Individual differences and adaptive genetic similarities among developmental classes of Drosophila melanogaster

In a series of papers we published since 1980s, an extensive study was proceeded of gene-enzyme polymorphisms at nine loci of three largest chromosomes of Drosophila melanogaster (Marinkovic et al. 1987; Cluster et al. 1988; Milosevic & Marinkovic 1989; Kovac & Marinkovic 1999; Marinković 1999, 2002, 2008, 2009). It has not been emphasized enough that observed flies were selected before for their egg-to-adult rate of development. Under standard and synchronous laboratory conditions for their growth in adequate cultured bottles, three groups of eclosed flies, as 3 days old adults (3 x 100 ind’s) have been selected for starch-gel electrophoretic analysis, whether their egg-to-adult development lasted less than ten days (F), 1213 days (I), or more than 16 days (S), with fourth group of 100 flies (R) randomly chosen among hatched individuals . Allelic polymorphism was individually observed at nine studied loci that control phosphor-sugar metabolic cycle (6Pgd-3 alleles,@gpd-2, Adh-2, Hk-2, Sod-2, Pgm-3, EstC-2, Odh-2, Acph-3). They may generate some 78700 potential genotypes, with a theoretical chance that two out of 400 observed flies should have the same genotype is 1/30.000! However, instead of 400 we determined a total of 160 allozymic variants, among which only 82 were monomorph, and 78 were present in 2-22 individuals, showing an adaptive polymorphism. The total list of 78 genotypes present in 318 analyzed individuals has been published in J. Zool. Syst. Evol. Res. vol. 37 (Marinkovic 1999), and list of unique genotypes from 82 observed individuals is published in our present paper (Table 1). This gives a chance for further analyses of the data, that may lead to new discoveries, corrections and conclusions. In this concise paper we shall concentrate our attention to the relationship between individual genetic polymorphism observed and available in here collected data, and adaptive variability of 400 Drosophila melanogaster individuals measured through their rates for developmental capacity. The main question we pose is whether drastic differences in ind’s growth’s capacities should be correlated with cumulative differences in kinds and amounts of available allelogenes, or with their relationships.

It has not been emphasized enough that observed flies were selected before for their egg-to-adult rate of development.Under standard and synchronous laboratory conditions for their growth in adequate cultured bottles, three groups of eclosed flies, as 3 days old adults (3 x 100 ind's) have been selected for starch-gel electrophoretic analysis, whether their egg-to-adult development lasted less than ten days (F), 12-13 days (I), or more than 16 days (S), with fourth group of 100 flies (R) randomly chosen among hatched individuals .
The total list of 78 genotypes present in 318 analyzed individuals has been published in J. Zool.Syst.Evol.Res.vol.37 (Marinkovic 1999), and list of unique genotypes from 82 observed individuals is published in our present paper (Table 1).This gives a chance for further analyses of the data, that may lead to new discoveries, corrections and conclusions.
In this concise paper we shall concentrate our attention to the relationship between individual genetic polymorphism observed and available in here collected data, and adaptive variability of 400 Drosophila melanogaster individuals measured through their rates for developmental capacity.The main question we pose is whether drastic differences in ind's growth's capacities should be correlated with cumulative differences in kinds and amounts of available allelogenes, or with their relationships.

Results
Of special significance is the analysis and comparison of observed and expected frequencies of the presence of 160 determined polygenetic variances.It comes out that among 78 individually repeatable variants only  Marinkovic 1999).The discrepancy is more emphasized among unique, i.e. monomorphic variants (our Table 1), where only 20 out of 82 are expected to be present.This means that 3/4 of such variants are adaptively polymorphic, with specific constitution that gives them the advantage in comparison with other genotypes, despite of their difference in statistical expectancy.
In Table 2 is given a survey of allelic polymorphisms at nine studied loci in four developmental groups of selected 4 x 100 individuals with Fast, Slow, Intermediate, or Random rate of egg-to-adult development.It can be concluded that samples of four distinguished developmental groups have approximately the same scope of allozymic polymorphism.Among 318 individuals with 78 allozymic variants repeatable 2-22 times, those with Fast (77), Slow (75), Intermediate (83), or Random rate of development ( 83) are obviously pretty the same.Similar situation is among 82 individuals with monomorphic (i.e.unique) variants (20 / 26 / 18 / 18, respectively).Such results suggest clearly that capacities to developmental rates of three out of four studied developmental groups are not primarily dependent on cumulative effects of present allelic variants, but rather on their combinative (dom./rec.or epistatic) relationships, which also maintain the genetic constitution and variability in following generations.

Conclusions
All presented results are suggesting how complex is to visualize and quantify the origins of individual similarities that exist among individuals of a species.For a nine-loci system that we chose here to analyze at three chromosomes of D. melanogaster, it comes out that no more than 1 pro mile of possible combinations of observed chromosomal markers could be present in spermatozoa of adult males before these gametes enter to produce viable zygotes.During gamete competition a further reduction of variability occurs (to <1%), which is relatively modest at the level of egg-to-adult survivals.Final reduction to adaptive geno-and phenotypes gives rise to individuals that are impressively similar to each other, which diversity is based mostly on combinative traits as basic targets of Darwinian selection, with GAMETES, and their highly selected genomes, as INITIALS OF NEW GENERATIONS.

Table 1 .
Unique genotypes detected electrophoretically at nine polymorphic loci of D. melanogaster, presented on the basis of their individual presence in 82 out of 400 analysed flies.F, S, I and R are developmental phenotypes of 4 x 100 inspected ind's.

Table 2 .
Developmental phenotypes (Fast, Slow, Intermediate, Random) of D. melanogaster flies, on the basis of their egg-to-adult growth rate and allozymic analysis of nine polymorphic loci at three largest chromosomes.

Table 3
shows a detailed analysis of observed and expected genotypes for nine allozymic loci distributed at three largest chromosomes of Drosophila melanogagster only in groups (2 x 100) with Fast and Slow eggto-adult development.At four loci of I&II chromosomes there are 18 common and 20 different genotypes of Fast and Slow group of fruit fly individuals, while at five loci of chr.III only 9 are common and 13 specific, out of 360 potential genotypes.Summarized at nine inspected loci, only 63 allozymic variants have been found among 'Fast' individuals out of 19440 potential variants, and this ratio for 'Slow' growth adults is 68 vs. 11664, i.e. less than 0.2%.Among 111 genotypes from both 'fast' and 'slow' growth phenotypes, 20 are common and 91 is specific, out of 78732 potential combinations.

Table 3 .
Observed and expected genotypes for nine allozymic loci distributed at three largest chromosomes of D. melanogaster individuals (2x100) with Fast and Slow preadult development.