Biochemical and evolutionary interactions between mitochondrial and nuclear genomes (‘mitonuclear interactions’) are proposed evolutionary drivers of sexual reproduction, sexual selection, adaptation, and speciation. We investigated the role of pre-mating isolation in maintaining functional mitonuclear interactions in wild populations bearing diverged proposed co-adapted mitonuclear genotypes. Two lineages of eastern yellow robin Eopsaltria australis—putatively climate-adapted to ’inland’ and ‘coastal’ climates—differ by ~7% of mitochondrial DNA positions, whereas nuclear genome differences are concentrated into a sex-linked region enriched with genes with mitochondrial functions. This pattern can be explained by female-linked selection accompanied by male-mediated gene flow across the narrow hybrid zone where the two lineages coexist. It remains unknown whether lineage divergence is driven by intrinsic incompatibilities (particularly in females, under Haldane’s rule), extrinsic incompatibilities, both, or other drivers. We tested whether lineage divergence could be facilitated by non-random mate-pairing with respect to partners’ mitolineage or nuclear Z sex-chromosome DNA sequences, which differ between the lineages. We used field-, Z-linked-, and mitolineage data from two locations where the lineages hybridize, to test whether females mate disproportionately with (1) males of their own mitolineage and/or bearing similar Z-linked variation, as might be expected if hybrids experience intrinsic incompatibilities, or (2) putatively locally-adapted males, as expected under environmental selection. Comparing field observations with simulations provided no evidence of non-random mating, thus the observed patterns consistent with reduced female gene flow likely occur post-mating. Future tests of female-biased mortality at different life stages and habitat selection may clarify any mechanisms of selection.

In a world where habitats are degrading and the climate is warming and becoming increasingly unpredictable, biodiversity conservation efforts and funding remain grossly inadequate. There is a clear need to shift from preserving small, remnant populations to a model of genetically connecting populations that recreate larger and more diverse populations in climate-secure environments. This is crucial to harness key evolutionary processes to promote species’ ability to adapt to changing environments and to increase the likelihood of population persistence. Here, we use the endangered Macquarie perch (Macquaria australasica) as a case study to develop a genetic strategy for metapopulation management aimed at promoting population growth and persistence. Macquarie perch habitat has been highly fragmented and remaining habitat is at risk of catastrophic degradation due to climate change. We integrate results of new and existing genetic analyses to illustrate how genetically depauperate populations can benefit from admixture, and how the outcomes of management interventions can be quantified through genetic monitoring. We also develop the pipeline JeDi (https://github.com/drobledoruiz/JeDi) for estimating unbiased genetic heterozygosity for individuals and populations (nucleotide diversity) from reduced-representation genome sequencing data. We use this pipeline to estimate baseline data for monitoring of Macquarie perch populations and show that combining two genetic sources of migrants during population restoration resulted in doubling of nucleotide diversity compared to either source. Genetic diversity estimated using our pipeline is comparable across studies, datasets and species, and suitable for evaluating the rate of global biodiversity change.

Identifying sex-linked markers in genomic datasets is important, because their analyses can reveal sex-specific biology, and their presence in supposedly neutral autosomal datasets can result in incorrect estimates of genetic diversity, population structure and parentage. But detecting sex-linked loci can be challenging, and available scripts neglect some categories of sex-linked variation. Here, we present new R functions to (1) identify and separate sex-linked loci in ZW and XY sex determination systems and (2) infer the genetic sex of individuals based on these loci. Two additional functions are presented, to (3) remove loci with artefactually high heterozygosity, and (4) produce input files for parentage analysis. We test these functions on genomic data for two sexually-monomorphic bird species, including one with a neo-sex chromosome system, by comparing biological inferences made before and after removing sex-linked loci using our function. We found that standard filters, such as low read depth and call rate, failed to remove up to 28.7% of sex-linked loci. This led to (i) overestimation of population FIS by ≤ 9%, and the number of private alleles by ≤ 8%; (ii) wrongly inferring significant sex-differences in heterozygosity, (iii) obscuring genetic population structure, and (iv) inferring ~11% fewer correct parentages. We discuss how failure to remove sex-linked markers can lead to incorrect biological inferences (e.g., sex-biased dispersal and cryptic population structure) and misleading management recommendations. For reduced-representation datasets with at least 15 known-sex individuals of each sex, our functions offer convenient, easy-to-use resources to avoid this, and to sex the remaining individuals.