Genetic rescue: a critique of the evidence supports maximizing genetic diversity rather than minimizing the introduction of putatively harmful genetic variation

Genetic rescue – ameliorating inbreeding depression and restoring genetic diversity of inbred populations through gene flow - is valuable in wildlife conservation. Empirically validated recommendations for genetic rescue supported by evolutionary genetics theory advise maximizing genetic diversity in target populations. Instead, recent papers based on genomic studies of island foxes, Isle Royal wolves, and simulation modeling claim it would be preferable to minimize introduction of harmful variation by avoiding genetic rescue altogether or by selecting partially-inbred sources presumed to have fewer harmful alleles. We examined the assertions and evidence underlying these new recommendations. The claim that long-term persistence of a few small inbred populations invalidates the small population paradigm commits the survivorship fallacy by ignoring population extinctions through inbreeding. The claim that island foxes show no inbreeding depression conflicts with elevated levels of putatively harmful alleles, low fecundity, and island-specific disease susceptibilities. The claim that the history of Isle Royale wolves represents likely outcomes of genetic rescues using immigrants from larger source populations is invalid: the unplanned addition of a single male to an inbred population capped at ~25 individuals does not represent sound genetic rescue. The simulations in Robinson et al. (2018, 2019) and Kyriazis et al. (2019 pre-print) apply several unrealistic assumptions and parameter distributions that disfavor large, outbred sources for genetic rescue. Accordingly, the simulations' conclusions conflict profoundly with those of >120 meta-analysed real datasets, and do not overturn current empirically validated recommendations to maximize genetic diversity in the target population.