Mixing Genetically and Morphologically Distinct Populations in Translocations: Asymmetrical Introgression in A Newly Established Population of the Boodie (Bettongia lesueur)

Abstract

The use of multiple source populations provides a way to maximise genetic variation and reduce the impacts of inbreeding depression in newly established translocated populations. However, there is a risk that individuals from different source populations will not interbreed, leading to population structure and smaller effective population sizes than expected. Here, we investigate the genetic consequences of mixing two isolated, morphologically distinct island populations of boodies (Bettongia lesueur) in a translocation to mainland Australia over three generations. Using 18 microsatellite loci and the mitochondrial D-loop region, we monitored the released animals and their offspring between 2010 and 2013. Despite high levels of divergence between the two source populations (FST = 0.42 and ϕST = 0.72), there was clear evidence of interbreeding between animals from different populations. However, interbreeding was non-random, with a significant bias towards crosses between the genetically smaller-sized Barrow Island males and the larger-sized Dorre Island females. This pattern of introgression was opposite to the expectation that male–male competition or female mate choice would favour larger males. This study shows how mixing diverged populations can bolster genetic variation in newly established mammal populations, but the ultimate outcome can be difficult to predict, highlighting the need for continued genetic monitoring to assess the long-term impacts of admixture.

Population Genomics of Bettongia lesueur: Admixing Increases Genetic Diversity with no Evidence of Outbreeding Depression

“…According to the decision tree for outbreeding depression published by Frankham et al [28], the risk of outbreeding depression in this translocation population is high due to the absence of gene flow between the two subspecies in the last 500 years. A previous study on the early state of this translocation using microsatellite markers and mitochondrial DNA found higher levels of genetic diversity in the mixed Matuwa population relative to one founder population (Shark Bay), but not the other (Barrow Island) [45]. They also detected asymmetrical introgression between the two sub-species due to higher than expected crosses between smaller-sized Barrow Island males and larger-sized Shark Bay females [45].…”

“…A previous study on the early state of this translocation using microsatellite markers and mitochondrial DNA found higher levels of genetic diversity in the mixed Matuwa population relative to one founder population (Shark Bay), but not the other (Barrow Island) [45]. They also detected asymmetrical introgression between the two sub-species due to higher than expected crosses between smaller-sized Barrow Island males and larger-sized Shark Bay females [45].…”

“…Genomic DNA was extracted from the biopsied ear tissue by the ‘salting-out’ method [48] with a modification of 10 mg/mL Proteinase K being added to 300 µL TNES and incubated at 56 ℃ [45]. Extracts were quantified using Qubit Fluorometric Quantitation as per manufacturer’s instructions.…”

“…The long-term geographical isolation (over 8000 years) and genetic distinctness [45] between the B. lesueur subspecies raises concerns regarding whether the admixing of these source populations will result in a single randomly mating population with no deleterious effects on fitness. According to the decision tree for outbreeding depression published by Frankham et al [28], the risk of outbreeding depression in this translocation population is high due to the absence of gene flow between the two subspecies in the last 500 years.…”

Genetic monitoring of the greater stick-nest rat meta-population for strategic supplementation planning

“…Establishing gene flow between isolated populations through supplementation (also termed 'reinforcement') can also improve or maintain the genetic diversity of small populations (Margan et al 1998). This has been demonstrated in species such as the alpine ibex (Capra ibex; Biebach and Keller 2012), boodie (Bettongia lesueur; Thavornkanlapachai et al 2019), mountain pygmy possum (Burramys parvus; Weeks et al 2017), Florida panther (Puma concolor coryi; Pimm et al 2006) and Tasmanian devil (Sarcophilus harrisii, McLennan et al 2020). However, assisted gene flow through translocations can be laborious and costly to sustain (Frankham et al 2017).…”