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dictyNews Volume 41 Number 07
dictyNews
Electronic Edition
Volume 41, number 7
April 10, 2015
Please submit abstracts of your papers as soon as they have been
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Abstracts
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Fitness trade-offs result in the illusion of social success
Jason B. Wolf1* Jennifer A. Howie2, Katie Parkinson2, Nicole
Gruenheit2, Diogo Melo3, Daniel Rozen4, and
Christopher R.L. Thompson2*
1 Department of Biology and Biochemistry, University of Bath,
Claverton Down, Bath, BA2 7AY, UK
2 Faculty of Life Sciences, Michael Smith Building, University
of Manchester, Oxford Rd, Manchester, M13 9PT, UK
3 Departamento de Gentica e Biologia Evolutiva, Instituto
de Biocincias, Universidade de So Paulo, So Paulo, SP, Brazil
4 Institute of Biology, Leiden University, Sylvius Laboratory,
Sylviusweg 72, PO Box 9505, 2300 RA Leiden, The Netherlands
* Corresponding authors
Current Biology, in press
Cooperation is ubiquitous across the tree of life, from
simple microbes to the complex social systems of animals [1].
Individuals cooperate by engaging in costly behaviours that
can be exploited by other individuals who benefit by avoiding
these associated costs. Thus, if successful exploitation of
social partners during cooperative interactions increases
relative fitness, then we expect selection to lead to the
emergence of a single optimal winning strategy in which
individuals maximize their gain from cooperation while
minimizing their associated costs [2]. Such social ÔcheatingÕ
appears to be widespread in nature [3], including several
microbial systems [4-11], but despite the fitness advantages
favouring social cheating, populations tend to harbour
significant variation in social success rather than a single
optimal winning strategy. Using the social amoeba Dictyostelium
discoideum we provide a possible explanation for the coexistence
of such variation. We find that genotypes typically designated
as ÔcheatersÕ [12] because they produce a disproportionate
number of spores in chimeric fruiting bodies, do not actually
gain higher fitness as a result of this apparent advantage
because they produce smaller, less viable, spores than putative
ÔlosersÕ. As a consequence of this trade-off between spore
number and viability, genotypes with different spore production
strategies, which give the appearance of differential social
success, ultimately have similar realised fitness. These
findings highlight the limitations of using single fitness
proxies in evolutionary studies and suggest that interpreting
social trait variation in terms of strategies like cheating
or cooperating may be misleading unless these behaviours are
considered in the context of the true multidimensional nature
of fitness.
Submitted by Chris Thompson [christopher.thompson@manchester.ac.uk]
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Genetic control of morphogenesis in Dictyostelium
William F. Loomis
University of California San Diego, La Jolla, CA 92093
Developmental Biology, in press
Cells grow, move, expand, shrink and die in the process of
generating the characteristic shapes of organisms. Although the
structures generated during development of the social amoeba
Dictyostelium discoideum look nothing like the structures seen
in metazoan embryogenesis, some of the morphogenetic processes
used in their making are surprisingly similar. Recent advances
in understanding the molecular basis for directed cell migration,
cell type specific sorting, differential adhesion, secretion of
matrix components, pattern formation, regulation and terminal
differentiation are reviewed. Genes involved in Dictyostelium
aggregation, slug formation, and culmination of fruiting bodies
are discussed.
Submitted by Bill Loomis [wloomis@ucsd.edu]
----------------------------------------------------------------------
Leaps and lulls in the developmental transcriptome of Dictyostelium
discoideum
Rafael David Rosengarten, Balaji Santhanam, Danny Fuller, Mariko
Katoh-Kurasawa, William F. Loomis, Blaz Zupan, and Gad Shaulsky
Department of Molecular and Human Genetics and Graduate Program
in Structural and Computational Biology and Molecular Biophysics,
Baylor College of Medicine
Section of Cell and Developmental Biology, University of
California San Diego
Faculty of Computer and Information Science, University of
Ljubljana
BMC Genomics, accepted 26 March 2015
Background. Development of the soil amoeba Dictyostelium discoideum
is triggered by starvation. When placed on a solid substrate, the
starving solitary amoebae cease growth, communicate via extracellular
cAMP, aggregate by tens of thousands and develop into multicellular
organisms. Early phases of the developmental program are often
studied in cells starved in suspension while cAMP is provided
exogenously. Previous studies revealed massive shifts in the
transcriptome under both developmental conditions and a close
relationship between gene expression and morphogenesis, but were
limited by the sampling frequency and the resolution of the methods.
Results. Here, we combine the superior depth and specificity of
RNA-seq-based analysis of mRNA abundance with high frequency
sampling during filter development and cAMP pulsing in suspension.
We found that the developmental transcriptome exhibits mostly
gradual changes interspersed by a few instances of large shifts.
For each time point we treated the entire transcriptome as single
phenotype, and were able to characterize development as groups
of similar time points separated by gaps. The grouped time points
represented gradual changes in mRNA abundance, or molecular
phenotype, and the gaps represented times during which many genes
are differentially expressed rapidly, and thus the phenotype
changes dramatically. Comparing development on solid substrate
to development in suspension revealed that gene expression in
filter developed cells lagged behind those treated with exogenous
cAMP in suspension. The high sampling frequency revealed many
genes whose regulation is reproducibly more complex than
indicated by previous studies. Gene Ontology enrichment analysis
suggested that the transition to multicellularity coincided with
rapid accumulation of transcripts associated with DNA processes
and mitosis. Later development included the up-regulation of
organic signaling molecules and co-factor biosynthesis. We
observed multiple instances of enrichment of oxidation-reduction
and reactive oxygen related terms. Our analysis also demonstrated
a high level of synchrony among the developing structures
throughout development.
Conclusions. Our data describe D. discoideum development as a
series of coordinated cellular and multicellular activities.
Coordination occurred within fields of aggregating cells and
among multicellular bodies, such as mounds or migratory slugs
that experience both cell-cell contact and various soluble
signaling regimes. These time courses, sampled at the highest
temporal resolution to date in this system, provide a
comprehensive resource for studies of developmental gene
expression.
Submitted by Gad Shaulsky [gadi@bcm.edu]
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[End dictyNews, volume 41, number 7]
