小さなアリの女王の謎を解明(Researchers Solve the Mystery of Tiny Ant Queens)

2024-03-29

2024-03-28 カリフォルニア大学リバーサイド校(UCR)

アリのコロニーは複雑な社会的ダイナミクスによって支えられており、女王、雄、労働者(不妊の雌)の各メンバーが共同体に貢献しています。一部の種では、非常に小さな女王が追加されることでこのダイナミックスに複雑さが加わります。カリフォルニア大学リバーサイド校の研究者らは、この追加の女王の存在を調査し、コミュニティ内の複雑な遺伝子構造であるスーパージーンに焦点を当てました。彼らの研究結果は、Current Biology誌の12月号に掲載されました。

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社会的拮抗関係がアリの超遺伝子拡大を促進する Social antagonism facilitates supergene expansion in ants

Giulia Scarparo,Marie Palanchon,Alan Brelsford,Jessica Purcell
Current Biology Published:November 17, 2023
DOI:https://doi.org/10.1016/j.cub.2023.10.049

Highlights

•A newly discovered supergene underlies ant queen miniaturization

•Miniature queens are only in multi-queen colonies, controlled by another supergene

•We propose that the novel supergene contains socially antagonistic alleles

•If true, this system is analogous to the formation of neo-sex chromosomes

Summary

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.