Size and shape in Formica ant workers
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Insectes Sociaux
EDITORIAL
Size and shape in Formica ant workers Miriam H. Richards1 Published online: 13 November 2020 © International Union for the Study of Social Insects (IUSSI) 2020
Allometry is the study of scaling relationships, especially between body size and the measurements of different body parts, or between body size and fundamental physiological traits, such as metabolic rate or lifespan (Shingleton 2010). Allometry began as the study of developmental relationships among body parts; differences in the growth rates of different body parts as individuals grow result in different body shapes or morphology by adulthood. For instance, if limbs grow relatively faster during development, then larger individuals will end up with proportionately longer legs compared to some other size measure (e.g. total body length), whereas those whose limbs grow relatively slowly would end up with proportionately shorter legs. Allometry now describes broader scaling relationships, including comparisons of relative proportions of body parts across species. When the proportions of body parts correlate with crucial aspects of an animal’s life history, interspecific comparisons may help to illuminate how natural selection produced both morphology and behaviour. In insects, body size influences individual fitness in myriad ways: for instance, larger females have an advantage in aggressive encounters, can lay more eggs, and may be more likely to survive hibernation. In social insects, large size is generally associated with higher rankings in dominance hierarchies and in eusocial insects, is clearly associated with caste. The size difference between queens and workers is a fundamental aspect of social insect castes; queens are so predictably larger than workers that the absence of a size difference is considered to be notable. Queen-worker size differences are clearly associated with reproductive division of labour, and when there are size-based allometries during development, this can produce morphological differences between castes. Some social insects, including thrips, aphids, termites, stingless bees, and ants, may produce distinct size-based worker morphs, such as soldiers, which * Miriam H. Richards [email protected] 1
Brock University, St. Catharines, Canada
are morphologically specialized for tasks such as colony defense. In such cases, individual workers follow different developmental programs, such that discrete subcastes exhibit distinct scaling relationships. This is referred to as ‘nonlinear allometry’. Alternatively, when all individuals follow the same developmental program, consistent scaling of body parts with body size can still produce different morphologies for different-sized individuals, a situation referred to as ‘linear allometry’. When body parts scale with a slope of 1 in a log–log comparison, all individuals have the same relative proportions, regardless of size, which is known as ‘isometry’. One way of investigating the nature of developmental programs that produce different morphologies assoc
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