1,721,235 research outputs found
Sex is also a matter of timing : an overview and an update of protandry studies in birds
No full textEarlier emergence or arrival of either sex at the breeding grounds is common in animals. Since the widespread
occurrence of differences in the timing of appearance of males and females at the breeding grounds has been
appreciated decades ago, diverse hypotheses have flourished to account for the selection pressures leading to
the evolution of earlier male (protandry) or female (protogyny) arrival. In birds, males typically arrive from
migration or, in resident species, start socio-sexual activities earlier than females, although protogyny occurs in
a restricted set of, mostly polyandrous species. Here, I will first review the numerous hypotheses and briefly
sketch modellistic approaches relevant to the interpretation of the evolution of protandry in birds. I will then
review the current knowledge on the patterns of variation in the relative timing of arrival of males and females
across bird species. The experimental study of the function of earlier male or delayed female arrival is
hampered by obvious practical limitations. However, the hypotheses for the evolution of protandry in birds
have been empirically scrutinized in a few comparative analyses of across species-variation in protandry in
relation to variation in traits that can differently constrain timing of arrival of either sex or influence the costs of
early arrival, as well as in relation to the intensity of sexual selection via eg sperm competition. I will discuss
the findings of these comparative studies while emphasizing the lack of data on sexually monomorphic species,
which owes to the only recent development of molecular techniques for sexing birds, and the methodological
issues in the study of protandry. I will therefore present novel findings on inter-specific variation in spring
migration protandry in a large set of both monochromatic and dichromatic species obtained by extensive
sampling at Ventotene island and molecular sexing. Climate change has affected migration phenology of birds.
However, climate change is likely to differentially affect the selection regime acting on migration and arrival
dates of males and females, suggesting that microevolutionary change in protandry may be under way. In the
end of the talk, I will outline current and future scenarios for the change in protandry under the effect of climate
change and how selection for protandry may be predicted to hasten or, conversely, to slow down adaptation to
rapidly changing environments
Mother’s mitochondria and optimal offspring sex ratio
No full textIn certain cases, predicted by evolutionary theory of sex-allocation and confirmed by empirical evidence, animals adaptively change their progeny sex-ratio according to individual circumstances. Here we argue that a similar response of offspring sex-ratio must exist in relation to genetic variation of mothers' mitochondria, as a consequence of maternal inheritance of these organelles and of their influence on fitness resulting from their crucial role in metabolism. In fact, a mathematical analysis of evolutionary dynamics of sex-allocation mutants demonstrates that natural selection promotes an evolutionarily stable allocation policy where mothers with defective mitochondria generate only sons, while those with optimal mitochondria have female biased progenies
Barn swallow chicks beg more loudly when broodmates are unrelated
No full textParents of a variety of animal species distribute critical resources among their offspring according to the intensity of begging displays. Kin selection theory predicts that offspring behave more selfishly in monopolizing parental care as relatedness with competitors declines. We cross-fostered two eggs between barn swallow (Hirundo rustica) clutches and compared the loudness of begging between mixed and control broods under normal feeding conditions and after a period of food deprivation. Begging loudness was higher in mixed broods under normal but not poor feeding conditions. Survival was reduced in mixed than control broods. Call features varied according to parentage, possibly serving as a cue for self-referent phenotype matching in mixed broods. This is the first evidence within a vertebrate species that competitive behaviour among broodmates depends on their relatedness. Thus, kin recognition and relatedness may be important determinants of communication among family members, care allocation and offspring viability in barn swallows
Environmental effects at two nested spatial scales on habitat choice and breeding performance of barn swallow
No full textParental effects comprise a wide range of mechanisms that individuals may adopt to enhance viability and adjust the phenotype of their offspring according to the conditions that the offspring will experience after birth. For example, individual choice of breeding habitat may mediate such parental effects via an effect of prenatal breeding conditions independently or in combination with offspring post-natal environment. However, ecological factors relevant to adaptive breeding habitat choice may vary at different spatial scales, which have been rarely investigated simultaneously. In the first part of the present study we use hierarchical linear models to disentangle micro- and macro-environmental variation in abundance and breeding performance of a small passerine bird, the barn swallow Hirundo rustica. We show that environmental conditions at the scale of nesting microhabitat are more influential than macro-environmental conditions at the scale of foraging range. We then experimentally investigate the effect of variation in micro-environmental conditions on growth and immunity of chicks by partially cross-fostering nestlings immediately after hatching between different nesting micro-habitats. Our results disclosed significant effects of environmental conditions where eggs were laid and incubated but not of those where nestlings grew-up on some components of nestling phenotype important for fitness. These results suggest that adults may enhance offspring quality by adjusting prenatal parental effects mediated by e.g., egg quality according to micro-habitat conditions where parents are breedin
Reproduction and migration in relation to senescence in the barn swallow Hirundo rustica : A study of avian “centenarians”
No full textA. P. Moller, F. de Lope and N. Saino: Reproduction and migration in relation to senescence in the barn swallow Hirundo rustica: A study of avian 'centenarians'. Senescence reflects the decrease in age-dependent residual reproductive value, and a previous study of a cohort of migratory barn swallows (Hirundo rustica) that had reached advanced ages for this species (at least five years old) provided evidence consistent with senescence such as reduced reproductive performance and increased abundance of parasites. We studied a population of migratory barn swallows over a number of years. Several questions were asked including 1) how do longer lived birds compare to shorter lived individuals of the same species, 2) is there a difference in individuals of the same species that live in different geographical regions, and 3) how do patterns of reproduction change during aging? We compared the phenotypes of 87 individuals from three populations in Denmark, Italy and Spain that had reached at least five years old with those of control individuals matched for sex, arrival date and breeding site. These controls only became one year old, i.e., they were not found thereafter and both groups of individuals were compared in their first year of life. Results showed that there were no significant differences in any of 11 morphological characters or in the abundance of three ectoparasites between the two groups of birds. Females that eventually became very old had relatively smaller first clutches as one year olds than did one year old controls, while males that eventually became very old had mates that laid clutches that were relatively larger than those of controls. Annual fecundity showed a similar pattern, with an increased sex difference in fecundity between birds from Spain than in Italy and in Denmark. Danish barn swallows that achieved older ages had relatively lower haematocrits than control individuals of the same sex, age and arrival date captured at the same site, while the difference in haematocrits between these two categories of individuals was small for Italian birds. Spring arrival date was relatively earlier in Danish males that eventually became very old compared to control males of the same age and tail length (a correlate of fitness) that arrived at the same site, while the two age categories of females did not differ in arrival date. In the Spanish population there was no difference in arrival date between the birds that aged most successfully and controls for either sex. We will discuss these findings in relation to current senescence theories
Examination marks of male university students positively correlate with finger length ratios (2D:4D)
No full textIntersexual and intrasexual variation in second to fourth digit length (2D:4D) in humans may result from differential exposure to fetal testosterone. 2D:4D predicts several physiological, psychological and performance traits in adulthood. These relationships may reflect the 'pleiotropic' effects of testosterone on development of digits and diverse organ systems, which are expressed in adulthood. We hypothesized that 2D:4D also predicts academic success of students. 2D:4D of right hand positively predicted examination marks of males from two three-year degree courses (TYDCs). Marks of females did not covary with 2D:4D. Males from the two TYDCs differed in 2D:4D. The present results thus add to the rapidly accumulating literature on 2D:4D showing correlations with phenotypic traits in humans. If testosterone affects 2D:4D and intellectual performance, our results suggest that testosterone levels are under stabilizing selection because of effects on performance traits documented in previous studies and antagonistic effects on intellectual performance (present study)
Seasonal changes in immune response and parasite impact on hosts
No full textSeasonal changes in the impact of parasites on hosts should result in seasonal changes in immune function. Since both ectoparasites and endoparasites time their reproduction to that of their hosts, we can predict that hosts have been selected to show an annual peak in their ability to raise an immune response during the reproductive season. We found large seasonal changes in immune function between the breeding and the nonbreeding season for a sample of temperate bird species. These changes amounted to a decrease in spleen mass from the breeding to the nonbreeding season by on average 18% across 71 species and a seasonal decrease in T-cell-mediated immunity by on average 33% across 13 species. These seasonal changes in immune function differed significantly among species. The condition dependence of immune function also differed between the breeding and the nonbreeding season, with individuals in prime condition particularly having greater immune responses during breeding. Analyses of ecological factors associated with interspecific differences in seasonal change of immune function revealed that hole-nesting species had a larger increase in immune function during the breeding season than did open nesters. Since hole nesters suffer greater reduction in breeding success because of virulent parasites than do open nesters, this seasonal change in immune function is suggested to have arisen as a response to the increased virulence of parasites attacking hole-nesting birds
Sex-related asymmetry in competitive ability of sexually monomorphic barn swallow nestlings
No full textIn diverse taxa, offspring solicit parental care using complex displays, which may evolve as reliable signals of condition or as mechanisms to manipulate parental investment. Differential sex allocation may therefore result from adaptive parental decisions or sex-related variation in competitive ability or because of sex-related asymmetries in kin selection. Under normal food provisioning, female barn swallow (Hirundo rustica) nestlings begged more loudly but did not receive more food than male nestlings. After food deprivation, begging call loudness of males but not females increased. Begging loudness positively predicted the number of feedings received by the nestlings, and males gained more mass than females after food deprivation. Male nestlings are more severely affected by chronic food reduction and may therefore accrue a larger benefit compared to females by increasing their food intake under short-term conditions of food scarcity. These results suggest that either females do not increase begging intensity to favour male broodmates which are more vulnerable to prolonged food stress, or that males prevail in scramble competition despite being similar in size to females
Ecological and phenological covariates of offspring sex ratio in barn swallows
No full textNon-random sex allocation in relation to parental, ecological and phenological factors has been investigated in several correlational studies of birds, mostly based on few breeding seasons and relatively small sample sizes, which have led to different results. We investigated sex ratio of nestling barn swallows (Hirundo rustica) in relation to adult sex ratio, laying date, clutch size, colony size and meteorological conditions in a sample of 553 broods (>2200 nestlings) during 10 years. At the population level, nestling sex ratio varied among years and deviated from parity in two years. Sex ratio among adults did not predict offspring sex ratio in the current or the following year. At the within-family level, the proportion of sons increased with laying date in large clutches, did not vary among clutches of intermediate size, and tended to decline with laying date in small clutches. Large colonies harbored more sons. The proportion of males increased with temperature during laying whereas the effects of temperature during the pre- or post-laying periods and that of rainfall were non-significant. These patterns of variation of offspring sex ratio did not differ between years. Thus, we identified several potential causal sources of variation in barn swallow offspring sex ratio, including temporal, phenological and ecological factors. The observation of an association of offspring sex with temperature during laying is novel for birds and may be mediated by effects on maternal steroid hormones profile. The ecological and evolutionary implications of present findings are discussed in the light of adaptive sex allocation theory
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