Michael Quetting

Artificial light at night advances avian reproductive physiology

Artificial light at night is a rapidly increasing phenomenon and it is presumed to have global implications. Light at night has been associated with health problems in humans as a consequence of altered biological rhythms. Effects on wild animals have been less investigated, but light at night has often been assumed to affect seasonal cycles of urban dwellers. Using light loggers attached to free-living European blackbirds (Turdus merula), we first measured light intensity at night which forest and city birds are subjected to in the wild. Then we used these measurements to test for the effect of light at night on timing of reproductive physiology. Captive city and forest blackbirds were exposed to either dark nights or very low light intensities at night (0.3 lux). Birds exposed to light at night developed their reproductive system up to one month earlier, and also moulted earlier, than birds kept under dark nights. Furthermore, city birds responded differently than forest individuals to the light at night treatment, suggesting that urbanization can alter the physiological phenotype of songbirds. Our results emphasize the impact of human-induced lighting on the ecology of millions of animals living in cities and call for an understanding of the fitness consequences of light pollution.

Hormone levels predict individual differences in reproductive success in a passerine bird

Hormones mediate major physiological and behavioural components of the reproductive phenotype of individuals. To understand basic evolutionary processes in the hormonal regulation of reproductive traits, we need to know whether, and during which reproductive phases, individual variation in hormone concentrations relates to fitness in natural populations. We related circulating concentrations of prolactin and corticosterone to parental behaviour and reproductive success during both the pre-breeding and the chick-rearing stages in both individuals of pairs of free-living house sparrows, Passer domesticus. Prolactin and baseline corticosterone concentrations in pre-breeding females, and prolactin concentrations in pre-breeding males, predicted total number of fledglings. When the strong effect of lay date on total fledgling number was corrected for, only pre-breeding baseline corticosterone, but not prolactin, was negatively correlated with the reproductive success of females. During the breeding season, nestling provisioning rates of both sexes were negatively correlated with stress-induced corticosterone levels. Lastly, individuals of both sexes with low baseline corticosterone before and high baseline corticosterone during breeding raised the most offspring, suggesting that either the plasticity of this trait contributes to reproductive success or that high parental effort leads to increased hormone concentrations. Thus hormone concentrations both before and during breeding, as well as their seasonal dynamics, predict reproductive success, suggesting that individual variation in absolute concentrations and in plasticity is functionally significant, and, if heritable, may be a target of selection.

Corticosterone and brood abandonment in a passerine bird

Hormones regulate decision-making strategies, in particular by translating an individuals physiological state into decisions on major behavioural and life-history processes, such as reproduction. Corticosterone, a glucocorticoid hormone, has been gaining attention as a mediator of reproductive effort, and experimentally elevated corticosterone concentrations have been shown to disrupt reproduction in avian species. Here, we tested whether individual variation in corticosterone concentrations is related to the decision for brood abandonment in free-living great tits, Parus major. Because of harsh environmental conditions, many adults abandoned their first broods in 2010, enabling us to ask which physiological, environmental and individual characteristics increased the probability of nest desertion by both males and females. The best predictors of nest desertion were high stress-induced corticosterone levels in males and low average nestling mass. Furthermore, high stress-induced corticosterone levels in 2010 appeared to represent plastic responses to environmental conditions and reproductive investment: individual males that abandoned their nests in 2010 had higher stress-induced corticosterone concentrations and produced nestlings with lower average mass than in 2009, when nesting successfully. Females that abandoned their nests in 2010 had higher baseline corticosterone concentrations than in 2009, when nesting successfully. Also, males that renested after abandonment in 2010 had lower stress-induced corticosterone concentrations and nestlings with higher mass. Finally, pairs that abandoned but renested later in 2010 had similar fledgling success at the end of the season as those that did not abandon. These results indicate that an individuals reproductive decision is the result of a plastic modulation of the corticosterone stress response that influences reproductive decisions according to environmental conditions.

Small increases in corticosterone before the breeding season increase parental investment but not fitness in a wild passerine bird

Correlative evidence from field studies has suggested that baseline concentrations of corticosterone, the main avian glucocorticoid hormone, affect reproductive strategies in vertebrate species. Such a role is conceivable in light of corticosterones function as a metabolic hormone in regulating glucose and fat metabolism. From such correlational studies, however, the question has remained open whether glucocorticoid concentrations change in advance of reproductive activities or whether corticosterone concentrations vary passively as a consequence of the individuals reproductive investment and workload. To test such causal relationships, we manipulated corticosterone concentrations prior to the breeding season in adult great tits (Parus major) and quantified reproductive investment and success. Two weeks before egg-laying, we administered subcutaneous silastic implants filled with corticosterone that elevated circulating levels within the baseline range for approximately 30 days to adult males and females. Corticosterone manipulation did not affect lay date or yearly offspring production. However, reproductive behaviors were affected by corticosterone treatment: males fed their mates more often during incubation, and females increased incubation of eggs and brooding of nestlings compared to control individuals. Other behaviors during the nestling stage, when the implants were no longer effective, did not differ between the two treatment groups. Our findings do not support the view that baseline corticosterone concentrations, at least at the time of year when we administered implants, change reproductive strategies per se. The current data suggest that baseline corticosterone levels represent internal signals that causally mediate reproductive effort in individuals of a wild bird species. By increasing reproductive investment, baseline corticosterone concentrations may have functions during the breeding season that diverge from the suppressive effects of stress-induced concentrations.

Endocrine phenotype, reproductive success and survival in the great tit, Parus major

A central goal in evolutionary ecology is to characterize and identify selection patterns on the optimal phenotype in different environments. Physiological traits, such as hormonal responses, provide important mechanisms by which individuals can adapt to fluctuating environmental conditions. It is therefore expected that selection shapes hormonal traits, but the strength and the direction of selection on plastic hormonal signals are still under investigation. Here, we determined whether, and in which way, selection is acting on the hormones corticosterone and prolactin by characterizing endocrine phenotypes and their relationship with fitness in free‐living great tits, Parus major. We quantified variation in circulating concentrations of baseline and stress‐induced corticosterone and in prolactin during the prebreeding (March) and the breeding season (May) for two consecutive years, and correlated these with reproductive success (yearly fledgling number) and overwinter survival in female and male individuals. In both years, individuals with high baseline corticosterone concentrations in March had the highest yearly fledgling numbers; while in May, individuals with low baseline corticosterone had the highest yearly reproductive success. Likewise, individuals that displayed strong seasonal plasticity in baseline corticosterone concentrations (high in March and low in May) had the highest reproductive success in each year. Prolactin concentrations were not related to reproductive success, but were positively correlated to the proximity to lay. Between‐year plasticity in stress‐induced corticosterone concentrations of males was related to yearly variation in food abundance, but not to overall reproductive success. These findings suggest that seasonally alternating directional selection is operating on baseline corticosterone concentrations in both sexes. The observed between‐year consistency in selection patterns indicates that a one‐time hormone sample in a given season can allow the prediction of individual fitness.

Enhancement of immunogenicity of a therapeutic cervical cancer DNA‐based vaccine by co‐application of sequence‐optimized genetic adjuvants

Treatment of patients with cervical cancer by conventional methods (mainly surgery, but also radiotherapy and chemotherapy) results in a significant loss in quality of life. A therapeutic DNA vaccine directed to tumor‐specific antigens of the human papilloma virus (HPV) could be an attractive treatment option. We have developed a nontransforming HPV‐16 E7‐based DNA vaccine containing all putative T cell epitopes (HPV‐16 E7SH). DNA vaccines, however, are less immunogenic than protein‐ or peptide‐based vaccines in larger animals and humans. In this study, we have investigated an adjuvant gene support of the HPV‐16 E7SH therapeutic cervical cancer vaccine. DNA encoded cytokines (IL‐2, IL‐12, GM‐CSF, IFN‐γ) and the chemokine MIP1‐α were co‐applied either simultaneously or at different time points pre‐ or post‐E7SH vaccination. In addition, sequence‐optimized adjuvant genes were compared to wild type genes. Three combinations investigated lead to an enhanced IFN‐γ response of the induced T cells in mice. Interestingly, IFN‐γ secretion of splenocytes did not strictly correlate with tumor response in tumor regression experiments. Gene‐encoded MIP‐1α applied 5 days prior to E7SH‐immunization combined with IFN‐γ or IL‐12 (3 days) or IL‐2 (5 days) postimmunization lead to a significantly enhanced tumor response that was clearly associated with granzyme B secretion and target cells lysis. Our results suggest that a conditioning application and combination with adjuvant genes may be a promising strategy to enhance synergistically immune responses by DNA immunization for the treatment of cervical cancer.

Long-Term Effects of Chronic Light Pollution on Seasonal Functions of European Blackbirds (Turdus merula)

Light pollution is known to affect important biological functions of wild animals, including daily and annual cycles. However, knowledge about long-term effects of chronic exposure to artificial light at night is still very limited. Here we present data on reproductive physiology, molt and locomotor activity during two-year cycles of European blackbirds (Turdus merula) exposed to either dark nights or 0.3 lux at night. As expected, control birds kept under dark nights exhibited two regular testicular and testosterone cycles during the two-year experiment. Control urban birds developed testes faster than their control rural conspecifics. Conversely, while in the first year blackbirds exposed to light at night showed a normal but earlier gonadal cycle compared to control birds, during the second year the reproductive system did not develop at all: both testicular size and testosterone concentration were at baseline levels in all birds. In addition, molt sequence in light-treated birds was more irregular than in control birds in both years. Analysis of locomotor activity showed that birds were still synchronized to the underlying light-dark cycle. We suggest that the lack of reproductive activity and irregular molt progression were possibly the results of i) birds being stuck in a photorefractory state and/or ii) chronic stress. Our data show that chronic low intensities of light at night can dramatically affect the reproductive system. Future studies are needed in order to investigate if and how urban animals avoid such negative impact and to elucidate the physiological mechanisms behind these profound long-term effects of artificial light at night. Finally we call for collaboration between scientists and policy makers to limit the impact of light pollution on animals and ecosystems.

Repeated stressors in adulthood increase the rate of biological ageing

BackgroundIndividuals of the same age can differ substantially in the degree to which they have accumulated tissue damage, akin to bodily wear and tear, from past experiences. This accumulated tissue damage reflects the individual’s biological age and may better predict physiological and behavioural performance than the individual‘s chronological age. However, at present it remains unclear how to reliably assess biological age in individual wild vertebrates.MethodsWe exposed hand-raised adult Eurasian blackbirds (Turdus merula) to a combination of repeated immune and disturbance stressors for over one year to determine the effects of chronic stress on potential biomarkers of biological ageing including telomere shortening, oxidative stress load, and glucocorticoid hormones. We also assessed general measures of individual condition including body mass and locomotor activity.ResultsBy the end of the experiment, stress-exposed birds showed greater decreases in telomere lengths. Stress-exposed birds also maintained higher circulating levels of oxidative damage compared with control birds. Other potential biomarkers such as concentrations of antioxidants and glucocorticoid hormone traits showed greater resilience and did not differ significantly between treatment groups.ConclusionsThe current data demonstrate that repeated exposure to experimental stressors affects the rate of biological ageing in adult Eurasian blackbirds. Both telomeres and oxidative damage were affected by repeated stress exposure and thus can serve as blood-derived biomarkers of biological ageing.

Becoming more like your mate: hormonal similarity reduces divorce rates in a wild songbird

In animals with biparental care, maintaining a pair bond is of adaptive value because it increases reproductive success and reduces costs, such as energy and time, for finding a new mate. Hormones are important mediators of social behaviours as well as parental care, and endocrine mechanisms are therefore likely to be involved in the decision whether to stay with the same mate or separate after a breeding season. Because behavioural compatibility has been shown to increase fitness and hormones have been shown to regulate behavioural traits, here we examined whether the degree of endocrine similarity is also related to reproductive success and pair bond longevity. We used a 3-year study on free-living great tits, Parus major, to test whether mates had similar hormone levels during the parental phase. We tested specifically whether the metabolic hormone corticosterone was related to pair bond longevity and reproductive success. Baseline, but not stress-induced, corticosterone concentrations were highly correlated among members of a pair and became more similar among members of pairs that stayed together for multiple years. Pairs that increased their hormonal similarity within a season (from prebreeding to breeding) had the highest reproductive success. Pairs with more similar baseline corticosterone levels and higher reproductive success were also more likely to remain together after the breeding season. The results of this study suggest that pair bond longevity is related to endocrine similarity and reproductive success, and raise the possibility that hormonal mechanisms may be under sexual selection.