Fig. 2.

Defining adaptive death. Top panel, true adaptive death. Here death of an individual increases its fitness through effects on inclusive fitness and / or by increasing fitness of a super-organism (e.g. S. cerevisiae colony) or organism (e.g. cells within an organism). Three forms of adaptive death are defined. Adaptive death is typically envisaged as consumer sacrifice; here two possible additional forms of adaptive death are defined. As potential examples: biomass sacrifice, S. cerevisiae where programmed cell death may support growth elsewhere in the yeast colony through release of nutrients (Váchová et al., 2012); defensive sacrifice, Leishmania spp., where programmed cell death of protozoan parasites under immune defense may blunt the host immune response against kin (Zangger et al., 2002). Colors represent fitness changes; red, cost; green, gain. Bottom panel, false adaptive death. Here death is a consequence of behaviors that increase inclusive fitness, but is not in itself adaptive. The difference between false adaptive death and other forms of fitness vs lifespan trade offs is only that death occurs immediately as a consequence of fitness-promoting behavior. As potential examples: "biomass sacrifice", matriphagy in black lace-weaver spiders; "defensive sacrifice", hive defense by honey bees, where stinging behavior is fatal to the deliverer.