Genomic signatures of inbreeding depression for a threatened Aotearoa New Zealand passerine

For small and isolated populations, the increased chance of mating between related individuals can result in a substantial reduction in individual and population fitness. Despite the increasing availability of genomic data to measure inbreeding accurately across the genome, inbreeding depression studies for threatened species are still scarce due to the difficulty of measuring fitness in the wild. Here, we investigate inbreeding and inbreeding depression for the extensively monitored Tiritiri Mātangi island population of a threatened Aotearoa New Zealand passerine, the hihi (Notiomystis cincta). First, using a custom 45 k single nucleotide polymorphism (SNP) array, we explore genomic inbreeding patterns by inferring homozygous segments across the genome. Although all individuals have similar levels of ancient inbreeding, highly inbred individuals are affected by recent inbreeding, which can probably be explained by bottleneck effects such as habitat loss after European arrival and their translocation to the island in the 1990s. Second, we investigate genomic inbreeding effects on fitness, measured as lifetime reproductive success, and its three components, juvenile survival, adult annual survival and annual reproductive success, in 363 hihi. We find that global inbreeding significantly affects juvenile survival but none of the remaining fitness traits. Finally, we employ a genome-wide association approach to test the locus-specific effects of inbreeding on fitness, and identify 13 SNPs significantly associated with lifetime reproductive success. Our findings suggest that inbreeding depression does impact hihi, but at different genomic scales for different traits, and that purging has therefore failed to remove all variants with deleterious effects from this population of conservation concern

Assembly of female and male hihi genomes (stitchbird; Notiomystis cincta) enables characterization of the W chromosome and resources for conservation genomics

A high-quality reference genome can be a valuable resource for threatened species by providing a foundation to assess their evolutionary potential to adapt to future pressures such as environmental change. We assembled the genome of a female hihi (Notiomysits cincta), a threatened passerine bird endemic to Aotearoa New Zealand. The assembled genome is 1.06 Gb, and is of high quality and highly contiguous, with a contig N50 of 7.0 Mb, estimated QV of 44 and a BUSCO completeness of 96.8%. A male assembly of comparable quality was generated in parallel. A population linkage map was used to scaffold the autosomal contigs into chromosomes. Female and male sequence coverage and comparative genomics analyses were used to identify Z-, and W-linked contigs. In total, 94.6% of the assembly length was assigned to putative nuclear chromosome scaffolds. Native DNA methylation was highly correlated between sexes, with the W chromosome contigs more highly methylated than autosomal chromosomes and Z contigs. 43 differentially methylated regions were identified, and these may represent interesting candidates for the establishment or maintenance of sex differences. By generating a high-quality reference assembly of the heterogametic sex, we have created a resource that enables characterization of genome-wide diversity and facilitates the investigation of female-specific evolutionary processes. The reference genomes will form the basis for fine-scale assessment of the impacts of low genetic diversity and inbreeding on the adaptive potential of the species and will therefore enable tailored and informed conservation management of this threatened taonga (treasured) species

The design and application of a 50 K SNP chip for a threatened Aotearoa New Zealand passerine, the hihi

Next-generation sequencing has transformed the fields of ecological and evolutionary genetics by allowing for cost-effective identification of genome-wide variation. Single nucleotide polymorphism (SNP) arrays, or “SNP chips”, enable very large numbers of individuals to be consistently genotyped at a selected set of these identified markers, and also offer the advantage of being able to analyse samples of variable DNA quality. We used reduced representation restriction-aided digest sequencing (RAD-seq) of 31 birds of the threatened hihi (Notiomystis cincta; stitchbird) and low-coverage whole genome sequencing (WGS) of 10 of these birds to develop an Affymetrix 50 K SNP chip. We overcame the limitations of having no hihi reference genome and a low quantity of sequence data by separate and pooled de novo assembly of each of the 10 WGS birds. Reads from all individuals were mapped back to these de novo assemblies to identify SNPs. A subset of RAD-seq and WGS SNPs were selected for inclusion on the chip, prioritising SNPs with the highest quality scores whose flanking sequence uniquely aligned to the zebra finch (Taeniopygia guttata) genome. Of the 58,466 SNPs manufactured on the chip, 72% passed filtering metrics and were polymorphic. By genotyping 1,536 hihi on the array, we found that SNPs detected in multiple assemblies were more likely to successfully genotype, representing a cost-effective approach to identify SNPs for genotyping. Here, we demonstrate the utility of the SNP chip by describing the high rates of linkage disequilibrium in the hihi genome, reflecting the history of population bottlenecks in the species

Evolution of flower color pattern through selection on regulatory small RNAs

Small RNAs (sRNAs) regulate genes in plants and animals. Here, we show that population-wide differences in color patterns in snapdragon flowers are caused by an inverted duplication that generates sRNAs. The complexity and size of the transcripts indicate that the duplication represents an intermediate on the pathway to microRNA evolution. The sRNAs repress a pigment biosynthesis gene, creating a yellow highlight at the site of pollinator entry. The inverted duplication exhibits steep clines in allele frequency in a natural hybrid zone, showing that the allele is under selection. Thus, regulatory interactions of evolutionarily recent sRNAs can be acted upon by selection and contribute to the evolution of phenotypic diversity

Los orígenes de un nuevo gen de diseño de alas de mariposa dentro de una familia de reguladores conservados del ciclo celular

A major challenge in evolutionary biology is to understand the origins of novel structures. The wing patterns of butterflies and moths are derived phenotypes unique to the Lepidoptera. Here we identify a gene that we name poikilomousa (poik), which regulates colour pattern switches in the mimetic Heliconius butterflies. Strong associations between phenotypic variation and DNA sequence variation are seen in three different Heliconius species, in addition to associations between gene expression and colour pattern. Colour pattern variants are also associated with differences in splicing of poik transcripts. poik is a member of the conserved fizzy family of cell cycle regulators. It belongs to a faster evolving subfamily, the closest functionally characterised orthologue being the cortex gene in Drosophila, a female germ-line specific protein involved in meiosis. poik appears to have adopted a novel function in the Lepidoptera and become a major target for natural selection acting on colour and pattern variation in this group

Molecular and genetic variation underlying the evolution of flower colour in Antirrhinum

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Genetic architecture and balancing selection: the life and death of differentiated variants

International audienceBalancing selection describes any form of natural selection, which results in the persistence of multiple variants of a trait at intermediate frequencies within populations. By offering up a snapshot of multiple co-occurring functional variants and their interactions , systems under balancing selection can reveal the evolutionary mechanisms favouring the emergence and persistence of adaptive variation in natural populations. We here focus on the mechanisms by which several functional variants for a given trait can arise, a process typically requiring multiple epistatic mutations. We highlight how balancing selection can favour specific features in the genetic architecture and review the evolutionary and molecular mechanisms shaping this architecture. First, balancing selection affects the number of loci underlying differentiated traits and their respective effects. Control by one or few loci favours the persistence of differentiated functional variants by limiting intergenic recombination, or its impact, and may sometimes lead to the evolution of supergenes. Chromosomal rearrangements, particularly inversions, preventing adaptive combinations from being dissociated are increasingly being noted as features of such systems. Similarly, due to the frequency of heterozy-gotes maintained by balancing selection, dominance may be a key property of adaptive variants. High heterozygosity and limited recombination also influence associated genetic load, as linked recessive deleterious mutations may be sheltered. The capture of deleterious elements in a locus under balancing selection may reinforce polymor-phism by further promoting heterozygotes. Finally, according to recent genomewide scans, balanced polymorphism might be more pervasive than generally thought. We stress the need for both functional and ecological studies to characterize the evolutionary mechanisms operating in these systems