# Plasticity in Caste-Fate Determination During the Adult Stage in Temperate Polistes Wasps

## TL;DR

This paper reviews how adult-stage caste determination in temperate Polistes wasps is highly flexible, influenced by environmental factors rather than larval nutrition.

## Contribution

The paper highlights the unique plasticity in caste determination during the adult stage in temperate Polistes wasps compared to other eusocial insects.

## Key findings

- Castes in temperate Polistes wasps are determined by adult environmental factors, not larval nutrition.
- Morphological and physiological caste differences are not present at emergence in these wasps.
- High adult-stage plasticity may allow for mating opportunities among worker-destined females.

## Abstract

In this review, we summarize caste determination systems in eusocial insects, with a focus on temperate Polistes paper wasps. We describe the plasticity of caste determination, a foundational characteristic of eusociality, during the adult stage. Studies associated with caste determination have advanced in honey bees and are progressing in paper wasps. Honey bees have morphological and physiological caste differences at emergence as a result of different nutrition provision during the larval stage. By contrast, castes in temperate Polistes wasps are ultimately determined by external factors during the adult stage, with preimaginal caste biases during the larval stage; therefore, paper wasps show a high degree of plasticity of caste determination during the adult stage. Thus, studies that explore the caste determination system in temperate Polistes wasps will contribute to understanding how eusociality evolves. We also consider the factors that led to the loss or maintenance of plasticity, based on differences in life history across species, and provide insight into the evolution of eusociality in the Hymenoptera.

The reproductive division of labor is a fundamental characteristic of eusociality; thus, understanding the caste determination system underlying the reproductive division of labor would shed more light on the evolution of eusociality. In this review, we summarize the factors associated with caste determination in temperate Polistes paper wasps and focus on life histories associated with the loss or maintenance of caste plasticity during the adult stage among eusocial Hymenoptera. In many species of eusocial Hymenoptera, caste trajectories are differentiated by nutrition during the larval stages, indicating that caste plasticity is either absent or has not yet been confirmed. However, in temperate Polistes wasps, nutrition during the larval stage only causes biases in caste trajectory, with castes ultimately determined by environmental factors, such as day length and temperature, and colony conditions during the adult stage, indicating high caste plasticity during this stage. Therefore, morphological dimorphism and physiological differences between castes, such as in dopamine levels, have not been found in temperate Polistes wasps at emergence. This plasticity in temperate paper wasps could reflect the fact that females destined to be workers also have a chance to mate with males (especially early males) after emergence, leaving the possibility that they can produce daughters in the emerging year.