Figure 1.
Cataglyphis bombycina ants are highly polyphenic.
Colonies contain one dealate queen (left), numerous workers (middle and bottom), and fewer large individuals with saber-shaped mandibles ‘ISM’ (soldiers, right). Photo © P. Landmann.
Figure 2.
Distinct adult castes exhibit distinct growth rules.
Growth rules of the worker (empty circles) and queen (empty triangles) castes for a theoretical pair of morphological traits ‘x’ and ‘y’ are illustrated by dashed lines. Increasing critical size of the worker growth rule leads to the production of adults that are larger and have a different shape due to allometry, i.e. major workers (black circles). However the range of possible phenotypes that can be produced is limited (grey area surrounding the workers’ curve). Alternatively, modifying both critical size and growth rate leads to the production of novel adult phenotypes that are outside of this range and accordingly do not belong to the worker caste, i.e. soldiers (empty squares). We suggest that this can be done either by combining parameters of the growth rules of existing worker and queen castes (‘recycled’ soldiers) or by evolving brand new growth rules (‘novel’ soldiers).
Figure 3.
Size of body parts differs between female types in most cases.
(52 workers, 47 macrogynes, 9 microgynes and 40 individuals with saber-shaped mandibles ‘ISM’). All Kruskal-Wallis rank tests are significant (P<0.001), and 38 out of 42 pairwise comparisons using Wilcoxon rank tests with Bonferroni-corrected P-values are significant (different letters indicate significant differences).
Figure 4.
Scanning electron micrographs of the thorax of macrogyne, individual with saber-shaped mandibles ‘ISM’, large worker and small worker.
(Resp. top, middle, bottom left and bottom right). The thorax of ‘ISM’ is simplified as in workers: sclerites are fused and mesonotum is reduced.
Figure 5.
Scanning electron micrographs of the mandibles of macrogyne, individual with saber-shaped mandibles ‘ISM’, large worker and small worker.
(Resp. top, middle, bottom left and bottom right). Macrogynes and workers have similar mandibles, but those of ‘ISM’ have a completely different shape and size.
Figure 6.
Growth rules of the four female types for one pair of morphological traits.
(See Table 1 for some of the other pairs). Circles, squares, diamonds and triangles represent workers, individuals with saber-shaped mandibles ‘ISM’, microgynes and macrogynes respectively. Dotted lines are major axis regression lines, with their slopes (allometry coefficients) indicated as numbers. These four growth rules differ significantly. However, the allometry coefficients (growth rates) of ‘ISM’ and microgynes are not significantly different, suggesting that ‘ISM’ recycle a queen-like developmental program for this pair of traits. Diagrams represent a small worker, a theoretical large worker of tibia length t produced by the allometric growth rules of the worker caste, and an ‘ISM’ of the same tibia length t produced by the new growth rules. The large worker and the ‘ISM’ clearly differ. This illustrates that worker growth rules cannot produce a major worker phenotype that would look like an ‘ISM’ (Fig. 2).
Table 1.
Growth rules of the four female types differ, revealing that they are distinct morphological castes.