Spring declines in Microtus pennsylvanicus and the role of steroid hormones

1. Spring declines are a common feature of small mammal demography. We tested the hypothesis that meadow voles from populations experiencing severe spring declines should exhibit severe stress responses as indicated by high free corticosterone levels. 2. Three populations in southern Ontario were live-trapped intensively in the spring of 1985, all animals were bled each time, and measurements of total corticosterone, corticosterone-binding globulin (CBG), and total androgen (testosterone and dihydrotestosterone) were obtained by radioimmunoassay. 3. Population density was correlated to stress responses: in populations with the highest densities, both males and females had the highest total corticosterone, lowest CBG, and highest free corticosterone levels; males had the highest wounding levels. However, these populations declined the least. In contrast, the population with the lowest density had males and females with the lowest total corticosterone, highest CBG, and lowest free corticosterone levels and males with the lowest wounding levels. This population declined the most. 4. Total corticosterone and CBG levels in males were about half those in females, and in females varied significantly with reproductive condition, with lactating and pregnant females having the highest levels. Only in pregnant females was body mass positively related to total corticosterone and CBG levels and this is probably related to impending parturition. In males, androgen levels were similar among populations and not correlated to total corticosterone or CBG levels nor to body mass. In females, androgen concentrations were only 4% that of males. In males, CBG, free corticosterone, androgen levels, and wounding rates showed significant repeatability. 5. We conclude that stress responses were not related to population demography in our study and reject the Christian stress hypothesis and the adaptive stress hypothesis of Lee and Cockburn as explanations for spring declines in this species. We propose an adaptive model to account for the differences in the hormonal response to breeding between species in which the males are semelparous and those in which males are iteroparous

A mechanistic link between chick diet and decline in seabirds?

A climatic regime shift during the mid-1970s in the North Pacific resulted in decreased availability of lipid-rich fish to seabirds and was followed by a dramatic decline in number of kittiwakes breeding on the Pribilof Islands. Although production of chicks in the mid-1970s was adequate to sustain kittiwake populations in the early 1980s, the disappearance of birds from breeding colonies apparently exceeded recruitment. No mechanism has been proposed to explain why recruitment would differ among fledglings fed lipid-rich or lipid-poor fish during development. Here we show that diets low in lipids induce nutritional stress and impair cognitive abilities in young red-legged kittiwakes, Rissa brevirostris. Specifically, growth retardation, increased secretion of stress hormones and inferior ability to associate food distribution with visual cues were observed in individuals fed lipid-poor diets. We conclude that lipid-poor diets during development affect the quality of young seabirds, which is likely to result in their increased mortality and low recruitment

Climatic effects on breeding and morphology: evidence for phenotypic plasticity

1. A trend towards increasing average spring temperatures has been observed in Europe over the past 25 years. This climatic variation has been attributed to a natural, large-scale atmospheric phenomenon, the North Atlantic Oscillation (NAO). A number of studies have reported associations between the winter NAO-index and both breeding phenology and cohort-specific morphology. These studies have been cross-sectional rather than longitudinal and therefore have not been able to determine whether the changes result from phenotypic plasticity or microevolutionary processes. 2. We analysed (i) cross-sectional correlations between the winter NAO-index and breeding performance (laying date, clutch size, fledging success and number of recruits produced) and morphological traits (tarsus and wing length), and (ii) within-individual variation in the same traits for individuals experiencing different values of the NAO-index in a population of collared flycatchers (Ficedula albicollis) breeding on Gotland, Sweden, over a period of 16 years (1980-95). 3. None of the four measures of breeding performance changed consistently over the study period, while tarsus length of males (and marginally females) decreased over time. Of the six traits investigated using cross-sectional data, only laying date was related to variation in the NAO-index. 4. All characters investigated showed significant repeatability within individuals among years, revealing the importance of factors specific to individuals in determining their value. However, within individuals the NAO-index significantly affected laying date and clutch size such that females laid earlier and produced larger clutches after warmer, moister winters. 5. Our data show a high degree of concordance between cross-sectional and longitudinal analyses of the effect of NAO on laying date and clutch size. The similarity of responses across and within individuals suggests that the population-level response to the NAO-index can be explained entirely as the result of phenotypic plasticity

Peak morphological diversity in an ecotone unveiled in the chukar partridge by a novel Estimator in a Dependent Sample (EDS)

1. Areas of environmental transition (i.e. ecotones) have recently been shown to play an important role in the maintenance of genetic diversity, divergence and in speciation processes. We test the hypothesis that ecotone populations maintain high phenotypic diversity compared to other populations across the distribution range