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Brommer J.E.,University of Turku | Karell P.,Novia University of Applied Sciences | Aaltonen E.,Vanhansahantie 13B 7 | Ahola K.,Tornihaukantie 8D 72 | Karstinen T.,Juusinkuja 1
Behavioral Ecology and Sociobiology | Year: 2015

Males can through their behavior (e.g., courtship feeding) exert an indirect effect on their partner’s reproductive traits, such as the seasonal timing and size of her clutch. Evidence for such indirect (male) effect on reproduction is starting to accumulate. We quantify female and male effects on reproduction in the tawny owl Strix aluco using a hierarchical mixed model on data collected in 1978–2013. We find that differences between males explain 7 % of the phenotypic variance in laying date (females 5 %). In contrast, females have a clear (11 %) effect on clutch size, whereas males have no effect. Based on multivariate hierarchical modeling, we find an individual-level correlation between the male-specific effect on laying date and his body mass (but not his plumage color or wing length). Heavy males may be able to affect their partner’s seasonal timing of laying because of an advantage in providing courtship feeding prior to reproduction. Our findings illustrate that males can be an important determinant of variation in reproduction and that multivariate mixed models present a general approach to pinpoint which individual characteristics could be associated with such indirect effects. © 2014, Springer-Verlag Berlin Heidelberg. Source


Koskenpato K.,University of Helsinki | Ahola K.,Tornihaukantie 8D 72 | Karstinen T.,Juusinkuja 1 | Karell P.,Abo Akademi University
Journal of Avian Biology | Year: 2016

In colour polymorphic species morphs are considered to be adaptations to different environments, where they have evolved and are maintained because of their differential sensitivity to the environment. In cold environments the plumage insulation capacity is essential for survival and it has been proposed that plumage colour is associated with feather structure and thereby the insulation capacity of the plumage. We studied the structure of contour feathers in the colour polymorphic tawny owl Strix aluco. A previous study of tawny owls in the same population has found strong selection against the brown morph in cold and snowy winters whereas this selection pressure is absent in mild winters. We predicted that grey morphs have a denser and more insulative plumage, enabling them to survive better in cold climate compared to brown ones. The insulative plumulaceous part of the dorsal contour feathers was larger and the fine structure of the plumulaceous part of the feather was denser in grey tawny owls than in brown ones. In the ventral contour feathers the plumulaceous part of the feather was denser in females than in males and in older birds without any differences between morphs. Our study suggests that insulative microscopical feather structures differ between colour morphs and we propose that feather structure may be a trait associated with morph-specific survival in cold environments. © 2016 Nordic Society Oikos. Source


Brommer J.E.,University of Turku | Karell P.,Abo Akademi University | Karell P.,Novia University of Applied Sciences | Ahola K.,Tornihaukantie 8D 72 | Karstinen T.,Juusinkuja 1
Behavioral Ecology | Year: 2014

Different behavioral traits often covary, forming a behavioral syndrome. It is poorly known whether this covariance occurs on the between-individual level and what its selective consequences are. We used repeated measures (N = 562 observation events) of individual tawny owl Strix aluco females (N = 237) to study the integrated effects of seasonal timing of reproduction and clutch size on boldness displayed during defense of their clutch, in relation to plumage coloration, including local recruit production as a selective force on these traits. Using a Bayesian multivariate mixed model, we quantified the covariances between these traits on phenotypic, residual, and between-individual level and used a structural equation modeling approach to test the significance of presumed causal relationship between these traits in an a priori hypothesized path. On the phenotypic level, boldness was determined through early timing of breeding and larger clutch size, and early breeding increased recruitment probability. However, this relationship was entirely due to residual covariances and was not present on the between-individual level. The low individual-level correlations did not constrain the capacity of the population to respond to evolution as quantified by average autonomy (a metric summarizing evolutionary constraint on multiple traits). In the tawny owl, the association between early breeding and bold behavior, which is favored by selection, is solely due to extrinsic, nonheritable factors. We conclude that phenotypic evidence is insufficient to demonstrate syndrome covariance. © 2014 The Author. Source


Karell P.,University of Helsinki | Karell P.,Lund University | Ahola K.,Tornihaukantie 8D 72 | Karstinen T.,Juusinkuja 1 | And 3 more authors.
Journal of Evolutionary Biology | Year: 2011

Parasites can mediate profound negative effects on host fitness. Colour polymorphism has been suggested to covary genetically with intrinsic physiological properties. Tawny owl colour polymorphism is highly heritable with two main morphs, grey and brown. We show that experimental medication acts to reduce blood parasites and that medicated grey females maintain body mass during breeding, whereas medicated brown females decline in body mass similar to control females of both morphs. We find no effect of medication on general immunoglobulin levels, antigen-specific humoral response or H/L ratio. In the descriptive data, both morphs have similar blood parasite infection rates, but blood parasite infection is associated with decreased body mass in brown but not in grey females. We conclude that blood parasite infection primarily has somatic costs, which differ between the two highly heritable tawny owl colour morphs with more pronounced costs in the grey (little pigmented) morph than in the brown (heavily pigmented) morph. Because our descriptive results imply the opposite pattern, our findings highlight the need of experimental manipulation when studying heritable variation in hosts' response to parasitism. © 2011 The Authors. Journal of Evolutionary Biology © 2011 European Society For Evolutionary Biology. Source


Karell P.,University of Helsinki | Ahola K.,Tornihaukantie 8D 72 | Karstinen T.,Juusinkuja 1 | Valkama J.,University of Helsinki | Brommer J.E.,University of Helsinki
Nature Communications | Year: 2011

To ensure long-term persistence, organisms must adapt to climate change, but an evolutionary response to a quantified selection pressure driven by climate change has not been empirically demonstrated in a wild population. Here, we show that pheomelanin-based plumage colouration in tawny owls is a highly heritable trait, consistent with a simple Mendelian pattern of brown (dark) dominance over grey (pale). We show that strong viability selection against the brown morph occurs, but only under snow-rich winters. As winter conditions became milder in the last decades, selection against the brown morph diminished. Concurrent with this reduced selection, the frequency of brown morphs increased rapidly in our study population during the last 28 years and nationwide during the last 48 years. Hence, we show the first evidence that recent climate change alters natural selection in a wild population leading to a microevolutionary response, which demonstrates the ability of wild populations to evolve in response to climate change. © 2011 Macmillan Publishers Limited. All rights reserved. Source

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