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Studying the behavioral and life history transitions from a cooperative, eusocial life history to exploitative social parasitism allows for deciphering the conditions under which changes in behavior and social organization lead to diversification. The Holarctic ant genus Formica is ideally suited for studying the evolution of social parasitism because half of its 172 species are confirmed or suspected social parasites, which includes all three major classes of social parasitism known in ants. However, the life history transitions associated with the evolution of social parasitism in this genus are largely unexplored. To test competing hypotheses regarding the origins and evolution of social parasitism, we reconstructed a global phylogeny of Formica ants. The genus originated in the Old World ∼30 Ma ago and dispersed multiple times to the New World and back. Within Formica , obligate dependent colony-founding behavior arose once from a facultatively polygynous common ancestor practicing independent and facultative dependent colony foundation. Temporary social parasitism likely preceded or arose concurrently with obligate dependent colony founding, and dulotic social parasitism evolved once within the obligate dependent colony-founding clade. Permanent social parasitism evolved twice from temporary social parasitic ancestors that rarely practiced colony budding, demonstrating that obligate social parasitism can originate from a facultative parasitic background in socially polymorphic organisms. In contrast to permanently socially parasitic ants in other genera, the high parasite diversity in Formica likely originated via allopatric speciation, highlighting the diversity of convergent evolutionary trajectories resulting in nearly identical parasitic life history syndromes. 

Supergenes, regions of the genome with suppressed recombination between sets of functional mutations, contribute to the evolution of complex phenotypes in diverse systems. Excluding sex chromosomes, most supergenes discovered so far appear to be young, being found in one species or a few closely related species. Here, we investigate how a chromosome harbouring an ancient supergene has evolved over about 30 million years (Ma). TheFormicasupergene underlies variation in colony queen number in at least five species. We expand previous analyses of sequence divergence on this chromosome to encompass about 90 species spanning theFormicaphylogeny. Within the nonrecombining region, the geneknockoutcontains 22 single nucleotide polymorphisms (SNPs) that are consistently differentiated between two alternative supergene haplotypes in divergent EuropeanFormicaspecies, and we show that these same SNPs are present in mostFormicaclades. In these clades, including an early diverging NearcticFormicaclade, individuals with alternative genotypes atknockoutalso have higher differentiation in other portions of this chromosome. We identify hotspots of SNPs along this chromosome that are present in multipleFormicaclades to detect genes that may have contributed to the emergence and maintenance of the genetic polymorphism. Finally, we infer three gene duplications on one haplotype, based on apparent heterozygosity within these genes in the genomes of haploid males. This study strengthens the evidence that this supergene originated early in the evolution ofFormicaand that just a few loci in this large region of suppressed recombination retain strongly differentiated alleles across contemporaryFormicalineages.

 

Morphometric research is being applied to a growing number and variety of organisms. Discoveries achieved via morphometric approaches are often considered highly transferable, in contrast to the tacit and idiosyncratic interpretation of discrete character states. The reliability of morphometric workflows in insect systematics has never been a subject of focused research, but such studies are sorely needed. In this paper, we assess the reproducibility of morphometric studies of ants where the mode of data collection is a shared routine.

We compared datasets generated by eleven independent gaugers, that is, collaborators, who measured 21 continuous morphometric traits on the same pool of individuals according to the same protocol. The gaugers possessed a wide range of morphometric skills, had varying expertise among insect groups, and differed in their facility with measuring equipment. We used intraclass correlation coefficients (ICC) to calculate repeatability and reproducibility values (i.e., intra‐ and intergauger agreements), and we performed a multivariate permutational multivariate analysis of variance (PERMANOVA) using the Morosita index of dissimilarity with 9,999 iterations.

The calculated average measure of intraclass correlation coefficients of different gaugers ranged fromR = 0.784 toR = 0.9897 and a significant correlation was found between the repeatability and the morphometric skills of gaugers (p = 0.016). There was no significant association with the magnification of the equipment in the case of these rather small ants. The intergauger agreement, that is the reproducibility, varied betweenR = 0.872 andR = 0.471 (meanR = 0.690), but all gaugers arrived at the same two‐species conclusion. A PERMANOVA test revealed no significant gauger effect on species identity (R² = 0.69,p = 0.58).

Our findings show that morphometric studies are reproducible when observers follow the standard protocol; hence, morphometric findings are widely transferable and will remain a valuable data source for alpha taxonomy.