Allopatric Speciation
Allopatric speciation is the process by which new species evolve from a common ancestor due to geographic isolation. It occurs when a population is divided by a physical barrier, such as a river or mountain range, preventing gene flow between the separated groups. Over time, genetic differences accumulate, leading to the formation of distinct species.
4 Key excerpts on "Allopatric Speciation"
eBook - ePubPlant Evolution
An Introduction to the History of Life
- Karl J. Niklas(Author)
- 2016(Publication Date)
- University of Chicago Press(Publisher)
...The paucity or absence of gene flow among allopatric subpopulations can result in speciation. The portrait of speciation owing to vicariant geographic isolation is called Allopatric Speciation (fig. 5.1 a). It involves three sequential steps: (1) subpopulations become spatially isolated from the main range of their parent population, (2) subpopulations genetically diverge from one another, and (3) selection leads to genotypic or phenotypic differences that preclude subpopulations from interbreeding with one another. In sum, a physical or biological barrier isolates members of the same species so that they cannot interbreed, allowing them to diverge in appearance or behavior. At some point the divergence may be so great that a new species comes into existence. Peripatric speciation is a variant of the Allopatric Speciation model. According to this model, one or more small peripheral subpopulations become separated from the main population of a species and undergo genotypic or phenotypic divergence (fig. 5.1 b). The principal difference between this model and the Allopatric Speciation model is that the splinter peripatric subpopulations are small and thus contain low genetic diversity. Under these circumstances, peripatric populations are subject to founder effects, selection bottlenecks, and genetic drift. As a consequence of reduced genetic variation, a peripatric population may not resemble its parent species (the founder effect) and thus may respond to different selection regimes resulting in phenotypic divergence (selection bottlenecks). Further, because the peripatric population is genetically unrepresentative of its parent population, there may be fewer copies of some alleles such that allele frequencies shift as offspring are produced (genetic drift) (fig. 5.2). These phenomena are expected to be prevalent in populations with no overlapping generations, as for example annual plants. Figure 5.2. An illustration of genetic drift using marbles in a jar...
eBook - ePubPhylogenetics
Theory and Practice of Phylogenetic Systematics
- E. O. Wiley, Bruce S. Lieberman(Authors)
- 2011(Publication Date)
- Wiley-Blackwell(Publisher)
...Not all groups of species will be amenable to detailed analysis of speciation or the identification of speciation modes using biogeographic patterns and phylogenetic hypothesis (see for example, Wiley and Mayden, 1985). However, if we understand how some of the basic patterns might arise, we will be equipped to deal with clades for which the assumptions are reasonable. Most authors recognize three basic modes of speciation. Allopatric Speciation involves the physical subdivision of an ancestral gene pool into two or more descendant gene pools. Sympatric speciation is speciation without geographic subdivision. Parapatric speciation is speciation that involves partial geographic subdivision and differentiation in spite of limited gene flow across a hybrid zone. Below we first begin our discussion of each of these modes from the neontological perspective. In essence, the focus will be on how we can use phylogenetics and biogeography to study speciation in recent faunas given various modes of speciation. After discussing the neontological perspective, we will discuss speciation in deep time and have a look at the tempo of speciation as well as its mode. It is in deep time that we can get at phenomena such as punctuated equilibria, phenomena that are harder to study in a neontological context. Allopartic Speciation The role of geographic subdivision and subsequent differentiation has long been recognized as a major mode for the origin of new species. Darwin recognized it in his notebooks and in the Origin, even if he did not accord it as high a place as sympatric speciation. Wallace (1855) recognized that closest relatives are more likely to be found in adjacent regions than together in sympatry. Mayr (1942, 1963, et seq.) accorded allopatry the primary role in species formation...
eBook - ePub- John N. Thompson(Author)
- 2014(Publication Date)
- University of Chicago Press(Publisher)
...CHAPTER 7 INTERACTION AND SPECIATION There are at least as many ways to consider patterns in speciation as there are subdisciplines in evolutionary theory. Emphases vary from biogeographical and populational approaches on the likelihood of speciation in allopatric, parapatric, and sympatric populations (Mayr, 1970; Bush, 1975; Endler, 1977) to paleobiological approaches on phyletic gradualism as compared with punctuated equilibrium (Eldredge and Gould, 1972; Gould and Eldredge, 1977); molecular approaches range from the relative importance of chromosomal as compared with allellic changes (White, 1968, 1978; Grant, 1971; Stebbins, 1971) to the importance of regulatory as compared with structural gene changes (Brittain and Davidson, 1971; Gould, 1977; Cherry et al., 1978). No single approach is adequate to understand speciation and each approach adds its own dimension to the intricacies of when, where, how, and why speciation occurs. This chapter explores patterns in speciation through an ecological approach based on how organisms interact and coevolve. The basic problem is this: if the different kinds of antagonistic and mutualistic interactions vary in their likelihood of coadaptation as suggested in the previous chapters, are there similar patterns in the likelihood of cospeciation? COSPECIATION First, to paraphrase Janzen (1980a), when is it cospeciation? As with coadaptation, the key phrase is reciprocal change. Coadaptation implies reciprocal patterns of defense or mutual attraction, and cospeciation implies reciprocal speciation resulting from an interaction between two or more species. If the interaction affects speciation in only one of the taxa, that is interesting evolutionarily but it is not cospeciation...
eBook - ePub- Joanna R. Freeland(Author)
- 2019(Publication Date)
- Wiley(Publisher)
...Larger rivers may present a semi‐permeable barrier to dispersal that could help to maintain distinct genetic groups (Vergara et al. 2015). Source: Photo by Joxerra Aihartza. Box 6.2 Metapopulations In the absence of barriers to dispersal, some species that live in fragmented habitat regularly disperse between suitable sites, and this may lead to what is known as a metapopulation. The concept of a metapopulation dates back to the 1930s, although the actual term is attributable to Levins (1969), who presented an explicit model of a metapopulation. Levins' model, which we now know as a classical metapopulation, refers to a “population of populations” that exist in a balance between extinction and recolonization, and are linked to one another by ongoing dispersal and gene flow. The widespread incorporation of the metapopulation concept in ecology began with Hanski and Gaggiotti (2004) who showed, among other things, that in the absence of dispersal the entire metapopulation would go extinct because repeated local extinctions would eventually eliminate all occupied patches. The process of repeated extinctions and recolonizations can affect the genetic structure of a metapopulation in different ways. Extinctions (sink populations) and recolonizations (from source populations) are typically accompanied by population bottlenecks, which, as we know from Chapter 5, lead to reduced N e, accelerated genetic drift, and depleted genetic variation. N e will be substantially reduced if all extant populations within a metapopulation descended relatively recently from a single ancestral population. Extinctions and recolonizations also affect the extent to which populations are genetically differentiated from one another...
