Our ring species formation model also provides an opportunity to clarify and analyze the role of geographic barriers. There is a dichotomy that can be easily understood: fairly rapid differentiation leads to several species as a result of isolation after distance (15), while slow differentiation leads to a single species (Fig. 2). However, our question is whether a third incident of ring species can be solidly formed so that they can be observed in the wild. When a population expands around a spatial barrier that limits its range, the interaction between the speed of range expansion and genetic differentiation determines the fate of terminal populations when they come into secondary contact. Increasing bearing capacity reduces differentiation (32) and increases speed. Other traits that influence this interaction are population traits (e.B. Growth rate, mating distance, rate of spread and mobility) and landscape characteristics (para. B width of the corridor, distance around the barrier). None of this ensures the stability of a ring species. We tested the robustness of the formation of the ring species in relation to variations in the geographical structure of the ring.
We hypothesized that the larger habitable zone near the secondary contact region increases the likelihood of ring species formation. Larger populations of divergent types inhibit genetic fluctuations that could lead to mating possibilities that reverse the speciation process (33). The simulations confirmed that if the excess area was moved to another location in the ring near the point of origin, which corresponds to a shift of the point of origin from south to north, the species in the ring were less likely, although the secondary contact time between the terminal populations remained the same (Fig. 3). Enlarged regions in the contact zone reduce genetic variability over time, and selection from rare types limits the overlap zone, thereby reducing the likelihood of fusion. Ring species often attract the interest of evolutionary biologists, systematists, and species researchers, leading to both stimulating ideas and confusion about their definition.  Contemporary researchers recognize that examples in nature have proven rare due to various factors such as the limitations of taxonomic delimitation or “taxonomic zeal” – explained by the fact that taxonomists classify organisms into “species”, while ring species often cannot meet this definition.  Other reasons such as the interruption of gene flow by the “divergence of the vicariate” and the fragmentation of populations due to climate instability have also been cited.  According to the BSC, “real” species cannot produce viable and fertile hybrid offspring in the laboratory. We simulated the formation of a ring species (Fig. 1) (20), explicitly including the topography of the ring and allowing a small initial population to grow as it expanded and differentiated around a geographical barrier (Fig.
S1). We used an individual model based on neutral replacement by local mating, migration and mutation (methods). Reproductive isolation is modeled by a multilocus generalization of the Bateson-Dobzhansky-Muller model, with the population evolving through nearly constant fitness combs (21, 22). The original population is located in a starting area, and individuals whose local mating area is underpopulated produce two offspring instead of one before dying. This allows the population to grow and expand to the carrying capacity of the entire available area. FALSE. The BSC states that “real” species cannot produce hybrid offspring under natural conditions; It does not pretend to the strange things that can happen in a laboratory or with biotechnology. The BSE criterion for distinguishing between two species is that there must be a barrier that prevents gene flow between species. Under natural conditions, the reproductive barrier usually involves geographical separation (allometry), although there are also other isolation mechanisms that can be important. If two species that are reproductively isolated (i.e., do not share gene flow) are brought together in a laboratory to hybridize, this does not violate the BSC definition of species. Herring gull (Larus argentatus) (front) and Dwarf gull (Larus fuscus) (back) in Norway: two phenotypes with distinct differences In biology, a ring species is a contiguous series of neighboring populations, each of which intersects closely related populations, but for which there are at least two “final” populations in the series that are too far from the crossing. although there is potential gene flow between each “linked” population.
 Such non-reproductive “final populations”, although genetically related, can coexist in the same region (sympatry) and thus close a “ring”. The German term Rassenkreis, which means a circle of races, is also used. Sister species are two species that have a youngest common ancestor. They are the result of the recent speciation event in their lineage. In the above tree, species A and C are sister species. Comparisons between closely related taxa that share a history of distribution expansion by the same barriers could provide empirical information on the relationship between species and landscape parameters in ring species formation. Old World warblers, genus Phylloscopus, are forest-dependent species, and the spread of their ancestral populations is thought to be associated with forest expansion after global warming after the Pleistocene glaciation (19). However, the only confirmed case of ring species for this group so far is the Greenland warbler (Phylloscopus trochiloides). Species of the Phylloscopus inornatus complex, for example, have been considered distinct species due to genetic and vocal divergences (36). Salamanders in western North America could be another interesting case.
Despite some taxonomic controversies, the E. The Eschscholtzii complex is still one of the few well-documented ring species (verified in reference 30), and it is present in sympatorias with other salamander genera (27). The simulations use an agent-based population model composed of haploid and hermaphrodite individuals identified by a binary chain of B-loci. Reproduction is limited by a mating area determined by a spatial distance, S, and a genetic distance, G, beyond which other individuals are not considered potential partners. .