To breed or not to breed? Maintaining genetic diversity in white sturgeon supplementation programs

Conservation-focused reintroduction or supplementation programs using wild-born individuals tend to be more successful than those based on release of captive-born individuals. Negative genetic consequences of captive breeding, such as genetic diversity loss, domestication selection, and inbreeding, may contribute to this lowered success. In this study, we compare genetic consequences of repatriation, or collection of wild-born juveniles for captive rearing and release, and broodstock-based breeding, where wild adults are bred in captivity, in a conservation program for white sturgeon, Acipenser transmontanus. Specifically, we use microsatellite markers to compare the genetic diversity and number of spawners, Nₛ, represented by each captive breeding strategy. We present a novel method to estimate Nₛ in which simulated known family configurations of varying complexity are used to identify appropriate inclusive and exclusive probability thresholds in the maximum likelihood-based pedigree reconstruction program Colony. These probability thresholds are then applied to reconstruct progeny arrays and estimate Nₛ in empirical datasets of two repatriation cohorts and a naturally produced year class. We find that a repatriation approach preserves more genetic diversity and represents more spawners than broodstock-based captive breeding. Furthermore, a repatriation approach represents levels of genetic diversity similar to those found in a wild cohort. These results are the first comparison of Nₛ between broodstock and repatriation-based methods with respect to a hatchery program, and provide evidence that when possible, repatriation can be a more effective strategy for conserving genetic diversity than broodstock-based breeding for supplementation and reintroduction