Imperial College London

DrJuliaSchroeder

Faculty of Natural SciencesDepartment of Life Sciences (Silwood Park)

Senior Lecturer
 
 
 
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Contact

 

+44 (0)20 7594 9086julia.schroeder

 
 
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Location

 

2.13MunroSilwood Park

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Summary

 

Publications

Publication Type
Year
to

71 results found

Alif Ž, Dunning J, Chik HYJ, Burke T, Schroeder Jet al., 2022, What is the best fitness measure in wild populations? A case study on the power of short-term fitness proxies to predict reproductive value, PLoS One, Vol: 17, ISSN: 1932-6203

Fitness is at the core of evolutionary theory, but it is difficult to measure accurately. One way to measure long-term fitness is by calculating the individual's reproductive value, which represents the expected number of allele copies an individual passes on to distant future generations. However, this metric of fitness is scarcely used because the estimation of individual's reproductive value requires long-term pedigree data, which is rarely available in wild populations where following individuals from birth to death is often impossible. Wild study systems therefore use short-term fitness metrics as proxies, such as the number of offspring produced. This study compared two frequently used short-term metrics for fitness obtained at different offspring life stages (eggs, hatchlings, fledglings and recruits), and compared their ability to predict reproductive values derived from the genetic pedigree of a wild passerine bird population. We used twenty years of precise field observations and a near-complete genetic pedigree to calculate reproductive success, individual growth rate and de-lifed fitness as lifetime fitness measures, and as annual de-lifed fitness. We compared the power of these metrics to predict reproductive values and lineage survival to the end of the study period. The three short-term fitness proxies predict the reproductive values and lineage survival only when measured at the recruit stage. There were no significant differences between the different fitness proxies at the same offspring stages in predicting the reproductive values and lineage survival. Annual fitness at one year old predicted reproductive values equally well as lifetime de-lifed fitness. However, none of the short-term fitness proxies were strongly associated with the reproductive values. The commonly used short-term fitness proxies best predict long-term fitness when measured at recruitment stage. Thus, because lifetime fitness measured at recruit stage and annual fitness in the

Journal article

Chik HYJ, Estrada C, Wang Y, Tank P, Lord A, Schroeder Jet al., 2022, Individual variation in reaction norms but no directional selection in reproductive plasticity of a wild passerine population, ECOLOGY AND EVOLUTION, Vol: 12, ISSN: 2045-7758

Journal article

Culina A, Adriaensen F, Bailey LD, Burgess MD, Charmantier A, Cole EF, Eeva T, Matthysen E, Nater CR, Sheldon BC, Saether B-E, Vriend SJG, Zajkova Z, Adamík P, Aplin LM, Angulo E, Artemyev A, Barba E, Barišić S, Belda E, Bilgin CC, Bleu J, Both C, Bouwhuis S, Branston CJ, Broggi J, Burke T, Bushuev A, Camacho C, Campobello D, Canal D, Cantarero A, Caro SP, Cauchoix M, Chaine A, Cichoń M, Ćiković D, Cusimano CA, Deimel C, Dhondt AA, Dingemanse NJ, Doligez B, Dominoni DM, Doutrelant C, Drobniak SM, Dubiec A, Eens M, Einar Erikstad K, Espín S, Farine DR, Figuerola J, Kavak Gülbeyaz P, Grégoire A, Hartley IR, Hau M, Hegyi G, Hille S, Hinde CA, Holtmann B, Ilyina T, Isaksson C, Iserbyt A, Ivankina E, Kania W, Kempenaers B, Kerimov A, Komdeur J, Korsten P, Král M, Krist M, Lambrechts M, Lara CE, Leivits A, Liker A, Lodjak J, Mägi M, Mainwaring MC, Mänd R, Massa B, Massemin S, Martínez-Padilla J, Mazgajski TD, Mennerat A, Moreno J, Mouchet A, Nakagawa S, Nilsson J-Å, Nilsson JF, Cláudia Norte A, van Oers K, Orell M, Potti J, Quinn JL, Réale D, Kristin Reiertsen T, Rosivall B, Russell AF, Rytkönen S, Sánchez-Virosta P, Santos ESA, Schroeder J, Senar JC, Seress G, Slagsvold T, Szulkin M, Teplitsky C, Tilgar V, Tolstoguzov A, Török J, Valcu M, Vatka E, Verhulst S, Watson H, Yuta T, Zamora-Marín JM, Visser MEet al., 2021, Connecting the data landscape of long-term ecological studies: The SPI-Birds data hub., Journal of Animal Ecology, Vol: 90, Pages: 2147-2160, ISSN: 0021-8790

The integration and synthesis of the data in different areas of science is drastically slowed and hindered by a lack of standards and networking programmes. Long-term studies of individually marked animals are not an exception. These studies are especially important as instrumental for understanding evolutionary and ecological processes in the wild. Furthermore, their number and global distribution provides a unique opportunity to assess the generality of patterns and to address broad-scale global issues (e.g. climate change). To solve data integration issues and enable a new scale of ecological and evolutionary research based on long-term studies of birds, we have created the SPI-Birds Network and Database (www.spibirds.org)-a large-scale initiative that connects data from, and researchers working on, studies of wild populations of individually recognizable (usually ringed) birds. Within year and a half since the establishment, SPI-Birds has recruited over 120 members, and currently hosts data on almost 1.5 million individual birds collected in 80 populations over 2,000 cumulative years, and counting. SPI-Birds acts as a data hub and a catalogue of studied populations. It prevents data loss, secures easy data finding, use and integration and thus facilitates collaboration and synthesis. We provide community-derived data and meta-data standards and improve data integrity guided by the principles of Findable, Accessible, Interoperable and Reusable (FAIR), and aligned with the existing metadata languages (e.g. ecological meta-data language). The encouraging community involvement stems from SPI-Bird's decentralized approach: research groups retain full control over data use and their way of data management, while SPI-Birds creates tailored pipelines to convert each unique data format into a standard format. We outline the lessons learned, so that other communities (e.g. those working on other taxa) can adapt our successful model. Creating community-specific hubs (such

Journal article

Eberhart-Hertel LJ, Rodrigues LF, Krietsch J, Eberhart-Hertel AG, Cruz-López M, Vázquez-Rojas KA, González-Medina E, Schroeder J, Küpper Cet al., 2021, Egg size variation in a long-lived polyandrous shorebird in the context of senescence and breeding phenology

<jats:p>We have withdrawn this manuscript due to a duplicate posting of manuscript number 240150. Therefore, we do not wish this work to be cited as reference for the project. If you have any questions, please contact Luke J. Eberhart-Hertel at <jats:email>luke.eberhart@orn.mpg.de</jats:email></jats:p>

Journal article

de Villemereuil P, Charmantier A, Arlt D, Bize P, Brekke P, Brouwer L, Cockburn A, Côté SD, Dobson FS, Evans SR, Festa-Bianchet M, Gamelon M, Hamel S, Hegelbach J, Jerstad K, Kempenaers B, Kruuk LEB, Kumpula J, Kvalnes T, McAdam AG, McFarlane SE, Morrissey MB, Pärt T, Pemberton JM, Qvarnström A, Røstad OW, Schroeder J, Senar JC, Sheldon BC, van de Pol M, Visser ME, Wheelwright NT, Tufto J, Chevin L-Met al., 2020, Fluctuating optimum and temporally variable selection on breeding date in birds and mammals., Proceedings of the National Academy of Sciences of USA, Vol: 117, Pages: 31969-31978, ISSN: 0027-8424

Temporal variation in natural selection is predicted to strongly impact the evolution and demography of natural populations, with consequences for the rate of adaptation, evolution of plasticity, and extinction risk. Most of the theory underlying these predictions assumes a moving optimum phenotype, with predictions expressed in terms of the temporal variance and autocorrelation of this optimum. However, empirical studies seldom estimate patterns of fluctuations of an optimum phenotype, precluding further progress in connecting theory with observations. To bridge this gap, we assess the evidence for temporal variation in selection on breeding date by modeling a fitness function with a fluctuating optimum, across 39 populations of 21 wild animals, one of the largest compilations of long-term datasets with individual measurements of trait and fitness components. We find compelling evidence for fluctuations in the fitness function, causing temporal variation in the magnitude, but not the direction of selection. However, fluctuations of the optimum phenotype need not directly translate into variation in selection gradients, because their impact can be buffered by partial tracking of the optimum by the mean phenotype. Analyzing individuals that reproduce in consecutive years, we find that plastic changes track movements of the optimum phenotype across years, especially in bird species, reducing temporal variation in directional selection. This suggests that phenological plasticity has evolved to cope with fluctuations in the optimum, despite their currently modest contribution to variation in selection.

Journal article

Plaza M, Burke T, Cox T, Flynn-Carroll A, Girndt A, Halford G, Martin DA, Sanchez-Fortun M, Sanchez-Tojar A, Somerville J, Schroeder Jet al., 2020, Repeatable social network node-based metrics across populations and contexts in a passerine, JOURNAL OF EVOLUTIONARY BIOLOGY, Vol: 33, Pages: 1634-1642, ISSN: 1010-061X

Journal article

Valdebenito JO, Martinez-de la Puente J, Castro M, Perez-Hurtado A, Tejera G, Szekely T, Halimubieke N, Schroeder J, Figuerola Jet al., 2020, Association of insularity and body condition to cloacal bacteria prevalence in a small shorebird, PLoS One, Vol: 15, Pages: 1-16, ISSN: 1932-6203

Do islands harbour less diverse disease communities than mainland? The island biogeography theory predicts more diverse communities on mainland than on islands due to more niches, more diverse habitats and availability of greater range of hosts. We compared bacteria prevalences of Campylobacter, Chlamydia and Salmonella in cloacal samples of a small shorebird, the Kentish plover (Charadrius alexandrinus) between two island populations of Macaronesia and two mainland locations in the Iberian Peninsula. Bacteria were found in all populations but, contrary to the expectations, prevalences did not differ between islands and mainland. Females had higher prevalences than males for Salmonella and when three bacteria genera were pooled together. Bacteria infection was unrelated to bird’s body condition but females from mainland were heavier than males and birds from mainland were heavier than those from islands. Abiotic variables consistent throughout breeding sites, like high salinity that is known to inhibit bacteria growth, could explain the lack of differences in the bacteria prevalence between areas. We argue about the possible drivers and implications of sex differences in bacteria prevalence in Kentish plovers.

Journal article

Eberhart-Hertel LJ, Rodrigues LF, Krietsch J, Eberhart-Hertel AG, Cruz-López M, Vázquez-Rojas KA, González-Medina E, Schroeder J, Küpper Cet al., 2020, Egg size variation in a long-lived polyandrous shorebird in the context of senescence and breeding phenology

<jats:title>Abstract</jats:title><jats:p>Anisogamy is a central component of sex role evolution, however, the effect of female- female mating competition on egg size variation in polyandrous species is unclear. Moreover, egg size may also be shaped by age-dependent trade-offs between reproductive investments and somatic maintenance that are responsible for senescence. Here we investigate how mating behaviour and senescence are associated with egg size variation in female snowy plovers (<jats:italic>Charadrius nivosus</jats:italic>). Snowy plovers are long-lived shorebirds (longevity record: 20 years) that often produce several nests each year, with females either sequentially changing partners between breeding attempts or remaining monogamous between attempts. We examined how age, seasonality, body size, and mating behaviour relate to within- and between-female variation in egg volume using repeated measures collected over a 15-year period. We found no evidence of reproductive senescence in egg volume in snowy plover females. Rather, egg volume, polyandry, and re-nesting were strongly linked to breeding phenology: early breeding females had a higher likelihood of being polyandrous or replacing failed clutches, yet these individuals laid smaller eggs likely due to physiological limitations associated with the early season. Older individuals and local recruits secured the earliest breeding opportunities in the season suggesting that prior experience could give an edge in the female-female competition for mates. Larger females laid the largest eggs, as expected, but there was no relationship between body size and lay date – implying that size may not provide an advantage in female-female competition. Our findings highlight the existence of several direct and indirect constraints on female reproductive investment that likely shape individual variation in lifetime reproductive success. Future research investigating reproductive senesce

Journal article

Van Lieshout SHJ, Froy H, Schroeder J, Burke T, Simons MJP, Dugdale HLet al., 2020, Slicing: A sustainable approach to structuring samples for analysis in long-term studies, METHODS IN ECOLOGY AND EVOLUTION, Vol: 11, Pages: 418-430, ISSN: 2041-210X

Journal article

Ihle M, Pick JL, Winney IS, Nakagawa S, Schroeder J, Burke Tet al., 2019, Rearing success does not improve with apparent pair coordination in offspring provisioning, Frontiers in Ecology Evolution, Vol: 7, Pages: 1-9, ISSN: 2296-701X

In species with biparental care, behavioral coordination in the provisioning of the progeny is hypothesized to increase the number of offspring that survive to independence. Coordination is often quantified by two metrics, alternation and synchrony. Turn-taking (leading to an alternation pattern) can result when one parent's investment strategy is based on the investment of its partner (i.e., conditional cooperation). This should increase the overall provisioning rate and improve offspring body condition. Synchrony might equalize food delivery among offspring and therefore decrease the variance in offspring body condition within the brood. Overall, offspring survival could be increased by parental coordination. Finally, pairs with low coordination, and with potentially lower reproductive success, are expected to be more likely to divorce. In this study, we use a dataset on 473 pairs of house sparrows in a natural insular population to test these hypotheses. We found no effect of the pair's apparent coordination on offspring condition, offspring survival, or divorce rate, questioning the adaptive significance of this behavior. We argue that, in this species, the detection of a higher frequency of alternation and synchrony, when compared to chance expectation, might be induced by the environment, rather than result from an emergent pair behavior selected for fitness benefits.

Journal article

Lattore M, Nakagawa S, Burke T, Plaza M, Schroeder Jet al., 2019, No evidence for kin recognition in a passerine bird, PLOS ONE, Vol: 14, ISSN: 1932-6203

Journal article

Vargas-Pellicer P, Watrobska C, Knowles S, Schroeder J, Banks-Leite Cet al., 2019, How should we store avian faecal samples for microbiota analyses? Comparing efficacy and cost-effectiveness, JOURNAL OF MICROBIOLOGICAL METHODS, Vol: 165, ISSN: 0167-7012

Journal article

Girndt A, Cockburn G, Sanchez-Tojar A, Hertel M, Burke T, Schroeder Jet al., 2019, Male age and its association with reproductive traits in captive and wild house sparrows, JOURNAL OF EVOLUTIONARY BIOLOGY, Vol: 32, Pages: 1432-1443, ISSN: 1010-061X

Journal article

Pipoly I, Szabo K, Bokony V, Preiszner B, Seress G, Vincze E, Schroeder J, Liker Aet al., 2019, Higher Frequency of Extra-Pair Offspring in Urban Than Forest Broods of Great Tits (Parus major), FRONTIERS IN ECOLOGY AND EVOLUTION, Vol: 7, ISSN: 2296-701X

Journal article

Schroeder J, Redfern C, Boothbu C, 2019, An evaluation of canes as management technique to reduce predation by gulls on ground nesting seabirds, Ibis, Vol: 161, Pages: 453-458, ISSN: 0019-1019

The best documented method to decrease predation of breeding seabirds by gulls are culling regimes; however, studies on the effectiveness of this method show ambiguous results. Here we tested an alternative method, using bamboo canes erected in four breeding sites of Arctic Tern Sterna paradisaea as a gull‐deterrent. Although we found fewer predation attempts in the caned areas than in the control areas, canes did not reduce the probability of predation success per attempt. This pilot study documents that the use of canes as a conservation strategy to reduce gull predation is promising, economic and simple, and is thus probably a versatile tool for conservation managers.

Journal article

Matsushima W, Brink K, Schroeder J, Miska EA, Gapp Ket al., 2019, Mature sperm small-RNA profile in the sparrow: implications for transgenerational effects of age on fitness, ENVIRONMENTAL EPIGENETICS, Vol: 5, ISSN: 2058-5888

Journal article

Matsushima W, Brink K, Schroeder J, Miska EA, Gapp Ket al., 2019, Mature sperm small RNA profile in the sparrow: implications for transgenerational effects of age on fitness

Mammalian sperm RNA has recently received a lot of interest due to its involvement in epigenetic germline inheritance. Studies of epigenetic germline inheritance have shown that environmental exposures can induce effects in the offspring without altering the DNA sequence of germ cells. Most mechanistic studies were conducted in laboratory rodents and C. elegans while observational studies confirm the phenotypic phenomenon in wild populations of humans and other species including birds. Prominently, paternal age in house sparrows affects offspring fitness, yet the mechanism is unknown. This study provides a first reference of house sparrow sperm small RNA as an attempt to uncover their role in the transmission of the effects of paternal age on the offspring. In this small scale pilot, we found no statistically significant differences between miRNA and tRNA fragments in aged and prime sparrow sperm. These results indicate a role of other epigenetic information carriers, such as distinct RNA classes, RNA modifications, DNA methylation and retained histones, and a clear necessity of future studies in wild populations.

Working paper

Sanchez-Tojar A, Nakagawa S, Sanchez-Fortun M, Martin DA, Ramani S, Girndt A, Bokony V, Kempenaers B, Liker A, Westneat DF, Burke T, Schroeder Jet al., 2018, Meta-analysis challenges a textbook example of status signalling and demonstrates publication bias, eLife, Vol: 7, Pages: 1-26, ISSN: 2050-084X

The status signalling hypothesis aims to explain within-species variation inornamentation by suggesting that some ornaments signal dominance status. Here, we usemultilevel meta-analytic models to challenge the textbook example of this hypothesis, the black bibof male house sparrows (Passer domesticus). We conducted a systematic review, and obtainedprimary data from published and unpublished studies to test whether dominance rank is positivelyassociated with bib size across studies. Contrary to previous studies, the overall effect size (i.e.meta-analytic mean) was small and uncertain. Furthermore, we found several biases in the literaturethat further question the support available for the status signalling hypothesis. We discuss severalexplanations including pleiotropic, population- and context-dependent effects. Our findings call forreconsidering this established textbook example in evolutionary and behavioural ecology, andshould stimulate renewed interest in understanding within-species variation in ornamental traits.

Journal article

Edwards HA, Schroeder J, Dugdale HL, 2018, Gender differences in authorships are not associated with publication bias in an evolutionary journal, PLoS ONE, Vol: 13, ISSN: 1932-6203

The loss of talented women from senior academic positions has partly resulted from a lower number of published papers and the accompanying reduced visibility of female compared to male scientists. The reasons for these gender-differences in authorship is unclear. One potential reason is a bias in the editorial and review process of scientific journals. We investigated whether patterns of authorship and editorial outcome were biased according to gender and geographic location in the Journal of Evolutionary Biology. Such potential bias may contribute to inequality in the field. We found patterns of gender differences in authorship, but this was unrelated to the editorial decision of whether to publish the manuscript. Female first-authors (the lead role) were six times less likely to be named as the corresponding author than male first-authors, and female first-authors were more likely to be displaced as corresponding authors by female co-authors than were male first-authors. We found an under-representation of female first- and last-authors compared to baseline populations of members of the European Society for Evolutionary Biology (which publishes the Journal of Evolutionary Biology) and of Evolutionary Biology faculty at the world top-10 universities for the Life Sciences. Also, manuscripts from Asia were five times more likely to be rejected on the final decision, independent of gender. Overall our results suggest that the peer review processes we investigated at the Journal of Evolutionary Biology are predominately gender-neutral, but not neutral to geographic location. Editorial gender-bias is thus unlikely to be a contributing factor to differences in authorship in this journal.

Journal article

Girndt A, Chng CWT, Burke T, Schroeder Jet al., 2018, Male age is associated with extra-pair paternity, but not with extra-pair mating behaviour, Publisher: Nature Publishing Group

Extra-pair paternity is the result of copulation between a female and a male other than her social partner. In socially monogamous birds, old males are most likely to sire extra-pair offspring. The male manipulation and female choice hypotheses predict that age-specific male mating behaviour could explain this old-over-young male advantage. These hypotheses have been difficult to test because copulations and the individuals involved are hard to observe. Here, we studied the mating behaviour and pairing contexts of captive house sparrows, Passer domesticus. Our set-up mimicked the complex social environment experienced by wild house sparrows. We found that middle-aged males, that would be considered old in natural populations, gained most extra-pair paternity. However, both female solicitation behaviour and subsequent extra-pair matings were unrelated to male age. Further, copulations were more likely when solicited by females than those initiated by males (i.e. unsolicited copulations), and unsolicited within-pair copulations were more common than unsolicited extra-pair copulations. To conclude, our results did not support either hypotheses regarding age-specific male mating behaviour. Instead, female choice, independent of male age, governed copulation success, especially in an extra-pair context and post-copulatory mechanisms might determine why older males sire more extra-pair offspring.

Working paper

Girndt A, Change WT, Burke T, Schroeder Jet al., 2018, Male age is associated with extra-pair paternity, but not with extra-pair mating behaviour, Scientific Reports, Vol: 8, ISSN: 2045-2322

Extra-pair paternity is the result of copulation between a female and a male other than her social partner. In socially monogamous birds, old males are most likely to sire extra-pair offspring. The male manipulation and female choice hypotheses predict that age-specific male mating behaviour could explain this old-over-young male advantage. These hypotheses have been difficult to test because copulations and the individuals involved are hard to observe. Here, we studied the mating behaviour and pairing contexts of captive house sparrows, Passer domesticus. Our set-up mimicked the complex social environment experienced by wild house sparrows. We found that middle-aged males, which would be considered old in natural populations, gained most extra-pair paternity. However, both, female solicitation behaviour and subsequent extra-pair matings were not associated with male age. Further, copulations were more likely when solicited by females than when initiated by males (i.e. unsolicited copulations). Male initiated within-pair copulations were more common than male initiated extra-pair copulations. To conclude, our results did not support either hypothesis regarding age-specific male mating behaviour. Instead, female choice, independent of male age, governed copulation success, especially in an extra-pair context. Post-copulatory mechanisms might determine why older males sire more extra-pair offspring.

Journal article

Girndt A, Chng CWT, Burke T, Schroeder Jet al., 2018, Male age is associated with extra-pair paternity, but not with extra-pair mating behaviour, Publisher: Cold Spring Harbor Laboratory

<jats:title>Abstract</jats:title><jats:p>Extra-pair paternity is the result of copulation between a female and a male other than her social partner. In socially monogamous birds, old males are most likely to sire extra-pair offspring. The male manipulation and female choice hypotheses predict that age-specific male mating behaviour could explain this old-over-young male advantage. These hypotheses have been difficult to test because copulations and the individuals involved are hard to observe. Here, we studied the mating behaviour and pairing contexts of captive house sparrows,<jats:italic>Passer domesticus</jats:italic>. Our set-up mimicked the complex social environment experienced by wild house sparrows. We found that middle-aged males, that would be considered old in natural populations, gained most extra-pair paternity. However, both female solicitation behaviour and subsequent extra-pair matings were unrelated to male age. Further, copulations were more likely when solicited by females than those initiated by males (i.e. unsolicited copulations), and unsolicited within-pair copulations were more common than unsolicited extrapair copulations. To conclude, our results did not support either hypotheses regarding age-specific male mating behaviour. Instead, female choice, independent of male age, governed copulation success, especially in an extra-pair context and post-copulatory mechanisms might determine why older males sire more extra-pair offspring.</jats:p>

Working paper

Sanchez-Tojar A, Schroeder J, Farine DR, 2018, A practical guide for inferring reliable dominance hierarchies and estimating their uncertainty, JOURNAL OF ANIMAL ECOLOGY, Vol: 87, Pages: 594-608, ISSN: 0021-8790

Journal article

Winney IS, Schroeder J, Nakagawa S, Hsu Y-H, Simons MJP, Sanchez-Tojar A, Mannarelli M-E, Burke Tet al., 2018, Heritability and social brood effects on personality in juvenile and adult life-history stages in a wild passerine, JOURNAL OF EVOLUTIONARY BIOLOGY, Vol: 31, Pages: 75-87, ISSN: 1010-061X

Journal article

Baugh AT, Senft RA, Firke M, Lauder A, Schroeder J, Meddle SL, van Oers K, Hau Met al., 2017, Risk-averse personalities have a systemically potentiated neuroendocrine stress axis: A multilevel experiment in Parus major, Hormones and Behavior, Vol: 93, Pages: 99-108, ISSN: 0018-506X

Hormonal pleiotropy-the simultaneous influence of a single hormone on multiple traits-has been hypothesized as an important mechanism underlying personality, and circulating glucocorticoids are central to this idea. A major gap in our understanding is the neural basis for this link. Here we examine the stability and structure of behavioral, endocrine and neuroendocrine traits in a population of songbirds (Parus major). Upon identifying stable and covarying behavioral and endocrine traits, we test the hypothesis that risk-averse personalities exhibit a neuroendocrine stress axis that is systemically potentiated-characterized by stronger glucocorticoid reactivity and weaker negative feedback. We show high among-individual variation and covariation (i.e. personality) in risk-taking behaviors and demonstrate that four aspects of glucocorticoid physiology (baseline, stress response, negative feedback strength and adrenal sensitivity) are also repeatable and covary. Further, we establish that high expression of mineralocorticoid and low expression of glucocorticoid receptor in the brain are linked with systemically elevated plasma glucocorticoid levels and more risk-averse personalities. Our findings support the hypothesis that steroid hormones can exert pleiotropic effects that organize behavioral phenotypes and provide novel evidence that neuroendocrine factors robustly explain a large fraction of endocrine and personality variation.

Journal article

Girndt A, Cockburn G, Sánchez-Tójar A, Løvlie H, Schroeder Jet al., 2017, Method matters: experimental evidence for shorter avian sperm in faecal compared to abdominal massage samples, PLOS One, Vol: 12, ISSN: 1932-6203

Birds are model organisms in sperm biology. Previous work in zebra finches, suggested that sperm sampled from males' faeces and ejaculates do not differ in size. Here, we tested this assumption in a captive population of house sparrows, Passer domesticus. We compared sperm length in samples from three collection techniques: female dummy, faecal and abdominal massage samples. We found that sperm were significantly shorter in faecal than abdominal massage samples, which was explained by shorter heads and midpieces, but not flagella. This result might indicate that faecal sampled sperm could be less mature than sperm collected by abdominal massage. The female dummy method resulted in an insufficient number of experimental ejaculates because most males ignored it. In light of these results, we recommend using abdominal massage as a preferred method for avian sperm sampling. Where avian sperm cannot be collected by abdominal massage alone, we advise controlling for sperm sampling protocol statistically.

Journal article

Schroeder J, Masero JA, Abad-Gomez JM, Gutierrez JS, Santiago-Quesada F, Senner NR, Sanchez-Guzman JM, Piersma T, Amat JA, Villegas Aet al., 2017, Wetland salinity induces sex-dependent carry-over effects on the individual performance of a long-distance migrant, Scientific Reports, Vol: 7, ISSN: 2045-2322

Salinization is having a major impact on wetlands and its biota worldwide. Specifically, many migratory animals that rely on wetlands are increasingly exposed to elevated salinity on their nonbreeding grounds. Experimental evidence suggests that physiological challenges associated with increasing salinity may disrupt self-maintenance processes in these species. Nonetheless, the potential role of salinity as a driver of ecological carry-over effects remains unstudied. Here, we investigated the extent to which the use of saline wetlands during winter – inferred from feather stable isotope values – induces residual effects that carry over and influence physiological traits relevant to fitness in black-tailed godwits Limosa limosa limosa on their northward migration. Overwintering males and females were segregated by wetland salinity in West Africa, with females mostly occupying freshwater wetlands. The use of these wetlands along a gradient of salinities was associated with differences in immune responsiveness to phytohaemagglutinin and sized-corrected body mass in godwits staging in southern Europe during northward migration – 3,000 km from the nonbreeding grounds – but in males only. These findings provide a window onto the processes by which wetland salinity can induce carry-over effects and can help predict how migratory species should respond to future climate-induced increases in salinity.

Journal article

Parau LG, Kingma SA, Weigl SE, Dugdale HL, Lessells CM, Schroeder Jet al., 2017, Dynamics in numbers of group-roosting individuals in relation to pair-sleeping occurrence and onset of egg-laying in European Bee-eaters Merops apiaster, Journal of Ornithology, Vol: 158, Pages: 1119-1122, ISSN: 0021-8375

Sleeping in the nest at the beginning of the breeding season is common for birds nesting in cavities. Here, we report evidence that European Bee-eaters Merops apiaster sleep in pairs in the nesting burrow. In 3.2% of the nest checks, we found two individuals sleeping together. This behaviour ceased once hatching started. A decrease in the number of birds at a communal roost coincided with the incidences of pair-sleeping and initiation of egg-laying. Thus, checking the burrows of European Bee-eaters at the beginning of the breeding season increases the chance of observing pair-sleeping.

Journal article

Hsu Y-H, Simons MJP, Schroeder J, Girndt A, Winney IS, Burke T, Nakagawa Set al., 2017, Age-dependent trajectories differ between within-pair and extra-pair paternity success, Journal of Evolutionary Biology, Vol: 30, Pages: 951-959, ISSN: 1010-061X

Reproductive success is associated with age in many taxa, increasing in early life followed by reproductive senescence. In socially monogamous but genetically polygamous species, this generates the interesting possibility of differential trajectories of within-pair and extra-pair siring success with age in males. We investigate these relationships simultaneously using within-individual analyses with 13 years of data from an insular house sparrow (Passer domesticus) population. As expected, we found that both within- and extra-pair paternity success increased with age, followed by a senescence-like decline. However, the age trajectories of within- and extra-pair paternity successes differed significantly, with the extra-pair paternity success increasing faster, although not significantly, in early life, and showing a delayed decline by 1.5 years on average later in life compared to within-pair paternity success. These different trajectories indicate that the two alternative mating tactics should have age-dependent pay-offs. Males may partition their reproductive effort between within- and extra-pair matings depending on their current age to reap the maximal combined benefit from both strategies. The interplay between these mating strategies and age-specific mortality may explain the variation in rates of extra-pair paternity observed within and between species.

Journal article

Sánchez-Tójar A, Schroeder J, Farine DR, 2017, A practical guide for inferring reliable dominance hierarchies and estimating their uncertainty

<jats:title>Abstract</jats:title><jats:p>Many animal social structures are organized hierarchically, with dominant individuals monopolizing resources. Dominance hierarchies have received great attention from behavioural and evolutionary ecologists. As a result, there are many methods for inferring hierarchies from social interactions. Yet, there are no clear guidelines about how many observed dominance interactions (i.e. sampling effort) are necessary for inferring reliable dominance hierarchies, nor are there any established tools for quantifying their uncertainty. In this study, we simulated interactions (winners and losers) in scenarios of varying steepness (the probability that a dominant defeats a subordinate based on their difference in rank). Using these data, we (1) quantify how the number of interactions recorded and hierarchy steepness affect the performance of three methods, (2) propose an amendment that improves the performance of a popular method, and (3) suggest two easy procedures to measure uncertainty in the inferred hierarchy. First, we found that the ratio of interactions to individuals required to infer reliable hierarchies is surprisingly low, but depends on the hierarchy steepness and method used. We then show that David’s score and our novel randomized Elo-rating are the two best methods, whereas the original Elo-rating and the recently described ADAGIO perform less well. Finally, we propose two simple methods to estimate uncertainty at the individual and group level. These uncertainty measures further allow to differentiate non-existent, very flat and highly uncertain hierarchies from intermediate, steep and certain hierarchies. Overall, we find that the methods for inferring dominance hierarchies are relatively robust, even when the ratio of observed interactions to individuals is as low as 10 to 20. However, we suggest that implementing simple procedures for estimating uncertainty will benefit researchers, and quanti

Journal article

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