Abstract Summary
Nurseries are limited in the numbers of coral genets (fragments originating from the same colony) they can propagate, raising questions as to whether the genetic diversity of natural populations is adequately represented, and whether sexual propagation of these limited individuals will result in excessive inbreeding. Additional concerns arise when considering assisted gene flow: transplanting individuals from distant locations could lead to outbreeding depression, a decrease in fitness of the next generation due to the swamping of locally adaptive genetic variants with maladaptive foreign ones. Here, we present results suggesting that these issues are not as problematic as they seem. Based on existing population genetic data, we show that collecting as few as 3-4 individual corals is sufficient to capture the majority of common genetic diversity within a population. Such a low per-population effort also facilitates collections from multiple populations spanning a range of environments. For the long-term genetic success of restoration efforts, it is imperative for outplanted corals to breed with each other and with local corals. It is therefore essential to keep track of the genetic origin of nursery-propagated fragments to ensure outplanting of genetically diverse coral groups capable of cross-fertilization. For nurseries equipped to breed, another option would be to generate crosses within nurseries and outplant offspring. Given that coral populations are generally highly genetically diverse, the potential risk of inbreeding is low in these first-generation offspring. Finally, a simulation analysis indicates that introducing ~0.1-1% of foreign corals into a local population would ensure efficient transfer of adaptive genetic diversity while greatly lowering the risk of outbreeding depression.
