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.     

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.     

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.     

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.     

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.     

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

In the peacock wrasse (Symphodus tinca), females either placetheir eggs in a nest under the care of a male or disperse theireggs widely so that they receive no protection. The same femalecan spawn in both modes. Females appear to prefer males withnests early in the nesting cycle, and they spawn less oftenthan expected in late-cycle nests and with non-nesting males.Survival and hatching success are consistently higher for eggsplaced in early nests, particularly in mid-season when egg predationis intense and hatching times are relatively long. Nevertheless,30%-80% of females place their eggs outside nests, even whenhatching success is more than four times greater with care.A model incorporating search time for nests correctly predictedthe qualitative changes in the tendency of females to choosecare or no care over the course of the mating season. Extensionsof the model suggest that in the early part of the season, whennests are rare and the relative survival advantage of parentalcare is small, females should sample no more than one nest beforeopting for no care. In mid-season, when the advantages of careare highest and between-nest travel times are low, females areestimated to visit at least 8 nests before abandoning the effort,corresponding to a giving-up time of about 43 min of search.Later in the season, when short hatching times reduce the relativebenefit of care, females are estimated to visit between 4 and5 nests before giving up, corresponding to about 31 min of search.We suggest that the variability in parental care in this speciesarises from seasonal changes in relative costs and benefitsof care for the two sexes.     

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.     

Garlic and vitamin E provides antioxidant defence in tissues of female rats treated with nicotine

Nicotine is known to induce oxidative stress in rat tissues and the antioxidant properties of garlic have been reported. This study was designed to determine if the peroxidative damage caused by nicotine administration can be effectively prevented with garlic juice, and vitamin E, a known antioxidant.Four groups of six rats each were divided into: Group I: (control) received 0.2ml of 0.9% normal saline, group II (received nicotine 0.6mg/kg b.w subcutaneously), group III (received nicotine 0.6mg/kg b.w + garlic juice 100mg/kg b.w orally), and group IV (received nicotine 0.6mg/kg b.w + Vitamin E 100mg/kg b.w orally). All animals were treated for 21 days. The pituitary gland, ovary, uterus, heart, liver and kidney of the animals were harvested, weighed and homogenized. Malondialdehyde (MDA), superoxide dismutase (SOD) and reduced glutathione (GSH) were then measured.Concentration of MDA was significantly increased in tissues of nicotine treated rats when compared with the control. In group III and IV, MDA levels were significantly reduced when compared with nicotine group. The activities of SOD and GSH significantly decreased in group II (nicotine only) rat tissues, while it was significantly increased in group III and IV rat tissues. The study showed that garlic juice extract (100mg/kg b.w) and vitamin E (100mg/kg b.w) administration prevented oxidative damage in rat tissues treated with nicotine. The study also showed that vitamin E has a more potent antioxidant activity than garlic juice in preventing nicotine induced oxidative damage in rat. Keywords: Nicotine, Vitamin E, Garlic, antioxidant.     

Corticosterone alone does not trigger a short term behavioural shift in incubating female common eiders Somateria mollissima, but does modify long term reproductive success

The trade-off between reproductive effort and adult survival in birds is modulated by several factors. Corticosterone and prolactin have additive effects on reproductive behaviour by stimulating foraging and parental behaviours, respectively. When incubation is associated with fasting, nest desertion is supposed to be activated by an unknown refeeding signal when body condition becomes critically deteriorated. The concomitant rise in corticosterone levels has been suggested to be the triggering factor. We tested the role of corticosterone on reproductive success by observing the effect of corticosterone implants on reproductive success and on plasma prolactin concentration in female common eiders Somateria mollissima . Implanted females showed a significant increase in corticosterone and a decrease in prolactin levels. Despite their enhanced daily body mass loss, females did not abandon incubation nor did they start to refeed in the four days following implantation. These data show that the experimentally induced rise in plasma corticosterone concentration alone does not trigger nest desertion. However, after 25 days of incubation, implanted females displayed a higher rate of egg loss, suggesting lower nest attentiveness towards the end of incubation. We suggest that the short-term effects of corticosterone may be dependent on the energy state of the bird. However, the late-induced change in reproductive success is indirectly linked to corticosterone, and we suggest that either a prolactin decrease, or a depletion in protein body reserves, may participate in the long-term adjustment of incubation behaviour in female eiders.     

International importance of the eastern Chukchi Sea as a staging area for migrating king eiders

The evaluation of habitats used by arctic birds on migration is crucial for their conservation. We explored the importance of the eastern Chukchi Sea (ECS) as a staging area for king eiders (Somateria spectabilis) migrating between breeding areas in Siberia and western North America and wintering areas in the Bering Sea. We tracked 190 king eiders with satellite transmitters between 1997 and 2007. In late summer, 74% of satellite-tracked king eiders migrating south staged in the ECS for 13 ± 13 (SD) days between late June and early November. During spring migration, king eiders staged in the ECS between mid-April and early June for 21 ± 10 days. All instrumented birds migrating to breeding grounds in western North America (n = 62), and 6 of 11 males migrating to breeding grounds in Siberia, used this area for at least 1 week during spring migration. The importance of this staging area renders it possible that industrial development could adversely affect king eider populations in both Siberia and North America.