DOI: 10.5061/dryad.kh18932fh
title: Lower adaptive immunity in invasive Egyptian geese compared to sympatric native waterfowls

description: Successful invasive species increase their spreading success by
 trading-off nutritional and metabolic resources allocated to reproduction
 and range expansion with other costly body functions. One proposed
 mechanism for the reallocation of resources is a trade-off with the immune
 function and the regulation of oxidative status. Relying on a panel of
 blood-based markers of immune function and oxidative status quantified in
 an invasive species (Egyptian goose) and two native competing species
 (mallard and mute swan) in Germany, we tested the hypothesis that the
 invasive species would have (i) lower investment in immune function, (ii)
 lower levels of oxidative damage, and (iii) no higher antioxidant defences
 compared to the native species. We found lower levels of adaptive immune
 markers (lymphocytes and immunoglobulin Y), in the invasive species
 compared to the two native species. Innate immune profile was generally
 similar between Egyptian geese and mallards. By contrast, mute swans
 showed higher levels of heterophils and lysozymes, and lower levels of
 bacteria killing ability compared to both Egyptian geese and mallards.
 Mute swans also showed higher levels of haemolysis and haemagglutination,
 but lower levels of monocytes and haematocrit compared to Egyptian geese.
 Reactive oxygen metabolites, a marker of oxidative damage, were higher in
 mallards and lower in Egyptian geese compared to the other waterfowl
 species, while levels of antioxidants were generally similar among the
 three species. Our results point to a reduced investment in adaptive
 immune function in the invasive species as a possible resources-saving
 immunological strategy due to the loss of co-evolved parasites in the new
 colonised habitats, as observed in a previous study. A lower investment in
 immune function may benefit other energy-demanding activities, such as
 reproduction, dispersal, and territoriality, while maintaining relatively
 higher innate immunity is beneficial since invasive species mainly
 encounter novel pathogens. Results pointed out also other important
 species-specific differences in baseline immune status, supporting
 previous findings on the relationship between species’ body mass and
 immune profile.
description: Adult individuals of the study species were live-trapped in June
 and July 2016 in the Rhine and Mosel area in Western Germany (50.4° N,
 7.6° E; Fig. S1). All individuals in this study were locally breeding and
 mostly in the phase of guiding goslings/ducklings at the time of sampling.
 Birds were caught using either loops or landing nets. Each bird was
 individually ringed, and body mass and sex were recorded. A blood sample
 from each bird was collected, either from the vena metatarsalia plantaris
 superficialis or the vena ulnaris, using a needle of 0.06 mm diameter.
 Blood samples were kept cool during field procedures, then centrifuged for
 15 minutes to separate plasma from red blood cells which were stored
 separately in liquid nitrogen within 8 hours from blood collection. At the
 end of fieldwork, samples were stored at -80 °C until laboratory
 analyses. The dataset included 74 actively reproducing
 individuals of which 28 were Egyptian geese, 10 were mallards, and 36 were
 mute swans. We collected blood samples from both female and male Egyptian
 geese (females = 12; males = 16) and mute swans (females = 21; males =
 15), and only female mallards (Table 1). We performed
 generalized linear models (GLMs) to assess the differences between species
 for each single marker. Therefore, for each model, we included one marker
 as a dependent variable and species as an independent variable. Family
 distribution of the models was chosen according to the nature of the data:
 quasibinomial distribution for proportion data, quasipoisson distribution
 for discrete data, gaussian or gamma for continuous non-negative data. We
 checked for normal distribution of residuals by means of Q-Q plots. If the
 distribution of model residuals was not normal, we log-transformed the
 dependent variables after which we performed again the model diagnostics.
 We also screened the models for the presence of outliers relying on the
 Cook’s distance with a fixed threshold of 0.25. When we detected outliers,
 we removed them and re-run the model. Subsequently, we
 implemented GLMs testing for the interaction between species and sex on a
 subset of the original dataset including only Egyptian geese and mute swan
 (the mallard was excluded because we sampled only females). Following the
 previous procedures, we removed outliers when detected, we log-transformed
 the data when necessary; we performed the model diagnostics by visual
 inspection of Q-Q plots. We explored the effect of interactions by
 likelihood ratio tests run for each GLM. Finally, to
 evaluate the robustness of our results, we compared standardized effect
 sizes between species, also including comparisons between same sex
 individuals, for each immune-physiological marker. Standardized effect
 sizes are analytical tools that enable to compare the magnitude and the
 direction of a biological effect (Garamszegi, 2006). We used means,
 standard deviations and sample sizes of immune-physiological markers of
 each species to calculate Hedges’ g effect sizes, which is a measure of
 how much one group differs from another one, accounting for small sample
 sizes (Cooper et al., 2009). We displayed effect sizes in forest plots
 comparing pairs of species by means of the forest function of the package
 metafor in R. We calculated the effect sizes and their confidence
 intervals in R using the compute.es package. The effect size is
 significant when the confidence interval does not include zero.
description: # Lower adaptive immunity in invasive Egyptian geese compared to sympatric
 native waterfowls
 [https://doi.org/10.5061/dryad.kh18932fh](https://doi.org/10.5061/dryad.kh18932fh) The dataset included 74 actively reproducing individuals of which 28 were Egyptian Geese, 10 Mallards, and 36 Mute Swans. We collected blood samples from both female and male Egyptian Geese (females = 12; males = 16), Mute Swans (females = 21; males = 15), and only female Mallards. Sample sizes varied slightly for different immunological markers due to limited amounts of blood for certain individuals (Table 1). ## Description of the data and file structure Species * CYOL Mute Swan * ANPL Mallard * ALEG Egyptian Goose Parameters * basos = basophils (cells/10000 erythrocytes) * eos = eosinophils (cells/10000 erythrocytes) * heteros = heterophils (cells/10000 erythrocytes) * lymphos = lymphocytes (cells/10000 erythrocytes) * monos = monocytes (cells/10000 erythrocytes) * hkt = haematocrit (Erythrocytes/ml) * lysozyme = lysozymes (ug/ml) * agglutination = haemagglutination (titer) * lysis = haemolysis (titer) * IgY = immunoglobulins-Y (Optical Density) * bka = bacteria-killing ability (%) * oxy = non-enzymatic antioxidant capacity (mM HOCL neutralized) * roms = reactive oxygen metabolites (mM H2O2 equivalents) * PCs = protein carbonyls (nmol/mg proteins) * gpx = glutathione peroxidase (units/mg proteins) * sod = superoxide dismutase (units/mg proteins) ##### NA = missing data