Photoperiod functions as a major cue for caste-fate determination in a paper wasp
Hideto Yoshimura, Yoshihiro Y. Yamada
Graduate school of Bioresources, Mie University, Tsu, Mie, Japan; Graduate school of Bioresources, Mie University, Tsu, Mie, Japan
Temperate paper wasps are one major group of primitive eusocial insects, and their gynes (potential queens of the next generation) are characterized by diapausing in winter. There has been a controversy about how and when the caste fate is determined in temperate paper wasps. Our recent experiments conducted in weather-controlled laboratory have revealed that photoperiod during the adult stage primarily determines the caste fate in a paper wasp Polistes jokahamae, and photoperiod during the pupal stage and adult size do so secondarily. This is quite different from results of experiments conducted by Bohm (1972) using P. metricus, in which environmental cues sensed (probably photoperiod) during the immature stage is primary. We explored reasons for the difference by adopting similar experimental procedures to Bohm’s ones: We collected P. jokahamae field nests in different colony phases and exposing emerging adults individually to short or long days at 25℃ for 2 weeks. We have verified largely our previous experimental results; that is, the above difference was not caused by the difference in environment (field or laboratory) for the immature. Furthermore, the following were disclosed: Some cues sensed by the first brood during the immature stage, probably increasing day length, weakened the effects of photoperiod during the adult stage. Moreover, early second-brood adults, ones emerging around summer solstice, most likely to mature eggs (i.e., unlikely to diapause) under long days, suggesting that nearly 16-h long days during the pupal stage likely produces non-diapausing adults under long days. These facts suggest that cues sensed during the immature stage is more important for the caste-fate determination than inferred based on our previous experiments. In addition, our results did not support the idea that smaller first-brood adults are more likely to be non-diapause-destined, which has been often believed to be mechanisms for the cast-fate determination.