Abstract
Reinforcement translocations are increasingly utilised in conservation with the goal of achieving genetic rescue. However, concerns regarding undesirable results, such as genetic homogenisation or replacement, are widespread. One factor influencing translocation outcomes is the rate at which the resident and the introduced individuals interbreed. Consequently, post-release mate choice is a key behaviour to consider in conservation planning. Here we studied mating, and its consequences for genomic admixture, in the North Island brown kiwi Apteryx mantelli population on Ponui Island which was founded by two translocation events over 50 years ago. The two source populations used are now recognised as belonging to two separate management units between which birds differ in size and are genetically differentiated. We examined the correlation between male and female morphometrics for 17 known pairs and quantified the relatedness of 20 pairs from this admixed population. In addition, we compared the genetic similarity and makeup of 106 Ponui Island birds, including 23 known pairs, to birds representing the source populations for the original translocations. We found no evidence for size-assortative mating. On the contrary, genomic SNP data suggested that kiwi of one feather did not flock together, meaning that mate choice resulted in pairing between individuals that were less related than expected by random chance. Furthermore, the birds in the current Ponui Island population were found to fall along a gradient of genomic composition consistent with non-clustered representation of the two parental genomes. These findings indicate potential for successful genetic rescue in future Apteryx reinforcement translocations, a potential that is currently under utilised due to restrictive translocation policies. In light of our findings, we suggest that reconsideration of these policies could render great benefits for the future diversity of this iconic genus in New Zealand.
Highlights
Translocations are increasingly utilised in conservation management to reintroduce species within their former ranges, introduce them to new sites predicted to be suitable for them, or reinforce already existing populations (IUCN/SSC, 2013)
Our results suggest that A. mantelli do not mate assortatively with genetically or morphologically similar mates
Pairs were on average found to be less related than expected. This behaviour has the potential to work as a counterforce that reduces inbreeding in general (Walters et al, 1988; Nelson-Flower, 2009; Nelson-Flower et al, 2012; Riehl and Stern, 2015; Riehl, 2017), and, importantly, it suggests that interbreeding between resident and introduced kiwi after reinforcement translocations is likely
Summary
Translocations are increasingly utilised in conservation management to reintroduce species within their former ranges, introduce them to new sites predicted to be suitable for them, or reinforce already existing populations (IUCN/SSC, 2013). Mate choice will directly impact reinforcement translocation outcomes These translocations commonly involve the movement of individuals from a genetically distinct source into a target population. When such interventions result in a fitness increase and/or increased population growth rate, it is referred to as genetic rescue (Ingvarsson, 2001; Hedrick et al, 2011; Whiteley et al, 2015; Bell et al, 2019). Support is growing for genetic rescue being an effective conservation tool, especially for target populations showing symptoms of inbreeding depression (Weeks et al, 2011; Frankham, 2015; Whiteley et al, 2015; Bell et al, 2019; Ralls et al, 2020). Post translocation mate choice, and, the presence of assortative mating, has the potential to greatly affect the outcome of this type of management (Bradley et al, 2014; Engler et al, 2019)
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