A theoretical model of the evolution of actuarial senescence under environmental stress

Site-Specific Impacts of Urbanisation on Annual Survival of a Forest Bird

Habitat changes associated with urbanization have major and complex effects on wildlife. In birds, urban populations often have lower reproductive success but are able to maintain similar or higher densities than non-urban populations. One explanation proposed for this paradox is that higher survival of birds in cities may compensate for lower reproduction. We use a 9-year dataset and Cormack-Jolly-Seber models to compare annual variation in apparent survival probabilities of adult great tits (Parus major) at two forests and two urban sites located in Hungary. Our analyses tested the effects of sex, age, year, population density on apparent survival, after correcting for the probability of detection. Apparent survival of great tits varied between 0.122 and 0.736, with study site and year having the greatest influence. Unexpectedly, urbanization did not have a consistent effect: the sites with the lowest and highest estimates of survival were both urban habitats. Survival probabilities at the two forest sites were similar to each other but were ~0.15 lower than survival in the best urban site and ~0.1. higher than survival in the worst urban site. Survival probabilities exhibited marked inter-annual variation in all sites, although temporal patterns were not consistent among sites suggesting the variation was not driven by inter-annual variation in regional scale factors. Survival probabilities decreased with bird age at both urban sites in most years, but such patterns were not detected at forest sites. Our results demonstrate that the impacts of aging on avian survival rates can diverge between urban and forest habitats, and that the demographic factors regulating urban populations can vary between locations. Age-specific variation should be taken into account in urban ecology and further exploration of the factors driving the heterogeneity will help inform conservation of biodiversity along rural-urban gradients.

Interactive effects of rising temperatures and urbanisation on birds across different climate zones: A mechanistic perspective

Climate change and urbanisation are among the most pervasive and rapidly growing threats to biodiversity worldwide. However, their impacts are usually considered in isolation, and interactions are rarely examined. Predicting species' responses to the combined effects of climate change and urbanisation, therefore, represents a pressing challenge in global change biology. Birds are important model taxa for exploring the impacts of both climate change and urbanisation, and their behaviour and physiology have been well studied in urban and non-urban systems. This understanding should allow interactive effects of rising temperatures and urbanisation to be inferred, yet considerations of these interactions are almost entirely lacking from empirical research. Here, we synthesise our current understanding of the potential mechanisms that could affect how species respond to the combined effects of rising temperatures and urbanisation, with a focus on avian taxa. We discuss potential interactive effects to motivate future in-depth research on this critically important, yet overlooked, aspect of global change biology. Increased temperatures are a pronounced consequence of both urbanisation (through the urban heat island effect) and climate change. The biological impact of this warming in urban and non-urban systems will likely differ in magnitude and direction when interacting with other factors that typically vary between these habitats, such as resource availability (e.g. water, food and microsites) and pollution levels. Furthermore, the nature of such interactions may differ for cities situated in different climate types, for example, tropical, arid, temperate, continental and polar. Within this article, we highlight the potential for interactive effects of climate and urban drivers on the mechanistic responses of birds, identify knowledge gaps and propose promising future research avenues. A deeper understanding of the behavioural and physiological mechanisms mediating species' responses to urbanisation and rising temperatures will provide novel insights into ecology and evolution under global change and may help better predict future population responses.

A procession of metabolic alterations accompanying muscle senescence in Manduca sexta

Biological aging profoundly impairs muscle function, performance, and metabolism. Because the progression of metabolic alterations associated with aging muscle has not been chronicled, we tracked the metabolic profiles of flight muscle from middle to advanced age in Manduca sexta to identify key molecules during the progression of muscle aging, as well as to evaluate the utility of the M. sexta system for molecular dissection of muscle aging. We identified a number of differences between Diel Time, Sexes, and Muscle Ages, including changes in metabolites related to energetics, extracellular matrix turnover, and glutathione metabolism. Increased abundances of glycolytic metabolites suggest a shift toward increased glycolysis with advancing age, whereas decreased abundances in lysolipids and acylcarnitines reflect decreasing beta-oxidation. We also observed a shift towards decreased polyamine metabolism with age, which might result in an age-related decline in lipid metabolism possibly due to regulation of energy metabolism by polyamines. Collectively, our findings demonstrate the feasibility of our system and approach and provide a deeper understanding of lepidopteran aging. More importantly, the results identify the key altered metabolic pathways that collectively contribute to the muscle aging phenotype and thereby improve our understanding of muscle senescence.

Co-existence of multiple trade-off currencies shapes evolutionary outcomes

Evolutionary studies often assume that energy is the primary resource (i.e. “currency”) at the heart of the survival-reproduction trade-off, despite recent evidence to the contrary. The evolutionary consequences of having a single trade-off currency versus multiple competing currencies are unknown. Using simulations, we modeled the evolution of either a single physiological currency between reproduction and survival, or of multiple such currencies. For a wide array of model specifications varying functional forms and strengths of the trade-offs, we show that the presence of multiple currencies (e.g. nutrients, time) generally results in the evolution of higher lifetime reproductive success through partial circumvention of such trade-offs. Evolution of the underlying physiology is also more highly contingent with multiple currencies. These results challenge the paradigm of a single survival-reproduction trade-off as central to life history evolution, suggesting greater roles for physiological constraints and contingency, and implying potential selection for evolution of multiple trade-off currencies.