Neotenic reproductives influence worker caste differentiation in the termite Reticulitermes speratus (Isoptera; Rhinotermitidae)

Yoshinobu Hayashi,Osamu Kitade,Nathan Lo,Hitoshi Miyata

doi:10.13102/sociobiology.v60i4.446-452

Abstract

Division of labor among castes in social insect colonies increases ergonomic efficiency and colony-level fitness, and has played a key role in the ecological success of social insects. Knowledge of the factors that regulate castes is important for understanding adaptive social organization. Our previous study on the termite Reticulitermes speratus demonstrated that the presence of a pair of nymphoid reproductives during development affected offspring caste ratios. In the present study, we investigated further the influence of individual neotenics on offspring caste ratios. Parthenogenetically-produced offspring were reared in worker-tended experimental colonies with the addition of different forms (nymphoid or ergatoid) and numbers of neotenics, and compared the caste ratios of the offspring between the different experimental treatments. We found that all offspring in worker-only tended colonies became nymphs, while a proportion of offspring in colonies with a single neotenic (with the exception of male ergatoids) differentiated into workers. These results show offspring caste ratios are influenced by the presence of single female ergatoids, single female and male nymphoids, while they remain unaffected by the presence of male ergatoids.

Highlights

A defining characteristic of social insect colonies is the presence of different castes
Our previous study (Hayashi et al, 2007) showed that presence of a pair of female and male nymphoids resulted in increased worker rate of offspring that were produced parthenogenetically, when compared to offspring raised by workers alone
The current study demonstrates that presence of single female ergatoids and single female and male nymphoids increased worker rate among offspring, and on the other hand, that of single male ergatoids did not

Summary

Introduction

A defining characteristic of social insect colonies is the presence of different castes. In our previous study of R. speratus (Hayashi et al, 2007) we carried out crossing with four possible combinations of ergatoids and nymphoids, and examined caste and sex of their offspring, which were reared under uniform environmental conditions. We showed that almost all of the offspring produced through parthenogenesis developed into nymphs when they were reared only with tending workers, while 24% of parthenogenetically-produced offspring differentiated into workers when reared with an additional pair of nymphoids (Hayashi et al, 2007) This suggests that the existence of pairs of nymphoids can influence the developmental trajectory of larvae. In this study, we focused on examining whether individual ergatoids and nymphoids influence proportion of worker caste among offspring. To examine variation of the influence on offspring caste ratio among different sexes and forms (nymphoid/ergatoid) of neotenics within a colony, we made replication of the experiment with neotenics collected from a single field colony

Materials and Methods

Experiments

Results

Discussion