in some species of social insects the increased genetic diversity from having multiple breeders in a colony has been shown to improve pathogen resistance. termite species typically found colonies from single mated pairs and therefore may lack the flexibility to buffer pathogen pressure with increased genetic diversity by varying the initial number of reproductives. However, they can later increase group diversity through colony merging, resulting in a genetically diverse, yet cohesive, workforce. in this study, we investigate whether the increased group diversity from colony fusion benefits social immunity in the subterranean termite Reticulitermes flavipes. We confirm previous findings that colonies of R. flavipes will readily merge and we show that workers will equally groom nestmates and non-nestmates after merging. Despite this, the survival of these merged colonies was not improved after exposure to a fungal pathogen, but instead leveled to that of the more susceptible or the more resistant colony. our study brings little support to the hypothesis that colony fusion may improve immunity through an increase of genetic diversity in R. flavipes. Instead, we find that following exposure to a lethal pathogen, one colony is heavily influential to the entire group's survival after merging. Social insects are among the most abundant and ecologically successful species 1. Their success is inextricably linked to their division of labor where workers engage in different tasks to benefit one or a few reproductives at the expense of their own reproduction. The low number of reproductives in colonies of most species results in high relatedness among nestmate workers, elevating indirect fitness benefits 2. Paradoxically, their social life also entails severe costs, as high worker densities, high relatedness, and closed nests strongly increase the chance of pathogen transmission, which would suggest that these species are vulnerable to disease outbreaks 3. Owing to such pathogenic pressure, social insects have evolved social immunity, whereby individual immune functions and behaviors collectively provide colony-wide disease protection 4-6. Social immunity includes self/allogrooming 7-14 , nest hygiene 15-22 , removal of diseased individuals 23-26 and the use of antimicrobial compounds either produced by individuals or from materials incorporated into the nest 27-38. These diverse immune strategies have undoubtedly reduced the costs of social living, facilitating the success of social insects. Colony resistance to pathogens is also associated with within-colony genetic diversity, as genetically distinct individuals may vary in their susceptibility to different disease strains 39-45. Therefore, a mix of distinct genotypes within a colony interferes with genotype x genotype interactions, such that a pathogen able to infect one genotype may fail to transmit to new hosts if it encounters host genotypes that it cannot infect. Consequently, a genetically diverse colony may reduce the overall spread of a pathogen. Although variatio...

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Social insect colonies are characterized by an efficient division of labor, allowing high-value individuals (i.e., reproductives and brood) to be sheltered from tasks associated with increased risk of pathogen exposure, such as foraging or corpse disposal. This social organization helps limit the transmission of disease throughout the colony. Further, individuals can actively respond to imminent disease threats by altering their behaviors as a means of social immunity. In subterranean termites, although workers typically avoid detected pathogens, they can be attracted to pathogen cues when a nestmate is infected. Infected termites are usually groomed, but they may instead be cannibalized if the infection has already become lethal. The mechanisms governing these changes in behavior are unclear. We set out to examine immediate changes in individual behaviors, investigating the role that the infected individual plays in communicating its infection status to nestmates. We also assessed gradual changes in social organization after the re-introduction of an infected termite to the colony. Our results reveal that infected termites likely do not signal their infection status to nestmates through shaking behaviors and reduced movements, suggesting the occurrence of other mechanisms used in communicating infection. We also found that infected termites do not self-isolate and may travel to the densest part of the colony, where they can potentially benefit from grooming by large groups of nestmates. These results provide new insights into how individual changes in immune behaviors contribute to overall colony health, highlighting that, at early stages of infection, termites favor a rescuing strategy rather than isolation and/or cannibalization.

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