On the Long-term Stability of Clines in Some Metabolic Genes in Drosophila melanogaster

Rodrigo Cogni,Kate Kuczynski,Emily L Behrman,Katherine R O'Brien,Spencer Koury,Walter F Eanes,Paul S Schmidt,Erik Lavington

doi:10.1038/srep42766

Abstract

Very little information exists for long-term changes in genetic variation in natural populations. Here we take the unique opportunity to compare a set of data for SNPs in 15 metabolic genes from eastern US collections of Drosophila melanogaster that span a large latitudinal range and represent two collections separated by 12 to 13 years. We also expand this to a 22-year interval for the Adh gene and approximately 30 years for the G6pd and Pgd genes. During these intervals, five genes showed a statistically significant change in average SNP allele frequency corrected for latitude. While much remains unchanged, we see five genes where latitudinal clines have been lost or gained and two where the slope significantly changes. The long-term frequency shift towards a southern favored Adh S allele reported in Australia populations is not observed in the eastern US over a period of 21 years. There is no general pattern of southern-favored or northern-favored alleles increasing in frequency across the genes. This observation points to the fluid nature of some allelic variation over this time period and the action of selective responses or migration that may be more regional than uniformly imposed across the cline.

Highlights

The study of geographic variation is an important approach in the inference of adaptation in evolutionary genetics, and work in Drosophila melanogaster has played a central role in these investigations over many decades
We first examined 15 genes from 10 US samples that were collected in 1997 by Brian Verrelli and the data reported by Sezgin and colleagues[8], and compared these results to a new collection of 18 samples made in 2009–2010 across the same latitudinal range[28]
We sampled the same amino acid polymorphisms in glucose-6-phosphate dehydrogenase (G6pd) and phosphogluconate dehydrogenase (Pgd) that were examined in North American collections made in the early 1980s12

Summary

Introduction

The study of geographic variation is an important approach in the inference of adaptation in evolutionary genetics, and work in Drosophila melanogaster has played a central role in these investigations over many decades. These studies found a number of parallel independent examples of clines in allozyme polymorphisms in the northern and southern hemispheres These early studies supported the theme of an underlying commonality of clinal selection regimes in both the Australian and North American populations, and these have formed the working hypothesis and context of many studies that suggest these latitudinal clines represent evidence of natural selection acting after colonization and population spread[7,14,15,16,17]. Out of these studies emerges the question as to how stable is the observed geographic variation over both short and long time scales? Our main goal is to describe patterns of changes over a 13-years interval in clines in 15 metabolic genes

Methods

Results

Conclusion