|Walz, Megan - North Carolina State University|
|Tarpy, David - North Carolina State University|
Submitted to: Biology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2016
Publication Date: 9/20/2016
Citation: Simone-Finstrom, M., Walz, M., Tarpy, D.R. 2016. Genetic diversity confers colony-level benefits due to individual immunity. Biology Letters. 12:20151007. doi:10.1098/rsbl.2016.1007
Interpretive Summary: Honeybees live in large social groups containing thousands of closely related individuals. Living in crowded, warm conditions creates the potential for parasites and pathogens to take advantage of this ready supply of hosts. To combat pressure from parasites, honeybees have evolved a number of physiological and behavioral mechanisms of resistance. One factor that influences the spread of disease within a colony is the level of genetic diversity or the relatedness of workers within a colony. A colony is headed by a single queen who produces all of the sister workers within a colony. However the queen mates with 5-40 different males resulting in various subfamilies within the worker population, so that the genetic diversity of the colony is a consequence of the number of mates the queen had. Previous research has shown that colonies headed by queens with higher mating numbers have less variable infections of decreased intensity, though the underlying mechanisms remain unclear. This study investigated larval immune response across colonies of differing levels of genetic diversity. The aim was to determine if this could be the mechanism to describe the effect of colony-level genetic diversity against pathogens. Our results, using the bacterial agent of American foulbrood disease as a model pathogen, suggest that larval immunity alone can be a strong driver to reduce symptoms of disease. We provide clear evidence for a mechanism that may explain previous studies documenting the same phenomenon for disease expression at the colony level. It is still likely, however, that in the hive setting individual immunity and group-level, social immunity behaviors work together to fight disease and parasites in colonies.
Technical Abstract: Several costs and benefits arise as a consequence of eusociality and group-living. With increasing group size, spread of disease among nest-mates poses selective pressure on both individual immunity and group-level mechanisms of disease resistance (social immunity). Another factor known to influence colony-level expression of disease is intracolony genetic diversity, which in honeybees (Apis mellifera) is a direct function of the number of mates of the queen. Colonies headed by queens with higher mating numbers have less variable infections of decreased intensity, though the underlying mechanisms remain unclear. By pathogen-challenging larvae in vitro, we decoupled larval immune response from mechanisms of social immunity. Our results show that baseline immunity and degree of immune response do not vary with genetic diversity. However, intracolony variance in antimicrobial peptide production after pathogen challenge decreases with increasing genetic diversity. This reduction in variability of the larval immune response could drive the mitigation of disease observed in genetically diverse colonies.