Allometry of workers of the fire ant, Solenopsis invicta

Abstract

The relationship between worker body size and the shape of their body parts was explored in the polymorphic ant, Solenopsis invicta . The data consisted of 20 measurements of body parts as well as sums of some of these measurements. Size-free shape variables were created by taking the ratios of relevant measures. After log-transformation, these ratios were regressed against the logarithm of total body length, or against the log of the size of the parent part. Slopes of zero indicated that shape did not change with size, and non-zero slopes signaled a size-related change of shape. Across the range of worker sizes, the head length retained a constant proportion to body length, but relative headwidth increased such that head shape changed from a barrel-profile to a somewhat heart-shaped profile. Antennae became relatively smaller, with the club contributing more to this decline than the other parts. The alinotum became relatively shorter and higher (more humped), and the gaster increased in both relative width and length, and therefore in volume. All three pairs of legs were isometric to body length. The component parts of the legs, with one exception, were isometric to their own total leg length. The body of S. invicta is therefore dominated by mostly modest allometries, giving large workers a somewhat different shape than small ones. None of these size-shape relationships was different for different colonies. The functional meaning of these shape changes is unknown, but that does not stop us from speculating. HL head length BL body length HW1 width across the eyes HW2 width above the eyes HW3 width below the eyes

Climbing, falling, and jamming during ant locomotion in confined environments

“…We measured the lateral limb span, x span , for free-falling ants and found that ants extended limbs maximally to a width of max(x span ) = 1.33 ± 0.22 L independent of tunnel size when D > 1.3 L. This measurement is consistent with the typical midlimb span of fire ants 1.31 ± 0.09 L reported in the literature (SI Text and Fig. S15) (48) and suggests ants are extending limbs maximally to re-engage the tunnel wall while falling. In tunnels whose diameter exceeded the physical reach of the ants, D > 1.3 L, ants were unable to engage walls and the arrest probability decreased substantially (Movie S5).…”

“…We thus hypothesized that the minimum tunnel diameter through which an ant can move is slightly larger than the animal's head width. Fire ant head width is 0.24 ± 0.01 L (48), and this sets the lower limit of the range of observable D/L values (shaded blue box Fig. 2D).…”

Effects of worker size on the dynamics of fire ant tunnel construction

“…Moreover, variation in body size ( polymorphism) in social insects can influence the likelihood and effectiveness of performing certain colony tasks such as the rearing of brood or foraging for food [31][32][33][34][35]. Since mandible width correlates with body size [36] and since tunnel excavation involves the use of mandibles to loosen and carry soil to the surface, a natural hypothesis is that body size correlates with digging proficiency. However, the relationship of ant size and tunnelling performance has not been investigated.…”

“…First, worker size in S. invicta is influenced by genetic and environmental factors [36][37][38], and workers display considerable variation in size. For example, worker head width varies continuously over a nearly threefold range (figure 1a).…”

Social selection and the evolution of a female weapon in queens of the antMessor pergandei(Hymenoptera: Formicidae)

“…A); (2) the length of the head from the posterior margin to the anterior edge of the clypeus (Fig. B); (3) the anterior–posterior length of the gaster from the edge of the petiole to the end of the first segment (only the first segment was measured due to telescoping of the gaster; Tschinkel, Mikheyev & Storz, ; Fig. C); (4) hind femur length measured from the base of a raised region located at the coxal side, to the end of the femur on the tibial side (Fig.…”