Alternative forms of brook trout nest site selection alter modeled offspring thermal experience and emergence phenology in groundwater-influenced streambeds

Although incubation temperature strongly influences salmonid phenotypic variation, few studies have considered the effect of competition on nest site selection and the resultant embryonic thermal experience. We combined field observations and simulations of brook trout ( Salvelinus fontinalis) spawning across a groundwater-induced thermal mosaic to assess whether habitat selection could alter spawning patch-level offspring thermal experience. We first assessed whether wild brook trout exhibited spawning behaviors consistent with competition for limited habitat. Given a fixed thermal habitat template, we then simulated offspring incubation temperature and temperature-dependent emergence timing following random, observed, and purely size-structured habitat selection scenarios. Brook trout generally selected warmer nest locations, but temperatures varied widely (1.8–8.1 °C) due in part to competition-related behaviors: minimum nest temperatures declined as breeder density increased, larger fish used warmer nests, and nest reuse frequency increased with nest temperature. Consequently, the three habitat selection scenarios generated biologically meaningful differences in simulated patch-level incubation temperatures and emergence dates. Studies evaluating the phenotypic and phenological consequences of incubation temperature may therefore benefit from considering alternative nesting behaviors that may substantially influence offspring thermal experience within populations.