Colony-Level Differences in the Scaling Rules Governing Wood Ant Compound Eye Structure

Abstract

Differential organ growth during development is essential for adults to maintain the correct proportions and achieve their characteristic shape. Organs scale with body size, a process known as allometry that has been studied extensively in a range of organisms. Such scaling rules, typically studied from a limited sample, are assumed to apply to all members of a population and/or species. Here we study scaling in the compound eyes of workers of the wood ant, Formica rufa, from different colonies within a single population. Workers' eye area increased with body size in all the colonies showing a negative allometry. However, both the slope and intercept of some allometric scaling relationships differed significantly among colonies. Moreover, though mean facet diameter and facet number increased with body size, some colonies primarily increased facet number whereas others increased facet diameter, showing that the cellular level processes underlying organ scaling differed among colonies. Thus, the rules that govern scaling at the organ and cellular levels can differ even within a single population.Understanding how organ size and shape is controlled during development is a major challenge in biology. The control of organ morphology is particularly problematic for organisms that need to develop organs to meet specific requirements under fluctuating conditions and resources. In natural environments, adults from a single species can vary enormously in body size due to a combination of genetic and environmental factors. The changes in organ size that accompany changes in body size can be characterised by allometric scaling relationships. The scaling of any feature with size can be described by:where x is a measure of body size, Y is the size of the organ in question, α is the scaling exponent and b is the initial growth index 1 . When no change occurs in the relative size of an organ with body size (α = 1) the relationship is described as isometric 2 . More typically, however, organs show negative allometries (α < 1) becoming relatively smaller as body size increases 3,4 . Even with negative allometries organs can be absolutely larger in animals with a greater body size, but relatively smaller when compared to smaller conspecifics 1,5,6 . In rare cases, organ size may show positive allometry increasing relatively faster than body size (α > 1) 7,8 . Such positive allometry is often associated with organs under sexual selection 7,8 . The scaling of different organs within a body is the product of differential growth; as an organism grows larger, certain organs grow at a faster rate than others 3,9 . This is thought to occur through differential resource allocation 9,10,11 , whereby resources are distributed to different organs at different rates. Scaling has been studied in many taxa including mammals and birds [12][13][14][15] and especially insects [15][16][17][18][19] . In part, this is due to the power of genetic tools available in the fruit fly Drosophila melanogaster 20 but also because of the mode of development of...

Daily activity and visual discrimination reflects the eye organization of weaver antOecophylla smaragdina(Insecta: Hymenoptera: Formicidae)

“…Ants like Cataglyphis albicans (Zollikofer et al, 1995) , C. fortis (Zollikofer et al, 1995), Camponotus pennsylvanicus and Melophorus bagoti increases facet number with body size to get better resolution (Menke et al, 2009; Menzel, 1972; Perl and Niven, 2016). In species like Bombus terrestris and Solenopsis sp., and Formica integroides both the facet number as well as size increases with body length (Perl and Niven, 2016). As a result compound eye length and area also increases with the size of the body to cope up with the resolution of the eye.…”

“…Ant worker’s eye size changes with its body size although a negative allometry is established with the eye and body size. In case of wood ants, the eye is further related to the size of the nest (Perl and Niven, 2016). Allometry of the eye size is checked with body size by measuring the facet number, diameter, and size of the eye.…”

Conservative whole‐organ scaling contrasts with highly labile suborgan scaling differences among compound eyes of closely related Formica ants

“…The facet diameter was measured as the diameter of the facet along its longest axis. The eye area was measured by approximating the eye as an oval, which correlates almost exactly with the eye area measured directly (Perl & Niven, 2016a). Facet diameters, femur lengths, and facet numbers were all measured and counted from their respective micrographs or photographs using ImageJ (Schneider, Rasband, & Eliceiri, 2012).…”

“…Despite these proposed limitations, however, there is substantial evidence showing that allometric scaling relationships can evolve (Emlen & Nijhout, 2000;Voje et al, 2014). This is supported by comparisons of static allometries that show they can differ within populations (Perl & Niven, 2016a), and among populations and species (Emlen & Nijhout, 2000;McGuigan, Nishimura, Currey, Hurwit, & Cresko, 2010;Simmons & Tomkins, 1996;Toju & Sota, 2006;Weber, 1990). Indeed, the idea that allometries can evolve is far from new: "… allometric trends are as subject to evolutionary alteration as are morphological features".…”

A sexual dimorphism in the spatial vision of band-winged grasshoppers

“…(Coimbra et al, 2013;Landgren et al, 2014) making extensive comparisons between the sexes not possible. More recent studies in insects have found variation in eye-scaling within insect species but have so far focused on the morphs of eusocial insects (Perl and Niven, 2016a;Perl and Niven, 2016b;Taylor et al, 2019). Because eye size is a major factor influencing visual performance (Cronin et al, 2014;Kirschfeld, 1976;Land and Nilsson, 2012), body size increases that lead to eye size increases could be utilized for VA improvements (Corral-López et al, 2017).…”