Fig. 3.

Incorporating leptin into SIR models. Individuals with higher fat stores and thus elevated leptin levels (top panel) have enhanced immune responses, are less susceptible and therefore less likely to become infectious (indicated by the thin arrow). Similarly, infectious animals with high leptin are more likely to recover quickly due to more robust immune defense and thus there would be a smaller window of time during which to transmit a pathogen to conspecifics (indicated by the thick arrow). Alternatively, animals with lower fat reserves and leptin levels are more likely to be susceptible and a larger number of these individuals will become infectious (indicated by the thick arrow). These same animals, once infectious, are also less likely to recover due to reduced immune defenses (indicated by the thin arrow).