Trends in Genetics
Volume 28, Issue 1, January 2012, Pages 14-21
Journal home page for Trends in Genetics

Review
The genomic impact of 100 million years of social evolution in seven ant species

https://doi.org/10.1016/j.tig.2011.08.005Get rights and content

Ants (Hymenoptera, Formicidae) represent one of the most successful eusocial taxa in terms of both their geographic distribution and species number. The publication of seven ant genomes within the past year was a quantum leap for socio- and ant genomics. The diversity of social organization in ants makes them excellent model organisms to study the evolution of social systems. Comparing the ant genomes with those of the honeybee, a lineage that evolved eusociality independently from ants, and solitary insects suggests that there are significant differences in key aspects of genome organization between social and solitary insects, as well as among ant species. Altogether, these seven ant genomes open exciting new research avenues and opportunities for understanding the genetic basis and regulation of social species, and adaptive complex systems in general.

Section snippets

Ant genomes: tools to study biological and social complexity

Ants (Hymenoptera, Formicidae; see Glossary) comprise a dominant component of most terrestrial habitats. The more than 14000 described species (http://www.antweb.org) show an enormous diversity in life-history features, ecological and behavioral adaptations and social organization, and are a prime example of a complex adaptive system 1, 2, 3, 4, 5. Current evidence suggests that the last common ancestor of the ants lived during the Jurassic and Cretaceous periods, 140–168 million years ago

Genomic and genetic features of the seven sequenced ant species

The use of different sequencing technologies and depth of coverage across the sequenced ant species (10.5–123×) has yielded genome assemblies with a ten-fold range of median scaffold sizes (N50 from 598 kb to 5154 kb; Table 2). The overall size of these genomes ranges from 250 Mb to 753 Mb, and most of the variation in genome size is attributable to differences in repetitive element content (Table 2). Solenopsis invicta is the largest ant genome sequenced (353 Mb assembled) [17] and, although no

Epigenetic control of caste determination

DNA methylation and histone modifications contribute to gene expression regulation and can be stably transmitted between cell division events [39]. Unlike genetic information, which changes slowly over the course of multiple generations, such epigenetic information can change quickly within an individual in response to changing environmental conditions (e.g. temperature, diet, and stress). Although an individual is only endowed with one nuclear genome, it can have multiple epigenomes that

Genetic control of caste programs

Pogonomyrmex barbatus promises the most insight into the genetic and epigenetic factors influencing caste determination because it is the only sequenced ant species known to use both environmental (ECD) and genetic forms of caste determination (GCD). Hence, genetic markers allow queen- or worker-destined individuals to be distinguished regardless of developmental stage 45, 46. This makes it possible to analyze stage-specific expression data, allowing for the identification of the developmental

Concluding remarks and future perspectives

The release of seven sequenced ant genomes and the development of new genomic tools for ants has laid the groundwork for an exciting new era of socio- and ant genomics 13, 14. It is now possible to study the molecular basis of social behavior in a second taxon that evolved eusociality independently from the honeybee lineage. The first analysis of the seven ant genomes revealed that ants have a different sociogenome compared with that of the honeybee and that there is also significant variation

Acknowledgments

The authors would like to thank Alex Wild and Myrmecos.net for providing images of the sequenced ant species used in Figure 1. JG and CRS were supported by a grant from the NSF (IOS-0920732). CDS was supported by a grant from the NIMH (5SC2MH086071). DS is supported by a Howard Hughes Medical Institute Collaborative Innovation Award #200900 to D. Reinberg, S. Berger, and J. Liebig. YW was supported by a European Research Council grant to Laurent Keller and JR was supported by a Swiss NSF grant

Glossary

Caste
a subset of individuals in an insect colony that are characterized either behaviorally or morphologically.
Environmental caste determination (ECD)
the differentiation between queens and worker castes is determined by environmental factors, such as exposure to hormones, temperature, or alternate food sources. This is thought to be the main mechanism of caste determination across eusocial species.
Epigenetics
the study of heritable molecular differences resulting in a measurable phenotype that

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