What,if anything,is a social niche?

The term “social niche” is rapidly increasing in usage, particularly in the context of “social niche construction.” But what (if anything) is a social niche? Here, we survey papers that have used the term to uncover commonalities and discrepancies in its definition. We aim to alert researchers to the need for more consistency in how the term is used in the literature, and we provide a working definition of “social niche:” the set of social environments in which the focal individual has non-zero inclusive fitness. We consider the extent to which a social niche is analogous to an ecological niche, discuss whether a population-level social niche can be meaningfully identified, and describe conceptual insights about the properties of social niches, focusing on social niche construction. We highlight questions about social niches that demand more theoretical and empirical attention.     

Osteocyte hypoxia: a novel mechanotransduction pathway

Bone is a unique tissue in which to examine mechanotransductiondue to its essential role in weight bearing. Within bone, the osteocyteis an ideal cellular mechanotransducer candidate. Because osteocytesreside distant from the blood supply, their metabolic needs are met bya combination of passive diffusion and enhanced diffusion, arising whenthe tissue is loaded during functional activity. Therefore, wehypothesized that depriving a bone of mechanical loading (and thuseliminating diffusion enhanced by loading) would rapidly induceosteocyte hypoxia. Using the avian ulna model of disuse osteopenia, wefound that 24 h of unloading results in significant osteocyte hypoxia(8.4 ± 1.8%) compared with control levels (1.1 ± 0.5%;P = 0.03). Additionally, we present preliminary data suggesting that a brief loading regimen is sufficient to rescue osteocytes from this fate. The rapid onset of the observed osteocyte hypoxia, the inhibition of hypoxia by brief loading, and thecellular consequences of oxygen deprivation are suggestive of a novelmechanotransduction pathway with implications across organ systems.

     

Effects of a high-voltage direct-current transmission line on beef cattle production

Two herds of beef cattle were maintained beneath a +/- 500 kV direct-current transmission line during a 30-month period, and were compared with two similar herds maintained away from the transmission line. Exposures of animals under the line were five to 30 times greater than those of control animals, depending on the parameter of interest, with average exposure magnitudes of 5.6 kV/m, 4.1 nA/m2, and 13 k ions/cm3, respectively, for electric field, ion current, and density of ions. Productivity and health status of cows and calves were similar between lines and control treatments. Mean body mass of cows increased with maturity, from 438 kg in 1985 to 496 kg in 1987. Calf gain averaged 0.93 kg per head per day. No unusual sources of mortality were observed. Based on this confinement study, beef cattle permitted to graze in the vicinity of a high-voltage, direct-current transmission lines are not expected to experience any decrease in frequency of conception, calving, growth rate, or survival.     

Defining the core structure of the alpha-lactalbumin molten globule state.

Molten globules are partially folded states of proteins which are generally believed to mimic structures formed during the folding process. In order to determine the minimal requirements for the formation of a molten globule state, we have prepared a set of peptide models of the molten globule state of human alpha-lactalbumin (alphaLA). A peptide consisting of residues 1-38 crosslinked, via the native 28-111 disulfide bond, to a peptide corresponding to residues 95-120 forms a partially folded state at pH 2.8 which has all of the characteristics of the molten globule state of alphaLA as judged by near and far UV CD, fluorescence, ANS binding and urea denaturation experiments. The structure of the peptide construct is the same at pH 7.0. Deletion of residues 95-100 from the construct has little effect. Thus, less than half the sequence is required to form a molten globule. Further truncation corresponding to the selective deletion of the A (residues 1-19) or D (residues 101-110) helices or the C-terminal 310 helix (residues 112-120) leads to a significant loss of structure. The loss of structure which results from the deletion of any of these three regions is much greater than that which would be expected based upon the non-cooperative loss of local helical structure. Deletion of residues corresponding to the region of the D helix or C-terminal 310 helix region results in a peptide construct which is largely unfolded and contains no more helical structure than is expected from the sum of the helicity of the two reduced peptides. These experiments have defined the minimum core structure of the alphaLA molten globule state.     

The effects of temporary removal of the alpha male on the behavior of subordinate male vervet monkeys

The effects of temporary removal of the alpha male on the behavior of subordinate adult male vervet monkeys were evaluated. Twelve subordinate males from six captive multimale, multifemale vervet monkey groups were observed in two conditions: when all group members were present and when the alpha male was temporarily removed from each group. In the absence of the alpha male, subordinate males initiated more affiliative behavior and increased the amount of time spent in proximity to females but their rates of aggression were unaltered. Increased affiliative behavior was selectively directed to high-ranking females and their offspring. Under removal conditions, subordinate male behavior did not resemble that of alpha males in intact conditions: they differed in their proximity to and affiliative behavior towards other group members. In the absence of the alpha male, females increased their aggression towards subordinate males. These observations suggest that the presence of alpha males strongly inhibits subordinate males' behavior. When the constraints of the alpha male's presence are removed, subordinate males rapidly engage in behavior that may enhance their likelihood of attaining high rank. In combination with prior studies, the data also indicate that the behaviors involved in the maintenance of high rank by alpha males differ from those subordinates use to acquire dominance. Finally the current study supports the view that aggression by female vervets may be highly influential in determining male ascendency to dominant rank.     

Intramolecular cyclization in irradiated nucleic acids: correlation between high-performance liquid chromatography and an immunochemical assay for 8,5'-cycloadenosine in irradiated poly(A)

A correlation between high-performance liquid chromatography (HPLC) analysis and an in situ enzyme-linked immunosorbent assay (ELISA) for 8,5'-cycloadenosine formation in irradiated poly(A) has been established. The correlation shows that the ELISA precisely reflects changes in the combined yield of R- and S-8,5'-cycloadenosine but that a correction factor must be applied to the ELISA values for accuracy. The HPLC analysis reveals that the intramolecular cyclization proceeds stereoselectively in irradiated poly(A) to preferentially produce the R isomer at pH 7.0 which is similar to the result for irradiated adenosine but in contrast to the result for 5'-AMP where the S isomer predominates at neutral pH. The HPLC analysis shows that two events originating in hydroxyl radical attack at the sugar phosphate backbone in poly(A); that is, adenine release and 8,5'-cycloadenosine formation have somewhat different dose-yield responses. The formation of 8-hydroxyadenosine was detected in the HPLC chromatograms of poly(A) irradiated under N2O at neutral pH, and the yield of this compound was similar to the yield observed in 5'-AMP or adenosine irradiated under similar conditions.     

An immunochemical probe for 8,5'-cycloadenosine-5'-monophosphate and its deoxy analog in irradiated nucleic acids

Polyclonal antisera specific for 8,5'-cycloadenosine-5'-monophosphate (8,5'-cyclo-AMP) or its deoxy analog (8,5'-cyclo-dAMP) were elicited by immunizing rabbits with a conjugate prepared by the method of Johnston et al. [Biochemistry 22, 3453-3460 (1983)]. A competitive enzyme-linked immunosorbent assay (ELISA) was developed and used to detect the formation of these products in irradiated solutions of polyadenylic acid [poly(A)] or DNA which were saturated with nitrous oxide, nitrogen, or oxygen. The 8,5'-cyclo-AMP or 8,5'-cyclo-dAMP moieties could be detected in poly(A) at 1.0 krad and in native DNA at 10 krad, respectively. The yield of 8,5'-cyclo-dAMP was found to be two to three times higher in irradiated double-stranded DNA than in single-stranded DNA. The hydroxyl radical appears to initiate 8,5'-cyclonucleotide formation in irradiated nucleic acids, as demonstrated by the inhibition of 8,5'-cyclo-AMP formation in irradiated poly(A) by dimethyl sulfoxide. However, irradiation under nitrous oxide, particularly at low doses, does not lead to the expected increases in the yield of the 8,5'-cyclonucleotide.