Graphical model representing how resources allocated to reproduction between a host and its parasite may vary. The surface of the circle represents the absolute amount of available resources accumulated by the host. The white portion is the amount of resources used by the host to produce its descendants, whereas the gray portion is diverted by the parasite to produce its own descendants. (a) non infected host: all the resources accumulated by the host are used for its reproduction. (b) host infected with a fully compatible parasite: an arbitrary proportion (a third in this case) of the resources accumulated by the host is diverted toward parasite reproduction. (c) host infected with a parasite with partially incompatible interaction: a part of the resources accumulated by the host are lost (dotted part of the circle), for instance due to the activation of host defenses, or to the inefficiency of resources use by the parasite. (c) illustrates the particular case where the relative diversion of resources by the parasite is the same as in case (b), but the absolute reproduction of both protagonists is lower.