Social antagonism facilitates supergene expansion in ants

Antagonistic selection has long been considered a major driver of the formation and expansion of sex chromosomes. For example, sexually antagonistic variation on an autosome can select for suppressed recombination between that autosome and the sex chromosome, leading to a neo-sex chromosome. Autosomal supergenes, chromosomal regions containing tightly linked variants affecting the same complex trait, share similarities with sex chromosomes, raising the possibility that sex chromosome evolution models can explain the evolution of genome structure and recombination in other contexts. We tested this premise in a Formica ant species, wherein we identified four supergene haplotypes on chromosome 3 underlying colony social organization and sex ratio. We discovered a novel rearranged supergene variant (9r) on chromosome 9 underlying queen miniaturization. The 9r is in strong linkage disequilibrium with one chromosome 3 haplotype (P2) found in multi-queen (polygyne) colonies. We suggest that queen miniaturization is strongly disfavored in the single-queen (monogyne) background and is thus socially antagonistic. As such, divergent selection experienced by ants living in alternative social "environments" (monogyne and polygyne) may have contributed to the emergence of a genetic polymorphism on chromosome 9 and associated queen-size dimorphism. Consequently, an ancestral polygyne-associated haplotype may have expanded to include the polymorphism on chromosome 9, resulting in a larger region of suppressed recombination spanning two chromosomes. This process is analogous to the formation of neo-sex chromosomes and consistent with models of expanding regions of suppressed recombination. We propose that miniaturized queens, 16%-20% smaller than queens without 9r, could be incipient intraspecific social parasites.

Foe to frenemy: predacious ant nest beetles use multiple strategies to fully integrate into ant nests

Ant nest beetles (Carabidae, Paussinae, Paussini; Paussus) are renowned myrmecophiles, mostly known for their bizarre and diverse antennal shape. While little is known about their development, behavior and host range, we do know they spend most of their lives inside ant nests, feeding upon the hemolymph of ant brood and teneral workers. Recent findings suggest these beetles use a surprisingly complex strategy for interacting and deceiving ants. They have managed to break into multiple communication channels that ants use to recognize and communicate with one another in order to deceive the ants and profit from the rich resources of the nest. Mounting evidence from structural, chemical, acoustic, and behavioral studies support the hypothesis that Paussus is among the most highly integrated parasite of social insects known to date.

Early queen joining and long-term queen associations in polygyne colonies of an invasive wasp revealed by longitudinal genetic analysis

Invasive social insects rank among the most damaging of terrestrial species. They are responsible for extensive damage and severely threaten the biodiversity of environments where they are introduced. Variation in colony social form commonly occurs in introduced populations of yellowjacket wasps (genus Vespula). In particular, invasive colonies may contain multiple queens (i.e., polygyne) and persist several years, while in the native range, the colonies are usually annual and harbor a single queen (i.e., monogyne). In this study, we used genome-wide loci obtained by double digest restriction site-associated DNA sequencing (RADseq) to investigate the genetic structure and queen turnover in colonies of the western yellowjacket, Vespula pensylvanica, in their introduced range in Hawaii. Of the 27 colonies monitored over four months (October-January), 19 were polygyne and already contained multiple queens on the first day of sampling. Contrary to previous speculation, this finding suggests that polygyny often arises early in the annual colony cycle, before the production of new queens in the fall. Furthermore, polygyne colonies exhibited a prolonged average lifespan relative to those headed by a single queen. As a result, there is no clear window during which colony eradication efforts would be more effective than upon first discovery. The relatedness among nestmate queens was slightly above zero, indicating that these colonies are generally composed of nonrelatives. The queen turnover within each colony was low, and we detected some full-sibling workers sampled up to four months apart. Finally, we did not detect any population structure among colonies, suggesting that queens disperse up to several kilometers. Taken together, our results provide the first insights into the requeening dynamics in this invasive and incipiently polygyne population and illuminate the early establishment of multiple long-lasting queens in these damaging colonies.