The Ecological Genetics of Abnormal Abdomen in Drosophila mercatorum

Abstract Natural populations of Drosophila mercatorum are polymorphic for a phenotypic syndrome known as abnormal abdomen (aa). This syndrome is characterized by a slow-down in egg-to-adult developmental time, retention of juvenile abdominal cuticle in the adult, increased early female fecundity, and decreased adult longevity. Previous studies revealed that the expression of this syndrome in females is controlled by two closely linked X chromosomal elements: the occurrence of an R1 insert in a third or more of the X-linked 28S ribosomal genes (rDNA), and the failure of replicative selection favoring uninserted 28S genes in larval polytene tissues. The expression of this syndrome in males in a laboratory stock was associated with the deletion of the rDNA normally found on the Y chromosome. In this paper we quantify the levels of genetic variation for these three components in a natural population of Drosophila mercatorum found near Kamuela, Hawaii. Extensive variation is found in the natural population for both of the X-linked components. Moreover, there is a significant association between variation in the proportion of R1 inserted 28S genes with allelic variation at the underreplication (ur) locus such that both of the necessary components for aa expression in females tend to cosegregate in the natural population. Accordingly, these two closely linked X chromosomal elements are behaving as a supergene in the natural population. Because of this association, we do not believe the R1 insert to be actively transposing to an appreciable extent. The Y chromosomes extracted from nature are also polymorphic, with 16% of the Ys lacking the Y-specific rDNA marker. The absence of this marker is significantly associated with the expression of aa in males. Hence, all three of the major genetic determinants of the abnormal abdomen syndrome are polymorphic in this natural population.

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The molecular through ecological genetics of abnormal abdomen in Drosophila mercatorum. VI. The non-neutrality of the Y chromosome rDNA polymorphism.

Genetics ◽

10.1093/genetics/136.4.1373 ◽

1994 ◽

Vol 136 (4) ◽

pp. 1373-1384

Author(s):

H Hollocher ◽

A R Templeton

Keyword(s):

Y Chromosome ◽

Adult Development ◽

Sexual Maturation ◽

Development Time ◽

Ecological Genetics ◽

Pleiotropic Effects ◽

Naturally Occurring ◽

Drosophila Mercatorum ◽

Rdna Polymorphism ◽

Male Expression

Abstract An association between quantitative variation of rDNA on the Y chromosome and male expression of the juvenilized, adult cuticle of the abnormal abdomen syndrome has been found for Drosophila mercatorum. Many pleiotropic effects of this syndrome have been described previously for females, but little was known about possible pleiotropic effects in males. The effects on males open up new avenues for the action of natural selection operating on the system. In females, the syndrome causes an increase in egg-to-adult development time, precocious sexual maturation, increased fecundity and decreased longevity. In addition to the cuticle phenotype, in males abnormal abdomen causes delayed sexual maturation, increased longevity, and decreased mating success, yet no change in egg-to-adult development time. Thus the syndrome has opposing fitness effects in the two sexes, which may help explain the genetic polymorphism observed in this system. Although investigated intensively, associations between naturally occurring Y-linked polymorphism and fitness phenotypes have not been found in Drosophila melanogaster.

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THE MOLECULAR THROUGH ECOLOGICAL GENETICS OF ABNORMAL ABDOMEN. II. RIBOSOMAL DNA POLYMORPHISM IS ASSOCIATED WITH THE ABNORMAL ABDOMEN SYNDROME IN DROSOPHILA MERCATORUM

Genetics ◽

10.1093/genetics/112.4.861 ◽

1986 ◽

Vol 112 (4) ◽

pp. 861-875

Author(s):

Rob DeSalle ◽

Jerry Slightom ◽

Elizabeth Zimmer

Keyword(s):

Blot Hybridization ◽

Ecological Genetics ◽

Rdna Repeat ◽

Dna Encoding ◽

Juvenile Hormone Esterase ◽

Repeat Units ◽

Drosophila Mercatorum ◽

Cytoplasmic Rnas ◽

Rdna Copy

ABSTRACT Restriction endonuclease cleavage analyses of cloned and genomic DNA samples indicate that the structure of the DNA encoding the large cytoplasmic RNAs (rDNAs) is altered in Drosophila mercatorum lines which exhibit an abnormal abdomen (aa) phenotype. In a majority of the rDNA repeat units from aa flies, the 28S coding sequence is interrupted by a large [5-6 kilobase pairs (kbp)] insert. A subclone containing this inserted DNA (ins 3) hybridizes primarily to rDNA-containing sequences in in situ and genomic blot hybridization experiments. Additionally, genomic nitrocellulose blot hybridization analyses show that ins - containing rDNA repeat units are clustered in a spontaneously arising aa mutant. This rDNA alteration in D. mercatorum flies with the aa phenotype more closely resembles the bobbed (bb) defect of D. hydei than the bb defect of D. melanogaster, which involves alterations in rDNA copy number. By analogy with the other Drosophila systems, we propose that the altered D. mercatorum rDNA repeat units are defective in rRNA production at a critical stage. The lowered levels of rRNA ultimately would limit the concentration of ribosomes needed to produce large quantities of a protein (in these cases, juvenile hormone esterase) needed for normal development.

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THE MOLECULAR THROUGH ECOLOGICAL GENETICS OF ABNORMAL ABDOMEN. III. TISSUE-SPECIFIC DIFFERENTIAL REPLICATION OF RIBOSOMAL GENES MODULATES THE ABNORMAL ABDOMEN PHENOTYPE IN DROSOPHILA MERCATORUM

Genetics ◽

10.1093/genetics/112.4.877 ◽

1986 ◽

Vol 112 (4) ◽

pp. 877-886

Author(s):

Rob DeSalle ◽

Alan R Templeton

Keyword(s):

Ribosomal Rna ◽

Molecular Basis ◽

Ribosomal Genes ◽

Ecological Genetics ◽

Wild Type ◽

Rdna Genes ◽

Tissue Specific ◽

Type D ◽

Drosophila Mercatorum ◽

Specific Control

ABSTRACT The abnormal abdomen (aa) syndrome in Drosophila mercatorum is controlled by two major X-linked genetic elements. We have previously shown that the major X-linked element of aa is associated with the presence of large inserts in the 28S gene of the ribosomal RNA (rDNA) genes. We show that, in polytene tissue of wild-type D. mercatorum, the uninterrupted rDNA repeats are overreplicated relative to interrupted repeats. Uninterrupted rDNA repeats are also overreplicated in polytene tissue of hybrid larval offspring from wild-type and aa parents. This overreplication of uninterrupted repeats is not observed in diploid tissues of wild-type hybrids (of wild-type and aa parents) and homozygous aa larvae or in polytene tissue of aa larvae. Furthermore, molecular analysis of an aa line that has reverted to the wild type indicates that the reversion phenomenon is associated with the ability to overreplicate uninterrupted rDNA repeats in polytene tissues. The patterns of differential replication of rDNA genes in wild-type hybrids and aa larvae of D. mercatorum offer a possible mechanism for the tissue-specific control of the aa phenotype and suggest that the molecular basis for the second X-linked genetic element of aa is involved in the control of differential replication in polytene tissues.

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The molecular through ecological genetics of abnormal abdomen in Drosophila mercatorum. V. Female phenotypic expression on natural genetic backgrounds and in natural environments.

Genetics ◽

10.1093/genetics/134.2.475 ◽

1993 ◽

Vol 134 (2) ◽

pp. 475-485 ◽

Cited By ~ 1

Author(s):

A R Templeton ◽

H Hollocher ◽

J S Johnston

Keyword(s):

Life History ◽

Phenotypic Expression ◽

Developmental Time ◽

Ecological Genetics ◽

Adult Longevity ◽

Natural Environments ◽

X Chromosomes ◽

Rdna Genes ◽

Drosophila Mercatorum ◽

Female Life History

Abstract The abnormal abdomen (aa) syndrome in Drosophila mercatorum depends on the presence of R1 inserts in a third or more of the X-linked 28S rDNA genes and the absence of selective underreplication of inserted repeats in polytene tissues that is controlled by an X-linked locus (ur) half a map unit from the rDNA complex. This syndrome affects both life history and morphology in the laboratory. Because abnormal morphologies are rarely encountered in nature, the purpose of this study is to see if the female life history traits are still affected under more natural genetic backgrounds and environmental conditions. Two outbred stocks were extracted from the natural population living near Kamuela, Hawaii: KaaX that has only X chromosomes with uraa alleles, and K+X that has only ur+ alleles. These two stocks have nonoverlapping distributions of insert proportions, indicating strong disequilibrium between the ur locus and the rDNA complex. The KaaX stock had almost no morphological penetrance of uraa, indicating that genetic background is important. KaaX expressed longer female egg-to-adult developmental times, increased early adult female fecundity, and decreased female adult longevity compared with K+X. By bagging natural rots of the cactus Opuntia megacantha near Kamuela, Hawaii, it was shown that egg-to-adult developmental time is slowed down by 0.92 days in females bearing uraa alleles in nature, with no detectable slowdown in uraa males. The bagged rot data also indicate that females bearing uraa alleles have a strong fecundity advantage in nature under some ecological conditions but not others.

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THE MOLECULAR THROUGH ECOLOGICAL GENETICS OF ABNORMAL ABDOMEN IN DROSOPHILA MERCATORUM. I. BASIC GENETICS

Genetics ◽

10.1093/genetics/111.4.805 ◽

1985 ◽

Vol 111 (4) ◽

pp. 805-818

Author(s):

Alan R Templeton ◽

Teresa J Crease ◽

Faith Shah

Keyword(s):

Gene Cluster ◽

X Chromosome ◽

Ribosomal Rna ◽

Ecological Genetics ◽

The Other ◽

Genetic Studies ◽

Rdna Gene ◽

Genetic Elements ◽

Drosophila Mercatorum ◽

Adult Abdomen

ABSTRACT The abnormal abdomen syndrome (aa) in Drosophila mercatorum is characterized by the persistence of juvenilized cuticle on the adult abdomen. The aa phenotype is shown to depend on at least two X-linked genetic elements that are about one map unit apart near the centromeric end of the X chromosome. These two genetic elements are necessary for aa expression; one behaves as a dominant element and the other as a recessive. Overlaying these genetic studies upon molecular work reported elsewhere, it is argued that the dominant element is the presence of a 5 kb insertion in a majority of the X-linked repeats coding for the 28S ribosomal RNA. The recessive element appears to be a locus controlling differential replication of noninserted over inserted 28S genes during polytenization. The aa syndrome requires both the presence of the inserted repeats and the failure to preferentially amplify noninserted repeats. Given the necessary X-linked elements for aa, a variety of modifiers are revealed. First, aa expression in males is Y-linked, apparently corresponding to a deletion of the 18S/28S rDNA gene cluster normally found on the Y. Moreover, all major autosomes can modify the penetrance of aa.

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