Mimicry of isozyme adaptive advantage by gene association II. Adh genotype frequency variations in Drosophila cage populations reared at different temperatures

The adaptive response of the Adh locus to different temperatures was determined in an experimental population with a stabilized gene pool in order to confirm the conclusions reached in a previous paper (Pieragostini et al., Genetica 56: 27–37, 1981) using as experimental material a laboratory population in which heterosis and strong interaction between loci were present.By sampling a stable lab population, three cage populations were constructed, heterozygous at the Adh locus and genetically identical but reared at different temperatures (P 18 °C, P 25 °C and P 28 °C). On these populations we studied the dynamics of Adh allele frequencies and of five metric traits up to the fifth generation of caging. The most interesting result is represented by the differences between P 28 °C and the other two populations (P 25 °C and P 18 °C). In particular P 25 °C and P 18 °C show a strong similarity with the original population both in Adh allele frequency and relationship between Adh genotype and the respective metric phenotype; this is not the case for P28 °C which differed from the original population and the other two newly founded ones not only in Adh allele frequencies but even in gene arrangements.Comparing these results with those obtained in the previous work it can be concluded that Adh frequency variations can be a side effect of the evolutionary pattern of the populations which in turn depends on the initial genetic composition.     

Mating patterns of different Adh genotypes of Drosophila melanogaster I. Differences in mating ability

The mating ability of the different Adh genotypes of D. melanogaster, from three natural populations, was estimated as the number of females inseminated by a single male in a 24-hour period. The data indicate that populations of D. melanogaster vary in mating properties, but a common tendency was found in all of them: the heterozygous individuals, especially the males, show a relative advantage with respect to homozygotes. On the other hand, our results suggest that the differences in mating patterns observed between populations may be correlated with the different degree of Adh polymorphism found in them.     

An association between ADH protein levels and polymorphic nucleotide variation in the Adh gene of Drosophila melanogaster.

Southern analysis of the Adh region of 212 Drosophila melanogaster lines collected from the Tahbilk winery revealed linkage disequilibrium between a 37-bp insertion [designated delta 2 by Kreitman (1983)] and the fast electrophoretic variant of alcohol dehydrogenase (ADH-F). Among these lines 34% contained the insert and encoded ADH-F, 33.5% encoded ADH-F and did not have the insert, and 32.5% encoded the slow electrophoretic variant of alcohol dehydrogenase (ADH-S). Strong linkage association between this insert and ADH-F is evident worldwide. Twenty-nine of the second chromosome lines were characterized for ADH protein quantity by using radial immunodiffusion. ADH quantity was estimated in both larvae and adult males raised in the presence and absence of alcohol supplement to each of two different food media. Analyses of variance indicated higher levels of ADH protein in larvae from lines with the insert (all ADH-F), compared with those without (both ADH-F and ADH-S), independent of either dietary alcohol or media type. No such difference in ADH quantity between insert- and noninsert-containing ADH-F lines was detected in adults, although the expected higher levels occurred in ADH-F lines compared with ADH-S lines. Given the high levels of linkage disequilibrium in the Adh region, these data suggest that either polymorphic nucleotide-site variants positively associated with delta 2 on the second chromosome or delta 2 itself increases larval levels of ADH protein.     

Redundant cis-acting elements control expression of the Drosophila affinidisjuncta Adh gene in the larval fat body.

The alcohol dehydrogenase (Adh) gene in the Hawaiian species of fruit fly, Drosophila affinidisjuncta, like the Adh genes from all Drosophila species analyzed, is expressed at high levels in the larval fat body via a larval-specific promoter. To identify the cis-acting elements involved in this highly conserved aspect of Adh gene expression, deleted D. affinidisjuncta genes were introduced into D. melanogaster by somatic transformation. Unlike previously described methods, this transformation system allows analysis of Adh gene expression specifically in the larval fat body. The arrangement of sequences influencing expression of the proximal promoter of this gene in the larval fat body differs markedly from that described for the Adh gene from the distant relative, D. melanogaster. Multiple redundant elements dispersed 5' and 3' to the gene, only some of which map to regions carrying evolutionarily conserved sequences, affect expression in the fat body. D. affinidisjuncta employs a novel mode of Adh gene regulation in which the proximal promoter is influenced by sequences having roles in expression of the distal promoter. This gene is also unique in that far upstream sequences can compensate for loss of sequences within 200 bp of the proximal RNA start site. Furthermore, expression is influenced in an unusual, context-dependent manner by a naturally-occurring 3' duplication of the proximal promoter--a feature found only in Hawaiian species.     

Isozyme variability in species of the genus Drosophila. I. A multiple allelic isozyme system in Drosophila busckii: Inheritance and general considerations

Starch gel electrophoretic analysis of a triallelic leucine aminopeptidase polymorphism in a laboratory population of Drosophila busckii is described. The three alleles involved are expressed without dominance. A series of single-pair matings revealed an excess of heterozygous types in most segregating families, suggesting selection against the homozygous genotypes. A few cases of heterogeneity among progeny extracted from a single family were the result of matings that produced Mendelian ratios. These few cases had no clear genetic explanation, but there is a suggestion of two isoalleles for the electrophoretically intermediate enzyme.The research reported here was begun at the University of Hawaii and completed at the University of Texas and was supported (in part) by Public Health Service Research Grant No. GM 11609 to W. S. Stone and M. R. Wheeler and by Training Grant No. 2 T1-GM-337-06 and GM 00337-07 to R. P. Wagner et al., from the National Institutes of Health.     

Temperature-related divergence in experimental populations of Drosophila melanogaster. II. Correlation between fitness and body dimensions

From a laboratory stock of Drosophila melanogaster (Oregon), reared for more than 20 years at 18° C, a new population was derived and maintained at 28° C for 8 years. The chromosomal and cytoplasmic contribution to genetic divergence between the two populations was estimated. Six body traits and reproductive fitness were taken into account. The third chromosome is responsible for the adaptive difference for temperature between the two lines. Temperature-selected genes which control body size are located on the second and third chromosomes, although the contribution of each chromosome depends on the environment in which the flies develop. The correlation between the chromosomal and cytoplasmic contributions to different traits and fitness, changes with temperature. At 28° C the correlation between fitness and each body trait is proportional to the response to selection exhibited by each of them, but this is not true at 18° C. Body size has, therefore, an adaptive significance in relation to temperature, which is expressed only in the environment where selection occurs. Cytoplasmic genes affect almost all characters to an extent similar to that of chromosomal genes. Inter-chromosomal and nucleo-cytoplasmic interactions are present and also change with temperature. In general, genes selected in a given environment produce greater phenotypic changes in that environment than in another. The population that experienced both temperatures is fitter in both environments, suggesting that the capacity to adapt to warm temperatures depends on genes other than those which are involved in the adaptation to cold.     

A clonal analysis of tergite development in Drosophila of ultraabdominal and paradoxical genotypes.

The developmental parameters of homeotic second abdominal anlage cells in flies with Ultraabdominal and paradoxical genotypes are compared with those of normal second abdominal anlage cells through the use of induced mitotic recombination to mark the clonal descendants of single anlage cells. Homeotic and normal second abdominal anlage cells show the same pattern of mitotic activity during development. The homeotic second abdominal anlage cells with Ultraabdominal genotype proliferate to the same extent as normal anlage cells during hemitergite formation. However, the proliferation of homeotic second abdominal anlage cells with paradoxical genotype is decreased due to the failure of some daughter cells either to divide or to differentiate normally. The number of anlage cells in a homeotic second abdominal histoblast with Ultraabdominal genotype is slightly smaller and more variable than that in a normal second abdominal histoblast. The number of anlage cells in a homeotic second abdominal histoblast with paradoxical genotype is much smaller and much more variable than that in a normal second abdominal histoblast. These results are discussed in relation to mechanisms governing cell determination. In addition, some aspects of pattern formation in incomplete homeotic second abdominal hemitergites are presented and discussed.     

MDH-polymorphism in Drosophila subobscura: I. Selection and hitch-hiking in laboratory populations

Summary The interrelation of genic polymorphism at the Malate dehydrogenase (Mdh)-locus and chromosomal polymorphism for superimposed gene arrangements was studied in 5 experimental populations of Drosophila subobscura. It could be shown that chromosomal polymorphism is maintained by balancing selection in favour of the heterozygotes. In contrast, selection at the Mdh-locus itself seems to be of minor importance. The changes of frequency observed for the Mdh-alleles are most probably due to hitch-hiking on the gene blocks enclosed by the chromosomal structures or to selection for tightly linked genes rather than to fitness differences between Mdh-genotypes. The results may be considered as a model for the situation found in natural populations of D. subobscura.     

Covariation of larval gene expression and adult body size in natural populations of Drosophila melanogaster

Understanding adaptive phenotypic variation is one of the most fundamental problems in evolutionary biology. Genes involved in adaptation are most likely those that affect traits most intimately connected to fitness: life-history traits. The genetics of quantitative trait variation (including life histories) is still poorly understood, but several studies suggest that (1) quantitative variation might be the result of variation in gene expression, rather than protein evolution, and (2) natural variation in gene expression underlies adaptation. The next step in studying the genetics of adaptive phenotypic variation is therefore an analysis of naturally occuring covariation of global gene expression and a life-history trait. Here, we report a microarray study addressing the covariation in larval gene expression and adult body weight, a life-history trait involved in adaptation. Natural populations of Drosophila melanogaster show adaptive geographic variation in adult body size, with larger animals at higher latitudes. Conditions during larval development also affect adult size with larger flies emerging at lower temperatures. We found statistically significant differences in normalized larval gene expression between geographic populations at one temperature (genetic variation) and within geographic populations between temperatures (developmental plasticity). Moreover, larval gene expression correlated highly with adult weight, explaining 81% of its natural variation. Of the genes that show a correlation of gene expression with adult weight, most are involved in cell growth or cell maintenance or are associated with growth pathways.     

Relationship between alcohol dehydrogenase activity and low-temperature in two maize genotypes, Silverado F1 and Adh1-Adh2- doubly null.

We have examined the role of alcohol dehydrogenase (ADH, E.C.1.1.1.1) in chilling tolerance using maize (Zea mays L.) Adh1(-)Adh2(-) doubly null mutant. Adh1(-)Adh2(-) doubly null seedlings were found to have lowered survival rates compared to non-doubly null maize seedlings (Silverado F(1)) when held at 2 degrees C for varying periods. Exposure to ethanol did not increase the chilling tolerance in either Silverado F(1) or Adh1(-)Adh2(-) doubly null. ADH activity in Silverado F(1) remained steady when held at 2 degrees C for up to 3 d. ADH1 protein accumulation in chilled Silverado F(1) seedlings remained unchanged throughout the period of cold exposure. Chilling led to a significant inhibition of the P-H(+)-ATPase (E.C. 3.6.3.6) activity in Adh1(-)Adh2(-)doubly null, but minimal inhibition was seen in Silverado F(1). Though P-H(+)-ATPase activity in Adh1(-)Adh2(-) decreased, P-H(+)-ATPase protein levels remained constant during the chilling period. Levels of ATP slightly fluctuated in both types of seedlings during the duration of chilling. Lipid peroxidation levels in Adh1(-)Adh2(-) doubly null increased with chilling exposure, but not in the Silverado F(1). We suggest that ADH activity may play a role in chilling tolerance that is not related to maintenance of glycolysis and ATP production as has been observed during oxygen depravation.     

Colonization of America by Drosophila subobscura: association between Odh gene haplotypes, lethal genes and chromosomal arrangements

The colonization of America by Drosophila subobscura has been a unique exper iment in nature that has allowed us to explore the effects of evolution on a continental scale. To analyze this evolutionary event, nucleotide sequences of the Odh (Octanol dehydrogenase) gene were obtained for 43 lethal chromosomal lines from colonizing populations of North America and 5 from South America, in addition to 5 chromosomal lines from Europe with different viabilities and 2 from laboratory marker stocks. Since 10 different Odh haplotypes were found in America, the minimum number of colonizers would be 5 (or 3 mated females). Only one Odh haplotype was found in American O(5) inversions confirming that only one copy of this inversion was included among the sample of colonizers. The same Odh haplotypes were detected in association with the same chromosomal arrangements and with identical lethal genes in both North and South America indicating that exactly the same chromosome types reached both hemispheres. These observations indicate that the two continental colonizations are not independent. They are derived from the same colonization event. The population from which the colonization started should contain the O(5) inversion, a non-negligible frequency of the O(3+4+7) arrangement and all other arrangements found in America. So far the only populations that fulfill all these requirements are those from Greece, indicating that these populations can be considered good candidates as a starting point for an in depth analysis of the origin of the American colonization by D. subobscura.     

Molecular basis of adaptive shift in body size in Drosophila melanogaster: functional and sequence analyses of the Dca gene

Latitudinal body size clines in animals conforming to Bergmann's rule occur on many continents but isolating their underlying genetic basis remains a challenge. In Drosophila melanogaster, the gene Dca accounts for approximately 5-10% of the natural wing size variation (McKechnie SW, Blacket MJ, Song SV, Rako L, Carroll X, Johnson TK, Jensen LT, Lee SF, Wee CW, Hoffmann AA. 2010. A clinally varying promoter polymorphism associated with adaptive variation in wing size in Drosophila. Mol Ecol. 19:775-784). We present here functional evidence that Dca is a negative regulator of wing size. A significant negative latitudinal cline of Dca gene expression was detected in synchronized third instar larvae. In addition, we clarified the evolutionary history of the three most common Dca promoter alleles (Dca237-1, Dca237-2, and Dca247) and showed that the insertion allele (Dca247), whose frequency increases with latitude, is associated with larger wing centroid size and higher average cell number in male flies. Finally, we showed that the overall linkage disequilibrium (LD) was low in the Dca promoter and that the insertion/deletion polymorphism that defines the Dca alleles was in strong LD with two other upstream sites. Our results provide strong support that Dca is a candidate for climatic adaptation in D. melanogaster.     

Temperature dependence of fitness components in geographical populations of Drosophila melanogaster: changing the association between size and fitness

Contrary to the conventional wisdom 'bigger is better', evolution at high temperature invariably leads to small individuals in Drosophila melanogaster . Natural selection is known to be responsible, meaning that genotypes that are small because of adaptation to high temperature must have some temperature dependent fitness advantage. In this study we consider both preadult and adult fitness components, and show that large adults from a cold adapted population significantly outperform small adults from a warm adapted population only when tested at low temperature and low larval density. In all other conditions 'bigger is not necessarily better', meaning that environmental influences are capable of altering the association between size and fitness. Yet, 'smaller wasn't better either' under any condition, when considering the overall measure of fitness. Examination of individual fitness components revealed population by temperature interaction in preadult survival; this interaction is potentially capable of explaining the temperature specific advantage of small adult body size. At high temperature, the warm adapted population exhibits superior preadult survival while producing small adults. Geographical variation in adult body size seems to be the result of selection on larval growth and competitive strategies, resulting in alterations in the association between fitness components.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 717–725.