Sequential gel electrophoretic analysis of esterase-2 in two populations of Drosophila buzzatii

Abstract

Sequential electrophoresis, using three different buffer systems on cellulose acetate gels, was used to characterize the allelic variation for esterase-2 in two populations of D. buzzatii in Australia that are separated by 550 km. Twenty-five alleles were detected, of which nine were unique to one population, eight unique to the other, and only eight were common to both populations. Allele frequencies within each population were significantly different between the two major chromosome sequences (standard and j inversion), and for each chromosome sequence allele frequencies were significantly different between populations. Observed allelic frequency distributions were not significantly different from those predicted for selective neutrality using the homozygosity test statistic. However, estimates of the effective sizes of the populations derived from their observed differentiation, together with the history of the species in Australia, provide support for some form of balancing selection affecting at least some of the alleles.

Selection at the Esterase-2 Locus of Drosophila buzzatii? Perturbation-Reperturbation Experiments

“…From one male in each isofemale line, and using the Antennapedia / Delta 5 ( Antp /Δ 5 ) second chromosome balancer stock, one line was derived which was isochromosomal for a wild chromosome 2, with the Y chromosome from the original wild male, chromosomes 3 and 4 from the original wild male and from the Antp /Δ 5 stock, and X chromosomes from the Antp /Δ 5 stock (see [11] for details).…”

“…As the Est-2 locus maps close to the proximal break points of the two more common inversions [26], [27], all lines were karyotyped for chromosome 2 sequences [11]. Of the Trinkey lines, 21 were ST , 46 j and four jz 3 , and the corresponding numbers for Hemmant were 20, 55 and one.…”

“…Of the Trinkey lines, 21 were ST , 46 j and four jz 3 , and the corresponding numbers for Hemmant were 20, 55 and one. All lines were characterised for their Est-2 genotype using sequential gel electrophoresis [11]. During the period of karyotyping and electrophoretic characterisation, all lines were maintained in four vials, five pairs per vial.…”

“…The allele in each line was that at the highest frequency in each of the a , b and c starch classes in the natural populations. These alleles (names as in [11]), line names and population frequencies (in the 147 pooled Trinkey (IT) and Hemmant (IH) lines) were:…”

“…The Esterase-2 locus of Drosophila buzzatii is highly polymorphic, with five common (designated a , b , c + , c and d ) and three rare electromorphs (designated a* , e and null ) detected using starch gel electrophoresis (starch GE) [9], [10] and 25 alleles using sequential gel electrophoresis (sequential GE) [11]. There is extensive evidence, from both natural populations and laboratory experiments, that selection is affecting the frequencies of the starch GE alleles, and consequently that variation at this locus may be adaptively significant:…”