Biomedical subjects

Stephen W McKechnie

Publications and source records attributed to Stephen W McKechnie.

5 recordsLinked to original sources

PubMed2006

An independent non-linear latitudinal cline for the sn-glycerol-3-phosphate (alpha- Gpdh ) polymorphism of Drosophila melanogaster from eastern Australia.

Latitudinal variation of the polymorphic sn-glycerol-3-phosphate (alpha-Gpdh) locus in Drosophila melanogaster has been characterized on several continents; however, apparent clinal patterns are potentially confounded by linkage with an inversion, close associations with other genetic markers that vary clinally, and a tandem alpha-Gpdh pseudogene. Here we compare clinal patterns in alpha-Gpdh with those of other linked markers by testing field flies from eastern Australian locations collected in two separate years. The alpha-Gpdh variation exhibited a consistent non-linear cline reflecting an increase in the alpha-GpdhF allele at extreme latitudes. This pattern was not influenced by the In(2L)t inversion wherein this locus is located, nor was it influenced by the presence of the alpha-Gpdh pseudogene, whose presence was ubiquitous and highly variable among populations. The alpha-Gpdh pattern was also independent of a cline in allozyme frequencies at the alcohol dehydrogenase (Adh) locus, and two length polymorphisms in the Adh gene. These results suggest clinal selection at the alpha-Gpdh locus that is partially or wholly unrelated to linear climatic gradients along the eastern coast of Australia.

Alleles↗

PubMed2005

Response to selection for rapid chill-coma recovery in Drosophila melanogaster: physiology and life-history traits.

Resistance to low temperatures can vary markedly among invertebrate species and is directly related to their distribution. Despite the ecological importance of cold resistance this trait has rarely been studied genetically, mainly because low and variable fitness of offspring from cold-stressed mothers makes it difficult to undertake selection experiments and compare cold resistance of parents and offspring. One measure of cold resistance that varies geographically in Drosophila melanogaster and that is amenable to genetic analysis is chill-coma recovery. Three replicate lines of D. melanogaster were selected every second generation, for over 30 generations, for decreased recovery time following exposure to 0 degrees C. Correlated responses were scored to characterize underlying physiological traits and to investigate interactions with other traits. Lines responded rapidly to the intermittent selection regime with realized heritabilities varying from 33% to 46%. Selected lines showed decreased recovery time after exposure to a broad range of low temperatures and also had a lower mortality following a more severe cold shock, indicating that a general mechanism underlying cold resistance had been selected. The selection response was independent of plastic changes in cold resistance because the selected lines maintained their ability to harden (i.e. a short-term exposure to cool temperature resulted in decreased recovery time in subsequent chill-coma assays). Changes in cold resistance were not associated with changes in resistance to high temperature exposure, and selected lines showed no changes in wing size, development time or viability. However, there was a decrease in longevity in the selected lines due to an earlier onset of ageing. These results indicate that chill-coma recovery can be rapidly altered by selection, as long as selection is undertaken every second generation to avoid carry-over effects, and suggest that lower thermal limits can be shifted towards increased cold resistance independently of upper thermal limits and without tradeoffs in many life-history traits.

Acclimatization↗

PubMed2005

The latitudinal cline in the In(3R)Payne inversion polymorphism has shifted in the last 20 years in Australian Drosophila melanogaster populations.

Clinal variation has been described in a number of inversions in Drosophila but these clines are often characterized by cytological techniques using small sample sizes, and associations with specific genes are rarely considered. Here we have developed a molecular assay for In(3R)Payne in Drosophila melanogaster from eastern Australia populations. It shows in repeated samples that the inversion cline is very tightly associated with latitude and is almost fixed in tropical populations while relatively rare in temperate populations. This steep cline has shifted in position in the last 20 years. The heat shock gene, hsr-omega, located centrally inside the inversion sequence, shows a different clinal pattern to In(3R)Payne. These results suggest strong ongoing selection on In(3R)Payne over the last 100 years since the colonization of Australia that is partly independent of hsr-omega.

Animals↗

PubMed2005

A cluster of diagnostic Hsp68 amino acid sites that are identified in Drosophila from the melanogaster species group are concentrated around beta-sheet residues involved with substrate binding.

The coding region of the hsp68 gene has been amplified, cloned, and sequenced from 10 Drosophila species, 5 from the melanogaster subgroup and 5 from the montium subgroup. When the predicted amino acid sequences are compared with available Hsp70 sequences, patterns of conservation suggest that the C-terminal region should be subdivided according to predominant secondary structure. Conservation levels between Hsp68 and Hsp70 proteins were high in the N-terminal ATPase and adjacent beta-sheet domains, medium in the alpha-helix domain, and low in the C-terminal mobile domain (78%, 72%, 41%, and 21% identity, respectively). A number of amino acid sites were found to be "diagnostic" for Hsp68 (28 of approximately 635 residues). A few of these occur in the ATPase domain (385 residues) but most (75%) are concentrated in the beta-sheet and alpha-helix domains (34% of the protein) with none in the short mobile domain. Five of the diagnostic sites in the beta-sheet domain are clustered around, but not coincident with, functional sites known to be involved in substrate binding. Nearly all of the Hsp70 family length variation occurs in the mobile domain. Within montium subgroup species, 2 nearly identical hsp68 PCR products that differed in length are either different alleles or products of an ancestral hsp68 duplication.

Adenosine Triphosphatases↗

PubMed2003

Immunocontraception for population control: will resistance evolve?

The prospect for successful biocontrol using immunocontraception is threatened if there is adaptation to the vaccine through natural selection of individuals that are genetically resistant to the contraceptive agent. To assess this possibility we examined the literature and found that little relevant data are available for any species on the appropriate trait, fertility variation among immunized individuals, or about appropriate population and genetic parameters influencing the likelihood of a selection response. Some data are available on variation in antibody response to immunocontraceptives, but the relationship between antibody response and fertility levels is poorly documented. The antibody response data indicate low heritability for this trait suggesting that fertility levels of contraceptive-resistant individuals will also have a low heritability. Slow evolution of contraception resistance might therefore be anticipated. The absence of information about relevant parameters makes the construction of quantitative models premature. We discuss factors in particular need of investigation if predictions about resistance evolution are to be made. These include: 1. the genetic basis of fertility retention, 2. the proportion of the population resistant to the contraceptive agent and how this is affected by gene flow from refuge populations, 3. the genetically-based fitness tradeoffs of resistant individuals that often accompany selection, 4. cross-generation effects that can thwart the effects of selection, and 5. the efficiency of delivery of the contraceptive agent. An understanding of the above for particular species, and the development of appropriate divergently acting multiple vaccines that can be used in temporal rotation or in mixtures, should facilitate the development of management options to minimize resistance evolution.

Animals↗