Molecular Population Genetics of the α-Esterase5 Gene Locus in Original and Colonized Populations of Drosophila buzzatii and Its Sibling Drosophila koepferae

Abstract

Several studies have suggested that esterase-2 (EST-2) may be the target of natural selection in the cactophilic fly Drosophila buzzatii. In this work, we analyzed nucleotide variation in a fragment of alpha-esterase5 (alphaE5), the gene encoding EST-2, in original (Argentinian) and colonized (Australian) populations of D. buzzatii and in its sibling D. koepferae. Estimates of nucleotide heterozygosity in D. buzzatii were similar in Australia and Argentina, although we detected a loss of singletons in colonized populations, suggesting a moderate founder effect. Interspecific comparisons revealed that D. buzzatii was more polymorphic for nonsynonymous variation, whereas D. koepferae was more variable for synonymous and noncoding sites. The two major chromosomal arrangements (2st and 2j) in D. buzzatii displayed similar levels of nucleotide variation, whereas 2jz3 was monomorphic. The sequenced region allowed the discrimination of a greater number of EST-2 protein variants in the Australian sample than in the Argentinean sample. In D. koepferae, nucleotide variation in alphaE5 does not depart from neutral expectations, although tests of population structure were significant for silent variation. In contrast, D. buzzatii has probably undergone a recent population expansion in its South American range. In addition, the McDonald and Kreitman test revealed an excess of nonsynonymous polymorphism in both original and colonized populations of this species.

Bottlenecks, population differentiation and apparent selection at microsatellite loci in Australian Drosophila buzzatii

“…Demographic history of D. buzzatii in Australia Previous comparisons of Australian populations with original ones in Argentina support a bottleneck at the time of introduction, with the former showing reduced variability for allozyme (Barker et al, 1985), mitochondrial DNA (Halliburton and Barker, 1993), microsatellite (Frydenberg et al, 2002; Table 1) and other molecular (Piccinali et al, 2007) polymorphisms. Distributions of the overall Australian and Argentinian allele frequencies at 15 microsatellite loci (Figure 4) show not only the reduced variability of the former, but also dramatic shifts at many of the loci-clear signals of a founding bottleneck.…”

The Transposon Galileo Generates Natural Chromosomal Inversions in Drosophila by Ectopic Recombination

“…This is in clear contrast with the ∼1 Myr and ∼0.5 Myr old inversions 2j and 2q 7 where 17 and 14 fixed nucleotide substitutions were observed, respectively [38], [60]. The monomorphism of the α-esterase5 gene in 2jz 3 chromosomes is also consistent with a recent origin of inversion 2z 3 [98]. In spite of being a very young inversion, 2z 3 exhibits a widespread distribution in natural populations (see Introduction), suggesting that it must have a considerable selective value.…”

Characterization of the shsp genes in Drosophila buzzatii and association between the frequency of Valine mutations in hsp23 and climatic variables along a longitudinal gradient in Australia

“…There is a great difference between the percentages of non-synonymous replacements in D. buzzatii hsp23, hsp26 and phsp26 and all of them are lower than the percentages for D. buzzatii Xdh, α-E5 and αE5 (Table 1; Gómez and Hasson 2003;Piccinali et al 2004Piccinali et al , 2007. But analyses of the DNA variation in different genes within and between Drosophila species have shown that there is great variation in the percentage of non-synonymous replacements both between genes within species and between species (Moriyama and Powell 1996;Andolfatto 2001;Piccinali et al 2004).…”

“…The levels of nucleotide heterozygosity of hsp23, hsp26 and phsp26 were estimated by means of π and θ and compared to π and θ values of other D. buzzatii genes (Table 1; Gómez and Hasson 2003;Piccinali et al 2004Piccinali et al , 2007. The total π and θ values for hsp23 and hsp26 were lower than that for Xdh, α-E5 and Est-A, whereas for phsp26 it was in between the values for the other genes.…”