A transitional stage between the ergatoid and winged male morph in the ant Cardiocondyla obscurior

Abstract

Males of the ant Cardiocondyla show a dispersal dimorphism of a winged and wingless morph. The loss of flight has lead to morphological reductions in the wingless (ergatoid) males and also affected body size, eye size and pigmentation. As ergatoid males mate exclusively inside the maternal nest, they underlie increased male-male competition and therefore have also evolved additional changes in behaviour and physiology: in contrast to winged males, ergatoid males are highly aggressive towards each other and their spermatogenesis is prolonged compared to all other hymenopteran males. In addition to these two male morphs, we found males with an intermediate appearance. These "intermorphic" males provide a transitional stage between normal males in most investigated morphological and physiological parameters. As they are produced extremely rarely and only in colonies that switch between pure ergatoid to mixed male production, we argue that they likely represent a developmental mistake. Parallels between the determination of male morphs and female castes (queen-worker dimorphism and worker polymorphism) might help to understand how the large potential of phenotypic plasticity in both sexes of social insects is realised during development.

Interruption points in the wing gene regulatory network underlying wing polyphenism evolved independently in male and female morphs in Cardiocondyla ants

“…The phylogeny of Cardiocondyla suggests that wingless males originated once at the base of the genus (Oettler, Suefuji, & Heinze, 2010)~20 million years ago (Ward, Brady, Fisher, & Schultz, 2014) and that the winged morph was lost several times independently. This is consistent with the highly variable nature of male phenotypic plasticity within the genus-several species produce wingless males exclusively, while others produce both morphs, and some species even consistently producing intermorphs between winged and wingless males (Cremer, Lautenschläger, & Heinze, 2002;Heinze, Aumeier, Bodenstein, Crewe, & Schrempf, 2012;Yamauchi, Asano, Lautenschläger, Trindl, & Heinze, 2005). This suggests that at the base of the genus, wing polyphenism in males evolved through the environmental induction of phenotypic variation; plastic-winged males may have produced a range of short-winged or wingless phenotypes that were eventually genetically accommodated leading to the evolution of a new developmental switch that gave rise to male wing polyphenism.…”

Wingless and intermorphic males in the ant Cardiocondyla venustula

“…The variability of male phenotype in C. venustula might therefore resemble the sporadic occurrence of intercastes, i.e., females with a mix of features typical of "gynomorphic" ant queens and "ergatomorphic" ant workers (e.g., Heinze, 1998), only that intermorphic males have retained their specific reproductive function. Similar intermorphic males have been produced in laboratory colonies of C. obscurior, which had been induced experimentally to switch from the production of wingless males to winged males (Cremer et al, 2002). This again suggests a strong environmental influence on the morphology of Cardiocondyla males.…”

A new type of male dimorphism with ergatoid and short-winged males in Cardiocondyla cf. kagutsuchi

“…Their wings are too small to fly and their pale body coloration and small compound eyes suggest that they mainly live in the nest underground. In addition, intermorphic males, which were morphologically intermediate between ergatoid and brachypterous males, occurred sporadically, probably due to inaccuracies during larval development (see also Cremer et al, 2002b). Similar to ergatoid males, brachypterous males are aggressive and compete for the acquisition of female sexuals.…”

“…The gaster was sagitally sectioned at 0.5 to 2 mm with a Histodiamond (Diatome) and a Reichert-Jung microtome and stained with methylene blue (Cremer et al, 2002b). Chromosomal preparations were made from the testes of 20 white pupae with pink eye coloration from each of five sub-colonies using an improved air-drying technique (Imai et al, 1988).…”