Food stoichiometry affects the outcome of Daphnia-parasite interaction

Abstract

Phosphorus (P) is an essential nutrient for growth in consumers. P-limitation and parasite infection comprise one of the most common stressor pairs consumers confront in nature. We conducted a life-table study using a Daphnia-microsporidian parasite model, feeding uninfected or infected Daphnia with either P-sufficient or P-limited algae, and assessed the impact of the two stressors on life-history traits of the host. Both infection and P-limitation negatively affected some life-history traits tested. However, under P-limitation, infected animals had higher juvenile growth rate as compared with uninfected animals. All P-limited individuals died before maturation, regardless of infection. The numbers of spore clusters of the microsporidian parasite did not differ in P-limited or P-sufficient hosts. P-limitation, but not infection, decreased body phosphorus content and ingestion rates of Daphnia tested in separate experiments. As parasite spore production did not suffer even under extreme P-limitation, our results suggest that parasite was less limited by P than the host. We discuss possible interpretations concerning the stoichiometrical demands of parasite and suggest that our results are explained by parasite-driven changes in carbon (C) allocation of the hosts. We conclude that the impact of nutrient starvation and parasite infection on consumers depends not only on the stoichiometric demands of host but also those of the parasite.

Keywords: Ecological stoichiometry; P-deficiency; host–parasite interaction; microsporidian; multiple stressors.

Figure 1

Water flea Daphnia magna.

Figure 2

Mean (±SE) juvenile growth rate (g_j) (A) and growth until maturation (g_m) (B) in response to infection status and food quality. Sample sizes (number of Daphnia measured) are indicated above the bars.

Figure 3

The growth of Daphnia magna over time for P-sufficient (filled dots), infected P-sufficient (open dots), P-limited (filled triangles), and infected P-limited (open triangles) treatments (A). Due to the large scale in panel (A) hiding the difference between the P-limited treatments, the growth curves for P-limited (filled triangles) and infected P-limited (open triangles) are presented (B). Means ± SE are depicted.

Figure 4

Mean (±SE) production age for each clutch (A) and size of the clutch for each clutch (B) in uninfected and infected P-sufficient individuals. Sample sizes (number of Daphnia measured) are indicated above the bars.

Figure 5

Percent of Daphnia magna hosts surviving over time between P-sufficient (filled dots), infected P-sufficient (open dots), P-limited (filled triangles), and infected P-limited (open triangles) treatments.

Figure 6

Mean (±SE) spore load in infected P-sufficient and P-limited Daphnia magna individuals. Sample sizes (number of Daphnia measured) are indicated above the bars.

Figure 7

Mean (±SE) body P content (A) and ingestion rate (B) in response to infection status and food quality. Sample sizes (number of replicates measured) are indicated above the bars.