Molecular phylogeny of Myriapoda provides insights into evolutionary patterns of the mode in post-embryonic development.

Myriapoda, a subphylum of Arthropoda, comprises four classes, Chilopoda, Diplopoda, Pauropoda, and Symphyla. While recent molecular evidence has shown that Myriapoda is monophyletic, the internal phylogeny, which is pivotal for understanding the evolutionary history of myriapods, remains unresolved. Here we report the results of phylogenetic analyses and estimations of divergence time and ancestral state of myriapods. Phylogenetic analyses were performed based on three nuclear protein-coding genes determined from 19 myriapods representing the four classes (17 orders) and 11 outgroup species. The results revealed that Symphyla whose phylogenetic position has long been debated is the sister lineage to all other myriapods, and that the interordinal relationships within classes were consistent with traditional classifications. Ancestral state estimation based on the tree topology suggests that myriapods evolved from an ancestral state that was characterized by a hemianamorphic mode of post-embryonic development and had a relatively low number of body segments and legs.

Survival rate and expression of Heat-shock protein 70 and Frost genes after temperature stress in Drosophila melanogaster lines that are selected for recovery time from temperature coma.

In this study, we investigated the physiological mechanisms underlying temperature tolerance using Drosophila melanogaster lines with rapid, intermediate, or slow recovery from heat or chill coma that were established by artificial selection or by free recombination without selection. Specifically, we focused on the relationships among their recovery from heat or chill coma, survival after severe heat or cold, and survival enhanced by rapid cold hardening (RCH) or heat hardening. The recovery time from heat coma was not related to the survival rate after severe heat. The line with rapid recovery from chill coma showed a higher survival rate after severe cold exposure, and therefore the same mechanisms are likely to underlie these phenotypes. The recovery time from chill coma and survival rate after severe cold were unrelated to RCH-enhanced survival. We also examined the expression of two genes, Heat-shock protein 70 (Hsp70) and Frost, in these lines to understand the contribution of these stress-inducible genes to intraspecific variation in recovery from temperature coma. The line showing rapid recovery from heat coma did not exhibit higher expression of Hsp70 and Frost. In addition, Hsp70 and Frost transcription levels were not correlated with the recovery time from chill coma. Thus, Hsp70 and Frost transcriptional regulation was not involved in the intraspecific variation in recovery from temperature coma.

Fatty acids of membrane phospholipids in Drosophila melanogaster lines showing rapid and slow recovery from chill coma.

We investigated the fatty acid compositions of phospholipids in Drosophila melanogaster lines showing rapid (CR), intermediate (CTL), or slow (CS) recovery from chill coma, which were established by artificial selection or by free recombination without selection. Compared to CTL, CS showed a low composition of dienoic acids and a small number of double bonds in the fatty acids. The ratio of unsaturated fatty acids and saturated fatty acids (UFAs/SFAs) was significantly lower in CS than in CTL. CR had higher monoenoic acid composition and lower dienoic acid composition than CTL. In addition, the amount of SFAs was lower and therefore the UFAs/SFAs ratio considerably higher in CR than in CTL. These changes in phospholipid fatty acids probably contributed to losing and maintaining the homeoviscosity of the cellular membranes in CS and CR, respectively, at low temperature and therefore produced their distinct phenotypes in recovery from chill coma.