In this scenario, the resulting hybrid population is an independent new species that is reproductively isolated from both. Speciation all species on earth thought to share single common ancestor that is life arose once, ca. Homoploid hybrid speciation in an extreme habitat zachariah gompert,1 james a. Charles darwin was the first to describe the role of natural selection in speciation in his 1859 book on the origin of species. It is wellestablished that the former is much rarer than the latter soltis and soltis 2009. In general, allopolyploid speciation through the hgd pathway has three important stages. It is often lamented that ecology has been overlooked in studies of speciation lewontin 1997. We investigate the genetic foundation of this poorly understood process through wholegenome analysis of the hybrid italian sparrow and its progenitors. Cytonuclear coevolution following homoploid hybrid. Most commonly, it is assumed that natural selection separates species originating from a single population on the basis of variation in traits that confer advantages for survival and reproduction.
Here we examined how interactions between recombination and gene flow shaped the phylogenomic landscape of red wolf to create nonrandom retention of introgressed ancestry. Homoploid hybrid speciation dissertation presented. Behavioural isolation may facilitate homoploid hybrid. The deme is a group of populations with common gene pool.
Homoploid hybrid origin of a new species is not equivalent to hybrid speciation schumer et al. The key shortcoming in most studies proposing hybrid speciation is the lack of evidence that hybridization played a role in the speciation process. Vose,2 and sergey gavrilets 4 5 6 1department of ecology and evolutionary biology, university of tennessee, knoxville, tn 37996. Galapagos finches have driven hypotheses of how speciation occurs. Homoploid hybrid speciation in louisiana iris by sunni j. Nice1 according to theory, homoploid hybrid speciation, which is hybrid speciation without a change in chromosome number, is facilitated by adaptation to a novel or extreme habitat. Background hybrids possess phenotypic traits that are often intermediate between their parental taxa, which commonly serves as evidence of hybridization in morphological analyses. Noland martin as hybridization necessarily occurs in sympatry, hybrid species may represent the most frequent mechanism of sympatric speciation, and, as such, hybrid speciation events. Previously, reproductive isolation between hybrids and their parents was thought to be particularly difficult to achieve, and thus hybrid species were thought to be extremely rare.
The development of reproductive isolation is a crucial step in the speciation process. Reproductive isolation is thought to occur through rapid chromosomal reorganization, ecological divergence, andor spatial isolation rieseberg 1997. In the absence of postmating isolation due to structural changes in the genome, or temporal or spatial premating isolation, another form of. Using molecular and ecological data, we found that the alpineadapted butterflies in the genus lycaeides are the product of hybrid speciation. S erpe 2 d avid c t ank 3 and j ames f s mith2 2 department of biological sciences, boise state university, 1910 university drive, boise, idaho 837251515 usa. The conditions that favour hybrid speciation and the maintenance of parental species are likely to differ from those that lead to hybrid speciation through the merger of species genomes. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within lineages.
Pdf extreme changes to gene expression associated with. Hybrid speciation rapid hybrid speciation in darwins finches sangeet lamichhaney, 1 fan han, matthew t. Pdf homoploid hybrid speciation is the origin of a hybrid species without change in chromosome number. In general, however, interspecific hybridization is easily confused with the formation of hybrid species. Ecological genetics of homoploid hybrid speciation. Hybrid speciation rapid hybrid speciation in darwins finches.
Hybridization is well recognized as a driver of speciation, yet it often remains difficult to parse phylogenomically in that post speciation gene flow frequently supersedes an ancestral signal. Homoploid hybrid speciation is the origin of a hybrid spe cies without change in chromosome number. Additive traits lead to feeding advantage and reproductive isolation, promoting homoploid hybrid speciation article pdf available in molecular biology and evolution 368 april 2019 with 289. The ecological genetics of homoploid hybrid speciation. Hybrid speciation galapagos finches have driven hypotheses of how speciation occurs.
It is often not easy to clearly differentiate hybrid speciation and derivatives of other evolutionary scenarios. This is a curious claim given that darwins focus was primarily on ecological divergence and that both dobzhansky 1937 and mayr 1942 argued that adaptation to different environments led to speciation. Genetic mechanisms of allopolyploid speciation through. Speciation is the formation of one or more new species from an existing species. Speciation is a fundamental issue in evolutionary biology, but it is both fascinating and frustrating. Reports homoploid hybrid speciation in an extreme habitat. In most proposed cases of homoploid hybrid speciation, authors have suggested that certain trait combinations were derived from hybridization and contributed to the emergence of reproductive isolation. Hybrid speciation is a form of speciation where hybridization between two different species leads to a new species, reproductively isolated from the parent species. S4 if a similar scenario were involved in the origin of h. Genetic divergence and the number of hybridizing species. Abbott1,3 1school of biology, mitchell building, university of st.
Speciation is the evolutionary process by which populations evolve to become distinct species. Based on 28 studies of homoploid and 34 studies of polyploid hybrid species i conclude that lati. Ecological speciation is the process by which ecologically based divergent selection between different environments leads to the creation of reproductive barriers between populations. Nevertheless, the reality of hybrid speciation, both allopolyploid ahs and homoploid hhs, within this class has been demonstrated.
Homoploid hybrid speciation hhs is the formation of a newhybridspecies, independent from its parents, via hybridization with no wholegenome duplication and thus no increase in ploidy. Hybrid speciation in butterflies in a jungle edgar a. Baum3,4 1department of ecology and evolutionary biology, yale university, p. The genomic mosaicism of hybrid speciation science advances. Hybridization in plants may result in hybrid speciation or introgression and, thus, is now widely understood to be an important mechanism of species diversity on an evolutionary time scale. Pdf homoploid hybrid speciation in an extreme habitat.
Homoploid hybrid speciation in an extreme habitat science. We propose criteria to determine the strength of evidence for homoploid hybrid speciation. Rapid hybrid speciation in darwins finches science. We have used experimental evolution in fruit flies drosophila to show that both the genetic difference between hybridizing species and the number of hybridizing. Extreme changes to gene expression associated with homoploid hybrid speciation.
Genomewide local ancestries discriminate homoploid hybrid. Hybridization is particularly common in ferns, as is polyploidy, which often results from hybrid crosses. However, we still know little about the conditions that are most conducive to hybrid speciation. Hybrid speciation is an important way to generate species diversity.
The likelihood of homoploid hybrid speciation heredity. Genetic divergence and the number of hybridizing species affect the path to homoploid hybrid speciation aaron a. Homoploid hybrid speciation in a rare endemic castilleja. The geography of hybrid speciation in plants kadereit. Pdf the ecological genetics of homoploid hybrid speciation. During homoploid hybrid speciation, a stable, fertile, and reproductively isolated hybrid derivative arises without a change in chromosomal number. Matutea,1 abiology department, university of north carolina, chapel hill, nc 27599 edited by david m. We find overall balanced yet heterogeneous levels of contribution from each parent species throughout the hybrid genome and. Pdf behavioural isolation may facilitate homoploid. Behavioural isolation may facilitate homoploid hybrid speciation in cichlid fish. Detecting hybrid speciation in the presence of incomplete lineage sorting using gene tree incongruence. Reproductive isolation following hybrid speciation in. Hybridization can promote speciation, and examples of putative hybrid species have now been identified across the tree of life.
This is often the result of selection over traits which are genetically correlated to reproductive isolation, thus speciation occurs as a byproduct of adaptive divergence. The ecological genetics of homoploid hybrid speciation b. However, the importance of hybridization as a route to speciation is poorly understood, and many claims have been made with insufficient evidence that hybridization played a role in the speciation process. Evidence for continual hybridization rather than hybrid. Stage i, where f 1 hybrid individuals are formed through interspecies crossing, marks the onset of allopolyploid speciation.
Texas state universitysan marcos december 2012 supervising professor. The hybrid individuals cannot be distinguished from other individuals of h. The two camps of evolutionary biologists best equipped to deal with speciation in terms of mechanism, population geneticists. Hybridization is widespread in nature and, in some instances, can result in the formation of a new hybrid species. Detecting hybrid speciation in the presence of incomplete.
Homoploid hybrid speciationthe process in which hybridization results in a stable, fertile, and reproductively isolated hybrid lineage where there is no change in ploidyhas been documented. Natural hybridization has been shown to occur frequently in ligularia asteraceae. Hybrid speciation is constrained by the homogenizing effects of gene flow from the parental species. According to theory, homoploid hybrid speciation, which is hybrid speciation without a change in chromosome number, is facilitated by adaptation to a novel or extreme habitat. Homoploid hybrid speciation hhs is the formation of a newhybridspecies, independent from its parents, via hybridization with no wholegenome duplication and. Premating isolation is often implicated in traditional models of divergence with gene flow, but the evolution of reproductive isolating mechanisms has been poorly explored in species resulting from hybrid speciation. It contrasts with the more frequent allopolyploid hybrid speciation in which there is whole genome duplication with diploid chromosome numbers of the two parent species being summed in the hybrid species. Homoploid hybrid speciation has traditionally been considered a rare event, dependent on the establishment of both a novel, balanced genotype and reproductive isolating barriers between the new. Both homoploid and polyploid hybrid speciation are commonly considered straightforward examples of sympatric speciation. Hybrid speciation can arise either through hhs or via allopolyploidy soltis and soltis 2009. Rosenthal,3,4 and peter andolfatto1,5 1department of ecology and evolutionary biology, princeton university, princeton, new jersey 08544 2email. Hybrid speciation is quite rare in animals, but it does occur naturally.