Department of Evolutionary and Environmental Biology, Institute of Evolution, University of Haifa, Haifa, Israel.
Sci Rep. 2020 Jul 14;10(1):11538. doi: 10.1038/s41598-020-67999-z.
Colony social organization of multiple Solenopsis fire ant species is determined by a supergene with two haplotypes SB and Sb, which are similar to X/Y sex chromosomes. The ancestral monogyne (single-queen) social form has been associated with homozygous SB/SB queens, while queens in colonies with the derived polygyne (multi-queen) social structure are heterozygous SB/Sb. By comparing 14 Solenopsis invicta genomes and the outgroup S. fugax, we dated the formation of the supergene to 1.1 (0.7-1.6) million years ago, much older than previous estimates, and close to the estimated time of speciation of the two socially polymorphic species S. invicta and S. richteri. We also used 12 S. invicta and S. richteri genomes to compare the evolutionary distances between these species and the distances between the social haplotypes, and found them to be similar. A phylogenetic analysis suggested that the monophyletic Sb clade is more closely related to S. richteri SB haplotypes than to S. invicta SB haplotypes. We conclude that the formation of the supergene occurred concomitantly with the process of speciation of the Solenopsis socially-polymorphic clade, and hypothesize that the Sb variant first arouse in one incipiently-speciating population and then introgressed into the other populations or species.
多种红火蚁物种的群体社会组织由具有两种单倍型 SB 和 Sb 的超基因决定，类似于 X/Y 性染色体。祖先的单后（单后）社会形式与纯合 SB/SB 后相关，而具有衍生的多后（多后）社会结构的群体中的后是杂合的 SB/Sb。通过比较 14 个红火蚁基因组和外群 S. fugax，我们将超基因的形成时间追溯到 110 万年前（0.7-1.6 百万年前），比以前的估计要早得多，接近于两种具有社会多态性的物种 S. invicta 和 S. richteri 的物种形成时间。我们还使用了 12 个红火蚁和 S. richteri 基因组来比较这些物种之间的进化距离和社会单倍型之间的距离，发现它们相似。系统发育分析表明，单倍型 Sb 支系与 S. richteri SB 单倍型的亲缘关系比与 S. invicta SB 单倍型的亲缘关系更密切。我们得出结论，超基因的形成与 Solenopsis 具有社会多态性的分支的物种形成过程同时发生，并且假设 Sb 变体首先在一个正在形成的种群中出现，然后渗入其他种群或物种。
