Reconciliation and third‐party affiliation in carrion crows

Conflicts are costly because they can damage social relationships. To buffer conflicts, various species use post‐conflict behaviour, such as reconciliation or third‐party affiliation. Both behaviours have predominantly been studied in non‐human primates. However, recently, studies revealed post‐conflict behaviour in other mammalian and some bird species (e.g., corvids). While third‐party affiliation has been reported in several corvid species, reconciliation has only rarely been observed. The social structure of the studied groups has been postulated as a reason for the absence of reconciliation. Here, we investigated whether post‐conflict behaviours in corvids indeed mirror the relationship structure. We studied the behaviour of a newly established group of juvenile carrion crows (Corvus corone corone), where pair bonds had not yet been established. We applied a combination of observations and food monopolisation experiments to quantify the use of post‐conflict behaviours. Provisioning food in one or two pieces induced different patterns of aggression during feeding and differently affected the affiliation patterns after feeding. Specifically, victims of severe aggression affiliated with third parties after conflicts in the two‐piece condition, while aggressors affiliated with victims of mild aggression in the one‐piece condition. We thus provide the first evidence that a corvid species, crows, flexibly engage in both third‐party affiliation and reconciliation.     

1α,25-Dihydroxyvitamin D3 receptor as a mediator of transrepression of retinoid signaling

The receptors for retinoic acid (RA) and for 1α,25-dihydroxyvitamin D₃ (VD), RAR, RXR, and VDR are ligand-inducible members of the nuclear receptor superfamily. These receptors mediate their regulatory effects by binding as dimeric complexes to response elements located in regulatory regions of hormone target genes. Sequence scanning of the tumor necrosis factor-α type I receptor (TNFαRI) gene identified a 3′ enhancer region composed of two directly repeated hexameric core motifs spaced by 2 nucleotides (DR2). On this novel DR2-type sequence, but not on a DR5-type RA response element, VD was shown to act through its receptor, the vitamin D receptor (VDR), as a repressor of retinoid signalling. The repression appears to be mediated by competitive protein–protein interactions between VDR, RAR, RXR, and possibly their cofactors. This VDR-mediated transrepression of retinoid signaling suggests a novel mechanism for the complex regulatory interaction between retinoids and VD. J. Cell. Biochem. 67:287–296, 1997. © 1997 Wiley-Liss, Inc.     

Field tests of cis-regulatory variation at the prairie vole avpr1a locus: association with V1aR abundance but not sexual or social fidelity

The neuropeptide vasopressin and its receptor V1aR are broadly implicated in social behavior and play a central role in several key aspects of male mating tactics in voles. In the prairie vole, a microsatellite in the cis-regulatory region of the gene encoding V1aR (avpr1a) provides a potential genetic basis for individual variation in neural phenotype and behavior; recent studies found that allele length predicts V1aR expression and male social attachment in the laboratory. Here, we explore the relationship between avpr1a microsatellite length, V1aR neural phenotype, and field measures of monogamy and fitness in male prairie voles. We found significant effects of allele length on V1aR expression in structures integral to pairbond formation. These effects did not, however, translate to differences in mating tactics or reproductive success. Together, these data suggest that, while length polymorphism in the avpr1a microsatellite influences neuronal phenotype, this variation does not contribute significantly to male reproductive success and field behavior. We propose that previously reported behavioral effects may be mediated primarily by sequence variation at this locus, for which allele length is an imperfect proxy. By combining genetic, neuronal and ecological approaches, these data provide novel insights into the contribution of genotype to natural diversity in brain and behavior.     

Functional Characterization of Phospholipid N-Methyltransferases from Arabidopsis and Soybean

Phospholipid N-methyltransferase (PLMT) enzymes catalyze the S-adenosylmethionine-dependent methylation of ethanolamine-containing phospholipids to produce the abundant membrane lipid phosphatidylcholine (PtdCho). In mammals and yeast, PLMT activities are required for the de novo synthesis of the choline headgroup found in PtdCho. PLMT enzyme activities have also been reported in plants, yet their roles in PtdCho biosynthesis are less clear because most plants can produce the choline headgroup entirely via soluble substrates, initiated by the methylation of free ethanolamine-phosphate. To gain further insights into the function of PLMT enzymes in plants, we isolated PLMT cDNAs from Arabidopsis and soybean (Glycine max) based upon primary amino acid sequence homology to the rat PLMT, phosphatidylethanolamine N-methyltransferase. Using a heterologous yeast expression system, it was shown that plant PLMTs methylate phosphatidylmonomethylethanolamine and phosphatidyldimethylethanolamine but cannot utilize phosphatidylethanolamine as a substrate. Identification of an Arabidopsis line containing a knock-out dissociator transposon insertion within the single copy AtPLMT gene allowed us to investigate the consequences of loss of PLMT function. Although the accumulation of the PLMT substrates phosphatidylmonomethylethanolamine and phosphatidyldimethylethanolamine was considerably elevated in the atplmt knock-out line, PtdCho levels remained normal, and no obvious differences were observed in plant morphology or development under standard growth conditions. However, because the metabolic routes through which PtdCho is synthesized in plants vary greatly among differing species, it is predicted that the degree with which PtdCho synthesis is dependent upon PLMT activities will also vary widely throughout the plant kingdom.Phosphatidylcholine (PtdCho)2 is the most abundant phospholipid in most non-plastid membranes of eukaryotes. PtdCho biosynthesis has been studied intensively in plants not only because of its importance as a structural membrane lipid, but also because of its role as a precursor to important lipid-based signaling molecules, such as phosphatidic acid, and phospholipase A₂-derived free fatty acids (1). The choline headgroup of PtdCho serves multiple functions as well. In addition to being an essential human nutrient (2), in many plant species choline can be oxidized to produce the potent osmoprotectant glycine betaine (3, 4).For over 2 decades it has been apparent that there are fundamental differences between the manner in which PtdCho is produced in plants versus how it is synthesized in mammals and fungi. In the latter two systems, PtdCho can be formed through two distinct pathways as follows: (a) the “nucleotide pathway” in which free choline is incorporated in PtdCho using CDP-choline as an intermediate, and (b) the “methylation pathway” whereby PtdCho is produced directly from phosphatidylethanolamine (PtdEtn) via three sequential methylation reactions using S-adenosylmethionine (AdoMet) as the methyl donor (5, 6). In contrast, PtdCho biosynthesis in plants occurs through a branched pathway that utilizes components of both the nucleotide and methylation pathways (7). The greatest distinction between the contrasting mechanisms of PtdCho biosynthesis can be attributed to the presence of plant enzymes that are capable of converting ethanolamine headgroups to choline at the phospho-base level, activities that are absent in mammals and yeast. Conversely, mammals and fungi possess methylation enzymes that act directly on PtdEtn, a reaction that cannot be detected in most plant systems investigated (reviewed in Ref. 7).A diagram of the most widely accepted model of phosphoamino alcohol biosynthesis in plants is shown in Fig. 1. Similar to animals and yeast, free choline can be directly incorporated into PtdCho via nucleotide pathway enzymes in plants. In the absence of choline, however, the methylation of Etn-phosphate represents the first committed step in PtdCho biosynthesis. The resulting monomethylethanolamine-phosphate (MMEtn-P) metabolite can be further methylated at the phospho-base level to produce Cho-P. Alternatively, MMEtn-P can be incorporated into phosphatidylmonomethylethanolamine (PtdMMEtn) via the cytidylyltransferase and amino alcohol phosphotransferase activities of the nucleotide pathway and then methylated at the phosphatidyl-base level to complete the synthesis of PtdCho (Fig. 1). The extent with which PtdCho is formed by the flow of metabolites through phospho-bases as opposed to phosphatidyl-bases varies greatly among different plant species. In most higher plants, it is likely that the methylation of the phosphoamino alcohol headgroups involves the flow of metabolites through both branches of the pathway, as has been shown in species such as barley, carrot, and tobacco (3, 8, 9). Nevertheless, examples have also been reported where only one of the branches appears to be utilized. In Lemna paucicostata, for example, the methylation steps in PtdCho biosynthesis were shown to occur almost exclusively at the phospho-base level (10). At the other end of the spectrum is soybean, where all methylations beyond the initial formation of MMEtn-P were reported to occur on phosphatidyl-bases (8, 11). The tremendous variability observed among plants with regard to PtdCho formation is also exemplified by a study conducted by Williams and Harwood (12) where it was shown that the predominant route of PtdCho synthesis in olive culture cells involved the first two methylation reactions taking place at the phospho-base level (producing dimethylethanolamine phosphate) and the final methylation occurring on a phosphatidyldimethylethanolamine (PtdDMEtn) substrate.Open in a separate windowFIGURE 1.Phosphatidylcholine biosynthetic pathways. Steps common to plants, mammals, and yeast are indicated by black arrows. Dashed arrows indicate pathways specific to plants. Methylation of PtdEtn, which occurs in mammals and yeast, is indicated by on open arrow. Enzymes catalyzing phosphoamino alcohol methylation reactions in plants, mammals, and yeast are indicated.Our understanding on the mechanisms by which plants synthesize PtdCho and regulate its accumulation has been further enhanced as the genes encoding the various steps of the phosphoamino alcohol pathway have been isolated and characterized. For example, molecular characterizations led to the conclusion that all of the amino alcohol phosphotransferase reactions depicted in Fig. 1 can be mediated by the product of a single gene (designated AAPT1) that displays a broad substrate specificity (13, 14). Similarly, it was the isolation of the phosphoethanolamine methyltransferase (PEAMT) genes from Arabidopsis and spinach that led to the discovery that all three phospho-base methylation reactions could be catalyzed by a single enzyme (15, 16). Inhibition of PEAMT gene function in Arabidopsis through T-DNA insertion or co-suppression revealed unexpected associations between the phosphoamino alcohol pathway and root development, salt hypersensitivity, and male sterility (17, 18).Although most of the reactions depicted in Fig. 1 have been characterized at the molecular genetic level, conspicuously absent is information on the plant genes/enzymes responsible for the methylation reactions conducted at the phosphatidyl-base level. In contrast, these reactions are among the most well characterized in animals and yeast, catalyzed by enzymes commonly referred to as phospholipid N-methyltransferases (PLMTs). In mammals, the 18-kDa integral membrane protein phosphatidylethanolamine N-methyltransferase (PEMT) is a PLMT that is expressed primarily in the liver (19). PEMT catalyzes all three of the methylation reactions needed to convert PtdEtn to PtdCho. Yeast uses two distinct PLMT enzymes to catalyze the three methylation reactions as follows: Cho2p/Pem1p that mediates the direct methylation of PtdEtn to produce PtdMMEtn (20, 21), and Opi3p/Pem2p, an enzyme homologous to the mammalian PEMT, that primarily catalyzes the methylation of PtdMMEtn to PtdDMEtn and PtdDMEtn to PtdCho, the final two steps of the methylation pathway (20, 22). PLMT activities are critical in both of these systems. Mice possessing pemt knock-out mutations are completely dependent on dietary choline for survival, and they display abnormal levels of choline metabolites within the liver and develop hepatic steatosis even when fed diets supplemented with choline (23). Yeast lacking PLMT activities (cho2/opi3 double mutants) are obligate choline auxotrophs, unable to synthesize PtdCho de novo in the absence of exogenous choline.To gain a greater understanding of the specific function of PLMT reactions in higher plants, and their contribution toward PtdCho biosynthesis, we cloned and characterized PLMT homologs from Arabidopsis and soybean. By expressing the candidate cDNAs in yeast, we were able to confirm that they encoded functional PLMT activities as well as to establish their substrate specificities. We also identified a mutant Arabidopsis line containing a knock-out allele in the single copy PLMT gene found in the Arabidopsis genome, allowing us to characterize the consequences of loss of gene function in this model species.     

Comparative population structure of Cynopterus fruit bats in peninsular Malaysia and southern Thailand

The extent to which response to environmental change is mediated by species-specific ecology is an important aspect of the population histories of tropical taxa. During the Pleistocene glacial cycles and associated sea level fluctuations, the Sunda region in Southeast Asia experienced concurrent changes in landmass area and the ratio of forest to open habitat, providing an ideal setting to test the expectation that habitat associations played an important role in determining species' response to the opportunity for geographic expansion. We used mitochondrial control region sequences and six microsatellite loci to compare the phylogeographic structure and demographic histories of four broadly sympatric species of Old World fruit bats in the genus, Cynopterus. Two forest-associated species and two open-habitat generalists were sampled along a latitudinal transect in Singapore, peninsular Malaysia, and southern Thailand. Contrary to expectations based on habitat associations, the geographic scale of population structure was not concordant across ecologically similar species. We found evidence for long and relatively stable demographic history in one forest and one open-habitat species, and inferred non-coincident demographic expansions in the second forest and open-habitat species. Thus, while these results indicate that Pleistocene climate change did not have a single effect on population structure across species, a correlation between habitat association and response to environmental change was supported in only two of four species. We conclude that interactions between multiple factors, including historical and contemporary environmental change, species-specific ecology and interspecific interactions, have shaped the recent evolutionary histories of Cynopterus fruit bats in Southeast Asia.