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Intraspecific variation in testis asymmetry in birds: evidence for naturally occurring compensation.

ABSTRACT: In many taxa, the left and right testes often differ in size. The compensation hypothesis states that one testis of the pair serves as a 'back-up' for any reduced function in the other and provides a mechanism to explain intraspecific variation in degree and direction of gonad asymmetry. Although testis asymmetry is common in birds, evidence for natural testis compensation is unknown. Using a novel quantitative approach that can be applied to any bilateral organ or structure, we show that testis compensation occurs naturally in birds and can be complete when one testis fails to develop. Owing to a recurrent risk of testis impairment and an evolutionary trade-off between natural and sexual selections acting on the arrangement of internal organs in species with abdominal and/or seasonal testes, compensation adds an important, but neglected, dimension to measures of male reproductive investment.

SUBMITTER: Calhim S

PROVIDER: S-EPMC2677609 | biostudies-literature | 2009 Jun

REPOSITORIES: biostudies-literature

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Intraspecific variation in testis asymmetry in birds: evidence for naturally occurring compensation.

Calhim Sara S Birkhead Tim R TR

Proceedings. Biological sciences 20090318 1665

In many taxa, the left and right testes often differ in size. The compensation hypothesis states that one testis of the pair serves as a 'back-up' for any reduced function in the other and provides a mechanism to explain intraspecific variation in degree and direction of gonad asymmetry. Although testis asymmetry is common in birds, evidence for natural testis compensation is unknown. Using a novel quantitative approach that can be applied to any bilateral organ or structure, we show that testis ...[more]

PMID: 19324740

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Project description:BackgroundTomato leaf curl Sudan virus (ToLCSDV) is a single-stranded DNA begomovirus of tomato that causes downward leaf curl, yellowing, and stunting. Leaf curl disease results in significant yield reduction in tomato crops in the Nile Basin. ToLCSDV symptoms resemble those caused by Tomato yellow leaf curl virus, a distinct and widespread begomovirus originating in the Middle East. In this study, tomato samples exhibiting leaf curl symptoms were collected from Gezira, Sudan. The associated viral genome was molecularly characterized, analyzed phylogenetically, and an infectious clone for one isolate was constructed.FindingsThe complete genomes for five newly discovered variants of ToLCSDV, ranging in size from 2765 to 2767-bp, were cloned and sequenced, and subjected to pairwise and phylogenetic analyses. Pairwise analysis indicated that the five Gezira isolates shared 97-100% nucleotide identity with each other. Further, these variants of ToLCSDV shared their highest nucleotide identity at 96-98%, 91-95%, 91-92%, and 91-92% with the Shambat, Gezira, Oman and Yemen strains of ToLCSDV, respectively. Based on the high maximum nucleotide identities shared between these ToLCSDV variants from Gezira and other previously recognized members of this taxonomic group, they are considered isolates of the Shambat strain of ToLCSDV. Analysis of the complete genome sequence for these new variants revealed that they were naturally occurring recombinants between two previously reported strains of ToLCSDV. Finally, a dimeric clone constructed from one representative ToLCSV genome from Gezira was shown to be infectious following inoculation to tomato and N. benthamiana plants.ConclusionFive new, naturally occurring recombinant begomovirus variants (>96% shared nt identity) were identified in tomato plants from Gezira in Sudan, and shown to be isolates of the Shambat strain of ToLCSDV. The cloned viral genome was infectious in N. benthamiana and tomato plants, and symptoms in tomato closely resembled those observed in field infected tomato plants, indicating the virus is the causal agent of the leaf curl disease. The symptoms that developed in tomato seedlings closely resembled those observed in field infected tomato plants, indicating that ToLCSDV is the causal agent of the leaf curl disease in Gezira.

Project description:Mitochondria are organelles found in nearly all eukaryotic cells that play a crucial role in cellular survival and function. Mitochondrial function is under the control of nuclear and mitochondrial genomes. While the latter has been the focus of most genetic research, we remain largely ignorant about the nuclear-encoded genomic control of inter-individual variability in mitochondrial function. Here, we used Drosophila melanogaster as our model organism to address this question.We quantified mitochondrial state 3 and state 4 respiration rates and P:O ratio in mitochondria isolated from the thoraces of 40 sequenced inbred lines of the Drosophila Genetic Reference Panel. We found significant within-population genetic variability for all mitochondrial traits. Hence, we performed genome-wide association mapping and identified 141 single nucleotide polymorphisms (SNPs) associated with differences in mitochondrial respiration and efficiency (P ?1?×?10-5). Gene-centered regression models showed that 2-3 SNPs can explain 31, 13, and 18% of the phenotypic variation in state 3, state 4, and P:O ratio, respectively. Most of the genes tagged by the SNPs are involved in organ development, second messenger-mediated signaling pathways, and cytoskeleton remodeling. One of these genes, sallimus (sls), encodes a component of the muscle sarcomere. We confirmed the direct effect of sls on mitochondrial respiration using two viable mutants and their coisogenic wild-type strain. Furthermore, correlation network analysis revealed that sls functions as a transcriptional hub in a co-regulated module associated with mitochondrial respiration and is connected to CG7834, which is predicted to encode a protein with mitochondrial electron transfer flavoprotein activity. This latter finding was also verified in the sls mutants.Our results provide novel insights into the genetic factors regulating natural variation in mitochondrial function in D. melanogaster. The integrative genomic approach used in our study allowed us to identify sls as a novel hub gene responsible for the regulation of mitochondrial respiration in muscle sarcomere and to provide evidence that sls might act via the electron transfer flavoprotein/ubiquinone oxidoreductase complex.

Dataset Information

Intraspecific variation in testis asymmetry in birds: evidence for naturally occurring compensation.

Publications

Intraspecific variation in testis asymmetry in birds: evidence for naturally occurring compensation.

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