Sandra M. Rehan; PNAS July 6, 2021 118 (27) e2109409118

Figure: Phylogeny of eusocial arthropod linages. While social Hymenoptera and termites have relatively small genomes and a diverse set of genomic resources, and are increasingly well studied, other social insect lineages remain underrepresented, including snapping shrimps, thrips, aphids, and ambrosia beetles. In PNAS, Chak et al. (9) compare snapping shrimp genome sizes and TE estimates, an important first step toward understanding this independent origin of eusociality. Silhouette images credit: Phylopic. Bee image credit: Melissa Broussard, licensed under CC BY 3.0. Beetle image credit: T. Michael Keesey. Termite image credit: JCGiron, licensed under CC BY 3.0. Aphid, thrips and shrimp images credit: Christoph Schomburg.

A fundamental challenge in biology is explaining the evolution of novel phenotypes such as the origins of eusocial behavior. Eusociality—defined by overlapping generations, reproductive division of labor, and cooperative brood care (1)—has evolved at least 17 times in arthropods (2): widespread in the social Hymenoptera (ants, bees, and wasps) and observed in other orders (aphids, ambrosia beetles, termites, thrips, and snapping shrimp; Fig. 1). Although it has been remarkably successful for some lineages, eusociality remains rare in nature and has been repeatedly lost in other lineages (aphids and bees), suggesting that there may be major barriers to its evolutionary emergence (3). It is well appreciated that eusocial organisms arose from solitary ancestors, and phylogenetic treatments support the notion that social complexity evolved through prolonged parental care, mutual tolerance, and cooperative breeding (4). While the ecological, behavioral, and theoretical genetic drivers of eusociality have long been studied (5), analyses of the molecular genomic mechanisms that give rise to social complexity are in their infancy. The study of social arthropod genomics has revealed the basic genome size and chromosome composition across numerous taxa, but understanding their architecture and regulatory networks remains unclear.