Sex and Ageing: The Role of Sexual Recombination in Longevity

I use a set of machines based on the concept of nested rule systems built on the a modified version of the Wolfram elemental cellular automata to investigate the role of recombination in providing resistance to ageing. Class III and class IV machines are observed to respond differently to recombination. Class IV machines show recombinational centring in their neutral networks whereas class III machines respond negatively to recombination. Rule 110 shows a unusual response to recombination. Recombination selects for resistance to recombination, the population moves to regions of genome space with high redundancy, this results in organisms with highly robust genomes, more likely to complete development and to be long lived. The increase in longevity may be sufficient to compensate for the costs of sex, including the two fold cost of sex, through increased reproductive potential in long lived organisms requiring long maturation times. Large complex species should therefore be resistant to invasion by asexual mutants whereas small simple organisms with early maturation should be vulnerable to invasion by asexual forms.

Sequence Diversity and Molecular Evolution of the Heat-Modifiable Outer Membrane Protein Gene (ompA) of Mannheimia(Pasteurella) haemolytica, Mannheimia glucosida, and Pasteurella trehalosi

ABSTRACT The OmpA (or heat-modifiable) protein is a major structural component of the outer membranes of gram-negative bacteria. The protein contains eight membrane-traversing β-strands and four surface-exposed loops. The genetic diversity and molecular evolution of OmpA were investigated in 31 Mannheimia (Pasteurella) haemolytica, 6 Mannheimia glucosida, and 4 Pasteurella trehalosi strains by comparative nucleotide sequence analysis. The OmpA proteins of M. haemolytica and M. glucosida contain four hypervariable domains located at the distal ends of the surface-exposed loops. The hypervariable domains of OmpA proteins from bovine and ovine M. haemolytica isolates are very different but are highly conserved among strains from each of these two host species. Fourteen different alleles representing four distinct phylogenetic classes, classes I to IV, were identified in M. haemolytica and M. glucosida. Class I, II, and IV alleles were associated with bovine M. haemolytica, ovine M. haemolytica, and M. glucosida strains, respectively, whereas class III alleles were present in certain M. haemolytica and M. glucosida isolates. Class I and II alleles were associated with divergent lineages of bovine and ovine M. haemolytica strains, respectively, indicating a history of horizontal DNA transfer and assortative (entire gene) recombination. Class III alleles have mosaic structures and were derived by horizontal DNA transfer and intragenic recombination. Our findings suggest that OmpA is under strong selective pressure from the host species and that it plays an important role in host adaptation. It is proposed that the OmpA protein of M. haemolytica acts as a ligand and is involved in binding to specific host cell receptor molecules in cattle and sheep. P. trehalosi expresses two OmpA homologs that are encoded by different tandemly arranged ompA genes. The P. trehalosi ompA genes are highly diverged from those of M. haemolytica and M. glucosida, and evidence is presented to suggest that at least one of these genes was acquired by horizontal DNA transfer.