Regardless of the cosmopolitan nature of body size clines in more than one Drosophila species, and the repeatability of laboratory thermal selection, the actual selective mechanisms controlling the genetic basis of body size variation are not fully understood.
In reptiles, behavioural thermal selection results in body temperatures that fluctuate narrowly around characteristic mean values [4].
As presented here, one can see that the protocol employed for the extended thermal selection experiments differs greatly from that of the acute thermal selection experiments.
We can draw two conclusions based upon the results of exposing the phage to acute thermal selection.
The Anc strain, which was used as the ancestral line for the acute thermal selection experiments, also includes Thr100.
None of the mutations identified in the acute thermal selection experiments appeared in the final sequenced surviving lines.
More puzzling information come from flies collected in the central area of the South American clines and kept under three different thermal selection regimes for two years.
Under both acute and extended thermal selection, we were able to observe mutations that occurred in response to excessive external pressures independent of concurrently evolving hosts.
Moreover, the mutations which occurred in the acute thermal selection experiments were not seen in the surviving long-term treatment isolates.
The results of the acute and extended thermal selection experiments, together, confirm that ΦX174 possesses an inherent means of tolerating elevated temperatures of 50°C.
Interestingly, expression levels of four previously reported candidate genes for thermotolerance in Drosophila (Hsp26, Hsp68, Fst, and Treh) were found to be correlated with past thermal selection regime.
