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Full Abstracts – EVOLUTION AND QUANTITATIVE GENETICS II
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126
In a variable thermal environment selection favors greater plasticity of cell membranes in
Drosophila melanogaster
.
Brandon S. Cooper
1
, Loubna A.
Hammad
2
, Nicholas P. Fisher
1
, Jonathan A. Karty
2
, Kristi L. Montooth
1
. 1) Department of Biology, Indiana University, Bloomington, IN; 2) METACyt
Biochemical Analysis Center, Department of Chemistry, Indiana University, Bloomington, IN.
Variable environments should favor the evolution of generalists that maintain performance across environmental gradients. Antagonistic pleiotropy and
mutation accumulation, however, can cause negative genetic correlations in fitness across environments leading to decreased performance of generalist
relative to specialist genotypes. When genetic variation for plasticity (i.e., the capacity to change phenotypic trajectory within a lifetime) exists within a
population, alleles that enable an organism to match their physiology to the current environment should be maintained at a high frequency. Theory predicts
that developmental plasticity should evolve when the environment varies sufficiently among generations, due to temporal (e.g., seasonal) variation or to
migration among environments. To test this prediction we characterized plasticity of cell membranes during development in populations of
Drosophila
melanogaster
experimentally evolved for over three years in either constant or temporally variable thermal environments. We used two measures of the lipid
composition of cell membranes as indices of physiological plasticity (a.k.a. acclimation): (1) change in the ratio of phosphatidylethanolamine (PE) to
phosphatidylcholine (PC) and (2) change in lipid saturation in cool (16ºC) relative to warm (25ºC) developmental conditions. We found that flies evolved
under variable environments have a significantly greater capacity to acclimate the PE/PC ratio compared to flies evolved in constant environments,
supporting the prediction that environments with high among-generation variance favor greater developmental plasticity. Our results are consistent with the
selective advantage of a more environmentally sensitive allele which may have associated costs in constant environments.
127
Epigenetics and evolution of TE control by piRNA: The significance of dose.
Justin P. Blumenstiel
1
, Dean M. Castillo
1
, Mauricio Galdos
1
, Chris
Harrison
1
, Michelle Wickersheim
1
, Kim S. Box
1
, Alex Abdullayev
1
, Dan Brown
1
, Jianwen Fang
2
. 1) Department of Ecology and Evolutionary Biology,
University of Kansas, Lawrence, KS; 2) Applied Bioinformatics Lab, University of Kansas, Lawrence, KS.
Transposable elements (TEs) are generally harmful genetic parasites that can cause mutation, shape genomes, and contribute to the architecture of gene
expression networks. Historically, natural selection has been considered to play the key role in limiting TE proliferation in populations. However, recent
studies have demonstrated that an adaptive system of genome defense by piRNA also limits TE proliferation. Using hybrid dysgenesis in
Drosophila virilis
as a model, we are examining how asymmetric inheritance of maternally provisioned piRNAs determines patterns of TE induced hybrid sterility. Our studies
indicate that TE dosage plays a key role both in the induction of TE mediated hybrid sterility and in maternally provisioned protection against it.
Furthermore, TE instability can be a general genomic property the can be propagated across generations, but repressed epigenetically. In light of the key role
that dosage plays, we will present studies on the molecular evolution of the piRNA machinery that suggest a complex co-evolutionary dynamic between TEs
and the machinery of genome defense. In particular, the dominant evolutionary response to increasing TE burden across the
Drosophila
genus seems to be
improved translational efficiency in the piRNA machinery, not an increased rate of evolution.
128
Probing Developmental Networks via Compensatory Evolution.
Sudarshan Chari, Ian Dworkin. Zoology & EEBB, Michigan State University, East
Lansing, MI.
Developmental networks though generally conserved can be flexibly utilized during evolution resulting in diverse phenotypes. A deleterious mutation
influencing the network output can shift a population from the phenotypic optimum leading to a fitness decline. There are several possible fates for such a
mutation and one of those is amelioration by compensatory mutations. While most studies of compensatory evolution focus on
de novo
mutations during the
evolutionary process, standing genetic variation for mutational effects may also be important. Furthermore, for a developmental system, network rewiring by
compensatory mutations has not been well studied. In order to understand aspects of flexibility of developmental systems via rewiring by compensatory
mutations, we have fixed a mutation in the
vestigial
gene,
vg
1
, in a large natural population of
Drosophila melanogaster
. This mutation severely perturbs
wing development leading to wing tissue loss and an associated fitness decline. Using
vg
1
populations, we have performed both experimental evolution (with
natural selection altering the population) and artificial selection directly for phenotypic compensation of the wing. In artificial selection lineages we have
observed almost a complete compensation of the wing phenotype (i.e. phenotypically wild-type) in only 13 generations. Interestingly, there has been no
phenotypic compensation in experimental evolution lineages. We postulate a behavioral compensation in these lineages, specifically, influencing courtship.
We are currently quantifying the differences in phenotypes and will detail some of the developmental and behavioral processes that have facilitated
compensation. Our results clearly show that despite considerable segregating compensatory genetic variation in natural populations, the two selection
regimes have exploited different optima to compensate for phenotypic and fitness loss by the same mutation. Our study not only explores the extent of
developmental flexibility but also has implications in the interpretation of adaptive landscapes and gain of phenotypes.
129
Emergence and diversification of a Drosophila pigmentation pattern through the assembly and evolution of a novel gene regulatory module.
Benjamin Prud'homme. IBDML, CNRS, Marseille, France.
The typical pattern of morphological evolution associated with the radiation of a group of related species is the emergence of a novel trait and its
subsequent diversification. From butterfly eyespots and their various colorful rings1 to the diversity of shapes assumed by vertebrate teeth2, seashells3 or
horn beetles4, this pattern of emergence-diversification holds for countless characters across most animal groups. Yet, the genetic mechanisms associated
with these two evolutionary steps are poorly characterized. Here we show that a spot of dark pigment on fly wings has first evolved from the assembly of a
novel gene regulatory module whereby pigmentation genes fell under the regulation of a common transcriptional activator. The primitive wing spot pattern
subsequently diversified through the sole changes in spatial distribution of this activator. These results suggest that the genetic changes underlying the
emergence and the diversification of the wing pigmentation patterns are partitioned within genetic networks. More generally, this two-step model accounts at
the gene regulatory level for the general pattern observed in animals and plants where morphological diversification mostly results from occasional novelties
and infinite variations on these new themes.