Bumble-bee foragers infected by a gut parasite have an impaired ability to utilize floral information

Abstract

Parasitic infection can influence a variety of behavioural mechanisms in animals, but little is known about the effects of infection on the cognitive processes underlying ecologically relevant behaviours. Here, we examined whether parasitic infection alters cognitive aspects of foraging in a social insect, the bumble-bee (Bombus impatiens). In controlled experiments, we assessed the ability of foraging bees to discriminate rewarding from non-rewarding flowers on the basis of colour and odour. We found that natural and experimental infection by a protozoan parasite (Crithidia bombi, which lives exclusively within the gut tract), impaired the ability of foragers to learn the colour of rewarding flowers. Parasitic infection can thus disrupt central nervous system pathways that mediate cognitive processes in bumble-bees and as a consequence, can reduce their ability to monitor floral resources and make economic foraging decisions. It is postulated that this infection-induced change to cognitive function in bumble-bees is the result of communication between immune and nervous systems. Parasitized animals, including invertebrates, can therefore show subtle behavioural changes that are nonetheless ecologically significant and reflect complex mechanisms.

Figure 1

The results of experiment 1 plotted as mean proportion of correct flower choices per block of 30 consecutive flower visits for infected (n=12; open circles) and uninfected (n=10 filled circles) bumble-bees. A correct choice is defined as a visit to a colour–odour combination containing sucrose reward. Error bars indicate standard error of the mean.

Figure 2

The results of experiment 1 plotted as mean proportion of choices to flowers of the correct colour and odour per block of 30 consecutive flower visits for infected (n=12) and uninfected (n=10) bumble-bees. A correct choice is defined as a visit to a flower containing sucrose reward. Error bars indicate standard error of the mean.

Figure 3

The results of experiment 2 plotted as mean proportion of correct flower choices per block of 10 consecutive flower visits for bumble-bees in the infected (n=14; open circles) and control (n=8 filled circles) treatments. A correct choice is defined as a visit to a colour containing sucrose reward. Values were adjusted for the effects of bee size. Error bars indicate standard error of the mean.