Are incubation costs in female pied flycatchers expressed in humoral immune responsiveness or breeding success?

Although clutch size variation has been a key target for studies of avian life history theory, most empirical work has only focused on the ability of parents to raise their altricial young. In this study, we test the hypothesis that costs incurred during incubation may be an additional factor constraining clutch size in altricial birds. In the pied flycatcher (Ficedula hypoleuca), we manipulated the incubation effort of the female by enlarging and reducing clutch sizes. To manipulate incubation effort only, the original clutch sizes were restored shortly after hatching. We found that fledging success was lower among broods whose clutches were enlarged during incubation. There was, however, no effect of manipulation on female body condition or on their ability to mount a humoral immune response to diphtheria or tetanus toxoid during the incubation or nestling provisioning period. Instead, we found that the original clutch size was related to the immune response so that females with seven eggs had significantly lower primary antibody responses against tetanus compared to those with six eggs. Our results suggest that incubating females are not willing to jeopardise their own condition and immune function, but instead pay the costs of incubating a larger clutch by lower offspring production. The results support the view that costs of producing and incubating eggs may be substantial and hence that these costs are likely to contribute to shaping the optimal clutch size in altricial birds.     

High feeding intensity increases the severity of fatty liver in the American mink (Neovison vison) with potential ameliorating role for long-chain n-3 polyunsaturated fatty acids

Background

Rapid body fat mobilization, obesity, and an inadequate supply of n-3 polyunsaturated fatty acids (PUFA) have been suggested to play roles in the etiology of fatty liver in the American mink (Neovison vison). This study examined the effects of feeding intensity and dietary fat source on fatty liver induced by fasting. In a multi-factorial design, 3 different fat sources (herring oil, rich in n-3 PUFA, soya oil, rich in n-6 PUFA, and canola oil, rich in n-9 monounsaturated fatty acids) were fed to mink at a low and high feeding intensity for 10 weeks, followed by an overnight or a 5-day fasting treatment to induce fatty liver.

Results

Fasting led to the development of fatty liver with increased severity in the mink fed at the high feeding intensity. The herring oil diet, high in long-chain n-3 PUFA, was found to decrease the severity of fatty liver in the mink at the high feeding intensity.

Conclusion

Preventing excessive weight gain and increasing dietary intake of n-3 long-chain PUFA may help prevent excessive lipid accumulation during prolonged periods of fasting or inappetence by promoting hepatic fatty acid oxidation.     

Winter locations of red‐throated divers from geolocation and feather isotope signatures

Migratory species have geographically separate distributions during their annual cycle, and these areas can vary between populations and individuals. This can lead to differential stress levels being experienced across a species range. Gathering information on the areas used during the annual cycle of red‐throated divers (RTDs; Gavia stellata) has become an increasingly pressing issue, as they are a species of concern when considering the effects of disturbance from offshore wind farms and the associated ship traffic. Here, we use light‐based geolocator tags, deployed during the summer breeding season, to determine the non‐breeding winter location of RTDs from breeding locations in Scotland, Finland, and Iceland. We also use δ¹⁵N and δ¹³C isotope signatures, from feather samples, to link population‐level differences in areas used in the molt period to population‐level differences in isotope signatures. We found from geolocator data that RTDs from the three different breeding locations did not overlap in their winter distributions. Differences in isotope signatures suggested this spatial separation was also evident in the molting period, when geolocation data were unavailable. We also found that of the three populations, RTDs breeding in Iceland moved the shortest distance from their breeding grounds to their wintering grounds. In contrast, RTDs breeding in Finland moved the furthest, with a westward migration from the Baltic into the southern North Sea. Overall, these results suggest that RTDs breeding in Finland are likely to encounter anthropogenic activity during the winter period, where they currently overlap with areas of future planned developments. Icelandic and Scottish birds are less likely to be affected, due to less ship activity and few or no offshore wind farms in their wintering distributions. We also demonstrate that separating the three populations isotopically is possible and suggest further work to allocate breeding individuals to wintering areas based solely on feather samples.     

Females prefer the scent of outbred males: good-genes-as-heterozygosity?

Background  

There is increasing interest to determine the relative importance of non-additive genetic benefits as opposed to additive ones for the evolution of mating preferences and maintenance of genetic variation in sexual ornaments. The 'good-genes-as-heterozygosity' hypothesis predicts that females should prefer to mate with more heterozygous males to gain more heterozygous (and less inbred) offspring. Heterozygosity increases males' sexual ornamentation, mating success and reproduction success, yet few experiments have tested whether females are preferentially attracted to heterozygous males, and none have tested whether females' own heterozygosity influences their preferences. Outbred females might have the luxury of being more choosey, but on the other hand, inbred females might have more to gain by mating with heterozygous males. We manipulated heterozygosity in wild-derived house mice (Mus musculus musculus) through inbreeding and tested whether the females are more attracted to the scent of outbred versus inbred males, and whether females' own inbreeding status affects their preferences. We also tested whether infecting both inbred and outbred males with Salmonella would magnify females' preferences for outbred males.     

Pollution related effects on immune function and stress in a free-living population of pied flycatcher Ficedula hypoleuca

We investigated whether exposure to heavy metal pollution affected the immune function of individuals in a free living population of a small insectivorous passerine bird, the pied flycatcher Ficedula hypoleuca . We measured humoral immune responses in two study areas: a polluted area in the vicinity of a copper smelter and a control area far from the smelter. Plasma corticosterone level and blood heterophil/lymphocyte ratio (H/L) were used as more general physiological measures of stress. The immune response of F. hypoleuca was not suppressed by pollution stress. In contrast, we found that F. hypoleuca males showed stronger humoral immune responses to a novel antigen (tetanus toxoid) in the polluted environment than in the unpolluted one. After the immunization of males, numbers of lymphocytes rose significantly more in the polluted area, leading to a smaller H/L ratio than in males from the control area. Females showed no pollution related effects on their immune responses. Corticosterone levels of males and nestlings were not related to pollution levels. Nestlings showed somewhat higher H/L ratios and lower fledging success in the polluted area, both factors indicating increased stress levels in a polluted area. Our results suggest that humoral immune response of male F. hypoleuca may be enhanced under moderate levels of heavy metal pollution. Enhanced immune function may, however, also be costly for birds and the higher humoral immune responses in polluted areas may thus have negative effects on the birds' breeding performance and survival.     

Is telomere length a molecular marker of past thermal stress in wild fish?

Telomeres protect eukaryotic chromosomes; variation in telomere length has been linked (primarily in homoeothermic animals) to variation in stress, cellular ageing and disease risk. Moreover, telomeres have been suggested to function as biomarker for quantifying past environmental stress, but studies in wild animals remain rare. Environmental stress, such as extreme environmental temperatures in poikilothermic animals, may result in oxidative stress that accelerates telomere attrition. However, growth, which may depend on temperature, can also contribute to telomere attrition. To test for associations between multitissue telomere length and past water temperature while accounting for the previous individual growth, we used quantitative PCR to analyse samples from 112 young‐of‐the‐year brown trout from 10 natural rivers with average water temperature differences of up to 6°C (and an absolute maximum of 23°C). We found negative associations between relative telomere length (RTL) and both average river temperature and individual body size. We found no indication of RTL–temperature association differences among six tissues, but we did find indications for differences among the tissues for associations between RTL and body size; size trends, albeit nonsignificant in their differences, were strongest in muscle and weakest in fin. Although causal relationships among temperature, growth, oxidative stress, and cross‐sectional telomere length remain largely unknown, our results indicate that telomere‐length variation in a poikilothermic wild animal is associated with both past temperature and growth.     

Fire in Australian savannas: from leaf to landscape

Savanna ecosystems comprise 22% of the global terrestrial surface and 25% of Australia (almost 1.9 million km²) and provide significant ecosystem services through carbon and water cycles and the maintenance of biodiversity. The current structure, composition and distribution of Australian savannas have coevolved with fire, yet remain driven by the dynamic constraints of their bioclimatic niche. Fire in Australian savannas influences both the biophysical and biogeochemical processes at multiple scales from leaf to landscape. Here, we present the latest emission estimates from Australian savanna biomass burning and their contribution to global greenhouse gas budgets. We then review our understanding of the impacts of fire on ecosystem function and local surface water and heat balances, which in turn influence regional climate. We show how savanna fires are coupled to the global climate through the carbon cycle and fire regimes. We present new research that climate change is likely to alter the structure and function of savannas through shifts in moisture availability and increases in atmospheric carbon dioxide, in turn altering fire regimes with further feedbacks to climate. We explore opportunities to reduce net greenhouse gas emissions from savanna ecosystems through changes in savanna fire management.     

Cell-autonomous FGF signaling regulates anteroposterior patterning and neuronal differentiation in the mesodiencephalic dopaminergic progenitor domain

The structure and projection patterns of adult mesodiencephalic dopaminergic (DA) neurons are one of the best characterized systems in the vertebrate brain. However, the early organization and development of these nuclei remain poorly understood. The induction of midbrain DA neurons requires sonic hedgehog (Shh) from the floor plate and fibroblast growth factor 8 (FGF8) from the isthmic organizer, but the way in which FGF8 regulates DA neuron development is unclear. We show that, during early embryogenesis, mesodiencephalic neurons consist of two distinct populations: a diencephalic domain, which is probably independent of isthmic FGFs; and a midbrain domain, which is dependent on FGFs. Within these domains, DA progenitors and precursors use partly different genetic programs. Furthermore, the diencephalic DA domain forms a distinct cell population, which also contains non-DA Pou4f1(+) cells. FGF signaling operates in proliferative midbrain DA progenitors, but is absent in postmitotic DA precursors. The loss of FGFR1/2-mediated signaling results in a maturation failure of the midbrain DA neurons and altered patterning of the midbrain floor. In FGFR mutants, the DA domain adopts characteristics that are typical for embryonic diencephalon, including the presence of Pou4f1(+) cells among TH(+) cells, and downregulation of genes typical of midbrain DA precursors. Finally, analyses of chimeric embryos indicate that FGF signaling regulates the development of the ventral midbrain cell autonomously.     

Adaptations to fasting in a terrestrial mustelid, the sable (Martes zibellina)

The aim of this study was to investigate whether the actively wintering Palearctic sable Martes zibellina has evolved physiological adaptations to tolerate nutritional scarcity. Sixteen farm-bred male sables were divided into a fed control group and an experimental group fasted for 4 days. The rate of weight loss in the sable was similar to other medium-sized mustelids. Fasting led to hypoglycaemia and to a decreased lymphocyte percentage. The sable derived metabolic energy from both subcutaneous and intraabdominal white adipose tissues and the relative decrease in fat mass was the largest for the retroperitoneal and subcutaneous depots. Metabolic energy derived partly from body proteins indicated by the increased plasma levels of urea, uric acid and total essential amino acids. Triacylglycerols accumulated in the livers of the fasted sables and the increased plasma aminotransferase activities suggested hepatic dysfunction. The decreased plasma insulin concentrations and the elevated cortisol levels probably contributed to stimulated lipolysis and protein catabolism. Moreover, fasting increased the plasma ghrelin concentrations of the sables and down-regulated the thyroid activity.