Selection on a eumelanic ornament is stronger in the tropics than in temperate zones in the worldwide-distributed barn owl.

Spatial variation in the pattern of natural selection can promote local adaptation and genetic differentiation between populations. Because heritable melanin-based ornaments can signal resistance to environmentally mediated elevation in glucocorticoids, to oxidative stress and parasites, populations may vary in the mean degree of melanic coloration if selection on these phenotypic aspects varies geographically. Within a population of Swiss barn owls (Tyto alba), the size of eumelanic spots is positively associated with survival, immunity and resistance to stress, but it is yet unknown whether Tyto species that face stressful environments evolved towards a darker eumelanic plumage. Because selection regimes vary along environmental gradients, we examined whether melanin-based traits vary clinally and are expressed to a larger extent in the tropics where parasites are more abundant than in temperate zones. To this end, we considered 39 barn owl species distributed worldwide. Barn owl species living in the tropics displayed larger eumelanic spots than those found in temperate zones. This was, however, verified in the northern hemisphere only. Parasites being particularly abundant in the tropics, they may promote the evolution of darker eumelanic ornaments.

Hybrid speciation in birds: allopatry more important than ecology?

Hybrid speciation was once thought to be rare in animals, but over the past decade, improved molecular analysis techniques and increased research attention have allowed scientists to uncover many examples. In this issue, two papers (Elgvin et al. 2011; Hermansen et al. 2011) present compelling evidence for the hybrid origin of the Italian sparrow based on nuclear and mitochondrial DNA sequences, microsatellites, and plumage coloration. These studies point to an important role for geographic isolation in the process of hybrid speciation, and provide a starting point for closer examination of the genetic and behavioural mechanisms involved.

Breeding rate is associated with pheomelanism in male and with eumelanism in female barn owls

Melanin-based coloration exists in 2 types: black eumelanism and reddish-brown pheomelanism, which both have a strong heritable component. To test whether these 2 types of melanism are associated with alternative adaptations, we carried out a correlative study over 8 years and an experiment in a Swiss population of barn owls, Tyto alba. This species varies in coloration from reddish-brown to white and from lightly to heavily marked with black spots. Based on the fact that plumage coloration and spottiness are male- and female-specific secondary sexual characters, respectively, we examined whether the probability of breeding is associated with the degree of pheomelanism in males and of eumelanism in females. In males, recruited nestlings were significantly less reddish-brown than their nonrecruited nest mates. In females, individuals displaying larger black spots started to breed at a younger age and had a higher survival, and females with experimentally reduced plumage spottiness bred less often than control females. Therefore, in the barn owl, the degree of male pheomelanism is associated with the probability of being recruited in the local population, whereas the degree of female eumelanism correlates with age at sexual maturity, survival probability, and also the probability of skipping reproduction.

Female-biased mortality in experimentally parasitized Alpine Swift Apus melba nestlings

1. Sex-biased mortality in adult vertebrates is often attributed to lower immunocompetence and higher parasite susceptibility of males. Although sex-specific mortality has also been reported during growth, the importance of sex-specific immunocompetence and parasite susceptibility in explaining male-biased mortality remains ambiguous in growing individuals because of potentially confounding sources of mortality such as sexual dimorphism. 2. Here, we investigated sex-specific susceptibility to the blood-sucking louse fly Crataerina melbae and sex differences in cell-mediated immunity in a bird species that is sexually monomorphic both in size and plumage coloration at the nestling stage, the Alpine Swift, Apus melba. 3. For this purpose, we manipulated ectoparasite loads by adding or removing flies to randomly chosen nests in two years, and injected nestlings with mitogenic phytohaemagglutinin (PHA) in another year. 4. There were no significant differences between male and female offspring in immune response towards PHA, parasite load, and parasite-induced decrease in growth rate. Secondary sex ratios were however biased toward males in parasitized broods, and this was explained by a greater mortality of females in parasitized than deparasitized broods. 5. Our findings are in contrast to the widely accepted hypothesis that males suffer a greater cost of parasitism. We discuss alternative hypotheses accounting for female-specific mortality.

Glover's rule in North American barn owls

Studying the geographic variation of phenotypic traits can provide key information about the potential adaptive function of alternative phenotypes. Gloger's rule posits that animals should be dark-vs. light-colored in warm and humid vs. cold and dry habitats, respectively. The rule is based on the assumption that melanin pigments and/or dark coloration confer selective advantages in warm and humid regions. This rule may not apply, however, if genes for color are acting on other traits conferring fitness benefits in specific climes. Covariation between coloration and climate will therefore depend on the relative importance of coloration or melanin pigments and the genetically correlated physiological and behavioral processes that enable an animal to deal with climatic factors. The Barn Owl (Tyto alba) displays three melanin-based plumage traits, and we tested whether geographic variation in these traits at the scale of the North American continent supported Gloger's rule. An analysis of variation of pheomelanin-based reddish coloration and of the number and size of black feather spots in 1,369 museum skin specimens showed that geographic variation was correlated with ambient temperature and precipitation. Owls were darker red in color and displayed larger but fewer black feather spots in colder regions. Owls also exhibited more and larger black spots in regions where the climate was dry in winter. We propose that the associations between pigmentation and ambient temperature are of opposite sign for reddish coloration and spot size vs. the number of spots because selection exerted by climate (or a correlated variable) is plumage trait-specific or because plumage traits are genetically correlated with different adaptations.

Experimental support for the make-up hypothesis in nestling tawny owls (Strix aluco)

Body condition can affect coloration of traits used in sexual selection and parent-offspring communication by inducing rapid internal changes in pigment concentration or aggregation, thickness of collagen arrays, or blood flux. The recent "makeup hypothesis" proposes an alternative honesty-reinforcing mechanism, with behaviorally mediated deposition of substances on body surfaces ("cosmetics") generating covariation between body condition and coloration. In birds, the uropygial gland wax is actively spread on feathers using the bill and changes in its deposition rate may cause rapid changes in bill and plumage coloration. Using tawny owl nestlings, we tested 3 predictions of the makeup hypothesis, namely that 1) quantity of preen wax deposited accounts for variation in bill coloration, 2) an immune stimulation (induced by injection of a lipopolysaccharide [LPS]) impairs uropygial gland wax production, and 3) different intensities of immune stimulations (strong vs. weak stimulations induced by injections of either LPS or phytohemagglutinin [PHA], respectively) and high versus low food availabilities result in different bill colorations. We found that 1) preen wax reduced bill brightness, 2) a challenge with LPS impaired uropygial gland development, and 3) nestlings challenged with LPS had a brighter bill than PHA-injected nestlings, whereas diet manipulation had no significant effect. Altogether, these results suggest that a strong immune challenge may decrease preen wax deposition rate on the bill of nestling birds, at least by impairing gland wax production, which causes a change in bill coloration. Our study therefore highlights that cosmetic colors might signal short-term variation in immunological status.

A link between eumelanism and calcium physiology in the barn owl.

In many animals, melanin-based coloration is strongly heritable and is largely insensitive to the environment and body condition. According to the handicap principle, such a trait may not reveal individual quality because the production of different melanin-based colorations often entails similar costs. However, a recent study showed that the production of eumelanin pigments requires relatively large amounts of calcium, potentially implying that melanin-based coloration is associated with physiological processes requiring calcium. If this is the case, eumelanism may be traded-off against other metabolic processes that require the same elements. We used a correlative approach to examine, for the first time, this proposition in the barn owl, a species in which individuals vary in the amount, size, and blackness of eumelanic spots. For this purpose, we measured calcium concentration in the left humerus of 85 dead owls. Results showed that the humeri of heavily spotted individuals had a higher concentration of calcium. This suggests either that plumage spottiness signals the ability to absorb calcium from the diet for both eumelanin production and storage in bones, or that lightly spotted individuals use more calcium for metabolic processes at the expense of calcium storage in bones. Our study supports the idea that eumelanin-based coloration is associated with a number of physiological processes requiring calcium.

Extra-pair paternity, testes size and testosterone level in relation to colour polymorphism in the barn owl Tyto alba

In many bird populations, individuals display one of several genetically inherited colour morphs. Colour polymorphism can be maintained by several mechanisms one of which being frequency-dependent selection with colour morphs signalling alternative mating strategies. One morph may be dominant and territorial, and another one adopt a sneaky behaviour to gain access to fertile females. We tested this hypothesis in the barn owl Tyto alba in which coloration varies from reddish-brown to white. This trait is heritable and neither sensitive to the environment in which individuals live nor to body condition. In Switzerland, reddish-brown males were observed to feed their brood at a higher rate and to produce more offspring than white males. This observation lead us to hypothesize that white males may equalise fitness by investing more effort in extra-pair copulations. This hypothesis predicts that lighter Coloured males produce more extra-pair young, have larger testes and higher levels of circulating testosterone. However, our results are not consistent with these three predictions. First, paternity analyses of 54 broods with a total of 211 offspring revealed that only one young was not sired by the male that was feeding it. Second, testes size was not correlated with male plumage coloration suggesting that white males are not sexually more active. Finally, in nestlings at the time of feather growth testosterone level was not related to plumage coloration suggesting that this androgen is not required for the expression of this plumage trait. Our study therefore indicates that in the barn owl colour polymorphism plays no role in the probability of producing extra-pair young.

Linkage disequilibrium between a melanin-based colour polymorphism and tail length in the barn owl

A linkage disequilibrium between sexually selected and life history traits can be explained by three mutually non-exclusive mechanisms. Genes coding for two traits may be located close on the same chromosome, genes responsible for variation in one of the trait may pleiotropically alter the other, and non-random pairing with respect to two traits may generate a non-physical linkage disequilibrium between their genes. Knowledge of which of these three mechanisms is responsible for a covariation between two traits is of interest to understand why differently ornamented individuals differ in several phenotypic aspects. In Switzerland, barn owls Tyto alba mate randomly with respect to a colour polymorphism generating a large range of variants between reddish-brown and white, males being lighter coloured than females. Several studies have shown that plumage coloration is not neutral with respect to some life history components. To test whether coloration is genetically associated with body size, partial cross-fostering experiments were performed by exchanging some hatchlings between nests. These experiments showed that darker biological fathers produce longer-tailed offspring. This sex-specific pattern is consistent with the hypothesis of non-physical linkage disequilibrium. In line with this hypothesis, darker coloured males were mated with longer-tailed females, whereas female coloration was not associated with tail length of their mate. The finding that dark nestlings had a longer tail than their pale siblings also supports the physical linkage and pleiotropy hypotheses. Therefore, non-random pairing can generate or strengthen a genetic covariation between a secondary sexual character and a morphological trait.

Characterising avian haemosporidian communities : ecological factors, parasite persistence and co-infection

Les parasites jouent un rôle clef dans l'évolution des comportements et des traits d'histoire de vie de leurs hôtes. Le parasitisme s'avère parfois dévastateur à l'échelle de population d'hôtes, et peut également altérer certains traits associés à la valeur sélective d'un individu infecté, tels que son succès reproducteur ou encore son taux de mortalité. La coévolution hôte/parasite, qui représente l'une des forces sélectives les plus puissantes dans l'évolution des organismes, peut également conduire les partenaires de l'association parasitaire à s'adapter localement à des environnements hétérogènes. Cette thèse porte sur l'étude de parasites aviaires, du genre Plasmodium, Haemopro- teus et Leucocytozoon (Haemosporidae), naturellement associés à différentes populations de mésanges charbonnières (Parus major) et d'hirondelles des fenêtres (Delichon ur- bicum). Dans un premier temps, nous avons cherché à déterminer comment se distribuent ces parasites au sein de différentes populations hôtes et si ces communautés de parasites sont structurées. Par la suite, la principale question à laquelle nous voulions répondre était de savoir comment ces parasites, et notamment après coexistence de plusieurs lignées génétiques d'Haemosporidae au sein dun même-individu (i.e. co-infection), affectent la physiologie et le succès de reproducteur des hôtes. Nos résultats suggèrent que la distribution des Haemosporidae est principalement gouvernée par la présence d'insectes vecteurs et que la persistance de l'infection chez les hôtes varie en fonction du genre d'Haemosporidae (Chapitre 1-2). Par ailleurs, nous avons trouvé que des lignées de parasite génétiquement distinctes peuvent avoir des effets contrastés sur leurs hôtes. Par exemple, les hôtes exhibent des différences de parasitémie marquées en fonction des lignées de parasites responsable de l'infection. De plus, le succès reproducteur ainsi que la charge parasitaire des mésanges infectées par Plasmodium ou Haemoproteus n'étaient pas affecté par l'infection simultanée avec Leucocytozoon (Chapitre 2-3). Dans le Chapitre 4, j'ai examiné la capacité immunitaire de mésanges charbonnières infectées par des hémosporidies. Les résultats n'ont pas été concluant, et je suggère fortement une réévaluation de ceux-ci dans de futures études. Les mésanges charbonnières ne semblent pas signaler leur statut infectieux par la coloration de leur plumage (Chapitre 5); toutefois, la coloration noire des plumes reflète l'état de stress oxydatif des mésanges, qui dépend lui-même de l'infection parasitaire. La coloration verte pourrait également indiquer la qualité des soins paxentaux délivrés par les mésanges adultes femelles à leurs petits, comme le suggère la corrélation que nous avons observée entre la masse des jeunes d'une nichée et la coloration de leur mère. Les hirondelles capturées en Algérie souffrent plus de l'infection que celles échantillon¬nées en Europe (Chapitre 6). Les similitudes observées entre les communautés de par¬asites affectant les populations européennes et celles des populations nord-africaines suggèrent que la transmission des parasites a lieu lors de la migration vers le sud. A l'instar de nos observations sur les mésanges dans les chapitres 2 et 3, les hirondelles co-infectées ne montrent pas d'altérations de leur condition physique. Cette thèse démontre qu'il existe, au sein des populations de mésanges charbonnières, des interactions antagonistes entre, d'une part, les parasites et leurs hôtes et d'autre part, entre différent parasites. Le résultat de ces interactions antagonistes varie en fonction des espèces et de la zone géographique considérée. Nous avons démontré que les interactions ne suivent pas toujours la théorie, puisque la coevolution qui, en suivant le concept de la virulence, devrait augmenter la charge parasitaire et diminuer la condition physique des hôtes, ne montre pourtant pas d'impact négatif sur les populations de mésanges. Nous pouvons maintenant concentrer nos efforts à la caractérisation des interactions antagonistes. De plus, grâce aux avancées des méthodes moléculaires, nous pouvons suivre et étudier en détails comment ces interactions se manifestent et quels sont leurs effets sur la condition physique des hôtes. - Parasites are key in shaping various behavioural and life-history traits of their hosts. The influence of parasitism on host populations varies from slight to devastating and might influence such parameters as mortality rates or reproductive success. Host-parasite coevolution is one of the most powerful selective forces in evolution and can lead to local adaptation of parasites and hosts in spatially structured environments. In this thesis, I studied haemosporidian parasites in different populations of great tits (Parus major) and house martins (Delichon urbicum). Firstly, I wanted to determine how parasites are distributed and if parasite communities are structured. The main question I wanted to address hereafter was how parasites, and specifically infection with multiple genera of parasites (i.e. co-infection) influenced host physiology and reproductive success. I found that parasite distribution is environmentally driven and could therefore be closely linked to vector prevalence; and that the stability of parasite infection over time is genus-dependent (Chapter 1 - 2). I further found that different haemosporidian lineages might interact differently with their hosts as parasitaemia was strongly lineage-specific and that the presence of Leucocytozoon parasites showed no correlation to Plasmodium or Haemoproteus parasitaemia, nor to great tit reproductive success (Chapter 2-3). In Chapter 4 I examined immune capacity of haemosporidian-infected great tits. The results proved inconclusive, and I strongly suggest re-evaluation hereof in future work. Great tits do not appear to signal parasite infection through plumage colouration (Chapter 5); however, infection did have a link to oxidative stress resistance which is strongly signalled through the black breast stripe, with darker males being more resistant and darker females less resistant. Females might incur different costs associated with darker stripes. This would allow reversal of signaling function. Green colouration could also serve as a cue for female provisioning quality as indicated by the strong correlation between colouration and chick body mass. Breeding house martins caught in Algeria suffer greater haemosporidian infection than European populations (Chapter 6). Similar parasite communities in European and North-African populations suggest transmission of parasites may occur during southward migration. Similarly to what was observed in great tits in Chapter 2 and 3, no relationship was found between parasite co-infection and Swiss house martin body condition. This thesis demonstrates that host-parasite and inter-parasite antagonistic interac¬tions exist in great tit populations. How these interactions play out is species dependent and varies geographically. I have demonstrated that interactions do not always follow the theory, as co-infection - which under the concept of virulence should increase parasitaemia and decrease body condition - showed no negative impact on great tit populations. We can now concentrate our efforts on characterising these antagonistic interactions, and with the advance in molecular methods, track and investigate how these interactions play out and what the effect on host fitness is.

Ontogeny of Sleeping in Color - Linking melanism to sleep architecture and rhythmicity variation in wild barn owl nestlings

The function of sleep remains unknown. To gain insight into the function of sleep in natural conditions, I assessed variation in sleep architecture and its link with fitness-related phenotypic traits. I considered melanin-based coloration because its underlying genetic basis is very well known giving an opportunity to examine whether some genes pleiotropically regulate both coloration and sleep. The melanocortin system is known to generate covariation between melanin-based coloration and other phenotypes like behaviour, physiology and life history traits. I investigated whether this system of genes could participate in the co-expression of coloration and sleep. I carried out a study with nestling barn owls (Tyto alba) in order to tackle the potential link between variation in color traits and the ontogeny of sleep under natural conditions. For this I established a suitable method for recording the brain activity (electroencephalogram) of owls in nature. Birds are especially interesting, because they convergently evolved sleep states similar to those exhibited by mammals. As in mammals, I found that in owlets time spent in rapid eye movement (REM) sleep declines with age, a relationship thought to eflect developmental changes in the brain. Thus this developmental trajectory appears to reflect a fundamental feature of sleep. Additionally, I discovered an association between a gene involved in melanism expressed in the feather follicles (proprotein convertase subtilisin/kexin type 2, PCSK2) and the age-related changes in sleep in the brain. Nestlings with higher expression levels of PCSK2 showed a more precocial pattern of sleep development and a higher degree of melanin-based coloration compared to nestlings with lower PCSK2 expression. Also sleep architecture and the development of rhythmicity in brain and physical activity was related to plumage traits of the nestlings and their biological parents. This pattern during ontogeny might reflect differences in life l history strategies, antipredator behaviour and developmental pace. Therefore, differently colored individuals may differentially deal with trade-offs between the costs and benefits of sleep which in turn lead to differences in brain organization and ultimately fitness. These results should stimulate evolutionary biologists to consider sleep as a major life history trait. Résumé La fonction du sommeil reste inconnue. Afin d'acquérir une meilleur compréhension de la fonction du sommeil dans les conditions naturelles, j'ai analysé la variation dans l'architecture du sommeil et son lien avec d'autres traits phénotypiques liés au succès reproducteur (fitness). J'ai choisi et examiné la coloration mélanique, car ses bases génétiques sont bien connues et il est ainsi possible d'étudier si certains gènes, de façon pléiotropique régulent à la fois la coloration et le sommeil. J'ai exploré si ce système génétique était impliqué dans la co-expression de la coloration et du sommeil. J'ai effectué mon étude sur des poussins de chouette effraie (Tyto alba) en condition naturelle, pour rechercher ce lien potentiel entre la variation de la coloration et l'ontogenèse du sommeil. Dans ce but, j'ai établi une méthodologie permettant d'enregistrer l'activité cérébrale (électroencéphalogramme) des chouettes dans la nature. Les oiseaux sont particulièrement intéressants car ils ont développé, par évolution convergente, des phases de sommeil similaires à celles des mammifères. De manière semblable à ce qui a été montré chez les mammifères, j'ai découvert que le temps passé dans le sommeil paradoxal diminue avec l'âge des poussins. On pense que ceci est dû aux changements développementaux au niveau du cerveau. Cette trajectoire développementale semble refléter une caractéristique fondamentale du sommeil. J'ai également découvert une association entre l'un des gènes impliqué dans le mélanisme, exprimé dans les follicules plumeux (proprotein convertase subtilisin/kexin type 2, PCSK2), et les changements dans la structure du sommeil avec l'âge. Les poussins ayant un niveau d'expression génétique élevé de la PCSK2 présentent une structure du sommeil plus précoce et un taux de coloration dû à la mélanine plus élevé que des poussins avec un niveau d'expression moindre de la PCSK2. L'architecture du sommeil et le développement de la rythmicité dans le cerveau ainsi que l'activité physique sont également liés à la coloration des plumes des poussins et pourraient ainsi refléter des différences de stratégies d'histoire de vie, de comportements anti-prédateur et de vitesses développementales. Ainsi, des individus de coloration différente sembleraient traiter différemment les coûts et les bénéfices du sommeil, ce qui aurait des conséquences sur l'organisation cérébrale et pour finir, sur le succès reproducteur. Ces résultats devraient encourager les biologistes évolutionnistes à considérer le sommeil comme un important trait d'histoire de vie. Zusammenfassung Die Funktion von Schlaf ist noch unbekannt. Um mehr Einsicht in diese unter natürlichen Bedingungen zu bekommen, habe ich die Variation in der Schlafarchitektur und die Verknüpfung mit phänotypischen Merkmalen, die mit der Fitness zusammenhängen, studiert. Ich habe mir melanin-basierte Färbung angesehen, da die zugrunde liegende genetische Basis bekannt ist und somit die Möglichkeit gegeben ist, zu untersuchen, ob einige Gene beides regulieren, Färbung und Schlaf. Das melanocortin System generiert eine Kovariation zwischen melanin-basierter Färbung und anderen phänotypischer Merkmale wie Verhalten, Physiologie und Überlebensstrategien. Ich habe untersucht, ob dieses Gensystem an einer gleichzeitigen Steuerung von Färbung und Schlaf beteiligt ist. Dazu habe ich Schleiereulen (Tyto alba) studiert um einen möglichen Zusammenhang zwischen der Variation in der Pigmentierung und der Entwicklung des Schlafs unter natürlichen Bedingungen zu entdecken. Für diese Studie entwickelte ich eine Methode um die Gehirnaktivität (Elektroenzephalogramm) bei Eulen in der Natur aufzunehmen. Vögel sind besonders interessant, da sie die gleichen Schlafstadien aufweisen wie Säugetiere und diese unabhängig konvergent entwickelt haben. Genauso wie bei Säugetieren nahm die Dauer des sogenannten ,,rapid eye movement" (REM) - Schlafes mit zunehmendem Alter ab. Es wird angenommen, dass dieser Zusammenhang die Entwicklung des Gehirns widerspiegelt. Daher scheint dieses Entwicklungsmuster ein fundamentaler Aspekt von Schlaf zu sein. Zusätzlich entdeckte ich einen Zusammenhang zwischen der Aktivität eines Gens in den Federfollikeln (proprotein convertase subtilisin/kexin type 2, PCSK2), das für die Ausprägung schwarzer Punkte auf den Federn der Eulen verantwortlich ist, und den altersabhängigen Änderungen im Schlafmuster im Gehirn. Küken mit höherer Aktivität von PCSK2 zeigten eine frühreifere Schlafentwicklung und eine dunklere Färbung als Küken mit niedriger PCSK2 Aktivität. Die Architekture des Schlafes und die Entwicklung der Rhythmik im Gehirn und die der physischen Aktivität ist mit der Färbung des Gefieders von den Küken und ihren Eltern verknüpft. Dieses Muster während der Entwicklung kann Unterschiede in Überlebensstrategien, Feindabwehrverhalten und in der Entwicklungsgeschwindigkeit reflektieren. Unterschiedlich gefärbte Individuen könnten unterschiedliche Strategien haben um zwischen den Kosten und Nutzen von Schlaf zu entscheiden, was zu Unterschieden in der Gehirnstruktur führen kann und letztendlich zur Fitness. Diese Ergebnisse sollten Evolutionsbiologen stimulieren Schlaf als einen wichtigen Bestandteil des Lebens zu behandeln.

Darker eumelanic barn owls better withstand food depletion through resistance to food deprivation and lower appetite.

The intensity of selection exerted on ornaments typically varies between environments. Reaction norms may help to identify the conditions under which ornamented individuals have a selective advantage over drab conspecifics. It has been recently hypothesized that in vertebrates eumelanin-based coloration reflects the ability to regulate the balance between energy intake and expenditure. We tested two predictions of this hypothesis in barn owl nestlings, namely that darker eumelanic individuals have a lower appetite and lose less weight when food-deprived. We found that individuals fed ad libitum during 24 h consumed less food when their plumage was marked with larger black spots. When food-deprived for 24 h nestlings displaying larger black spots lost less weight. Thus, in the barn owl the degree of eumelanin-based coloration reflects the ability to withstand periods of food depletion through lower appetite and resistance to food restriction. Eumelanic coloration may therefore be associated with adaptations to environments where the risk of food depletion is high.

Proximate basis of the covariation between a melanin-based female ornament and offspring quality.

In contradiction to sexual selection theory, several studies showed that although the expression of melanin-based ornaments is usually under strong genetic control and weakly sensitive to the environment and body condition, they can signal individual quality. Covariation between a melanin-based ornament and phenotypic quality may result from pleiotropic effects of genes involved in the production of melanin pigments. Two categories of genes responsible for variation in melanin production may be relevant, namely those that trigger melanin production (yes or no response) and those that determine the amount of pigments produced. To investigate which of these two hypotheses is the most likely, I reanalysed data collected from barn owls ( Tyto alba). The underparts of this bird vary from immaculate to heavily marked with black spots of varying size. Published cross-fostering experiments have shown that the proportion of the plumage surface covered with black spots, a eumelanin composite trait so-called "plumage spottiness", in females positively covaries with offspring humoral immunocompetence, and negatively with offspring parasite resistance (i.show $132#e. the ability to reduce fecundity of ectoparasites) and fluctuating asymmetry of wing feathers. However, it is unclear which component of plumage spottiness causes these relationships, namely genes responsible for variation in number of spots or in spot diameter. Number of spots reflects variation in the expression of genes triggering the switch from no eumelanin production to production, whereas spot diameter reflects variation in the expression of genes determining the amount of eumelanin produced per spot. In the present study, multiple regression analyses, performed on the same data sets, showed that humoral immunocompetence, parasite resistance and wing fluctuating asymmetry of cross-fostered offspring covary with spot diameter measured in their genetic mother, but not with number of spots. This suggests that genes responsible for variation in the quantity of eumelanin produced per spot are responsible for covariation between a melanin ornament and individual attributes. In contrast, genes responsible for variation in number of black spots may not play a significant role. Covariation between a eumelanin female trait and offspring quality may therefore be due to an indirect effect of melanin production.

Manipulating sex ratio to increase population growth: the example of the Lesser Kestrel

Small or decreasing populations call for emergency actions like, for example, captive breeding programs. Such programs aim at rapidly increasing population sizes in order to reduce the loss of genetic variability and to avoid possible Allee effects. The Lesser Kestrel Falco naumanni is one of the species that is currently supported in several captive breeding programs at various locations. Here, we model the demographic and genetic consequences of potential management strategies that are based on offspring sex ratio manipulation. Increased population growth could be achieved by manipulating female conditions and/or male attractiveness in the captive breeders and consequently shifting the offspring sex ratio towards more female offspring, which are then used for reintroduction. Fragmenting populations into wild-breeding and captive-breeding demes and manipulating population sex ratio both immediately increase the inbreeding coefficient in the next generation (i.e. decrease N-e) but may, in the long term, reduce the loss of genetic variability if population growth is restricted by the number of females. We use the Lesser Kestrel and the wealth of information that is available on this species to predict the long-term consequences of various kinds of sex-ratio manipulation. We find that, in our example and possibly in many other cases, a sex-ratio manipulation that seems realistic could have a beneficial effect on the captive breeding program. However, the possible long-term costs and benefits of such measures need to be carefully optimized.

Melanic color-dependent anti-predator behavior strategies in barn owl nestlings

The arms race between predators and prey has led to morphological and behavioral adaptations. Different antipredator strategies can coexist within a population if each strategy is the result of a trade-off with competing demands. Antipredator behavior can be associated with morphological traits, like color patterns, either because in the context of sexual selection, coloration signals the ability to avoid predators or because coloration is a naturally selected trait useful in avoiding predators. Because in the barn owl (Tyto alba), heritable eumelanic plumage coloration is associated with the glucocorticoid-dependent response to stress, we tested whether antipredator behavior is also related to this trait. Compared with small-spotted nestlings, individuals displaying larger black spots hissed more intensely in the presence of humans, feigned death longer, had a lower breathing rate under stress, and were more docile when handled. Cross-fostering experiments showed that the covariation between the spot size and the duration of feigning death was inherited from the biological mother, whereas covariation between spot size and docility was inherited from the biological father. Our results confirm that melanin-based coloration is associated with suites of behavioral traits, which are under both genetic and environmental influence. Coloration can thus evolve as a direct or indirect response to predation, but it can also be a signal of antipredator strategies to potential mates.