Therefore, a question that bears directly on conditions presumed to have characterized the threshold of insect social evolution [10] is to ask whether the differentiation of workers and gynes (presumptive foundresses and, therefore, presumptive future queens) in anatomically monomorphic "primitively eusocial" Hymenoptera also has an ontogenetic component, as in advanced eusocial forms.
Occupational data allowing differentiation of health workers are available for 18 countries through this source [ 30].
Using expressed sequence tags (ESTs) for Polistes metricus we selected candidate genes differentially expressed in other insects in three categories: 1) diapause vs. non-diapause phenotypes and/or worker vs. queen differentiation, 2) behavioral subcastes of worker honey bees, and 3) no a priori expectation of a role in worker/gyne development.
However, SHE alone does not impact caste differentiation, survivorship, or any other aspect of worker biology [ 7, 12, 18].
Furthermore, according to the ovarian and reproductive groundplan hypotheses [ 60- 62], genes involved in reproduction have been co-opted to play a role in queen-worker caste differentiation and worker division of labor.
The work required for the construction of the track demonstrates that they had advanced woodworking skills and suggests some differentiation of occupation among the workers.
Another avenue of research is to consider the role of phenotypic plasticity as a source of differentiation among workers.
Furthermore, caste differentiation (differentiation of fertile queen and sterile worker, polyphenism) and sex determination via haplodiploidy (haploids and diploids develop into males and females, respectively) are specific to some hymenopterans such as honey bees, among the holometabolous insects.
A recent intriguing finding underlining hepatocyte plasticity has been reported by Sahin and co-workers, who described differentiation of hepatocytes into liver progenitor cells [ 20].
Epigenetic regulation is responsible for the differentiation of females into workers and queens two castes with strongly diverging life span potential and a plastic pattern of worker longevity that appears to be determined by the social behavior and colony setting rather than chronological age.
