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The relationship between the genetic (cM) and the physical (Mb) position of markers in the best-order map built based on the draft sequence of the zebra finch genome. Red and blue circles indicate the female- and male-specific genetic map, respectively. The length of the x -axis reflects the total physical size of the chromosome, as given by the genome assembly. Only chromosomes with > 10 markers are included.
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Understanding the causes and consequences of variation in the rate of recombination is essential since this parameter is considered to affect levels of genetic variability, the efficacy of selection, and the design of association and linkage mapping studies. However, there is limited knowledge about the factors governing recombination rate variatio...
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... one other marker in a two-point analysis. The resulting framework map consisted of 32 different linkage groups ranging from 0 to 118 cM. It contained 443 markers and covered 1341 cM in total. Linkage groups were equivalent to chromosomes 1-28 (except for chromosome 22 that was not covered in our analysis), plus the Z chromosome (Sup- plemental Fig. 2). Marker order in all linkage groups of the framework map was essentially identical to the order of markers in the physical assembly of the draft genome sequence. The only exceptions were TGU2, TGU26, and TGU28, which thus contain either assembly or linkage map errors; these chromosomes were ex- cluded from the subsequent analysis of ...
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... (Fig. 1). A closer inspection of the variation in recombination rate along chromosomes revealed a sharp increase toward telomeric regions. Moreover, there were extremely low rates of recombination in the central parts of the larger chromosomes, giving rise to a sigmoid relationship between the cumulative genetic length and physical position ( Fig. 2; Sup- plemental Figs. 2, 3). As an example, the two distal 15 Mb of chro- mosome TGU1A measured 42 and 41 cM, while the genetic dis- tance in the interior 44 Mb of this chromosome was only 6 cM. For microchromosomes (chromosomes <20 Mb) the rate of re- combination was uniformly high over the entire chromosome (Fig. 2), and was similar ...
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... length and physical position ( Fig. 2; Sup- plemental Figs. 2, 3). As an example, the two distal 15 Mb of chro- mosome TGU1A measured 42 and 41 cM, while the genetic dis- tance in the interior 44 Mb of this chromosome was only 6 cM. For microchromosomes (chromosomes <20 Mb) the rate of re- combination was uniformly high over the entire chromosome (Fig. 2), and was similar to the rate in distal parts of larger chromosomes (see below). It is also clear from the distribution that male and female rates show good concordance across most of the genome, although there is a lack of concordance in a small proportion of regions. Notably, the sharp increase in recombination toward chromosome ends ...
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... rates in the distal 5-20 Mb regions, with rates of 5-10 cM/Mb in megabase windows closest to chromosome ends, and extremely low rates in central parts of chromosomes. The combined effect leads to the peculiar sigmoid relationship between cumulative genetic distance and physical position along chromosomes observed in the larger chro- mosomes (Fig. 2). About 90% of the total amount of recom- bination in zebra finch is concentrated to »23% of the genome. For the three largest chromosomes (TGU1-TGU3), 110-150 Mb in size, the interior ''recombination desert'' extends over »100 Mb with an average rate as low as »0.1 cM/Mb over these long in- tervals. The extent of recombination deserts ...
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Citations
... Reliable tools for the detection of these chromosomes were developed that contributed to identifying chicken microchromosome syntenies across many avian groups . Indeed, until recently, the very smallest of the microchromosomes, the 'D group' (chromosomes [33][34][35][36][37][38][39] , had no sequences associated with them in the genome assembly (Figure 1a). Unlike research performed on mammalian chromosomes, hybridization across a greater evolutionary distance (i.e., beyond the phylogenetic Class) is possible with chicken chromosome paints. ...
... Further sequence analysis may reveal signature features of these chromosomes that may indicate a biological reason as to why these chromosomes are left intact. If there is any correlation with the size of the chromosomes and their lack of rearrangement, then this would suggest that the very smallest 'D-group' chicken microchromosomes (33)(34)(35)(36)(37)(38)(39) are also less prone to chromosomal fusion. In fact, upon the exclusion of the two most rearranged lineages (parrots and falcons), a discernible pattern emerges where species from various orders appear to have accumulated primarily species-specific microchromosomal rearrangements rather than a shared characteristic. ...
Subjects: Evolutionary Biology.
Contributors: Rebecca O'Connor, Rafael Kretschmer, Michael N. Romanov, Darren Griffin.
Birds (Aves) are the most speciose of terrestrial vertebrates, displaying Class-specific characteristics yet incredible external phenotypic diversity. Critical to agriculture and as model organisms, birds have adapted to many habitats. The only extant examples of dinosaurs, birds emerged ~150 mya and >10% are currently threatened with extinction. 1. Avian Biology and Its Importance With around 10,500 extant representatives, birds are the most species-rich of tetrapod vertebrates. Modern birds belong to the phylogenetic Class Aves and the subclass Neornithes. They are characterized by a combination of features not seen together in other vertebrates including homeothermy, flight (except for penguins, ratites and some others who have lost the ability), oviparity, nesting, the presence of a beak (without teeth), a high metabolic rate, feathers, and a lightweight skeleton. Occupying almost all terrestrial and many aquatic habitats, birds have adapted to a range of climate extremes from inland Antarctica to the tropics. The highest levels of species diversity is seen in tropical regions. The phenotypic diversity seen in birds is extraordinary; sizes range from the bee hummingbird (Mellisuga helena) at approximately 5 cm in length to the ostrich (Struthio camelus), which stands at over 2 m tall. Birds have a high core body temperature (39-41 °C), high blood glucose levels, and energy expenditure levels that are five or more times higher than those commonly seen in mammals. Comparisons with similar sized mammals show that birds tend to live longer, despite the higher energy use. Birds are social, with varying degrees of communication complexity including the use of calls and song (in some cases communicating by visual display); they can be socially cooperative, exhibiting behaviors such as flocking and mobbing. Most birds also provide an extended period of parental care that is often shared between parents and/or with other birds. Birds are critical to agriculture (both meat and eggs) and are also model organisms for studies of virology, immunology, and developmental biology, e.g., ; they can also be valuable companion animals for humans. From an evolutionary point of view, the Aves Class is the only extant example of the Dinosauria (Theropoda) clade, e.g., , sharing a common ancestor with mammals around 310 million years ago (mya). In addition, approximately 1400 extant birds (>10%) are currently listed as threatened with extinction, with over 160 species becoming extinct in the last 500 years. Many of these extinctions are considered to be a result of anthropogenic climate and habitat change, in particular due to the introduction of alien species such as rats into island habitats. Further understanding of birds from an evolutionary point.
... Reliable tools for the detection of these chromosomes were developed that contributed to identifying chicken microchromosome syntenies across many avian groups [132]. Indeed, until recently, the very smallest of the microchromosomes, the 'D group' (chromosomes [33][34][35][36][37][38][39] [20], had no sequences associated with them in the genome assembly (Figure 1a). At the time of writing, all chicken macro-and microchromosomes now have respective sequences assigned to them and are annotated thanks to the recent work of Huang et al. [133], although there are still 172 scaffolds to be placed or localized (Figure 1b). ...
... Reliable tools for the detection of these chromosomes were developed that contributed to identifying chicken microchromosome syntenies across many avian groups [131]. Indeed, until recently, the very smallest of the microchromosomes, the 'D group' (chromosomes [33][34][35][36][37][38][39] [20], had no sequences associated with them in the genome assembly (Figure 1a). At the time of writing, all chicken macro-and microchromosomes now have respective sequences assigned to them and are annotated thanks to the recent work of Huang et al. [132], although there are still 172 scaffolds to be placed or localized ( Figure 1b). ...
... Further sequence analysis may reveal signature features of these chromosomes that may indicate a biological reason as to why these chromosomes are left intact. If there is any correlation with the size of the chromosomes and their lack of rearrangement, then this would suggest that the very smallest 'D-group' chicken microchromosomes (33)(34)(35)(36)(37)(38)(39) [20] are also less prone to chromosomal fusion. In fact, upon the exclusion of the two most rearranged lineages (parrots and falcons), a discernible pattern emerges where species from various orders appear to have accumulated primarily species-specific microchromosomal rearrangements rather than a shared characteristic. ...
Birds (Aves) are the most speciose of terrestrial vertebrates, displaying Class-specific characteristics yet incredible external phenotypic diversity. Critical to agriculture and as model organisms, birds have adapted to many habitats. The only extant examples of dinosaurs, birds emerged ~150 mya and >10% are currently threatened with extinction. This review is a comprehensive overview of avian genome ("chromosomic") organization research based mostly on chromosome painting and BAC-based studies. We discuss traditional and contemporary tools for reliably generating chromosome-level assemblies and analyzing multiple species at a higher resolution and wider phylogenetic distance than previously possible. These results permit more detailed investigations into inter- and intrachromosomal rearrangements, providing unique insights into evolution and speciation mechanisms. The 'signature' avian karyotype likely arose~250 mya and remained largely unchanged in most groups including extinct dinosaurs. Exceptions include Psittaciformes, Falconiformes, Caprimulgiformes, Cuculiformes, Suliformes, occasional Passeriformes, Ciconiiformes, and Pelecaniformes. The reasons for this remarkable conservation may be the greater diploid chromosome number generating variation (the driver of natural selection) through a greater possible combination of gametes and/or an increase in recombination rate. A deeper understanding of avian genomic structure permits the exploration of fundamental biological questions pertaining to the role of evolutionary breakpoint regions and homologous synteny blocks.
... Interference affected the distribution of MLH1 foci along the SC1 in all species examined, as shown in Figure 6. The recombination landscapes of the SC1 of the cardueline finches are rather similar to those described in other birds analyzed both cytologically [23,46] and genetically [47,48]. Clear peaks of MLH1 foci are located at the SC ends while the pericentromeric area of most SCs contains few or no foci. ...
... Clear peaks of MLH1 foci are located at the SC ends while the pericentromeric area of most SCs contains few or no foci. [23,46] and genetically [47,48]. Clear peaks of MLH1 foci are located at the SC ends while the pericentromeric area of most SCs contains few or no foci. ...
... Species with regional and metapolycentromeres did not differ in the average distance to the centromere from the proximal MLH1 foci (Figure 7). [23,46] and genetically [47,48]. Clear peaks of MLH1 foci are located at the SC ends while the pericentromeric area of most SCs contains few or no foci. ...
Simple Summary
Meiotic recombination, which involves the reshuffling of genes, plays an important role in generating biodiversity. However, studies on this process in bird chromosomes are scarce. Using antibodies targeting proteins involved in recombination, we examined the number of recombination events across the entire genome and their distribution along the largest chromosome in the germ cells of four closely related songbird species: Common linnet, Eurasian bullfinch, Eurasian siskin, and European goldfinch. We found significant variance in the frequency of recombination events among these species, as well as individual variability within each species. Across all four species, the distribution of recombination events on chromosome 1 was remarkably consistent, with more events occurring toward the chromosome ends and fewer near the centromere. The proximity of these events to the centromere depended on how many events took place on that chromosome, with more events being associated with closer locations. Interestingly, the size and type of the centromere did not influence this pattern. We propose that the scarcity of recombination events near the centromere may result from their sequential occurrence along the chromosome, starting from the chromosome ends, rather than from any specific influence from the centromere itself.
Abstract
Meiotic recombination is an important source of genetic diversity. Using immunolocalization of several meiotic proteins at the spreads of male pachytene cells, we estimated the number of recombination nodules per cell and their distribution along the macrochromosome 1 of the Common linnet, Eurasian bullfinch, Eurasian siskin, and European goldfinch. The macrochromosomes of the two former species have metapolycentromeres, composed of several centromeric domains. We detected significant interspecies differences in the mean numbers of recombination nodules per genome: 52.9 ± 2.8 in the linnet, 49.5 ± 3.5 in the bullfinch, 61.5 ± 6.3 in the siskin and 52.2 ± 2.7 in the goldfinch. Recombination patterns on macrochromosome 1 were similar across species, with more nodules localized near chromosome ends and fewer around centromeres. The distance from the proximal nodule to the centromere depended on the nodule count per chromosome arm, with more events leading to a closer location. However, species with different centromere types showed no difference in this regard. We propose that the deficiency of recombination sites near centromeres could be due to the sequential occurrence of crossovers starting from the chromosome ends and may not be attributed to any suppressive effect of the centromere itself.
... Here we present a complete species-level phylogeny for the parrotfinches (genus Erythrura). This genus is within the family Estrildidae (the waxbills, munias, and allies), which includes well-studied non-model systems such as Pyrenestes ostrinus (e.g., Smith, 1993;vonHoldt et al., 2018), Poephila acuticauda (e.g., Rowe et al., 2015;Hooper et al., 2019), and the model-system Taeniopygia guttata (e.g., Backström et al., 2010). Olsson and Alström (2020) showed that the Gouldian Finch (Chloebia gouldiae) and all sampled Erythrura species formed a clade sharing a common ancestor at ~10.5 ma, quite old considering the deepest split in the entire Estrildidae family was estimated at ~11 ma. ...
Identifying species boundaries and phylogenetic relationships among groups of closely related species provides a necessary framework for understanding how biodiversity evolves in natural systems. Here we present a complete phylogeny of the avian genus Erythrura (family Estrildidae) commonly known as parrotfinches, which includes species threatened by habitat loss and the pet trade. Using both mitogenome and reduced-representation genome-wide nuclear DNA sequence data, we reconstructed the evolutionary history of the group by sampling all 12 recognized species, four of which had not previously been studied in a phylogenetic context. We included intra-species geographic sampling that allowed us to comment on species limits in some taxa. We recovered the Gouldian Finch (Chloebia gouldiae) of Australia which has often been placed in the monotypic genus Chloebia, as being sister to a clade comprising all Erythrura species. In addition, we recovered a well-supported clade comprising eight species distributed throughout the Pacific Island eco-region, whereas those species occurring in continental southeast Asian, the Greater Sundas, and the Philippines, were recovered as earlier branching lineages. Of note was the early branching of the Fiji-endemic E. kleinschmidti which corroborates its unique phenotype. We also found a deep phylogenetic split (8.59% corrected, 7.89% uncorrected divergence in the mitochondrial gene ND2) between the Java and Philippine populations of E. hyperythra, indicating unrecognized species-level diversity within this taxon. In contrast, genome-wide nuclear data suggested that the New Guinea endemic species E. papuana is embedded within the widespread species E. trichroa in all phylogenetic reconstructions, corroborating previously published mitochondrial data that suggested a similar pattern. By generating a phylogenetic hypothesis for the relationships among all species of Erythrura parrotfinches, we provide a framework for better understanding the extant diversity and evolutionary history of this group.
... cM/Mb), and that explains why the association between chromosome size and recombination was nonsignificant. Negative associations between both variables have been observed in different taxonomic groups, for example, yeast (Kaback et al. 1992), humans and rodents (Jensen-Seaman et al. 2004), birds (Backström et al. 2010), cattle (Mouresan et al. 2019), and butterflies (Martin et al. 2019;Shipilina et al. 2022). Such a relationship is expected as crossovers are necessary for correct chromosome segregation during meiosis (Pardo-Manuel de Villena and Sapienza 2001; Smith and Nambiar 2020). ...
Recombination is a key molecular mechanism that has profound implications on both micro- and macroevolutionary processes. However, the determinants of recombination rate variation in holocentric organisms are poorly understood, in particular in Lepidoptera (moths and butterflies). The wood white butterfly ( Leptidea sinapis ) shows considerable intraspecific variation in chromosome numbers and is a suitable system for studying regional recombination rate variation and its potential molecular underpinnings. Here, we developed a large whole-genome resequencing data set from a population of wood whites to obtain high-resolution recombination maps using linkage disequilibrium information. The analyses revealed that larger chromosomes had a bimodal recombination landscape, potentially caused by interference between simultaneous chiasmata. The recombination rate was significantly lower in subtelomeric regions, with exceptions associated with segregating chromosome rearrangements, showing that fissions and fusions can have considerable effects on the recombination landscape. There was no association between the inferred recombination rate and base composition, supporting a limited influence of GC-biased gene conversion in butterflies. We found significant but variable associations between the recombination rate and the density of different classes of transposable elements, most notably a significant enrichment of short interspersed nucleotide elements in genomic regions with higher recombination rate. Finally, the analyses unveiled significant enrichment of genes involved in farnesyltranstransferase activity in recombination coldspots, potentially indicating that expression of transferases can inhibit formation of chiasmata during meiotic division. Our results provide novel information about recombination rate variation in holocentric organisms and have particular implications for forthcoming research in population genetics, molecular/genome evolution, and speciation.
... GONE can infer the demographic history within the past 100 generations in higher resolution by analysis of linkage disequilibrium (LD). As there are currently no studies that have calculated the recombination rate for the Chinese crested tern or other closely related species, we used the recombination rate (1.5 cM/Mb) of zebra nch (Taeniopygia guttata) 79 as a reference for the GONE analysis. To test whether the magnitude of the recombination rate affected the population trends of these two species, we also inferred the demographic histories of both crested tern species using the default recombination rate (1 cM/Mb) in GONE. ...
Endangered species serve as valuable models to understand the genetic legacy of historical demographic bottlenecks. Genomic erosion compromises the e ciency of purifying selection on deleterious mutations, thus reducing species' adaptive potential. Untangling demographic history and its genetic legacy remains a signi cant challenge for endangered species. Comparing genomic characteristics between a critically endangered seabird, the Chinese crested tern and its abundant sister species, the Great crested tern, we show that the current small population size (< 150 individuals) of the Chinese crested tern is due to massive reduction of effective population size by 98.8% through the Last Glacial Maximum. We found evidence of inbreeding depression in the Chinese crested tern because of elevated expression of deleterious mutations, and more pathogenic variants of disease-related genes, likely leading to tness loss. These ndings highlight the power of conservation genomics between species with different conservation status to understand genomic erosion and inform future conservation management.
... It has, for a long time, been considered the highest among birds. It was suggested that such a high recombination rate could have resulted from domestication and strong artificial selection [Groenen et al., 2009;Backström et al., 2010]. Further studies clarified the intermediate position of the chicken recombination rate between those of the white wagtail (3805 cM) and the black tern (2155 cM) Semenov et al. [2018]. ...
The chicken continues to hold its position as a leading model organism within many areas of research, as well as a being major source of protein for human consumption. The First Report on Chicken Genes and Chromosomes [Schmid et al., 2000], which was published in 2000, was the brainchild of the late, and sadly missed, Prof Michael Schmid of the University of Würzburg. It was a publication bringing together updates on the latest research and resources in chicken genomics and cytogenetics. The success of this First report led to the subsequent publication of the Second [Schmid et al., 2005] and Third [Schmid et al., 2015] reports proving popular references for the research community. It is now our pleasure to be able to introduce publication of the Fourth report. Being seven years since the last report, this publication captures the many advances that have taken place during that time. This includes presentation of the detailed genomic resources that are now available, largely due to increasing capabilities of sequencing technologies and which herald the pangenomic age, allowing for a much richer and more complete knowledge of the avian genome. Ongoing cytogenetic work also allows for examination of chromosomes, specific elements within chromosomes and the evolutionary history and comparison of karyotypes. We also examine chicken research efforts with a much more ‘global’ outlook with a greater impact on food security and the impact of climate change, and highlight the efforts of international consortia, such as the Chicken Diversity Consortium. We dedicate this Report to Michael.
... Foote et al., 2021;Peripolli et al., 2018;Stoffel et al., 2021). Recombination rate is approximated to be 1 cM/ Mb, at the lower range of avian estimates, due to small N e across Berthelot's pipit range (Backström et al., 2010;Burri et al., 2015). As ...
Genomes retain evidence of the demographic history and evolutionary forces that have shaped populations and drive speciation. Across island systems, contemporary patterns of genetic diversity reflect population demography, including colonisation events, bottlenecks, gene flow and genetic drift. Here, we investigate genome‐wide diversity and the distribution of runs of homozygosity (ROH) using whole‐genome resequencing of individuals (>22X coverage) from six populations across three archipelagos of Berthelot's pipit (Anthus berthelotii) ‐ a passerine that has recently undergone island speciation. We show the most dramatic reduction in diversity occurs between the mainland sister species (the tawny pipit) and Berthelot's pipit and is lowest in the populations that have experienced sequential bottlenecks (i.e., the Madeiran and Selvagens populations). Pairwise sequential Markovian coalescent (PSMC) analyses estimated that Berthelot's pipit diverged from its sister species approximately two million years ago, with the Madeiran archipelago founded 50,000 years ago, and the Selvagens colonised 8,000 years ago. We identify many long ROH (>1 Mb) in these most recently colonised populations. Population expansion within the last 100 years may have eroded long ROH in the Madeiran archipelago, resulting in a prevalence of short ROH (<1 Mb). However, the extensive long and short ROH detected in the Selvagens suggest strong recent inbreeding and bottleneck effects, with as much as 38% of the autosomes comprised of ROH >250 kb. These findings highlight the importance of demographic history, as well as selection and genetic drift, in shaping contemporary patterns of genomic diversity across diverging populations.
... cM / Mb), which explains why the association between chromosome size and recombination was non-significant. Negative associations between recombination rate and chromosome length have repeatedly been observed in different taxonomic groups, for example yeast (Kaback et al. 1992), humans and rodents (Jensen-Seaman et al. 2004), birds (Backström et al. 2010), cattle (Mouresan et al. 2019) and butterflies (Martin et al. 2019, Shipilina et al. 2022. Such a relationship is expected given that crossovers are necessary for correct segregation of chromosomes during meiosis (Pardo-Manuel de Villena and Sapienza 2001, Smith and Nambiar 2020). ...
Genetic recombination is a key molecular mechanism that has profound implications on both micro- and macro-evolutionary processes. However, the determinants of recombination rate variation in holocentric organisms are poorly understood, in particular in Lepidoptera (moths and butterflies). The wood white butterfly (Leptidea sinapis) shows considerable intraspecific variation in chromosome numbers and is a suitable system for studying regional recombination rate variation and its potential molecular underpinnings. Here, we developed a large whole genome resequencing data set from a population of wood whites to obtain high-resolution recombination maps using linkage disequilibrium information. The analyses revealed that larger chromosomes had a bimodal recombination landscape, potentially due to interference between simultaneous chiasmata. The recombination rate was significantly lower in subtelomeric regions, with exceptions associated with segregating chromosome rearrangements, showing that fissions and fusions can have considerable effects on the recombination landscape. There was no association between the inferred recombination rate and base composition, supporting a negligible influence of GC-biased gene conversion in butterflies. We found significant but variable associations between the recombination rate and the density of different classes of transposable elements (TEs), most notably a significant enrichment of SINEs in genomic regions with higher recombination rate. Finally, the analyses unveiled significant enrichment of genes involved in farnesyltranstransferase activity in recombination cold-spots, potentially indicating that expression of transferases can inhibit formation of chiasmata during meiotic division. Our results provide novel information about recombination rate variation in holocentric organisms and has particular implications for forthcoming research in population genetics, molecular/genome evolution and speciation.
... The TMRCA was approximated for ROH of different length classes, where the expected length of ROH L = 100/(2 t) centimorgans (cM), where t is time back to the common ancestor in generations (see, for examples,Foote et al., 2021;Peripolli et al., 2018; Stoffel et al., 2021). Recombination rate is approximated to be 1 cM/ Mb, at the lower range of avian estimates, due to small N e across Berthelot's pipit range(Backström et al., 2010;Burri et al., 2015). As Berthelot's pipits have a relatively short generation time (~2 years), the minimum ROH length threshold of >250 kb reflects the expected1365294x, 2023, 8, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/mec.16865 ...
Genomes retain evidence of the demographic history and evolutionary forces that have shaped populations. Across island systems, contemporary patterns of genetic diversity reflect complex population demography, including colonisation events, bottlenecks, gene flow and genetic drift. Here, we investigate whether island founder events have prolonged effects on genome-wide diversity and runs of homozygosity (ROH) distributions, using whole genome resequencing from six populations across three archipelagos of Berthelot’s pipit ( Anthus berthelotii ) - a passerine which has undergone island speciation relatively recently. Pairwise sequential Markovian coalescent (PSMC) analyses estimated divergence from its sister species approximately two million years ago. Results indicate that all Berthelot’s pipit populations had shared ancestry until approximately 50,000 years ago, when the Madeiran archipelago populations were founded, while the Selvagens were colonised within the last 8,000 years. We identify extensive long ROH (>1 Mb) in genomes in the most recently colonised populations of Madeira and Selvagens which have experienced sequential island founder events and population crashes. Population expansion within the last 100 years may have eroded long ROH in the Madeiran archipelago, resulting in a prevalence of short ROH (<1 Mb). Extensive long and short ROH in the Selvagens reflects strong recent inbreeding, small contemporary effective population size and past bottleneck effects, with as much as 37.7% of the autosomes comprised of ROH >250 kb in length. These findings highlight the importance of demographic history, as well as selection and genetic drift, in shaping contemporary patterns of genomic diversity across diverging populations.
