Biomedical subjects

Carla M Sgrò

Publications and source records attributed to Carla M Sgrò.

5 recordsLinked to original sources

PubMed2006

Very low additive genetic variance and evolutionary potential in multiple populations of two rainforest Drosophila species.

Most quantitative traits are thought to exhibit high levels of genetic variance and evolutionary potential. However, this conclusion may be biased by a lack of studies on nonmodel organisms and may not generalize to restricted species. A recent study on a single, southern population of the rainforest-restricted Drosophila birchii failed to find significant additive genetic variance for the desiccation resistance trait; however, it is unclear whether this pattern extends to other D. birchii populations or to other rainforest species. Here we use an animal model design to show very low levels of additive genetic variance for desiccation resistance in multiple populations of two highly sensitive rainforest species of Drosophila from tropical northeastern Australia. In contrast, relatively high levels of genetic variance were found for morphological traits in all populations of the species tested. This indicates limited evolutionary potential for evolving increased desiccation resistance in these rainforest restricted species.

Animals↗

PubMed2004

Lifespan extension by dietary restriction in female Drosophila melanogaster is not caused by a reduction in vitellogenesis or ovarian activity.

Dietary restriction (DR) extends lifespan in a wide range of organisms. DR also reduces daily and lifetime fecundity. The latter may be an evolutionary adaptation to survive periods of food shortage. Reproductive rate is often negatively correlated with lifespan, and a reduced cost of reproduction could be the mechanism by which DR extends lifespan. We tested this hypothesis in Drosophila melanogaster females, by directly suppressing different aspects of reproduction and measuring the effect on the response of lifespan and age-specific mortality to DR. DR resulted in lifespan extension in females kept with males, in females kept without males, in females with vitellogenesis blocked by the mutant ovoD1 and in females with no germline as a result of X-irradiation. Moreover, rapid (48 h) changes in age-specific mortality, previously seen in fertile females switched between full feeding and DR, were also seen in ovoD1 females. Furthermore, these rapid changes in age-specific mortality in cohorts of fertile wild type females were not accompanied by concurrent changes in egg-production. These results indicate either that reduced reproduction is not necessary for lifespan extension by DR in Drosophila females, or that the relevant aspects of reproduction act upstream of our interventions and were therefore not blocked in our experiments.

Animals↗

PubMed2004

Chromosomal inversion polymorphisms and adaptation.

Chromosomal inversion polymorphisms continue to be identified from an increasing number of populations of insects, plants, bacteria and humans. In the fruit fly Drosophila, chromosomal polymorphisms were used in classic studies of natural selection. Recent molecular genetic studies suggest that inversion polymorphisms are dynamical systems. These studies also indicate patterns of disequilibrium and variation that are consistent with co-adapted gene complexes. Although these complexes have yet to be identified, recent studies have identified traits, such as body size, that are linked to inversion polymorphisms. Selection acting on these polymorphisms is strong because latitudinal clines in inversion frequency become re-established rapidly after a new continent is colonized. A combined molecular and phenotypic approach is helping to identify the role of inversion polymorphisms in adaptive divergence, but the genes responsible for associations between traits and inversion polymorphisms remain to be identified.

Journal Article↗

PubMed2004

The genetic covariance among clinal environments after adaptation to an environmental gradient in Drosophila serrata.

We examined the genetic basis of clinal adaptation by determining the evolutionary response of life-history traits to laboratory natural selection along a gradient of thermal stress in Drosophila serrata. A gradient of heat stress was created by exposing larvae to a heat stress of 36 degrees for 4 hr for 0, 1, 2, 3, 4, or 5 days of larval development, with the remainder of development taking place at 25 degrees. Replicated lines were exposed to each level of this stress every second generation for 30 generations. At the end of selection, we conducted a complete reciprocal transfer experiment where all populations were raised in all environments, to estimate the realized additive genetic covariance matrix among clinal environments in three life-history traits. Visualization of the genetic covariance functions of the life-history traits revealed that the genetic correlation between environments generally declined as environments became more different and even became negative between the most different environments in some cases. One exception to this general pattern was a life-history trait representing the classic trade-off between development time and body size, which responded to selection in a similar genetic fashion across all environments. Adaptation to clinal environments may involve a number of distinct genetic effects along the length of the cline, the complexity of which may not be fully revealed by focusing primarily on populations at the ends of the cline.

Adaptation, Biological↗

PubMed2003

Evolution of additive and nonadditive genetic variance in development time along a cline in Drosophila serrata.

Latitudinal clines provide natural systems that may allow the effect of natural selection on the genetic variance to be determined. Ten clinal populations of Drosophila serrata collected from the eastern coast of Australia were used to examine clinal patterns in the trait mean and genetic variance of the life-history trait egg-to-adult development time. Development time significantly lengthened from tropical areas to temperate areas. The additive genetic variance for development time in each population was not associated with latitude but was associated with the population mean development time. Additive genetic variance tended to be larger in populations with more extreme development times and appeared to be consistent with allele frequency change. In contrast, the nonadditive genetic variance was not associated with the population mean but was associated with latitude. Levels of nonadditive genetic variance were greatest in the region of the cline where the gradient in the change in mean was greatest, consistent with Barton's (1999) conjecture that the generation of linkage disequilibrium may become an important component of the genetic variance in systems with a spatially varying optimum.

Analysis of Variance↗