Genetic diversity confers colony-level benefits due to individual immunity

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.

Keywords: Apis mellifera; individual versus social immunity; polyandry; social insects.

Figure 1.

Relative expression of abaecin and hymenoptaecin in unchallenged (control) and challenged larvae from colonies ranging in level of genetic diversity. There was no significant relationship for relative expression and mating frequency for either gene based on linear regressions (hymenoptaecin—unchallenged: R² = 0.002, p = 0.48; challenged: R² = 0.009, p = 0.16; abaecin—unchallenged: R² = 0.002, p = 0.61; challenged: R² = 0.003, p = 0.49).

Figure 2.

Intracolony variance in hymenoptaecin expression after challenge with American foulbrood decreases as genetic diversity increases, with each point indicating the variance among samples from a single colony (R² = 0.14, p = 0.04).