Multi-generational genetic consequences of reinforcement in a bird metapopulation

Peter S Ranke,Bernt-Erik Sæther,Henrik Jensen,Henrik Pärn,Sigrun Skjelseth,Åsa Alexandra Borg Pedersen,Ingerid Julie Hagen,Thor Harald Ringsby,Anna Maria Billing

doi:10.1007/s10592-020-01273-7

Abstract

Translocation of conspecific individuals to reduce extinction risk of small, isolated populations and prevent genetic depletion is a powerful tool in conservation biology. An important question is how the translocated individuals influence the long-term genetic composition of the recipient population. Here, we experimentally reinforced a house sparrow (Passer domesticus) population, and examined the impact of this translocation on allele frequencies, levels of heterozygosity and genetic differentiation over six cohorts. We found no permanent increase in the mean number of alleles across loci or levels of observed heterozygosity, but a few alleles private to the translocated individuals remained in the population and we found a short-term increase in heterozygosity. Consequently, genetic differentiation of the recipient population compared to the genetic composition prior to reinforcement was small. The limited genetic impact was due to combined effects of a small probability of establishment and low mating success for the translocated individuals, together with increased genetic drift in the recipient population. Our findings emphasize the importance of selection and genetic drift as forces that may decrease the genetic contribution of reinforcement, especially in small populations. Conservation managers should aim to improve habitat quality in the recipient population to reduce genetic drift following translocation and thereby avoid the need for continued reinforcement. Furthermore, by facilitating establishment success and selecting individuals expected to have high mating success, possibly indicated by sexually selected traits, genetic contribution of released individuals is increased which in turn will decrease reproductive skew and genetic drift.

Highlights

Human-induced habitat destruction and over-harvesting are important causes for population declines and threats to biodiversity (Clavero and García-Berthou 2005; Haddad et al 2015)
Small and isolated populations are strongly influenced by genetic drift (Wright 1931; Frankham et al 2011) and increased levels of inbreeding (Keller and Waller 2002), which may decrease levels of heterozygosity, reduce fitness (Charlesworth and Charlesworth 1999), and increase extinction risk (Saccheri et al 1998; Willi et al 2006)
The small genetic differences between the source and resident populations (Fig. 4; Online Appendix B) are likely a result of genetic drift counteracted by low levels of gene flow (Holand et al 2011)

Summary

Introduction

Human-induced habitat destruction and over-harvesting are important causes for population declines and threats to biodiversity (Clavero and García-Berthou 2005; Haddad et al 2015). Immigration may introduce novel alleles (Hansson et al 2000; Keller et al 2001), increase genetic variation (Willi et al 2006), and decrease levels of inbreeding in receiver populations (Keller et al 2001; Vilà et al 2003). Survival and heterozygosity increased following reinforcement in Florida panther (Puma concolor coryi) (Johnson et al 2010). Such examples of genetic rescue from reinforcement in conservation are still few (Frankham et al 2014; Frankham 2015). Experimentally derived information complementing knowledge from conservation is important for our understanding of long-term genetic consequences of reinforcements

Methods

Results

Conclusion