Handling stress of female common eiders during avian cholera outbreaks

Researchers often consider the importance of minimizing holding time during research activities; however, the long-term costs of such handling stress is rarely measured explicitly. As part of an ongoing study of common eiders (Somateria mollissima) at a breeding colony in East Bay, Southampton Island, Nunavut, we recorded duration of restraint for females captured during avian cholera epizootics (2007 and 2008) and monitored female fates (breeding probability, onset of laying, and survival) relative to holding time. Probability of death increased with holding time in 2007 from an estimated 0.05 for females held 20 min to 0.33 for females held for 150 min. In 2008, we responded by limiting holding time to <90 min and mortality was no longer positively correlated with holding time, although total mortality was greater due to increased severity of avian cholera. In both years, longer restraint durations delayed onset of egg-laying after capture by 0.5 days for each 10 min of additional restraint but did not prevent breeding. This delay of nest initiation did not enhance survival probability. Our results show that prolonged holding time can exacerbate mortality during epizootics and emphasize the importance of minimizing restraint time in wild birds, especially in the presence of diseases. © 2011 The Wildlife Society.     

Body mass regulation during incubation in female common eiders Somateria mollissima

We investigated changes in incubation behaviour induced by body fuel depletion in incubating female common eiders, which, in contrast to pelagic seabirds, fast despite being close to marine food sources. In the Svalbard Archipelago, electronic scales were placed under eider nests and the incubation of six birds was prolonged by using wax-filled eggs. Based on changes in the rate of body mass loss in normally incubating females and in ten captive birds that did not incubate, body reserves neared depletion on average four days after hatching. During prolonged incubation, females took more frequent and longer recesses. Nest attentiveness consequently decreased, but was still high. In contrast to recesses during normal incubation, during which body mass of the birds decreased, mass remained constant during the recesses of prolonged incubation. The body stores of female eiders seemed to enable them to complete incubation with a limited safety margin. A further drop in body mass is avoided when a critical body mass is reached, because birds then start feeding enough to maintain mass while continuing incubation. Presumably, a similar mechanism will enable eiders to continue incubation when body reserves are prematurely depleted before hatching.     

Genetic evidence for kin-based female social structure in common eiders (Somateria mollissima)

Kin-based social groups are commonly studied among cooperativelybreeding species but have been less studied in "nontraditional"group breeding systems. We investigated the presence of kin-basedsociality among females in the common eider (Somateria mollisima),a colonial nesting sea duck that exhibits high levels of natalphilopatry in females. Previous studies of female socialityin common eiders have been restricted to observations duringbrood rearing. However, aggregations of female common eidersare also observed during other periods of the life cycle suchas colony arrival and nesting. Here we apply a novel, empiricalframework using molecular markers and field sampling to geneticallycharacterize female social groups at several stages of the commoneider life cycle. When compared with mean estimates of interindividualrelatedness for the entire colony, significantly higher levelsof relatedness were found between females within groups arrivingto the colony in flight, between females and nearest neighborsat the time of nest site selection, and between groups of femalesdeparting the colony with ducklings. Both full-sibling and half-siblingequivalent relationships were also found within these groups.Therefore, throughout each of several stages including in-flightcolony arrival, nesting, and brood rearing, we provide the firstgenetically confirmed evidence of female kin-based social groupsin common eiders and anseriformes in general.     

Parental effort and reproductive skew in coalitions of brood rearing female common eiders

Members of breeding groups face conflicts over parental effort when balancing antipredatory vigilance and feeding. Empirical evidence has shown disparate responses to manipulations of parental effort. We develop a model in which we determine the evolutionarily stable effort of partners given their body conditions, allowing the benefits of shared care to be unevenly divided, and we test this model's predictions with data on common eiders (Somateria mollissima). Eiders show uniparental female care; females may share brood rearing, or they may tend alone, and their body condition at hatching of the young shows large environmentally induced variation. The model predicts that parental effort (vigilance) in a coalition is lower than when tending alone, controlling for parental condition; this prediction is supported by the data. The parental effort in a coalition should be positively correlated with body condition, and this prediction is also supported. Finally, parental effort should increase when partner condition decreases and vice versa; this prediction is partially supported. The Nash bargaining game may provide promising avenues by which to determine the precise settlement of reproductive skew and effort between coalition partners in the future.     

Phytohemagglutinin response and immunoglobulin index decrease during incubation fasting in female common eiders

To maximize their fitness, long-lived species face trade-offs between survival and reproduction. The cost of reproduction, which is defined as the negative effect of current parental investment on chances of adult survival and future reproduction, may affect immune function, possibly through hormonal changes. In this study, components of acquired immunity and plasma corticosterone levels of female eiders (Somateria mollissima) have been measured throughout the incubation period as a function of clutch size. These precocial birds lay up to six eggs and fast completely during incubation. Birds were sampled early and late in the incubation period, with clutches ranging from one to four eggs. T-cell-mediated immune response and humoral immunity were assessed by phytohemagglutinin (PHA) skin tests (a challenging method) and measurements of serum immunoglobulins (a monitoring method), respectively. During incubation, responses to PHA injection and immunoglobulin index significantly decreased, by about 40% and 25%, respectively. These observed decreases occurred independently of the number of eggs laid by the females. Corticosterone did not vary significantly during incubation, whatever the clutch size. We conclude that female eiders seem to reallocate their resources from immune function to reproductive effort independently of clutch size or corticosterone levels.     

Effects of implanted satellite transmitters on behavior and survival of female common eiders

Surgically implanted satellite transmitters have been widely used in studies of avian ecology, yet little is known about their potential impacts on birds. We implanted satellite transmitters with percutaneous antennae (approx. 50 g) in 17 female common eiders (Somateria mollissima) at a breeding colony in Arctic Canada. Among females implanted during incubation, 11 of 12 nests were abandoned within 1 week of being radioed. We observed no differences in the proportion of time that implanted female eiders allocated to basic behaviors. Radioed birds were more likely to pick or preen their abdominal (site of surgical incision) and posterior–dorsal (site of antenna exit) regions than unmarked females, although these behaviors were rare (approx. 0.3% of total time budget). Three of 10 females re-observed had a pronounced limp following surgery, but we observed no walking difficulties among these females in subsequent seasons, and we observed some implanted eiders nesting in subsequent years. Mark–resighting models suggest eiders with transmitters had lower apparent survival the year after implantation (67.0%; 85% CI: 47.8–81.9%) than did color-banded eiders (87.5%, 85% CI: 82.5–91.2%), but there was no model support for a survival difference in subsequent years. We conclude that transmitter implantation in common eiders leads to short-term changes in behavior and a decline in first year survival. We encourage researchers to collect similar data on their study subjects where possible and use it to determine the degree to which data are representative of the greater population. © 2011 The Wildlife Society.     

Large feet are beneficial for eiders Somateria mollissima

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Triploid plover female provides support for a role of the W chromosome in avian sex determination

Two models, Z Dosage and Dominant W, have been proposed to explain sex determination in birds, in which males are characterized by the presence of two Z chromosomes, and females are hemizygous with a Z and a W chromosome. According to the Z Dosage model, high dosage of a Z-linked gene triggers male development, whereas the Dominant W model postulates that a still unknown W-linked gene triggers female development. Using 33 polymorphic microsatellite markers, we describe a female triploid Kentish plover Charadrius alexandrinus identified by characteristic triallelic genotypes at 14 autosomal markers that produced viable diploid offspring. Chromatogram analysis showed that the sex chromosome composition of this female was ZZW. Together with two previously described ZZW female birds, our results suggest a prominent role for a female determining gene on the W chromosome. These results imply that avian sex determination is more dynamic and complex than currently envisioned.     

Inducible nitric oxide synthase provides protection against injury-induced thrombosis in female mice

Nitric oxide (NO) is an important vasoactive molecule produced by three NO synthase (NOS) enzymes: neuronal (nNOS), inducible (iNOS), and endothelial NOS (eNOS). While eNOS contributes to blood vessel dilation that protects against the development of hypertension, iNOS has been primarily implicated as a disease-promoting isoform during atherogenesis. Despite this, iNOS may play a physiological role via the modulation of cyclooxygenase and thromboregulatory eicosanoid production. Herein, we examined the role of iNOS in a murine model of thrombosis. Blood flow was measured in carotid arteries of male and female wild-type (WT) and iNOS-deficient mice following ferric chloride-induced thrombosis. Female WT mice were more resistant to thrombotic occlusion than male counterparts but became more susceptible upon iNOS deletion. In contrast, male mice (with and without iNOS deletion) were equally susceptible to thrombosis. Deletion of iNOS was not associated with a change in the balance of thromboxane A(2) (TxA(2)) or antithrombotic prostacyclin (PGI(2)). Compared with male counterparts, female WT mice exhibited increased urinary nitrite and nitrate levels and enhanced ex vivo induction of iNOS in hearts and aortas. Our findings suggest that iNOS-derived NO in female WT mice may attenuate the effects of vascular injury. Thus, although iNOS is detrimental during atherogenesis, physiological iNOS levels may contribute to providing protection against thrombotic occlusion, a phenomenon that may be enhanced in female mice.     

Male and female preferences for nest characteristics under paternal care

Nests play a critical role for offspring development across the animal kingdom. Nest quality may contribute to the builder's extended phenotype and serve as an ornament during mate choice. We examined male and female nest choice in the common goby (Pomatoschistus microps), a benthic fish with male‐only parental care where females deposit eggs in male‐built nests. Using prebuilt nest models, we independently manipulated two candidate nest quality traits: (a) nest entrance width with a role in oxygen ventilation, and (b) extent of sand cover with a role in camouflage. In simultaneous choice trials, male gobies exhibited no preference for any nest model type. This suggests that initial characteristics of a nesting substrate have minor importance for males, which usually remodel the nest. Females were given a choice between two males occupying either entrance‐ or cover‐manipulated nests. The same pair of males was then exposed to a second female but now with alternated nest types assigned. Most females were consistent in choosing the same, typically the heavier male of the two regardless of nest properties. However, the females that chose the same nest regardless of the male preferred low over high sand coverage and narrow over wide nest entrance. Our results indicate that females base their mating decision on a combination of male phenotype and nest traits. While we found no indication that females are attracted to highly decorated nests, our study is the first in fishes to disentangle a preference for narrow (and thus more protective) nest entrances independent of nest coverage.     

Reproductive versus ecological advantages to larger body size in female snakes, Vipera aspis

Body size can influence an organism's microevolutionary fitness either via ecological factors (ecological selection) or changes in reproductive output (sexual or fecundity selection). Published studies on sexual dimorphism in reptiles have generally focussed on sexual-selective forces on males, under the implicit assumption that the intensity of fecundity selection in females (and hence, overall selection on female body size) is likely to be relatively consistent among lineages. In this paper, we explore the degree to which larger body size enhances ecological attributes (e.g., food intake, growth, survival) and reproductive output (reproductive frequency, litter size, offspring size, offspring viability) in free-ranging female aspic vipers, Vipera aspis . The less-than-annual reproductive frequency of these animals allows us to make a direct comparison between females in years during which they concentrate on "ecological" challenges (especially building energy reserves) versus reproductive challenges (producing a litter). Because female snakes have limited abdominal space to hold the clutch (litter), we expect that fecundity should depend on body size. However, our data show that larger body size had a more consistent effect on ecological attributes (such as feeding rates and "costs of reproduction") than on reproductive output per se. Indeed, total reproductive output was maximised at intermediate body sizes. These results suggest that variation in female body size among and within species (and hence, in the degree of sexual dimorphism) may be driven by the ecological as well as reproductive consequences of body size variation in both sexes.     

Dynamics of female choice for parental care in a fish species where care is facultative

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Shared parental care is costly for nestlings of common cuckoos and their great reed warbler hosts

Obligate avian brood parasitism typically involves one of 2strategies: parasite chicks are either 1) virulent and evictall other eggs and nest mates to be raised alone or 2) moretolerant and share foster parental care with host chicks forsome or the entirety of the nestling period. We studied theconsequences of experimentally forced mixed broods of age-matchedone common cuckoo (Cuculus canorus) and 2 great reed warbler(Acrocephalus arundinaceus) chicks. In these broods, both cuckooand host chicks grew slower than did either individual cuckoosor great reed warblers in broods of 1 parasite or 3 host chicks,respectively. Video records showed that in mixed broods, cuckoochicks received feedings less frequently than the 33% predictedby chance at 4 days of age but parental food allocations increasedto chance levels at 8 days of age. The consistent patterns oflower growth rates arose even though chicks in broods of 1 parasiteand 2 hosts received the largest prey items per feeding. Inaddition, several other measures of parental provisioning alsodid not predict species and brood-specific differences in nestlinggrowth rates across the different treatments. However, variationin begging displays and its specific costs on host and parasitechicks in the different nest treatments were not quantifiedin this study. We conclude that young of nest mate–evictorcommon cuckoos benefit from the sole occupancy of host nestsin part owing to an initial competitive disadvantage for parentalcare in broods with age-matched great reed warbler chicks.     

A model for evolution of male parental care and female multiple mating

In most animals, males gain a fitness benefit by mating with many females, whereas the number of progeny per female is unlikely to increase as a function of additional mates. Furthermore, males of internally fertilizing species run the risk of investing in offspring of other males if they provide parental care. Nevertheless, males of many avian species and a minority of mammalian species provide parental care, and females of various species mate with multiple males. I investigate a two-locus genetic model for evolution of male parental care and female multiple mating in which females gain a direct benefit by multiple mating from the paternal care they thereby elicit for their offspring. The model suggests that, first, male parental care can evolve when it strongly enhances offspring survival and the direct costs of female multiple mating (e.g., loss of energy, risk of injury, exposure to infectious diseases) are greater than its indirect benefit (e.g., acquisition of good genes, increased genetic diversity among offspring); second, female multiple mating can evolve when paternal care is important for offspring survival or the indirect benefit of multiple mating is larger than its direct cost; and, finally, male parental care and female multiple mating can co-occur.