Explaining patterns of age-specific performance

Individual life histories are frequently studied to gain insight into the mechanisms of ageing. However, various challenges complicate the accurate quantification of age-specific variation in fitness. In this thesis I develop and apply methods to accurately characterise patterns of ageing, and to explain why such patterns arise. All mammals and birds have an upper bound on litter size, and for many species this limit is quite low. In addition, in many species, not all individuals breed at every possible opportunity. Reproduction should consequently be considered as two processes: whether an individual breeds or not and the number of offspring produced. These processes mean that reproduction in many species does not follow a Poisson process as is often assumed in analyses of breeding performance. A more appropriate model for a repeated ordinal response like annual reproductive success is a proportional odds model with a random intercept for individuals. Such a model has not previously been used in ecology or evolutionary biology. I apply this model to analyse age and temporal variation in the number of fledglings produced annually by male and female common terns (Sterna hirundo). I use data collected from this intensively studied, long-lived species, repeatedly throughout the thesis. The proportional odds analysis reveal that reproductive performance in females initially increased with age, before declining as individuals began to senesce. But why does this pattern arise? Is it purely an effect of getting physiologically older or are other processes involved? I estimate the effect of the length of time spent with the current partner using the common tern data. Despite the quality of the data, it is not always obvious if unmarked partners are new or not. I use a hierarchical Bayesian model of the steps that lead to the number of fledglings. Modelling this complicated process requires a complex model, but results show that no substantial amount of observed age-related patterns in reproductive performance can be attributed to length of pair bond. While the proportional odds and Bayesian analyses account for repeated measures on individuals they do not account for compositional change. Such a change in the composition of the population caused by heterogeneity between individuals can mask true rates of individual change. I develop a novel retrospective decomposition method related to the Price equation to address this issue. The equation gives the exact contributions of selective disappearance and average change in individual performance among survivors to the aggregate change at the level of the population. This equation can be extended by including a term for the compositional change due to selective appearance of individuals in the study population. I apply this decomposition to the common tern dataset to disentangle whether apparent increases and decreases in reproductive performance with age reflect genuine changes within individuals or are an artefact of compositional change in a heterogeneous population. I show an improvement in average reproductive performance of individuals over most of adult life and give support for reproductive senescence at old ages. I show that the contribution of compositional change is of minor importance, suggesting that population-level averages accurately capture the individual-level ageing process well. Can the decomposition method I develop be applied to other systems? Does it lead to similar conclusions? I apply it to two different datasets dealing with functioning at old age in humans: the ability to live independently in the Danish 1905-cohort, and cognitive functioning for people aged 80 and older participating in the Chinese Longitudinal Health and Longevity Survey. In both studies I reveal that average individual functioning declines at old ages. Although the decline is also apparent at the population level it is less strong due to the tendency of individuals with lower functioning to drop out earlier. Finally, I illustrate the general use of the decomposition by applying it to epidemiological and economic studies in the appendix. Overall, I find that reproductive performance improves over many age classes before senescence begins. Numerous processes can influence rates of age-related change, with results apparently specific to the trait and population under study

Generating impact maps from automatically detected bomb craters in aerial wartime images using marked point processes

The aftermath of wartime attacks is often felt long after the war ended, as numerous unexploded bombs may still exist in the ground. Typically, such areas are documented in so-called impact maps which are based on the detection of bomb craters. This paper proposes a method for the automatic detection of bomb craters in aerial wartime images that were taken during the Second World War. The object model for the bomb craters is represented by ellipses. A probabilistic approach based on marked point processes determines the most likely configuration of objects within the scene. Adding and removing new objects to and from the current configuration, respectively, changing their positions and modifying the ellipse parameters randomly creates new object configurations. Each configuration is evaluated using an energy function. High gradient magnitudes along the border of the ellipse are favored and overlapping ellipses are penalized. Reversible Jump Markov Chain Monte Carlo sampling in combination with simulated annealing provides the global energy optimum, which describes the conformance with a predefined model. For generating the impact map a probability map is defined which is created from the automatic detections via kernel density estimation. By setting a threshold, areas around the detections are classified as contaminated or uncontaminated sites, respectively. Our results show the general potential of the method for the automatic detection of bomb craters and its automated generation of an impact map in a heterogeneous image stock. © Authors 2018

Costs of Reproduction and Terminal Investment by Females in a Semelparous Marsupial

Evolutionary explanations for life history diversity are based on the idea of costs of reproduction, particularly on the concept of a trade-off between age-specific reproduction and parental survival, and between expenditure on current and future offspring. Such trade-offs are often difficult to detect in population studies of wild mammals. Terminal investment theory predicts that reproductive effort by older parents should increase, because individual offspring become more valuable to parents as the conflict between current versus potential future offspring declines with age. In order to demonstrate this phenomenon in females, there must be an increase in maternal expenditure on offspring with age, imposing a fitness cost on the mother. Clear evidence of both the expenditure and fitness cost components has rarely been found. In this study, we quantify costs of reproduction throughout the lifespan of female antechinuses. Antechinuses are nocturnal, insectivorous, forest-dwelling small (20–40 g) marsupials, which nest in tree hollows. They have a single synchronized mating season of around three weeks, which occurs on predictable dates each year in a population. Females produce only one litter per year. Unlike almost all other mammals, all males, and in the smaller species, most females are semelparous. We show that increased allocation to current reproduction reduces maternal survival, and that offspring growth and survival in the first breeding season is traded-off with performance of the second litter in iteroparous females. In iteroparous females, increased allocation to second litters is associated with severe weight loss in late lactation and post-lactation death of mothers, but increased offspring growth in late lactation and survival to weaning. These findings are consistent with terminal investment. Iteroparity did not increase lifetime reproductive success, indicating that terminal investment in the first breeding season at the expense of maternal survival (i.e. semelparity) is likely to be advantageous for females

Lifelong leukocyte telomere dynamics and survival in a free-living mammal

Telomeres play a fundamental role in the maintenance of genomic integrity at a cellular level, and average leukocyte telomere length (LTL) has been proposed as a biomarker of organismal aging. However, studies tracking LTL across the entire life course of individuals are lacking. Here, we examined lifelong patterns of variation in LTL among four birth cohorts of female Soay sheep (Ovis aries) that were longitudinally monitored and sampled from birth to death. Over the first 4 months of life, there was within‐individual loss of LTL, consistent with findings in the human and primate literature, but there was little evidence of consistent LTL loss associated with age after this point. Overall, we observed only weak evidence of individual consistency in LTL across years and over the entire lifespan: Within‐individual variation was considerable, and birth cohorts differed markedly in their telomere dynamics. Despite the high levels of LTL variation within the lifetimes of individuals, there remained significant associations between LTL and longevity. Detailed analysis of the longitudinal data set showed that this association was driven by improved survival of individuals with longer LTL over the first 2 years of life. There was no evidence that LTL predicted survival in later adulthood. Our data provide the first evidence from a mammal that LTL can predict mortality and lifespan under natural conditions, and also highlight the potentially dynamic nature of LTL within the lifetimes of individuals experiencing a complex and highly variable environment

Explaining patterns of age-specific performance

Individual life histories are frequently studied to gain insight into the mechanisms of ageing. However, various challenges complicate the accurate quantification of age-specific variation in fitness. In this thesis I develop and apply methods to accurately characterise patterns of ageing, and to explain why such patterns arise. All mammals and birds have an upper bound on litter size, and for many species this limit is quite low. In addition, in many species, not all individuals breed at every possible opportunity. Reproduction should consequently be considered as two processes: whether an individual breeds or not and the number of offspring produced. These processes mean that reproduction in many species does not follow a Poisson process as is often assumed in analyses of breeding performance. A more appropriate model for a repeated ordinal response like annual reproductive success is a proportional odds model with a random intercept for individuals. Such a model has not previously been used in ecology or evolutionary biology. I apply this model to analyse age and temporal variation in the number of fledglings produced annually by male and female common terns (Sterna hirundo). I use data collected from this intensively studied, long-lived species, repeatedly throughout the thesis. The proportional odds analysis reveal that reproductive performance in females initially increased with age, before declining as individuals began to senesce. But why does this pattern arise? Is it purely an effect of getting physiologically older or are other processes involved? I estimate the effect of the length of time spent with the current partner using the common tern data. Despite the quality of the data, it is not always obvious if unmarked partners are new or not. I use a hierarchical Bayesian model of the steps that lead to the number of fledglings. Modelling this complicated process requires a complex model, but results show that no substantial amount of observed age-related patterns in reproductive performance can be attributed to length of pair bond. While the proportional odds and Bayesian analyses account for repeated measures on individuals they do not account for compositional change. Such a change in the composition of the population caused by heterogeneity between individuals can mask true rates of individual change. I develop a novel retrospective decomposition method related to the Price equation to address this issue. The equation gives the exact contributions of selective disappearance and average change in individual performance among survivors to the aggregate change at the level of the population. This equation can be extended by including a term for the compositional change due to selective appearance of individuals in the study population. I apply this decomposition to the common tern dataset to disentangle whether apparent increases and decreases in reproductive performance with age reflect genuine changes within individuals or are an artefact of compositional change in a heterogeneous population. I show an improvement in average reproductive performance of individuals over most of adult life and give support for reproductive senescence at old ages. I show that the contribution of compositional change is of minor importance, suggesting that population-level averages accurately capture the individual-level ageing process well. Can the decomposition method I develop be applied to other systems? Does it lead to similar conclusions? I apply it to two different datasets dealing with functioning at old age in humans: the ability to live independently in the Danish 1905-cohort, and cognitive functioning for people aged 80 and older participating in the Chinese Longitudinal Health and Longevity Survey. In both studies I reveal that average individual functioning declines at old ages. Although the decline is also apparent at the population level it is less strong due to the tendency of individuals with lower functioning to drop out earlier. Finally, I illustrate the general use of the decomposition by applying it to epidemiological and economic studies in the appendix. Overall, I find that reproductive performance improves over many age classes before senescence begins. Numerous processes can influence rates of age-related change, with results apparently specific to the trait and population under study.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Data for: Attraction of nocturnally migrating birds to artificial light: the influence of colour, intensity and blinking mode under different cloud cover conditions

The folder includes the following files: Main data files used for the paper - They include the number of individually flying small birds recorded in the thermal imaging video frames from the camera with the telephoto lens (file: Rebke_et_al_BiolConserv_telephoto_lens_Data.csv) or the wide angle lens (file: Rebke_et_al_BiolConserv_wide_angle_lens_Data.csv) summed over each 15 minutes block of light or darkness. These data were collected in autumn 2013, spring 2014 and autumn 2014 near Hörnum in the south of the island of Sylt, which is situated in the German part of the Wadden Sea. Additional data files used for the paper - They include the number of audio files with bird calls summed over each 15 minutes block of light or darkness for the three most common species in our data set: Redwings Turdus iliacus (file: Rebke_et_al_BiolConserv_audio_recordings_Turdus_iliacus_AddData.csv), Song Thrushes T. philomelos (file: Rebke_et_al_BiolConserv_audio_recordings_Turdus_philomelos_AddData.csv) or Common Blackbirds T. merula (file: Rebke_et_al_BiolConserv_audio_recordings_Turdus_merula_AddData.csv)

Data from: Better the devil you know: common terns stay with a previous partner although pair bond duration does not affect breeding output

In a monogamous species two partners contribute to the breeding process. We study pair formation as well as the effect of pair bond length and age on breeding performance, incorporating individual heterogeneity, based on a high-quality dataset of a long-lived seabird, the common tern (Sterna hirundo). To handle missing information and model the complicated processes driving reproduction, we use a hierarchical Bayesian model of the steps that lead to the number of fledglings, including processes at the individual and the pair level. The results show that the age of both partners is important for reproductive performance, with similar patterns for both sexes and individual heterogeneity in reproductive performance, but pair bond length is not. The terns are more likely to choose a former partner independent of the previous breeding outcome with that partner, which suggests a tendency to retain the partner chosen at the beginning of the breeding career