Reproductive success in presenescent common gulls (Larus canus): the importance of the last year of life.

Survival selection against individuals of inferior quality (measured as breeding success) has been proposed to account for the increase in average reproductive success with advancing age in presenescent birds. This so-called selection hypothesis relies on quality-dependent survival. In the present breeding performance study of common gulls, Larus canus, this assumption was not verified. In particular, omitting the last breeding year from the analysis resulted in the disappearance of the correlation between breeding success and survival. A positive correlation in the full dataset was thus solely based on the poor breeding success of ultimate breeders. Indeed, presenescent individuals were shown to have a specifically low breeding success in their terminal breeding event. The poor success of ultimate breeders thus reflects an abruptly declined condition rather than the birds' overall quality. A comparison of the survival of poor and good performers, involving last-time breeders, thus needs not to be a proper test of the selection hypothesis. Longitudinal analysis revealed a steady increase of individual breeding success until the tenth breeding year. The results suggest that an increase of breeding success with age often found in cross-sectional analyses is primarily a result of age-related improvements of competence and/or increased reproductive effort

Life History of the Common Gull (Larus canus) : A Long-Term Individual-Based Study

An individual’s life history is a sequence of events which eventually determine its contribution to the next generation, or fitness. These events are affected by environmental factors, genetic make-up and decisions made by an individual and its breeding partner. Recognition of these determinants helps to understand both short-term ecological changes and long-term evolutionary dynamics in a population. In this thesis long-term individual-based data on common gull (Larus canus) is used to study age-dependent reproductive success, survival, pair retention and breeding time. Collected pedigree data enabled to study genetic variation of traits and the selection on them. The reproductive success of common gulls increased steadily until very old age. This increase cannot be explained by selection effects, since individuals with lower breeding success were shown not to have lower survival. Consequently, this gain must be ascribed primarily to an age-related improvements of individual competence and/or increased reproductive effort. Annual survival of adult birds was age- and year-dependent. The latter was partly explained by winter severity. The size of the white spots on five outermost primaries predicted the bird’s future survival and divorce probabilities and hence, pair endurance capability. Gulls with larger spots enjoyed higher survival and lower divorce rates compared to birds with smaller spots. This suggests that the wing tip pattern might function as a condition dependent signal, revealing individual variation in quality. One of the advantages of persistent pair bond was the ability to start breeding early in the season. The timing of breeding of firm pairs advanced with time not only due to mates’ increasing age, but also owing to their experience together. Although both sexes had phenotypic effects on laying date, it was heritable only in females. On the phenotypic and genotypic level, early laying was under positive fecundity and survival selection in females

Life History of the Common Gull (Larus canus) : A Long-Term Individual-Based Study

An individual’s life history is a sequence of events which eventually determine its contribution to the next generation, or fitness. These events are affected by environmental factors, genetic make-up and decisions made by an individual and its breeding partner. Recognition of these determinants helps to understand both short-term ecological changes and long-term evolutionary dynamics in a population. In this thesis long-term individual-based data on common gull (Larus canus) is used to study age-dependent reproductive success, survival, pair retention and breeding time. Collected pedigree data enabled to study genetic variation of traits and the selection on them. The reproductive success of common gulls increased steadily until very old age. This increase cannot be explained by selection effects, since individuals with lower breeding success were shown not to have lower survival. Consequently, this gain must be ascribed primarily to an age-related improvements of individual competence and/or increased reproductive effort. Annual survival of adult birds was age- and year-dependent. The latter was partly explained by winter severity. The size of the white spots on five outermost primaries predicted the bird’s future survival and divorce probabilities and hence, pair endurance capability. Gulls with larger spots enjoyed higher survival and lower divorce rates compared to birds with smaller spots. This suggests that the wing tip pattern might function as a condition dependent signal, revealing individual variation in quality. One of the advantages of persistent pair bond was the ability to start breeding early in the season. The timing of breeding of firm pairs advanced with time not only due to mates’ increasing age, but also owing to their experience together. Although both sexes had phenotypic effects on laying date, it was heritable only in females. On the phenotypic and genotypic level, early laying was under positive fecundity and survival selection in females

Life History of the Common Gull (Larus canus) : A Long-Term Individual-Based Study

An individual’s life history is a sequence of events which eventually determine its contribution to the next generation, or fitness. These events are affected by environmental factors, genetic make-up and decisions made by an individual and its breeding partner. Recognition of these determinants helps to understand both short-term ecological changes and long-term evolutionary dynamics in a population. In this thesis long-term individual-based data on common gull (Larus canus) is used to study age-dependent reproductive success, survival, pair retention and breeding time. Collected pedigree data enabled to study genetic variation of traits and the selection on them. The reproductive success of common gulls increased steadily until very old age. This increase cannot be explained by selection effects, since individuals with lower breeding success were shown not to have lower survival. Consequently, this gain must be ascribed primarily to an age-related improvements of individual competence and/or increased reproductive effort. Annual survival of adult birds was age- and year-dependent. The latter was partly explained by winter severity. The size of the white spots on five outermost primaries predicted the bird’s future survival and divorce probabilities and hence, pair endurance capability. Gulls with larger spots enjoyed higher survival and lower divorce rates compared to birds with smaller spots. This suggests that the wing tip pattern might function as a condition dependent signal, revealing individual variation in quality. One of the advantages of persistent pair bond was the ability to start breeding early in the season. The timing of breeding of firm pairs advanced with time not only due to mates’ increasing age, but also owing to their experience together. Although both sexes had phenotypic effects on laying date, it was heritable only in females. On the phenotypic and genotypic level, early laying was under positive fecundity and survival selection in females

Heritability of head size in the common gull Larus canus in relation to environmental conditions during growth.

We studied the heritability of head length in a common gull (Larus canus) population breeding in western Estonia. Heritability estimates obtained from offspring-parent regressions were moderate to high and significantly different from zero. Head size might hence respond evolutionarily to phenotypic selection. Offspring-mother and offspring-father regressions yielded similar heritability estimates. This indicated that size-related maternal or paternal effects were absent or weak. Heritability and additive genetic variance estimates obtained from offspringparent regressions and full-sib analyses were higher when offspring had grown up under good environmental conditions than under poor environmental conditions. Such a pattern has previously been found in some other studies of birds. This suggests that genotype-environment interactions might be frequent within the range of conditions experienced by natural bird populations

Exploring plasticity in the wild: laying date–temperature reaction norms in the common gull Larus canus

Exploration of causal components of plasticity is important for insight into evolutionary dynamics and an organism's ability to respond to climate change. Among individuals, variation in plasticity can be due to genotype–environment interaction (G×E) or a result from environmental effects associated with an individual. We investigated plasticity for laying date in the common gulls Larus canus, using data collected in Estonia during 37 years (n=11 624 records on 2262 females, with 472 relatives). We used a sliding window approach to find the period in spring during which mean temperature best explained the annual mean laying date. Then, considering the spring temperature as a quantitative description of the environment, we used pedigree information and a random regression animal model to determine the variation in plasticity for the laying date–temperature relationship. We found that individuals differ in the plasticity of laying date (such that there is increased variation among individuals for the laying date in warmer springs), and that approximately 11% of variation in the laying date is heritable, but we found no statistical support for G×E. Plasticity in this species is not constrained by warmer springs

Age‐dependent expression of cancer‐related genes in a long‐lived seabird

International audienceStudies of model animals like mice and rats have led to great advances in our understanding of the process of tumorigenesis, but this line of study has less to offer for understanding the mechanisms of cancer resistance. Increasing the diversity of nonmodel species from the perspective of molecular mechanisms of natural cancer resistance can lead to new insights into the evolution of protective mechanisms against neoplastic processes and to a wider understanding of natural cancer defense mechanisms. Such knowledge could then eventually be harnessed for the development of human cancer therapies. We suggest here that seabirds are promising, albeit currently completely ignored candidates for studying cancer defense mechanisms, as they have a longer maximum life span than expected from their body size and rates of energy metabolism and may have thus evolved mechanisms to limit neoplasia progression, especially at older ages. We here apply a novel, intraspecific approachof comparing old and young seabirds for improving our understanding of aging and neoplastic processes in natural settings. We used the long-lived common gulls (Larus canus) for studying the age-related pattern of expression of cancer-related genes, based on transcriptome analysis and databases of orthologues of human cancer genes. The analysis of differently expressed cancer-related genes between young and old gulls indicated that similarly to humans, age is potentially affecting cancer risk in this species. Out of eleven differentially expressed cancer-related genes between the groups, three were likely artifactually linked to cancer. The remaining eight were downregulated in old gulls compared to young ones. The downregulation of five of them could be interpreted as a mechanism suppressing neoplasia risk and three as increasing the risk. Based on these results, we suggest that old gulls differ from young ones both from the aspect of cancer susceptibility and tumor suppression atthe genetic level

Data from: Age-specific patterns of maternal investment in common gull egg yolk

While the general patterns of age-specific changes in reproductive success are quite well established in long-lived animals, we still do not know if allocation patterns of maternally-transmitted compounds are related to maternal age. We measured yolk testosterone, carotenoids and vitamins A and E levels in a population of known-aged common gulls (Larus canus) and found an age-specific pattern in yolk lutein and vitamin A concentrations. Middle-aged mothers allocated more of these substances to yolk compared to young and old mothers. These results can be explained through differences in age-specific foraging, absorption, or deposition patterns of carotenoids and vitamins into yolk. If these molecules play a role in antioxidant defense and immune modulation, our results suggest a possible physiological pathway behind the age-specific changes in reproductive success of long-lived birds in the wild