Biomedical subjects

Nathan Pike

Publications and source records attributed to Nathan Pike.

3 recordsLinked to original sources

PubMed2004

The effect of autocorrelation in environmental variability on the persistence of populations: an experimental test.

Despite its significance regarding the conservation and management of biological resources, the body of theory predicting that the correlation between successive environmental states can profoundly influence extinction has not been empirically validated. Identical clonal populations from a model experimental system based on the collembolan Folsomia candida were used in the present study to investigate the effect of environmental autocorrelation on time to extinction. Environmental variation was imposed by variable implementation (present/absent) of a culling procedure according to treatments that represented six patterns of environmental autocorrelation. The average number of culling events was held constant across treatments but, as environmental autocorrelation increased, longer runs of both favourable and unfavourable culling tended to occur. While no difference was found among the survival functions for the various treatments, the time taken for 50% of the component populations to become extinct decreased significantly with increasing environmental autocorrelation. Similarly, analysis of all extinct populations demonstrated that time to extinction was shortened as environmental autocorrelation increased. However, this acceleration of extinction can be fully offset if sequential introduction is used in place of simultaneous introduction when founding the populations.

Animals↗

PubMed2004

The allelic spectra of common diseases may resemble the allelic spectrum of the full genome.

Identification of the genes responsible for common human diseases promises to be one of the most significant advances in medical knowledge and treatment. To date, the numerous attempts to identify the genes responsible for complex and multi-factorial common diseases have met with only a handful of successes. The key to calculating the optimal effort and ideal approach to successful identifications lies with understanding the likely allelic spectrum of the target disease. The allelic spectrum describes the number of disease loci and the frequency of each disease allele. It has been implicitly assumed that disease spectra are biased towards either commonness or rareness relative to the allelic spectrum of the overall human genome. We present a hypothesis that the allelic spectra of common diseases are generally similar to the spectrum that characterizes the entire genome. This hypothesis is supported by the fact that only a few loci have major significance to familial disease risks and that there may be many disease loci which each make a minor contribution to a disease. Additionally, although relatively few alleles of the human genome have been examined for disease involvement, current estimates of the number of disease genes are very high. Because selection will have been operating only weakly and for a relatively short time on most of the alleles associated with complex diseases, spectra that are characteristic of near-neutral selection may well apply. We thus propose that the hitherto neglected hypothesis that puts the likely allelic spectra of common diseases in the middle ground between the prevailing hypotheses of spectral skew towards rareness or commonness is the most likely. By using this hypothesis as the null, research resources may be optimally allocated and greater success in identifying disease genes may be achieved.

Alleles↗

PubMed2002

How aphids lose their marbles.

Insects provide examples of many cunning stratagems to cope with the challenges of living in a world dominated by surface forces. Despite being the current masters of the land environment, they are at constant risk of being entrapped in liquids, which they prevent by having waxy and hairy surfaces. The problem is particularly acute in an enclosed space, such as a plant gall. Using secreted wax to efficiently parcel and transport their own excrement, aphids were able to solve this problem 200 Myr ago. Here, we report on the physical and physiological significance of this ingenious solution. The secreted powdery wax has three distinct roles: (i) it is hydrophobic, (ii) it creates a microscopically rough inner gall surface made of weakly compacted wax needles making the gall ultra-hydrophobic, and (iii) it coats the honeydew droplets converting them into liquid marbles, that can be rapidly and efficiently moved.

Animals↗