Browsing by Subject "introgression"

Sort by: Order: Results:

Now showing items 1-7 of 7
  • Guo, Baocheng; Fang, Bohao; Shikano, Takahito; Momigliano, Paolo; Wang, Cui; Kravchenko, Alexandra; Merilä, Juha (2019)
    Hybridization and convergent evolution are phenomena of broad interest in evolutionary biology, but their occurrence poses challenges for reconstructing evolutionary affinities among affected taxa. Sticklebacks in the genus Pungitius are a case in point: evolutionary relationships and taxonomic validity of different species and populations in this circumpolarly distributed species complex remain contentious due to convergent evolution of traits regarded as diagnostic in their taxonomy, and possibly also due to frequent hybridization among taxa. To clarify the evolutionary relationships among different Pungitius species and populations globally, as well as to study the prevalence and extent of introgression among recognized species, genomic data sets of both reference genome-anchored single nucleotide polymorphisms and de novo assembled RAD-tag loci were constructed with RAD-seq data. Both data sets yielded topologically identical and well-supported species trees. Incongruence between nuclear and mitochondrial DNA-based trees was found and suggested possibly frequent hybridization and mitogenome capture during the evolution of Pungitius sticklebacks. Further analyses revealed evidence for frequent nuclear genetic introgression among Pungitius species, although the estimated proportions of autosomal introgression were low. Apart from providing evidence for frequent hybridization, the results challenge earlier mitochondrial and morphology-based hypotheses regarding the number of species and their affinities in this genus: at least seven extant species can be recognized on the basis of genetic data. The results also shed new light on the biogeographical history of the Pungitius-complex, including suggestion of several trans-Arctic invasions of Europe from the Northern Pacific. The well-resolved phylogeny should facilitate the utility of this genus as a model system for future comparative evolutionary studies.
  • Savriama, Yoland; Valtonen, Mia; Kammonen, Juhana I.; Rastas, Pasi; Smolander, Olli-Pekka; Lyyski, Annina; Häkkinen, Teemu J.; Corfe, Ian J.; Gerber, Sylvain; Salazar-Ciudad, Isaac; Paulin, Lars; Holm, Liisa; Löytynoja, Ari; Auvinen, Petri; Jernvall, Jukka (2018)
    An increasing number of mammalian species have been shown to have a history of hybridization and introgression based on genetic analyses. Only relatively few fossils, however, preserve genetic material, and morphology must be used to identify the species and determine whether morphologically intermediate fossils could represent hybrids. Because dental and cranial fossils are typically the key body parts studied in mammalian palaeontology, here we bracket the potential for phenotypically extreme hybridizations by examining uniquely preserved cranio-dental material of a captive hybrid between grey and ringed seals. We analysed how distinct these species are genetically and morphologically, how easy it is to identify the hybrids using morphology and whether comparable hybridizations happen in the wild. We show that the genetic distance between these species is more than twice the modern human–Neanderthal distance, but still within that of morphologically similar species pairs known to hybridize. By contrast, morphological and developmental analyses show grey and ringed seals to be highly disparate, and that the hybrid is a predictable intermediate. Genetic analyses of the parent populations reveal introgression in the wild, suggesting that grey–ringed seal hybridization is not limited to captivity. Taken together, we postulate that there is considerable potential for mammalian hybridization between phenotypically disparate taxa.
  • Pulido-Santacruz, Paola; Aleixo, Alexandre; Weir, Jason T. (2020)
    The incidence of introgression during the diversification process and the timespan following divergence when introgression is possible are poorly understood in the neotropics where high species richness could provide extensive opportunities for genetic exchange. We used thousands of genome-wide SNPs to infer phylogenetic relationships, calculate ages of splitting, and to estimate the timing of introgression in a widespread avian neotropical genus of woodcreepers. Five distinct introgression events were reconstructed involving taxa classified both as subspecies and species including lineages descending from the basal-most split, dated to 7.3 million years ago. Introgression occurred between just a few hundred thousand to about 2.5 million years following divergence, suggesting substantial portions of the genome are capable of introgressing across taxa boundaries during a protracted time window of a few million years following divergence. Despite this protracted time window, we found that the proportion of the genome introgressing (6-11%) declines with the time of introgression following divergence, suggesting that the genome becomes progressively more immune to introgression as reproductive isolation increases.
  • Hirase, Shotaro; Yamasaki, Yo Y.; Sekino, Masashi; Nishisako, Masato; Ikeda, Minoru; Hara, Motoyuki; Merilä, Juha; Kikuchi, Kiyoshi (2021)
    How early stages of speciation in free-spawning marine invertebrates proceed is poorly understood. The Western Pacific abalones, Haliotis discus, H. madaka, and H. gigantea, occur in sympatry with shared breeding season and are capable of producing viable F-1 hybrids in spite of being ecologically differentiated. Population genomic analyses revealed that although the three species are genetically distinct, there is evidence for historical and ongoing gene flow among these species. Evidence from demographic modeling suggests that reproductive isolation among the three species started to build in allopatry and has proceeded with gene flow, possibly driven by ecological selection. We identified 27 differentiation islands between the closely related H. discus and H. madaka characterized by high F-ST and d(A), but not high d(XY) values, as well as high genetic diversity in one H. madaka population. These genomic signatures suggest differentiation driven by recent ecological divergent selection in presence of gene flow outside of the genomic islands of differentiation. The differentiation islands showed low polymorphism in H. gigantea, and both high F-ST, d(XY), and d(A) values between H. discus and H. gigantea, as well as between H. madaka and H. gigantea. Collectively, the Western Pacific abalones appear to occupy the early stages speciation continuum, and the differentiation islands associated with ecological divergence among the abalones do not appear to have acted as barrier loci to gene flow in the younger divergences but appear to do so in older divergences.
  • Miraldo, Andreia; Duplouy, Anne (2019)
    Determining the drivers of diversity is a major topic in biology. Due to its high level of micro-endemism in many taxa, Madagascar has been described as one of Earth's biodiversity hotspot. The exceptional Malagasy biodiversity has been shown to be the result of various eco-evolutionary mechanisms that have taken place on this large island since its isolation from other landmasses. Extensive phylogenetic analyses have, for example, revealed that most of the dung beetle radiation events have arisen due to allopatric speciation, and adaptation to altitudinal and/or longitudinal gradients. But other biotic factors, that have yet to be identified, might also be at play. Wolbachia is a maternally transmitted endosymbiotic bacterium widespread in insects. The bacterium is well-known for its ability to modify its host reproductive system in ways that may lead to either discordance patterns between the host mitochondrial and nuclear phylogenies, and in some cases to speciation. Here, we used theMultiLocus Sequence Typing system, to identify and characterize five Wolbachia strains infecting several species within the Nanos clypeatus dung beetle clade. We discuss the implications of these Wolbachia strains for the evolution and diversification of their dung beetle hosts in Madagascar.
  • Ahovuo, Aura Elina (Helsingin yliopisto, 2020)
    Isolating mechanisms of the species usually prevent interspecific hybridisation. At times, these mechanisms might break down temporarily and lead to the birth of interspecific hybrids. Introgression is a term related to a set of consecutive backcrossings in which the hybrids reproduce with one of their parental species. It is characterised as a long process associated with alleles which are transferred from a population of one of the parental species to a population of the other parental species. Introgression is adaptive if phenotypic variation is increased in the recipient population by the genetic variants of the donor population and maintained by natural selection. The Baltic grey seal (Halichoerus grypus) and the Baltic ringed seal (Pusa hispida botnica) have interbred when they were kept in captivity in a shared pond. According to the findings from a previous study, interbreeding could have happened in the wild as well. The purpose of this study is to examine the proportion of introgression between the Baltic grey and ringed seals. The genomewide introgression is analysed using Patterson’s D-statistic, F4-ratio test and specific introgression intervals defined from the seals of analysed data. Introgression is assumed to have contributed intraspecific morphological variation detected in phocine teeth. Therefore, it is also examined whether the genes involved in tooth development express signs of introgression in the grey and ringed seals and whether the introgression intervals include potential variants. The results of Patterson D-statistic and F4-ratio test show both hybridisation and introgression between the Baltic grey and ringed seals. Based on the introgression intervals, a longer period has passed since the species interbred. Similar proportions of introgressed DNA as those defined from the genomes of the ringed seals have been detected in brown bears, bovines and modern humans. Furthermore, several genes affecting the shape of a developing mammalian tooth show signs of introgression in the seals. The individuals also carry variants in their introgression intervals. Introgression and the variants can account for the intraspecific morphological variation in the phocine dentitions. Potential introgressed genome intervals in the regulatory sequences of the tooth genes might also affect phocine tooth shape, which should be examined more in the future.
  • Wang, Cui; Shikano, Takahito; Persat, Henri; Merila, Juha (2017)
    Pleistocene glaciations have strongly affected the biogeography of many species residing in periglacial and previously glaciated regions. Smoothtail nine-spined sticklebacks (Pungitius laevis) have three highly divergent mitochondrial lineages in France, one of which shares the same mitochondrial cluster with a congener P. pungitius. To understand if interspecific introgression has happened between the two species, we carried out phylogeographic and population genetic analyses using mitochondrial and nuclear gene sequences. Our results indicated asymmetric mitochondrial introgression from P. pungitius to P. laevis and genetic admixture of these species in one of the P. laevis lineages, suggesting historical hybridization. Deep intraspecific mitochondrial divergence within P. laevis in central and southern France mostly coinciding with major drainages suggests that these areas were important glacial refugia for the species explaining the observed intraspecific divergence. The historical hybridization between P. laevis and P. pungitius likely occurred in a refugium at central France, and the newly formed P. laevis lineage spread northward during postglacial recolonization. The study adds to the long list of species showing complete mitogenome capture owing to historical hybridizations, and highlights the reticulate nature of population differentiation in taxa subject to postglacial range-expansions.