Maria I. Sandell

Dominance, prior occupancy and Winter residency in the great tit (Parus major)

SummaryThis study reports an aviary experiment aimed at determining what affects social dominance in the great tit (Parus major), especially why older birds (adults) in nature normally dominate younger ones (juveniles). When birds were matched with respect to age, prior residency determined dominance. Without a difference in prior residency older birds dominated younger ones. However, when juvenile birds had a prior residency advantage over adult birds, they often became dominant. This was especially so when the juvenile bird was large relative to the adult bird. When a resident juvenile male was also consorted by a female, he became dominant over an adult male on most occasions. An experiment where the dominant bird was removed and later returned to the aviary failed to produce more than one shift in dominance. However, the proportion of reversals in dominance interactions increased with separation time. It is argued that the fact that dominance depends on prior residency selects for winter residency in the great tit.

Transgenerational priming of immunity: maternal exposure to a bacterial antigen enhances offspring humoral immunity

Young vertebrates have limited capacity to synthesize antibodies and are dependent on the protection of maternally transmitted antibodies for humoral disease resistance early in life. However, mothers may enhance fitness by priming their offsprings immune systems to elevate disease resistance. Transgenerational induced defences have been documented in plants and invertebrates, but maternal priming of offspring immunity in vertebrates has been essentially neglected. To test the ability of mothers to stimulate the immune systems of offspring, we manipulated maternal and offspring antigen exposure in a wild population of birds, pied flycatchers (Ficedula hypoleuca). We show that immunization of the mother before egg laying apparently stimulates a transgenerational defence against pathogens by elevating endogenous offspring antibody production. If the disease environments encountered by mothers and offspring are similar, this transgenerational immune priming may allow young to better cope with the local pathogen fauna.

Scent-marking and its territorial significance in stoats, Mustela erminea

Abstract Stoats ( Mustela erminea ) and weasels ( Mustela nivalis ) perform two types of marking behaviour: anal drag and body rubbing. In stoats the two secretions have different chemical composition, and individual differences were found in the anal sac secretion. Dominant male and female stoats marked more frequently than did subordinates. Different messages were probably carried out by the two marks; body rubbing occurred associated with agonistic interactions and seemed to have a threat significance. Anal drag is probably used to impregnante the area with the individuals odour. Scentmarking is considered to be important in allowing assessment of the asymmetry in a conflict, as between a territory owner and an intruder.

Anal sac secretion in mustelids a comparison

The chemical compositions of anal sac secretions of seven mustelid species were examined by thin-layer chromatography, gas chromatography, and mass spectrometry. The analyses showed great similarities between species belonging to the genusMustela, i.e.,M. erminea,M. nivalis,M. vison, andM. putorius, whereasMaries martes, Luira lutra, andMeles meles each showed a different pattern. Benzaldehyde was the predominant compound in the secretion ofM. martes. Sulfur-containing compounds (thietanes and dithiacyclopentanes) were characteristic for theMustela species. Some of the compounds were species-specific and the relative amounts of the compounds in common varied between the species. The chemical results are in agreement with systematics at the generic level. Species-specific chemical composition makes exchange of information possible between coexisting mustelids. The presence of the sulfur-containing compounds in the small mustelids may be an effect of the defense function of the anal sac secretion.

Yolk testosterone modulates persistence of neophobic responses in adult zebra finches, Taeniopygia guttata

Individual differences in animal behavior can be attributed to genetic as well as non-genetic influences. One mechanism by which the behavioral phenotype of an individual can be shaped is via transmission of maternal sex steroids. In this study, we examined the role of yolk testosterone (T) in controlling neophobia in 9-month-old, sexually mature zebra finches (Taeniopygia guttata). Offspring hatched from either T-treated or control eggs were subjected to a sequential series of behavioral tests in which we measured the neophobic response and its persistence towards two unfamiliar stimuli. Birds from T-treated and control eggs did not differ in their latencies to approach and eat a novel food source during their first encounter. However, egg treatment affected subsequent habituation. Latencies decreased in both groups over a habituation period of 5 days, but considerably more so in T-offspring. Although males appeared to approach novel food faster than females, there was no overall sex effect during the habituation period. When a novel object was added in combination with the previously learned food stimulus, this caused an behavioral shift in approach latencies. In males, control offspring had significantly shorter latencies than T-offspring, whereas there was no difference among females. The latency to eat in the same test was not significantly affected by sex or egg treatment. Our results demonstrate long-term effects of prenatal T on neophobic responses in adult zebra finches. We hypothesize that prenatal T may be one underlying mechanism for individual differences routine formation.

Sex-specific effects of prenatal testosterone on nestling plasma antioxidant capacity in the zebra finch.

SUMMARY Trans-generational transfer of non-genetic, maternal resources such as hormones can have a substantial influence on offspring phenotype in many vertebrate species. In birds, maternal androgens enhance both growth and competitive behaviour, but also suppress the immune system. It has been hypothesised that high levels of egg androgens could also influence the prooxidant–antioxidant balance through their positive effect on growth and metabolism. We tested this hypothesis in the zebra finch (Taeniopygia guttata). Eggs were injected with testosterone dissolved in sesame oil or sesame oil only (control). We subsequently assessed the effect of the egg hormone manipulation on nestling growth and nestling plasma total antioxidant capacity (TAC). Growth rates of zebra finch nestlings were not significantly affected by egg hormone treatment. However, male offspring hatched from eggs with experimentally elevated testosterone had reduced plasma TAC at 10 days of age compared with male offspring hatching from control eggs. At the age of 34 days, males had similar plasma TAC irrespective of egg treatment. No effects of egg testosterone manipulation on nestling plasma TAC were found in females. Our results demonstrate that embryonic exposure to elevated levels of testosterone modulates chick antioxidant status, but this seems to be independent of chick growth. Sex-specific effects of prenatal testosterone on plasma TAC of zebra finch nestlings may have important consequences for sex allocation.

Exogenous testosterone increases female aggression in the European starling (Sturnus vulgaris)

In the European starling, Sturnus vulgaris, optimal mating systems differ between males and females. Males gain from polygyny, whereas monogamy increases female fitness. The cost of polygyny to females lead to intense female–female competition, and it has previously been shown that the intensity of female aggression during the pre-breeding period can predict the realised mating system. The physiological regulation of such female aggression in starlings is not yet known. This study examines the role of testosterone in mediating aggressive behaviours involved in intra-specific reproductive competition in female starlings. Testosterone levels were experimentally elevated with testosterone implants in females during the pre-laying period. To simulate a situation in which an additional female tried to mate with the focal female’s mate, a caged female was presented close to a nest-site to which the male could attract a secondary female. Testosterone was significantly related to several behaviours involved in female–female interactions. Females with testosterone implants spent significantly more time close to the caged female and produced more song bouts than control females. In contrast, male behaviour was unrelated to the experimental status of the mate. Females mated to males that attracted a secondary female were less aggressive towards the caged female than those that remained monogamously mated. The effect of exogenous testosterone in this study indicates that androgens may mediate social behaviours in female starlings during the breeding season.

Intraspecific brood parasitism: a strategy for floating females in the European starling

In many bird species, there is a floating population of females that are excluded from breeding because of competition for limited breeding resources. Female floaters may enhance their reproductive success by engaging in intraspecific brood parasitism. We studied female floaters in a population of European starlings, Sturnus vulgaris, in order to determine their identity and potential parasitic behaviour. Females were caught after being attracted to nestboxes with artificial nests during 1993-1995. None of the females was known to have a nest of her own at capture but 47% of the females either laid an egg in the nest or carried a fully developed egg within the reproductive tract, indicating that they were intraspecific brood parasites. The floating females were significantly younger and smaller than breeding females. Of 13 females equipped with radiotransmitters and followed daily, all but one started a breeding attempt of their own after 3-8 days and the majority settled as secondary females or mated with males where the original female had disappeared. This suggests that females that are unable to compete successfully for nest sites or males early in the breeding season may use intraspecific brood parasitism to enhance reproductive success during the period that they are constrained from breeding. The importance of settling rapidly because of a seasonal decline in reproductive success may also promote the evolution of intraspecific brood parasitism in the starling. The relative reproductive success of combining egg dumping with breeding compared with traditional breeding will depend on the costs of delaying breeding as well as the probability of finding a mate later in the breeding season. Copyright 1999 The Association for the Study of Animal Behaviour.

Maternal androgens in the pied flycatcher: timing of breeding and within-female consistency.

Maternal hormones can have substantial phenotypic effects in the progeny of many vertebrates. It has been proposed that mothers adaptively adjust hormone levels experienced by particular young to optimize their reproductive output. In birds, systematic variation in egg hormone levels has been related to different female reproductive strategies. Because in many bird species prospects of the offspring change seasonally and with brood number, strategic adjustment of yolk androgen levels would be expected. To test this idea, we induced pied flycatcher (Ficedula hypoleuca) females to nest twice during the same season by removing their first clutches shortly after clutch completion. We collected eggs of first and replacement clutches to measure yolk concentrations of androstenedione (A4) and testosterone (T) and captured the females that laid these clutches for phenotypic measurements. Although average egg androgen levels were remarkably consistent within females, hormone patterns differed considerably between first and replacement clutches. Eggs of replacement clutches were heavier with larger yolks compared to first clutches, but they contained on average lower levels of androgens. Within clutches, androgen concentration increased over the laying sequence in the first clutch, but decreased or remained more constant over the laying sequence in the replacement clutch. Mean yolk T, but not A4 levels, were negatively associated with laying date for both breeding attempts. Moreover, females in good body condition produced eggs containing lower levels of androgens than females in poor condition. Our results are consistent with the idea that differences in yolk androgen levels may be one mechanism underlying seasonal variation in reproductive success and it is possible that changes in egg androgen patterns may reflect a change in female reproductive strategy. High within-female consistency also highlights the possibility that there may be some underlying genetic variation in yolk androgen levels.

Paternal care in the European starling, Sturnus vulgaris: nestling provisioning

Abstract The extent to which male birds in polygynous species with biparental care assist in nestling feeding often varies considerably between nests of different mating status. Both how much polygynous males assist and how they divide their effort between nests may have a profound effect on the evolution of mating systems. In this study we investigated how males in the facultatively polygynous European starling Sturnus vulgaris invested in their different nests. The amount of male assistance affected the quality of the offspring. Polygynous males invested as much as monogamous males, but divided their effort asymmetrically between nests, predominantly feeding nestlings of first-mated (primary) females. Although females partly compensated for loss of male assistance, total feeding frequency was lower at primary females’ nests than at monogamous females nests. Secondary females received even less assistance with nestling rearing, and the extent to which males assisted decreased with the length of the interval between the hatching of the primary and secondary clutches. These results are contrasted with those from a Belgian populations of starlings with a much more protracted breeding season and thus greater opportunities for males to attract additional mates during the nestling rearing period. The results show that both the “defence of male parental investment model” and the “asynchronous settlement model” have explanatory power, but that their validity depends on the potential length of the breeding season.