The developmental stress hypothesis: A special case of the evolution of condition-dependent sexual traits

The idea that sexually selected traits might be condition dependent is far from novel (Zahavi 1975); however, the developmental stress hypothesis was proposed as a special case because of a highly plausible mechanism: the development of the neural circuits controlling song output coincides with a period of time during which developing birds are likely to be susceptible to stress. The elegant aspect of the hypothesis is that the mechanism is defined and effects can be readily tested (Nowicki et al. 1998; Buchanan et al. 2003). Compared with more general hypotheses about the evolution of condition-dependent sexual traits (Buchanan 2000), the second particularly interesting aspect of the developmental stress hypothesis is that, in some species, individuals may suffer historical markers of stress. This is because in species with a fixed period for neural growth and song learning, there is no possibility for compensation in later life for stress experienced during early development. Females using such a marker of stress may benefit by obtaining a partner whose other cognitive functions have not been impaired by stress.