Kalev Rattiste

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 organisms 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.

“Hidden” Reproductive Conflict Between Mates in a Wild Bird Population

Abstract Environmental conditions experienced by a female prior to reproducing may be influenced by her mate. Part of such an indirect effect of a male on his partners reproduction may be genetic (indirect genetic effect). However, a females direct and a males indirect genetic effects need not align. We analyzed 10,652 records of seasonal timing of laying, an important reproductive trait in many organisms, of 1864 male and 1916 female common gulls Larus canus collected during 37 years. We show that there is both a direct (female) and an indirect (male) genetic effect (explaining 14.5% and 4.8% of the REML estimated variance in laying date, respectively), but these are significantly negatively correlated (−0.53 ± 0.22 SE), indicating that genes for early laying in females are associated with genes for a delaying male effect on his partners laying date (and vice versa). There is strong selection for laying early in this population, and these sexually antagonistic genetic effects may contribute in maintaining the variation in laying date. Our findings provide an empirical demonstration of a hitherto largely unstudied level of conflict between mates, with important ramifications for our understanding of evolutionary dynamics and mate choice in nature.

The rate of ageing in a long-lived bird is not heritable

A senescent decline in performance occurs in late age in many organisms, and is thought to be partly due to additive genetic effects. Here annual fitness, estimated as the age-specific sum of survival and reproduction, was used to test for genetic variance in ageing in a population of common gulls, Larus canus. Data on 3986 individuals collected over a 34-year period indicate a dramatic senescent decline in late life. We also find that annual fitness is heritable and that individuals vary in their rates of ageing. However, counter to theoretical expectations, we find no support for a heritable component to the variance in rates of senescence. Increases in the among-individual (permanent environment) and residual variance components initiate an increase in the total phenotypic variance for annual fitness with age. This finding suggests that older birds are more sensitive to environmental effects, and that old age causes an overall pattern of declining h2 of annual fitness. Our findings suggest that individual-specific factors do have a role in determining the rate of senescence in this population, but that additive genetic variance for the rate of senescence is either absent or small.

Comparative analysis reveals a possible immunity-related absence of blood parasites in Common Gulls (Larus canus) and Black-headed Gulls (Chroicocephalus ridibundus)

AbstractBlood parasites often incur a substantial fitness cost to the infected individuals, sometimes resulting in death of the host. Some bird species, however, are apparently free of blood parasites, presumably due to the lack of exposure to blood parasite vectors. Protective immunity may be also responsible for the absence of infections by haematozoa. In this study, we tested the presence of blood parasites in Common Gulls (Larus canus) and Black-headed Gulls (Chroicocephalus ridibundus) nesting in environments with varying vector exposure. We failed to find blood parasites in Common Gulls irrespective of vector exposure, whereas infection rates of Black-headed Gulls were generally very low. We propose that the absence of haematozoa and low prevalence of blood parasites in these species of gulls is probably not a function of vector exposure and suggest alternative explanations such as enhanced immunity.ZusammenfassungVergleichende Analysen zeigen eine möglicherweise mit dem Immunsystem zusammenhängende Abwesenheit von Blutparasiten bei Sturmmöwen (Larus canus) und Lachmöwen (Chroicocephalus ridibundus) Blutparasiten bedingen oft substantielle Fitness-Aufwendungen für die betroffenen Individuen, die nicht selten zum Tod des Wirts führen. Manche Vogelarten sind jedoch offensichtlich frei von Blutparasiten, vermutlich deshalb, weil sie deren Überträgern nicht ausgesetzt sind. Diese Art von schützender Immunität ist wahrscheinlich auch dafür verantwortlich, dass es bei ihnen keine durch Hämatozoen bedingte Infektionen gibt. In unserer Studie untersuchten wir das Vorhandensein von Blutparasiten bei Sturm- und Lachmöwen, die ihre Nester in Umgebungen gebaut hatten, in denen sie in unterschiedlicher Weise einer möglichen Übertragung der Parasiten ausgesetzt waren. Unabhängig davon, wie sehr sie einer möglichen Übertragung ausgesetzt waren, konnten wir bei den Sturmmöwen gar keine Blutparasiten nachweisen, und bei den Lachmöwen war die Infektionsrate durchweg sehr niedrig. Wir vermuten deshalb, dass bei diesen Vogelarten das Fehlen von Hämatozoen und die geringe Verbreitung von Blutparasiten nicht davon abhängen, ob und wie sehr sie den Überträgern ausgesetzt sind. Stattdessen vermuten wir hier andere Erklärungen wie z. B. ein stärkeres Immunsystem.

Variation in the Markers of Nutritional and Oxidative State in a Long-Lived Seabird: Associations with Age and Longevity

Age-related declines in life-history traits have been widely observed in free-living animals. Several theories link senescence to oxidative stress. The aim of this study was to measure several widely used markers of oxidative and nutritional state in a long-lived seabird, the common gull (Larus canus), in order to assess the suitability of these markers for describing deterioration in physiological condition associated with chronological age and survival. Associations with longevity and individual consistency of these parameters over the years (repeatability) were also assessed. Senescence in fitness parameters was observed during the study period: in females, laying date and clutch mass were related to bird age in a curvilinear manner, with middle-aged birds breeding earlier and laying heavier eggs. The only parameter associated with aging processes was glutathione concentration in erythrocytes, which was lower in female birds with longer life spans. Of indexes of nutritional state, plasma triglyceride concentration showed a between-individual increase with age, suggesting selective mortality of birds with low levels. Additionally, total plasma protein levels of individual males increased with age. The mostly negative results of this study hint that the commonly used parameters of physiological condition and oxidative state used in this study do not adequately reflect an individual’s long-term health condition. Alternatively, it is possible that in common gulls, senescence occurs in reproductive mechanisms but not in mechanisms responsible for maintaining an organism’s redox balance, consistent with the idea that different aspects of an organism’s physiological condition age at different rates. Significant interannual repeatability was detected in three plasma constituents—carotenoids, uric acid, and total protein—all of which can possibly be linked to variation in dietary habits.

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 the levels of yolk testosterone, carotenoids and vitamins A and E 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 defence and immune modulation, our results suggest a possible physiological pathway underlying the age-specific changes in reproductive success of long-lived birds in the wild.