TheperiodGene Thr-Gly Polymorphism in Australian and AfricanDrosophila melanogasterPopulations: Implications for Selection

Abstract

The period gene is a key regulator of biological rhythmicity in Drosophila melanogaster. The central part of the gene encodes a dipeptide Thr-Gly repeat that has been implicated in the evolution of both circadian and ultradian rhythms. We have previously observed that length variation in the repeat follows a latitudinal cline in Europe and North Africa, so we have sought to extend this observation to the southern hemisphere. We observe a parallel cline in Australia for one of the two major length variants and find higher levels of some Thr-Gly length variants, particularly at the tropical latitudes, that are extremely rare in Europe. In addition we examined .40 haplotypes from sub-Saharan Africa and find a very different and far more variable profile of Thr-Gly sequences. Statistical analysis of the periodicity and codon content of the repeat from all three continents reveals a possible mechanism that may explain how the repeat initially arose in the ancestors of the D. melanogaster subgroup of species. Our results further reinforce the view that thermal selection may have contributed to shaping the continental patterns of ThrGly variability.

A cline in the Drosophila melanogaster period gene in Australia: neither down nor under

“…We would like to point out that in an extensive study of Thr-Gly variation in Australia and Africa, we find a significant cline for one of the major Thr-Gly length variants in Australia that is consistent with the one in Europe (Sawyer et al, 2006). Although this cline is weaker than that found in Europe, we concluded that this may be because D. melanogaster had been introduced to Australia only 80-90 years before our collections were made (compared with c. 10-15 000 years in Europe, David & Capy, 1988).…”

“…Their implicit assumption is that European samples must have the same number of alleles as Australia, and that Costa et al (1992) misclassified these. However, from a similar collection of flies sampled from eastern Australia in 1993 (James et al, 1995(James et al, , 1997, which we used to examine Thr-Gly length polymorphism (Sawyer et al, 2006), we resolved all eight of these Thr-Gly length alleles, and at similar frequencies to Weeks et al (2006). In addition, the frequencies of the rarer Australian alleles that fell outside of the 14-17-20-23 Thr-Gly repeat periodicity, were also similar to those of Weeks et al (2006).…”

Measuring individual locomotor rhythms in honey bees, paper wasps and similar sized insects

“…This finding is surprising because the ability to maintain a fixed endogenous period throughout a range of physiological temperatures (temperature compensation) is a defining feature of circadian rhythms (Zehring et al, 1984). Moreover, population genetic studies in Drosophila indicate that temperature compensation is under natural selection and is important for adapting to high latitudes (Sawyer et al, 1997;Sawyer et al, 2006). A possible explanation to the observed alterations of temperature compensation in honey bees could be that because they tightly regulate their hive temperature (Winston, 1987;Jones et al, 2004), the selective pressure to maintain this trait has been eliminated or reduced.…”

Physical mapping of the Period gene on meiotic chromosomes of South American grasshoppers (Acridomorpha, Orthoptera)

“…Most of the research done with this gene was the molecular characterization of the threonine-glycine repeating regions in some groups, mainly Diptera and Lepidoptera, allowing the use of this gene as a marker in phylogeographic studies, molecular systematics, and evolution. These studies demonstrated the considerable level of evolutionary conservation and feasibility of using this gene, alone or combined with other markers, for applications in systematic, taxonomic, and population studies of insect groups (Rosato and Kyriacou, 2001;Miyatake et al, 2002;Barr et al, 2005;Mazzotta et al, 2005;Lankinen and Forsman, 2006;Sawyer et al, 2006;Matsumoto et al, 2008).…”