The influence of environmental conditions on immune responses, morphology and recapture probability of nestling house martins (Delichon urbica)

Nestling birds produced later in the season are hypothesized to be of poor quality with a low probability of survival and recruitment. In a Spanish population of house martins (Delichon urbica), we first compared reproductive success, immune responses and morphological traits between the first and the second broods. Second, we investigated the effects of an ectoparasite treatment and breeding date on the recapture rate the following year. Due probably to a reverse situation in weather conditions during the experiment, with more rain during rearing of the first brood, nestlings reared during the second brood were in better condition and had stronger immune responses compared with nestlings from the first brood. Contrary to other findings on house martins, we found a similar recapture rate for chicks reared during the first and the second brood. Furthermore, ectoparasitic house martin bugs had no significant effect on the recapture rate. Recaptured birds had similar morphology but higher immunoglobulin levels when nestlings compared with non-recaptured birds. This result implies that a measure of immune function is a better predictor of survival than body condition per se.     

Energetics of growth in House martins (Delichon urbica)

Energy requirements for growth and maintenance of nestling House martins was studied in relation to brood size and age. Parallel studies of feeding rates and faecal output were made. The effect of mutual insulation between members of the brood on metabolism was of significance for reducing maintenance energy requirements. Of great value for predicting the peak energy demand of the brood was the number of young and their individual requirements for growth and maintenance at different ages. Power equations are given for predicting brood assimilation, faecal output and feeding frequency in relation to brood size. The impact of food scarcity on growth patterns was assessed. The large lipid stores of nestlings served as an energy reserve during adverse conditions both before and after fledging. Asynchronous hatching in large broods is interpreted as a mechanism which serves to minimize the peak in energy demand which occurs about 12 days after the brood hatches.     

Increase in a heat-shock protein from blood cells in response of nestling house martins (Delichon urbica) to parasitism: an experimental approach

Heat-shock proteins (HSPs) are synthesized by animals and plants in response to various stressors. The level of the HSP60 stress protein was measured from the cell fraction of peripheral blood obtained from nestling house martins (Delichon urbica) to test whether ectoparasitism increased the concentration of stress protein. We assessed HSP from nestlings raised in nests previously treated with an insecticide or infested with 50 martin bugs (Oeciacus hirundinis). In addition, haematozoa infections were checked in blood smears. Nestlings from parasite-infested nests, or nestlings infected with trypanosomes, had increased levels of HSP in their blood cells. Nestling growth as determined from wing length was negatively related to HSP60 levels and within-brood variation in wing length increased with increasing levels of the stress protein independently of treatment and infection by trypanosomes. These results suggest HSPs may play a role in host-parasite interactions, and that they can be used reliably for measuring physiological responses to parasites. Received: 4 February 1998 / Accepted: 4 May 1998     

Ontogeny of metabolism,thermoregulation and torpor in the house martin Delichon u. urbica (L.) and its ecological significance

Summary Special energetic adaptations are of great evolutionary significance for birds that encounter transient problems in finding food during the breeding season. House martins, as aerial insectivores, encounter such problems during spells of bad weather, when they must survive on body reserves. This species employs the following behavioural and physiological adaptations to save energy: Low basal metabolic rate (only 43% of the values predicted by allometric equations); low thermal conductance 51% (day) and 67% (night) of the predicted values; clustering behaviour; high tolerance of the young to periods of low food supply; and the ability to become torpid, found in adults and young from the age of 11 days on. House martins are the first passerine birds in which torpor has been found. These adaptations might have played a role in the great success of the house martin, one of the 10–15 most abundant bird species in Europe.Abbreviations BMR Basal metabolic rate, J/g·h - C Thermal conductance, J/g·h°C - M Energy metabolism, J/g·h - Ta Ambient temperature, °C - Tb Body temperature, °C - W Body mass, g A great part of these investigations were done in the laboratory of Prof. Dr. E. Kulzer, Physiologische Ökologie, Auf der Morgenstelle 28, D-7400 Tübingen, FRG     

Huddling house sparrows remain euthermic at night,and conserve body mass

An advantage of huddling in the cold is that the individual animals involved can maintain body temperature while saving energy. Since house sparrows Passer domesticus biblicus store little fat, but inhabit relatively cold climates, we tested the hypothesis that they huddle at night. While recording body temperature and body mass of 18 house sparrows when they were either caged individually, or free in an aviary, we observed that when free in the aviary, the sparrows huddled at low ambient temperatures and more birds huddled, in tighter and tighter formation, as ambient temperature decreased. However, their body temperatures were not significantly different from when they spent the night individually caged. When free to huddle, the birds lost significantly less body mass during the course of a day than when individually caged. This reduction in body mass loss may be of particular importance during periods of adverse environmental conditions, especially for small birds that manage their energy budgets on a daily basis.     

Determinants of variation in adult body height

Final body height is achieved as the result of a combination of genetic and environmental factors. The aim of this article is to review past studies on body height that have followed different scientific traditions. In modern Western societies, about 20% of variation in body height is due to environmental variation. In poorer environments, this proportion is probably larger, with lower heritability of body height as well as larger socioeconomic body height differences. The role of childhood environment is seen in the increase in body height during the 20th century simultaneously with the increase in the standard of living. The most important non-genetic factors affecting growth and adult body height are nutrition and diseases. Short stature is associated with poorer education and lower social position in adulthood. This is mainly due to family background, but other environmental factors in childhood also contribute to this association. Body height is a good indicator of childhood living conditions, not only in developing countries but also in modern Western societies. Future studies combining different scientific traditions in auxology are needed to create a more holistic view of body height.     

Malaria infection and feather growth rate predict reproductive success in house martins

Carry-over effects take place when events occurring in one season influence individual performance in a subsequent season. Blood parasites (e.g. Plasmodium and Haemoproteus) have strong negative effects on the body condition of their hosts and could slow the rate of feather growth on the wintering grounds. In turn, these winter moult costs could reduce reproductive success in the following breeding season. In house martins Delichon urbica captured and studied at a breeding site in Europe, we used ptilochronology to measure growth rate of tail feathers moulted on the winter range in Africa, and assessed infection status of blood parasites transmitted on the wintering grounds. We found a negative association between haemosporidian parasite infection status and inferred growth rate of tail feathers. A low feather growth rate and blood parasite infections were related to a delay in laying date in their European breeding quarters. In addition, clutch size and the number of fledglings were negatively related to a delayed laying date and blood parasite infection. These results stress the importance of blood parasites and feather growth rate as potentially mechanisms driving carry-over effects to explain fitness differences in wild populations of migratory birds.     

Density-dependent variation in body mass of voles

We studied inter-annual, spatial and sexual variation in the body mass of bank volesMyodes glareolus Schreber, 1780 and grey-sided volesMyodes rufocanus Sundevall, 1846 using live trappings from two grids on the southand north-facing slopes of a mountain valley in Southern Norway. Variation in spring density of the four populations was consistent with cyclic dynamics (n=7,s-values >0.5). Individuals caught on the south-facing slope were larger than those caught on the north-facing slope. Reproductively mature bank vole males were smaller than females, whereas reproductively mature grey-sided vole males were larger than females. Body mass was related to density in both species. In bank voles, we found a direct positive density dependence caused by a higher rate of survival at higher densities resulting from individual allocation of resources from reproduction to survival and growth. In grey-sided voles, we found a negative delayed density dependence resulting from grazing on preferred plants that determined the resource available for individual vole growth the following year.     

Quantitative genetics of immune function and body size in the house cricket,Acheta domesticus

Female house crickets are attracted to male calling song containing a relatively high number of syllables per ‘chirp’, which tends to be produced by large males. In a previous study, we showed that this song characteristic is also positively and independently correlated with haemocyte load, an important determinant of the ability to produce an encapsulation response in insects. Females will therefore tend to select males with high encapsulation ability (and large body size) as mates. The present study demonstrates that variation in haemocyte load and body size, together with a second parameter of immune function (the ability to encapsulate a synthetic substrate), is heritable in the same population. Moreover, all three traits are shown to be positively genetically correlated. In favouring males that produce calling song with the preferred characteristics, females should therefore also tend to produce larger offspring with a greater ability to produce an encapsulation response.     

Parasitism, host immune defence and dispersal

Host-parasite interactions have been hypothesized to affect the evolution of dispersal by providing a possibility for hosts to escape debilitating parasites, and by influencing the level of local adaptation. We used a comparative approach to investigate the relationship between a component of host immune function (which reflects the evolutionary history of parasite-induced natural selection) and dispersal in birds. We used a sample of 46 species of birds for which we had obtained field estimates of T-cell response for nestlings, mainly from our own field studies in Denmark and Spain. Bird species with longer natal, but not with longer breeding dispersal distances had a stronger mean T-cell-mediated immune response in nestlings than species with short dispersal distances. That was also the case when controlling for the potentially confounding effect of migration from breeding to wintering area, which is known from previous studies to be positively associated with dispersal distance. These relationships held even when controlling for similarity among species because of common ancestry. Avian hosts with a larger number of different breeding habitats had weaker mean T-cell-mediated immune responses than habitat specialists. This relationship held even when controlling for similarity among species because of common ancestry. Therefore, T-cell-mediated immunity is an important predictor of evolutionary changes in dispersal ability among common European birds.     

Intraseasonal patterns in shorebird nest survival are related to nest age and defence behaviour

Nest survival may vary throughout the breeding season for many bird species, and the nature of this temporal variation can reveal the links between birds, their predators, and other components of the ecosystem. We used program Mark to model patterns in nest survival within the breeding season for shorebirds nesting on arctic tundra. From 2000 to 2007, we monitored 521 nests of five shorebird species and found strong evidence for variation in nest survival within a nesting season. Daily nest survival was lowest in the mid-season in 5 of 8 years, but the timing and magnitude of the lows varied. We found no evidence that this quadratic time effect was driven by seasonal changes in weather or the abundance of predators. Contrary to our prediction, the risk of predation was not greatest when the number of active shorebird nests was highest. Although nest abundance reached a maximum near the middle of the breeding season, a daily index of shorebird nest activity was not supported as a predictor of nest survival in the models. Predators’ access to other diet items, in addition to shorebird nests, may instead determine the temporal patterns of nest predation. Nest survival also displayed a positive, linear relationship with nest age; however, this effect was most pronounced among species with biparental incubation. Among biparental species, parents defended older nests with greater intensity. We did not detect a similar relationship among uniparental species, and conclude that the stronger relationship between nest age and both nest defence and nest survival for biparental species reflects that their nest defence is more effective.     

Exposure to sexual signals during rearing increases immune defence in adult field crickets

Increased investment in immunity is expected to be beneficial under crowded conditions because of the greater risk of pathogen and parasite transmission, but the evolution of this facultative response relies on the ability to accurately assess social cues in the environment and adjust immune defences accordingly. Because of their highly conspicuous nature, long-range sexual signals are prime candidates to be used in evaluating the social conditions likely to be experienced upon adulthood in continuously breeding species; however, their role in mediating immune responses is unknown. We tested whether exposure to acoustic sexual signals in the field cricket Teleogryllus oceanicus affects immunity by manipulating male juvenile experience of acoustic signals, and measuring the effect on adult immunity. Adult males exposed to song during rearing showed stronger immune responses than males reared in silence: they were better able to encapsulate artificial nylon implants and showed higher levels of antimicrobial lysozyme-like activity in their haemolymph. Experience of sexual signals thus translates into increased immunity, which suggests that such signals may play a role in conveying information about population demography and shaping density-dependent responses in unintended receivers.     

Seasonal variation in body composition and morphology of adult muskrats in central Saskatchewan, Canada

We quantified seasonal variation in body composition and morphology of adult muskrats ( Ondatra zibethicus ) inhabiting freshwater marsh environments in central Saskatchewan, Canada. The study areas were characterized by long and cold winters extending over six months during which muskrats were restricted to foraging under ice. A total of 162 adult muskrats were collected during nine sampling periods across the year. The large accumulation of fat reserves (16% of body mass) during winter and the concurrent decline in protein mass suggested a reduced maintenance requirement associated with the presence of energy-rich food resources. Dietary fibre content increased significantly during mid-summer and was manifested by changes in gut morphology. Mobilization of fat reserves during summer months by both sexes reflected high energetic demands for reproduction. Males depleted fat reserves soon after spring break-up, while near-exhaustion of fat reserves in females occurred 4–6 weeks later, during lactation. Pregnant females contained significantly greater fat and protein reserves compared to non-pregnant and lactating females. The dynamics of body reserves in muskrats should be viewed as an integral part of the sex-specific life-history traits of this important herbivore species of marsh environments.     

Between‐male variation in sperm size,velocity and longevity in sand martins Riparia riparia

Sperm mobility is known to be an important determinant of a male's sperm competitive ability. Although more debated, sperm length and its relation to sperm swimming ability has also been proposed to determine a male's fertilisation potential. Furthermore, both mobility and length may covary with a male's phenotype, either positively (the phenotype‐linked fertility hypothesis) or negatively if, for instance, low‐quality males have less access to females but invest more in sperm production. Using dummy females, we collected sperm samples from wild sand martins Riparia raparia males. We investigated the relationship between sperm length and sperm swimming speed as measured by sperm straight line velocity (VSL), and determined whether sperm traits are correlated with male body size and condition. We found that total sperm length is repeatable within‐ejaculate and shows substantial inter‐male variation. Sperm length was associated with sperm velocity: males with short sperm have sperm that swim initially faster but die sooner, whereas males with longer sperm have sperm that swim more slowly but for a longer time. Smaller males produced sperm with higher overall velocity. This correlation between male size and sperm behaviour may reflect alternative fertilisation strategies where small males having less mating opportunities invest more in sperm competitive ability. The existence of such alternative strategies would participate in maintaining variation in sperm length and velocity in this species.     

The relationship between body mass index, semen and sex hormones in adult male

This study was aimed at evaluating the relationship between body mass index, sex hormones and semen characteristics in male adults. 120 male adults aged 20 to 50 years who consented to participate in the study were used. Serum samples collected from each subject were analyzed for Luteinizing hormone (LH), Follicle stimulating hormone (FSH), Prolactin (PRL), Progesterone, Estradiol and testosterone by classical ELISA method. Semen samples obtained by masturbation after 72 hours of abstinence were analyzed for sperm count and motility. The results showed statistically significant correlations at 99% confidence level between body mass index and serum concentrations of progesterone and oestradiol and sperm count. No significant correlations were observed between body mass index and sperm motility, serum concentrations of prolactin, testosterone and luteinizing hormone. In conclusion, this study has shown that statistically significant correlations exist between body mass index, semen characteristics and male sex hormones and may broaden our understanding of the physiology of male fertility/infertility. Keywords: Body mass index, Semen quality, Male sex hormones, Fertility/infertility.     

Interrelationships between egg mass and adult body mass and metabolism among passerine birds

Summary The regression of egg mass of Passeriformes against female body mass (n=1244) and basal metabolic rate of Passeriformes against body mass (n=159) have similar slopes, indicating that for this group egg mass is directly proportional to basal metabolic rate and that the relative egg mass (% of body mass) is directly proportional to the weight-specific metabolism. This relationship and the average caloric density of passerine eggs (n=38) provides an estimate of the cost of egg production, which for single eggs is 41 % of the basal metabolic rate.

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Beziehungen zwischen Eigewicht, Körpergewicht und Stoffwechsel bei Sperlingsvögeln

Zusammenfassung Die Regressionsgeraden von Eigewichten der Passeriformes und weiblicher Körpergewichte (N=1244) einerseits sowie von Ruheumsatz und Körpergewichten (N=159) andererseits haben vergleichbare Steigungen. Das bedeutet, (1) daß für diese Vogelordnung das Eigewicht proportional zum Ruheumsatz und (2) daß das relative Eigewicht (% des Körpergewichtes) proportional zum gewichtspezifischen Stoffwechsel ist. Dieses Verhältnis und der durchschnittliche kalorische Wert der Eier (N=38) erlauben die Kosten der Eiproduktion zu schätzen: sie betragen für das einzelne Ei 41 % des Ruheumsatzes.