Drivers of within- and among-individual variation in risk-taking behaviour during reproduction in a long-lived bird

Plastic and selective mechanisms govern parental investment adjustments to predation threat. We investigated the relative importance of plasticity and selection in risk-taking propensity of incubating female common eiders Somateria mollissima facing unprecedented predation in SW Finland, Baltic Sea. Using a 12-year individual-based dataset, we examined within- and among-individual variation in flight initiation distance (FID), in relation to predation risk, nest detectability, individual traits and reproductive investment (NFID = 1009; Nindividual = 559). We expected females nesting in riskier environments (higher predation risk, lower nest concealment) to mitigate environmentally imposed risk by exhibiting longer FIDs, and females investing more in current reproduction (older, in better condition or laying larger clutches) to display shorter FIDs. The target of predation-adult or offspring-affected the mechanisms adapting risk-taking propensity; females plastically increased their FID under higher adult predation risk, while risk-avoiding breeders were predominant on islands with higher nest predation risk. Risk-taking females selected thicker nest cover, consistent with personality-matching habitat choice. Females plastically attenuated their anti-predator response (shorter FIDs) with advancing age, and females in better body condition were more risk-taking, a result explained by selection processes. Future research should consider predator type when investigating the fitness consequences of risk-taking strategies.

Eiders, nutrients and eagles: Bottom-up and top-down population dynamics in a marine bird

The main objective of this long-term study (1978-2016) was to find the underlying factors behind the declining trends of eider Somateria mollissima in the Baltic/Wadden Sea. Specifically, we aimed at quantifying the bottom-up effect of nutrients, through mussel stocks, on reproduction and abundance of eider, and the top-down effects caused by white-tailed eagle Haliaeetus albicilla predation. Bottom-up effects increase marine primary productivity with subsequent effects on food availability for a major mussel predator. Top-down effects may also regulate eider populations because during incubation female eiders are vulnerable to predation by eagles. Our structural equation modelling explained a large percentage of the variance in eider abundance. We conclude that the Baltic/Wadden Sea eider population was regulated directly by white-tailed sea eagle predation on incubating females and indirectly by the amount of nutrients in seawater affecting both mussel stocks and the breeding success of eiders, reflecting density dependence. These findings may explain the decreasing trend in the Baltic/Wadden Sea eider population during the last decades as an additive effect of top-down and bottom-up factors, and likely as an interaction between them.

It is marine: distinguishing a new species of Catatropis (Digenea: Notocotylidae) from its freshwater twin

The morphology of sexual adults is the cornerstone of digenean systematics. In addition, life cycle data have always been significant. The integration of these approaches, supplemented with molecular data, has allowed us to detect a new species that many researchers may have previously seen, but not recognized. Sexual adults from common eiders that we found in northern European seas were extremely similar to other notocotylids, but the discovery of their intermediate host, a marine snail, revealed the true nature of this material. Here we describe sexual adults, rediae and cercariae of Catatropis onobae sp. nov. We discuss how 'Catatropis verrucosa' should be regarded, justify designation of the new species C. onobae for our material and explain why it can be considered a cryptic species. The phylogenetic position of C. onobae within Notocotylidae, along with other evidence, highlights the challenges for the taxonomy of the family, for which two major genera appear to be polyphyletic and life cycle data likely undervalued.

First case of Plasmodium relictum lineage pGRW11 infection in a captive-bred common eider (Somateria Mollissima) in Europe

A 4-year-old, female common Eider (Somateria mollissima) was presented for mild lethargy with no previous medical history. Numerous intraerythrocytic, round-shaped inclusions were visualized on blood smears, later morphologically identified as Plasmodium relictum parasites. Despite oral doxycycline treatment, clinical condition declined 48 h later. Supportive care was initiated, but the bird died rapidly. Necropsy revealed acute, internal hemorrhages (lungs, air sacs) and subcutaneous, diffuse cervical hematoma, associated with resuscitation attempts. Marked, multicentric amyloidosis (kidney, liver, spleen) was the main histological finding. Molecular analysis identified lineage pGRW11 of P. relictum. This is the first reported case of P. relictum lineage pGRW11 infection in a common Eider. This report describes the clinical features, diagnosis, treatment and associated pathological findings of infection by P. relictum lineage pGRW11 in a common Eider.

Pathology and Plasma Biochemistry of Common Eider (Somateria mollissima) Males Wintering in the Danish Part of the Western Baltic

Blood biochemistry, body mass, and gross pathology of male eiders (Somateria mollissima) wintering in the Inner Danish Waters of the western Baltic Sea (the Great Belt Strait) were assessed in this study. In November 2015, 14 specimens were obtained from the area defined for examination. Of the subject animals captured, 1 had dilated intestines and 2 had granulomas with encapsulated shotgun pellets considered to be chronic in nature. All 14 males were determined to have enteritis along with acanthocephalan and trematode endoparasites. Compared with reference values for captive eiders, plasma values of alanine aminotransferase (93%), total bilirubin (45%), gamma-glutamyl transferase (41%), and alkaline phosphatase (92%) showed significant increases in all 14 male birds. Altogether, the plasma biochemistry and gross pathology findings suggest that up to as many as 20% of the eider males in the Inner Danish Waters of the western Baltic Sea may suffer from liver and bile duct lesions and enteritis. The overall effect on the bird's survival from the results of this investigation is unknown. Therefore, the authors emphasize that more research is required on wintering eiders in the western Baltic to obtain a better understanding of their overall health status during winter, as well as their responses to wound-related lesions associated with gunshot pellets.

Sex-specific effects of the in ovo environment on early-life phenotypes in eiders

Maternal effects affect offspring phenotype and fitness. However, the roles of offspring sex-specific sensitivity to maternal glucocorticoids and sex-biased maternal investment remain unclear. It is also uncertain whether telomere length (a marker associated with lifespan) depends on early growth in a sex-specific manner. We assessed whether maternal traits including corticosterone (CORT; the main avian glucocorticoid) and in ovo growth rate are sex-specifically related to offspring CORT exposure, relative telomere length (RTL) and body condition in eiders (Somateria mollissima). We measured feather CORT (fCORT), RTL and body condition of newly hatched ducklings, and growth rate in ovo was expressed as tarsus length at hatching per incubation duration. Maternal traits included baseline plasma CORT, RTL, body condition and breeding experience. We found that fCORT was negatively associated with growth rate in daughters, while it showed a positive association in sons. Lower offspring fCORT was associated with higher maternal baseline plasma CORT, and fCORT was higher in larger clutches and in those hatching later. The RTL of daughters was negatively associated with maternal RTL, whereas that of males was nearly independent of maternal RTL. Higher fCORT in ovo was associated with longer RTL at hatching in both sexes. Duckling body condition was mainly explained by egg weight, and sons had a slightly lower body condition. Our correlational results suggest that maternal effects may have heterogeneous and even diametrically opposed effects between the sexes during early development. Our findings also challenge the view that prenatal CORT exposure is invariably associated with shorter telomeres.

Anti-parasite treatment results in decreased estimated survival with increasing lead (Pb) levels in the common eider Somateria mollissima

Field experiments where parasites are removed through treatment and contaminant levels in host tissues are recorded can provide insight into the combined effects of parasitism and contaminants in wild populations. In 2013 and 2014, we treated northern common eider ducks (Somateria mollissima) arriving at a breeding colony with either a broad-spectrum antihelminthic (PANACUR^®) or distilled water, and measured their blood lead (Pb) levels. Breeding propensity and clutch sizes were inversely related to Pb in both treatment groups. In comparison, a negative effect of Pb on resight probability the following year was observed only in the anti-parasitic treatment (APT) group. These contrasting patterns suggest a long-term benefit to survival of intestinal parasitism in eiders experiencing Pb exposure. The arrival date of hens explained some, but not all, of the effects of Pb. We weigh the merits of different hypotheses in explaining our results, including protective bioaccumulation of Pb by parasites, condition-linked thresholds to costly reproduction and the direct effects of APT on eider health. We conclude that variation in helminth parasitism influences survival in this migratory bird in counterintuitive ways.

Experimental Infection of Common Eider Ducklings with Wellfleet Bay Virus, a Newly Characterized Orthomyxovirus

Wellfleet Bay virus (WFBV), a novel orthomyxovirus in the genus Quaranjavirus, was first isolated in 2006 from carcasses of common eider (Somateria mollissima) during a mortality event in Wellfleet Bay (Barnstable County, Massachusetts, USA) and has since been repeatedly isolated during recurrent mortality events in this location. Hepatic, pancreatic, splenic, and intestinal necrosis was observed in dead eiders. We inoculated 6-week-old common eider ducklings with WFBV in an attempt to recreate the naturally occurring disease. Approximately 25% of inoculated eiders had onset of clinical disease and required euthanasia; an additional 18.75% were adversely affected based on net weight loss during the trial. Control ducklings did not become infected and did not have clinical disease. Infected ducklings with clinical disease had pathologic lesions consistent with those observed during natural mortality events. WFBV was reisolated from 37.5% of the inoculated ducklings. Ducklings surviving to 5 days postinoculation developed serum antibody titers to WFBV.

Hepatic trace element concentrations of breeding female common eiders across a latitudinal gradient in the eastern Canadian Arctic

We examined hepatic concentrations of arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), manganese (Mn), mercury (Hg), rubidium (Rb), selenium (Se) and zinc (Zn) in 10 breeding female common eiders (Somateria mollissima) from each of three colonies across 20° of latitude. Levels of many elements were elevated in eiders, although generally below levels of toxicological concern. We found significant differences in concentrations of As, Rb, Hg, Mn and Se among colonies, but not in a consistent pattern with latitude, and Hg:Se molar ratios did not vary among colonies. Furthermore, overlap in element concentrations from birds at different colonies meant that we could not reliably differentiate birds from different colonies based on a suite of their hepatic trace element concentrations. We encourage other researchers to assess baseline trace element levels on this important, harvested species, as a means of tracking contamination of nearshore benthic environments in the circumpolar Arctic.

State-dependent capital and income breeding: a novel approach to evaluating individual strategies with stable isotopes

Background

Species-specific strategies for financing the costs of reproduction are well understood, forming a continuum ranging from high to low reliance on stored nutrients. Animals relying mostly on stored reserves are termed ‘capital breeders’, whereas ‘income breeders’ rely mostly on concurrent intake when financing the costs of reproduction. The role and adaptive value of individual variation in these strategies remain elusive. Life-history theory posits that capital breeding should be favoured when offspring reproductive value peaks, typically occurring early in the season, and that current income should increasingly be used with progressing season. Because resource limitation may hamper flexible resource allocation, a corollary prediction is that only good-condition individuals may show the expected seasonal shift in resource use. To test this prediction, we examined stable isotopes (δ¹³C and δ¹⁵N) in blood and lipid-free egg yolk of breeding eider females (Somateria mollissima) from the Baltic Sea to assess the role of individual variation in the use of proteins from local diet vs. stored reserves.

Results

We show for the first time that individuals from a single population differ in their utilization of stored reserves and concurrent intake to finance the costs of reproduction. Consistent with our prediction, heavy females predominantly used stored reserves for producing egg yolks early in the season, increasingly relying on local feeding with later onset of breeding, whereas light females showed no seasonal change in allocation strategy.

Conclusions

Stable isotope profiling at the individual level is a powerful tool for monitoring relative changes in investment strategies through time, showing promise as an early warning indicator of ecological change in food webs.

Reproductive investment is connected to innate immunity in a long-lived animal

Life-history theory predicts that organisms optimize their resource allocation strategy to maximize lifetime reproductive success. Individuals can flexibly reallocate resources depending on their life-history stage, and environmental and physiological factors, which lead to variable life-history strategies even within species. Physiological trade-offs between immunity and reproduction are particularly relevant for long-lived species that need to balance current reproduction against future survival and reproduction, but their underlying mechanisms are poorly understood. A major unresolved issue is whether the first-line innate immune function is suppressed by reproductive investment. In this paper, we tested if reproductive investment is associated with the suppression of innate immunity, and how this potential trade-off is resolved depending on physiological state and residual reproductive value. We used long-lived capital-breeding female eiders (Somateria mollissima) as a model. We showed that the innate immune response, measured by plasma bacteria-killing capacity (BKC), was negatively associated with increasing reproductive investment, i.e., with increasing clutch size and advancing incubation stage. Females in a better physiological state, as indexed by low heterophil-to-lymphocyte (H/L) ratios, showed higher BKC during early incubation, but this capacity decreased as incubation progressed, whereas females in poorer state showed low BKC capacity throughout incubation. Although plasma BKC generally declined with increasing H/L ratios, this decrease was most pronounced in young females. Our results demonstrate that reproductive investment can suppress constitutive first-line immune defence in a long-lived bird, but the degree of immunosuppression depends on physiological state and age.

Trace elements in eggs of common eiders (Somateria mollissima) breeding in Nova Scotia, Canada

We provide the first report on trace element concentrations in eggs of common eiders (Somateria mollissima), a coastal benthic foraging sea duck, from Nova Scotia, Canada, and compare those to known values from this species elsewhere. Most trace elements of toxicological concern (Hg, Se, Cd, Cu, Zn) were lower in eider eggs from Nova Scotia than from eider eggs collected farther north in Canada, although As was elevated. Our data provide strong support for a pattern of increasing Hg at higher latitudes for this species.

Increasing cadmium and zinc levels in wild common eiders breeding along Canada's remote northern coastline

The common eider (Somateria mollissima) is an abundant sea duck breeding around the circumpolar Arctic, and is an important component of subsistence and sport harvest in some regions. We determined hepatic cadmium (Cd) and zinc (Zn) concentrations in the livers of breeding females sampled during three time periods including 1992/3, 2001/2 and 2008 at three sites spanning 53.7°N-75.8°N in the eastern Canadian Arctic. At all sites, concentrations of both Cd and Zn increased ~300% over this time period. The reasons for this rapid increase in concentrations are unclear.

Context dependency of baseline glucocorticoids as indicators of individual quality in a capital breeder

Identifying markers of individual quality is a central goal of life-history theory and conservation biology. The 'corticosterone (CORT)-fitness hypothesis' postulates that low fitness signals impaired ability to cope with the environment, resulting in elevated baseline CORT levels. CORT can, however, be negatively, positively or neutrally related to fitness, depending on the context. In order to clarify this controversial issue, we elucidate the utility of using baseline CORT as a correlate of individual fitness in incubating female eiders across variable environments. An increase in serum CORT with decreasing body condition was evident in older, more experienced breeders, while increased clutch mass was associated with elevated serum CORT in females breeding late in the season. For faecal CORT, the expected negative association with body condition was observed only in early breeders. We found a strong increase in faecal CORT with increasing baseline body temperature, indicating the utility of body temperature as a complementary stress indicator. Females in good body condition had a lower baseline body temperature, but this effect was only observed on open islands, a harsher breeding habitat less buffered against weather variability. Females with higher reproductive investment also maintained a lower baseline body temperature. Nest success strongly decreased with increasing serum and faecal CORT concentrations, and individual stress hormone and body temperature profiles were repeatable over years. Although our data support the tenet that baseline CORT is negatively related to fitness, the complex context-dependent effects call for cautious interpretation of relationships between stress physiology and phenotypic quality.