Scaling relationships in Formica ants with continuous worker size variation
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Insectes Sociaux
RESEARCH ARTICLE
Scaling relationships in Formica ants with continuous worker size variation S. Tawdros1 · M. West1 · J. Purcell1 Received: 14 March 2020 / Revised: 13 June 2020 / Accepted: 5 August 2020 © International Union for the Study of Social Insects (IUSSI) 2020
Abstract 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. Keywords Allometry · Body plan · Scaling · Morphology · Formica glacialis · Formica neoclara · Formica aserva · Formica obscuriventris
Introduction Within eusocial insect colonies, individuals often exhibit dramatically different body plans. The most striking example of this variation is associated with the reproductive division of labor. Reproductive queens often differ in both size and shape from their non-reproductive worker daughters (Wheeler 1986; Trible and Kronauer 2017). Additionally, some species produce morphologically discrete worker subcastes, wherein workers from different size classes also differ in the relative scaling of their heads or appendages (Hö lldobler and Wilson 1990; Miura 2005; Wills et al. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00040-020-00779-0) contains supplementary material, which is available to authorized users. * J. Purcell [email protected] 1
Department of Entomology, University of California Riverside, Riverside, CA 92521, USA
2018). For example, in the ant species Pheidole bicarinata, minor workers specialize in foraging and brood care, while larger soldier workers, which possess disproportionately large heads, specialize in colony defense. These Pheidole minor workers and s
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