Irreversible transfer of brood care duties and insights into the burden of caregiving in incipient subterranean termite colonies

1. In incipient termite colonies, biparental brood care rapidly shifts towards alloparental brood care. This transition was suggested to recapitulate the evolutionary trajectory from subsocial wood roach ancestors to eusociality in termites. 2. Incipient colonies of the subterranean termite Coptotermes gestroi (Wasmann) were investigated to determine if this transition was irreversible and if the burden of brood care on the first alloparents could be measured. To do so, the initial size of the work force necessary for an incipient colony to survive once the brood care became alloparental was determined. 3. The results of the study show that within 5months after foundation, brood care duties were fully transferred to workers and the primary reproductives became irreversibly dependent on these workers for survival, reproduction, and colony growth. 4. Once the brood care became strictly alloparental, the presence of a single worker was enough to maintain the survival of the king and queen, confirming that reversed parental care' was also achieved. However, major brood loss and suppressed egg-laying activity from the queen was observed, suggesting that the burden of brood care was too high for a single worker to absorb. Therefore, once brood care has shifted to alloparents, a critical number of workers is necessary to prevent brood loss and initiate colony growth. 5. As the initial cost of brood care is rapidly absorbed with colony growth in termites, the performance in brood care of the first few alloparents in a subsocial wood roach ancestor may have contributed to the emergence of eusociality in this clade.