bioRxiv | 2019
Divergent population recovery trajectories following sex-biased perturbation in life history traits
Abstract
Uncertainty in risks posed by emerging stressors such as synthetic hormones impedes the management and conservation of threatened and endangered long-lived vertebrate populations. Synthetic hormones often induce sex-biased perturbations in exposed animals by disrupting gonad development and early life-history stage transitions, threatening population persistence. We use a spatially-explicit biophysical model to evaluate how sex-biased perturbations in life history traits of individuals (maternal investment in egg production and sex determination) modulate year class strength and population recovery trajectories of a long-lived, migratory fish– shovelnose sturgeon (Scaphirhynchus platorynchus)–under spatially and temporally dynamic synthetic androgen exposure. Simulations revealed that reduced efficiency of maternal energetic investment in gonad development prolonged maturation time, increased the probability of skipped spawning, and, in turn, gradually shrunk spawner biomass, ultimately weakening year class strength and extending recovery time at higher exposure. Demographic perturbation in individuals emerged as vastly different population projection and recovery trajectories: the responses to skewed sex allocation were delayed at the population level by more than two decades, followed by an abrupt shift in year class strength and population size, ultimately reaching an alternate state without any sign of recovery. When energetics and demographics were both perturbed, they acted antagonistically, allowing the population to gradually recover without reaching a stable state. The emergent patterns in long-term population projections suggest the complexity of cumulative effects of sex-biased perturbation in life history traits of individuals exposed to low-level (often below detection) synthetic hormones, which can be further obscured by lagged responses and environmental stochasticity. Our study illustrates that the recovery from skewed sex allocation can pose greater conservation challenges than diminished maternal investment in egg production–highlighting the importance of population monitoring for restoring depleted long-lived populations such as Scaphirhynchus sturgeon in ever-changing large rivers.