Natural history of

Negative effects of human presence and activities on breeding success and survival of many water bird species are well documented. The New Zealand dabchick (Poliocephalus rufopectus) is a protected endemic New Zealand grebe, confined to the North Island mainland and classified as vulnerable. A third of the total New Zealand dabchick population live on the lakes of the central volcanic plateau, where there is potential conflict between humans and dabchicks. We used data from two independent surveys describing the distribution of New Zealand dabchicks to investigate the effect that human-made structures (i.e. jetties and houses) and human recreational activities (i.e. boating) have on the numbers of New Zealand dabchick pairs, chicks and nests in the bays of Lake Rotoiti, Tarawera and Okareka. Our results suggest that human-made structures and recreational activities are not significantly affecting the numbers and distribution of New Zealand dabchick pairs or nests at this time. Furthermore, the number of human-made structures was positively correlated with the number of chicks in the sampled bays. Humans and dabchicks may be distributed similarly around the lakes because factors such as wind exposure and shoreline topography made certain sites preferable for both species. Alternatively, humanmade structures may provide protected nesting environments and/or cover for chicks from predators, refuges from harassment by other bird species, or other benefits. Pairs may therefore be able to raise chicks to the fledging stage more successfully. However, little is currently known about dabchick life history or population dynamics. We recommend that a method of capturing and marking be developed so that further monitoring of behavioural and population changes can be carried out. It is also necessary to conduct research on how boats and human activities at jetties affect incubating dabchicks and their young during the nesting phase.     

Natural history of the maldescended testis

In a series of 545 boys with undescended testis, 91 had bilateral spontaneous descent after the age of 10. Forty-five accepted to take part in an investigation of their fertility based on history, clinical examination, sperm analysis and estimation of serum FSH levels. In the majority, the volume of the testis was below normal and the sperm concentration was below the lower limit of the normal range. It is concluded that late spontaneous bilateral descent of the testis carries a serious risk of later impaired spermatogenesis.     

Natural selection and history

In “Spandrels,” Gould and Lewontin criticized what they took to be an all-too-common conviction, namely, that adaptation to current environments determines organic form. They stressed instead the importance of history. In this paper, we elaborate upon their concerns by appealing to other writings in which those issues are treated in greater detail. Gould and Lewontin’s combined emphasis on history was three-fold. First, evolution by natural selection does not start from scratch, but always refashions preexisting forms. Second, preexisting forms are refashioned by the selection of whatever mutational variations happen to arise: the historical order of mutations needs to be taken into account. Third, the order of environments and selection pressures also needs to be taken into account.     

Natural history of Ashkenazi intelligence

This paper elaborates the hypothesis that the unique demography and sociology of Ashkenazim in medieval Europe selected for intelligence. Ashkenazi literacy, economic specialization, and closure to inward gene flow led to a social environment in which there was high fitness payoff to intelligence, specifically verbal and mathematical intelligence but not spatial ability. As with any regime of strong directional selection on a quantitative trait, genetic variants that were otherwise fitness reducing rose in frequency. In particular we propose that the well-known clusters of Ashkenazi genetic diseases, the sphingolipid cluster and the DNA repair cluster in particular, increase intelligence in heterozygotes. Other Ashkenazi disorders are known to increase intelligence. Although these disorders have been attributed to a bottleneck in Ashkenazi history and consequent genetic drift, there is no evidence of any bottleneck. Gene frequencies at a large number of autosomal loci show that if there was a bottleneck then subsequent gene flow from Europeans must have been very large, obliterating the effects of any bottleneck. The clustering of the disorders in only a few pathways and the presence at elevated frequency of more than one deleterious allele at many of them could not have been produced by drift. Instead these are signatures of strong and recent natural selection.     

Natural history of autoimmune thyroiditis.

One hundred and sixty-three asymptomatic people with thyroid antibodies or raised serum thyrotrophin (TSH) concentrations, or both, and 209 age-matched and sex-matched controls without either marker of thyroid disorder were followed up for four years to determine the natural history of autoimmune thyroiditis. Mildly raised TSH concentrations alone and the presence of thyroid antibodies alone did not significantly increase the risk of developing overt hypothyroidism during the four years compared with the controls. Overt hypothyroidism developed at the rate of 5% a year in women who initially had both raised TSH concentrations and thyroid antibodies. Prophylactic treatment with thyroxine may be justified in women found to have both markers of impending thyroid failure. The cost effectiveness of screening the adult population remains to be evaluated.     

Natural history of murine gamma-herpesvirus infection

Murine gamma-herpesvirus 68 (MHV-68) is a natural pathogen of small rodents and insectivores (mice, voles and shrews). The primary infection is characterized by virus replication in lung epithelial cells and the establishment of a latent infection in B lymphocytes. The virus is also observed to persist in lung epithelial cells, dendritic cells and macrophages. Splenomegaly is observed two weeks after infection, in which there is a CD4+ T-cell-mediated expansion of B and T cells in the spleen. At three weeks post-infection an infectious mononucleosis-like syndrome is observed involving a major expansion of Vbeta4+CD8+ T cells. Later in the course of persistent infection, ca. 10% of mice develop lymphoproliferative disease characterized as lymphomas of B-cell origin. The genome from MHV-68 strain g2.4 has been sequenced and contains ca. 73 genes, the majority of which are collinear and homologous to other gamma-herpesviruses. The genome includes cellular homologues for a complement-regulatory protein, Bcl-2, cyclin D and interleukin-8 receptor and a set of novel genes M1 to M4. The function of these genes in the context of latent infections, evasion of immune responses and virus-mediated pathologies is discussed. Both innate and adaptive immune responses play an active role in limiting virus infection. The absence of type I interferon (IFN) results in a lethal MHV-68 infection, emphasizing the central role of these cytokines at the initial stages of infection. In contrast, type II IFN is not essential for the recovery from infection in the lung, but a failure of type II IFN receptor signalling results in the atrophy of lymphoid tissue associated with virus persistence. Splenic atrophy appears to be the result of immunopathology, since in the absence of CD8+ T cells no pathology occurs. CD8+ T cells play a major role in recovery from the primary infection, and also in regulating latently infected cells expressing the M2 gene product. CD4+ T cells have a key role in surveillance against virus recurrences in the lung, in part mediated through 'help' in the genesis of neutralizing antibodies. In the absence of CD4+ T cells, virus-specific CD8+ T cells are able to control the primary infection in the respiratory tract, yet surprisingly the memory CD8+ T cells generated are unable to inhibit virus recurrences in the lung. This could be explained in part by the observations that this virus can downregulate major histocompatibility complex class I expression and also restrict inflammatory cell responses by producing a chemokine-binding protein (M3 gene product). MHV-68 provides an excellent model to explore methods for controlling gamma-herpesvirus infection through vaccination and chemotherapy. Vaccination with gp150 (a homologue of gp350 of Epstein-Barr virus) results in a reduction in splenomegaly and virus latency but does not block replication in the lung, nor the establishment of a latent infection. Even when lung virus infection is greatly reduced following the action of CD8+ T cells, induced via a prime-boost vaccination strategy, a latent infection is established. Potent antiviral compounds such as the nucleoside analogue 2'deoxy-5-ethyl-beta-4'-thiouridine, which disrupts virus replication in vivo, cannot inhibit the establishment of a latent infection. Clearly, devising strategies to interrupt the establishment of latent virus infections may well prove impossible with existing methods.     

Natural history and experimental evolution of the genetic code

The standard genetic code is a set of rules that relates the 20 canonical amino acids in proteins to groups of three bases in the mRNA. It evolved from a more primitive form and the attempts to reconstruct its natural history are based on its present-day features. Genetic code engineering as a new research field was developed independently in a few laboratories during the last 15 years. The main intention is to re-program protein synthesis by expanding the coding capacities of the genetic code via re-assignment of specific codons to un-natural amino acids. This article focuses on the question as to which extent hypothetical scenarios that led to codon re-assignments during the evolution of the genetic code are relevant for its further evolution in the laboratory. Current attempts to engineer the genetic code are reviewed with reference to theoretical works on its natural history. Integration of the theoretical considerations into experimental concepts will bring us closer to designer cells with target-engineered genetic codes that should open not only tremendous possibilities for the biotechnology of the twenty-first century but will also provide a basis for the design of novel life forms.     

Natural history of cystic echinococcosis in humans

This study provides a contribution to understanding of the natural history of the hydatid cyst during its evolution in the human liver examining the high morphostructural variability of larval forms of Echinococcus granulosus. A detailed study of a large sample of intact cysts removed from patients surgically treated by means of total pericystectomy, has enabled to outline the different developmental stages of the parasite over time, up to its death and complete degeneration.