is remains unclear where, when and to what extent this occurs within populations. This project will examine interactions between immune function and inbreeding in two bottlenecked bird species, where level of inbreeding and known extent of pathogenic infection vary between individuals. In avian field studies, immune function in birds has most commonly been measured using the Phytohaemaglutinin (PHA) skin test. PHA response has been shown to be significantly reduced in a severely bottlenecked robin population and to be significantly elevated in hybridised versus pure-bred parakeets. The technique has recently been histologically validated in birds. This project will measure individual levels of immunocompetence amongst two endemic bird species whose restored populations have been intensively-monitored for the past 25 years. The endangered Mauritius parakeet (Psittacula echo) and endangered Mauritius pink pigeon (Columba mayeri) have both experienced a severe population bottleneck over the past 30 years. Long-term management has produced detailed pedigree records and complete life histories for all individuals since the bottleneck. Both bottlenecked populations are infected with introduced pathogens. The Mauritius parakeet suffered a recent outbreak of Psittacene Beak and Feather Virus (PBFV). The pink pigeon is host to two blood pathogens; Trichomonas gallinae and Leucocytozoon marchouxi, whose prevalence has been intensively monitored. PBFV was introduced by feral ringneck parakeets and T. Gallinae/L. Marchouxi by feral ground dove populations on Mauritius. Genetic and pedigree information has confirmed considerable variation in inbreeding within each endangered bird population. Sympatric populations of the introduced Indian ringneck parakeet and barred ground dove will provide out-bred 'control' populations. Each population is closely monitored each year as part of the ongoing recovery programme. Field aviaries on Mauritius will enable replicate measurement of an individuals' immunocompetence across breeding and non-breeding seasons and provide estimates of heritability of immune response. Existing studies assume low immunocompetence to reflect reduced resistance to infection. However, on Mauritius, immunocompetence can be re-measured in free-living infected birds to evaluate change in immune function as infection progresses. The project will use confirmed pedigrees to identify individual inbreeding coefficients; validate measures of immunocompetence for known inbreeding coefficients and observed level of infection in the free-living populations to identify interactions between inbreeding and immune function. Genetically confirmed pedigrees already exist for the Mauritius parakeet population, and pigeon pedigrees will be confirmed using archived samples. Immunocompetence will be measured in ~180 birds from each of the four populations using the PHA skin test and hemolysis-haemagglutination assays. PHA methods will be calibrated in captivity before use on free-living populations. General linear models will identify effects of inbreeding on immunocompetence from effects of inbreeding on immunocompetence from effects of season/life-history.