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1.
RICHARD L. SIMMONS MARTIN L. LIPSCHULTZ ANGELYN RIOS PRASANTA K. RAY 《Nature: New biology》1971,231(21):111-112
DURING outbred pregnancy the mother is exposed to genetically foreign tissue because the offspring inherits transplantation antigens from the father. The survival of the foetus is ensured by the intervention of the trophoblast which does not express transplantation antigens between mother and foetus: mouse trophoblast is not rejected even when transplanted into immune recipients1,3. The mechanism of this failure to express histocompatibility antigens is not understood1–4, but Kirby et al. have suggested that the extracellular fibrinoid surrounding trophoblast cells is involved5,6. Currie has suggested that the thick sialomucinous glycocalyx of the trophoblast cell might “mask” the histocompatibility antigens on the trophoblast7,8 and has demonstrated that neuraminidase unmasked these antigens8. Our experiments, however, show that trophoblast incubated with neuraminidase cannot sensitize allogeneic mice to donor histocompatibility antigens. Furthermore, pretreatment of trophoblastic implants with neuraminidase did not interfere with their proliferation and growth in highly immune allogeneic recipients. 相似文献
2.
ROBERT E. SIMMONS 《Ibis》1993,135(4):394-402
Increased population density often reduces reproductive output in breeding birds, but the underlying mechanisms (adaptive restraint v reduced food resources) behind decreased productivity are poorly understood. Here I correlatively and experimentally investigated the roles of food, breeding density, latitude, altitude and rainfall in limiting productivity of Wahlberg's Eagles Aquila wahlbergi throughout Africa. Breeding success in equatorial and subtropical Africa (0°–30°S) was highly density-dependent but showed no latitudinal or rainfall-related trends. Pairs in dense populations produced half as many young annually as pairs in low-density populations. Density (but not rainfall or latitude) also explained much of the geographic variation in the mean proportion of pairs attempting to breed each year and the incidence of two-egg clutches.
Breeding within populations was consistent with these density-dependent trends: incidence of two-egg clutches increased in a declining population, and productivity was inversely related to breeding density and rainfall combined. To determine if reduced food resources accounted for reduced output in dense populations, eight pairs were food supplemented: supplementary food failed to induce nonbreeding pairs to breed: nor did it induce earlier laying or increase egg size or clutch-size. Population density itself was unrelated to two correlates of food resources, rainfall and latitude. I conclude that population density influences most aspects of breeding in Wahlberg's Eagles, and reduced food resources do not appear to explain these trends. Hence, adaptive restraint may account for decreased annual reproduction in this species. 相似文献
Breeding within populations was consistent with these density-dependent trends: incidence of two-egg clutches increased in a declining population, and productivity was inversely related to breeding density and rainfall combined. To determine if reduced food resources accounted for reduced output in dense populations, eight pairs were food supplemented: supplementary food failed to induce nonbreeding pairs to breed: nor did it induce earlier laying or increase egg size or clutch-size. Population density itself was unrelated to two correlates of food resources, rainfall and latitude. I conclude that population density influences most aspects of breeding in Wahlberg's Eagles, and reduced food resources do not appear to explain these trends. Hence, adaptive restraint may account for decreased annual reproduction in this species. 相似文献
3.
We have evaluated codon usage bias in Drosophila histone genes and have
obtained the nucleotide sequence of a 5,161-bp D. hydei histone gene repeat
unit. This repeat contains genes for all five histone proteins (H1, H2a,
H2b, H3, and H4) and differs from the previously reported one by a second
EcoRI site. These D. hydei repeats have been aligned to each other and to
the 5.0-kb (i.e., long) and 4.8-kb (i.e., short) histone repeat types from
D. melanogaster. In each species, base composition at synonymous sites is
similar to the average genomic composition and approaches that in the small
intergenic spacers of the histone gene repeats. Accumulation of synonymous
changes at synonymous sites after the species diverged is quite high. Both
of these features are consistent with the relatively low codon usage bias
observed in these genes when compared with other Drosophila genes. Thus,
the generalization that abundantly expressed genes in Drosophila have high
codon bias and low rates of silent substitution does not hold for the
histone genes.
相似文献
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5.
CHARLOTTA KVARNEMO LEIGH W. SIMMONS 《Biological journal of the Linnean Society. Linnean Society of London》2004,83(3):369-376
Externally fertilizing fishes are predicted to invest heavily in testes, because large numbers of sperm should be favoured by the high risk of sperm competition from sneaker males, and/or the dilution of ejaculates when shed into open water. Using museum specimens, we measured testes mass and body mass of 83 mature males, belonging to 21 genera of the family Syngnathidae (pipefishes and seahorses). In this family all species show paternal care, ranging in degree from eggs being attached to the skin of the male, to eggs being completely enclosed and nurtured within a brood pouch. The former, 'unprotected' group, is thought to have external fertilization, whereas in the latter, 'protected' group, males fertilize the eggs internally in their brood pouch. Smaller relative testes investment was thus predicted for genera that have protected compared with unprotected brood care. However, we found this not to be the case. Instead, all genera showed the same relationship between testes and body mass, regardless of brooding type. The possible implications of this surprising result are discussed, including the possibility that the mode of fertilization might have been misjudged for the pouchless syngnathids. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 369–376. 相似文献
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9.
MICHAEL WERNER LEIGH W. SIMMONS 《Biological journal of the Linnean Society. Linnean Society of London》2008,93(2):257-266
It is now widely recognized that sexual selection has been important in the rapid and divergent evolution of male genital morphology. However, distinguishing among putative mechanisms of sexual selection acting on male genital morphology represents a considerable challenge. Although there is growing evidence that variation in the size and/or shape of male genital structures can determine a male's success in gaining fertilizations, our knowledge of the functional morphology of male genitalia remains limited. Here we examine the functional morphology of genital sclerites that are known to influence paternity in the dung beetle Onthophagus taurus . We show that three of the sclerites form a functionally integrated unit that generates the tubular-shaped spermatophore and delivers its opening to the female's spermathecal duct. A fourth sclerite acts as a holdfast device during copulation. Our observations shed light on the mechanism by which these sclerites influence a male's paternity, and their patterns of phenotypic and genetic (co)variation. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 257–266. 相似文献
10.
Microsatellite loci were isolated from Dawson's burrowing bee, Amegilla dawsoni, a species endemic to Western Australia. Twelve polymorphic loci were found with an observed number of alleles ranging from two to 24 and observed heterozygosities between 0.17 and 0.85. These 12 loci were tested for amplification in three additional species of Amegilla. The loci will be used for sex determination and the examination of mating frequency in this species. 相似文献