Ergatoid queen development in the ant Myrmecina nipponica : modular and heterochronic regulation of caste differentiation

Abstract

Caste polyphenism in social insects provides us with excellent opportunities to examine the plasticity and robustness underlying developmental pathways. Several ant species have evolved unusual castes showing intermediate morphologies between alate queens and wingless workers. In some low-temperature habitats, the ant Myrmecina nipponica produces such intermediate reproductives (i.e. ergatoids), which can mate and store sperm but cannot fly. To gain insight into the developmental and evolutionary aspects associated with ergatoid production, we conducted morphological and histological examinations of the post-embryonic development of compound eyes, gonads and wings during the process of caste differentiation. In compound eyes, both the queen-worker and ergatoid-worker differences were already recognized at the third larval instar. In gonads, queen-worker differentiation began at the larval stage, and ergatoid-worker differentiation began between the prepupal and pupal stages. Wing development in ergatoids was generally similar to that in workers throughout post-embryonic development. Our results showed that the developmental rate and timing of differentiation in body parts differed among castes and among body parts. These differences suggest that the rearrangement of modular body parts by heterochronic developmental regulation is responsible for the origination of novel castes, which are considered to be adaptations to specific ecological niches.

Caste development and evolution in ants: it's all about size

“…Caste-associated phenotypes (variation in ovarioles, spermatheca, ocelli, eyes and wings) result from variation in development of these imaginal disks (Wilson, 1953;Brian, 1979;Miyazaki et al, 2010). The suite of queen-like phenotypes is similar to the ancestral state of holometabolous insects, with fully developed adult tissues, while the suite of worker-like phenotypes results primarily from reduced growth of caste-associated tissues.…”

“…Caste differentiation factors can influence tissue growth at different times in development (Miyazaki et al, 2010). This effect is clearly seen in the wingless castes in the genus Pheidole, in which most species possess workers, soldiers and queens, but some species also have a super-soldier caste that is intermediate in size between soldiers and queens (Huang and Wheeler, 2011).…”

“…We assume that increased body mass correlates with increased body length, and that increased ovariole, eye/ocellus and wing development correlate with increased abdomen width, head width and thorax width, respectively. pupae differentiate in a worker-or queen-like manner in association with size (Miyazaki et al, 2010).…”

Heterochrony of cuticular differentiation in eusocial corbiculate bees

“…Heterochrony can be caused by environmental stimuli, which may generate intraspecific alterations in the life cycle, caste, or gender (Miyazaki et al 2010) and even in speciation events (Gould 1977). The environment does not act in the evolutionary process solely through natural selection, but also as an active agent in the development (West-Eberhard 1989.…”

Histone deacetylases control module-specific phenotypic plasticity in beetle weapons

“…Given that different organs may form at different times during development (26)(27)(28)(29), mandible progenitor cells may retain the developmental flexibility to allow phenotypic plasticity until late stages, whereas other somatic/genital precursor cells may lose such flexibility at earlier stages of development. If such is the case, HDAC KDs at an early developmental stage may have non-organspecific morphogenetic effects.…”