Genomic Screening Reveals That the Endangered Eucalyptus paludicola (Myrtaceae) Is a Hybrid

Abstract

A hybrid origin for a conservation listed taxon will influence its status and management options. Here, we investigate the genetic origins of a nationally endangered listed taxon—Eucalyptus paludicola—a tree that is restricted to the Fleurieu Peninsula and Kangaroo Island of South Australia. Since its description in 1995, there have been suggestions that this taxon may potentially be a stable hybrid species. Using a high throughput sequencing approach, we developed a panel of polymorphic loci that were screened across E. paludicola and its putative parental species E. cosmophylla and E. ovata. Bayesian clustering of the genotype data identified separate groups comprising E. ovata and E. cosmophylla while E. paludicola individuals were admixed between these two, consistent with a hybrid origin. Hybrid class assignment tests indicate that the majority of E. paludicola individuals (~70%) are F1 hybrids with a low incidence of backcrossing. Most of the post-F1 hybrids were associated with revegetation sites suggesting they may be maladapted and rarely reach maturity under natural conditions. These data support the hypothesis that E. paludicola is a transient hybrid entity rather than a distinct hybrid species. We briefly discuss the conservation implications of our findings.