To mix or not to mix the sources of relocated plants? The case of the endangered Iris lortetii

Active management of endangered species is required for the persistence of many rare species. Species translocation, a common practice used to mitigate the negative effects of small population sizes, entails risks of outbreeding depression due to dilution of local adaptations, and therefore must be weighed against the costs of a hands-off conservation approach. Iris lortetii is an endangered rhizomatous plant, growing in a small number of isolated populations in northern Israel. We implemented a quasi-in-situ reintroduction program by planting 234 rhizomes from diverse origins in five new sites. All new sites were selected to be as similar as possible to those of the largest natural population. We recorded plant survival and flowering in the field after four years. Flowering plants were artificially crossed either with plants from the same population of origin (within population) or with plants from different origin (between populations). We found no differences in survival between populations of origin and only some indication of local adaptations in the form of increased flowering of the local population. Nonetheless, seed set was significantly higher (a 73% increase) in crosses between populations of origin, compared to within-population crosses, suggesting low genetic diversity within the natural populations. The ability to combine active conservation with rigid testing of theoretical hypothesis, while avoiding all risk to natural populations, highlights the value of the quasi-in-situ approach for restoration. Our results indicate that, in the case of Iris lortetii, active relocation of genotypes, seeds or pollen can enhance the survival of natural populations over time.