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Abstract Most supergenes discovered so far are young, occurring in one species or a few closely related species. An ancient supergene in the ant genusFormicapresents an unusual opportunity to compare supergene‐associated phenotypes and the factors that influence the persistence of polymorphism in different species. We investigate the genetic architecture of social organization inFormica francoeuri, an ant species native to low‐ and mid‐elevation semiarid regions of southern California, and describe an efficient technique for estimating mode of social organization using population genomic data. Using this technique, we show thatF. francoeuriexhibits polymorphism in colony social organization and that the phenotypic polymorphism is strongly associated with genotypes within theFormicasocial supergene region. The distribution of supergene haplotypes inF. francoeuridiffers from that of related speciesFormica selysiin that colonies with multiple queens contain almost exclusively workers that are heterozygous for alternative supergene haplotypes. Moreover, heterozygous workers exhibit allele‐specific expression of the polygyne‐associated haplotype at the candidate geneKnockout,which is thought to influence social organization. We also report geographic population structure and variation in worker size across a large fraction of the species range. Our results suggest that, although theFormicasupergene is conserved within the genus, the mechanisms that maintain the supergene and its associated polymorphisms differ among species.
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Scaling relationships in Formica ants with continuous worker size variation.
Social insects exhibit highly variable body plans at multiple scales: within colonies, between conspecific colonies, and across different species. The interspecific variation in the existence and prevalence of morphologically discrete worker subcastes in social insects raises questions about the ontogeny and functional importance of alternative worker body plans. Here, we examine the allometry of four Formica species. Formica are among the most common ants in the northern hemisphere temperate zone, and species vary greatly in the degree of worker size variation. However, no Formica species exhibit obvious worker subcastes. By carefully measuring head width, head height, scape length, thorax length, hind femur length, and hind tibia length in 180 individuals, we confirm that Formica workers exhibit continuous linear scaling, meaning that they lack discrete morphological subcastes. Most measurements scale allometrically. Different colonies of the same species are generally consistent in the slope of these relationships, and we detect unexpected similarities in scaling relationships among the four Formica species as well. Some scaling relationships, including a proportionally shorter scape and larger head in large-bodied workers, were also previously found in fire ants. Identifying worker size and shape distributions among different species is a vital step in understanding the selection pressures shaping division of labor in insect societies.
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- Award ID(s):
- 1631776
- PAR ID:
- 10286771
- Date Published:
- Journal Name:
- Insects
- Volume:
- 67
- ISSN:
- 2075-4450
- Page Range / eLocation ID:
- 463–472
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/https://doi.org/10.1007/s00040-020-00779-0
