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8 Molecular Evolutionary Analyses of Insect Societies--BRIELLE J. FISCHMAN, S. HOLLIS WOODARD, and GENE E. ROBINSON
Pages 167-190

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From page 167...
... Draw ing from whole-genome comparisons, candidate gene approaches, and a genome-scale comparative analysis of protein-coding sequence, we highlight novel insights gained for five major biological processes: chemical signaling, brain development and function, immunity, reproduction, and metabolism and nutrition. Lastly, we make comparisons across these diverse approaches and social insect lineages and discuss potential common themes of eusocial evolution, as well as challenges and prospects for future research in the field.
From page 168...
... . Some studies have performed targeted molecular evolutionary analyses of candidate genes that have been particularly valuable in species for which large amounts of genomic sequence are not yet available.
From page 169...
... . whole-genome sequence, which is currently available for six social insects, the honey bee, Apis mellifera (Honeybee Genome Sequencing Consortium, 2006)
From page 170...
... We also speculate on the potential adaptive significance of these molecular changes and consider whether these changes evolved in response to the origin, maintenance, or elaboration of eusociality, because each case likely involved a distinct set of selective forces. For the purposes of interpreting and synthesizing results across multiple studies, we present each process separately, but it is important to recognize that these biological processes may evolve in concert and that some molecular TABLE 8.1 Genes Implicated in the Origin or Maintenance of Insect Society by Molecular Evolutionary Research Type of Changea Gene Function Evidence Chemical signaling Gland development Rapid evolution 1 decapentaplegic ( Bradley et al., 2003; i n eusocial bees H arris et al., 2007)
From page 171...
... Reproduction piRNA pathway Rapid evolution in 1 tudor ( Siomi et al., 2010) p rimitively eusocial b ees (Woodard et al., 2 011)
From page 172...
... 2 006, 2007) Key regulator of Rapid evolution 1 phosphofructokinase glycolysis (Kunieda i n eusocial bees e t al., 2006)
From page 173...
... Gland Development Our bee molecular evolution study identified ~200 genes evolving more rapidly in social relative to nonsocial bee lineages (Woodard et al., 2011)
From page 174...
... Because diversification of gland function is a common characteristic shared by all social insects, it would be fruitful to investigate the sequence evolution and function of these genes in other social insect groups. It is possible that molecular changes in the same or similar genes were involved in gland evolution across other independent eusocial lineages.
From page 175...
... . The specific molecular changes that have occurred in Neofem2 as it evolved this new social function remain to be discovered.
From page 176...
... It is likely that molecular changes affecting nervous s ystem development and function were important in the evolution o f social insect behaviors, but very little is currently known. Brain Evolution in Primitively Eusocial Bees Our bee molecular evolution study detected a strong signal of rapid evolution in brain-related genes in primitively eusocial, but not highly eusocial lineages across two independent origins of each lifestyle (Woodard et al., 2011)
From page 177...
... relative to primitively eusocial bees, one might have assumed that the cognitive demands of social living are strongest in highly eusocial species and lead to stronger selection on brain-related genes. Unique features of insect sociality and the primitively eusocial life style may help to explain why selection on brain evolution appears to have been stronger in the primitively eusocial bees.
From page 178...
... . Molecular evolutionary analyses of immune genes have provided some of the best examples of positive selection acting in social insect genomes.
From page 179...
... . By contrast, molecular evolutionary analysis of individual immune genes in social Hymenoptera has provided evidence that sociality has driven immune gene sequence evolution.
From page 180...
... . A different study of 13 Nasutitermes termite species also found evidence that gene duplication and positive selection are involved in termite immune gene evolution (Bulmer and Crozier, 2006)
From page 181...
... These genes are par ticularly good candidates for further study, because the tissue specificity of the piRNA pathway suggests that selection on these genes is specifically directed at changes related to reproductive processes, in contrast t o genes with broader ranges of tissue expression, where the functional target of selection is harder to infer. Additional ovary developmentrelated genes unrelated to the piRNA pathway also showed a signature of rapid evolution in these primitively eusocial bees (Woodard et al., 2011)
From page 182...
... determination but influences many aspects of social insect biology that are influenced by kinship and degrees of relatedness, including kin selection and the genetic composition of colonies, which are important for division of labor and colony immunity (C.
From page 183...
... . Given these fundamental connections to eusociality, nutritional and metabolic pathways are well studied in social insects and several molecular evolutionary studies have identified changes associated with their function.
From page 184...
... , the evolution of the mrjp genes in honey bees appears to be associated with the elaboration of eusociality and may have been cor related with or dependent on other evolutionary changes, such as changes in gland function. Hexamerins The work done on the termite hexamerins is another excellent exam ple of linking genetic changes to protein function and social phenotype.
From page 185...
... Our bee molecular evolution study revealed that genes involved in carbohydrate metabolism are evolving more rapidly in eusocial relative to noneusocial bee lineages and are evolving most rapidly in highly eusocial lineages (Woodard et al., 2011)
From page 186...
... If the m olecular changes in carbohydrate metabolism genes in highly euso cial bees were attributable to selection for extended queen life span, it c an be predicted that similar molecular changes may also be found in independent social insect lineages that also exhibit extended queen life spans (Wilson, 1971)
From page 187...
... The rapidly evolving gland development g enes identified in our bee molecular evolution study (Woodard et al., 2011) are also good candidates for further study, because the gene functions are relatively well characterized, and gland diversification is a universal phenomenon in social insect evolution.
From page 188...
... primitively eusocial bees, as well as in ant and wasp species that share the primitively eusocial bee lifestyle feature of solitary nest-founding. The molecular changes and biological processes highlighted in this review are currently the most well studied in social insects.
From page 189...
... . Despite these challenges, molecular evolutionary analysis of social insect societies holds promise for testing venerable theories of social evolution using genomic data.


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