Biodiversity decline and genetic erosion are among the most challenging conservation issues. Genetic admixture, the mixing of two or more genetically differentiated populations, can increase genetic diversity of admixed individuals. However, genetic admixture for conservation purposes is rare due to concerns over outbreeding depression, loss of local adaptations and scepticism regarding the benefits of mixing populations. We used an introduced population of Tasmanian devils (Sarcophilus harrisii) descended from two genetically differentiated source populations to illustrate the benefits of genetic admixture for translocation programs. Devils are endangered due to an infectious cancer causing 80% population declines across their range since disease emergence in 1996. Devil populations are known to be structured on an east-west cline across Tasmania. As part of their conservation management, devils were introduced to Maria Island, Tasmania in an assisted colonisation in 2012 with supplementations in 2013 and 2017. Of the released individuals (N = 34), 23 were western (13M; 10F), four were eastern (4F), and seven were of mixed origin (2M; 5F). The genetic composition of devils born on Maria Island (N = 185) was examined using 927 SNP loci. Using a reconstructed pedigree for each individual, we examined the proportion of founding origin (east, west or mixed) and used Shannon’s Diversity Index to quantify the evenness of founder origin. Individuals with mixed origins (N = 102) had higher genetic diversity than purebred individuals (N = 83), and increased evenness of founder origin was positively correlated with genetic diversity. Increased genetic diversity had no influence on reproductive success. For a genetically depauperate species, mixing individuals descended from differentiated populations, resulted in increased diversity in subsequent generations. This finding permits conservation managers to select individuals for translocation that produce offspring with higher genetic diversity, creating high-diversity source populations that can be used when augmenting other declining wild populations.

This file contains 1) the genotypes of 290 Tasmanian devils generated using reduced representation sequencing, 2) the founder origins of 185 Tasmanian devils living on an offshore island including individual standardised heterozygosity calculated using the GenHet package for R, 3) the number of offspring produced by each resident Tasmanian devil on the island over their lifetime, 4) a binary response as to whether each devil bred in a given year on the island, and 5) the number of offpsring produced by each devil on the island annually.