Isolation and characterization of 21 microsatellite markers in the barn owl (Tyto alba)

We report 21 new polymorphic microsatellite markers in the European barn owl (Tyto alba). The polymorphism of the reported markers was evaluated in a population situated in western Switzerland and in another from Tenerife, Canary Islands. The number of alleles per locus varies between two and 31, and expected heterozygosity per population ranges from 0.16 to 0.95. All loci are in Hardy-Weinberg equilibrium and no linkage disequilibrium was detected. Two loci exhibit a null allele in the Tenerife population.     

Nonrandom pairing by male barn owls (Tyto alba) with respect to a female plumage trait

In socially monogamous species it is rare for females to bemore intensely colored than males. The barn owl (Tyto alba)is one of the exceptions, as females usually exhibit more andlarger black spots on the plumage. The evolution of sexual dimorphismin plumage traits is commonly assumed to be the result of sexualselection. I therefore examined the prediction that male barnowls do not pair randomly with respect to female plumage spottinessduring a 5-year study in Switzerland. The prediction was supported,as males that changed mates acquired a new female that was similarlyspotted to the previous one, and pairing with respect to plumage spottinesswas positively assortative. Significant repeatability in male pairingwas presumably neither the consequence of sharing the same habitats withfemales displaying a given plumage spottiness nor of morphological characteristicsof the males that could influence mate sampling. A resemblance inplumage spottiness between the mates of sons and of their fathersuggests that repeatability could have resulted from sexualimprinting and/or heritable variance in male preference forspotted females. To test whether males assess female plumagespottiness, I either cut off black spots or small pieces of feathersbut not the spots of already mated females. Males mated to females withreduced plumage spottiness fed their brood at a lower cadencyand achieved a lower reproductive success than other males.This experiment further suggests that female plumage spottinessis a stimulus for males.     

巴基斯坦旁遮普中部仓鸮食性的季节性变化

在巴基斯坦对仓鸮食性的季节变化进行了研究。通过分析连续3年在6个地区搜集的2 360个仓鸮回吐食物团,发现其食物主要是小型哺乳动物(95.6 %)。其中,家(Suncus murinus)有最高的比例,达65.6%(冬季最多78%,夏季最少27%)。就生物量而言,小型哺乳动物占仓鸮食物总生物量的99% 。     

Origin-related, environmental, sex, and age determinants of immunocompetence, susceptibility to ectoparasites, and disease symptoms in the barn owl

Knowledge of the role of origin‐related, environmental, sex, and age factors on host defence mechanisms is important to understand variation in parasite intensity. Because alternative components of parasite defence may be differently sensitive to various factors, they may not necessarily covary. Many components should therefore be considered to tackle the evolution of host–parasite interactions. In a population of barn owls (Tyto alba), we investigated the role of origin‐related, environmental (i.e. year, season, nest of rearing, and body condition), sex, and age factors on 12 traits linked to immune responses [humoral immune responses towards sheep red blood cells (SRBC), human serum albumin (HSA) and toxoid toxin TT, T‐cell mediated immune response towards the mitogen phytohemagglutinin (PHA)], susceptibility to ectoparasites (number and fecundity of Carnus haemapterus, number of Ixodes ricinus), and disease symptoms (size of the bursa of Fabricius and spleen, proportion of proteins that are immunoglobulins, haematocrit and blood concentration in leucocytes). Cross‐fostering experiments allowed us to detect a heritable component of variation in only four out of nine immune and parasitic parameters (i.e. SRBC‐ and HSA‐responses, haematocrit, and number of C. haemapterus). However, because nestlings were not always cross‐fostered just after hatching, the finding that 44% of the immune and parasitic parameters were heritable is probably an overestimation. These experiments also showed that five out of these nine parameters were sensitive to the nest environment (i.e. SRBC‐ and PHA‐responses, number of C. haemapterus, haematocrit and blood concentration in leucocytes). Female nestlings were more infested by the blood‐sucking fly C. haemapterus than their male nestmates, and their blood was less concentrated in leucocytes. The effect of year, season, age (i.e. reflecting the degree of maturation of the immune system), brood size, position in the within‐brood age hierarchy, and body mass strongly differed between the 12 parameters. Different components of host defence mechanisms are therefore not equally heritable and sensitive to environmental, sex, and age factors, potentially explaining why most of these components did not covary. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90 , 703–718.     

Directional hearing in the barn owl (Tyto alba)

Summary The acoustical properties of the external ear of the barn owl (Tyto alba) were studied by measuring sound pressure in the ear canal and outer ear cavity. Under normal conditions, pressure amplification by the external ear reaches about 20 dB between 3–9 kHz but decreases sharply above 10 kHz. The acoustic gain curve of the outer ear cavity alone is close to that of a finite-length exponential horn between 1.2–13 kHz with maximum gain reaching 20 dB between 5–9 kHz. Pressure gain by the facial ruff produces a maximum of 12 dB between 5–8 kHz and decreases rapidly above 9 kHz.The directional sensitivity of the external ear was obtained from pressure measurements in the ear canal. Directivity of the major lobe is explained, to a first approximation, by the sound diffraction properties of a circular aperture. Aperture size is based on the average radius (30 mm) of the open face of the ruff. Above 5 kHz, the external ear becomes highly directional and there is a 26° disparity in elevation between the acoustic axis of the left and right ear. In azimuth, directivity patterns are relocated closer to the midline as frequency increases and the acoustic axis moves at a rate of 20°/octave between 2–13 kHz. Movement of the axis can be explained, to a first approximation, by the acoustical diffraction properties of an obliquely truncated horn, due to the asymmetrical shape of the outer ear cavity.The directional sensitivity of the barn owl ear was studied by recording cochlear microphonic (CM) potentials from the round window membrane. Between 3–9 kHz, CM directivity patterns are clearly different to the directivity patterns of the external ear; CM directionality is abruptly lost above 10 kHz. Above 5 kHz, CM directivity patterns are characterized by an elongated major lobe containing the CM axis, forming a tilted band of high amplitude but low directionality (CM axial plane), closely bordered by minima or nulls. The highest directionality is found in theCM directional plane, approximately perpendicular to the CM axial plane. The left and right ear axial planes are symmetrical about the interaural midline (tilted 12° to the right of the midline of the head) and inclined by an average of 60° to the left and right respectively. In azimuth, the CM axis moves towards the midline at a rate of 37°/octave as frequency increases from 2–9 kHz, crossing into contralateral space near 7 kHz. In the CM directional plane, the directivity of the major lobe suggests that a pressure gradient may occur at the TM. The region of frontal space mapped by movement of the CM axis in azimuth closely matches the angle of sound incidence which would be expected to produce the maximum driving pressure at the TM. It is suggested that acoustical interference at the TM results from sound transmission through the interaural canal and therefore the ear is inherently directional. It is proposed that ear directionality in the barn owl may be explained by the combined effect of sound diffraction by the outer ear cavity and a pressure gradient at the TM.Abbreviations CM cochlear microphonic - RMS root mean square - SPL sound pressure level - TM tympanic membrane     

Female‐ and male‐specific signals of quality in the barn owl

Most bird studies of female signalling have been confined to species in which females display a male‐ornament in a vestigial form. However, a great deal of benefit may be gained from considering phenotypic traits that are specific to females. This is because (1) sex‐specific traits may signal sex‐specific qualities and (2) females may develop a male‐ornament not because they are selected to do so, but because fathers transmit to daughters the underlying genes for its expression (genetic correlation between the sexes). We investigated these two propositions in the barn owl Tyto alba, a species in which male plumage is lighter in colour and less marked with black spots than that of females. Firstly, we present published evidence that female plumage spottiness reflects parasite resistance ability. We also show that male plumage coloration is correlated with reproductive success, male feeding rate and heart mass. Secondly, cross‐fostering experiments demonstrate that plumage coloration and spottiness are genetically correlated between the sexes. This implies that if a given trait value is selected in one sex, the other sex will indirectly evolve towards a similar value. This prediction is supported by the observation that female plumage coloration and spottiness resembled that of males, in comparisons at the level of Tyto alba alba populations, Tyto alba subspecies and Tyto species. Our results therefore support the hypothesis that sex‐specific traits signal sex‐specific qualities and that a gene for a sex‐specific trait can be expressed in the other sex as the consequence of a genetic correlation between the sexes.     

Changes in the food of British Barn Owls (Tyto alba) between 1974 and 1997

Comparison of the results of a 1993–97 Barn Owl Tyto alba pellet survey with those of a similar survey from 1956–74 showed that Barn Owl diet had changed significantly. The primary differences were a widespread decrease in the percentage of Common Shrew Sorex araneus, combined with an increase in Pygmy Shrew Sorex minutus. The percentage of Wood and Yellow‐necked mice Apodemus sylvaticus and A. flavicollis and Bank Vole Clethrionomys glareolus in the diet also increased. Changes in Barn Owl diet since 1974 were independent of land‐class group, but were dependent upon region. This was due primarily to a large increase in the percentage of Apodemus spp. in Eastern England. Whilst the percentage of Pygmy Shrew in Barn Owl diet showed significant regional variation, there was no significant variation between land‐class groups. The diversity of Barn Owl diet increased between 1974 and 1997, although it was still lower in 1997 than earlier in the century. This increase was dependent upon region, but independent of land‐class group. The combined results of both surveys showed significant interland‐class group variation in dietary diversity. Changes in diet are discussed in relation to the intensification of agriculture and other changes in land management since the 1970s. The effects on Barn Owls of these changes in prey abundance are discussed, particularly in relation to the decline in Barn Owl numbers during the twentieth century.     

Isolation and characterization of major histocompatibility complex (MHC) class II B genes in the Barn owl (Aves: Tyto alba)

We isolated major histocompatibility complex class II B (MHCIIB) genes in the Barn owl (Tyto alba). A PCR-based approach combined with primer walking on genomic and complementary DNA as well as Southern blot analyses revealed the presence of two MHCIIB genes, both being expressed in spleen, liver, and blood. Characteristic structural features of MHCIIB genes as well as their expression and high non-synonymous substitution rates in the region involved in antigen binding suggest that both genes are functional. MHC organization in the Barn owl is simple compared to passerine species that show multiple duplications, and resembles the minimal essential MHC of chicken.     

Microsatellite markers characterized in the barn owl (Tyto alba) and of high utility in other owls (Strigiformes: AVES)

We have identified 15 polymorphic microsatellite loci for the barn owl (Tyto alba), five from testing published owl loci and 10 from testing non‐owl loci, including loci known to be of high utility in passerines and shorebirds. All 15 loci were sequenced in barn owl, and new primer sets were designed for eight loci. The 15 polymorphic loci displayed two to 26 alleles in 56–58 barn owls. When tested in 10 other owl species (n = 1–6 individuals), between four and nine loci were polymorphic per species. These loci are suitable for studies of population structure and parentage in owls.     

Sexually dimorphic melanin‐based colour polymorphism,feather melanin content,and wing feather structure in the barn owl (Tyto alba)

Feathers confer protection against biophysical agents and determine flying ability. The geometry and arrangement of the barbs, together with the keratin and pigments deposited in the feathers, determine the mechanical stability of the vane, and its stiffness and resistance to abrasive agents. In colour‐polymorphic species, individuals display alternative colour morphs, which can be associated with different foraging strategies. Each morph may therefore require specific flying abilities, and their feathers may be exposed to different abrasive agents. Feathers of differently coloured individuals may thus have a specific structure, and colour pigments may help resist abrasive agents and improve stiffness. We examined these predictions in the barn owl (Tyto alba), a species for which the ventral body side varies from white to dark reddish pheomelanic, and in the number and size of black spots located at the tip of the feathers. White and reddish birds show different foraging strategies, and the size of black feather spots is associated with several phenotypic attributes. We found that birds displaying a darker reddish coloration on the ventral body side deposit more melanin pigments in their remiges, which also have fewer barbs. This suggests that wear resistance increases with darkness, whereas feathers of lighter coloured birds may bend less easily. Accordingly, individuals displaying a lighter reddish coloration on the ventral body side, and those displaying larger black spots, displayed more black transverse bars on their remiges: as larger‐spotted individuals are heavier and longer‐winged birds also have more transverse bars, these bars may reduce feather bending when flying. We conclude that differently coloured individuals produce wing feathers of different strengths to adopt alternative behavioural and life history strategies. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 562–573.     

Female mating biases for bright ultraviolet iridescence in the butterfly Eurema hecabe (Pieridae)

Exaggerated male-limited coloration is widespread among butterflies,yet convincing demonstrations of intraspecific mating preferencesfor signal brightness and/or chromaticity are relatively rarein this group. Here, I couple behavioral experiments involvingmanipulations of ambient light environments and male reflectancepatterns with observation of wild mating patterns to investigatevisual mating biases in the large grass yellow (Eurema hecabe).Males in this species possess exaggerated, limited-view ultraviolet(UV) iridescence across most of their dorsal wing surface thathas putative sexual signaling function. In the first experiment,conducted in small (0.7–m³) cages, individuals were significantlyless likely to copulate when the UV portion of natural ambientillumination (i.e., 300–400 nm) was strongly reduced.In 2 subsequent experiments, conducted under full-spectrum sunlightin small and large (5 x 6 x 4 m) cages, males with their UVsignal artificially dulled by 25% consistently copulated withfewer, and smaller, females than sham-control individuals. Importantly,the manipulated levels of UV brightness in these experimentsfall well within the naturally occurring bounds of variationin male UV reflectance. These findings therefore unanimouslysupport the presence of a UV signal–based female bias.In apparent contrast, comparison of 161 in-copula and 188 free-flyingmales from a high-density field assemblage revealed that copulatingmales were significantly older and henceforth actually possessed(subtly) less UV bright wings. Copulating male UV brightnesswas, however, positively related to the size of their mate,which echoes the experimental findings and may represent a signatureof mutual mate choice. I discuss these results in light of thefull complexities of the butterfly mating system and the potentialsignaling value of iridescent coloration in butterflies andanimals generally.     

Female signals enhance the efficiency of mate assessment in satin bowerbirds (Ptilonorhynchus violaceus)

Recent evidence suggests that males adjust their sexually selecteddisplay traits in response to female behaviors during courtships.Little is known, however, about whether females signal to influencemale displays and whether females benefit from this interaction.Male courtship displays in the satin bowerbird (Ptilonorhynchusviolaceus) are highly intense and aggressive. Females may usethese displays as indicators of mating benefits, but these displaysoften startle females and disrupt courtship. Previous studieshave shown that successful males decrease female startling byadjusting their display intensity according to female crouchingbehaviors, suggesting that crouching behaviors function as signals.Here we address whether female crouching is a signal by usingobservations of natural courtship behaviors. In addition, weexamine why females differ in signaling and whether femalesbenefit from signaling. First, we find that female crouchingis related to the likelihood that females will be startled bymale displays, suggesting that crouching signals the degreeof display intensity that females will tolerate from a malewithout being startled. Second, we find that female tolerancefor intense display increases during successive courtships asfemales assess potential mates, and that female tolerance mayalso be affected by age and condition. Third, we find evidencethat females that reduce startling by signaling their intensitytolerance are more efficient in mate searching. These resultssuggest that females signal to influence how males display theirsexually selected traits, and by doing so, females may increasetheir benefits in mate choice.     

Female control of sperm ejection and retention in the cornsilk fly Euxesta eluta (Diptera: Ulidiidae)

Promiscuous mating systems provide the opportunity for females to bias fertilization toward particular males. However, distinguishing between male sperm competition and active female sperm choice is difficult for species with internal fertilization. Nevertheless, species that store and use sperm of different males in different storing structures and species where females are able to expel all or part of the ejaculates after copulation may be able to bias fertilization. We report a series of experiments aimed at providing evidence of female sperm choice in Euxesta eluta (Hendel), a species of ulidiid fly that expels and consumes ejaculates after copulation. We found no evidence of greater reproductive success for females mated singly, multiply with the same male, or mated multiply with different males. Female E. eluta possesses two spherical spermathecae and a bursa copulatrix for sperm storage, with a ventral receptacle. There was no significant difference in storing more sperm in spermathecae 24 h after copulation than immediately after copulation. Females mated with protein-fed males had greater reproductive success than similar females mated to protein-deprived males. Protein-fed females prevented to consume the ejaculate, retained more sperm when mated to protein-fed males than when mated to protein-deprived males. Our results suggest that female E. eluta can exert control of sperm retention of higher quality males through ejaculate ejection.     

Female resistance behaviour and progeny sex ratio in two Bradysia species (Diptera: Sciaridae) with paternal genome elimination

The relationship between female mating preferences and sex allocation has received considerable theoretical and empirical support. Typically, choosier females adjust their progeny sex ratio towards sons, who inherit the attractive traits of their father. However, in species with paternal genome elimination, where male sperm do not contain the paternal genome, predictions for the direction of progeny sex ratio biases and their relationship with female choosiness are atypical. Paternal genome elimination also creates a potential for male–female conflict over sex allocation, and any influence of female mate choice on sex ratio outcomes have interesting implications for sexually antagonistic coevolution. Within the Sciaridae (Diptera) are species that produce single‐sex progeny (monogenic species) and others in which progeny comprise both sexes (digenic species). Paternal genome elimination occurs in both species. We explore female mate resistance behaviour in a monogenic and digenic species of mushroom gnat from the genus Bradysia. Our experiments confirmed our theoretical predictions, revealing that in the monogenic and digenic species, females producing female‐biased progeny were more likely to have resisted at least one mating attempt.     

Radial growth and climate responses of white oak (Quercus alba) and northern red oak (Quercus rubra) at the northern distribution limit of white oak in Quebec, Canada

Aim The objectives of this study were: (1) to compare radial growth patterns between white oak (Quercus alba L.) and northern red oak (Quercus rubra L.) growing at the northern distribution limit of white oak; and (2) to assess if the radial growth of white oak at its northern distribution limit is controlled by cold temperature. Location The study was conducted in three regions of the Ottawa valley in southern Québec. All stands selected were located at the northern limit of distribution of Q. alba. Methods Twelve mixed red and white oak stands were sampled and increment cores were extracted for radial growth analyses. For each oak species, 12 chronologies were derived from tree‐ring measurement (residual chronologies). Principal components analysis and redundancy analysis were used to highlight the difference between radial growth in both species and to determine their radial growth–climate association. Results There was little difference between the radial growth of each species; Q. alba, however, exhibits more year‐to‐year variation in growth than Q. rubra. More than 65% of the variance in radial growth was shared among sites and species. Both species showed a similar response to climate, which suggested that the limit of distribution of Q. alba might not be determined by effects on growth. Both species had a classic response to climate and drought in the early growing season. Main conclusions The northern distribution limit of Q. alba does not appear to be directly controlled by effects on growth processes as indicated by the similarities in radial growth and response to climate between the two species. The location of the stands on southern aspects suggested that cold temperature could have been a major factor controlling the distribution limit of Q. alba. However, it is speculated that stands growing on southern aspects may be more prone to forest fires or to drought, which would favour the maintenance and establishment of oaks, and of Q. alba in particular. Models relating the northern distribution limits of species to broad climate parameters like annual mean temperature will need to be reviewed to incorporate more biologically relevant information. Such assessments will in turn provide better estimates of the effect of climate changes on species distribution.