Subspecies hybridization as a potential conservation tool in species reintroductions

Abstract

Reintroductions are a powerful tool for the recovery of endangered species. However, their long‐term success is strongly influenced by the genetic diversity of the reintroduced population. The chances of population persistence can be improved by enhancing the population's adaptive ability through the mixing of individuals from different sources. However, where source populations are too diverse the reintroduced population could also suffer from outbreeding depression or unsuccessful admixture due to behavioural or genetic barriers. For the reintroduction of Asiatic wild ass Equus hemionus ssp. in Israel, a breeding core was created from individuals of two different subspecies (E. h. onager & E. h. kulan). Today the population comprises approximately 300 individuals and displays no signs of outbreeding depression. The aim of this study was a population genomic evaluation of this conservation reintroduction protocol. We used maximum likelihood methods and genetic clustering analyses to investigate subspecies admixture and test for spatial autocorrelation based on subspecies ancestry. Further, we analysed heterozygosity and effective population sizes in the breeding core prior to release and the current wild population. We discovered high levels of subspecies admixture in the breeding core and wild population, consistent with a significant heterozygote excess in the breeding core. Furthermore, we found no signs of spatial autocorrelation associated with subspecies ancestry in the wild population. Inbreeding and variance effective population size estimates were low. Our results indicate no genetic or behavioural barriers to admixture between the subspecies and suggest that their hybridization has led to greater genetic diversity in the reintroduced population. The study provides rare empirical evidence of the successful application of subspecies hybridization in a reintroduction. It supports use of intraspecific hybridization as a tool to increase genetic diversity in conservation translocations.

Mixed Mating in a Multi-Origin Population Suggests High Potential for Genetic Rescue in North Island Brown Kiwi, Apteryx mantelli

“…We agree with other recent publications stressing that behaviour in the context of conservation needs more attention (Caro and Sherman, 2011;Renan et al, 2018;Zecherle et al, 2021). Consequently, we hope that this case study can contribute to the ongoing discussions concerning (1) attempting genetic rescue, (2) identifying suitable source populations for translocations, (3) the usefulness of genomics and epigenomics to take behavioural research to a population level and add a temporal scale, (4) how knowledge of social behaviour post translocations is important for appropriate conservation management design, and (5) how conservation management plans would benefit from incorporating the opportunity to express the full range of natural behaviours as an explicit goal and a part of how conservation success is defined.…”

“…Firstly, it is indicative of a post translocation behaviour that has the potential to increase the speed of admixture between genetically distinct groups, and this rate of admixture is directly linked to the potential for genetic rescue. Mate choice and mating system will drastically impact translocation outcomes (Anthony and Blumstein, 2000;Renan et al, 2018;Zecherle et al, 2021). Promiscuity, polygamy, and/or consecutive alteration of breeding units will all potentially increase the speed of admixture and reduce the long-term impact of initial mating after translocation events (Sander et al, 1997).…”

“…Hesitation toward translocations between genetically distinct lineages (populations, subspecies, or species) remains widespread. This is despite the fact that an increasing number of empirical studies, theoretical studies, and meta-studies suggests that admixture reduces genetic load and symptoms of inbreeding depression, increases heterozygosity and genetic diversity, boosts resilience and recovery rates, and can introduce favourable genetic variation that can increase the ability to cope with change especially in a situation of environmental change (Frankham et al, 2011;Weeks et al, 2011;Frankham, 2015;Jamieson, 2015;Whiteley et al, 2015;Ralls et al, 2018;Zecherle et al, 2021). An interesting parallel to the A. mantelli population on Ponui Island is the population of burrowing bettongs (or boodie, Bettongia lesuer) in Matuwa (Western Australia).…”

“…Further studies are needed into the mechanisms of genetic rescue and outbreeding depression to increase the predictability of translocation outcomes (Undin et al, 2021b). In relation to behaviour, particular focus is needed to elucidate the effects of source site identity, translocation timing, number of individuals released, as well as population density for post translocation on mate choice and thus on the rate of admixture (see further Zecherle et al, 2021).…”

Positive selection in gamete interaction proteins inCarnivora

“…Conservation of these key proteins between such species would represent an advantage in challenging times and even save them from extinction. Moreover, the use of hybridization as a way to rapidly increase genetic diversity in a waning population or in reintroduction programs can serve as an effective tool in conservation efforts (Zecherle et al, 2021) and would, in some cases, even be useful to save a highly endangered species from extinction. This, of course, brings up an interesting debate in the field of species conservation as it transgresses a purist conception of a species identity and involves the concept of hybridization-induced-extinction (Todesco et al, 2016).…”