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Poster Full Abstracts - Evolution and Quantitative Genetics
Poster board number is above title. The first author is the presenter
271
mustard oil formation. Here, we investigate the mechanism of mustard oil detoxification in two herbivores,
Scaptomyza flava
and
S. nigrita
, nested within
the
Drosophila
. Using
Arabidopsis thaliana
mutants deficient in glucosinolate biosynthesis, we show mustard oils induce glutathione-
S
-transferase activity
in larvae coupled with formation of isothiocyanate-glutathione conjugates, implicating the general mechanism used to detoxify isothiocyanates and other
toxins in many non-herbivorous organisms, including humans. Molecular cloning of Glutathione-
S
-transferase D1 (GSTD1), which catalyzes conjugation of
electrophilic molecules to glutathione, reveals gene duplication followed by positive selection in the ancestor of these mustard-specialists. In addition,
S.
flava
and
S. nigrita
GSTD1 enzymes conjugate glutathione to isothiocyanates in vitro more efficiently than GSTD1 from other
Drosophila
and
Scaptomyza
;
this is, to our knowledge, the first demonstration that a single arthropod GST catalyzes isothiocyanate detoxification. A preliminary crystal structure shows
some positively selected substitutions in a potential toxin binding pocket, at sites otherwise highly conserved across
Drosophila
. Together, these results
suggest evolution of a canonical detoxification mechanism, rather than generation of a novel one, enabled specialization on a group of well-defended plants
in these herbivorous drosophilids.
522C
Identifying ‘soft sweeps’ in egg size variation by re-sequencing experimentally evolved populations of Drosophila melanogaster.
Aashish R. Jha
1,3
,
Cecelia Miles
2
, Cristopher D. Brown
1,3
, Kevin P. White
1,2,3
, Martin Kreitman
2,3
. 1) Department of Human Genetics, The University of Chicago, Chicago, IL;
2) Department of Ecology and Evolution, The University of Chicago, Chicago, IL; 3) Institute of Genomics and Systems Biology, The University of
Chicago, Chicago, IL.
Egg size is a classic quantitative trait that is directly related to fitness of both the parents and offspring. However, genetic factors influencing variation in
egg size remain elusive. We undertook an experimental selection experiment in which nine Drosophila melanogaster populations derived from a single
panmictic population (based on 120 isofemale lines) were selected for divergent egg volume in three treatment groups: large eggs, small eggs, and control (3
replicate populations per group). Ultra-deep population re-sequencing (~820X total genome coverage) with high power to detect variants segregating at low
allele frequencies coupled with a novel method (MQVCCI) developed to detect variations and their frequencies from population re-sequencing data revealed
a total of 1. 7M unique genetic variants of which a large proportion was shared between and among the treatment groups. Although the abundance of genetic
variation suggests that there are plenty of genetic variations for positive selection to act upon, genomic scans in 100kb windows in all five chromosome arms
in all evolved populations failed to identify classic sweeps in any of the populations suggesting that egg size is a complex and highly polygenic trait and
adaptation may have occurred due to ‘soft sweeps’ which causes subtle shifts in frequencies of many alleles across the genome. We tested the hypothesis
that soft sweeps are detectable by comparing frequency differences and their directions between the ancestral population and terminal populations. Genetic
drift is expected to randomly change allele frequencies in control populations; however, in evolved populations alleles under positive selection will have
shifted in the same direction more than expected by random drift. Candidate loci with shifts in frequencies will be further tested for potential functional
roles.
523A
Emergence of essential mitotic function in the young gene Umbrea.
Benjamin Ross
1
, Leah Rosin
2
, Danielle Vermaak
1
, Mary Alice Hiatt
1
, Barbara
Mellone
2
, Harmit Malik
1,3
. 1) MCB/Basic Sciences Dept, University of Washington/FHCRC, Seattle, WA; 2) MCB Dept, University of Connecticut, Storrs,
CT; 3) Howard Hughes Medical Institute.
Genes that encode centromeric and kinetochore proteins are essential, yet can evolve rapidly as a consequence of selfish centromere competition during
female meiosis in plants and animals. Nevertheless, their essential function in chromosome segregation restricts their adaptive landscape. We have found
that the young gene
Umbrea/HP6
encodes a protein that has acquired centromeric localization and essential mitotic function in Drosophila within 10 million
years of its birth. Born by gene duplication from
Heterochromatin Protein 1B (HP1B)
,
Umbrea
neofunctionalized by domain loss, the acquisition of two
distinct gain-of-function interactions, and persistent selective pressure, resulting in a dramatic alteration in subcellular localization. While HP1B localized to
heterochromatin in S2 cells, Umbrea colocalized with CenH3/Cid at all centromeres. Centromere localization may be important for Umbrea function, since
loss of function of Umbrea in null mutants or constitutive knockdown by RNAi during development resulted in pupal lethality. Moreover, knockdown of
Umbrea by RNAi in cultured cells induced an increase in chromosome congression defects during metaphase, and lagging chromosomes during anaphase.
Despite these results, we found that positively selected residues fall in Umbrea's centromere targeting domains. Selective pressure may act on Umbrea to
maintain centromere localization and function, since Umbrea orthologs lost centromeric localization with increased divergence when expressed in
D.
melanogaster
cells. Our findings reveal the evolutionary steps underlying the acquisition of mitotic function in
Umbrea
, and suggest that centromere
competition can drive not only diversifying selection in existing centromere genes but also essential neofunctionalization.
524B
Genetic basis for DDT resistance associated with CYP6g1 in Drosophila simulans.
Julianna Bozler, Todd Schlenke. Emory University, Atlanta, GA.
Transposable elements can be a powerful adaptive force, and have driven the rapid evolution of many phenotypes. Previous studies have linked TE
insertions to significant population-wide changes in the expression of metabolic and detoxifying enzymes. One classic example of such a mutation is the
Accord transposon inserted in the 5' regulatory region of the DDT-resistance gene CYP6g1 of Drosophila melanogaster. This mutation is associated with
constitutive Cyp6g1 over-expression and insecticide resistance. A similar mutation was found in Drosophila simulans, whereby a Doc transposable element
inserted in the 5' regulatory region of Cyp6g1 also associated with increased Cyp6g1 expression and insecticide resistance. We have made several reporter
constructs to identify the specific Doc gene sequences necessary for Cyp6g1 over-expression. Furthermore, to better understand the functional consequences
of the D. simulans Cyp6g1 Doc insertion, we are characterizing the tissue-specific expression pattern of CYP6g1 in Doc+ and Doc- strains.
525C
The Influence of Feeding Rate on Dietary Restriction Treatments in Drosophila.
Payal Daya, Mary Durham, Jeff Leips. Biological Sciences, University
of Maryland, Baltimore County, Baltimore, MD.
Dietary Restriction, a decrease in nutrient intake without malnutrition, has been shown to increase life span nearly universally among many species,
including humans, and is highly linked to feeding behavior. Previous dietary restriction experiments have shown that spiders and other insects regulate and