dictyNews
Electronic Edition
Volume 41, number 7
April 10, 2015

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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 Genética e Biologia Evolutiva, Instituto 
de Biociências, Universidade de São Paulo, São 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 ‘cheating’ 
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 ‘cheaters’ [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 
‘losers’. 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 [[log in to unmask]] 
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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 [[log in to unmask]]
----------------------------------------------------------------------


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 [[log in to unmask]] 
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[End dictyNews, volume 41, number 7]