Isabelle Henry

Spatio-temporal population genetic structure of the parasitic mite Spinturnix bechsteini is shaped by its own demography and the social system of its bat host.

Information about the population genetic structures of parasites is important for an understanding of parasite transmission pathways and ultimately the co‐evolution with their hosts. If parasites cannot disperse independently of their hosts, a parasite’s population structure will depend upon the host’s spatial distribution. Geographical barriers affecting host dispersal can therefore lead to structured parasite populations. However, how the host’s social system affects the genetic structure of parasite populations is largely unknown. We used mitochondrial DNA (mtDNA) to describe the spatio‐temporal population structure of a contact‐transmitted parasitic wing mite (Spinturnix bechsteini) and compared it to that of its social host, the Bechstein’s bat (Myotis bechsteinii). We observed no genetic differentiation between mites living on different bats within a colony. This suggests that mites can move freely among bats of the same colony. As expected in case of restricted inter‐colony dispersal, we observed a strong genetic differentiation of mites among demographically isolated bat colonies. In contrast, we found a strong genetic turnover between years when we investigated the temporal variation of mite haplotypes within colonies. This can be explained with mite dispersal occuring between colonies and bottlenecks of mite populations within colonies. The observed absence of isolation by distance could be the result from genetic drift and/or from mites dispersing even between remote bat colonies, whose members may meet at mating sites in autumn or in hibernacula in winter. Our data show that the population structure of this parasitic wing mite is influenced by its own demography and the peculiar social system of its bat host.

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 24xa0h consumed less food when their plumage was marked with larger black spots. When food-deprived for 24xa0h 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.

Linking melanism to brain development: expression of a melanism-related gene in barn owl feather follicles covaries with sleep ontogeny

BackgroundIntra-specific variation in melanocyte pigmentation, common in the animal kingdom, has caught the eye of naturalists and biologists for centuries. In vertebrates, dark, eumelanin pigmentation is often genetically determined and associated with various behavioral and physiological traits, suggesting that the genes involved in melanism have far reaching pleiotropic effects. The mechanisms linking these traits remain poorly understood, and the potential involvement of developmental processes occurring in the brain early in life has not been investigated. We examined the ontogeny of rapid eye movement (REM) sleep, a state involved in brain development, in a wild population of barn owls (Tyto alba) exhibiting inter-individual variation in melanism and covarying traits. In addition to sleep, we measured melanistic feather spots and the expression of a gene in the feather follicles implicated in melanism (PCSK2).ResultsAs in mammals, REM sleep declined with age across a period of brain development in owlets. In addition, inter-individual variation in REM sleep around this developmental trajectory was predicted by variation in PCSK2 expression in the feather follicles, with individuals expressing higher levels exhibiting a more precocial pattern characterized by less REM sleep. Finally, PCSK2 expression was positively correlated with feather spotting.ConclusionsWe demonstrate that the pace of brain development, as reflected in age-related changes in REM sleep, covaries with the peripheral activation of the melanocortin system. Given its role in brain development, variation in nestling REM sleep may lead to variation in adult brain organization, and thereby contribute to the behavioral and physiological differences observed between adults expressing different degrees of melanism.

Melanin-specific life-history strategies.

The maintenance of genetic variation is a long-standing issue because the adaptive value of life-history strategies associated with each genetic variant is usually unknown. However, evidence for the coexistence of alternative evolutionary fixed strategies at the population level remains scarce. Because in the tawny owl (Strix aluco) heritable melanin-based coloration shows different physiological and behavioral norms of reaction, we investigated whether coloration is associated with investment in maintenance and reproduction. Light melanic owls had lower adult survival compared to dark melanic conspecifics, and color variation was related to the trade-off between offspring number and quality. When we experimentally enlarged brood size, light melanic males produced more fledglings but in poorer condition, and they were less often recruited in the local breeding population than those of darker melanic conspecifics. Our results also suggest that dark melanic males allocate a constant effort to raise their brood independently of environmental conditions, whereas lighter melanic males finely adjust reproductive effort in relation to changes in environmental conditions. Color traits can therefore be associated with life-history strategies, and stochastic environmental perturbation can temporarily favor one phenotype over others. The existence of fixed strategies implies that some phenotypes can sometimes display a “maladapted” strategy. Long-term population monitoring is therefore vital for a full understanding of how different genotypes deal with trade-offs.

Barn Owl (Tyto alba) breeding biology in relation to breeding season climate

AbstractWinter weather has a strong influence on Barn Owl (Tyto alba) breeding biology. Here, we analyzed the impacts of weather conditions on reproductive performance during the breeding season using data collected over 22xa0years in a Swiss Barn Owl population. Variations in rain and temperature during the breeding season played an important role in within-year variation in Barn Owl reproduction. An increase in rainfall during the period from 4 to 2xa0weeks preceding egg laying had a positive effect on clutch size. In contrast, fledgling body mass was negatively influenced by rainfall during the 24xa0h preceding the measurements. Finally, ambient temperature during the rearing period was positively associated with brood size at fledging. In conclusion, weather conditions during the breeding season place constraints on Barn Owl reproduction.ZusammenfassungDer Einfluss der Witterung während der Brutzeit auf die Brutbiologie der Schleiereule (Tyto alba)n Jährliche Unterschiede im Wetter im Winter und Unterschiede in den Nahrungsbedingungen kurz vor der Brutperiode haben einen großen Einfluss auf die Brutbiologie der Schleiereule. Anhand eines Langzeitdatensatzes von 22 Jahren untersuchten wir verschiedene Wettereinflüsse auf die Fortpflanzungsleistung einer schweizerischen Schleiereulenpopulation. Regenmenge und Temperatur während der Brutsaison spielten eine wichtige Rolle, um den individuellen Unterschied in der Fortpflanzung der Schleiereulenpaare zu erklären. Je mehr es während vier bis zwei Wochen vor Legebeginn regnete, desto grösser war das Gelege. Die Körpermasse der Nestlinge kurz vor dem Ausfliegen war dagegen durch Regen während 24 Stunden vor der Messung beeinträchtigt. Auch hatte die Umgebungstemperatur während der Aufzuchtzeit einen positiven Effekt auf die Anzahl Nestlinge, die bis zum Ausfliegen überlebten. Zusammenfassend kann gesagt werden, dass sich die Wetterbedingungen während der Brutsaison limitierend auf die Fortpflanzung der Schleiereulen auswirken.

Multiple paternity in polyandrous barn owls (Tyto alba).

In polyandrous species females produce successive clutches with several males. Female barn owls (Tyto alba) often desert their offspring and mate to produce a 2nd annual brood with a second male. We tested whether copulating during chick rearing at the 1st annual brood increases the males likelihood to obtain paternity at the 2nd annual breeding attempt of his female mate in case she deserts their brood to produce a second brood with a different male. Using molecular paternity analyses we found that 2 out of 26 (8%) second annual broods of deserting females contained in total 6 extra-pair young out of 15 nestlings. These young were all sired by the male with whom the female had produced the 1st annual brood. In contrast, none of the 49 1st annual breeding attempts (219 offspring) and of the 20 2nd annual breeding attempts (93 offspring) of non-deserting females contained extra-pair young. We suggest that female desertion can select male counter-strategies to increase paternity and hence individual fitness. Alternatively, females may copulate with the 1st male to derive genetic benefits, since he is usually of higher quality than the 2nd male which is commonly a yearling individual.

Barn owls do not interrupt their siblings

Animals communicate with conspecifics to resolve conflicts over how resources are shared. Since signals reflect individuals resource-holding potential and motivation to compete, it is crucial that opponents efficiently transmit and receive information to adjust investment optimally in competitive interactions. Acoustic communication is particularly flexible as it can be quickly modulated according to background noise and audience. Diverse mechanisms have evolved to minimize acoustic signal interference, one being the avoidance of signal overlap by adjusting the timing of call production to alternate calls with those of competitors. However, the occurrence and function of overlap avoidance in the resolution of competition among relatives have barely been studied. Using young barn owl siblings, Tyto alba, which vocally negotiate over who will have priority access to food provided by parents, we investigated the extent to which nestlings avoid calling simultaneously and the function of this behaviour. We found that nestlings overlapped both their live siblings calls and experimentally broadcast calls at least five times less often than expected at random. Furthermore, a focal nestling engaged more intensely in vocal negotiation when competing with nestmates that called simultaneously compared to those that did not overlap their respective calls. This suggests that barn owl nestlings avoid calling simultaneously, as overlapped calls are less efficient at deterring siblings from competing. Overlap avoidance reduces signal interference and, as a consequence, would improve the efficiency of communication among kin.

Sex- and melanism-specific variations in the oxidative status of adult tawny owls in response to manipulated reproductive effort.

ABSTRACT Oxidative stress, determined by the balance between the production of damaging reactive oxygen species (ROS) and antioxidant defences, is hypothesized to play an important role in shaping the cost of reproduction and life history trade-offs. To test this hypothesis, we manipulated reproductive effort in 94 breeding pairs of tawny owls (Strix aluco) to investigate the sex- and melanism-specific effects on markers of oxidative stress in red blood cells (RBCs). This colour polymorphic bird species shows sex-specific division of labour and melanism-specific history strategies. Brood sizes at hatching were experimentally enlarged or reduced to increase or decrease reproductive effort, respectively. We obtained an integrative measure of the oxidative balance by measuring ROS production by RBCs, intracellular antioxidant glutathione levels and membrane resistance to ROS. We found that light melanic males (the sex undertaking offspring food provisioning) produced more ROS than darker conspecifics, but only when rearing an enlarged brood. In both sexes, light melanic individuals had also a larger pool of intracellular antioxidant glutathione than darker owls under relaxed reproductive conditions (i.e. reduced brood), but not when investing substantial effort in current reproduction (enlarged brood). Finally, resistance to oxidative stress was differently affected by the brood size manipulation experiment in males and females independently of their plumage coloration. Altogether, our results support the hypothesis that reproductive effort can alter the oxidative balance in a sex- and colour-specific way. This further emphasizes the close link between melanin-based coloration and life history strategies. Summary: Effects of manipulated reproductive effort on oxidative status differ between sexes and colour morphs in a melanin-based polymorphic raptor species with a strong division of labour between the sexes.

Nocturnal, diurnal and bimodal patterns of locomotion, sibling interactions and sleep in nestling Barn Owls

AbstractTemporal variation in physical activity is mainly determined by the day–night cycle. While this may be true for diurnal species whose vision at night is often poor, the situation might be more complex in nocturnal animals as many such species can see both in the dark and in the daylight. We examined in Barn Owl (Tyto alba) nestlings whether temporal variation of behavioural activities and sleep is shaped by parental feeding visits occurring during the first part of the night and the extent to which they also occur during daylight hours. We measured several behaviours in 280 individuals from 90 broods recorded in 4 years. Parental feeding visits progressively declined in frequency from the beginning to the end of the night, and a number of offspring behaviours followed the same pattern of activity (feeding, vocalization and self-preening). Surprisingly, nestlings were awake not only at sunset, but also at sunrise. Several behaviours (locomotion, wing flapping and sibling interactions, such as pecking and allopreening among nestlings) showed peaks of activity at sunset and sunrise, suggesting that they were performed for other reasons than to interact with parents. Allopreening was performed more often during the day than at night. We conclude that although adult Barn Owls are nocturnal, nestlings display a complex temporal pattern of activity that is governed not only by feeding but also by other unknown factors.ZusammenfassungNächtliche, tägliche und bimodale Muster der Lokomotion, der Interaktionen mit Geschwistern und des Schlafs bei Schleiereulennestlingenn Der zeitliche Verlauf der körperlichen Aktivität wird hauptsächlich vom Tag-Nacht-Rhythmus bestimmt. Besonders tagaktive Arten sind oft nicht in der Lage nachts zu sehen, während nachtaktive Arten sowohl am Tag als auch nachts sehen können. Wir untersuchten an Schleiereulennestlingen (Tyto alba), ob zeitliche Variation von Verhalten und Gehirnaktivität von den elterlichen Besuchen in der ersten Hälfte der Nacht abhängen und ob Aktivitäten während des Tages ausgeführt werden. Wir bestimmten Verhaltensweisen von 280 Individuen aus 90 Bruten über vier Jahre. Elterliche Fütterungsbesuche nahmen über die Nacht stetig in der Frequenz ab, und einige der Verhaltensweisen der Nestlinge folgten diesem Muster (Fressen, Rufen und Putzen). Erstaunlicherweise waren Nestlinge nicht nur bei Sonnenuntergang wach, sondern auch bei Sonnenaufgang. Einige Verhaltensweisen (Lokomotion, Flügel schlagen und Interaktionen mit Geschwistern wie Picken und gegenseitiges Putzen) zeigten hohe Aktivität bei Sonnenuntergang und –aufgang, was darauf hindeutet, dass sie aus anderen Gründen ausgeführt wurden als mit den Eltern zu interagieren. Gegenseitiges Putzen wurde tagsüber öfter durchgeführt als nachts. Zusammenfassend ist zu sagen, dass Schleiereulen zwar nachtaktiv sind, Nestlinge aber ein komplexes Aktivitätsmuster zeigen, das durch die elterliche Fütterung vorgegeben ist, aber auch durch weitere, noch unbekannte Faktoren bestimmt ist.

Ultradian Rhythmicity in Sleep-Wakefulness Is Related to Color in Nestling Barn Owls:

The possession of a rhythm is usually described as an important adaptation to regular changing environmental conditions such as the light-dark cycle. However, recent studies have suggested plasticity in the expression of a rhythm depending on life history and environmental factors. Barn owl (Tyto alba) nestlings show variations in behavior and physiology in relation to the size of black feather spots, a trait associated with many behavioral and physiological phenotypes including the circadian expression of corticosterone and the regulation of body mass. This raises the possibility that individual spottiness could be associated with rhythmicity in sleep-wakefulness. Owlets showed ultradian rhythms in sleep-wakefulness, with a period length of 4.5 to 4.9 h. The period length of wakefulness and non-REM sleep was shorter in heavily compared to lightly spotted female nestlings, whereas in males, the opposite result was found. Furthermore, male and female nestlings displaying small black spots showed strong rhythmicity levels in wakefulness and REM sleep. This might be an advantage in a stable environment with predictable periodic changes in light, temperature, or social interactions. Heavily spotted nestlings displayed weak rhythms in wakefulness and REM sleep, which might enable them to be more flexible in reactions to unexpected events such as predation or might be a mechanism to save energy. These findings are consistent with previous findings showing that large-spotted nestlings switch more frequently between wakefulness and sleep, resulting in higher levels of vigilance compared to small-spotted conspecifics. Thus, nestlings with larger black feather spots might differently handle the trade-off between wakefulness and sleep, attention, and social interactions compared to nestlings with smaller black spots.