Effects of increased begging and vitamin E supplements on oxidative stress and fledging probability

Offspring often use begging displays to demand food from parents. Begging is supposed to be a costly behavior, and oxidative stress is one potential cost of begging. We experimentally manipulated the begging intensity of great tit nestlings and the availability of vitamin E, an important antioxidant. The results suggest that oxidative stress is rather a minor cost of begging. However, nestlings supplemented with vitamin E were more likely to fledg

Ultraviolet reflectance of plumage for parent-offspring communication in the great tit (Parus major)

Ultraviolet (UV) reflectance has been implicated in mate selection. Yet, in some bird species the plumage of young varies in UV reflectance already in the nest and long before mate choice and sexual selection come into play. Most birds molt the juvenile body plumage before reaching sexual maturity, and thus, some conspicuous traits of the juvenile body plumage may rather have evolved by natural selection, possibly via predation or parental preference. This second hypothesis is largely untested and predicts a differential allocation of food between fledging and total independence, which is a time period of 2-3 weeks where offspring mortality is also highest. Here, we test the prediction that parents use the individual variation in UV reflectance among fledglings for differential food allocation. We manipulated UV reflectance of the plumage of fledgling great tits Parus major by treating chest and cheek feathers with a lotion that either did or did not contain UV blockers and then recorded food allocation by parents in an outdoor design simulating postfledging conditions. The visible spectrum was minimally affected by this treatment. Females were found to feed UV-reflecting offspring preferentially, whereas males had no preference. It is the first evidence showing that the UV reflectance of the feathers of young birds has a signaling function in parent-offspring communication and suggests that the UV traits evolved via parental preferenc

Partial incubation and its function in great tits (Parus major)—an experimental test

In many bird species, females incubate the eggs for short periods before clutch completion. The role of such partial incubation and the effective egg temperatures attained are controversial. Possible functions depend on whether temperatures reach the critical values required for embryogenesis and include the protection of the clutch from predators, brood parasites, and environmental factors; inhibition of bacterial growth on eggs; control of hatching asynchrony; or energy saving by parents. In this study, in a natural population of great tits, we first investigated the occurrence and extent of partial incubation, and second, we evaluated some potential functions by experimental simulation of the observed patterns of partial incubation. We found that egg temperatures during partial incubation were clearly raised above the physiological zero temperature for embryo development. Simulation of partial incubation did not affect any breeding parameters or nestling morphological traits compared with controls. It suggests that partial incubation with temperatures above the minimum temperature for embryo development does not serve to increase the variation in nestling morphology and thus competitiveness, in particular, does not increase hatching asynchrony within brood as one of its currently most discussed function

Dynamics of Hen Flea Ceratophyllus gallinae Subpopulations in Blue Tit Nests

The hen flea is a common parasite in bird nests, in particular, in tit species, and imposes considerable fitness costs for the host. These costs are expected to lead to selection for increased host defense, which in turn should select for better-adapted parasites. Our understanding of the coevolution of this host-parasite system is currently limited by the insufficient knowledge of both the timing of flea generations and their reproductive behavior within the nesting period of their hosts. In the present study we (1) followed the demography of experimental flea subpopulations during the host's breeding cycle, (2) assessed the importance of time-temperature effects in the nest by recording temperatures within the nest material, and (3) investigated the influence of variation in host timing and duration of the breeding period on flea development. We found the following. (1) Fleas completed either one or two generations within the birds' nesting cycle, leading to two well-defined periods of cocoon formation. (2) Within-nest temperatures during the warm period of the host breeding cycle—i.e., the incubation and nestling periods—depended on both outdoor temperatures and heat production from the breeding birds. Day-degree availability, a measure of physiological time, during the host incubation was significantly explained by the duration of incubation period and its timing in the season. Similarly, day-degrees during the warmer nestling period were significantly explained by its duration and its timing in the season. (3) The number of flea larvae found in the nests correlated with the host's timing and duration of the warm period available for their development; this was not the case, however, for the number of adult fleas. These results underline the importance of time-temperature effects as determinants of flea demography within the nests. The life-cycle and time-temperature effects are discussed in the light of potential host selection on parasite behavior and life historie

Carotenoid-based colour expression is determined early in nestling life

Carotenoid-based colours are widespread in animals and are used as signals in intra- and interspecific communication. In nestling birds, the carotenoids used for feather pigmentation may derive via three pathways: (1) via maternal transfer to egg yolk; (2) via paternal feeds early after hatching when females are mainly brooding; or (3) via feeds from both parents later in nestling life. We analysed the relative importance of the proposed carotenoid sources in a field experiment on great tit nestlings (Parus major). In a within-brood design we supplemented nestlings with carotenoids shortly after hatching, later on in the nestling life, or with a placebo. We show that the carotenoid-based colour expression of nestlings is modified maximally during the first 6 days after hatching. It reveals that the observed variation in carotenoid-based coloration is based only on mechanisms acting during a short period of time in early nestling life. The experiment further suggests that paternally derived carotenoids are the most important determinants of nestling plumage colou

Oxidative status and reproductive effort of great tits in a handicapping experiment

Father's contribution in child care matters. Using an experimental approach, we showed that handicapped great tit fathers are more likely to reduce investment in their offspring compared with control fathers. In contrast, handicapped mothers did not reduce investment in their offspring. Furthermore, cellular stress levels differed between males and females, supporting the idea that males and females follow different lifetime strategies when it comes to the trade-off between self-maintenance and reproductio

Ectoparasite reproductive performance when host condition varies

Host condition can influence both the nutritive resources available to parasites and the strength of host defences. Since these factors are likely to be correlated, it is unclear whether parasites would be more successful on hosts in good, intermediate or poor conditions. For more complex parasites, like fleas, where larvae depend on adults to extract and make available some essential host resources, host condition can act at two levels. First, it can affect the investment of females into eggs, and second, it can influence offspring growth. In a two-step experiment, we first let female hen fleas Ceratophyllus gallinae feed on nestlings of reduced, control or enlarged great tit Parus major broods and secondly used the blood from these nestlings as a food source for flea larvae reared in the laboratory. We then assessed the effect of brood size manipulation on reproductive investment and survival of female fleas, and on survival, developmental time, mass and size of pre-imago larvae and adults of the first generation. Although host condition, measured as body mass controlled for body size, was significantly influenced by brood size manipulation, it did not affect the female fleas' reproductive investment and survival. Larvae fed with blood from nestlings of reduced broods lived longer, however, than larvae fed on blood from enlarged or control broods. Additionally, F1 adults grew shorter tibiae when their mother had fed on hosts of reduced broods. The finding that brood size manipulation influenced parasite reproduction suggests that it affected nutritive resources and/or host defence, but the precise mechanism or balance between the two requires further investigatio

Sperm morphology, swimming velocity, and longevity in the house sparrow Passer domesticus

Sperm competition exerts strong selection on males to produce spermatozoa with an optimal morphology that maximizes their fertilization success. Long sperm were first suggested to be favored because they should swim faster. However, studies that investigated the relationship between sperm length and sperm competitive ability or sperm swimming velocity yielded contradictory results. More recently, ratios of the different sections of a spermatozoon (the head, midpiece, and flagellum) were suggested to be more crucial in determining swimming velocity. Additionally, sperm ability to remain and survive in the female storage organs may also influence fertilization success, so that optimal sperm morphology may rather maximize sperm longevity than velocity. In this study, we investigated how sperm morphology is related to sperm velocity and sperm longevity in the house sparrow Passer domesticus. Sperm velocity was found to be correlated with head/flagellum ratio. Sperm with small heads relative to their flagellum showed higher swimming velocity. Additionally, shorter sperm were found to live longer. Finally, we found sperm morphological traits to vary substantially within males and the head/flagellum ratio to be unrelated to total sperm length. We discuss the hypothesis that the substantial within-male variation in sperm morphology reflects a male strategy to produce a diversity of sperm from long, fast-swimming to short, long-living sperm to maximize their fertilization success in a context of sperm competitio

Parasite- and predator-induced maternal effects in the great tit (Parus major)

Organisms often face the simultaneous risk of predation and parasitism and a trade-off among the responses is predicted. Concurrent exposure of great tit mothers before reproduction to both of these stressors showed no interactive effect on growth and phenotype of offspring via maternal responses conveyed through eggs. Parasites, both via maternal effects and via direct exposure of nestlings, negatively influenced offspring phenotype, while risk of predation had no significant effec