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31.
Carlos Martínez del Rio Pablo Sabat Richard Anderson-Sprecher Sandra P. Gonzalez 《Oecologia》2009,161(1):149-159
By comparing the isotopic composition of tissues deposited at different times, we can identify individuals that shift diets
over time and individuals with constant diets. We define an individual as an isotopic specialist if tissues deposited at different
times have similar isotopic composition. If tissues deposited at different times differ in isotopic composition we define
an individual as an isotopic generalist. Individuals can be dietary generalists but isotopic specialists if they feed on the
same resource mixture at all times. We assessed the degree of isotopic and dietary specialization in three related Chilean
bird species that occupy coastal and/or freshwater environments: Cinclodes oustaleti, Cinclodes patagonicus, and Cinclodes nigrofumosus. C. oustaleti individuals were both isotopic and dietary generalists. Tissues deposited in winter (liver and muscle) had distinct stable
C (δ13C) and stable N isotope ratio (δ15N) values from tissues deposited in the summer (wing feathers) suggesting that birds changed the resources that they used
seasonally from freshwater habitats in the summer to coastal habitats in the winter. Although the magnitude of seasonal isotopic
change was high, the direction of isotopic change varied little among individuals. C. patagonicus included both isotopic specialists and generalists, as well as dietary specialists and generalists. The isotopic composition
of the feathers and liver of some C. patagonicus individuals was similar, whereas that of others differed. In C. patagonicus, there were large inter-individual differences in the magnitude and the direction of seasonal isotopic change. All individuals
of C. nigrofumosus were both isotopic and dietary specialists. The distribution of δ13C and δ15N values overlapped broadly among tissues and clustered in a small, and distinctly intertidal, region of δ space. Assessing
individual specialization and unraveling the factors that influence it, have been key questions in animal ecology for decades.
Stable isotope analyses of several tissues in appropriate study systems provide an unparalleled opportunity to answer them. 相似文献
32.
Shaun A Tauck Jesse R Olsen Jarrod RC Wilkinson Riley J Wedlake Kathleen C Davis James G Berardinelli 《Reproductive biology and endocrinology : RB&E》2010,8(1):89
Background
The physiological mechanism by which bulls stimulate resumption of ovarian cycling activity in postpartum, anovular, suckled cows after calving may involve the concurrent activation of the hypothalamic-hypophyseal-ovarian (HPO) axis and hypothalamic-hypophyseal-adrenal (HPA) axis. Thus, the objectives of this experiment were to determine if characteristics of temporal patterns of cortisol and luteinizing hormone (LH) in postpartum, anovular, beef cows are influenced by acute exposure to bulls. The null hypotheses were that daily, temporal characteristics of cortisol and LH concentration patterns do not differ between cows exposed acutely to bulls or steers. 相似文献33.
On the origins of esterases 总被引:8,自引:0,他引:8
Comparisons among the primary sequences of five cloned eukaryotic esterases
reveal two distinct lineages, neither bearing any significant overall
sequence similarity to the functionally related serine protease multigene
family. We have not eliminated the possibility that the esterases may have
residual conformational similarities to the serine proteases. However, our
profile analysis and analyses of the predicted conformations of the
esterases reveal little similarity to the serine proteases. Four of the
esterase proteins share 27%-53% overall sequence similarity and evidence of
a catalytic mechanism involving the same Arg- Asp-Ser or His-Asp-Ser charge
relay. We propose that these four esterases, three of them cholinesterases,
form part of a multigene family essentially separate from the serine
proteases.
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